Abstract
In this study the mixed oxides ZrO2-SiO2, were synthesized by the sol-gel method with a molar ratio of 95:5 (Si/metal) and characterized by X-ray diffraction, absorption-desorption of N2, Fourier transform infrared spectroscopy, thermal gravimetric analysis, temperature-programmed desorption of ammonia, and acidity test by titration. The synthesized materials, which are amorphous to X-rays, are composed of a mixture of micro- and mesopores. They show a higher acid strength than the separate oxides, indicating that the ZrO2 is highly dispersed in the silica matrix.
Highlights
The continuous evolution of science and the general call for the protection of the environment have created an increased demand for new technologies and new materials
The acidic mixed oxides play an important role in applications such as the cyclization of citronellal to isopulegol[16,17], isomerization of α-pinene and dehydration of 4-methyl-2pentanol[18], Fischer-Tropsch process[19], ammonia oxidation[20], hydrogenation of alkenes[21], synthesis of alcohols[22], and biodiesel production[23]
The solids were synthesized by means of the solgel process (SGP), a comparatively simple method for the synthesis of mixed oxides, which promotes high homogeneity of the metal on the surface of the matrix, better control of particle size, and higher purity[36]
Summary
The continuous evolution of science and the general call for the protection of the environment have created an increased demand for new technologies and new materials. Among the most frequently employed methods for the synthesis of mixed oxides are the coprecipitation[24], hydrothermal routes[25], sonochemical processes[26], the oxalate route[27], and the sol-gel process[28] From all these processes, the sol-gel process (SGP) has attracted attention due to its versatility in the development of new materials, owing to the simplicity and flexibility of the synthesis, which permits the preparation of highly pure and homogeneous products with controlled porosity[29]. The sol-gel process (SGP) has attracted attention due to its versatility in the development of new materials, owing to the simplicity and flexibility of the synthesis, which permits the preparation of highly pure and homogeneous products with controlled porosity[29] This process is environmentally friendly compared to the traditional routes for the preparation of ceramics and glasses[30]. Based on the above considerations, the objective of this work was the synthesis and characterization of the mixed oxide ZrO2-SiO2 as well as the modification of its acid force and its hydrophilic character, followed by an preliminary assessment of the catalyst in the esterification of oleic acid with methanol, aiming at a future application in the production of biodiesel from high free fatty acid feedstocks
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