First-principles study of selective CO2 activation to methanol on PdZn/TiO2: Unveiling Zn/Pd ratio on catalysis performance

Abstract

In this study, a series of Pd(8-n)Znn/TiO2(n=0–8) were investigated via density functional theory (DFT) to understand the influence of Zn/Pd ratio on their catalysis performance of conversion CO2 to methanol. It is revealed that Zn prefers to replace the bottom-layered Pd when its molar concentration in composition increases. For all surface models, interface between cluster and support plays a key role in CO2 stabilization and activation. Increasing Zn/Pd ratio could weaken the binding strength of CO2 over catalyst, which further hinders the “RWGS” pathway while promotes the “Formate” pathway. Based on the calculation results, a Brønsted–Evans–Polanyi (BEP) relation between the activation barrier (Ea) of key elementary steps from both mechanisms and the binding strength of key intermediates has been established, from which the optimum Zn/Pd ratio leading to the best catalysis performance has been determined. Moreover, it is found that water inclusion in the system does not change the Ea of rate-determining step much even though it has a promotion effect on OH formation steps. Overall, this work provides some meaningful insight into the influence of cluster composition on the catalysis performance of PdZn-based catalyst and provides valuable information about rational design of the supported bimetallic catalyst.