Tailoring the Synergistic Bronsted-Lewis acidic effects in Heteropolyacid catalysts: Applied in Esterification and Transesterification Reactions

Abstract

In order to investigate the influences of Lewis metals on acidic properties and catalytic activities, a series of Keggin heteropolyacid (HPA) catalysts, H n PW 11 MO 39 (M = Ti IV, Cu II, Al III, Sn IV, Fe III, Cr III, Zr IV and Zn II; for Ti and Zr, the number of oxygen is 40), were prepared and applied in the esterification and transesterification reactions. Only those cations with moderate Lewis acidity had a higher impact. Ti Substituted HPA, H 5 PW 11 TiO 40, posse lower acid content compared with Ti x H 3-4x PW 12 O 40 (Ti partial exchanged protons in saturated H 3 PW 12 O 40), which demonstrated that the Lewis metal as an addenda atom (H 5 PW 11 TiO 40) was less efficient than those as counter cations (Ti x H 3-4x PW 12 O 40). On the other hand, the highest conversion reached 92.2% in transesterification and 97.4% in esterification. Meanwhile, a good result was achieved by H 5 PW 11 TiO 40 in which the total selectivity of DAG and TGA was 96.7%. In addition, calcination treatment to H 5 PW 11 TiO 40 make it insoluble in water which resulted in a heterogeneous catalyst feasible for reuse.