CO2 hydrogenation to HCOOH on PdZn surface and supported PdZn Cluster: A Comparative DFT study

• The structure modification of PdZn surface to a supported subnanometer cluster offers better stability of the intermediates. • At temperature >400 K, KPd 5 Zn/ZrO 2 (101) produces more HCOOH than PdZn(101) and PdZn(111) surfaces. • HCOO and COOH pathways are competing in Pd 5 Zn/ZrO 2 (101), whereas the HCOO pathway is favored on the PdZn(101) surface. • In the two observed pathways, the HCOO and COOH formation are the rate-limiting steps for both catalyst systems. Modifying heterogeneous catalysts for supported cluster-based types is important to design catalysts with better activity, stability, and selectivity. Alloying Pd with Zn and supported by ZrO 2 is a promising way to design catalysts for CO 2 hydrogenation to HCOOH, but the nature of the active catalytic sites and the mechanism remain unknown. Two representative models have been investigated: subnanometer cluster Pd 5 Zn/ZrO 2 and PdZn(101) surface. DFT calculations combined with microkinetic simulations are used to identify the optimum structure and configurations for the reaction. Compared to the PdZn(101) surface, the Pd 5 Zn/ZrO 2 offers much more stable adsorption and formation of intermediate species. Moreover, the formate route is more likely to proceed on PdZn(101) surface from the viewpoint of thermodynamic and kinetic. In contrast, the supported Pd 5 Zn/ZrO 2 cluster prefers the carboxyl pathway, where the interface site between cluster-support is ascribed to a far more stable configuration. Electronic structure analysis reveals the nature of the transition state on intermediate formation, particularly the role of Pd and Zn edge atoms on the selectivity towards the carboxyl pathway on Pd 5 Zn/ZrO 2 . Finally, the comparison of microkinetic simulation results shows a preference for HCOOH formation on Pd 5 Zn/ZrO 2 than PdZn(101) surface at medium to higher temperature.