共查询到20条相似文献,搜索用时 15 毫秒
1.
2.
Lourdes Vzquez-Gmez Sandro Cattarin Paolo Guerriero Marco Musiani 《Electrochimica acta》2007,52(28):8055-8063
RuO2 particles were co-deposited with Ni matrices, under experimental conditions known to produce porous Ni deposits, to yield Ni + RuO2 composites of large effective area, to be used as cathodes for the hydrogen evolution reaction. These conditions involved the use of NiCl2, NH4Cl solutions (pH 4.5) and large deposition current densities. The morphology and composition of these composites were studied by SEM–EDX and compared to those of either Ni + Co3O4 composites or Ni + RuO2 composites obtained from Watt's baths. EIS was used to obtain information on the porosity of the deposited materials, and to measure the capacity of the composites and its dependence on deposition charge. The hydrogen evolution reaction was studied in both acid and basic media. Porous Ni + RuO2 cathodes performed better than analogous materials prepared from Watt's baths. 相似文献
3.
The primary reason why the RuO2(1 1 0) surface is much more active in the oxidation of CO than the corresponding metal Ru(0 0 0 1) surface is correlated with the weaker oxygen bonding on RuO2(1 1 0) compared to chemisorbed oxygen on Ru(0 0 0 1). The RuO2(1 1 0) surface stabilizes at least two potentially active oxygen species, i.e., bridging O and on-top O atoms. Together with various adsorption sites for CO during the reaction, the CO oxidation reaction over RuO2(1 1 0) becomes quite complex. Using the techniques of temperature programmed reaction and desorption in combination with state-of-the-art density functional theory calculation we studied the CO oxidation reaction over RuO2(1 1 0) in the temperature range of 300–400 K. We show that the CO oxidation on RuO2(1 1 0) surface is not dominated by the recombination of CO with on-top O, although the binding energy of the on-top O is 1.4 eV lower than that of the bridging O atom. 相似文献
4.
We reported an asymmetric supercapacitor technology where RuO2/TiO2 nanotube composite was used as positive electrode and the activated carbon as negative electrode in 1 mol/L KOH electrolyte solution. The electrochemical capacitance performance of the asymmetric supercapacitor was tested by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge tests. The results show that the asymmetric supercapacitor has electrochemical capacitance performance within potential range 0–1.4 V. A power density 1207 W/kg was obtained with an energy density of 5.7 W h/kg at a charge–discharge current density of 120 mA/cm2. The supercapacitor also exhibits a good cycling performance and keep 90% of initial capacity over 1000 cycles. 相似文献
5.
The effects of pretreatment of catalyst on its surface properties and the HDS activity of a 0.49% Ru/Al2O3 catalyst were studied in a single-pass, differential microreactor. The surface properties of the catalyst were measured by NH3-TPD and XPS analysis. The Ru/Al2O3 catalyst was pretreated in three ways: reduced in H2 (Ru-R catalyst), oxidized in air and subsequently reduced in H2 (Ru-OR catalyst), or sulfided in H2S/H2 (Ru-S catalyst). Three types of peaks (low, middle, and high temperatures) were observed in the NH3-TPD study. The predominant high-temperature peak was observed for both the Ru-OR and Ru-S catalyst, pretreated at 300°C. Mass spectrometry showed that the high-temperature peak in NH3-TPD consisted of N2 and H2 formed from the decomposition of NH3 on the ruthenium sites. NO adsorption of unsaturated Ru species was related to the low-temperature peak in the NH3-TPD. The XPS analysis showed that the peaks at 279.9 eV, 280.6 eV, and 282.5 eV were ascribed to metallic ruthenium, RuO2, and RuO3, respectively. The low-, middle-, and high-temperature peaks were assigned to RuO2, acid sites on alumina, and metallic Ru, respectively. Metallic ruthenium was effective in the HDS of thiophene and the decomposition of NH3. 相似文献
6.
Surface-phase ZrO2 on SiO2 (SZrOs) and surface-phase La2O3 on Al2O3 (SLaOs) were prepared with various loadings of ZrO2 and La2O3, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH4/CO2 reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al2O3 and Pt/SiO2 catalysts. CO2 or CH4 pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.
