Oxidative esterification of 1, 2-propanediol to methyl lactate over Au/CuxAlOy catalysts in methanol without the presence of a base

A series of Au catalysts supported on different CuAl composite oxide supports were designed for the oxidative esterification of 1,2-propanediol to methyl lactate in an alkali-free methanol system. A conversion of 52.8% and a methyl lactate selectivity of 67.0% were obtained over the optimized Au/Cu_1.5AlO₃ catalyst under the conditions of 140 °C and 1.0 MPa O₂. The Au in the catalyst was revealed to be pivotal, providing the essential active sites necessary for the oxidative esterification of 1,2-propanediol. Moreover, the inclusion of Cu in the CuAl composite oxide support was discovered to markedly enhance the catalytic performance of the Au catalysts. The synergistic interaction between Au and Cu is posited to alter the electronic and geometric properties of the gold sites, thereby enhancing the catalyst's ability to oxidize the primary hydroxyl group of 1,2-propanediol. This strategic modification of the Au sites by Cu is instrumental in improving the selectivity for methyl lactate during the oxidative esterification process.

Graphical Abstract