A comparative study on the performance of mesoporous SBA-15 supported Pd–Zn catalysts in partial oxidation and steam reforming of methanol for hydrogen production

Abstract

Abstract Using mesoporous SBA-15 (Santa Barbara Amorphous No. 15, a mesoporous material) as support, Pd–Zn nanocatalysts with varying Pd and Zn content were tested for hydrogen production from methanol by partial oxidation and steam reforming reactions. The physico-chemical characteristics of the synthesized SBA-15 support were confirmed by XRD, N 2 adsorption, SEM and TEM analyses. The PdZn alloy formation during the reduction of Pd–Zn/SBA-15 was revealed by XRD and DRIFT study of adsorbed CO. Also, the correlation between Pd and Zn loadings and PdZn alloy formation was studied by XRD and TPR analyses. The metallic Pd surface area and total uptakes of CO and H 2 were measured by chemisorption at 35 °C. The metallic Pd surface area values are in linear proportion with the Pd loading. The formation of PdZn alloy during high temperature reduction was confirmed by a shift in absorption frequency of CO on Pd sites to lower frequency due to higher electron density at metal particles resulted from back-donation. The reduced Pd–Zn/SBA-15 catalysts were tested for partial oxidation of methanol at different temperatures and found that catalyst with 4.5 wt% Pd and 6.75 wt% Zn on SBA-15 showed better H 2 selectivity with suppressed CO formation due to the enhanced Pd dispersion as well as larger Pd metallic surface area. The O 2 /CH 3 OH ratio is found to play a significant role in CH 3 OH conversion and H 2 selectivity. The performance of 4.5 wt% Pd–6.75 wt% Zn/SBA-15 catalyst in steam reforming of methanol was also tested. Comparatively, the H 2 selectivity is significantly higher than that in partial oxidation, even though the CH 3 OH conversion is less. Finally, the long term stability of the catalyst was tested and the nature of PdZn alloy after the reactions was found to be stable as revealed from the XRD pattern of the spent catalysts.