Dry reforming of methane over Ni/MFI catalysts: Role of the zeolite support acidity

Abstract

Dry reforming of methane (DRM) was studied over 5 wt%Ni/MFI catalysts with different Si/Al atomic ratios (40, 100 and ∞). The 5Ni/ZSM-5(40) catalyst, showing the highest acidity (largest Al content), led to the best Ni dispersion with smaller particles (~6 nm). Additionally, for this material the only reduction peak observed at very high temperature (715 ºC) through H2-TPR analysis, together with the binding energy of Ni2+ (856.19 eV) in the XPS spectra, denoted a strong interaction of the NiO nanoparticles with the zeolite. In contrast, the same techniques applied to the other catalysts with lower or no Al content showed larger Ni particles with little interaction with the support. Through temperature-programmed DRM tests, it was found that the onset temperature of CH4 conversion was much lower (327 ºC) for 5Ni/ZSM-5(40) than for the other catalysts prepared with supports of lower acidity (367–474 ºC). Isothermal tests over 5Ni/ZSM-5(40) denoted that DRM was the predominant reaction at 500, 550 and 600 ºC, according to the obtained H2/CO ratio (~1). However, DRM only prevailed at 600 ºC with the other two catalysts while other competing reactions (mainly catalytic decomposition of methane) occurred at 500 and 550 ºC. 5Ni/ZSM-5(40) produced the lowest amount of carbon, especially at 600 ºC (~2 wt%). Therefore, these results evidence the key beneficial role of acidity of the zeolite in the development of selective and stable DRM catalysts operating at relatively low temperatures.