Preparation of tungstophosphoric acid intercalated MgAl layered double hydroxides with a tunable interlayer spacing and their catalytic esterification performance in the deacidification of model crude oil

Abstract

This study demonstrates the synthesis of MgAl layered double hydroxides (LDHs) intercalated with tungstophosphoric acid (H3PW12O40, HPW) by an ion exchange method, and different interlayer spacings (d003) are obtained by adjusting the ion exchange temperature and time. The crystalline structures, molecular structures, compositions, acidity, and specific surface areas of the LDH samples are characterized. A relatively high ion exchange temperature is favorable for the formation of a large d003 value of around 1.46 nm, while a long exchange time is favorable for the formation of a small d003 value of around 1.05 nm. The different values of d003 are the result of different orientations of HPW anions within the interlayer space. Here, d003 around 1.46 nm is obtained when P2W18O6 − 62 and PW11O7 − 39 anions are arranged in the interlayer with their C2 axes respectively tilted toward and perpendicular to the LDH layer planes. In contrast, d003 around 1.05 nm is obtained when PW12O3 − 40 anions are grafted onto the LDH layers with their C2 axis perpendicular to the layer planes. Furthermore, the catalytic esterification performance of the samples is investigated for the deacidification of a model crude oil. Compared with PW12O3 − 40 anions, the presence of P2W18O6 − 62 and PW11O7 − 39 anions in the interlayer produces a higher proportion of acidic sites with medium acidity, which could act as catalytic sites. Moreover, the large d003 facilitates the diffusion of reactants into the interlayer, which enhances their contact with the catalytic sites, and thereby increases the catalytic esterification performance of the LDHs in the deacidification of model crude oil.