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.
Highlights
Introduction published maps and institutional affilCarbon dioxide (CO2 ) is a greenhouse gas produced globally as a byproduct of fossil fuel combustion and industrial activity [1]
In situ X-ray Diffraction (XRD) was performed during temperature programmed reduction (TPR) of the unsupported molybdenum phosphide (MoP) nanoparticles to characterize crystalline phase evolution in the catalyst as a function of temperature under reducing conditions (Figure 1A)
We revealed how the formation of MoP phase at high temperature is deeply influenced by the nature of the support and promoters when we started the thermal synthesis of MoP from inorganic precursors dispersed onto the support [12,35]
Summary
A low temperature colloidal method was employed to synthesize amorphous MoP nanoparticles, which could be dispersed across different high surface area metal oxide supports to conduct a systematic study on the supported MoP catalyst system. EV inatthe first derivative decreases, while crystallization occurs the difference spectra temperatures exceeding withproper the difference between crys◦ C when the feature at 20,013 eV and 20,019 eV, that are characteristic of rapidly above talline MoP and with the as-synthesized colloidal nanoparticles 450 ◦ C, well-formed MoP to conclude that the activation process is nearly complete below 450 °C and minimal nanoparticles are present, and the XANES region does not significantly evolve further with changes develop at higher temperatures.
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