FT-IR spectroscopic studies of tin-modified rhenium alumina-silica metathesis catalyst

FT-IR spec tra of the products obtained in each step of the tetramethyltin (TMT)/3-wt. % Re2O7/Al2O3-SiO2 and TMT/Al2O3-SiO2 systems preparation are p resented and discussed. The obtained spectra show that TMT reacts with alum ina-silica hydroxyl groups already at room temperature, yielding surface me thyltin compounds; NH4ReO4 reacts with alumina-silica surface at temperatur es up to 423 K, yielding rhenium surface species and ammonia, which is stro ngly bonded by acidic sites of the Bronsted kind. FT-IR spectrum of the sys tem TMT/3-wt. % Re2O7/Al2O3-SiO2 indicated the absence of surface methyl ti n compounds observed on the surface system TMT/AL(2)O(3)-SiO2, and the pres ence of physically adsorbed TMT; after 5 h of evacuation of the TMT/3-wt. % Re2O7/ALO(3)-SiO2 system, the FT-IR spectrum indicated the presence of onl y a single band at 2977 cm(-1), which may be assigned to the C-H bond stret ching of the methyl group in the surface bridged (O, O') Re(=O)(2)CH3 compl exes formed. Analysis of FT-IR results suggests formation of a new phase co ntaining rhenium and aluminium ions, on which olefin sites active in olefin metathesis are formed in the system studied.