ZIF-67-Derived Nanoreactors for Controlling Product Selectivity in CO2 Hydrogenation

CO2 hydrogenation to produce useful C1 chemicals (such as CO, CH4, and CH3OH) plays a pivotal role in future energy conversion and storage, in which catalysts lie at the heart. However, our fundamental understanding of the correlation between catalyst structures and product selectivity is still limited because in most cases the catalyst structures in nanoscale are not well-defined. Herein, we report the design and synthesis of nanoreactors by phase transformations of sandwich-structured ZIF-67@Pt@mSiO2 nanocubes via a simple water-soaking method where ZIF-67 serves not only as a morphological template but also as a sacrificial cobalt source. The resultant porous mazelike nanoreactors are highly active in gas-phase CO2 hydrogenation, in which the reaction pathway involves (i) dissociation of CO2 to form CO over Pt site via reverse water–gas shift reaction and then (ii) methanation of CO catalyzed by the nearby cobalt site. It was found that the overall "long retention time" for feed gases on catalysts significantly affected the product distribution. Thus, the specific activity (in the form of turnover frequency) of the nanoreactor having prolonged diffusion paths was around six times as much as that of other comparative catalysts with shorter diffusion paths. This work contributes insights to the CO2 hydrogenation to methane over bifunctional nanoreactors with designed structures.