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

Abstract

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.