Thermoanalytical investigations on supported chromia catalysts
TL;DR: In this article, Ceria-and titania-supported chromia catalysts were prepared by wet impregnation technique and their thermal stability as well as redox behavior were examined by evolved gas analysis (EGA), thermogravimetric analysis (TGA), and temperature programmed reduction (TPR).
About: This article is published in Thermochimica Acta.The article was published on 2003-03-24. It has received 10 citations till now. The article focuses on the topics: Chromia & Temperature-programmed reduction.
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TL;DR: In this article, different bulk transition-metal oxides (NiO, CuO, Mn2O3, Cr2O2, NiO), NiO and Co3O4) were tested for the combustion of methane−air lean mixtures (1000−5000 ppmv of CH4).
Abstract: Different bulk transition-metal oxides (NiO, CuO, Mn2O3, Cr2O3, and Co3O4) were prepared, by precipitation from nitrate precursors, and tested for the combustion of methane−air lean mixtures (1000−5000 ppmv of CH4). Catalyst performances were compared in terms of both intrinsic activity and resistance to self-deactivation. Methane combustion experiments were carried out at ambient pressure and a space velocity of 62 h−1 [weight hourly space velocity (WHSV)]. The activity of the studied catalysts (determined by the recording of light-off curves in the interval of 250−600 °C) decreases in the order: Co3O4 > Mn2O2 > Cr2O3 > CuO > NiO. However, deactivation studies, carried out both at constant temperature (620 °C) and in hysteresis experiments, reveal that Mn2O3 is the most stable catalyst.
68 citations
TL;DR: The analytical applications of the evolved gas analysis (EGA) performed by mass spectrometry, for the period extending from 2001 to 2004, are collected in this review.
61 citations
TL;DR: The physicochemical properties of ZnO-ZnCr 2 O 4 (Zn-Cr-O) mixed oxides were determined by adsorption and spectroscopic methods as discussed by the authors.
Abstract: The physicochemical characteristics of ZnO–ZnCr 2 O 4 (Zn–Cr–O) mixed oxides were determined by adsorption and spectroscopic methods. The catalytic activities of Zn–Cr–O was investigated for dehydrocyclization of ethylenediamine and aqueous glycerol to synthesize 2-methylpyrazine (2MP). Reductive pre-treatment was required for better 2MP yields and rate of 2MP was dependent upon strong basicity of Zn–Cr–O. Product distribution revealed that cyclocondensation of glycerol and ethylenediamine followed by homo-coupling of 2-pyrazinylmethanol occurred on moderate acid and strong base sites. On the contrary weak to moderate acidic and base sites were inefficient for homo-coupling of 2-pyrazinylmethanol. Role of acid-base properties was examined by pyridine and 2,6-dimethylpyridine poisoning studies.
45 citations
TL;DR: In this article, a series of vanadium oxide catalysts with different vanadium loadings has been prepared by two different methods: wet impregnation using ammonium metavanadate as a vanadium precursor and grafting using VOCl3.
Abstract: A series of Al2O3, SiO2 and TiO2-supported vanadium oxide catalysts with different vanadium loadings has been prepared by two different methods: wet impregnation using ammonium metavanadate as a vanadium precursor and grafting using VOCl3. Characterization of these catalysts by XRD, FTIR, TEM, SEM, EDX, DR and TGA techniques revealed that the structure of vanadium oxide VO
x
species depends on the preparation method, the type of the support and loadings of vanadium on the oxides surfaces. Monomeric vanadium oxide species are predominant at low vanadium loadings while polymeric vanadium oxide species increase with higher loadings. The catalytic activity of the prepared catalysts was evaluated for the liquid-phase oxidation of cyclohexane as a model reaction to obtain cyclohexylhydroperoxide, cyclohexanol and cyclohexanone with PCA as co-catalyst. The results show that the catalysts exhibit good cyclohexane conversion and remarkable selectivity to the target products and high turnover numbers (TON).
35 citations
TL;DR: In this paper, MgO-supported vanadium oxide catalysts with different vanadium loadings have been prepared by wet impregnation and grafting using ammonium metavanadate or VOCl 3 as precursor, respectively.
Abstract: MgO-supported vanadium oxide catalysts with different vanadium loadings have been prepared by wet impregnation and grafting using ammonium metavanadate or VOCl 3 as precursor, respectively. The prepared catalysts have been characterized by several techniques such as XRD, FT-IR, DR-spectroscopy, BET, 51 V solid-state NMR, SEM and EDX. For comparison, three different phases of magnesium vanadate (meta-β-MgV 2 O 6 , pyro-α-Mg 2 V 2 O 7 , and ortho-Mg 3 V 2 O 8 ) have been synthesized as reference materials for the structural characterization. The catalytic activity of the prepared catalysts was evaluated for the liquid-phase oxidation of cyclohexane as a model reaction to obtain cyclohexylhydroperoxide, cyclohexanol and cyclohexanone with PCA as co-catalyst. The results show that VO x /MgO catalysts containing isolated VO 4 species either impregnated or grafted do not show considerable activity in the oxidation process. In contrary, catalysts with higher vanadium loading, which contain ortho-Mg 3 V 2 O 8 , pyro-Mg 2 V 2 O 7 and V 2 O 5 phases as surface species show conversions up to 70% and TONs up to 34,700. Compared to previously studied support materials for this catalytic system the leaching behavior is significantly improved.
24 citations
References
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TL;DR: This work focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides and the mechanics of hydrogenation-dehydrogenation reactions.
Abstract: Focuses on the surface chemistry and spectroscopy of chromium in inorganic oxides. Characterization of the molecular structures of chromium; Mechanics of hydrogenation-dehydrogenation reactions; Mobility and reactivity on oxidic surfaces.
728 citations
TL;DR: In this paper, the success or otherwise of catalyst preparation or modification depends on the availability of suitable characterization techniques to determine the condition of the catalyst, and none of these techniques has proved to be wholly reliable or generally applicable to the characterization of catalysts under working conditions.
Abstract: The success or otherwise of catalyst preparation or modification depends on the availability of suitable characterization techniques to determine the condition of the catalyst. There are many techniques available for this purpose including x-ray powder diffraction, electron microscopy, photoelectron spectroscopy, and infrared spectroscopy. However, none of these techniques has proved to be wholly reliable or generally applicable to the characterization of catalysts under working conditions.
467 citations
TL;DR: In this article, the infrared spectra of the hydroxyl region and that of surface chemisorbed CO 2 species for Re 2 O 7 /Al 2 O 3, CrO 3/Al 2O 3, MoO 3 /Al2 O 3, V 2 O 5 /Al O 3 ), TiO 2 /Al 3, and Nb 2 O 6 /Al 1 O 3 catalytic systems were investigated.
Abstract: The infrared spectra of the hydroxyl region and that of surface chemisorbed CO 2 species for Re 2 O 7 /Al 2 O 3 , CrO 3 /Al 2 O 3 , MoO 3 /Al 2 O 3 , V 2 O 5 /Al 2 O 3 , TiO 2 /Al 2 O 3 , and Nb 2 O 5 /Al 2 O 3 catalytic systems have been investigated. A sequential consumption of the alumina OH groups upon deposition of the supported metal oxide has been found for all the investigated catalytic systems. A possible relationship between BrOnsted acidity and a new low-frequency band in the hydroxyl region observed at high loadings of the supported metal oxide systems is postulated
305 citations
243 citations
TL;DR: The chromium oxide-alumina catalysts of the Cr loading varying between 1 and 50 Cr nm −2 have been characterized by different physicochemical techniques and probe reactions of acid-basic properties and of the catalyst oxygen reactivity.
205 citations