Metal-organic Framework (MOF) compounds are made by linking Metal-containing units [secondary building units (SBUs)] together with organic ligands, using strong bonds (network synthesis) to create an open crystalline framework with permanent porosity. Over the past few decades, their variable flexibility in geometry, size, and function has allowed more than 20 000 different MOFs to be reported and studied^[1,2].

A substance that can change the chemical reaction rate of other substances in a chemical reaction without changing its mass and chemical properties before and after the reaction is called a catalyst (also known as a catalyst), which is widely used in laboratories and industrial production. According to the phase state of the reaction system, it can be divided into homogeneous catalyst and heterogeneous catalyst. Homogeneous catalyst generally has good catalytic effect because of its large contact surface and high reaction utilization rate, but after catalysis, the activity and selectivity of the catalyst are greatly reduced and it is difficult to recover. Heterogeneous catalyst can realize the recycling of catalyst and effectively reduce the cost of industrial production, but the catalytic effect is relatively poor and the dosage is large. MOFs have many advantages in homogeneous and heterogeneous catalysis due to their very open structure, high specific surface area, adjustable pore size and high density of active centers, which have attracted wide attention of scholars at home and abroad. For example, MOFs can be used to support homogeneous catalysts, stabilize short-lived catalysts, and encapsulate catalysts within their pores^[3]. In 1994, Fujita et al. Constructed Cd(4,4’-bpy)₂(NO₃)₂ MOF clathrate through the reaction of Cd(NO₃)₂（ (cadmium nitrate) and 4,4 '-bpy (4,4' -bipyridine), and used it as a heterogeneous catalyst for the cyanosilylation of aldehydes. Since then, the application of MOFs materials in the catalytic transformation of organic molecules has been reported^[4]. In many organic reactions, carbon-carbon bond formation and oxidation-reduction of unsaturated hydrocarbons are the basic reactions for the preparation of organic compounds, which have been widely used in pharmaceutical, cosmetic and agrochemicals industries^[5⇓~7]. At present, there are some reviews on the types, synthetic materials, synthetic methods, applications in catalysis and application strategies of MOFs, but there is no review on the most common and general organic classical reactions such as carbon-carbon bond formation, oxidation and reduction of unsaturated hydrocarbons.In this paper, several common and widely used organic chemical reactions catalyzed by MOFs as catalysts are reviewed, and the development trend of their catalytic applications is prospected^[8⇓~10].

Knoevenagel condensation reaction is the reaction between aldehydes (or ketones) and compounds with active methylene groups (with two electron-withdrawing groups). It is one of the most common and versatile organic reactions of C − C bond formation, and is widely used in the synthesis of heterocyclic compounds and bioactive substances. The condensation reaction is catalyzed by a base or a Lewis acid at a relatively high temperature or under microwave irradiation (as shown in fig. 1), but the use of a base catalyst causes difficulties in separation and waste^[11,12]. Studies have shown that heterogeneous catalysts have ecological advantages and can avoid these disadvantages. MOFs are ideal candidates because of their structural flexibility, ease of separation, and adaptability to a variety of reaction conditions. At present, a large number of different kinds of MOFs have been reported as catalysts for the Knoevenagel condensation reaction, and the most widely studied is the Knoevenagel condensation reaction with benzaldehyde and malononitrile as substrates. Among these materials, the non-functionalized MOF: UiO-66 has a certain catalytic ability, but its catalytic activity is very low and often negligible, for example, the yield of benzaldehyde and malononitrile using UiO-66 in toluene at 23 ℃ for 2 H is less than 1%^[13]. Under the same reaction conditions, the yield of the modified UiO-66-NH₂ was increased to 5%. The UiO-66-NH-RNH₂ obtained after further functionalization of primary aliphatic amine on the basis of UiO-66-NH₂ showed higher catalytic activity with a yield of up to 97% (Fig. 2)^[13]. The enhancement mechanism is that the ability to directly abstract protons from active methylene compounds is enhanced by enhancing the alkaline strength of the basic site of the MOF, resulting in the formation of more carbanions, and more carbanions attack the carbonyl carbon atom of benzaldehyde, ultimately achieving a higher yield^[13]. Therefore, in many MOFs catalysts, in order to promote the reaction or catalyze the cascade reaction, certain modifications are often made on the basic MOFs materials, such as the introduction of coordinatively unsaturated metal sites-immobilized diamine, amino group on the ligand, alkaline earth metal center, etc^[14][15][16].

