Acrylic acid synthesis from lactic acid over hydroxyapatite catalysts with various cations and anions

摘要

We prepared substituted hydroxyapatite catalysts, such as Ca,o(P04)6(OH)2, Sr_(10)(PO4)6(OH)2, Pbio(PO4)6(OH)2, Ca_(10)(VO4)6(OH)2, and Sr_(10)(VO4)6(OH)2, and carried out conversions of lactic acid over the prepared catalysts. The hydroxyapatite catalysts had stabilities for the reaction media under flowing gas including lactic acid and water at 623 K. The hydroxyapatite catalysts exhibited markedly higher acrylic acid yields than those of P2O5/SiO2 and MgO catalysts. In the lactic acid conversions, the relatively acidic catalysts, such as P2O5/SiO2, Ca_(10)(VO4)6(OH)2 and Sr_(10)(VO4)6(OH)2 catalysts, accelerated the formations of acetaldehyde and propionic acid, whereas the relatively basic catalysts, such as MgO and Pb_(10)(PO4)6(OH)2 catalysts, gave large amounts of unidentified products. On the other hand, the moderate acid-base catalysts, such as Ca_(10)(PO4)6(OH)2 and Sr_(10)(PO4)6(OH)2 catalysts, selectively accelerated the dehydration of lactic acid into acrylic acid.