Research groups led by Prof. XIONG Yujie, Prof. LIU Dong and Prof. ZHANG Ning from the University of Science and Technology of China (USTC) developed a novel catalyst Au/BiOx-TiO2 for efficient, selective and stable photocatalytic light-driven oxidative coupling of methane (OCM). The study was published in Science Advances.
Producing value-added chemicals through OCM is a promising approach to alleviate energy issues. However, OCM requires strict reaction conditions due to its high reaction energy barrier. Compared with the anaerobic coupling of methane, the aerobic coupling of methane has a lower reaction barrier, yet it still faces challenges such as poor product selectivity and slow reaction rate. Therefore, it is necessary to design efficient catalysts and optimize reaction pathways to address issues of stability, selectivity and reactivity in OCM.
The group designed and synthesized a dual-site photocatalyst, Au/BiOx-TiO2, which is a composite system of BiOx clusters and Au nanoparticles. The BiOx clusters are uniformly distributed around the Au nanoparticles, tightly bound together. The synergistic effect of Au nanoparticles and BiOx clusters enables the activation of C-H bonds in CH4 and the coupling of CH3 at separate sites, preventing overoxidation of CH4 at a single site. This significantly improves the selectivity for C2+ products.
Using a self-designed flow reactor, the photocatalytic OCM achieved a CH4 conversion rate of 20.8 mmol g−1 h−1 and a C2H6 production rate of 9.6 mmol g−1 h−1. The selectivity for C2+ products exceeded 97%, with stability lasting up to 50 hours, outperforming many previously reported catalysts.
The group also verified mechanism of lattice oxygen participation in OCM based on in-situ spectroscopy and theoretical calculations. The lattice oxygen can effectively enhance the C-H activation, and introducing an appropriate amount of oxygen can replenish lattice oxygen via the Mars-Van Krevelen mechanism, achieving high selectivity and stability simultaneously.
This work highlights the importance of employing catalytic site engineering in chemical reaction and sheds lights on sustainable and energy- efficient CH4 conversion.