Han et al. Synthesized a bifunctional MOF：Yb-BDC-NH₂（Yb= ytterbium; BDC = terephthalic acid) was used in the tandem decondensation of benzaldehyde dimethyl acetal, and the resulting benzaldehyde was subjected to Knoevenagel condensation with malononitrile at 50 ℃ for 24 H with a high yield of 97%, due to the strong Lewis acidity and small ionic radius of the ytterbium-based MOF center^[17]. Xu et al. Synthesized three different Zn-MOFs by using dicarboxylic acids and different Zn-containing ligands, and the three catalysts showed 100% selectivity for Knoevenagel condensation. Among them, the Zn-MOF with three-dimensional hollow sphere structure has the highest conversion rate of benzaldehyde, which can reach 90%^[18]. Dong et al. Reported a Pd-nanoparticle-loaded, pH-tunable polymer-grafted UiO-66 type NMOF-based Pickering interfacial catalyst Pd @ PDEAEMA-g-UiO-66 (PDEAEMA = poly [2- (diethylamino) ethyl methacrylate]), which can well promote the one-pot two-phase Knoevenagel condensation, hydrogenation cascade reaction at room temperature, and can be recycled for the next catalysis^[19].

In summary, MOFs are widely used in heterogeneous reactions of aldehydes (or ketones) and active methylene compounds. The catalytic activity of MOFs modified by different modification methods is different, so the appropriate MOFs should be selected as the catalyst according to the type of reaction substrate in order to obtain a better reaction yield.

The Suzuki-Miyaura reaction is the most common C − C cross-coupling reaction between halogen compounds and organic borides and their derivatives catalyzed by palladium or nickel under alkaline conditions (Figure 3), which usually occurs under very mild conditions^[20]. Suzuki-Miyaura reaction is widely used in industry and pharmaceutical industry, but it needs to consider the reaction conditions without water and oxygen. In this reaction, the activity and selectivity of palladium catalyst are greatly reduced and difficult to recover, which greatly increases the cost of pharmaceutical enterprises. MOFs have unique advantages as recyclable heterogeneous catalysts in this reaction, and in addition, the robustness of MOFs catalysts allows them to solve the dilemma of using nickel-based catalysts.

Madrahimov et al. Developed a new MOFs catalyst ：UiO-66(L₃)（ as shown in Fig. 4) to catalyze the Suzuki-Miyaura reaction of bromobenzene and phenylboronic acid, which used potassium carbonate as the base and acetonitrile as the solvent at 65 ° C for 12 H with a yield of up to 96%, and the catalyst could be reused for more than 7 times^[21]. Bian et al. Reported a core-shell magnetic catalyst Fe₃O₄@PDA-Pd@[Cu₃(btc)₂](PDA= polydopamine for the reaction of bromobenzene and phenylboronic acid; btc = 1,3,5-benzoic acid), potassium carbonate as base, ethanol ∶ water (V/V = 1 ∶ 1) as solvent, reaction temperature 75 ℃, reaction time 30 min, the yield can reach 97%, and the catalyst can be reused more than 8 times after magnetic recovery. The excellent performance is attributed to the strong synergistic effect between Fe₃O₄@PDA-Pd and [Cu₃(btc)₂]^[22]. The magnetic Fe₃O₄-Pd catalyst ：Fe₃O₄@La-MOF-Schiff base-Pd, synthesized by Sun and Dragutan et al., can also be used to catalyze the Suzuki-Miyaura reaction of various aryl halides with arylboronic acids, and the yield can reach more than 99% at 80 ° C for 30 min with potassium carbonate as the base and ethanol as the solvent, and the catalyst can be reused for more than 12 times without any significant decrease in the reaction yield. The addition of lanthanum ion improves the stability of the palladium part and the synergistic effect between palladium and lanthanum nodes, so that the Fe₃O₄@La-MOF-Schiff base-Pd has better activity and stability^[23]. Zhou et al. Reported a new MOF catalyst: PCN-160-Pd (PCN = porous coordination network), which was obtained by direct coordination of Pd on azobenzene linker through a suitable modification method. The heterogeneous nature of the catalyst and its stability were proved by "hot filtration" and recovery experiments. In addition, it was demonstrated that the MOFs packed column promoted the reaction of phenylboronic acid and bromobenzene under microflow conditions with a yield of 85%, which provides a potential for the industrial application of MOFs catalysts in efficient, recyclable, and continuous flow systems^[24].

