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1.
Two series of Mo/Al2O3 catalysts were prepared by equilibrium adsorption and incipient wetness impregnation methods. The effect of preparation method on the surface coverages of the calcined catalysts was investigated by the combined use of CO2 chemisorption, low temperature CO adsorption and ion scattering spectroscopy (ISS). For a given Mo loading, the CO2 and CO adsorption results showed little difference between the two preparation methods. As previously noted, the CO2 chemisorption method overestimated the Mo surface coverage. In contrast to the adsorption methods, the ISS technique gave different Mo surface coverage values for a given Mo content of the two series of catalysts. This apparent discrepancy was attributed to different repartition of the Mo phase between the internal and external surfaces which can only be detected by ISS. This interpretation is supported by the observed agreement between the coverage values measured from ISS and low temperature CO adsorption for presumably uniform catalysts obtained by the equilibrium adsorption method.  相似文献   

2.
CO2 reforming of methane was performed on Pt/ZrO2 and Pt/Ce-ZrO2 catalysts at 1073K under different reactions conditions: (i) atmospheric pressure and CH4:CO2 ratio of 1:1 and 2:1; (ii) in the presence of water and CH4:CO2 ratio of 2:1; (iii) under pressure (105 and 190 psig) and CH4:CO2 ratio of 2:1. The Pt supported on ceria-promoted ZrO2 catalyst was more stable than the Pt/ZrO2 catalyst under all reaction conditions. We ascribe this higher stability to the higher density of oxygen vacancies on the promoted support, which favors the cleaning mechanism of the metal particle. The increase of either the CH4:CO2 ratio or total pressure causes a decrease in activity for both catalysts, because under either case the rate of methane decomposition becomes higher than the rate of oxygen transfer. The Pt/Ce-ZrO2 catalyst was always more stable than the Pt/ZrO2 catalyst, demonstrating the important role of the support on this reaction.  相似文献   

3.
A series of Mo/Al2O3 and Mo/TiO2-Al2O3 catalysts were investigated by temperature programmed sulfiding (TPS) and laser Raman spectroscopy (LRS). The effect of TiO2 on the sulfidability of molybdena was studied in detail. It is found that Mo/Al2O3 catalysts can be partially sulfided by O-S exchange at low temperature, forming molybdenum oxysulfide. The Mo-S bond subsequently ruptures in the presence of H2 to produce H2S. At 530–550 K deep sulfiding of molybdenum oxysulfide occurs forming crystalline MoS2. When the surface of Al2O3 was covered by a monolayer of TiO2, the sulfiding rate of molybdena at low temperature was not only greatly increased, but H2S produced in the reduction of Mo-S species caused deep sulfiding of the catalyst which resulted in a decrease of the TPS peak temperature by 80–100 K. The results indicate that this promotion of the sulfiding of molybdena is enhanced with TiO2 loading. The function of TiO2 is explained by the weakened interaction between MoO3 and Al2O3 due to the coverage of the Al2O3 surface by TiO2.  相似文献   

4.
Hydrogenation of adsorbed ethene over ZrO2 at low temperature was observed by in situ infrared transmission spectroscopy. It was found that di-hydrogen was directly activated on the site where ethene was already adsorbed, which was confirmed by the comparison of adsorbed species produced during the reaction and adsorbed ethane species.  相似文献   

5.
The interaction of CO2 with K-promoted Mo2C/Mo(100) has been studied with high-resolution electron energy loss spectroscopy, work function measurements and temperature-programmed desorption. Pre-adsorbed potassium dramatically affects the adsorption behavior of CO2 on the Mo2C/Mo(100) surface. It increases the rate of adsorption, the binding energy of CO2 and it induces the dissociation of CO2 through the formation of negatively charged CO2. Potassium adatoms also promote the dissociation of adsorbed CO over Mo2C. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

6.
ZrO2 and Pt/ZrO2 catalysts have been investigated by TPR, hydrogen chemisorption, TPDH and in the conversion ofn-hexane. At high temperature, ZrO2 takes up hydrogen. High temperature hydrogen treatment is a precondition of the catalytic activity in then-hexane conversion. Possibly, catalytically active acid sites are formed by this hydrogen treatment. The high temperature hydrogen treatment induces a strong Pt-ZrO2 interaction.  相似文献   

7.
EXAFS investigations at the Rh K edge of lanthana-promoted Rh/SiO2 catalysts showed that the local environment of the Rh ions in the oxidic catalyst precursor state did not depend on the La2O3 content and resembled that of Rh2O3. No LaRhO3 formation could be detected. In the reduced state, EXAFS as well as H2 and CO chemisorption demonstrated that La2O3 increased the Rh dispersion. Covering of the Rh metal particles by La2O3 was minor, because during catalyst preparation, La was impregnated prior to Rh.  相似文献   

