Intrinsic Mechanism for Carbon Dioxide Methanation over Ru-Based Nanocatalysts
Chongya Yang, Tianyu Zhang, Yusen Chen, Weijue Wang, Hongying Zhuo, Xiaofeng Yang, Yanqiang Huang
Abstract
Ruthenium-based supported catalysts are of great potential for CO 2 methanation, while the catalytic mechanisms remain elusive owing to the conjunction of the metal size and support effect, as well as the possible strong metal/support interactions (SMSI) in a practical catalyst. Herein, with the deposition of alumina over the Ru/SiC model nanocatalysts by the method of the atomic layer deposition (ALD) technique, the corrugated (10 1 1) surface of Ru nanoparticles can be selectively insulated due to its preference for alumina deposition, and the intrinsic activity of CO 2 conversion was confirmed to depend crucially on the residual planar (0001) surface. Characterizations including in situ infrared spectroscopy (IR) combined with density functional theory (DFT) calculation and the microkinetic modeling revealed that the competitive kinetics of H 2 and CO 2 activation on the Ru surface governs the activity and selectivity of methanation. The terrace sites of Ru nanocatalysts serve as the genuine active site through the HCOO* intermediate with the surface occupied by the H* species for further methanation. The (10 1 1) surface suffers from a lower capability for hydrogenation due to its preference toward CO 2 adsorption and results in the surface poisoning by the *C and *CH species, which thus makes it a negligible contribution toward methanation over Ru nanocatalysts. However, the presence of the alumina overlayer on the corrugated surface also improves the stability of the Ru nanocatalyst, to keep its activity even at a high temperature pretreatment. Our results demonstrate the terrace sites as the intrinsic active sites for CO 2 methanation and also deepen insights on the catalytic mechanism of CO 2 transformation over Ru-based nanocatalysts.