Dr. Liuqingqing Yang is a Postdoctoral Researcher at the UM-SJTU Joint Institute, Shanghai Jiao Tong University, under the supervision of Dr. Yulian He. Dr. Yang received her Ph.D. in the Chemical and Process Engineering from University of Surrey in 2021. Her works are fully funded by the Shanghai Post-doctoral Excellence Program, and her research focuses on the development (synthesis and characterization) of advanced heterogeneous catalysts, mainly transition-metal-oxides-based materials for the conversion of carbon dioxide and methane to valuable products.
The CO2 catalytic hydrogenation presents one of the most promising routes to utilize CO2 directly. Ni-based catalysts have shown good activities and CH4 selectivity in CO2 hydrogenation reactions. But it has been reported that the CO2 hydrogenation reaction is structure-sensitive over Ni-based catalysts. Nickel species are prone to sintering under elevated temperatures, leading to unstable catalytic performance. In the present study, we find a unique structure-activity relationship for silica supported nickel catalysts during the CO2 hydrogenation at 400oC. An interesting anti-sintering phenomenon were observed on both 9% Ni/SiO2 and 1% Ni/SiO2 samples, where Ni nanoparticles/nanoclusters on the as-prepared samples were found to be redistributed into highly dispersed Ni species. The anti-sintering phenomenon were indicated by different characterization techniques, including X-ray absorption near-edge spectroscopy (XANES), extended X-ray absorption fine structure spectroscopy (EXAFS), low-temperature CO-temperature-programmed desorption measurements, N2 adsorption/desorption experiment and quasi in situ X-ray photoelectron spectroscopy (XPS), leading to distinct outcomes for two catalysts in terms of their catalytic performance. For 9% Ni/SiO2, its catalytic performance increased with reaction progress as more dispersed nickel formed from redistribution (Figure 1a). For 1% Ni/SiO2, the redistribution was accompanied by the occupation of mesoporous of silica support, leading to a decreasing in its catalytic performance in terms of both CO2 conversion and CH4 selectivity due to less active sites (Figure 1b). Besides, we found that after pre-treatment with 5% H2, CH4 still can be produced at the initial stage of the reaction over 1Ni/SiO2, and the selectivity of CH4 is quickly diminishing within 1 h (Figure 2a). While no CH4 was obtained after treatment by 45% H2 (Figure 2b). This indicates that the anti-sintering phenomenon could be related to the presence of H2. These remarkable findings provide in-depth insights into the structural evolution of Ni-based catalysts, and it reveals a novel strategy in terms of product selectivity control in CO2 hydrogenation reactions.