Al-functionalized mesoporous SBA-15 with enhanced acidity for hydroisomerization of n-octane

SBA-15, possessing uniform mesopore system and large specific surface area, shows a tremendous mass transfer advantage in the reactions involving reactant, intermediate or product whose dynamic diameter is larger than the pore size of microporous zeolites, but the low acidity greatly limits its application in acid-catalyzed reactions (e.g., hydroisomerization). Herein, we report an Al-functionalized SBA-15 molecular sieve (Al-SBA-15) with enhanced acidity obtained via a pH-adjusted prehydrolysis synthesis approach for hydroisomerization. Its physicochemical properties and catalytic performance were carefully characterized, evaluated in hydroisomerization of n-octane after loading active component Pt, and compared with a pure silica SBA-15 and two Alcontaining samples (AlSBA-15 and Al/SBA-15) produced through direct synthesis and wetness impregnation, respectively. The results show that the acidity of three Al-functionalized samples is prominently improved, and thus the conversion of n-octane over them is greatly increased when compared with siliceous SBA-15. Moreover, among three Al-containing SBA-15 materials, Al-SBA-15 with the largest pore diameter and moderate acidity exhibits relatively high n-octane conversion and di-branched isomers selectivity but minimal cracking selectivity. These results demonstrate that pH-adjusted prehydrolysis is an effective route to preparing Al-functionalized SBA-15 with suitable acidity for the hydroisomerization of alkanes.