Aldol condensation of methyl acetate with formaldehyde produces methyl acrylate (MA). Herein, we report a relatively thorough study on the reaction network for methyl acetate and formaldehyde (in various forms, i.e., 1,3,5-trioxane, formalin, or methanol solution) over CeO2-based catalysts, which possess redox and acid–base sites. Five types of reactions are involved: (i) aldol condensation, e.g., methyl acetate and its derivatives (methyl propionate, acetone, etc.) with formaldehyde to produce unsaturated intermediates such as methyl acrylate (methyl methacrylate and methyl vinyl ketone, which can subsequently undergo transfer hydrogenation to yield saturated products like 2-butanone); (ii) hydrogenation or transfer hydrogenation of methyl acrylate (or other unsaturated compounds containing a C═C bond) with H2/CH3OH to methyl propionate (or the corresponding saturated compounds); (iii) hydrolysis of methyl acetate to acetic acid and methanol; (iv) ketonization of acetic acid to acetone; and (v) dehydrogenation of methanol to formaldehyde and H2. Al-, La-, or Pr-doped CeO2 improves the selectivity of methyl acrylate. Al-doped CeO2 shows the highest selectivity of methyl acrylate (48%) in the investigated CeO2-based catalysts owing to its balanced acid–base properties. This study will be of benefit to the catalyst design for the aldol condensation reaction and the understanding of the chemical reaction mechanism over CeO2-based catalysts.
Wang et al. (Mon,) studied this question.