ZSM-5 zeolite, first synthesized by Argauer and Landolt in 1972, is a mesoporous 10-membered ring (10 MR) silica-alumina molecular sieve material with MFI topology^[14]. Its crystal structure consists of an elliptical through channel (0.51 nm × 5.4 nm) parallel to the (010) crystal plane and a nearly circular sinusoidal channel (0.54 nm × 5.56 nm) parallel to the (100) crystal plane. The schematic diagram of the framework structure is shown in Figure 1. In the unique three-dimensional (3D) structural network of MFI, a nanometer-sized confined space with a diameter of about 8.99 Å is formed at the intersection of ten-membered ring channels, which provides a suitable place for the formation of active intermediates in methanol conversion reaction and subsequent catalytic reactions^[15,16].

H-ZSM-5 zeolite has strong acidity, so the products of methanol conversion are mainly long chain alkanes and aromatics, and light olefins are not the dominant products. Therefore, ZSM-5 catalyst is often used in methanol to gasoline (MTG) and methanol to aromatics (MTA) processes, and there is no other type of molecular sieve material with better performance than ZSM-5 in the field of methanol to aromatics. In addition, researchers have found that by changing the silica-alumina ratio of ZSM-5 zeolite, adjusting the acidity of the outer surface of the grain and modifying the pore structure, the acid strength of H-ZSM-5 can be effectively reduced, and the selectivity of light olefins in methanol conversion reaction can be greatly enhanced by enhancing the shape selectivity effect of its confined space^[17,18]. The modified H-ZSM-5 is an ideal catalyst for methanol to propene (MTP). Inspired by this, modified MCM-22 molecular sieve (MWW topology, with abundant two-dimensional sinusoidal ten-membered ring cross channels, supercages and external surface pockets) and modified ITQ-2 molecular sieve (MWW topology, with two-dimensional sinusoidal ten-membered ring cross channels and external surface pockets) have also been found to be potential MTP catalytic materials in recent years^[19⇓~21]. With the development of zeolite diffusion research, researchers have found that the multi-scale diffusion behavior of guest molecules in ZSM-5 zeolite grains is anisotropic, and aromatic species only diffuse to the outer surface of the crystal through the through channels parallel to the (010) crystal plane.The short b-axis sheet-like ZSM-5 catalyst can inhibit the carbon deposition on the molecular sieve grain by regulating the diffusion behavior of guest molecules (especially polytoluene and other polycyclic aromatic hydrocarbon carbon deposition precursors) in the grain interior, thereby prolonging the catalyst life^[22]. Currently, this field has attracted extensive attention from researchers in molecular sieve synthesis, catalytic material characterization, and molecular diffusion^[23,24].

Silicoaluminophosphate series molecular sieve SAPO-n (n stands for structure type) was first developed by the Molecular Sieve Research and Development Department of Union Carbide Corporation in 1984^[25,26]. SAPO series molecular sieves have a wide range of pore size distribution (ranging from eight-membered rings to twelve-membered rings, with a pore size distribution of 0. 3 ~ 0.8 nm), moderate acid strength, and good hydrothermal stability, which have attracted the attention of a large number of researchers from academia and industry since they came out. As an important member of the SAPO-34 family, SAPO-34 is a chabazite (CHA) type molecular sieve, which belongs to the trigonal (triclinic) crystal system with the space symmetry group of R3m, and has an eight-membered ring pore size of about 0.38 nm × 0.38 nm and a three-dimensional cross pore structure.The ellipsoidal supercage space formed at the intersection of the eight-membered ring orifice and the three-dimensional pore channel has a size of about 1.09 nm × 0.67 nm × 0.67 nm, belonging to the molecular sieve with a small pore and a large cage structure, and its skeleton structure is shown in Figure 2. The unique cage structure provides a suitable space for the generation and stabilization of aromatic hydrocarbon active intermediates in the methanol catalytic conversion process, and the small pore size also limits the diffusion of hydrocarbon species with larger molecular size out of the nano-molecular reactor, thereby realizing the efficient and high-selectivity production of low-carbon olefins. However, this structure also leads to the rapid formation and accumulation of a large number of bulky and low-activity polycyclic aromatic hydrocarbon species in the cage, which are difficult to diffuse out of the molecular sieve nanocage. The shape-selective effect of SAPO-34 molecular sieve is gradually modified by the accumulation and dynamic evolution of polycyclic aromatic hydrocarbons in the CHA cage: on the one hand, the shape-selective catalysis of small molecules (such as ethylene and propylene) is further enhanced^[27]; On the other hand, when the mass transfer of methanol is hindered by carbon deposition, the cage SAPO-34 catalyst will eventually be deactivated^[28,29]. These dynamic processes occur at the mesoscale level spanning acid sites, molecular sieve nanocages, and molecular sieve crystals, and involve host-guest chemical interactions in complex confined spaces, including chemical reactions and physical diffusion processes, which are important research contents of catalytic chemistry from the perspective of condensed matter chemistry. The MTO process with SAPO-34 as the core catalyst is usually combined with the circulating fluidized bed reaction process to achieve continuous production of light olefins (commercially successful DMTO process)^[4,30]. At present, the commonly used catalyst control methods include adjusting the Si content of catalyst grains, controlling the distribution of acid sites, reducing the grain size of molecular sieves, introducing mesopores and macropores, and metal modification^{[31][26][32][33][34]}. In recent years, with the advancement of industrialization and the deepening of basic research, researchers have gradually realized the importance of molecular sieve carbon deposition regulation and the "double-edged sword" nature of carbon deposition species in MTO reaction. Inspired by this, the development of MTO process with high pressure hydrogen and water, the pre-carbon deposition technology of light olefins (forming and accumulating part of active "carbon deposition" species in CHA cage before reaction) and the incomplete regeneration technology of carbon deposition catalyst combined with steam treatment (directionally converting the carbon deposition of deactivated catalyst into part of "active" intermediate species accumulated in CHA cage,The development of carbon deposition has gradually become a key research direction of common concern in basic research and industrial applications^{[35,36][37][38⇓⇓~41]}. These strategies endow condensed catalytic materials with more excellent catalytic properties, achieve efficient and highly selective conversion, and respond to the requirements of the times for the low-carbon development of MTO process under the current "two-carbon" background.

