Preparation, characterization and catalytic application of Barium molybdate (BaMoO 4 ) and Barium tungstate (BaWO 4 ) in the gas-phase oxidation of toluene

Abstract

Barium molybdate and Barium tungstate are important materials due their photoluminescent properties and they also have catalysis and photocatalysis applications. In this work, powders of these compounds were prepared by microwave-assisted hydrothermal (MAH) method and polymeric precursor method (PPM) and their structural and optical properties were studied. Furthermore, these materials were employed as solid catalysts towards gas phase toluene oxidation reactions. X-ray diffraction confirms the purity of materials at both preparation methods and reveals a preferential growth when the powders are prepared by MAH due polymeric agents and processing using microwave, which was confirmed by Field emission scanning electron microscopy. Photoluminesce emission was attributed to the charge-transfer transitions within the [WO 4 ] 2and [MoO 4 ] 2complexes. The H 2 Temperature-Programmed Reduction (H 2 -TPR), O 2 -chemisorption and extended X-ray absorption fine structure (EXAFS) results indicated that BaWO 4 samples, compared with BaMoO 4 samples, have higher oxygen mobility and oxygen vacancies that appear as key factors for the achievement of better catalytic performances.

Heterogeneous catalysis for thioanisole oxidation using hydrogen peroxide and Copper, Nickel and Zinc tungstates prepared by the polymeric precursor method

“…Comparing the results of BET, it could be concluded that specific surface areas had no influence on the catalytic activities presented in this work. The superior performance presented by CuWO4 was attributed to its higher reducibility and oxygen mobility (higher hydrogen consumption, according to H2-TPR measurements) [46]. The hydrogen consumption (Table 3) for…”

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

“…In this paper, CaWO 4 powders were synthesized by microwave-assisted hydrothermal (MAH) method and polymeric precursor method (PPM). PPM allows to obtain high-purity homogeneous systems at the molecular scale due the immobilization of the metal cations in a polymeric networks, which can be annealed at relatively low temperatures (700 ºC) [14][15] . Microwave-assisted hydrothermal method is able to synthesize inorganic materials, such as tungstates, because the high frequency of the electromagnetic radiation promotes a rapid heating accelerating the chemical reactions [16][17][18] .…”

“…No significant change is observed in these XANES spectra as a function of the preparation method for CaWO 4 samples. EXAFS spectra at W L III -edge were also measured in order to obtain quantitative information at local structure such as the number, position and identity of atoms surrounding the absorbing element as well as structural disorder within the coordination spheres 14 . Fig.…”

“…Thus, abundant mobility of active lattice oxygen species improves the catalytic activity in the toluene oxidation. Toluene oxidation promoted by BaWO 4 and BaMoO 4 catalysts was described in our previous paper in which we considered the role of oxygen mobility and oxygen vacancies in the process 14 . In the occasion, the H 2 -TPR, O 2 -chemisorption and EXAFS results indicated that BaWO 4 catalysts, compared with BaMoO 4 catalysts, had higher oxygen mobility and oxygen vacancies that appear to be the key factors for the achievement of better catalytic performances.…”

Effective photoreduction of graphene oxide for photodegradation of volatile organic compounds

“…11 Commonly, metal oxides such as titanium dioxide and zinc oxide are used to carry out PCO studies. [15][16][17] For instance, methanol PCO was previously explored in a few studies with metal oxide-based photocatalysts. [18][19][20][21] In contrast to metal oxide-based photocatalysis, a carbonbased catalyst is a metal-free option that is low in cost and uses carbon, which has high abundance in the earth.…”