8.
CH4/CO2 reforming over Pt/ZrO2, Pt/CeO2 and Pt/ZrO2 with CeO2 was investigated at 2 MPa. Pt/ZrO2, which shows stable activity under 0.1 MPa, and Pt/CeO2 showed gradual deactivation with time at the high pressure. The deactivation was suppressed drastically on Pt/ZrO2 with CeO2 prepared by different impregnation order (co-impregnation of Pt and CeO2 on ZrO2, and consecutive impregnation of Pt and CeO2 on ZrO2). The amount of coke deposition was found insignificant and similar among all the catalysts (including Pt/ZrO2 and Pt/CeO2). Catalytic activity after the reaction for 24 h was in agreement with Pt particle size after the reaction for same period, indicating that the difference of the catalytic stability is mainly dependent on the extent of Pt aggregation through catalyst preparation, H2 reduction, and the CH4/CO2 reforming. Pt aggregation and the amount of coke deposition were least pronounced on (Pt–Ce)/ZrO2 prepared by impregnation of CeO2 on Pt/ZrO2 and the catalyst showed highest stability.  相似文献   

9.
A 10%Co/ZrO2 catalyst prepared by impregnation was tested for its activity for the oxidation of CO to CO2 in excess oxygen. Activity tests showed that conversion could be obtained at temperatures as low as 20 °C. Time-on-stream studies showed no loss of activity in these experiments, indicating that this catalyst is stable in the experimental oxidizing conditions. The activation energy for the CO to CO2 oxidation reaction was calculated as Ea = 54 kJ/mol over this catalyst. Characterization of the material by thermogravimetric analysis, temperature-programmed techniques, X-ray photoelectron spectroscopy, and laser Raman spectroscopy indicate that Co3O4 is present on monoclinic ZrO2 after the calcination of the catalyst.  相似文献   

10.
Cu/ZnO/ZrO2 catalysts were prepared by a route of solid-state reaction and tested for the synthesis of methanol from CO2 hydrogenation. The effects of calcination temperature on the physicochemical properties of as-prepared catalysts were investigated by N2 adsorption, XRD, TEM, N2O titration and H2-TPR techniques. The results show that the dispersion of copper species decreases with the increase in calcination temperature. Meanwhile, the phase transformation of zirconia from tetragonal to monoclinic was observed. The highest activity was achieved over the catalyst calcined at 400 °C. This method is a promising alternative for the preparation of highly efficient Cu/ZnO/ZrO2 catalysts.  相似文献   

11.
CO2 reforming of methane was studied over modified Ni/Al2O3 catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al2O3, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO2 reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

12.
The hydrogenation of CO2 was studied on supported noble metal catalysts in the presence of H2S. In the reaction gas mixture containing 22 ppm H2S the reaction rate increased on TiO2 and on CeO2 supported metals (Ru, Rh, Pd), but on all other supported catalysts or when the H2S content was higher (116 ppm) the reaction was poisoned. FTIR measurements revealed that in the surface interaction of H2 + CO2 on Rh/TiO2 Rh carbonyl hydride, surface formate, carbonates and surface formyl were formed. On the H2S pretreated catalyst surface formyl species were missing. TPD measurements showed that adsorbed H2S desorbed as SO2, both from TiO2-supported metals and from the support. IR, XP spectroscopy and TPD measurements demonstrated that the metal became apparently more positive when the catalysts were treated with H2S and when the sulfur was built into the support. The promotion effect of H2S was explained by the formation of new centers at the metal/support interface.  相似文献   

13.
Rh/CeO2–ZrO2 catalysts with various CeO2/ZrO2 ratios have been applied to H2 production from ethanol steam reforming at low temperatures. The catalysts all deactivated with time on stream (TOS) at 350 °C. The addition of 0.5% K has a beneficial effect on catalyst stability, while 5% K has a negative effect on catalytic activity. The catalyst could be regenerated considerably even at ambient temperature and could recover its initial activity after regeneration above 200 °C with 1% O2. The results are most consistent with catalyst deactivation due to carbonaceous deposition on the catalyst.  相似文献   

14.
By performing the CH4 + CO2 and CD4 + CO2 reactions alternately over SiO2-supported nickel catalysts in a pulse micro-reactor, normal deuterium isotope effects on both the methane conversion reaction and on the CO formation reaction have been observed in the process of CO2 reforming of methane. Based on the observed CH4/CD4 isotope effects, the pathways for the formation of CO are discussed.  相似文献   

15.
The mixed metal oxides TiO2-Fe2O3 and ZrO2-Fe2O3 were examined as potential catalysts for the dehydrogenation reaction of ethylbenzene. The acidic and basic properties and surface area, pore volume and pore size distribution of these catalysts were measured. The catalytic activities can be correlated very well with the surface area and the acidity and basicity of ZrO2-Fe2O3 catalysts. However, for TiO2-Fe2O3 catalysts, the surface area, the amount of acidic and basic sites and TiFe2O5 crystallinity are all important factors affecting the catalytic activities for ethylbenzene dehydrogenation. A synergistic effect was found for the TiO2-Fe2O3 and ZrO2-Fe2O3 catalyst system and also for the TiO2-Fe2O3-ZrO2 system, i.e. the activities of these catalysts can be ranked in the following order: TiO2-Fe2O3-ZrO2>TiO2-Fe2O3 >ZrO2>Fe2O3>TiO2. Meanwhile, all of these catalysts showed higher activities than the conventional potassium-promoted iron catalysts.  相似文献   

