The special route toward conversion of methane to methanol on a fluffy metal‐free carbon nitride photocatalyst in the presence of H ₂ O ₂

Abstract

Summary A fluffy mesoporous graphitic carbon nitride (g‐CN) was synthesized and investigated, as the first metal‐free polymeric semiconductor photocatalyst, for partial oxidation of methane to methanol at a mild condition (35°C) in the presence of hydrogen peroxide (H2O2). The addition of g‐CN photocatalyst enhanced the methanol production with H2O2 by 10 times under visible light and this production was 3‐folds that when WO3 was used. Besides, while attaining a comparable saturated production of CH3OH, the visible‐light‐driven reactions allowed a higher utilization ratio of H2O2 compared with those under the irradiation of simulated AM1.5G sunlight. More importantly, via electron spin resonance technique, scavenger experiments and isotope tracer investigations, as well as studies on the effects of reaction condition variations, the specific reaction mechanisms were revealed under both visible light and simulated full sunlight, respectively, which should shed some new insights on photocatalytic oxidation of CH4 to value‐added chemicals.

Nanostructured Photocatalysts for the Production of Methanol from Methane and Water

“…[20][21][22] Previous works have demonstrated that such properties strongly influence the oxidation of methane. [23][24][25] For instance, a comparison of the photocatalytic performance of materials from each category (TiO 2 , NiO, and WO 3 ) shows that the latter exhibited a higher methanol selectivity. [23] The maximum conversion rates of methane to methanol over WO 3 , TiO 2 , and NiO were 29 %, 21 %, and 20 %, respectively.…”

“…For instance, Shi et al studied the performance of a C 3 N 4 photocatalyst in the selective oxidation of methane, finding that this material can only generate methanol in the presence of H 2 O 2 . [25] To better elucidate the reaction mechanisms, the authors used three radical scavengers to identify the role of h + , O �À 2 , and HO * radicals. Unlike previous works, the results indicated that the photogenerated holes along with the superoxide radical also contribute to the generation of methanol [Eqs.…”

“…Recently, a fluffy mesoporous graphitic carbon nitride (g-C 3 N 4 ) material with a surface area of 76 m 2 g À 1 was also studied for this selective oxidation. [25] This metal-free photocatalyst possesses a proper conduction band that enables the gener-ation of hydrogen, which prevents the self-reduction of the material. However, the photogenerated holes are not able to produce hydroxyl radicals from water, requiring the addition of H 2 O 2 as * OH source to promote the formation of methanol.…”

“…F) Methanol generation over a C 3 N 4 photocatalyst before and after visible and sun-like irradiation. Reproduced from ref [25]…”

Direct conversion of methane to oxygenates catalyzed by iron( III ) chloride in water at near ambient temperature

“…Recently, Xiao et al reported an AuPd@ZSM‐5 catalyst for methane oxidation by in situ generated H 2 O 2 at a mild temperature (70°C), and the methanol productivity was up to 91.6 mmol/g AuPd ∙h 17 . Also, our group have reported that graphitic carbon nitride as metal‐free photocatalyst was effective for the conversion of methane to methanol at 35°C in the presence of H 2 O 2 , and the methanol production was promoted by ~10 times under visible light 24 …”