The zirconia can be homogeneously dispersed on SiO2 to form a stable surface-phase oxide. The lanthana cannot be spread well on Al2O3, but it forms a stable amorphous oxide with Al2O3. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO2 and Pt/Al2O3 by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO2 and Pt/Al2O3 catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO2 adsorbed on the basic sites of SZrOs and SLaOs. 相似文献
7.
The surface composition of a thermally prepared RuO2 electrode was studied by X-ray photoelectron spectroscopy (XPS) to investigate structural and surface composition changes occurring during the hydrogen evolution reaction. This was done using an electrochemical cell (EC) attached directly to the ultra high vacuum (UHV) chamber of the spectrometer, allowing the direct transfer of the electrode from the EC to the UHV chamber without exposure to ambient conditions. All the treatments have been performed in this cell, using 1N H2SO4. After a polarization of the electrode to −0.5 V versus standard calomel electrode (SCE), the XPS spectrum showed no shift in the binding energy of the Ru core level peaks, indicating that no reduction of Ru(IV) occurs. Further analysis of the O 1s core level spectrum also revealed that the adsorption of sulfate anions is maximum at −0.5 V versus SCE. 相似文献
8.
Zhenhua LI Jia HE Haiyang WANG Baowei WANG Xinbin MA 《Frontiers of Chemical Science and Engineering》2015,9(1):33
A series of unsupported MoS2 catalysts with or without Al2O3 modification was prepared using a modified thermal decomposition approach. The catalysts were tested for the methanation of carbon monoxide and the optimum one has 25.6 wt-% Al2O3 content. The catalysts were characterized by nitrogen adsorption measurement, X-ray diffraction and transmission electron microscopy. The results show that adding appropriate amount of Al2O3 increases the dispersion of MoS2, and the increased interaction force between MoS2 and Al2O3 can inhibit the sintering of active MoS2 to some extent. 相似文献
9.
The influence of different metal oxide supports (i.e. ZrO2, ThO2, UO2, TiO2 and SiO2) on the performance of Ni- and/or Co-containing catalysts [Ni and/or Co/MO2 mole ratio (where M=Zr, Th, U, Ti or Si)=1.0] in the oxidative methane-to-syngas conversion at very low contact time (GHSV=5.2×105 cm3 g−1 h−1 at STP) was investigated. The nickel-containing ZrO2, ThO2 and UO2 catalysts (with or without pre-reduction by hydrogen at 500°C) showed good performance in the process; the order of their performance is NiO–ThO2>NiO–UO2>NiO–ZrO2. The NiO–TiO2 showed appreciable catalytic activity only after its reduction at 800°C. However, this catalyst and the NiO–SiO2 catalyst showed poor performance in the process. These two catalysts are also deactivated very fast, mostly because of sintering of Ni and/or formation of catalytically inactive binary metal oxide phases by solid–solid reaction at the high catalyst calcination and/or catalytic reaction temperature. Although the Ni-containing ThO2, UO2 and ZrO2 catalysts showed good performance, carbon deposition on them during the process is fast. However, because of the addition of cobalt to these catalysts (with Co/Ni=1.0), the rate of carbon deposition on them in the process is drastically reduced. This Co addition however resulted in a significant decrease in both the conversion and selectivity; the decrease in the selectivity was small. 相似文献
10.
Reforming of methane with carbon dioxide into syngas over Ni/γ-Al2O3 catalysts modified by potassium, MnO and CeO2 was studied. The catalysts were prepared by impregnation technique and were characterized by N2 adsorption/desorption isotherm, BET surface area, pore volume, and BJH pore size distribution measurements, and by X-ray diffraction and scanning electron microscopy. The performance of these catalysts was evaluated by conducting the reforming reaction in a fixed bed reactor. The coke content of the catalysts was determined by oxidation conducted in a thermo-gravimetric analyzer. Incorporation of potassium and CeO2 (or MnO) onto the catalyst significantly reduced the coke formation without significantly affecting the methane conversion and hydrogen yield. The stability and the lower amount of coking on promoted catalysts were attributed to partial coverage of the surface of nickel by patches of promoters and to their increased CO2 adsorption, forming a surface reactive carbonate species. Addition of CeO2 or MnO reduced the particle size of nickel, thus increasing Ni dispersion. For Ni–K/CeO2–Al2O3 catalysts, the improved stability was further attributed to the oxidative properties of CeO2. Results of the investigation suggest that stable Ni/Al2O3 catalysts for the carbon dioxide reforming of methane can be prepared by addition of both potassium and CeO2 (or MnO) as promoters. 相似文献
11.
