Revealing the promoting effect of Zn on Ni-based CO2 hydrogenation catalysts

Hydrogenation of CO2 to produce high-value chemicals is a response to increasing environmental and energy concerns. The target products of CO2 hydrogenation, methane and CO, are both important energy sources and raw materials for the production of higher hydrocarbons. Therefore, it is very important to understand the mechanism of selectivity control of catalysts. In this work, we aim to elucidate the selectivity regulation of Zn on Ni catalysts, which has been extensively studied in the literature without reaching a consensus. We have prepared a series of catalysts with different Zn content and systematically investigated the relationship between their structural evolution and selectivity. It is found that the introduction of Zn preferentially forms an alloy with Ni and at higher loadings is present as ZnOx, which participates in the strong metal-support interaction (SMSI). The conversion of the active sites into a Ni-Zn alloy hinders further hydrogenation of the adsorbed CO intermediates and makes the catalyst CO-selective. The presence of the Ni-ZnOx interface changes the CO2 activation mechanism from an association pathway to a redox pathway.