Topic
Mixed oxide
About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.
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TL;DR: In this paper, the surface properties of Tantala oxide were investigated using XRD, UV-vis-DR, FTIR, and FT-Raman spectroscopy to determine the nature of the surface Tantala species.
Abstract: Silica-, alumina-, and zirconia-supported tantalum oxide and supported vanadia-tantala mixed oxide catalysts were investigated by XRD, UV−vis-DR, FTIR, and FT-Raman spectroscopy to determine the nature of the surface tantala species. Two types of surface TaOx species were identified. On the SiO2 support, at low coverages tetrahedral TaO4 species exist, with a TaO bond and three bridging Ta−O-support bonds. At higher coverages, octahedral TaO6 species occur. On Al2O3 and ZrO2 both surface species exist already at considerably low Ta loading. The acidic properties of the catalysts were investigated by an FTIR study of adsorbed pyridine. Supported tantala is clearly more Lewis acidic in comparison to vanadia. The oxidation of methanol was used to probe the catalytic performance of the supported oxide species and from the activity and product distribution it is concluded that supported tantala predominantly shows acidic over redox behavior.
62 citations
TL;DR: In this paper, a combined experimental and theoretical study was used to reveal the mechanism of the deactivation caused be the alkali metals, which indicated that the doping of alkali metal atoms on the catalyst surface greatly decreases the surface acidity and reducibility.
Abstract: Alkali metals were found to be poisonous to the Ce‐Ti oxide catalyst. The NO conversion of the catalyst decreased by more than 80 % at temperatures from 250 to 450 °C with the doping of either 3.71 atom % K or 3.74 atom % Na. A combined experimental and theoretical study was used to reveal the mechanism of the deactivation caused be the alkali metals. The results indicated that the doping of alkali metal atoms on the catalyst surface greatly decreases the surface acidity and reducibility. XPS characterization revealed that the interaction between the alkali atoms and the oxygen atom of cerium oxide inhibits the transformation between Ce3+ and Ce4+, which effects a decrease in the proportion of Ce3+. The theoretical results show that the alkali atoms strongly interact with the cerium oxygen and titanium oxygen, which causes the degradation of reducibility and surface acidity, respectively. This causes a serious deactivation of the Ce‐Ti oxide catalyst.
61 citations
TL;DR: In this article, several semiconductive oxides are tested as sensors for the detection of NO, NO2, CO and CO2, including mixed oxide (Al2O3)0.5(V2O5) 0.5, which is excellent not only in its selectivity for detecting NO and NO2 but also in its sensitivity.
61 citations
TL;DR: In this paper, the relationship existing between aging conditions, redox behavior, and surface/bulk structural properties of two thermally aged ceria−zirconia mixed oxides, CZ-MO and cZ-SO, is analyzed.
Abstract: The relationship existing between aging conditions, redox behavior, and surface/bulk structural properties of two thermally aged ceria−zirconia mixed oxides, CZ-MO and CZ-SO, is analyzed. The samples were prepared by applying to a fresh Ce0.62Zr0.38O2 mixed oxide two alternative aging routines consisting of a reduction with H2 at 1223 K (5 h), followed by either a mild, CZ-MO, or severe, CZ-SO, re-oxidation treatment. By combining high-resolution electron microscopy and a number of chemical charcterization techniques, it is shown that the nanostructure of the aged oxides, specifically the total amount and surface presence of the phase exhibiting an ordered cationic sublattice (κ-like phase), is a key factor in determining their redox response. In the low-temperature reduction range (Tredn ≤ 773 K), the enhanced reducibility of the CZ-MO sample is proposed to be kinetically controlled by its surface structure mainly consisting of the κ-like phase. In accordance with the reported results, the surface activa...
61 citations
TL;DR: In this article, the acid-base properties of AMO-LDH-based oxide catalysts with various ratios of Mg/Al were studied for the chemical and physical properties and the activity on esterification of benzoic acid with 2-ethylhexanol.
Abstract: Proven to possess distinguishable physical and acid-base properties superior to conventional LDHs, Aqueous Miscible Organic solvent-Layered Double Hydroxides (AMO-LDHs) were thus synthesized and used as precursors to prepare the Mg/Al mixed oxide catalysts in this work. The AMO-LDH based oxide catalysts with various ratios of Mg/Al were studied for the chemical and physical properties and the activity on esterification of benzoic acid with 2-ethylhexanol. The catalysts were characterized using BET, XRD, TGA, and XPS. Moreover, the acid-base properties were studied by using NH3-TPD, CO2-TPD, and X-ray Absorption Spectroscopy (XAS) techniques, both XANES and EXAFS. As a result, the Mg/Al mixed oxides after calcination at 500 °C still had the clay structure, and were found to possess both acid and base sites. As the Mg/Al ratio increased, the total density of acid and basic sites decreased. Moreover, the acid-basic strength depended on their phase compositions and coordination number. The activity of calcined LDHs catalysts was tested for the esterification of benzoic acid with 2-ethylhexanol, aimed at producing 2-ethylhexyl benzoate as the desired chemical. The products were analyzed using GC–MS/TOF. In summary, the conversion of benzoic acid was enhanced significantly using the Mg Al mixed oxides as the catalysts, owing to the acid-base sites (both Mg2+ O2− and Al3+ O2− pairs) of the catalysts. The catalyst with the Mg/Al ratio of 4:1 can convert 66% benzoic acid to 2-ethylhexyl benzoate. Moreover, the other products were composed of 2-ethylhexanal, 3-heptanone, and 3-heptanol because of acid-base pairs.
61 citations