The influence of Zr presence in short channel SBA-15 on state and activity of metallic modifiers (Ag, Au, Cu, Fe)

Abstract

Abstract Mesoporous silicas, SBA-15, synthesized with the addition of zirconium oxychloride (ZrOCl2) which ensures obtaining short channels, were used as supports for metallic modifiers including silver, copper, gold and iron. Different preparation routes of these materials, denoted as SBA-S (S stands for short channels), resulted in different morphologies and different contents of zirconium left after the preparation. Samples SBA-S1 and SBA-S2 were obtained after treatment with sulfuric acid (leaching of ca. 98.5% of zirconium ions), whereas SBA-S3 was not treated with H2SO4, which resulted in a higher zirconium content. Metallic catalysts were prepared by grafting of metal species on organosilane functionalized supports. Characterizations by X-ray diffraction, ultraviolet–visible spectroscopy and X-ray photoelectron spectroscopy allowed determination of the oxidation state of metallic modifiers and evidenced the interactions between the modifier (Ag, Au, Cu, Fe) and the zirconium that remained in the silica support. The reaction of 2-propanol decomposition and Fourier-transform infrared spectroscopy combined with adsorption of pyridine clearly showed the effect of zirconium on surface properties of metallic catalysts. Strong acidic Zr4+ species modified the surface acidic-basic properties of the catalysts. This phenomenon should be taken into account when the SBA-S materials are used as supports for potential catalytic applications. The reference material was the long channel SBA-15 (denoted as SBA-L) prepared and modified with metals by the same routes as the short channel materials.