Fine-Tuning the Acid–Base Properties of Boron-Doped Magnesium Oxide Catalyst for the Selective Aldol Condensation

Controlled incorporation of dopants into the structure of metal oxide catalysts can be used to fine-tune their topological, chemical, and electronic properties. Conventional preparation methods (coprecipitation and impregnation) tend to produce materials with a limited extent of chemical interaction between metal oxide and dopant, small pore volume, and disconnected pore structure. Herein, we describe a combustion method to optimize both the porous structure of metal oxides and the chemical interaction with dopants. By exploiting the differences in melting points between metal oxide (MgO) and dopant (B), it is possible to create hierarchical mixed oxides with tailored chemical structure. As a model reaction, we employed the aldol condensation of acetaldehyde to crotyl alcohol, a key intermediate step in the conversion of bioethanol to 1,3-butadiene, to show the unique characteristics of these materials. The B–Mg mixed oxide prepared by combustion exhibits an order of magnitude higher productivity of C4 products than conventional MgO and B–MgO. We anticipate that our approach could be extended to the development of other dual oxides with open structure for unrestricted diffusion and enhanced chemical interaction of acid and basic metal oxides.