Abstract
Recently, mixed metal aluminate as a highly active, stable, and reusable nanocatalyst was extremely used in chemical reactions such as esterification. The preparation of the samples via a simple, rapid, and cost-effective method is one of the main problems on the front of the industrial application of these materials. For this purpose, the solution combustion method (SCM) was assessed for the fabrication of spinel CoAl2O4, and the effects of fuel-to-oxidizer (F/O) ratio on crystalline structure, surface functional groups, surface area, morphology, and porosity were analyzed. The activity of the samples, which was impregnated by the sulfate group was evaluated in the esterification reaction. Morphology and texture properties of the samples indicated the crystallinity, surface area, and pore diameter of CoAl2O4 were enhanced by increasing the F/O ratio. It can be related to increasing the combustion reaction time and temperature. However, at F/O ratios above two, due to limited diffusion of oxygen into the reaction medium, the reaction terminated immaturely. Sulfated cobalt aluminate fabricated at F/O ratio of two was successfully synthesized in nanoscale with same particle size. Moreover, it did not show impurity in its structure that is related to the ability of the combustion method for the fabrication of pure nanocatalyst. Evaluation of the catalytic activity of the SO42−/CoAl2O4 nanocatalysts in the esterification reaction confirmed the results of physicochemical studies. For instance, the sample prepared at F/O ratio of two presented the highest conversion (96.7%) at methanol/oleic acid molar ratio of nine, catalyst amount of 3 wt. %, and reaction temperature and time of 120 °C and 4 h, respectively. In addition to preserving its activity for four runs (conversion > 85%), its activity was simply recovered upon regeneration by sulfate group, making it a promising alternative for industrial production of biodiesel.Graphic abstract
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