Abstract
Methanol synthesis by means of direct CO2 hydrogenation has the potential to contribute to climate change mitigation by turning the most important greenhouse gas into a commodity. However, for this process to become industrially relevant, catalytic systems with improved activity, selectivity, and stability are required. Here, we explore the potential of metal- organic frameworks (MOFs) as precursors for synthesis of Co3O4 -supported In2O3 oxide composites for the direct CO2 hydrogenation to methanol. Stepwise pyrolytic-oxidative decomposition of indium-impregnated ZIF-67(Co) MOFs affords the formation of a nanostructured In2O3 @Co3O4 reticulated shell composite material able to reach a maximum methanol production rate of 0.65 g(MeOH center dot)g(cat)(-1).H-1 with selectivity as high as 87% over 100 h on stream. Textural characteristics of the sacrificial ZIF-67(Co) matrix and In-loading were found to be important variables for optimizing the catalyst performance such as induction time, methanol productivity, and selectivity. The structural investigation on the catalytic system reveals that the catalyst undergoes reorganization under reaction conditions, transforming from Co3O4 with an amorphous In2O3 shell into Co3InC0.75 covered by a layer consisting of a mixture of amorphous CoOx and In2O3 oxides. Structural reorganization is responsible for the observed induction period, while the amorphous mixed cobalt indium oxide shell is responsible for the high methanol yield and selectivity. Additionally, these results demonstrate the tunable performance of MOF-derived In2O3@Co3O4 catalysts as a function of the reaction conditions which allows us to establish a reasonable trade-off between high methanol yield and selectivity in a wide temperature and pressure window.