Encouraged by the successful industrialization of DMTO technology with eight-membered ring and cage structure SAPO-34 molecular sieve as the core catalytic material, basic research has systematically studied the application of cage structure molecular sieve with eight-membered ring pore in MTO reaction system.A unified cage control theory based on the principle of shape selectivity in confined space is established, and a deeper understanding of the latter will provide practical theoretical guidance for researchers to find the next generation of efficient light olefin catalysts^[7,42]. Researchers have systematically studied the methanol catalytic conversion reactions of SAPO-35 (AEI), SAPO-34 (CHA), SAPO-18 (AEI), DNL-6 (RHO) and SAPO-14 (AFN) molecular sieves, and found that they show different product distributions^[42][43]. Their cage structure is shown in Fig. 3. Unlike SAPO-34, which is rich in ethylene and propylene, ethylene is the main product of SAPO-35 molecular sieve with small cage size (cage size 7.33 Å × 6.33 Å × 6.33 Å). SAPO-18 and DNL-6 have larger cage sizes (12.77 Å × 11.66 Å × 11.66 Å for the former and 11.44 Å × 11.44 Å × 11.4 Å for the latter), and propylene and butylene are the main products of methanol conversion catalyzed by them; SAPO-14 molecular sieve with ultra-small cage (5.33 Å × 5.33 Å × 10.55 Å) shows an ultra-high propylene selectivity of 77.3% (currently significantly better than all other catalytic materials); The methanol conversion products of SAPO-42 (pore dimensions 4.11 Å × 4.11 Å, cage dimensions 11.44 Å × 11.44 Å) with LTA topology are dominated by C₄₊ alkenes; SAPO-56 with AFX topology (pore dimensions 3.44 Å × 3.66 Å, cage dimensions 13.00 Å × 8.33 Å × 8.33 Å) favors the production of ethylene and propylene^[44]. These reaction results and the catalytic reaction mechanism show that the structure and size of the nanocage cavity of the molecular sieve catalyst determine the type of the active hydrocarbon pool intermediate in the MTO reaction, and then control the MTO reaction network and product distribution (product selectivity).Based on the traditional theory of reactant form selection, transition state form selection and product form selection, a unified cage controlled form selection mechanism of "cage structure size-active intermediate-product distribution" is established.Nriching the connotation of the shape-selective principle of the catalytic reaction occurring in the molecular sieve nano-confined space,Cage-controlled shape-selective catalysis, including cage-controlled reaction pathway, cage-controlled formation of intermediates, cage-controlled formation of dominant products, and cage-governed mass transfer of reactants and products, is an important part of molecular sieve-catalyzed gas-solid heterogeneous catalytic reactions in the development of condensed matter chemistry.

in situ/ex situ or in situ (in/ex situ or operando) infrared spectroscopy (FT-IR), ultraviolet-visible spectroscopy (UV-vis), solid-state nuclear magnetic resonance (solid state NMR), electron spin resonance (ESR) or electron paramagnetic resonance (EPR) have been used to study the formation of C — C bonds in MTO products from C1starting materials (methanol) without C — C bonds.Combining isotope labeling technology and theoretical calculation methods, more than 20 direct reaction mechanisms have been proposed, named after key reactive intermediates and transition state species.For example, methoxymethylene cation mechanism, methane-formaldehyde mechanism, extraframework aluminum species (EFAL) -assisted initial C — C bond formation mechanism, oxonium ylide mechanism, carbene mechanism, free radical mechanism, carbonylation mechanism, organic impurity mechanism hypothesis, etc^{[47⇓⇓⇓⇓⇓⇓⇓⇓⇓⇓~58]}. Wu et al. Directly captured the signal peak at 69 ppm by in-situ ssNMR under real reaction conditions and assigned it to the surface methoxy-like species, which comes from the surface methoxy species.SMS) and trimethyloxonium ions (TMO) with the framework oxygen sites of the molecular sieve to form activated dimethyl ether. Based on the experimental evidence and theoretical calculation results, a direct reaction mechanism for the activation of methanol/dimethyl ether to form initial C — C bonds catalyzed by surface methoxy/trimethyloxonium ions and framework oxygen sites was established (Fig. 6)^[57]. Subsequently, they used 2D¹³C-¹³C ssNMR, in-situ ssNMR, in-situ DRIFTS and theoretical calculation to trace the evolution of surface active centers from the formation of initial C — C to the initiation of efficient co-catalysis: SMS is the active intermediate species in the initial reaction stage, which guides the activation of methanol; As the reaction proceeds, the alkenyl and phenyl carbocation species will gradually relay the SMS to cooperate with the molecular sieve framework to form a supramolecular reaction active center with higher activity, which will continue to guide methanol to achieve efficient catalytic conversion, and the reaction will enter the apparent efficient conversion stage^[69]. In more detail, they found that after the formation of the initial C-C bond-containing surface species, the pentamethylcyclopentenyl carbocation appeared earlier than the pentamethylbenzene carbocation as the reaction progressed.It is proposed that the pentamethylcyclopentene species is a bridge between the direct and indirect mechanisms, and is an important part of the multi-level and complex catalytic reaction network in MTO chemistry^[70]. These concepts push the understanding of MTO catalytic chemistry to the level of dynamic condensed matter chemistry, and a complete and accurate description of this complex reaction system may require the intervention of data science and artificial intelligence.

The indirect mechanism of methanol catalytic conversion to light olefins by "hydrocarbon pool species" was proposed in the 1970s. In 1982, Dessau and Lapierre of Mobil Company proposed that methanol conversion follows an indirect reaction mechanism of continuous methylation and cracking of olefins^[71]. The feed methanol and the olefin species formed in the initial stage and the induction period are subjected to methylation reaction to form long-chain olefin species, and after the chain propagation reaction, the long-chain olefin is subjected to elimination reaction to generate low-carbon olefin products and recover the original initial olefin species, so that the catalytic cycle is realized. At the same time, the reaction rates of methylation and cracking are faster than that of methanol via direct mechanism in the induction period, so light olefins are considered to play the role of co-catalyst. Similarly, the co-catalyst effect of aromatic species (i.e., the mechanism of side chain methylation cleavage of aromatic species) was discovered by Mole et al. In 1983^[72,73]. In the following decades, studies have shown that olefins and aromatics co-catalysts cooperate to guide the complex dynamic reaction process^[74]. In the early 1990s, Dahl and Kolboe proposed the famous "hydrocarbon pool mechanism" for SAPO-34 molecular sieve system by using hydrocarbon pool mechanism isotope labeling technology, inspired by the early MTO reaction mechanism research^[75,76]. In the early conceptual model, (CH₂)_n represents hydrocarbon pool species generated and adsorbed near the active sites of the molecular sieve and "confined" by the nano-confined space of the molecular sieve pore, which act as active intermediates for the formation of light olefins. As highly active co-catalysts, these hydrocarbon compounds (hydrocarbon pool species) "relay" molecular sieve Brønsted acid sites to interact with the feedstock methanol through successive side-chain methylation and subsequent elimination reactions to complete the catalytic cycle and participate in the efficient catalytic conversion of methanol to light olefins. The core of the hydrocarbon pool mechanism is that the formation of all hydrocarbon products (including light olefins and carbon deposits) in the MTO process comes from active unsaturated hydrocarbon intermediates, that is, hydrocarbon pool species^[29].

