Abstract
La-exchanged 12-tungstophosphoric acid (LaxTPA) and 12-molybdophosphoric acid (LaxMPA) 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), N2-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 LaxTPA samples which exhibited high activity compared to LaxMPA samples due to having more active basic sites and a larger surface area. Calcined LaxTPA 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.
Highlights
The growth in demand for conventional petroleum based fuels, diesel, has resulted in enormous concern regarding increased greenhouse gas emissions from the consumption of diesel [1,2].It is well known that the emission of greenhouse gases is responsible for global warming [3]
Cesium salts of TPA were used for transesterification of vegetable oil and superior catalytic performance was observed as shown in the case of homogeneous catalysts (NaOH or H2 SO4 ) with additional advantages of easy separation of the catalyst from the reaction mixture and its reuse [11]
It is interesting to note that the X-ray diffraction (XRD) patterns of Lax MPA samples exhibited few broad humps due to the presence of an unknown amorphous material, which was not observed in the case of Lax TPA samples
Summary
The growth in demand for conventional petroleum based fuels, diesel, has resulted in enormous concern regarding increased greenhouse gas emissions from the consumption of diesel [1,2]. Acidic catalysts have an edge in the production of biodiesel due to providing both esterification of fatty acids and transesterification of triglycerides processes. Cesium salts of TPA were used for transesterification of vegetable oil and superior catalytic performance was observed as shown in the case of homogeneous catalysts (NaOH or H2 SO4 ) with additional advantages of easy separation of the catalyst from the reaction mixture and its reuse [11]. Cs salts of TPA are active catalysts for esterification of palmitic acid and transesterification of glyceryl tributyrate, which are essential reactions for biodiesel production. It was observed that incorporation of metal cations such as Cs+ in place of H+ cations resulted in interesting effects on the surface area, pore structure, and solubility These properties are significant for any catalyst, as they play a role in the resistance against deactivation through solvents and improve their recycling potential [13]. The correlation between the catalytic performance and physico-chemical characteristics of the catalysts was studied
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