Abstract
La-exchanged 12-tungstophosphoric acid (La(x)TPA) and 12-molybdophosphoric acid (La(x)MPA) salts (x = 0.25, 0.50, 0.75 and 1.00) were prepared via an ion exchange method. The physico-chemical characteristics of the materials were analyzed by using elemental analysis, X-ray diffraction (XRD), Fourier transformed infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), N-2-physical adsorption, X-ray photoelectron spectroscopy (XPS), and acidity-basicity measurements. The results indicated that La was introduced into the secondary structure of heteropolyacid (HPA) and have not influenced the primary structure, which effectively improved the surface area and pore size. Acidity-basicity studies indicated that incorporation of La resulted in a decrease in the number of acid sites and an increase in the number of basic sites. The catalytic activity of samples was studied in transesterification of glyceryl tributyrate with methanol and La(x)TPA samples which exhibited high activity compared to La(x)MPA samples due to having more active basic sites and a larger surface area. Calcined La(x)TPA samples showed excellent stability, outstanding recyclability, and high activity for one pot transesterification and esterification processes. This outcome was attributed to the presence of balanced acidic and basic sites.