磷钨酸插层MgAl水滑石层间距的调变及催化酯化脱酸性能

通过改变离子交换温度和时间合成了具有不同层间距的磷钨酸(H_3PW_(12)O_(40),HPW)插层MgAl水滑石(LDHs),采用XRD、FT-IR、Raman、~(31)P MAS NMR、ICP-AES和Hammett指示剂-正丁胺滴定法等表征其性质,并研究其对模型原油的催化酯化脱酸性能。高的离子交换温度有利于形成较大的层间距(d_(003)约1.46 nm),较长的交换时间有利于形成较小的层间距(d_(003)约1.05 nm)。不同的层间距源自HPW在层间不同的存在形式,P_2W_(18)O_(62)~(6-)以C_2轴倾斜于层板和PW_(11)O_(39)~(7-)以C_2轴垂直于层板的方式排列于层间时,形成d_(003)约1.46 nm的层间距;PW_(12)O_(40)~(3-)与层板发生嫁接,并以C_2轴垂直于层板的方向排列于层间时,形成d_(003)约1.05 nm的层间距。层间P_2W_(18)O_(62)~(6-)和PW_(11)O_(39)~(7-)能产生更高比例的中强酸中心,同时大的层间距有利于反应物扩散进入层间与酸中心接触,能够提高LDHs的催化酯化脱酸性能。

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

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, atomic compositions, acidity, and specific surface areas of the LDH samples are rigorously characterized. A relatively high ion exchange temperature is demonstrated to be 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=1.46 nm is obtained when P₂W₁₈O₆₂^6- and PW₁₁O₃₉^7- anions are arranged in the interlayer with their C₂ axes respectively tilted toward and perpendicular to the LDH layer planes. In contrast, d₀₀₃=1.05 nm is obtained when PW₁₂O₄₀^3- 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 PW₁₂O₄₀^3- anions, the presence of P₂W₁₈O₆₂^6- and PW₁₁O₃₉^7- anions in the interlayer produce a higher proportion of sites with intermediate acidity that function as catalytic sites. Moreover, a large value of 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 crude oil.