Bifunctional Catalysts with Core–Shell Distributed ZrO2 and Co Nanoparticles Derived from MOF-on-MOF Heterostructures for Economical One-Pot Tandem CO2 Fixation

The N-formylation of aryl amines with CO2 is an emerging strategy to simultaneously reduce carbon emission and produce high-value formamides. Considering that aryl amines are usually produced from the hydrogenation of their corresponding nitroarenes in the chemical industry, the one-pot tandem hydrogenation–formylation of nitroarenes with CO2 to formamides is obviously a much more economical but still unexploited strategy for efficient CO2 fixation. Herein, we report the rational synthesis of bifunctional catalysts with core–shell distributed ZrO2 and Co nanoparticles (NPs) from the controlled pyrolysis of a ZIF-67-on-UiO-66 heterostructure for this one-pot tandem reaction. To fabricate such MOF-on-MOF heterostructures, we develop a facile surfactant-assisted strategy to seed ZIF-8 nuclei on the UiO-66 surface, followed by the successful growth of a thickness-controlled ZIF-67 shell on the UIO-66 core. Based on further pyrolysis, the highly mesoporous derivants with core–shell distributed ZrO2 and Co NPs can be obtained, of which the reductive Co and Lewis basic ZrO2 can serve as highly active sites for the hydrogenation of nitroarenes and the N-formylation of aryl amines with CO2, respectively, due to their favorable electronic structures and good mass diffusion of reactants/intermediates. Impressively, the optimized core–shell catalyst achieves a much higher yield of N-(4-methoxyphenyl)formamide (99.5%) than its ZrO2/C (0%), Co-NC (14.1%), and physically mixed counterparts (52.3%) for the one-pot tandem hydrogenation–formylation between 4-nitroanisole and CO2 with good recyclability and a broad substrate scope, shedding light on the rational design of efficient bifunctional catalysts for this tandem CO2 fixation reaction.