Topic
Mixed oxide
About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.
Papers published on a yearly basis
Papers
More filters
••
TL;DR: In this article, two different synthesis routes were applied to prepare TiO2-XSiO2 (X denotes mol% of silica in titania-silica mixed oxides) with different silica concentrations by using ammonia water as hydrolysis catalyst.
Abstract: Two different synthesis routes were applied to prepare TiO2–XSiO2 (X denotes mol% of silica in titania–silica mixed oxides) with different silica concentrations by using ammonia water as hydrolysis catalyst. Through comparing the photocatalytic performance of two sets of mixed oxides, we found that the photocatalytic activity of mixed oxides prepared via the route which can promote homogeneity, was significantly enhanced as compared with that of counterparts prepared via the another route, and the highest photocatalytic activity obtained by adding about 9.1 mol% silica into titania was much higher than that of pure TiO2. The mixed oxides were investigated by means of XRD, thermal analysis, UV–vis, FT-IR and XPS. The characterization results suggest that, in comparison with pure TiO2, the mixed oxides exhibit smaller crystallite size and higher thermal stability which can elevate the temperature of anatase to rutile phase transformation due to the addition of silica. Furthermore, Bronsted acidity, which is associated with the formation of Ti O Si hetero linkages where tetrahedrally coordinated silica is chemically mixed with the octahedral titania matrix, may be a very important contribution to the enhanced photocatalytic activity of titania–silica mixed oxides as well.
112 citations
••
TL;DR: In this paper, the interpretation of X-ray absorption near-edge structure (XANES) data using factor analysis to follow the temperature-programmed reduction (TPR) of CuPd/KL-zeolite catalysts was described.
Abstract: In this paper we describe the interpretation of X-ray absorption near-edge structure (XANES) data using factor analysis to follow the temperature-programmed reduction (TPR) of CuPd/KL-zeolite catalysts. With this tool it is possible to identify and quantify the chemical compounds in which a metal is present during a reduction treatment. When the method is applied to the Cu K-edge XANES-TPR spectra of two bimetallic catalysts containing (1% Pd + 0.5% Cu), and (1% Pd + 0.25% Cu), it is shown that Cu is initially present in both as two oxidic species, a Cu-Pd mixed oxide and a Cu-exchanged in L-zeolite. Both catalysts show a similar behavior under reduction yielding only one zero valent phase, a Cu-Pd alloy. 25 refs., 6 figs., 3 tabs.
111 citations
••
TL;DR: The catalytic activity of the surface metal oxide sites was found to decrease upon reduction of these sites and the most active surface sites were the fully oxidized surface cations, which reflected the chemical nature of surface active sites.
Abstract: CH3OH temperature programmed surface reaction (TPSR) spectroscopy was employed to determine the chemical nature of active surface sites for bulk mixed metal oxide catalysts. The CH3OH-TPSR spectra peak temperature, Tp, for model supported metal oxides and bulk, pure metal oxides was found to be sensitive to the specific surface metal oxide as well as its oxidation state. The catalytic activity of the surface metal oxide sites was found to decrease upon reduction of these sites and the most active surface sites were the fully oxidized surface cations. The surface V5+ sites were found to be more active than the surface Mo6+ sites, which in turn were significantly more active than the surface Nb5+ and Te4+ sites. Furthermore, the reaction products formed also reflected the chemical nature of surface active sites. Surface redox sites are able to liberate oxygen and yield H2CO, while surface acidic sites are not able to liberate oxygen, contain either H+ or oxygen vacancies, and produce CH3OCH3. Surface V5+, Mo6+, and Te4+ sites behave as redox sites, and surface Nb5+ sites are Lewis acid sites. This experimental information was used to determine the chemical nature of the different surface cations in bulk Mo-V-Te-Nb-Ox mixed oxide catalysts (Mo(0.6)V(1.5)Ox, Mo(1.0)V(0.5)Te(0.16)Ox, Mo(1.0)V(0.3)Te(0.16)Nb(0.12)Ox). The bulk Mo(0.6)V(1.5)Ox and Mo(1.0)V(0.5)Te(0.16)Ox mixed oxide catalytic characteristics were dominated by the catalytic properties of the surface V5+ redox sites. The surface enrichment of these bulk mixed oxide by surface V5+ is related to its high mobility, V5+ possesses the lowest Tammann temperature among the different oxide cations, and the lower surface free energy associated with the surface termination of V=O bonds. The quaternary bulk Mo(1.0)V(0.3)Te(0.16)Nb(0.12)Ox mixed oxide possessed both surface redox and acidic sites. The surface redox sites reflect the characteristics of surface V5+ and the surface acidic sites reflect the properties normally associated with supported Mo6+. The major roles of Nb5+ and Te4+ appear to be that of ligand promoters for the more active surface V and Mo sites. These reactivity trends for CH3OH ODH parallel the reactivity trends of propane ODH because of their similar rate-determining step involving cleavage of a C-H bond. This novel CH3OH-TPSR spectroscopic method is a universal method that has also been successfully applied to other bulk mixed metal oxide systems to determine the chemical nature of the active surface sites.
111 citations
••
TL;DR: In this paper, the catalytic activity of the nonequilibrated and equilibrate catalysts for inn-butane andn-pentane oxidation was studied and compared; the chemical physical features of the two catalysts were studied by means of XRD, FT-IR, chemical analysis, TGA, XPS, and TPD.
111 citations
••
TL;DR: In this article, the authors investigated the catalytic activity of methanol-based alkylating agents for methylation of phenol and 2,6-xylenol.
111 citations