Efficient Conversion of Bio-Lactic Acid to 2,3-Pentanedione on Cesium-Doped Hydroxyapatite Catalysts with Balanced Acid-Base Sites

We report the design and synthesis of cesium-doped hydroxyapatite for direct and high-yield conversion of biobased lactic acid to 2,3-pentanedione (72.3%). Cs species derived from CsNO3 at high temperature of calcination is introduced into the hydroxyapatite structure to regulate its acid-base properties. It is found that a balance of acid-base chemistry favors the condensation of lactic acid to 2,3-pentanedione. As a result, the undesired reactions such as lactic acid dehydration, decarbonylation, and coking are suppressed. Instead, a concerted catalysis between surface basic site and acidic site for lactic acid condensation to 2,3-pentanedione dominates on the cesium-doped hydroxyapatite catalyst, leading to a highly selective process for direct conversion of bio-lactic acid to 2,3-pentanedione.