Characterisation of ceria supported chromia catalysts
TL;DR: A series of ceria supported chromia catalysts of different loading were prepared and the effect of support in stabilising various chemical and molecular states of chromium with the calcination temperature were studied as discussed by the authors.
Abstract: A series of ceria supported chromia catalysts of different loading were prepared and the effect of support in stabilising various chemical and molecular states of chromium with the calcination temperature were studied. XRD results showed that the chromia phase is randomly dispersed, disordered, and the crystallite size may be smaller than the detection limit. BET surface area and pore volume results suggested some plugging of pores on the support by chromia phase. EGA analysis suggested the existence of the surface heterogenity involving weakly and strongly chemisorbed CO 2 . EGA and NIR DRS studies revealed the bulk-like behaviour in the catalysts having chromia loading of more than 5 wt.%. EGA, FTIR and UV–VIS–DRS studies supported the formation of anchored surface chromium species. Moreover, the nature of molecular states of chromium and the coordinative environment under various thermal conditions were investigated using FTIR and UV–VIS–DRS techniques.
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TL;DR: In this paper, a review of the most popular IR spectroscopy applications for catalytic applications is presented, starting from the very general basis of the spectroscopic method applied and focusing on the adsorption of chelating compounds on surfaces of mineral oxides.
433 citations
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TL;DR: Various chromium-containing catalysts were tested for the total oxidation of trichloroethylene (TCE) as a model reaction for the catalytic combustion of chlorinated organic pollutants to demonstrate higher activity and higher CO2 selectivity than traditional alumina supported chromia.
Abstract: Various chromium-containing catalysts were tested for the total oxidation of trichloroethylene (TCE) as a model reaction for the catalytic combustion of chlorinated organic pollutants. A spinel-type cobalt chromite (CoCr2O4) among others was proven to be a very promising catalyst showing higher activity and higher CO2 selectivity than traditional alumina supported chromia. Even if both Cr3+ and Cr6+ species were observed on the surface of CoCr2O4, the Cr6+ species was stable under reducing environment. The presence of Cr3+-Cr6+ pair sites and the effect of redox treatments on the activity were investigated to explain the nature of possible active sites for TCE decomposition. Higher selectivity to CO2 of CoCr2O4 was ascribed to the abundance of its Cr3+ species, together with its activity for water gas shift reaction.
108 citations
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TL;DR: In this paper, a possible pathway of soot oxidation over Cu0.05Ce0.95-CA is proposed, based on the relationship of the performance and physicochemical features of catalysts, which pathway follows the mechanism associated with redox couple and oxygen spill over effect.
62 citations
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TL;DR: In this paper, the role of chromium oxides and ceria and their synergistic effect in textural properties, redox performance and surface species over the Cr1−xCex/TP catalysts were investigated in detail by means of Brunauer-Emmertt-Teller (BET) surface area analysis, X-ray diffraction (XRD), transmission electron microscope (TEM), temperature-programmed reduction of H2 (H2-TPR), NO-TPD), photoluminescence spectra, and in situ diffuse reflectance infrared
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TL;DR: In this paper, mesoporous ceria and SBA-15 silica were modified with iron and chromium oxide nanoparticles and characterized by XRD, N2-physisorption, FTIR, UV-vis, Moessbauer spectroscopy and TPR-TG in hydrogen.
30 citations
References
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TL;DR: In this article, the Melamed theory was employed to obtain extinction coefficients from the optical reflection spectra for a series of coprecipitated chromia samples calcined between 500° and 1400°C and the Racah parameter B and the wavenumbers of the visible transition in ruby (1400°C calcination) arising from Cr3+ gradually decreased with increasing chromia content.
Abstract: The optical reflection spectra from 12 500 to 50 000 cm—1 were studied for a series of coprecipitated chromia—alumina samples calcined between 500° and 1400°C. The Melamed theory was employed to obtain extinction coefficients from these spectra. The Racah parameter B and the wavenumbers of the two visible transitions in ruby (1400°C calcination) arising from Cr3+ gradually decreased with increasing chromia content. The Racah parameter B and the wavenumber Δ of the 4A2→4T2 transition in high chromia content samples calcined at 500°, 750°, and 900°C. were unusually low due to the formation of chromia rich solid solutions. In the oxidized state the samples calcined below 1400°C showed an intense ultraviolet absorption due to Cr6+.
53 citations
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TL;DR: In this article, the Cr-Ce-O catalysts of different Cr content have been synthesized using co-precipitation or impregnation techniques, and tested in the oxidative dehydrogenation of isobutane.
Abstract: The Cr–Ce–O catalysts of different Cr content have been synthesised using co-precipitation or impregnation techniques, and tested in the oxidative dehydrogenation of isobutane. The Ce–-Cr–O system has already been found to be active and selective in this reaction at low temperatures around 270°C, with the selectivities to isobutene of about 60% at 10% isobutane conversion and a maximum yield of isobutene of about 8%. The total specific activity increases with the increase in the Cr content to a constant value observed for the samples prepared by precipitation at Cr/Ce ratio equal to 1, and those obtained by the impregnation at the Cr content of 10 At Cr nm −2 . The maximum specific activity does not depend considerably on the preparation technique, slightly higher yields are found, however, for the samples prepared by impregnation. Nevertheless, the co-precipitation technique leads to the less reproducible catalysts in which the potassium impurity may exert a poisoning effect.
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TL;DR: In this paper, the titania catalysts containing chromium loading ranged from 0 up to 8 mol% Cr have been prepared and calcined at high temperature (500°C) and were tested for the selective catalytic reduction of NO by NH3in excess of O2 at relatively high reaction temperatures (250-450°C).
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TL;DR: In this article, a series of catalysts containing 0.5 to 30 wt% chromia was prepared by impregnation with aqueous chromium nitrate solution, and the catalysts exhibited high activity for SCR in the low temperature range (T 720 K).
34 citations