Nature of the acid sites in the metal triflates immobilized in SBA-15 and their role in the Friedel–Crafts acylation of naphthalene

The Zn-triflate molecules loaded (5–30 mol%) in mesoporous SBA-15 silicate exhibited considerably higher catalytic activity for liquid-phase Friedel–Crafts (FC) acylation of naphthalene with p-toluoyl chloride, as compared to the corresponding triflates of La, Ce and Y. In situ FTIR studies revealed that the triflate molecules occluded in the channels of SBA-15 may cause severe perturbation of surface hydroxyl groups, without undergoing an electronic binding. The metal cations of the triflate molecules, on the other hand, participated in direct bonding of the reactant molecules and also helped in the formation of some Brönsted type surface acid sites. This article discusses the role of the acid sites generated on occlusion of metal triflates in SBA-15, as monitored by using NH3-TPD and pyridine-IR spectroscopy, in the Friedel–Crafts acylation of naphthalene.

Graphical abstractThe acid sites responsible for acylation of naphthalene over metal triflate loaded SBA-15 are monitored by NH3-TPD and pyridine-IR measurements. Whereas large triflate groups assist in the geometric confinement in the pores of SBA-15, the metal cations are found to be responsible for the direct binding of reactant molecules and hence for the catalytic activity.Figure optionsDownload full-size imageDownload high-quality image (44 K)Download as PowerPoint slide