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

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.