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

12-tungstophosphoric acid (H₃PW₁₂O₄₀, HPW) intercalated layered double hydroxides (LDHs) with various Mg/Al molar ratios were synthesized by an ion-exchange method. The samples were characterized by XRD, FT-IR, Raman, ICP-AES and TG-DSC. The acid strength and amount of acidic sites of catalysts were measured by Hammett indicator and n-butylamine titration technique. Furthermore, HPW intercalated LDHs were used as esterification catalysts for deacidification of crude oil and compared with their nitrate LDHs precursors. The relationship between the catalytic activity and the property of HPW intercalated LDHs was investigated. It is found that the catalytic activity of LDHs mainly depends on the acidity and the specific surface area. HPW intercalated LDHs exhibit a much higher catalytic activity than nitrate LDHs owing to the increased acidity and specific surface area. Due to the poorer acidity, the activity of nitrate LDHs is proportional to their specific surface area. The nitrate LDH with Mg/Al molar ratio of 4 exhibits the highest specific surface area and deacidification ratio. However, for highly acidic HPW intercalated LDHs, the amount of acidic sites dominates the catalytic activity and the HPW intercalated LDH with Mg/Al molar ratio of 2 has the highest acidity and esterification activity.