Since the types of pool species and the specific reaction routes were not explicitly given in the initial pool mechanism model, the basic research work for a long time thereafter focused on the confirmation of the chemical structure of pool species and how they play a role in the subsequent catalytic conversion of methanol. Through the use of ¹³C isotope labeling, co-feed experiments, inorganic acid dissolved skeleton/organic solvent extraction "carbon deposition" combined with GC-MS analysis, solid nuclear magnetic resonance, infrared spectroscopy and other technologies, after nearly 30 years of unremitting efforts.Polymethylcyclopentenylcarbenium ion, polymethylcyclohexenylcarbenium ion, polymethylbenzenecarbenium ion and polymethylindenecarbenium ions, as well as their neutral species, have been found in a variety of zeolites with different topological structures.The reaction energy barrier and catalytic cycle of their participation in methanol catalytic conversion were calculated by density functional theory, and their catalytic mechanism was clarified^[13,46]. Table 1 summarizes a series of carbocations observed by solid-state NMR techniques. In addition to the side chain alkylation/cracking mechanism, Van Speybroeck et al. Proposed a paring mechanism with ring contraction and expansion of aromatic species as the core process in 2009^[77]. It is worth noting that Haw et al. Proposed the concept of supramolecular catalytic system in 2005 based on the strong and complex non-chemical bond interaction between unsaturated hydrocarbon pool species and molecular sieve framework^[78]. They believe that the change of molecular structure, electronic state and chemical properties of confined polymethylbenzene and the confined microenvironment of SAPO-34 molecular sieve play a role in catalyzing the efficient conversion of methanol. From the perspective of condensed matter chemistry theory, this multi-level concept proposed 17 years ago beyond the molecular and atomic level is undoubtedly forward-looking and enlightening. At the same time, it will also be an important research direction of methanol conversion catalyzed by molecular sieves from the perspective of condensed matter chemistry.

In 2006, Olsbye et al. Continued the idea of Dahl and Kolboe, clarified the role of olefin species and aromatic species in catalytic methanol conversion, and proposed a dual-cycle mechanism on this basis^[59,79,80]. They proposed that in ZSM-5, ethylene is mainly produced by aromatics cycle catalysis, while propylene and higher olefins are produced by olefins cycle catalysis. In addition, the two catalytic cycles can be converted to each other. On the one hand, a small amount of propylene produced by the aromatics cycle can be used as a co-catalyst to directly participate in the olefin cycle; On the other hand, the higher alkenyl species produced in the olefin cycle can generate new aromatic hydrocarbon pool species through aromatization reactions. Subsequent extended studies and theoretical computational studies have confirmed that the two-cycle mechanism has some universality in the MTO reaction catalyzed by molecular sieves^[28]. It should be noted that due to the complexity of the MTO catalytic reaction network, researchers usually infer the dominant catalytic reaction pathway through the species of reactive intermediates captured by experimental methods and the energy barrier of the reaction path simulated by theoretical calculation methods, and then compare the contribution of each catalytic cycle to the formation of light olefins.

The evolution from olefin pool to aromatic pool has also attracted the attention of many basic researchers. Polymethylcyclopentene species and polymethylcyclohexene species are critical^[81]. As shown in fig. 7, Zhang et al. Proposed a catalytic cycle based on methylcyclopentadienes (MCP)^[60,70]. In the initial stage of MTO reaction, olefin cycle dominates the MTO reaction, and then olefin species gradually evolve into aromatic species through multi-methylcyclopentene species. After the formation of aromatic species, the reaction gradually enters the stage of efficient conversion, and olefin cycle, cyclopentene cycle and aromatic cycle play a co-catalytic role at the same time. These theoretical breakthroughs, on the one hand, serve as a supplement to the traditional two-cycle mechanism, and on the other hand, explain the specific paths of mutual transformation between the olefin cycle and the aromatics cycle, making the depicted MTO reaction mechanism network closer to the real complex reaction system. The established multi-level dynamic catalytic network, which contains multiple independent and interrelated catalytic cycles, is very consistent with the concept of condensed matter chemistry, and is also an important theoretical breakthrough in the field of condensed matter catalytic chemistry.

With the gradual clarification of the chemical structure of hydrocarbon pool species and their role in the catalytic cycle, as well as the improvement of the MTO reaction mechanism network,Evolution of initial C-C bond-containing olefin species to pool species,The evolution of active hydrocarbon pool species to carbon deposition species (carbon deposition precursor) and the understanding and quantitative description of the dynamic evolution mechanism path of hydrocarbon products in MTO reaction (including gas phase products and catalyst phase organic species) have gradually become the focus of current condensed matter chemistry research.The solution of these important scientific problems will depend on the development of advanced characterization techniques and advanced theoretical computational methods.

The deactivation modes of catalyst in heterogeneous catalytic reaction can be divided into metal sintering, catalyst phase change, thermal decomposition and carbon deposition, etc. Metal sintering leads to permanent deactivation of catalyst, while molecular sieve carbon deposition is temporary deactivation, which can be regenerated by carbon elimination to restore the activity of catalyst^[68,82,83]. As an important part of molecular sieve catalytic reaction, molecular sieve carbon deposition also involves complex physical and chemical processes, spanning multiple scales and levels, such as atoms, molecules, secondary structural units, nano-pore/cage structures, molecular sieve crystals, etc. The formation and spatio-temporal evolution of carbon deposition is a direct manifestation of molecular sieve shape-selective catalysis, which directly affects the life of catalyst and product selectivity, determines the form of reactor, regenerator and the selection of corresponding process routes, and is an important scientific issue in condensed chemistry and condensed materials engineering. From the perspective of condensed matter chemistry, the most important scientific issues of carbon deposition on molecular sieves include the structure, location, spatiotemporal dynamic evolution of carbon deposition species and their role in the catalytic process. The deactivation of molecular sieve due to carbon deposition is more significant in the MTO reaction. The supercage structure in the zeolite molecular sieve or the rich nanometer confined space of the crossed pore canal can promote the activation of C1 molecules by changing the electronic energy level of guest molecules, and accommodate a large volume of methylbenzene carbocations or other annular reaction intermediates to provide a place for the subsequent efficient catalytic conversion of methanol,However, the smaller pore size (orifice) will significantly restrict the diffusion of bulky phenyl carbonium ions, so that they can be retained in the supercage or cross pore of molecular sieve to play a co-catalyst role for a long time.But on the other hand, it will inevitably accelerate the evolution of these unsaturated active intermediates to larger polycyclic aromatic hydrocarbon species and form carbon deposition species. There are two main ways of MTO catalyst deactivation due to carbon deposition: carbon deposition covers the acid sites of the catalyst, resulting in a decrease in its activity; Carbon deposits block the pores of the catalyst and hinder the molecular mass transfer of reactants and products^{[67,84⇓~86]}.