The Mizoroki-Heck reaction, discovered by Mizoroki and Heck, is the palladium (0) -catalyzed coupling of a vinyl, aryl, or benzyl halide with an olefin (Figure 5)^[25][26]. Palladium-catalyzed Mizoroki − Heck coupling between alkenes and aryl electrophiles has become one of the most powerful tools for C — C bond formation since it was first reported in the 1970s. In addition, it is suitable for different kinds of functional groups, so it has been widely used in the synthesis of drugs, organic materials and natural products^[27].

The Mizoroki-Heck reaction usually requires the addition of a ligand with relatively strong coordination ability with the molecular palladium catalyst, such as palladium bis (acetylacetonate) with or without triphenylphosphine, which is the most commonly used, but the activity of palladium bis (acetylacetonate) and palladium nanoparticles will be reduced due to aggregation.Some MOFs can be combined with palladium catalysts by themselves, or pyrolyzed at 100 ℃ to produce a large number of pores, each of which exists independently and contains many active Pd sites, thus solving the problem of deactivation caused by catalyst aggregation^[28]. Shaikh et al. Reported the transformation of hexagonal ZIF-8 (ZIF = imidazolate zeolite framework) microcrystals into rod-like and flower-like PdNPs @ ZIF-8 under controlled addition of formic acid. PdNPs @ ZIF-8 catalyzed the Heck coupling of aryl halides with substituted styrenes in up to 98% yield^[29]. The palladium-based microporous organic nanotube framework-supported catalyst Pd@NH₂-MONFs synthesized by Huang et al. Gave yields between 94% and 99% for the Heck reaction of various aryl iodides and methyl acrylate at 90 ° C, and the catalyst was recycled for more than six times without a significant decrease in catalytic activity^[30]. Dou and Li et al. Synthesized several palladium-based MOFs-derived catalysts Pd@Co₃O₄, Pd@Co₃O₄/C, and Pd@Co/CNT（Pd@Co₃O₄ as shown in Fig. 6) (CNT = carbon nanotube) through the pyrolysis of Pd @ ZIF-67 to catalyze the Heck reaction of styrene and iodobenzene at 120 ° C with high yields (94% – 99%). Among them, Pd @ Co/CNT can be reused for 5 times without loss of activity^[31]. Under solvothermal conditions, Dong et al. Reported an MOF catalyst containing a palladium N-heterocyclic bis-carbene dicarboxylate ligand: UiO-67-Pd-NHDC, which catalyzed the Heck coupling reaction of aryl halides and ethyl acrylate in up to 99% yield^[32]. Zou and Martin-Matute et al. Combined operando X-ray absorption spectroscopy (XAS), X-ray powder diffraction, transmission electron microscopy (TEM) and hydrogen nuclear magnetic resonance spectroscopy (¹H NMR) to study the mechanism of Heck reaction in Pd @ MOF catalyst. The results show that the Pd^II complex is dominant at the beginning of the reaction, and Pd⁰ nanoclusters containing an average of 13 to 20 palladium atoms are gradually formed in the subsequent reaction, and the Cl^- produced during the reaction is coordinated with the surface of the cluster, which can prolong the lifetime of the catalyst^[33].

Aldol condensation reaction, also known as Aldol condensation reaction, refers to the nucleophilic addition of compounds containing active α-hydrogen atoms, such as aldehydes, ketones, carboxylic acids and esters, to carbonyl compounds under the action of acid or base to obtain α-hydroxyaldehydes or acids, or further dehydration to obtain α, β-unsaturated aldehydes or esters (Figure 7). Aldol reaction is also an important organic reaction of C — C bond formation, which is widely used in organic synthesis^[34,35]. Basic MOFs proved to be catalytically active in various aldol reactions between ketones (e.g. Acetone, cyclohexanone, acetophenone, and cyclopentanone) and aldehydes (e.g. Aromatic aldehydes with different substituents)^[36⇓~38].

