Understanding Selectivity in CO2 Hydrogenation to Methanol for MoP Nanoparticle Catalysts Using In Situ Techniques

Abstract

Molybdenum phosphide (MoP) catalyzes the hydrogenation of CO, CO2 , and their mixtures to methanol, and it is investigated as a high-activity catalyst that overcomes deactivation issues (e.g., formate poisoning) faced by conventional transition metal catalysts. MoP as a new catalyst for hydrogenating CO2 to methanol is particularly appealing for the use of CO2 as chemical feedstock. Herein, we use a colloidal synthesis technique that connects the presence of MoP to the formation of methanol from CO2 , regardless of the support being used. By conducting a systematic support study, we see that zirconia (ZrO2 ) has the striking ability to shift the selectivity towards methanol by increasing the rate of methanol conversion by two orders of magnitude compared to other supports, at a CO2 conversion of 1.4% and methanol selectivity of 55.4%. In situ X-ray Absorption Spectroscopy (XAS) and in situ X-ray Diffraction (XRD) indicate that under reaction conditions the catalyst is pure MoP in a partially crystalline phase. Results from Diffuse Reflectance Infrared Fourier Transform Spectroscopy coupled with Temperature Programmed Surface Reaction (DRIFTSTPSR) point towards a highly reactive monodentate formate intermediate stabilized by the strong interaction of MoP and ZrO2 . This study definitively shows that the presence of a MoP phase leads to methanol formation from CO2 , regardless of support and that the formate intermediate on MoP governs methanol formation rate.