Cascade Catalysis for the Hydrogenation of Carbon Dioxide to Methyl Formate Using a Molecular Ru-Phosphine Complex and the Metal-Organic Framework UiO-66 as Heterogeneous Acid

The direct incorporation of CO2 into value-added base chemicals, such as methyl formate (MF), is a grand challenge to chemical science. In this work, a base-free cascade catalysis system is described to effectively convert carbon dioxide into MF. In the initial step a well-established Ru complex (i.e., RuHCl(dppm)2, dppm = 1,1-bis(diphenylphosphino)methane) is able to hydrogenate CO2 into formic acid, which subsequently undergoes a heterogeneous acid catalyzed esterification with methanol to selectively produce MF. Here, the small pore MOF UiO-66, a Zr-terephthalate, is identified as a promising heterogeneous acid and its Zr6 cluster is modified to understand the effect of Bronsted/Lewis acidity on the performance. Moreover, this heterogeneous acid catalyst could be reused for multiple times without significantly losing its activity.