Postsynthesis modification of alum inophosphates by reaction with silicon tetrachloride

Abstract

Silicon tetrachloride was reacted with fixed beds of AIP0 4-5 at temperatures between 450 and 750°C. Crystalline samples which showed properties different from the parent AIPO 4-5 materials resulted from most treatments. Samples were prepared with silicon mole fractions between 0.04 to 0.11 and oxygen monolayer volumes between 19.6 and 82.2 STP cm 3/g. The samples showed increasing silicon content and decreasing oxygen monolayer volumes for increasing treatment temperature. The samples showing the smaller O 2 monolayer volumes may have silicon-rich material in the pores. Crystalline, aluminum phosphate (AIPO 4-5), and the modified samples were characterized by ammonia titration, pyridine IR spectroscopy, and two probe reactions: toluene methylation and cumene cracking. These SiCl 4-treated samples showed ammonia retentions 50–80% greater than those of the untreated sample and toluene methylation activities three to four times that of the untreated AIPO 4-5. However, the SiCl 4 treatment conferred to the samples no increase in cumene cracking rates and the pyridine IR spectra over the modified samples showed only Lewis-bound pyridine, which was observed in the untreated AIP0 4-5. The xylene product distribution for the methylation reaction over the modified AIPO 4-5 ( o/ p/ m = 0.51/0.27/0.22) was similar to that expected for a Freidel-Crafts alkylation ( o/ p/ m = 0.54/0.29/0.17).