For the MTO reaction with distinct dynamic co-catalytic characteristics, the hydrocarbon pool species, namely the long-chain olefin intermediate and the aromatic hydrocarbon intermediate, are not only the primary products of methanol conversion, but also the core catalyst for catalyzing methanol conversion with high efficiency (forming a dynamic supramolecular active center with the molecular sieve skeleton and acting as a co-catalyst).It can be said that the essence of the regulation of molecular sieve-catalyzed MTO reaction is to regulate the carbon number range and chemical properties of unsaturated hydrocarbon species in the confined space of the pore channel-the activity of low olefin molecules is not high enough, and the highly unsaturated polycyclic aromatic hydrocarbon molecules are difficult to continue the methylation reaction to complete the catalytic cycle^[87]. Therefore, the carbon deposition behavior of molecular sieve is closely related to the dynamic evolution of hydrocarbon pool species, which is difficult to separate.The research on the behavior of coking and decoking on molecular sieves and the underlying chemistries involved in coking and decoking needs to be closely integrated with the mechanism of methanol catalytic conversion and the dynamic evolution of hydrocarbon products (including gas phase products, surface reactive intermediate species, and carbon deposition in confined space) in the MTO full spectrum. At the same time, the carbon deposition behavior of the catalyst is significantly affected by the crystal topology, acid properties, grain size and reaction conditions of the molecular sieve material. Therefore, the key conclusions must be carefully considered from multiple perspectives and levels (mainly atomic, molecular, mesoscopic condensed state, crystal scale) by using a variety of technical means.

The shape selectivity of molecular sieves is determined by their topological structure, that is, the reactants, active intermediates and reaction products are regulated by the restriction of nano-sized confined space, which can be further subdivided into reactant shape selectivity, transition state shape selectivity and product shape selectivity^[12]. The chemical structure, condensation state in confined space, and the formation and growth mode of carbon deposition species are controlled by the principle of shape selectivity (mainly transition state selectivity and product selectivity). As shown in Fig. 8, Haw et al. Summarized and pointed out in 2003 that with the progress of methanol conversion reaction, the confined polymethylbenzene species were gradually converted into polymethylnaphthalene, phenanthrene, pyrene and other polycyclic aromatic hydrocarbon species in a CHA cage^[15]. Based on the size of the CHA cage, they suggested that pyrene and its low methyl homologues with four benzene ring structures are the largest arene molecules that can be accommodated inside the SAPO-34 nanocage. At the same time, due to the steric effect, it is difficult for bulky pyrene molecules to continue the methylation reaction, so it is difficult to play the role of co-catalyst. The formation and accumulation of polycyclic aromatic hydrocarbons in SAPO-34 cage not only occupy the catalytic active sites, making it difficult for reactant methanol molecules to contact the catalytic active sites, but also block the diffusion channels of guest molecules due to the large volume, which together lead to the deactivation of SAPO-34 molecular sieve catalyst. Using HP¹²⁹Xe ssNMR, pulsed gradient field NMR and confocal fluorescence microscopy (CFM), Gao et al. Found that the fluorescence signals generated by the deposited carbon species initially appeared at the edge and eight vertices of the SAPO-34 cubic crystal, and with the progress of the MTO reaction, the fluorescence region moved to the crystal core region along the diffusion channel of the grain boundary or crystal interface^[61]. At the same time, they used in situ infrared spectroscopy to find that there are still a large number of acidic sites not covered by polycyclic aromatic hydrocarbons in the completely deactivated SAPO-34 molecular sieve grains, and the formation of carbon species in the outer cage of the molecular sieve grains will hinder the intragranular diffusion of methanol molecules, resulting in a sharp decline in the volume of accessible pores in the molecular sieve crystals. According to the molecular composition of carbon deposition species, carbon deposition space, diffusion properties of carbon deposition molecular sieve and the change of accessible acid sites of molecular sieve crystal with MTO reaction, they summarized and proposed a relatively complete SAPO-34 carbon deposition deactivation mechanism as shown in Fig. 9.From the point of view of the spatial and temporal distribution of carbon deposition and the intragranular diffusion of molecular sieves, combined with multi-scale information, it is confirmed that when the nanocage of SAPO-34 grains is occupied by a large area of polycyclic aromatic hydrocarbons, the lower mass transfer rate of guest molecules is the main reason for the deactivation of SAPO-34. This research idea of focusing on multi-scale and multi-level structure is in line with the research content and paradigm emphasized by condensed matter chemistry. Weckhuysen et al. Studied the catalytic performance and carbon deposition behavior of SAPO-34 and SSZ-13 zeolites with CHA structure in methanol conversion reaction by in situ UV-Vis diffuse reflectance spectroscopy in the temperature range of 300 ~ 500 ℃^[88,89]. They found that in the reaction temperature range of 300 ~ 325 ℃, the MTO carbon deposition species were mainly polymethylbenzenes. When the temperature rises to 350 ℃, the carbon deposition species are mainly polymethylbenzene and methylnaphthalene. When the reaction temperature is further increased to above 400 ℃, the carbon deposition species evolve into polycyclic aromatic hydrocarbons such as polymethylnaphthalene, phenanthrene and pyrene. At the same time, they also found that the polymethylnaphthalene species that led to the deactivation of the catalyst at low temperature evolved into reactive intermediates at higher reaction temperatures and played the role of co-catalyst, while the bulky polycyclic aromatic molecules with heavier molecular weight played the role of carbon deposition species that led to the deactivation of the catalyst. These results indicate that the behavior of carbon deposition on molecular sieves is not only dynamic in time and space, but also dynamic in the role of carbon deposition species in catalytic reactions.

