Synthesis and characterization of 12-tungstophosphoric acid intercalated layered double hydroxides and their application as esterification catalysts for deacidification of crude oil

Abstract

12-tungstophosphoric acid (H3PW12O40, HPW) intercalated layered double hydroxides (LDH) (M2+/Al3+=2, M2+=Mg2+, Zn2+, Ni2+) were prepared by an ion-exchange method. The as-prepared LDH show a strong reflection around 8.4° corresponding to a basal spacing of 1.05nm, which is considered as heteropolyacid salts or polytungstate intercalated LDH in almost all literature. Further systemic experiments and characterizations demonstrated that such reflection can be attributed to the intercalation of HPW, in which HPW may graft with the vacancies in the layer and orient in the interlayer with the C2 axis perpendicular to the layers. HPW intercalated LDH show higher catalytic activity than nitrate LDH for the esterification between ethylene glycol and naphthenic acids in crude oil. It is found that the total amount of acidic sites dominates the esterification activity. Due to the immobilized HPW active sites and the enlarged interlayer space, HPW intercalated LDH may act as an interlayer catalytic reactor to improve the esterification activity.