Decoration of chitosan microspheres with Brønsted heteropolyacids and Lewis ion Ti: trifunctional catalysts for esterification to biodiesel

H 3 PW 12 O 40 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 H 3 PW 12 O 40 , chitosan and Ti 4+ had been fabricated giving H 3 PW 12 O 40 /Ti/chitosan tri-functional hybrids. Such hybrids exhibited higher activity in esterification reactions due to the existence of Brønsted acid from H 3 PW 12 O 40 , Lewis acid from Ti 4+ , and base sites from the –NH 2 group of chitosan, and all also due to the generation of pores in chitosan through introduction of the Ti ions. Furthermore, H 3 PW 12 O 40 /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 Ti 4+ and H 3 PW 12 O 40 from the support chitosan.