The NiSO4 supported on Fe2O3-promoted ZrO2 catalysts were prepared by the impregnation method. Fe2O3-promoted ZrO2 was prepared by the coprecipitation method using a mixed aqueous solution of zirconium oxychloride and iron nitrate solution followed by adding an aqueous ammonia solution. No diffraction line of nickel sulfate was observed up to 20 wt.%, indicating good dispersion of nickel sulfate on the surface of Fe2O3–ZrO2. The addition of nickel sulfate (or Fe2O3) to ZrO2 shifted the phase transition of ZrO2 (from amorphous to tetragonal) to higher temperatures because of the interaction between nickel sulfate (or Fe2O3) and ZrO2. 15-NiSO4/5-Fe2O3–ZrO2 containing 15 wt.% NiSO4 and 5 mol% Fe2O3, and calcined at 500 °C exhibited a maximum catalytic activity for ethylene dimerization. NiSO4/Fe2O3–ZrO2 catalysts was very effective for ethylene dimerization even at room temperature, but Fe2O3–ZrO2 without NiSO4 did not exhibit any catalytic activity at all. The catalytic activities were correlated with the acidity of catalysts measured by the ammonia chemisorption method. The addition of Fe2O3 up to 5 mol% enhanced the acidity, surface area, thermal property, and catalytic activities of catalysts gradually, due to the interaction between Fe2O3 and ZrO2 and due to consequent formation of Fe–O–Zr bond. 相似文献
12.
The activity and selectivity of rhenium promoted cobalt Fischer–Tropsch catalysts supported on Al2O3, TiO2 and SiO2 have been studied in a fixed-bed reactor at 483 K and 20 bar. Exposure of the catalysts to water added to the feed deactivates the Al2O3 supported catalyst, while the activity of the TiO2 and SiO2 supported catalysts increased. However, at high concentrations of water both the SiO2 and TiO2 supported catalyst deactivated. Common for all catalysts was an increase in C5+ selectivity and a decrease in the CH4 selectivity by increasing the water partial pressure. The catalysts have been characterized by scanning transmission electron microscope (STEM), BET, H2 chemisorption and X-ray diffraction (XRD). 相似文献
13.
Xinmei LIU Shaofen BAI Huidong ZHUANG Zifeng YAN 《Frontiers of Chemical Science and Engineering》2012,6(1):47
Cu/ZrO2 catalysts for methanol synthesis from CO2/H2 were respectively prepared by deposition coprecipitation (DP) and solid state reaction (SR) methods. There is an intimate interaction between copper and zirconia, which strongly affects the reduction property and catalytic performance of the catalysts. The stronger the interaction, the lower the reduction temperature and the better the performance of the catalysts. Surface area, pore structure and crystal structure of the catalysts are mainly controlled by preparation methods and alkalinity of synthesis system. The conversion of CO2 and selectivity of methanol are higher for DP catalysts than for SP catalysts. 相似文献
14.
Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。 相似文献
15.
Motonobu Kobayashi Ryoji Kuma Sinyuki Masaki Noboru Sugishima 《Applied catalysis. B, Environmental》2005,60(3-4):173-179
TiO2-SiO2 with various compositions prepared by the coprecipitation method and vanadia loaded on TiO2-SiO2 were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH3 and in the undesired oxidation of SO2 to SO3, using BET, XRD, XPS, NH3-TPD, acidity measurement by the titration method and activity test. TiO2-SiO2, compared with pure TiO2, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V2O5. The SCR activity and N2 selectivity are found to be more excellent over vanadia loaded on TiO2-SiO2 with 10–20 mol% of SiO2 than over that on pure TiO2, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH3 adsorbed on the catalysts. With increasing SiO2 content, the remarkable activity decrease in the oxidation of SO2 to SO3, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V4+ on TiO2-SiO2, while V5+ exists on TiO2, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO2-SiO2 with low SiO2 content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NOx activity but also the low SO2 oxidation performance. 相似文献
16.