The study of the evolution mechanism path of active hydrocarbon pool species to carbon deposition species is an important bridge between the MTO reaction mechanism and the carbon deposition chemistry of molecular sieves, and is the basis for defining the complex reaction network of molecular sieves catalyzed MTO. However, the reaction of aromatic species in the nanoconfined space of molecular sieves involves a variety of reactants and intermediates, and their interconversion process is transient and complex, which heavily depends on the development of advanced experimental characterization techniques and theoretical simulation methods, so the study of the evolution of carbon deposition species is very important but difficult to carry out. Yu et al. Successfully captured three important carbon deposition precursors for the conversion of monocyclic aromatics to bicyclic aromatics, namely tetrahydro-1,8-dimethylnaphthalene, dihydro-1,5,6-trimethyl-indene and 1,2-dimethyl-3- (2-butenyl) benzene, by using the optimized GC-MS technique when studying the conversion of methanol to olefins catalyzed by SAPO-34 at 350 ℃^[90]. Based on these carbon deposition precursors, a mechanism pathway for the conversion of highly reactive multi-methylbenzene species to less reactive naphthalene species on SAPO-34 molecular sieve was proposed, which is an important breakthrough in the evolution of carbon deposition species in molecular sieve condensed catalytic materials. The simulation results of DFT calculation show that this reaction path is reasonable in energy and is likely to occur (Fig. 10).

The carbon species produced under the guidance of CHA topology not only present the structure of polycyclic aromatic hydrocarbons. Based on the special experimental phenomenon that the SAPO-34 molecular sieve deactivated at low temperature is basically milky white, rather than dark green or black brown when deactivated at high temperature, Wei et al.It was found that the main reason for the deactivation of SAPO-34 by carbon deposition at low temperature was the accumulation of saturated cyclic compounds, adamantanes, in the CHA nanocage, which hindered the diffusion of guest molecules in the molecular sieve pores (Fig. 11)^[91]. The formation of adamantane and its methyl homologues in SAPO-34 nanocages leads to the discovery of the low-temperature deactivation mechanism of MTO reaction, which enriches the molecular composition and multi-level condensation state of the guest molecules of molecular sieve materials.It deepens the theory of carbon deposition and deactivation of condensed molecular sieve materials, expands the principle of C1 chemistry and molecular sieve catalytic chemical shape-selective control, and more importantly, provides an important theoretical basis for the smooth start-up of MTO industrial plant.

The real and full-spectrum molecular analysis of the dynamic evolution of carbon deposition species is a long-term pursuit in the field of molecular sieve catalytic chemistry and carbon deposition chemistry, and is also an urgent need for the development of practical industrial processes. Previously, the understanding of carbon deposition in molecular sieves was summarized as simple polycyclic aromatic hydrocarbon species inside the molecular sieve or graphitized carbon deposition on the outer surface of the molecular sieve, and it was difficult to correlate the exact evolution path of carbon deposition. It is of great practical significance to analyze the structure of carbon deposition species at the molecular level and track the evolution of carbon deposition species for carbon deposition deactivation and catalyst regeneration. Recently, Wang et al. Used advanced high-resolution matrix-assisted laser desorption/ionization Fourier-transform ion cyclotron resonance mass spectrometry (MALDI-TOF-MS).MALDI FT-ICR MS, isotope labeling technology, ¹³C magic angle spinning solid state nuclear magnetic resonance and DFT based theoretical simulation method were combined to determine the accurate molecular structure of heavy carbon deposition species with molecular weight of 300 ~ 2000 Da (which has existed for a long time but has not been resolved).At the same time, based on the existing understanding of carbon deposition, the real-time quantitative tracking of the molecular evolution of carbon deposition species in the restricted space of molecular sieve was realized, and the concept of "carbon atom footprint distribution" was put forward.It covers and distinguishes the main reaction of MTO process (the directional conversion of methanol to the target product light olefins guided by active hydrocarbon pool species) and the carbon deposition process (the evolution from active hydrocarbon pool species to cross-caged carbon deposition clusters).The full spectrum of MTO products, especially the complete "cradle-to-grave" evolution of organic species formed in the pore channels of molecular sieves, was described qualitatively and quantitatively, and a "full spectrum" molecular evolution picture for the important molecular sieve catalytic coking chemistry in condensed matter chemistry was proposed^[64][39]. Furthermore, by systematically studying the crosslinking growth process of initial carbon deposition species between SAPO-34 molecular sieve cages under the confinement of SAPO-34 molecular sieve micropores, a growth mechanism of PAH crosslinking across the cages was proposed.A relatively complete evolution path of carbon deposition in methanol to olefins reaction was given, in which the active hydrocarbon pool species in SAPO-34 molecular sieve cage (long-chain olefins and multi-methylbenzenes trapped in CHA nanocage) gradually expanded and fused to form carbon deposition precursors with 3 ~ 4 rings (soluble "carbon deposition").Subsequently, these carbon deposition structural motifs are cross-linked across the cage through covalent bonds guided by hydrogen transfer reactions to form polynuclear, nanographene-like polycyclic aromatic hydrocarbon species (insoluble carbon deposition clusters) occupying 2 to 4 CHA cages, as shown in Figure 12A. Therefore, it is proposed that the carbon deposition deactivation of CHA-structured zeolite molecular sieve condensed state materials is caused by the occupation of local CHA cages by carbonaceous deposits, which is not only caused by the long chain olefins with branched chains, adamantane and pyrene species "confined" in a single CHA cage.More importantly, with the further cross-linking coupling of organic molecules, the deactivation of molecular sieves is accelerated by the formation and accumulation of cross-cage cross-linked condensed species of polycyclic aromatic hydrocarbons in the nanoconfined space of molecular sieves. On the one hand, the evolution behavior of spontaneous dynamic carbon deposition crosslinking condensation explains the steep "reverse S" (gradually accelerating) catalyst deactivation curve of CHA materials at higher temperatures.This is in sharp contrast to the relatively gentle deactivation curve at lower reaction temperatures or in channel-structured ZSM-5 zeolites (in both cases, the cross-cage-crosslinking condensation behavior of polycyclic aromatic molecules is not significant), on the other hand, it provides ideas for the design of condensed catalytic materials such as molecular sieves and the development of efficient catalytic systems. By systematically studying the molecular structure of carbon deposition species in eight-membered ring molecular sieves with different cage structures, it was found that the condensation behavior of carbon deposition cross-linked across the cage was common in the catalytic system of cage-structured molecular sieves (Figure 12B). The significant differences in the molecular structure of aromatic units (naphthalene, pyrene and coronene) in the cage and the crosslinking mode of carbon deposition across the cage indicate that the carbon deposition across the cage of molecular sieves is dominated by the "cage" control principle of shape-selective catalysis of molecular sieves. The discovery of adamantyl low-temperature carbon deposition species and the breakthrough of molecular sieve cross-linked carbon deposition mechanism have greatly expanded the classical theory of carbon deposition deactivation of SAPO-34 zeolite molecular sieve with cage structure caused by polycyclic aromatic hydrocarbons such as naphthalene, phenanthrene, pyrene and adamantane species.Promote the establishment of molecular sieve carbon deposition chemistry based on molecular sieve catalysis from the perspective of condensed matter chemistry and engineering.

