Methane Photooxidation with Nearly 100 % Selectivity Towards Oxygenates: Proton Rebound Ensures the Regeneration of Methanol

Abstract

Restrained by uncontrollable dehydrogenation process, the target products of methane direct conversion would suffer from an inevitable overoxidation, which is deemed as one of the most challenging issues in catalysis. Herein, based on the concept of a hydrogen bonding trap, we proposed a novel concept to modulate the methane conversion pathway to hinder the overoxidation of target products. Taking boron nitride as a proof-of-concept model, for the first time it is found that the designed NÀ H bonds can work as a hydrogen bonding trap to attract electrons. Benefitting from this property, the NÀ H bonds on the BN surface rather than CÀ H bonds in formaldehyde prefer to cleave, greatly suppressing the continuous dehydrogenation process. More importantly, formaldehyde will combine with the released protons, which leads to a proton rebound process to regenerate methanol. As a result, BN shows a high methane conversion rate (8.5 %) and nearly 100 % product selectivity to oxygenates under atmospheric pressure.

Interstitial Zinc Defects Enriched ZnO Tuning O2 Adsorption and Conversion Pathway for Superior Photocatalytic CH4 Oxygenation

“…The efficiency and selectivity of photocatalytic CH 4 conversion into oxygenates is determined by the active oxygen species (such as •OH and •OOH radical species) generation and their reaction pathway with CH 4 . − Under anaerobic conditions, H 2 O is oxidized by the photogenerated holes on the photocatalyst into •OH to drive the conversion of CH 4 into a key intermediate of methyl radicals (•CH 3 ), but the slow oxidation kinetics of H 2 O results in a low efficiency of •OH generation. The yield of liquid oxygenates is often lower than 400 μmol g –1 h –1 . − Moreover, the photogenerated electrons are consumed by the reduction of hydrogen protons but are not fully exploited in the generation of liquid oxygenates. On the contrary, photocatalytic CH 4 aerobic conversion can make full use of both photogenerated holes and electrons for the reaction with H 2 O and O 2 into active oxygen species, respectively. , On the one hand, O 2 had the strong ability for electron capture to promote the separation of photogenerated charges and in turn improve the availability of holes for the oxidation of H 2 O into •OH active species .…”