Effect of Acidic Properties of Mesoporous Zeolites Supporting Pt Nanoparticles on Hydrogenative Conversion of Methylcyclopentane

摘要

The effect of acidic properties of mesoporous zeolites on the control of product selectivity during the hydrogenative isomerization of methylcyclopentane has been investigated. A series of mesoporous zeolites with controlled acidic properties were prepared by postdealumination process with hydrochloric acid under hydrothermal conditions, and the resultant zeolites used for supporting colloidal Pt nanoparticles (NPs) with a mean size of 2.5 nm (±0.6 nm). As compared to the pure Pt NPs supported on catalytically inert mesoporous silica (MCF-17) as the reference catalyst that can produce isomers most selectively (～80%), the Pt NPs supported on mesoporous zeolites produced C_6-cyclic hydrocarbons (i.e., cyclohexane and benzene) most dominantly. The type and strength of the Bronsted (B) and Lewis (L) acid sites of those zeolites with a controlled Al amount are analyzed by using FT-IR after the adsorption of pyridine and NH_3 temperature-programmed desorption measurements, and they are correlated with the selectivity change between cyclohexane and benzene. From this investigation, we found a linear relationship between the number of Bronsted acid sites and the formation rate for cyclohexane. In addition, we revealed that more Lewis acidic zeolite having relatively smaller B/L ratio is effective for the cyclohexane formation, whereas more Bronsted acidic zeolite having relatively larger B/L ratio is effective for the benzene formation.