Characterisation of acidic properties of the surface of SiO2–SnO2 obtained by sol-gel method in anhydrous conditions

Resumo

A series of SiO₂–SnO₂ samples of the Sn/Si molar fractions of 0.05, 0.1, 0.25, 0.5 and 1.0 were synthesised by the sol-gel method in anhydrous conditions. The SiO₂–SnO₂ samples were characterised by XRD, low-temperature nitrogen adsorption, SEM, 29Si MAS NMR and TPD, using pyridine and acetonitrile as probes. It has been proved that incorporation of small or even insignificant amount of tin in the structure of SiO₂ gel lattice considerably increased the number and power of acidic centres accessible to the probe molecules in the samples synthesised by the sol-gel method in anhydrous conditions. The increase in the number and power of acidic centres can substantially improve the catalytic properties of the SiO₂–SnO₂ system.