The magnesium-based MOF material Mg₃(PDC)(OH)₃(H₂O)₂（PDC=3, 5-pyrazoledicarboxylic acid ）<sub>, </sub > has some basic properties of MOFs materials and can be used to catalyze aldol reactions. During the reaction, the aldol reaction was carried out in the presence of an excess of ketone in order to avoid self-condensation of the aldehyde^[36,37]. When Koner et al. Used a mixture of THF/H₂O as the reaction medium to catalyze the reaction of acetone with p-nitrobenzaldehyde with Mg₃(PDC)(OH)₃(H₂O)₂, the highest yield of the β-aldol product (82%) was obtained in a reaction medium of 3:1 THF/H₂O. In the reaction studied, all aldehydes were converted to the corresponding β-alcohols as individual products. The catalytic activity of Mg₃(PDC)(OH)₃(H₂O)₂ was also compared with that of traditional solid base magnesia. For the Aldol condensation of acetone and p-nitrobenzaldehyde, the yield was 82% in 6 H with Mg₃(PDC)(OH)₃(H₂O)₂ as the catalyst, while the yield was 75% in 24 H with solid basic magnesium oxide as the catalyst^[39]. This indicates that the catalytic performance of the Mg-based MOF material Mg₃(PDC)(OH)₃(H₂O)₂ is superior to that of the traditional solid alkali magnesium oxide in the Aldol condensation reaction.

In addition to magnesium-based MOF, another alkaline earth metal, barium-based MOF：Ba(PDC)H₂O, was also active in the aldol reaction, and the yield of barium-based MOF was 67% when it catalyzed the reaction of acetone and benzaldehyde, which was higher than that of magnesium- based MOF (58%). Upon catalyzing the reaction between acetone and p-nitrobenzaldehyde, the yield of barium-based MOF was 96%, which was significantly higher than that of magnesium-based MOF (82%)^[39,40].

The A³ coupling reaction is a three-component coupling reaction involving alkyne, aldehyde and amine. Under the catalysis of various transition metal catalysts such as cuprous bromide and ruthenium trichloride, the reaction will produce propargylamine compounds. The reaction can be carried out in an aqueous medium (Figure 8). The reaction conditions are mild, the atom utilization rate is high, the by-product is only water, and the heavy metal catalyst adopts a catalytic amount, so the method is more environment-friendly^[41]. Some research groups have used MOFs catalysts for A³ coupling reaction and achieved good results.

N-Heterocyclic carbenes (NHC) are catalysts for a wide range of valuable chemical reactions and are widely used for the formation or cleavage of carbon – carbon, carbon – nitrogen, and carbon – oxygen bonds. Therefore, the integration of NHC into MOF can tightly combine multiple different catalytic sites in one structure, thus improving the catalytic efficiency^[32].

Verpoort et al. Used the developed Ag-NHC-MOF for the A³ coupling reaction of paraformaldehyde, phenylacetylene and diisopropylamine in CH₂Cl₂ at room temperature for 1 H with a yield of 97%, and the catalyst was recycled four times and could be further used for the A³ coupling reaction with other substrates^[42]. Wang et al. Synthesized core-shell AgNP @ IRMOF-3 with an average size of 5.2 nm in only 5 min on the basis of IRMOF-3 (IRMOF = network metal-organic framework material) with an average size of 91.5 nm, which had high activity for the A³ coupling reaction of amine, aldehyde and acetylene, and the catalyst could be reused for 8 times without loss of catalytic activity^[43]. Zhang et al. Synthesized a series of Au/MOF-199 (Fig. 9) within 2 min under microwave irradiation, which catalyzed the A³ coupling of formaldehyde, phenylacetylene and piperidine in 1,4-dioxane, and the yield was as high as 93% at 120 ° C for 5 min. The catalyst was reused for five times without significant loss of activity^[44]. Yang and Jiang reported that MOF containing Au^δ+ and Au⁰ nanoparticles was obtained by modification after synthesis of MIL-101-NH₂(MIL= Lavashir framework series materials),The catalytic performance of the two catalysts in A³ coupling was compared, and they found that the activity of the Au^δ+ catalyst was 11 times higher than that of the Au^0[45]. Liu and Tai et al. Reported a method to synthesize salicylaldehyde-functionalized MOF by nucleophilic addition of salicylaldehyde to the amino group of NH₂-MIL-53(Al), then encapsulating Au^Ⅲ into the MOF, and then reducing Au^Ⅲ into encapsulated Au nanoparticles, which can catalyze the A³ coupling of various aromatic or aliphatic aldehydes, aromatic alkynes, and pyridines, and the catalyst can be recycled four times^[46].

In order to reduce the emission of CO₂ and make full use of this cheap, green and inexhaustible carbon source, the conversion of carbon dioxide into valuable fine chemicals is considered to be one of the most important strategies to achieve a carbon-neutral society.Cyclic carbonates of epoxides obtained from the catalytic cycloaddition of CO₂ as monomers, intermediates, solvents, and additives are a growing area of research as a way to convert CO₂ into value-added products (Figure 10)^{[47⇓~49][50]}.

