CO2 hydrogenation over mesoporous Ni-Pt/SiO2 nanorod catalysts: Determining CH4/CO selectivity by surface ratio of Ni/Pt
Herein, we fabricated a series of bimetallic Pt-Ni catalysts supported on mesoporous silica nanorods ( m SNR, specific BET surface area of 1802 m 2 g −1 ) to study the effect of Ni/Pt ratio on the product selectivity in CO 2 hydrogenation. Both monometallic Pt/ m SNR and Ni 50 Pt 50 / m SNR 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 Ni 50 Pt 50 / m SNR catalyst). The Pt/Ni ratio was crucial in determining the CH 4 /CO selectivity, and the addition of a tiny amount of Pt could improve the catalytic performance and stability of Ni/ m SNR. Among the different catalysts, Ni 98 Pt 2 / m SNR showed the best CO 2 conversion (59%) and CH 4 selectivity (96%) at 400 °C, 0.1 MPa, 9600 mL h −1 g cat −1 , and H 2 /CO 2 of 3. In-situ DRIFTS and temperature-programmed surface experiments suggested that the dissociated adsorption of CO 2 on the Pt site led to CO*, but the strongly adsorbed CO* cannot be further hydrogenated to CH 4 over the Pt site. In contrast, CO* could be further hydrogenated into CH 4 via CH x O* intermediates on adjacent Ni sites.
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