Chemisorption of pyridine was applied as a method for studying the acidic properties of titania-silica nanoparticles prepared by sol-gel method.   The infrared spectra of adsorbed pyridine were used to evaluate the concentration and the relative strengths of different acid sites. These studies showed that the amount pyridine bound to different acid sites follow the order Lpy&gt;Hpy&gt;Bpy, and the relative thermal stabilites for different sites was found to be LA&gt;BA&gt;H-bond.  In order to determine the role of acid sites on these mixed oxide catalysts, a model compound, acetaldehyde adsorption was examined at different temperatures.  It has been found that at 233 K, acetaldehyde adsorbed through hydrogen bonding to surface hydroxyl groups as well as through Lewis acid sites, and upon warming to room temperature, the formation of 2-butenal was observed as the product of aldol condensation reaction. However, the adsorption of acetaldehyde over pyridine-covered surface indicated that the extent of aldehyde adsorption is significantly reduced which in turn affected the aldol condensation reaction.  This suggests that the acid sites play an important role in catalyzing the condensation reaction.

Investigation of the influence of acid-base sites on aldol condensation of acetaldehyde on mixed oxide surface

ACS Spring Meeting 2021

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