Characterization and Fourier transform infrared spectroscopic study of surface acidity in NiMo/TiO2-Al2O3 catalysts

Catalysts consisting of Mo and Ni oxides supported on Al2O3 and TiO2 and on mixtures of both have been prepared by co-impregnation of the supports with aqueous solutions of Mo(VI) and Ni(II) salts, and have been characterized by X-ray diffraction, Fourier transform-infrared (FTIR) and vis-UV/diffuse reflectance spectroscopies and surface texture by nitrogen adsorption; surface acidity has been measured by FT-IR monitoring of pyridine adsorption. Incorporation of TiO2 to the support Al2O3 leads to a larger dispersion of molybdena on the catalyst support. The solids (specially those with low TiO2 content) are not microporous, but have pores open at both ends. The increase in the TiO2 content leads to a larger concentration of surface Bronsted (Mo-OH) acid sites, associated with an increase in the number of dispersed molybdate species.