Surface Investigation of Tungstophosphoric Acid Supported on Ordered Mesoporous Aluminosilicates for Biodiesel Synthesis.

Abstract

Aluminosilicates with ordered hexagonal mesopores denoted as MAS-7 and MAS-9 with uniform size were synthesized from zeolite β assembly and ZSM-5 precursors, respectively, with P123 as a surfactant, via the cooperative self-assembly pathway. A series of 12 tungstophosphoric acid (TPA) supported on MAS-7 and MAS-9 (H3PW12O40/MAS-7/MAS-9) catalysts for biodiesel production were synthesized via the wet impregnation technique. The characterization of the supports and catalysts was done using N2 adsorption–desorption analysis, X-ray diffraction (XRD), and pyridine adsorption Fourier transform infrared and Raman spectroscopies. Also, the 29Si magic-angle spinning and cross-polarization/MAS nuclear magnetic resonance (NMR) techniques were employed to study MAS-7/MAS-9 and the supported solid acid catalyst surfaces. The nitrogen sorption analysis and XRD patterns indicated the formation of well-defined mesoporous materials, whereas IR spectroscopy confirmed the presence of four distinct types of OH groups with varying degrees of acidity. 29Si MAS NMR signified a stronger interaction between the framework of mesoporous aluminosilicates and H3PW12O40. The X-ray absorption near-edge spectra of L1- and L3-edge tungsten showed that W in the H3PW12O40/MAS-9 sample exists as W6+, indicating the tungsten environment similar to that of H2WO4 with Oh symmetry. The catalytic activity of the synthesized catalysts was investigated for biodiesel synthesis using unrefined green seed canola oil as a feedstock, giving a methyl ester yield of 76.5–88.7 wt % under optimized reaction conditions. The catalyst activities were strongly correlated with the surface chemistry of the TPA-supported MAS-7 and MAS-9 catalysts.