Aldol Condensations Using Bio-oil Model Compounds: The Role of Acid-Base Bi-functionality

The aldol condensation of acetaldehyde, acetone, and methyl ethyl ketone, which represent model bio-oil compounds, in the condensed phase, was performed using a bi-functional aluminophosphate catalyst. It was found that increasing the number and strength of the basic sites while decreasing acid sites on the catalyst caused a reduction in yield of the condensation products. In contrast, the addition of organic acids such as acetic acid at low concentrations to the catalyst-containing reaction mixture was found to increase activity. The presence of both acid and base sites was found to be necessary and their relative number was important for both the activity and selectivity of the condensation reaction. A mechanism explaining the observed phenomena was proposed.