16.
Supported nickel catalysts of composition Ni/Y2O3–ZrO2 were synthesized in one step by the polymerization method and compared with a nickel catalyst prepared by wet impregnation. Stronger interactions were observed in the formed catalysts between NiO species and the oxygen vacancies of the Y2O3–ZrO2 in the catalysts made by polymerization, and these were attributed to less agglomeration of the NiO during the synthesis of the catalysts in one step. The dry reforming of ethanol was catalyzed with a maximum CO2 conversion of 61% on the 5NiYZ catalyst at 800 °C, representing a better response than for the catalyst of the same composition prepared by wet impregnation.  相似文献   

17.
The activation and dehydrogenation of CH2 on Mo2C and MO2C/ZSM-5 have been investigated under non-oxidizing conditions. Unsupported Mo2C exhibited very little activity towards methane decomposition at 973 K. The main reaction pathway was the decomposition of methane to give hydrogen and carbon with a trace amount of ethane. Mixing Mo2C with ZSM-5 support somewhat enhanced its catalytic activity, but did not change the products of the reaction. A dramatic change in the product formation occurred on partially oxidized Mo2C/ZSM-5 catalyst; besides some hydrocarbons benzene was produced with a selectivity of 70–80% at a conversion of 5–7%. Carburization of highly dispersed MoO3 on ZSM-5 also led to a very active catalyst: the conversion of methane at the steady state was 5–6% and the selectivity of benzene formation was 85%.This laboratory is a part of the Center for Catalysis, Surface and Material Science at the University of Szeged.  相似文献   

18.
Activity and selectivity of selective CO oxidation in an H2-rich gas stream over Co3O4/CeO2/ZrO2, Ag/CeO2/ZrO2, and MnO2/CeO2/ZrO2 catalysts were studied. Effects of the metaloxide types and metaloxide molar ratios were investigated. XRD, SEM, and N2 physisorption techniques were used to characterize the catalysts. All catalysts showed mesoporous structure. The best activity was obtained from 80/10/10 Co3O4/CeO2/ZrO2 catalyst, which resulted in 90% CO conversion at 200°C and selectivity greater than 80% at 125°C. Activity of the Co3O4/CeO2/ZrO2 catalyst increased with increase in Co3O4 molar ratio.  相似文献   

19.
Abstract

A series of Cu-K/Al2O3 catalysts were synthesized by wet impregnation technique. The reduced catalysts were further used for conversion of carbon dioxide to methane and carbon monoxide. Moreover, the fresh and used catalysts were characterized to investigate the changes in the surface morphology, metal dispersion, surface area, crystalline phases, and functional groups of studied catalysts. The SEM analysis of fresh and spent catalysts showed no remarkable difference in surface morphology with irregular shaped agglomerated particles. Furthermore, TEM micrographs presented the well distribution of metal catalyst over alumina support. The decrease in surface area from 115 to 77?m2/g for Cu1.62-K0.5/Al2O3 after reaction was related to sintering and oxidation of catalyst during reaction. XRD revealed the disappearance of some minor peaks which can be associated with the sintering of spent catalyst. FTIR also presented some new peak for spent catalyst which can be linked with metal oxides. Moreover, various reaction conditions of temperature (230, 400, and 600?°C), pressure (1 and 7?bar), and feed molar ratio of H2/CO2 (2:1 and 4:1) were investigated using different Cu loading (0, 1, 1.25, 1.62, and 4 weight percent). A maximum CO2 conversion of 63% with 39% CH4 selectivity was achieved by using Cu1.62-K0.5/Al2O3 at 600?°C, molar ratio of H2/CO2 4 under 7?bar. The presence of K on the surface of synthesized catalyst increased the CO2 conversion from 48% (Cu1/Al2O3) to 55% (Cu1-K0.5/Al2O3) at above mentioned reaction conditions which suggested the promoter effect of K during conversion of carbon dioxide.  相似文献   

20.
The selective catalytic reduction (SCR) of NO by decane under an oxidising atmosphere has been carried out on Cu/ZrO2 and Cu/ZrO2(SO 4 2– ). Zirconia-supported Cu catalysts were prepared by ligand exchange with Cu acetylacetonate followed by calcination at 773 K. The solids obtained were characterised by temperature programmed reduction (TPR) by hydrogen and temperature programmed desorption (TPD) of NO. Cu/ZrO2 is active and selective in the reduction of NO by decane at low temperature (< 600 K) but oxidises NO to NO2 between 640 and 770 K. By contrast, whatever the temperature, a total selectivity to nitrogen is obtained with Cu/ZrO2(SO 4 2– ). About 40% NO conversion to N2 is observed with GHSV of 70 000 h–1. The promoting effect of sulfate is attributed to the large increase of acidity and the strong interaction between copper and sulfur species which is evidenced by TPD of NO and TPR by H2.  相似文献   

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