Effect of Lewis basicity on the continuous gas phase condensation of benzaldehyde with acetophenone over MgO

Abstract

We have investigated the effect of Lewis basicity in the continuous gas phase condensation of acetophenone + benzaldehyde over MgO. The catalysts were prepared by ammonia precipitation, hydration and calcination to generate MgO with modified Lewis basicity (from CO2-TPD), dXRD (4−20 nm) and specific surface area (SSA = 58−246 m2 g−1); a direct correlation between SSA and Lewis basicity is presented. The introduction of Li+ and Cs+ served to decrease SSA and increase dXRD and Lewis basicity, linked to diffusion of the cations within the crystal structure (confirmed by XRD/STEM-EDX). All MgO systems delivered the exclusive and time invariant formation of target benzylideneacetophenone. Benzylideneacetophenone production rate is sensitive to the specific (per m2) Lewis basicity. The Cs10MgO_H(773) catalyst delivered the highest rate, attributed to high density of (Lewis basic) -O2− sites involved in the rate-determining step. Our results establish the feasibility of continuous chalcone synthesis using MgO catalysts with controlled Lewis basicity.