Previous studies by Zhao et al. Found that copper-based MOFs could effectively catalyze the cycloaddition of CO₂ with aziridines to obtain oxazolidinones under mild conditions, as well as the carboxylation of terminal alkynes with carbon dioxide to produce carboxylate compounds under mild conditions. Inspired by these works, they then designed and constructed stable Cu_xI_y cluster-based heterometallic MOF：(NH₂C₂H₆)_0.75[Cu₄I₄·L₃·In_0.75]·DMF·H₂O（DMF=N,N- dimethylformamide) and efficiently catalyzed the cycloaddition of propargylic alcohols with CO₂ in up to 99% yield under the addition of quantitative triethylamine. Follow-up studies found that the synergistic effect between Cu^Ⅰ and In^Ⅲ was responsible for catalyzing the conversion of CO₂^[51]. Jiang et al. Reported nitrogen-doped carbon-coated porous zinc oxide nanoparticles: ZnO @ NPC-Ox-700 (Fig. 11). They pyrolyzed ZIF-8 at 700 ℃, and the product was oxidized with sodium hypochlorite to produce ZnO @ NPC-Ox-700. The catalyst catalyzes the cycloaddition reaction of CO₂ with epoxides at 60 ° C in the presence of tetrabutylammonium bromide, which provides a synergistic effect for catalytic activation due to the presence of phenol, carboxylic acid and lactone groups on the porous carbon surface of ZnO @ NPC-Ox-700, resulting in 100% selectivity and 98% conversion of the reaction, and the catalyst can be recycled 10 times. In addition, zinc oxide can be reacted at relatively low temperature and carbon dioxide pressure compared with porous materials such as porous carbon and ZIF^[52]. Sheng and Zhu et al. Synthesized nanoclusters using [Au₁₂Ag₃₂(SR)₃₀]⁴⁻ and [Zn²⁺]₂, and then reacted them with ZIF-8 precursor 2-methylimidazole in methanol for 24 H to obtain Au₁₂Ag₃₂(SR)₃₀@ZIF-8. The nanomaterial catalyzed the addition of CO₂ to phenylacetylene to phenylpropionate in the presence of base (cesium carbonate or potassium carbonate), and the catalytic performance exceeded that of most reported catalysts, and the catalyst was reused five times^[53].

In organic synthesis, the oxidation of unsaturated hydrocarbons is the key to the introduction and modification of functional groups, which is widely used in organic synthesis. Reports on the catalytic oxidation of unsaturated hydrocarbons by MOF-based catalysts involve various reaction types using tert-butyl hydroperoxide, hydrogen peroxide, and oxygen as oxidants (Figure 12)^[54].

Spodine et al. Used the synthesized [Cu(H₂btec)(bpy)](H₄btec= pyromellitic acid) as a catalyst for cyclohexene epoxidation and styrene oxidation, cyclohexene was oxidized at 75 ° C for 24 H with a selectivity of 73.1% and a conversion of 64.5%. Under the same conditions, the conversion of styrene was 71%. In their work, tert-butyl hydroperoxide was used in equimolar amounts, and thus, from the perspective of hydrogen peroxide consumption, the copper MOFs exhibited high selectivity for oxidation, minimizing tert-butyl hydroperoxide decomposition for other reasons. However, the reuse of the catalyst in the oxidation reaction as well as the stability studies were not reported^[55]. Recently, some groups have reported the application of more complex MOFs catalysts in catalytic oxidation, in which Fan et al. Prepared a multi-component MOF nanomaterial Zn₁Co₁-ZIF and applied it to the reaction of styrene catalytic oxidation (MOF catalyst is shown in Fig. 13), with a selectivity of 70% and a conversion rate of up to 99%^[56]. Han et al. Synthesized an Au/Zn-MOF with a sub-nanometer (0.8 nm) size. In the presence of oxygen, the Au/Zn-MOF catalyzed the oxidation of cyclohexene at 100 ℃ for 8 H, showing high activity (82% conversion) and 98% selectivity^[57]. Tsung and Nguyen cleverly designed a bifunctional catalyst Pd @ UiO-66- (sal) Mo. They first used (sal)Mo^Ⅵ（sal= salicylaldimine) to modify the surface of the UiO-66-NH₂, and then encapsulated palladium in it.The encapsulated palladium nanoparticles contact with H₂ and O₂ to generate hydrogen peroxide, while the large olefin substrate is prevented from contacting with the encapsulated palladium nanoparticles by the MOF. Then, the (sal) Mo part uses the generated hydrogen peroxide to oxidize the olefin. This catalyst well connects the generation of the oxidant with the catalytic oxidation^[58]. Gao and Wang et al. Synthesized Cu-CuFe₂O₄@HKUST-1, which has high catalytic activity (conversion of 99%) and selectivity (99%) in the catalytic oxidation of fluorene at 60 ℃ and oxygen. The good catalytic performance comes from the active sites on the CuFe₂O₄ and the adsorption of oxygen by MOF. In addition, the magnetic catalyst was easily separated and reused 10 times after recovery^[59].

