Decoration of chitosan microspheres with Brønsted heteropolyacids and Lewis ion Ti: trifunctional catalysts for esterification to biodiesel†
H3PW12O40 is a commonly used Brønsted acid catalyst in esterification and transesterification reactions to produce biodiesel, whose homogeneous form and single acid sites lead to difficulties in separation and relatively less activity. Herein, the water-insoluble and multifunctional active sites based on H3PW12O40, chitosan and Ti4+ had been fabricated giving H3PW12O40/Ti/chitosan tri-functional hybrids. Such hybrids exhibited higher activity in esterification reactions due to the existence of Brønsted acid from H3PW12O40, Lewis acid from Ti4+, and base sites from the –NH2 group of chitosan, and all also due to the generation of pores in chitosan through introduction of the Ti ions. Furthermore, H3PW12O40/Ti/chitosan acted as heterogeneous catalysts and could be separated for reuse at least six times without significant loss of activity and with little leaching of Ti4+ and H3PW12O40 from the support chitosan.