As an important carbon-based small molecule, methane is widely distributed in nature and is the main component of natural gas, shale gas, combustible ice, biogas and so on. To date, the use of methane has been dominated by combustion, resulting in the emission of large amounts of carbon dioxide. Methane as a chemical raw material is mainly used for the synthesis of ammonia, methanol and its derivatives, but its consumption accounts for only 5%-7% of natural gas consumption. Although methane reserves far exceed oil reserves, its development as a chemical raw material is far from comparable to that of oil. How to convert the huge reserves of methane resources into fuels or chemical products with higher economic added value has important scientific significance and application prospects. Solar energy, the most abundant and clean energy source, can be photocatalyzed to convert methane into multi-carbon fuels or chemicals under mild conditions. In recent years, the research team of Professor Xiong Yujie and Professor Long Ran of the University of Science and Technology of China has developed a series of light/photocatalytic methods to achieve the highly selective conversion of methane to ethane, ethylene and ethylene glycol (J. Am. Chem. Soc. 2021, 143, 269；Angew. Chem. Int. Ed. 2021, 60, 9357）。
Recently, the research team of Professor Xiong Yujie and Professor Long Ran cooperated with Fu Cenfeng, associate researcher of academician Yang Jinlong team of the University of Science and Technology of China, and Professor Yao Yingfang of the team of academician Zou Zhigang of Nanjing University, to develop a photocatalytic methane oxygen-free coupling (NOCM) method, which achieved highly selective preparation of ethane and hydrogen, and the efficiency reached the level of medium temperature thermocatalytic NOCM, published in the journal× Nat. Commun. DOI: 10.1038/s41467-022-30532-z）。
Photocatalytic NOCM, which can simultaneously acquire polycarbons and hydrogen under mild conditions, is an attractive route. With its good light utilization rate and excellent oxidation capacity, oxide semiconductors are widely used in the study of photocatalytic NOCM. However, the photogenerated holes used to activate methane are mainly concentrated in the lattice oxygen site of the oxide semiconductor, making methane extremely susceptible to excessive oxidation by lattice oxygen atoms to produce carbon monoxide, carbon dioxide and other by-products. In this work, Xiong Yujie and Long Ran’s team proposed to regulate the valence band electronic structure of the photocatalyst by means of single-atom coordination loading to obtain a NOCM photocatalyst with high activity, selectivity and stability. Taking the most common titanium dioxide as an example, the “palladium-oxygen” coordination structure constructed on its surface can concentrate photogenerated holes on the “palladium-oxygen” coordination structure unit, thereby improving the photocatalytic NOCM performance while reducing the degree of excessive oxidation of methane. Based on this strategy, hydrogen products with 94.3% ethane selectivity, 0.91 mmol g-1 h-1 ethane yield and isotometric ratio were realized. Further, by the method of element doping, the stability of lattice oxygen in the catalyst is improved, thereby prolonging the stability of the catalytic performance. This work provides new ideas for the development of efficient photocatalytic NOCM catalysts.
The in situ characterization of synchrotron radiation near atmospheric pressure photoelectron spectroscopy and infrared spectroscopy was supported by the cooperation of Professor Liu Zhi of Shanghai Light Source, Qi Zeming of Hefei Light Source, and Engineer Liu Hengjie, respectively. The research work has been funded by the National Key Research and Development Program, the National Science Foundation for Outstanding Young People, the National Science Foundation for Outstanding Youth, and the Special Cultivation Project of Class B Pilot Science and Technology of the Chinese Academy of Sciences.
Thesis link: https://www.nature.com/articles/s41467-022-30532-z
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