Simultaneously Accelerating Carrier Transfer and Enhancing O₂/CH₄ Activation via Tailoring the Oxygen-Vacancy-Rich Surface Layer for Cocatalyst-Free Selective Photocatalytic CH₄ Conversion

Abstract

Solar energy-driven direct CH4 conversion to liquid oxygenates provides a promising avenue toward green and sustainable CH4 industry, yet still confronts issues of low selectivity toward single oxygenate and use of noble-metal cocatalysts. Herein, for the first time, we report a defect-engineering strategy that rationally regulates the defective layer over TiO2 for selective aerobic photocatalytic CH4 conversion to HCHO without using noble-metal cocatalysts. (Photo)­electrochemical and in situ EPR/Raman spectroscopic measurements reveal that an optimized oxygen-vacancy-rich surface disorder layer with a thickness of 1.37 nm can simultaneously promote the separation and migration of photogenerated charge carriers and enhance the activation of O2 and CH4, respectively, to •OH and •CH3 radicals, thereby synergistically boosting HCHO production in aerobic photocatalytic CH4 conversion. As a result, a HCHO production rate up to 3.16 mmol g–1 h–1 with 81.2% selectivity is achieved, outperforming those of the reported state-of-the-art photocatalytic systems. This work sheds light on the mechanism of O2-participated photocatalytic CH4 conversion on defective metal oxides and expands the application of defect engineering in designing low-cost and efficient photocatalysts.

Efficiently Light-Driven Nonoxidative Coupling of Methane on Ag/NaTaO3: A Case for Molecular-Level Understanding of the Coupling Mechanism

“…Figure 4a shows EPR signals of Ag/NaTaO 3 under UV 254 nm light irradiation without or with CH 4 at 120 K. In the dark, the Ag/NaTaO 3 sample displayed an EPR signal at g = 2.003 assigned to the oxygen vacancies. 42 Upon light irradiation, the EPR signal intensity of the defect sites declined due to the capture of photogenerated electrons in defect sites; meanwhile, a set of EPR signals at g = 2.012 and g = 2.001 was produced, which can be attributed to O •− species originated from trapping the photogenerated hole by the lattice oxygen atom. 43−46 When CH 4 was injected into light-irradiated Ag/NaTaO 3 , the EPR signals of O •− species were markedly reduced (Figure 4b).…”

Atomically Dispersed Nickel Anchored on a Nitrogen‐Doped Carbon/TiO2Composite for Efficient and Selective Photocatalytic CH4Oxidation to Oxygenates

“…The excellent photocatalytic performance observed over NiÀ NC/TiO 2 is comparable to or even outperforms most reported photocatalysts decorated with either noble metal or non-noble metal cocatalysts under similar experiment conditions (Table S2). [12,13,16,17,19,20,[22][23][24][25][38][39][40] Reactions without photocatalyst, without light or replacing CH 4 with Ar did not yield any product. Isotope labelling experiment using 13 CH 4 was performed to elucidate the source of carbon atoms of the products.…”

Atomically Dispersed Nickel Anchored on a Nitrogen‐Doped Carbon/TiO2Composite for Efficient and Selective Photocatalytic CH4Oxidation to Oxygenates

“…The excellent photocatalytic performance observed over Ni−NC/TiO 2 is comparable to or even outperforms most reported photocatalysts decorated with either noble metal or non‐noble metal cocatalysts under similar experiment conditions (Table S2). [ 12 , 13 , 16 , 17 , 19 , 20 , 22 , 23 , 24 , 25 , 38 , 39 , 40 ]…”