Acetaldehyde Condensation-Cyclodehydration to Aromatics over Mg-Al Oxides

Acetaldehyde is a constituent of many biomass-derived feedstocks, but its high reactivity and tendency to polymerize make it challenging to upgrade into compounds for incorporation into chemical and fuel infrastructures. Mg-Al oxide catalysts derived from calcined layered double hydroxides are used in a multiple condensation-cyclodehydration reaction of acetaldehyde to produce benzene and methylbenzaldehydes, the latter of which are precursors to terephthalic acid. By varying the Mg/Al ratio in the catalysts, conversion and selectivity profiles are impacted as a function of time on stream (TOS). Carbon selectivity towards methylbenzaldehydes reaches 33% over the catalyst with Mg/Al=3. Despite deactivation due to the formation of non-volatile carbonaceous deposits, selectivity towards methylbenzaldehydes stabilizes at 20% after 18 hours TOS. Changes in selectivity with deactivation, as well as the difference in selectivity over the varying Mg/Al catalysts, indicate different mechanisms are activated over different site types.