Effect of Impregnation with Ammonia vs Silica Support Textural Properties on Ni Nanoparticle Catalysts for Dry Reforming of Methane

Abstract

In this work, Ni(0) nanoparticles (3.5 and 5 wt %) highly dispersed on silica were obtained by reducing the calcined solid resulting from the impregnation of a nonporous siliceous support (here Aerosil-380) by aqueous nickel(II) nitrate in the presence of aqueous ammonia. The great effect of that base could be emphasized by the comparison with the solid prepared in the absence of ammonia. It was also clearly shown to be superior to the physical barrier effect induced by SBA-15, a mesostructured silica support, impregnated, using a "two-solvents"method, with a similar amount of aqueous precursor (5 wt % of Ni) in the absence of ammonia. In the protocol involving NH3, nickel phases could be hardly detected by X-ray diffraction (XRD) before and after reduction. However, the presence of Ni could be confirmed by X-ray photoelectron spectroscopy (XPS) and H2-TPR. After reduction, transmission electron microscopy (TEM) observations as well as H2 chemisorption highlighted the important dispersion of Ni(0) nanoparticles (up to 42% for 3.5 wt % of Ni). Aerosil-380-based catalysts prepared in the presence of NH3 revealed great performances in the dry reforming of methane at 650 °C for 12 h using a gas hourly space velocity of 960 L g-1 h-1 and an equimolar ratio of CH4 and CO2 reactants. Moreover, they showed a great resistance toward sintering and coke deposition. The formation of Ni phyllosilicate intermediate phases, which are at the origin of this excellent stability, could be evidenced by Fourier transform infrared (FTIR) and 29Si solid-state nuclear magnetic resonance (NMR).