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 (DRIFTS-TPSR) 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.

In Situ Studies of the Formation of MoP Catalysts and Their Structure under Reaction Conditions for Higher Alcohol Synthesis: The Role of Promoters and Mesoporous Supports

“…The presence of a K promoter is essential for ethanol production. A separate study looking at MoP nanoparticles found that in the absence of K, MeOH was the main product in the CO 2 hydrogenation reaction . XRD revealed the presence of potassium pyrophosphate, which has not been previously reported in the literature and could be participating in the promotion of the reaction.…”

“…A separate study looking at MoP nanoparticles found that in the absence of K, MeOH was the main product in the CO 2 hydrogenation reaction. 51 XRD revealed the presence of potassium pyrophosphate, which has not been previously reported in the literature and could be participating in the promotion of the reaction. This K phase appears simultaneously with the MoP phase at low temperatures, and its amount decreases as the MoP XRD pattern increases in intensity at high temperatures.…”

CO2 Conversion via Reverse Water Gas Shift Reaction Using Fully Selective Mo–P Multicomponent Catalysts

“…Although transition metal phosphides (TMPs) have been investigated in the energy industry, − in the past decades, the research dealing with TMPs catalysts for CO 2 upgrading reactions are still relatively scarce compared to the materials listed above. Among the TMPs, molybdenum phosphide (MoP) catalysts exhibit stable performance toward methanol synthesis from CO 2 and CO. , During high pressure CO 2 hydrogenation experiments for methanol synthesis, MoP catalysts have been observed to catalyze some CO formation as a byproduct. , The molybdenum phosphide phase is theoretically expected to remain stable under hydrogenating conditions and has been shown experimentally to retain its chemical structure up to 950 °C in hydrogen, making it a suitable catalyst for the RWGS reaction. Our group has previously used a DFT-based mechanistic study to explore the potential activity of MoP (0001) for the RWGS reaction and found that this surface is an active phase for the RWGS reaction .…”

Influence of Ag Metal Dispersion on the Catalyzed Reduction of CO2 into Chemical Fuels over Ag–ZrO2 Catalysts

“…Meanwhile, oxides also act as support materials to stabilize catalysts and provide preferable electron conduction and species transport for the reduction process. 29 , 30 Duyar et al 31 found that ZrO 2 has the striking ability to modify formate binding, and therefore, the MoP/ZrO 2 catalyst can shift the selectivity toward methanol of 55.4%.…”