R. S. G. Ferreira P. G. P. de Oliveira F. B. Noronha 《Applied catalysis. B, Environmental》2004,50(4):243-249
The role of vanadium oxide and palladium on the benzene oxidation reaction over Pd/V2O5/Al2O3 catalysts was investigated. The Pd/V2O5/Al2O3 catalysts were more active than V2O5/Al2O3 and Pd/Al2O3 catalysts. The increase of vanadium oxide content decreased the Pd dispersion and increased the benzene conversion. A strong Pd particle size effect on benzene oxidation reaction was observed. Although the catalysts containing high amount of V4+ species were more active, the Pd particle size effect was responsible for the higher activity. 相似文献
17.
Chunlei Shi Arden B. Walters M. Albert Vannice 《Applied catalysis. B, Environmental》1997,14(3-4):175-188
Dispersing La2O3 on δ- or γ-Al2O3 significantly enhances the rate of NO reduction by CH4 in 1% O2, compared to unsupported La2O3. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La2O3 precursor used, the pretreatment, and the La2O3 loading. The most active family of catalysts consisted of La2O3 on γ-Al2O3 prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m2) occurred between the addition of one and two theoretical monolayers of La2O3 on the γ-Al2O3 surface. The best catalyst, 40% La2O3/γ-Al2O3, had a turnover frequency at 700°C of 0.05 s−1, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La2O3/Al2O3 catalysts exhibited stable activity under high conversion conditions as well as high CH4 selectivity (CH4 + NO vs. CH4 + O2). The addition of Sr to a 20% La2O3/γ-Al2O3 sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO=4 to the latter Sr-promoted La2O3/Al2O3 catalyst decreased activity although sulfate increased the activity of Sr-promoted La2O3. Dispersing La2O3 on SiO2 produced catalysts with extremely low specific activities, and rates were even lower than with pure La2O3. This is presumably due to water sensitivity and silicate formation. The La2O3/Al2O3 catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications. 相似文献
18.
The effects of carbon dioxide on the dehydrogenation of C3H8 to produce C3H6 were investigated over several Cr2O3 catalysts supported on Al2O3, active carbon and SiO2. Carbon dioxide exerted promoting effects only on SiO2-supported Cr2O3 catalysts. The promoting effects of carbon dioxide over a Cr2O3/SiO2 catalyst were to enhance the yield of C3H6 and to suppress the catalyst deactivation. 相似文献
19.
Ha Heon Phil Maddigapu Pratap Reddy Pullur Anil Kumar Lee Kyung Ju Jung Soon Hyo 《Applied catalysis. B, Environmental》2008,78(3-4):301-308
To get the low temperature sulfur resistant V2O5/TiO2 catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V2O5/TiO2 catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V2O5/TiO2 catalysts showed high catalytic activity for NH3 selective catalytic reduction (NH3-SCR) of NOx carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V2O5/TiO2 > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V2O5/TiO2 for maximum NOx conversion, which also showed high resistance to SO2 in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V2O5/TiO2 and compared with commercial W(10%)V2O5/TiO2 catalyst. High electrical conductivity difference (ΔG) for Sb(2%)/V2O5/TiO2 catalyst with temperature was observed. SO2 deactivation experiments were carried out for Sb(2%)/V2O5/TiO2 and W(10%)/V2O5/TiO2 at a temperature of 230 °C for 90 h, resulted Sb(2%)/V2O5/TiO2 was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V2O5/TiO2 than Sb(2%)/V2O5/TiO2 catalyst. 相似文献
20.
Five Si3N4---Al2O3 ceramic grades were prepared by hot pressing at 1650°C. Backscattered electron micrographs revealed four different phases. Quantitative electron probe microanalysis allowed the identification of these phases as X-sialon, -Al2O3, O'-sialon and β-sialon. The maximum solubility of Al2O3 in Si3N4 and in Si2N2O at 1650°C was determined as well as the chemical composition of X-sialon. Based on these results, a slightly revised phase diagram is proposed. The general features describing the microstructure of the various phases have been investigated by transmission electron microscopy. The influence of the various phases on the mechanical properties was investigated; hardness, fracture toughness and elastic modulus were measured. The oxidation behaviour has been studied in air at 1300°C and 1450°C. The metastable phase diagram of Al2O3---SiO2 in the absence of mullite can be used to predict the oxidation products and relative amounts formed in the oxide layers. 相似文献