Methane oxidation to methanol over copper-containing zeolite

Direct oxidation of methane to methanol is a highly attractive route for upgrading into valued-added product. In June’s issue Chem, Landong Li and colleagues reported state-of-art Cu/CHA catalyst, which exhibited outstanding space-time yield 543 mmol/molCu/h with selectivity up 91%. Methane promising future energy because its large reserves that have already discovered in shale gas the breakthroughs exploitation techniques. addition burning as fuel, upgradation value-added chemicals or liquid fuels more make full utilization this abundant low-cost carbon source. Currently, industrial transformation reforming partial syngas, subsequently transformed Cn+ product through Fischer-Tropsch synthesis—albeit indirect process requires quite input. On other hand, direct high-value under mild conditions considered golden convert economically efficiently. However, it extremely difficult handle barrier first C-H bond activation simultaneously suppress functional group products, leaving grand challenge called “Holy Grail” chemical conversion. For example, selective regarded dream reaction 100% atom economy widespread use feedstock. The possibility converting was established early 20th century. initial studies, production based on high-pressure combustion systems. Given low (<60% 1.6% conversion) high pressures around 100 bar, system had been abandoned afterward. 1970s, homogeneous catalysts (e.g., platinum, mercuric, palladium complexes) emerged successively, where mainly methyl esters, needed be recovered further hydrolysis.1Ravi M. Ranocchiari van Bokhoven J.A. catalytic methanol-A critical assessment.Angew. Chem. Int. Ed. Engl. 2017; 56: 16464-16483Crossref PubMed Scopus (351) Google Scholar Despite derivatives, liquid-phase has not favored usage concentrated acid medium such sulfuric trifluoroacetic acid. Meanwhile, inspired by natural monooxygenase (MMO)—a multi-copper/iron enzyme methanotrophic bacteria could at ambient temperature pressure—zeolites containing Cu Fe clusters were widely investigated mimic structure activity MMOs (Figure 1A).2Ross M.O. MacMillan F. Wang J. Nisthal A. Lawton T.J. Olafson B.D. Mayo S.L. Rosenzweig A.C. Hoffman B.M. Particulate contains only mononuclear copper centers.Science. 2019; 364: 566-570Crossref (150) past decades, progress made over certain Cu-containing zeolite-using looping process, stepwise method consists several steps including activation, extraction. instance, 204 mmol/molCu can produced Cu/MOR 97% typical system.4Sushkevich V.L. Palagin D. Selective anaerobic enables synthesis methanol.Science. 356: 523-527Crossref (449) work Jeroen et al. certainly exciting but still scale consideration issues efficiency. Generally, will take few hours complete one cycle, per cycle very limited number active sites catalysts. Moreover, catalyst (regeneration) typically higher than temperature, leading swings, operation involving complex heat transfer order circumvent disadvantage route, Narsimhan designed continuous molecular oxygen variety copper-exchanged zeolites temperatures (483 K–498 K).5Narsimhan K. Iyoki Dinh Román-Leshkov Y. Catalytic temperature.ACS Cent. Sci. 2016; 2: 424-429Crossref (272) This undoubtedly an important improvement; however, system, lower 10 mmol/molCu/h, 70.6%, call improvement. June dramatically promoted 91% his coworkers.3Sun L. C. Xie Z. Guan N. Water-involved methane-selective dioxygen zeolites.Chem. 2021; 7: 1557-1568Abstract Full Text PDF (21) Such performance great significance considering obtained one-step methanol, extraordinary stability evidenced 500-h operation. Of importance, O2 together H2O oxidant instead expensive hazardous reagents, H2O2, N2O, NO, would preferred commercial interest. As most common molecules, water unavoidable influence documented late 18th century, latest.6Mellor J.W. History problem.J. Phys. 1903; 557-567https://doi.org/10.1021/j150053a001Crossref Nowadays, well acknowledged play role many heterogeneous catalysis reactions CO oxidation, propene epoxidation, synthesis, electro- photochemical reactions. It also found presence promote either facilitating desorption extracting from feedstock,7Freakley S.J. Dimitratos Willock D.J. Taylor S.H. Kiely C.J. Hutchings G.J. water.Acc. Res. 54: 2614-2623Crossref (22) stabilizing intermediates blocking surface prevent deep oxidation,8Liu Huang E. Orozco I. Liao W. Palomino R.M. Rui Ducho? T. Nemšák S. Grinter D.C. Mahapatra al.Water-promoted interfacial pathways CeO2-Cu2O catalyst.Science. 2020; 368: 513-517Crossref (95) serving directly soft regenerating sites.9Koishybay Shantz D.F. Water source flow reactor Cu-SSZ-13.J. Am. Soc. 142: 11962-11966Crossref (48) study Sun al., uncovered initiating providing hydroxyl part methanol.3Sun generation Cu(II)-OH shown catalytically Fourier transform infrared spectroscopy (FTIR) spectroscopy. combined fact below 30% without participation water. productivity H2 far suggesting reaction. Therefore, balance element oxygen, probably comes reactants, i.e., O2. With help ultraviolet-visible-near-infrared (UV-vis-NIR), authors pointed out indispensable fast regeneration sites, alone cannot accomplish. explained phenomenon participation, greatly enhances conversion significantly lowering selectivity. actually dominant way. Because bis(-oxo) dicooper site proposed Cu-zeolites Goothaert co-workers,10Groothaert M.H. Smeets P.J. Sels B.F. Jacobs P.A. Schoonheydt R.A. bis(mu-oxo)dicopper core stabilized ZSM-5 mordenite zeolites.J. 2005; 127: 1394-1395Crossref (488) nature heavily debated different ranging monocopper species clusters. To elucidate Cu/CHA, co-authors conducted set situ experiments atmospheres, dynamic changes copper-based monitored UV-vis-NIR FTIR (Figures 1B 1C). decrease Cu2+ carbonyl Cu+ after introduction CH4 verified Cu+. co-introduction removed [Cu-CH3]+ intermediate. redox between recognized methanol. addition, evolution monomer examined spin-polarized density theory calculations. dimeric centers fully excluded, identification working real various may undergo interconversion mentioned authors. Another concern about substantially decreasing increasing since products are much reactive methane. suggested colleagues, excessive both generate byproduct, CO, H2, CO2.3Sun susceptible conditions. Obviously, co-workers efforts optimize formula, e.g., concentration O2, Si/Al Cu/Al ratios zeolites. summary, reports water-assisted Compared previous systems, efficiently produce dioxgen. We believe findings inspire studies “holy grail” understanding toward precise control activation. zeolitesSun al.ChemMarch 19, 2021In BriefThe functionalization, remains key hot topic controversy. Herein, we report water-involved zeolites, state-of-the-art Both monomeric dicopper confined zeolite catalyze methane-to-methanol they employed Full-Text Open Archive