The polycyclic aromatic hydrocarbon molecule undergoes a speciation process of self-crosslinking, self-assembly and condensation under the unique confinement brought about by the periodic interconnected cage structure environment, and a dynamic molecular evolution mode of "quasi-quantization" with the inherent characteristics of increasing intramolecular unsaturation iteration step size.It not only reflects the space-time dynamic characteristics of MTO reaction and carbon deposition chemical behavior of catalytic reaction in molecular sieve condensed materials, but also greatly enriches the molecular recognition concept of molecular sieve based on the principle of "cage control" and the molecular understanding of shape-selective catalysis principle of molecular sieve catalytic chemical characteristics^[39]. Combined with the study of the spatio-temporal evolution of these cross-linked condensed carbon deposition species in the crystal scale of molecular sieves, it spans the atomic, molecular, nanocage structure and crystal levels, and from the perspective of mesoscopic multi-level structure.It enriches the connotation of host-guest interaction of condensed molecular sieve catalytic materials, and the breakthrough of this important research direction will provide important theoretical support for the design of new generation molecular sieve catalytic materials and the construction of low-carbon and efficient catalytic systems.

Unlike SAPO-34 zeolite, which has a bulky cage structure, ZSM-5 zeolite has a MFI topology, and the space at the intersection of three-dimensional channels is small. Early researchers believed that only low-order multi-methylbenzene species could be generated and accommodated in this space.At the same time, most of these species will diffuse to the outer surface of the zeolite grain and the gas phase through the 10-ring sinusoidal channel, and continue to undergo shape-non-selective thermal conversion process to form graphitized carbon deposition. This structural characteristic determines that the carbon content in the pore of ZSM-5 is low, and the main reason for deactivation is that the graphitized carbon layer formed on the outer surface of zeolite grain covers the pore. Wang et al. Pointed out that the straight-through channel is the main diffusion channel of polymethylbenzene, and the straight-through channel is more likely to be blocked by polymethylbenzene than the sinusoidal channel^[22]. In 2015, on the basis of previous research results, M Müller et al pointed out that the deactivation of ZSM-5 started from the coverage of acidic sites by oxygenated compounds (generated by the carbonylation reaction of surface methoxy groups), and then they reacted with olefin products to generate subsequent aromatics and carbon precursors, which led to the complete deactivation of ZSM-5^[92]. Recently, Wennmacher et al. used an advanced single crystal electron diffraction system to confirm that the formation and accumulation of carbon deposits at the intersection of MFI three-dimensional channels is the direct cause of the decline in catalytic activity of ZSM-5 (Fig. 13)^[93]. Lee et al. Proved through systematic research that the effect of carbon deposition in the pore channel on the catalytic activity is more significant than that of carbon on the external surface, and they also pointed out that at the real MTO reaction temperature (> 450 ℃), the zeolite framework will undergo "breathing" stretching movement as a whole.It is clear that the naphthyl species accommodated at the intersection of the three-dimensional channels of the MFI structure will grow and agglomerate through the intermediate containing methylene along with the reaction, and form a network of large molecular weight graphitized condensed aromatic hydrocarbon species inside the channels^[94]. To sum up, their research not only deepens the theory of molecular sieve carbon deposition deactivation mechanism, but also conforms to the development direction of condensed matter catalytic chemistry theory through multi-level research ideas and conclusions spanning molecular level, pore crossing space and molecular sieve crystal level.

The framework acidity (acid strength and acid density) of zeolite also affects the carbon deposition and deactivation behavior of the catalyst. The higher the acid density of the molecular sieve framework, the higher the concentration of olefin products in the CHA cage, and the greater the rate of their formation of carbon deposition species through hydrogen transfer, cyclization, and aromatization reactions, which in turn further strengthens the restriction on the diffusion of olefin species, resulting in rapid carbon deposition on the catalyst and catalyst deactivation^[95]. At the same time, a higher acid density means a smaller average distance between adjacent acid centers,The higher the probability of continuous conversion reactions (such as hydrogen transfer, polycondensation, etc.) occurring on adjacent acid sites during the diffusion of unsaturated reaction intermediates out of the molecular sieve grains, the more favorable the conversion of lower olefin species into condensed aromatic species^[96]. At the same time, the increase of acid strength of molecular sieve also accelerates the catalytic chemical reaction, the rapid deposition of carbon deposition species and precursors, and ultimately accelerates the deactivation of molecular sieve catalytic materials^[97⇓~99].

The effect of zeolite crystal size on MTO reaction is mainly reflected in the diffusion limitation of product molecules. The diffusion of small guest molecules in the micropores of molecular sieves belongs to configurational diffusion (also known as intracrystalline diffusion or molecular diffusion, that is, the molecular size is of the same order of magnitude as the pore size), and a small change in molecular size will cause a change in the order of magnitude of the diffusion coefficient. The larger the grain size of zeolite molecular sieve is, the longer the diffusion path of product molecules in the grain is, and the easier it is to form carbon deposition species through hydrogen transfer, cyclization and other reactions, which accelerates the deactivation of catalyst. However, this does not mean that the smaller the grain size, the better, because the appropriate degree of configurational diffusion restriction will further enhance the sieving effect of molecular sieve materials on light olefins such as ethylene and propylene.Inspired by this principle, the initial ethylene selectivity of MTO reaction was improved by pre-carbon deposition technology and appropriate metal ion modification^[37][34]. It can be seen that for the regulation of MTO reaction, it is far from enough to consider only from the molecular and skeletal acid center level, and it is necessary to consider the molecular diffusion behavior of guest molecules in the condensed molecular sieve material crystal from the perspective of mesoscopic multi-level structure. Considering these two factors, the following two ways are often used to improve the mass transfer effect and slow down the deactivation of catalyst carbon deposition: on the one hand, to reduce the grain size of molecular sieve and prepare nano-sized efficient molecular sieve; On the other hand, mesoporous or macroporous channels connected with microporous channels are introduced into the molecular sieve crystal grains to prepare the multistage porous catalyst^[100⇓~102].

