Base-Free Conversion of 1, 2-Propanediol to Methyl Lactate in Methanol Over Cu-Modified Au/ Hydroxylapatite Catalysts

The catalytic oxidative esterification of 1, 2-propanediol to methyl lactate in a base-free methanol system over Cu-modified Au/HAP catalysts was investigated. The catalysts demonstrated efficient activity in converting 1, 2-propanediol to methyl lactate without any base additives, achieving a conversion of 91.2% and a selectivity of 45% for methyl lactate under optimized conditions of 160 degrees C, 2 h, and 1.0 MPa O2 over 2Au12Cu/HAP catalyst. The Au sites were identified as pivotal in catalyzing the oxidation of 1, 2-propanediol, and the basic sites of HAP was hypothesized to play a similar role with base additives to enhance the catalytic activity of Au. Furthermore, modification of Cu to Au was observed to promote the oxidation of the hydroxyacetone intermediate to methyl lactate while effectively suppressing the over-oxidation of methyl lactate, thus increased selectivity of methyl lactate.Graphical Abstract1,2-propanediol was convertedto methyl lactateefficientlyin a base-free methanol system over Au-Cu/HAP catalysts