Novel Keggin-type H4PVMo11O40-based ionic liquid catalysts for n-caprylic acid esterification

• Ionic liquid functionalized heteropolyacid catalysts were prepared and characterized.
• The catalyst exhibited high effiency, convenient recovery and steady reuse.
• Experimental parameters in esterification of n-caprylic acid were optimized by RSM.

A series of new Keggin-type heteropolyacid (HPA)-based ionic liquid catalysts were synthesized from molybdovanadophosphoric acid (H4PVMo11O40) and propane sulfonated ionic liquid (MIM-PS). The physicochemical properties of these inorganic–organic composite catalysts were characterized by various techniques such as FT-IR, TGA, high-resolution 1H and 13C NMR, and solid-state 31P MAS NMR. Their catalytic performances were evaluated for esterification of n-caprylic acid to methyl caprylate, among them, the [MIM-PSH]2.0H2.0PVMo11O40 catalyst revealed an optimal reaction activity. Moreover, an experimental design was exploited via response surface methodology (RSM) on the basis of the Box–Behnken design (BBD). Accordingly, a maximum methyl caprylate yield of 95.6% was obtained over the [MIM-PSH]2.0H2.0PVMo11O40 catalyst under the