Hydrogenation of olefins is one of the main reactions in chemical industry and organic synthesis. MOF catalysts containing palladium are often used to catalyze the reduction of unsaturated hydrocarbons, and are one of the most effective catalysts for the hydrogenation of unsaturated carbon-carbon bonds (Figure 14)^[7].

Zhang et al. Synthesized Pd/F-ZnO @ ZIF-8 by using flower-like zinc oxide as the carrier of palladium nanoparticles and the zinc source of ZIF-8. The catalyst was used to catalyze the hydrogenation of 1-hexene to 1-hexane, and the conversion rate reached 99. 8% after 10 H^[60]. The bimetallic catalyst PdZn @ ZIF-8C synthesized by Chen and Zhou et al. Showed a selectivity of 80% and a conversion of nearly 100% in the selective hydrogenation of acetylene to ethylene, but the aggregation of nanoparticles occurred, which reduced the catalytic performance of PdZn @ ZIF-8C^[61]. Pd @ CN prepared by Chen et al. By calcining ZIF-67 showed good catalytic performance (conversion of 95.6% and selectivity of 94.9% after 95 min) and good stability (no significant decrease after the fourth cycle) for the hydrogenation of phenol to cyclohexanone^[62]. Yamashita et al. Reported the pyrolysis of Ni-MOF-74 at 300 ℃ to obtain NiNP-C/Ni-MOF-74 core-shell nanomaterials, which showed high catalytic performance for 1-octene hydrogenation (97% conversion after 0.5 H) due to the small and highly dispersed nickel nanoparticle core^[63]. The improvement of the catalytic performance is mainly attributed to the fact that the MOF increases the contact opportunity between the metal catalyst and the reaction substrate, thereby increasing the yield of the reaction.

Catalysis plays a vital role in the conversion of chemicals, whether in the laboratory or in industry.As one of the interfacial metal-organic catalysts, MOFs have good application prospects in the field of interfacial metal-organic chemistry catalysis because of their large specific surface area, high porosity, and tunable structure and properties. Because the reaction conditions of different reactions are quite different, in order to meet the catalytic requirements of various different conditions, it is necessary to select the appropriate MOFs, which puts forward high requirements for the stability, selectivity and efficiency of MOFs catalysts. The thermal stability and water stability of MOFs are the main considerations. At present, UiO-66, ZIF-8, MIL-101, MOF-74, etc. Have been proved to have good durability and resistance to harsh catalytic conditions and environments, which is very beneficial for industrial production. However, the catalytic performance of some high oxidation state metal nodes, such as Ti^IV (titanium) and Zr^Ⅳ (zirconium), needs to be further improved.

For MOFs catalysts, the loaded metal nanoparticles must be very small, preferably sub-nanometer in size, but the efficiency sometimes decreases when the nanoparticle size is reduced below a specific number of atoms. However, the difference of MOFs as a heterogeneous catalyst is that the single-atom ligand is strictly maintained in the solid matrix, and a stable framework environment can be constructed around the catalytic center, which can better catalyze some of the classical chemical reactions mentioned above. In a sense, organometallic chemistry has contributed to the understanding of MOFs catalysis, and in turn, MOFs catalysis has contributed to the understanding of heterogeneous catalysis. However, there is still progress to be made in characterization techniques to determine such catalysts and their detailed behavior during catalysis. Although MOFs present new opportunities in the field of heterogeneous catalysis, there is still a need to ensure their stability, activity, and selectivity under reaction conditions,Leaching of metals or organic components into the reaction medium is an undesirable process in heterogeneous catalysis and, therefore, must be confirmed during the reaction, which can be detected by chemical analysis of the reaction filtrate or by hot filtration tests.

All in all, MOFs will certainly continue to trigger more and more research in the future, using earth-abundant elements for catalysis to effectively solve the most challenging chemical, energy, and environmental problems of our time.