Synergistic role of acid sites in the Ce-enhanced activity of mesoporous Ce-Al-MCM-41 catalysts in alkylation reactions: FTIR and TPD-ammonia studies

The acidic properties of Ce-x-Al-y-MCM-41 with different Ce/Al/Si atomic ratios were examined by pyridine-FTIR and ammonia-TPD methods. Both the density and the strength of the acid sites were considerably higher in the samples containing both Ce and Al than in the samples with only one of these substituents. The IR spectra of chemisorbed pyridine revealed that the Ce-Al-MCM-41 samples contained at least two distinct Lewis acid sites, L-2 (1595-1444 cm(-1)) and L-1 (1613-1452 cm(-1)), where the L-2/L-1 ratio increased progressively with increasing Ce/Al atomic ratio in a series of samples with similar Si/Al ratios. In addition, the density of the Bronsted acid sites (B) as well as the B/L-1 ratio increased with increasing Ce/Al molar ratio in these samples. The findings of this study help us understand the synergistic role played by Lewis and Bronsted acid sites in the catalytic activity of these catalysts for the benzylation of toluene. (c) 2006 Elsevier Inc. All rights reserved.