Chemical application processes involving co-feed water and steam are very common in the field of industrial catalysis, such as fluid catalytic cracking, methanol to olefins, selective reduction denitrification, etc. At the same time, the working environment of molecular sieve catalysts is often more stringent hydrothermal conditions^{[103][4,45][104,105]}. In the MTO reaction, one molecular equivalent of water will be removed from the raw material methanol in the catalytic conversion process, and the introduction of co-feed water can promote the timely removal of reaction heat and maintain the temperature of the catalyst bed constant in a certain range. Therefore, the effect of water on MTO reaction and carbon deposition on zeolite molecular sieves is not only an important scientific issue in the field of condensed matter chemistry and engineering, but also of practical significance in guiding the optimization of industrial processes. The mechanism research in this area can be traced back to the early 1990s. However, due to the complexity of the MTO reaction system and the significant influence of water on the acid properties of the molecular sieve framework, the effect of water on the MTO reaction lacks appropriate characterization means and accurate and representative descriptors, and the number of specific research work is limited^[54,106]. In their early work, Marchi and Forment, Gayubo et al. And Wu and Anthony considered that water molecules and olefin products compete for adsorption at the active sites of SAPO-34 molecular sieve, and the adsorption capacity of active sites for polar water molecules is stronger than that for olefins. The introduction of water will inhibit the occurrence of side reactions such as hydrogen transfer and aromatization, increase the selectivity of light olefins, and delay the formation rate of carbon deposition^{[107][108][109]}. De Wispelaere et al. Studied the effect of water on SAPO-34-catalyzed MTO reaction from both theoretical and experimental perspectives by molecular dynamics simulation combined with in situ spectroscopy-microscopic imaging technique^[110]. They found that at 330 ℃, the mobility of protons on the framework of acidic zeolites was affected by the competitive adsorption of water, which was not conducive to the protonation of methanol and the formation of methoxyl groups on the surface, while water and propylene were competitively adsorbed at acidic sites.The oligomerization and cyclization of propylene are inhibited, thereby slowing down the formation of hydrocarbon pool species and their evolution to carbon deposition species, which promotes the diffusion of methanol and propylene into the grain interior and improves the utilization rate of molecular sieve catalyst grains. The results of in situ microscopic UV-visible spectroscopy and in situ confocal fluorescence imaging show that the introduction of co-feed water makes the "carbon deposition" more uniformly distributed in the molecular sieve crystal, which further confirms that water improves the utilization rate of molecular sieve crystal MTO reaction (Fig. 14). Zhao et al. Prolonged the MTO reaction lifetime of SAPO-34 by 200 times at 450 ° C using a high-pressure co-feed of water and hydrogen^[36]. Recently, Wang et al. Explained this phenomenon at the molecular level by using MALDI FT-ICR MS technology, and a large amount of co-feed water selectively inhibited the formation of nano-graphene-like polycyclic aromatic hydrocarbon species by cross-linking of polycyclic aromatic hydrocarbon structural units across the cage.Keeping the "carbon deposition" species in the range of active hydrocarbon pool species in the cage and prolonging the life of active hydrocarbon pool species are the fundamental reasons for prolonging the life of MTO reaction by co-feeding water and hydrogen^[39]. At the same time, they made it clear that the water molecules produced by methanol dehydration were not enough to produce such effects. When Wang et al studied the reaction of ethylene conversion to aromatics catalyzed by ZSM-5 at 300 ℃, they found that co-feed water and ethylene would compete for adsorption on Brønsted acid sites through canonical Monte Carlo simulation (GCMC).Water will preferentially adsorb on the acid sites, forming Z-OH…H₂O hydrogen-bonded complexes and H⁺(H₂O)_n species, thus occupying the pore channels and acid sites, inhibiting olefin oligomerization, ethylene-directed hydrogen transfer reactions and catalytic cycles with hydrocarbon pool species as the core^[111]. The water clusters adsorbed/aggregated in the pores can be desorbed by heating (> 350 ℃). Nevertheless, the enhanced confinement effect within the zeolite caused by partially physisorbed water molecules (clusters) still affects the operation of the hydrocarbon pool species, showing the overall effect of changing the aromatic product distribution without changing the catalytic conversion of ethylene.

Although the MTO process has been successfully commercialized, and research over the past decades has answered many questions about the MTO reaction mechanism and the deactivation mechanism of molecular sieve carbon deposition, there are still some key scientific and technical challenges to be solved. For example, smaller-sized arene species (e.g., polymethylbenzene and methylnaphthalene species) can serve as active reaction intermediates in the two-cycle mechanism, whereas the carbon-deposited species responsible for catalyst deactivation are usually composed of bulkier fused-ring arene structures. However, the boundary between active and inactive species, as well as the detailed mechanistic pathway of the evolution of active species to inactive species, is not yet clear; The mechanism of the effect of bulky trans-cage polycyclic aromatic hydrocarbons formed by carbon deposition and trans-cage crosslinking in the confined space of molecular sieve crystals on the diffusion of guest molecules needs to be studied. To solve these important scientific problems, we need to think from the multi-level and multi-scale perspective guided by condensed matter chemistry.

As an important part of the catalytic cycle, catalyst regeneration refers to the process of recovering the catalytic performance of the deactivated catalyst to a certain extent or completely by taking appropriate measures. The selection of regeneration method depends on the type of catalyst deactivation. For the deactivation of molecular sieve catalyst caused by carbon deposition, the main regeneration methods include oxygen/ozone /NO_x oxidation carbon deposition, steam/carbon dioxide gasification carbon deposition, hydrogen/alkane reduction carbon deposition and organic solvent extraction carbon deposition^[41,68].

The research and development of catalyst deactivation and regeneration process not only contains many important scientific problems, but also has a wide and important industrial application background, involving a wide range of contents.Including: (1) applied basic research on deactivation and regeneration at nanoscale, microscale and reactor scale to understand reaction-deactivation-regeneration mechanism and catalysis-carbon deposition-carbon elimination chemistry; (2) Measurement of deactivation rate and regeneration rate at laboratory reactor scale to develop and establish reaction kinetics, catalyst deactivation kinetics and regeneration kinetics, which is of great significance for scale-up process; (3) Carry out catalyst surface, particle and reactor-scale deactivation and regeneration process model studies to control and optimize scale-up and other related processes. It can be seen that the optimization and development of industrially important catalyst regeneration methods require theoretical knowledge beyond the theory and engineering of carbon elimination regeneration, covering catalyst material design and synthesis, reaction mechanism and deactivation mechanism.It is a complex field that needs comprehensive consideration, and it is also an important research direction of condensed matter chemistry and engineering, in which a clear and profound understanding of catalyst deactivation mechanism is the basis. For molecular sieve catalysts, it is a prerequisite to establish the molecular basis of carbon deposition chemistry and carbon elimination chemistry (including the complete and accurate molecular structure of carbon deposition, the complete mechanism path of species growth, spatial and temporal dynamic evolution, and elimination).

