Thermodynamics Perspective on the Stepwise Conversion of Methane to Methanol over Cu-Exchanged SSZ-13

ACS Catalysis, Journal Year: 2021, Volume and Issue: 11(13), P. 7719 - 7734

Published: June 11, 2021

Transition-metal exchanged zeolites are known to convert methane methanol with high selectivity, in a stepwise process, involving exposure oxidants, followed by methane, and finally water vapor. However, comprehensive theoretical study on the nature of possible active sites their respective changes during this process is still lacking. Here, we use combination density functional theory calculations its generalized-gradient approximation (DFT-GGA) post-DFT methods identify thermodynamically preferred Cu-exchanged zeolite SSZ-13 conversion methanol. We develop thermodynamic model for an extensive set sites, that is, Cu monomers, dimers, trimers, which anchored different ring structures supported series local Al distributions. Subsequently, phase diagrams constructed used favored at each step find O2, hydroxylated dimers—Cu2O2H2 and, depending configuration, Cu2OH—are preferred. Upon site-bound molecules formed. With subsequent increase vapor pressure, preference monoatomic release observed. Furthermore, compare our predicted results experimental measurements published literature close agreement terms coordination number bond distances some considered. expect insights obtained here can be improve understanding reaction mechanism optimize

Language: Английский

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Continuous Synthesis of Methanol from Methane and Steam over Copper-Mordenite

ACS Catalysis, Journal Year: 2021, Volume and Issue: 11(3), P. 1065 - 1070

Published: Jan. 8, 2021

One-step methane-to-methanol conversion is a "dream reaction" for chemists. In this Letter, continuous direct of methane into methanol with steam under mild conditions using Cu(II)-exchanged mordenite reported. The production rate depended on the Si/Al ratio, Cu/Al presence Brønsted acid sites, and O2 concentration in feed. Cu-H-mordenite Cu-Na-mordenite showed comparable rates, but former provided higher selectivity. At given gave volcano plot as function selectivity decreased increasing ratio. These experimental data DFT calculation implied that binuclear copper species are more active than mononuclear oxide clusters favorable total oxidation.

Language: Английский

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Identification of atomically dispersed Fe-oxo species as new active sites in HZSM-5 for efficient non-oxidative methane dehydroaromatization

Journal of Catalysis, Journal Year: 2021, Volume and Issue: 396, P. 224 - 241

Published: March 5, 2021

Language: Английский

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Selective Formation of α-Fe(II) Sites on Fe-Zeolites through One-Pot Synthesis

Journal of the American Chemical Society, Journal Year: 2021, Volume and Issue: 143(39), P. 16243 - 16255

Published: Sept. 27, 2021

α-Fe(II) active sites in iron zeolites catalyze N2O decomposition and form highly reactive α-O that selectively oxidizes unreactive hydrocarbons, such as methane. How these are formed remains unclear. Here different methods of introduction into compared to derive the limiting factors Fe speciation α-Fe(II). Postsynthetic procedures on small pore suffer from limited diffusion dispersion leading oxides. In contrast, by introducing Fe(III) hydrothermal synthesis mixture zeolite (one-pot synthesis) right treatment, crystalline CHA can be prepared with >1.6 wt % Fe, which >70% is The effect crystallization investigated, intermediate species tracked using UV-vis-NIR, FT-IR, Mössbauer spectroscopy. These data supplemented online mass spectrometry each step, reactivity tests formation methanol yields stoichiometric methane activation at room temperature pressure. We recover up 134 μmol per gram a single cycle through H2O/CH3CN extraction 183 μmol/g steam desorption, record yield for zeolites. A general scheme proposed steps drying, calcination, activation. two cohorts discovered, one before after high propose latter cohort depends reshuffling aluminum lattice accommodate thermodynamically favored

Language: Английский

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Low-Cost CuX Catalyst from Blast Furnace Slag Waste for Low-Temperature NH₃-SCR: Nature of Cu Active Sites and Influence of SO₂/H₂O

ACS Sustainable Chemistry & Engineering, Journal Year: 2022, Volume and Issue: 10(23), P. 7739 - 7751

Published: June 2, 2022

A series of Cu-exchanged zeolite NaX (derived from blast furnace slag) catalysts were synthesized by an ion-exchanged method. The low-temperature catalytic activity and SO2 or/and H2O resistance the studied as well. results found that Cu(N)X catalyst exhibited excellent selective reduction (SCR) activity, whose NO conversion was nearly 100% at ca. 175 °C remained stable, while Cu(C)X showed poorest performance. When introduced, declined to 60%, it could recover 63% after cutting off H2O. More isolated Cu2+ species surface chemisorbed oxygen on provide more active sites for SCR reaction, vacancies accelerated oxidation absorbed NH3 species. Besides, higher acidity redox ability promoted reaction In addition, poisoning SO2/H2O, decreased, became poor, Cu less than catalyst, indicating consumed during reaction. Furthermore, also be generated sulfate occupied main reduced varieties nitrate intermediates, thereby reducing catalyst.

Language: Английский

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