Effect of Different Synthesis Methods on the Textural Properties of Calcium Tungstate (CaWO4) and Its Catalytic Properties in the Toluene Oxidation

Abstract

Calcium tungstate (CaWO 4) crystals were prepared by microwave-assisted hydrothermal (MAH) and polymeric precursor methods (PPM). These crystals were structurally characterized by X-ray diffraction (XRD), N 2 adsorption, X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) measurements. The morphology and size of these crystals were observed by field emission scanning electron microscopy (FE-SEM). Their optical properties were investigated by ultraviolet visible (UV-Vis) absorption and photoluminescence (PL) measurements. Moreover, these materials were employed as catalysts towards gas phase toluene oxidation reaction. XRD indicates the purity of materials for both preparation methods and MAH process produced crystalline powders synthesized at lower temperatures and shorter processing time compared to the ones prepared by PPM. FE-SEM images showed particles with rounded morphology and particles in clusters dumbbellslike shaped. PL spectra exhibit a broad band covering the visible electromagnetic spectrum in the range of 360 to 750 nm. XANES and EXAFS results show that preparation method does not introduce high disorders into the structure, however the H 2-TPR results indicated that the catalyst reducibility is affected by the preparation method of the samples.

Current progress on catalytic oxidation of toluene: a review

“…The influence of various synthesis techniques on the textural properties of calcium tungstate (CaWO4) and its catalytic properties in the toluene degradation was investigated where CaWO4 crystals were synthesized by microwaveassisted hydrothermal (MAH) and polymeric precursor methods (PPM). The experimental results showed that CaWO4 synthesized by MAH, compared to CaWO4 sample synthesized by PPM, have higher oxygen mobility that appears to be a key factor for excellent catalytic activities (Alencar et al 2018).…”

Synthesis and optical properties of Mn-doped CaWO4 nanoparticles

“…Later on by using different methods such as solid-state method [10], co-precipitation [11], solvo-thermal [12], sol-gel [13], reverse micellar reactions [14], microwave hydrothermal [11], combustion and hydrothermal [15] synthesis of CaWO 4 NPs were carried out. Till now most of the work has been concentrated around doping a rare earth element into CaWO 4 NPs [15][16][17]. The reason for doping rare earth element may be attributed to their high energy transfer between them and the host lattice, because of which these materials are the best candidates for luminescent applications.…”