In addition, it should be noted that catalyst carbon removal and regeneration is a non-spontaneous process, which often consumes energy and resources-usually carbon deposition is converted into carbon dioxide, which wastes carbon resources and breaks the carbon balance on the one hand, and aggravates climate problems such as greenhouse effect on the other. The research on the regeneration of carbon deposition catalyst is not only the mission of scientists and industrial application development engineers, but also attracts great interest of engineering managers, economists and environmentalists. Therefore, relying on the modern chemical industry system with a huge volume, a huge amount of carbon deposits (composed of a large number of aromatic hydrocarbons and polycyclic aromatic hydrocarbons, containing a large amount of energy, can be regarded as fixed carbon resources) can be utilized as resources.It is one of the important frontier issues in the development of industrial catalysis to establish an industrial catalyst regeneration strategy that couples the carbon removal regeneration of low-carbon emission carbon deposition catalyst and the conversion of carbon deposition into high value-added chemicals or platform compounds.At the same time, it is also an important part of the optimization and innovation of the national energy structure under the current "double carbon" background, which is of great significance to the low-carbon development of traditional energy and chemical industry as a pillar^[66].

In 2021, Zhou et al. reported that high temperature steam (680 ℃) could directionally convert the carbon deposition species in the deactivated SAPO-34 into naphthalene (as shown in Fig. 15), which could improve the initial olefin selectivity of the regenerated catalyst on the one hand, reduce the carbon dioxide emission in the catalyst regeneration process on the other hand, and improve the utilization rate of carbon atoms and hydrogen atoms^[40]. Subsequently, they verified this technology on a circulating fluidized bed reaction-regeneration pilot plant, and the results of continuous and stable operation showed that the recyclable syngas components (CO and H₂) in the gas phase products of the regenerator exceeded the 88%,CO₂ by less than 5%; The selectivity of ethylene and propylene in the reactor can reach 85%. This technology realizes the regulation of MTO reaction through regeneration, further improves the economy of the process, reduces CO₂ emissions, and has an important impact on the sustainable development of MTO technology and industry^[38,41]. It is worth noting that SAPO-34 molecular sieve has good hydrothermal stability at high temperature (the crystallinity of the sample treated at 800 ℃ for 45 H is still above 90%), which avoids the dealumination of the molecular sieve and the permanent deactivation of the catalyst caused by high temperature steam, and the carbon deposition has a "protective" effect on the molecular sieve framework, which provides an important basis for the regeneration of carbon removal by high temperature steam^{[112][113,114]}. The ²⁷Al, ²⁹Si, ³¹P NMR spectrum and chemical environment of Al, Si and P species of carbon deposition SAPO-34 before and after water treatment did not change significantly, which also proved this point^[115].

To develop more efficient and low-carbon catalytic systems to meet the requirements of the "double carbon" policy, it is a prerequisite to analyze the complete reduction mechanism network of molecular sieve carbon deposition species at the molecular level. Wang et al. Used high-resolution MALDI FT-ICR mass spectrometry to systematically study the effects of steam treatment temperature (475 ~ 650 ℃), steam partial pressure (0.1 ~ 2 MPa) and treatment time on the decomposition process of carbon deposition under high temperature hydrothermal conditions.The positive and different effects of water on the two important processes of inhibiting the formation of carbon deposit and promoting the decomposition of carbon deposit were clarified, that is, under the condition of MTO reaction, the co-feed water selectively inhibited the cross-linking of active hydrocarbon pool species and aromatic structural units in the cage, and slowed down the deactivation of catalyst by carbon deposit^[39]; However, in the high-temperature regeneration process, the water molecules with high local concentration can greatly restore the catalyst activity by decomposing the formed cross-linked polycyclic aromatic hydrocarbon species into cage hydrocarbon pool species in situ, and further converting them into H₂ and CO. Through the comparative experiments of methanol-water and methanol-argon co-feed MTO, it was found that the water produced in situ by MTO reaction was not enough to inhibit the cross-cage crosslinking of aromatic structural elements in the cage. By directly capturing and observing the diaryl and biphenyl reaction intermediate species for the decomposition of cross-cage crosslinking carbon deposition species in SAPO-34, they gave a relatively complete mechanism network for the decomposition of carbon deposition in methanol to olefins reaction:The decomposition of the cross-cage carbon species in the confined space of SAPO-34 molecular sieve starts from the cracking of the local anti-aromatic structure (four-membered ring or five-membered ring structure) between the cages, and the produced intra-cage aromatic structural elements as primary cracking products are further decomposed into CO and H₂ by light olefins (as shown in Fig. 16). To decipher the reversible and dynamic evolution trajectory of MTO full lineage carbon deposition and elaborate the detailed molecular path, which provides a molecular basis for the establishment of molecular sieve catalytic carbon elimination chemistry from the perspective of condensed matter chemistry. Based on the breakthrough understanding of the mechanism of carbon deposition deactivation and carbon elimination regeneration of SAPO-34 molecular sieve, especially the deciphering of the decomposition mechanism of cross-linked polycyclic aromatic hydrocarbons in the restricted space of molecular sieve,The steam regeneration strategy of new generation carbon deposition catalyst was proposed under the conditions of 650 ℃ and 2 MPa water partial pressure, which combined the resource utilization of carbon deposition (the gas phase products of steam regeneration were mainly H₂(50 vol%) and CO (40 vol%)) and the avoidance of CO₂ emission in the carbon removal process. In the extended study, the coke on FCC catalyst was treated with steam at 650 ℃ and 2 MPa water partial pressure, and it was found that the coke on the catalyst was basically eliminated and the reaction performance was greatly restored after steam regeneration, and the sum of H₂ and CO in the gas phase products accounted for more than 90%. The ²⁷Al NMR spectra of coke deposited commercial FCC catalyst (mainly containing zeolite Y with a small amount of zeolite ZSM-5 as well as co-catalyst and binder) before and after steam treatment at high temperature and high pressure were basically consistent, indicating that the chemical environment of Al species did not change significantly^[39]. This may be due to the fact that the industrial FCC catalyst has been subjected to ultrastabilization treatment, and the hydrothermal conditions required for carbon removal and regeneration are milder than those required for ultrastabilization treatment, which is not enough to dealuminate the zeolite component in the FCC catalyst within the service life and cause permanent deactivation. This further shows that the high temperature steam regeneration strategy has certain applicability in the FCC process. To sum up, this environmentally friendly high-temperature steam regeneration strategy with high carbon atom cycle economy has good universality in the important FCC process in petrochemical industry and the important MTO process in coal chemical industry.It provides a feasible technical route for accelerating the adjustment of China's overall energy structure and industrial upgrading, as well as building a "green", low-carbon and efficient national energy innovation system.