CO2 hydrogenation over mesoporous Ni-Pt/SiO2 nanorod catalysts: Determining CH4/CO selectivity by surface ratio of Ni/Pt

Abstract

Herein, we fabricated a series of bimetallic Pt-Ni catalysts supported on mesoporous silica nanorods (mSNR, specific BET surface area of 1802 m2 g−1) to study the effect of Ni/Pt ratio on the product selectivity in CO2 hydrogenation. Both monometallic Pt/mSNR and Ni50Pt50/mSNR catalysts revealed negligible methane selectivity. However, methane became the major product only when increasing the Ni/Pt ratio up to 9. X-ray photoelectron spectroscopy (XPS) and inductively coupled plasma (ICP) characterizations showed that the Pt/Ni ratio on the catalyst surface was appreciably higher than the bulk composition, suggesting the enrichment of Pt on the surface (e.g., Pt/Ni of 61/39 for Ni50Pt50/mSNR catalyst). The Pt/Ni ratio was crucial in determining the CH4/CO selectivity, and the addition of a tiny amount of Pt could improve the catalytic performance and stability of Ni/mSNR. Among the different catalysts, Ni98Pt2/mSNR showed the best CO2 conversion (59%) and CH4 selectivity (96%) at 400 °C, 0.1 MPa, 9600 mL h−1gcat−1, and H2/CO2 of 3. In-situ DRIFTS and temperature-programmed surface experiments suggested that the dissociated adsorption of CO2 on the Pt site led to CO*, but the strongly adsorbed CO* cannot be further hydrogenated to CH4 over the Pt site. In contrast, CO* could be further hydrogenated into CH4via CHxO* intermediates on adjacent Ni sites.