Mixed oxide

About: Mixed oxide is a research topic. Over the lifetime, 5224 publications have been published within this topic receiving 115567 citations.

Supported CeO2 catalysts in technical form for sustainable chlorine production

Abstract: Bulk CeO 2 has been recently reported as a promising catalyst for the oxidation of HCl to Cl 2 . In order to undertake the scale up of this system, various oxides (TiO 2 , Al 2 O 3 , and low- and high-surface area ZrO 2 ) have been evaluated as carriers. Supported CeO 2 catalysts (3–20 wt.% Ce) prepared by dry impregnation were isothermally tested at the lab scale. Their performance was ranked as: CeO 2 /ZrO 2 ≫ CeO 2 /Al 2 O 3 ≥ CeO 2 /TiO 2 . Kinetic data revealed a lower activation energy and a similar activity dependence on the partial pressure of O 2 for CeO 2 /ZrO 2 compared to bulk CeO 2 . Pilot-scale testing over 3-mm pellets of this catalyst evidenced outstanding stability for 700 h on stream. In-depth characterization of the carriers and fresh catalysts by N 2 sorption, Hg porosimetry, X-ray diffraction, temperature-programmed reduction with H 2 , Raman spectroscopy, electron microscopy, and in situ prompt gamma activation analysis, enabled to rationalize the different catalytic behavior of the materials. ZrO 2 stabilizes nanostructures of CeO 2 and a Ce–Zr mixed oxide phase, which offer high dispersion and improved oxidation properties. The catalyst also shows reduced chlorine uptake, and overall stands as a better Deacon material compared to bulk CeO 2 and other supported systems. CeO 2 is present on Al 2 O 3 predominantly as well-distributed nanoparticles. Still, alumina does not induce any electronic effect, thus the supported phase behaves similarly to bulk ceria. TiO 2 , likely due to the structural collapse and dramatic sintering suffered during calcination, leads to the formation of very large ceria particles. Based on our results, CeO 2 /ZrO 2 appears as a robust and cost-effective alternative to the current RuO 2 -based catalysts for large-scale chlorine recovery.

Facile preparation of highly-dispersed cobalt-silicon mixed oxide nanosphere and its catalytic application in cyclohexane selective oxidation.

Abstract: Highly dispersed cobalt-silicon mixed oxide [Co-SiO2] nanosphere was successfully prepared with a modified reverse-phase microemulsion method. This material was characterized in detail by X-ray diffraction, transmission electron microscopy, Fourier transform infrared, ultraviolet-visible diffuse reflectance spectra, X-ray absorption spectroscopy near-edge structure, and N2 adsorption-desorption measurements. High valence state cobalt could be easily obtained without calcination, which is fascinating for the catalytic application for its strong oxidation ability. In the selective oxidation of cyclohexane, Co-SiO2 acted as an efficient catalyst, and good activity could be obtained under mild conditions.

Photocatalytic activity of ZnO-WO3 for diclofenac degradation under visible light irradiation

Abstract: Diclofenac is known to be a persistent pharmaceutical compound, and their effective removal from water sources has been a rising concern. This study reports the visible light irradiated photocatalytic degradation of diclofenac using ZnO-WO3 mixed oxide catalysts, prepared by the hydrothermal method with variation in molar ratios of tungsten precursor. The prepared catalysts were characterized using a different technique, and the photocatalytic activity has been tested under visible light irradiation. Adsorption isotherm studies were performed to elucidate the preferential adsorption nature of the mixed oxide catalyst. The interaction of diclofenac and the prepared mixed oxides is based on the positively charged ZnO-WO3 surface and anionic diclofenac at solution pH 6. The adsorption and photodegradation kinetics is best expressed by the Langmuir isotherm model and pseudo-first-order kinetic model, respectively. Results indicated that all the prepared catalysts exhibited better catalytic activity than the bare ZnO under the visible light irradiation. The catalyst prepared with a molar ratio of 10:1 is proven to be an efficient catalyst and achieved 76%mineralization of diclofenac during the irradiation. The effect of operating variables like pH, initial diclofenac concentration, and catalyst loading was investigated and reported. The ZnO-WO3 mixed oxide catalysts were showed better stability, and the results revealed that the photocatalytic efficiency was retained up to 80% over the repeated reaction cycles. Several intermediate compounds formed during the photocatalytic reaction have been analyzed using LC–MS, and their degradation pathways have been found to primarily follows hydroxylation, dechlorination and decarboxylation reactions.

Novel CeO2 promoted TiO2–ZrO2 nano-oxide catalysts for oxidative dehydrogenation of p-diethylbenzene utilizing CO2 as soft oxidant

Abstract: The influence of ceria on structural and catalytic properties of TiO2–ZrO2 mixed oxide was investigated for oxidative dehydrogenation (ODH) of p-diethylbenzene (DEB) to p-divinylbenzene (DVB) utilizing CO2 as soft oxidant. The investigated catalysts were synthesized by coprecipitation and impregnation methods involving microwave treatment. Catalyst characterization was achieved using X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), BET surface area and temperature programmed desorption/oxidation (TPD/TPO) methods. The XRD and TEM results revealed that the prepared samples are in nanocrystalline form with 10–20 nm size. The presence of acid–base sites and their distribution was examined by NH3 and CO2 TPD measurements. The ceria promoted sample exhibited more number of acid sites. The TPO measurements revealed that CO2 dissociates over the reduced surface of the catalysts. Among various catalysts investigated, the microwave treated CeO2/TiO2–ZrO2 sample exhibited better conversion and a high product selectivity. The time-on-stream studies revealed that ceria promoted TiO2–ZrO2 catalysts exhibit higher stability for ODH of DEB.