Photocatalytic conversion of methane to C2 Products in a flow reactor

• Main Author: Li, Xiyi
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: UCL (University College London) 2022
• Subjects: Methane hydrate
• Online Access: https://discovery.ucl.ac.uk/id/eprint/10157545/1/Xiyi-thesis-finalised%20clean%20%28without%20signature%29.pdf; https://discovery.ucl.ac.uk/id/eprint/10157545/

The predicted substantial reserve of methane hydrate and shale gas, far beyond the sum of other fossil fuels, indicates an extremely attractive while challenging chemical synthesis process in which methane, instead of crude oil can be used as a building block for diverse chemical synthesis in a potentially low-carbon process. Among various direct methane conversion to value-added chemicals processes, photocatalytic oxidative coupling of two methane molecules to produce C2 products (C2H6/C2H4) is one of the most general and highly profitable but challenge processes for long chain chemical synthesis. However, due to the highly stable methane molecules and the more reactive C2 products, there is an obvious dilemma: an extreme condition (e.g., high energy or strong oxidants) required to activate the highly stable C-H bonds in methane, while a mild condition needed to avoid the overoxidation of C2 products. In the project, a flow system for photocatalytic oxidative coupling of methane was designed for the first time, which allows the manipulation of residence time and the CH4/O2 ratio for precise evaluation of the potential photocatalysts. The robust and classic anatase TiO2 was selected as a basic semiconductor for the investigation of methane activation. The most general electron acceptor in photocatalysis, Pt nanoparticles, and the widely used species for methane activation in thermocatalysis, CuOx clusters were introduced on TiO2 to work synergistically. The optimised sample Cu0.1Pt0.5/TiO2 shows the highest yield of C2 product of 6.8 μmol h-1 at a space velocity of 24000 ml g-1 h-1, more than twice the sum of the activity of Pt/TiO2 (1.07 μmol h-1) and Cu/TiO2 (1.9 μmol h-1), it was also the highest among photocatalytic methane conversion under atmospheric pressure when it was published. High C2 selectivity of 60% is also comparable to that attained by conventional high-temperature (>943 K) thermal catalysis. Characterisation data confirms that Pt acts as an electron acceptor to promote the charge separation, ...