Light‐Induced Nonoxidative Coupling of Methane Using Stable Solid Solutions

Abstract

Achieving efficient and direct conversion of methane under mild conditions is of great significance for innovations in the chemical industry. However, the efficiency and lifetime of most catalysts remain too far from practical requirements, since it is difficult to break the first C−H bond of methane as well as to suppress the following complete dehydrogenation (or overoxidation) and the resulting carbonaceous deposition (or CO2). Here, we report that wurtzite GaN:ZnO solid solutions exhibit unique and unprecedented photocatalytic performances for the nonoxidative coupling of methane at room temperature, exclusively generating ethane with nearly stoichiometric H2. High conversion rate (>330 μmol g−1 h−1), long‐term stability (>70 h), and superior coke‐resistance were achieved. At 293 K, the methane conversion exceeds 7 %, comparable to the equilibrium conversion of thermal catalysis at 910 K. Mechanistic studies revealed that the N‐ZnGa‐ON units and the absence of acid sites on the surface played crucial roles in reactivity and coke resistance, respectively.

Critical impacts of interfacial water on the photocatalytic C–H conversion of methane

“…This result is possibly due to the overstabilization of the intermediates (~90 kJ/mol, Fig. S4-3a); the highly stabilized and strongly adsorbed C-H activated species would be overoxidized and thus cause deactivation of the photocatalyst; this scenario is strongly supported by previous experimental observations in which the photocatalyst was covered with carbonaceous deposit and had a poor performance under dry reaction conditions [29][30][31] . In comparison with these experimental and theoretical results under dry conditions, we can conclude that the interaction of methane with interfacial water plays a key role not only in substantially lowering the barrier for the C-H cleavage, but also in preventing the overstabilization of surface intermediate radical species, resulting in substantial promotion of photocatalytic methane conversion under ambient conditions.…”

“…1a,c,e), although water itself is not involved in the equation of methane coupling reaction (2CH4 → C2H6 + H2). Thus, the ethane formation under the wet conditions must be mechanistically different from the non-oxidative coupling of methane previously reported in the absence of water [29][30][31] . This implies that the interfacial water species contribute to catalyzing the first oxidative C-H cleavage process (CH4 → • CH3) and promote the subsequent homocoupling (2 • CH3 → C2H6) 13,17 .…”

“…1a. Under the dry conditions, only ethane and hydrogen were detected, indicating the occurrence of photocatalytic non-oxidative methane coupling (2CH4 → C2H6 + H2) [29][30][31] . In this case, the conversion rate was extremely low (~0.2 μmol/h).…”

“…S4-3b). This overstabilization hinders the homocoupling of • CH3 to form ethane (2 • CH3 → C2H6), and results in further hydrogen abstraction from • CH3 to form other hydrocarbon species and coke [29][30][31] . This overstabilization is drastically altered by water.…”

Design of frustrated Lewis pair in defective TiO2 for photocatalytic non-oxidative methane coupling

“…Photocatalytic non-oxidative coupling of methane (NOCM) is one of the effective approaches to selectively producing ethane and hydrogen under mild conditions [4][5][6][7] . Our previous work has veri ed that Pt δ+ -Pt pair loaded on TiO 2 can promote the photocatalytic C-H polarization at room temperature 5,8 .…”