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91.
Bo Hyun Ryu Sang Yup Lee Dong Hyun Lee Gui Young Han Tae-Jin Lee Ki June Yoon 《Catalysis Today》2007,123(1-4):303-309
Carbon black has recently been reported to act as an effective catalyst for methane decomposition and to exhibit stable catalytic behavior despite carbon deposition, and thus it can be used for CO2-free production of hydrogen from natural gas. In this work, various carbon blacks with different primary particle size were investigated with respect to methane decomposition under atmospheric pressure from 1123 to 1223 K. Catalytic characteristics, such as activity, activation energy and reaction order, were investigated and compared. It was observed that with decreasing primary particle size (or increasing specific surface area), the specific activity increased and the activation energy decreased. The reaction orders for various pelletized, rubber-reinforcing carbon blacks were 0.6–0.7, about the same regardless of the primary particle size, while they were near 1 for fluffy carbon blacks. Fluffy carbon black showed higher activity and activation energy than the pelletized carbon black of the same primary particle size. Changes of the surface morphology during carbon deposition were observed by TEM. Variations of the number of active sites were discussed in regard of the primary particle size, carbon deposition and binder. The presence of different types of active sites was also suggested. 相似文献
92.
Direct nitric oxide decomposition over perovskites is fairly slow and complex, its mechanism changing dramatically with temperature. Previous kinetic study for three representative compositions (La0.87Sr0.13Mn0.2Ni0.8O3−δ, La0.66Sr0.34Ni0.3Co0.7O3−δ and La0.8Sr0.2Cu0.15Fe0.85O3−δ) has shown that depending on the temperature range, the inhibition effect of oxygen either increases or decreases with temperature. This paper deals with the effect of CO2, H2O and CH4 on the nitric oxide decomposition over the same perovskites studied at a steady-state in a plug-flow reactor with 1 g catalyst and total flowrates of 50 or 100 ml/min of 2 or 5% NO. The effect of carbon dioxide (0.5–10%) was evaluated between 873 and 923 K, whereas that of H2O vapor (1.6 or 2.5%) from 723 to 923 K. Both CO2 and H2O inhibit the NO decomposition, but inhibition by CO2 is considerably stronger. For all three catalysts, these effects increase with temperature. Kinetic parameters for the inhibiting effects of CO2 and H2O over the three perovskites were determined. Addition of methane to the feed (NO/CH4=4) increases conversion of NO to N2 about two to four times, depending on the initial NO concentration and on temperature. This, however, is still much too low for practical applications. Furthermore, the rates of methane oxidation by nitric oxide over perovskites are substantially slower than those of methane oxidation by oxygen. Thus, perovskites do not seem to be suitable for catalytic selective NO reduction with methane. 相似文献
93.
Shampa Kandoi Jeff Greeley Marco A. Sanchez-Castillo Steven T. Evans Amit A. Gokhale James A. Dumesic Manos Mavrikakis 《Topics in Catalysis》2006,37(1):17-28
A microkinetic model for methanol decomposition on platinum is presented. The model incorporates competitive decomposition
pathways, beginning with both O–H and C–H bond scission in methanol, and uses results from density functional theory (DFT)
calculations [Greeley and Mavrikakis, J. Am. Chem. Soc. 124 (2002) 7193, Greeley and Mavrikakis, J. Am. Chem. Soc. 126 (2004)
3910]. Results from reaction kinetics experiments show that the rate of H2 production increases with increasing temperature and methanol concentration in the feed and is only nominally affected by
the presence of CO or H2 with methanol. The model, based on the values of binding energies, pre-exponential factors and activation energy barriers
derived from first principles calculations, accurately predicts experimental reaction rates and orders. The model also gives
insight into the most favorable reaction pathway, the rate-limiting step, the apparent activation energy, coverages, and the
effects of pressure. It is found that the pathway beginning with the C–H bond scission (CH3OH→H2COH→HCOH→CO) is dominant compared with the path beginning with O–H bond scission. The cleavage of the first C–H bond in methanol
is the rate-controlling step. The surface is highly poisoned by CO, whereas COH appears to be a spectator species. 相似文献
94.
Photocatalytic activities for water decomposition were examined for photocatalysts using hexa- and octa-titanates and TiO2(B) with different tunnel space in the structure. Using RuO2 as promoter, M2Ti6O13 (M = Li, Na, K, Rb) showed the stoichiometric production of Hz and O2 except for Li, whereas H2Ti8O17 and TiO2(B) had very low activity producing only hydrogen as a product. The effects of promoters on Na2Ti6O13 showed that the activity increased in the order of RuO2 > RuO2 + IrO2 > IrO2 > RuO2 + Pt > MnO2. These effects along with other related ones are discussed: it emerges that the presence of the tunnels is important for the achievement of high photocatalytic activity. 相似文献
95.
A decomposition algorithm for scheduling problems based on timed automata (TA) model is proposed. The problem is represented as an optimal state transition problem for TA. The model comprises of the parallel composition of submodels such as jobs and resources. The procedure of the proposed methodology can be divided into two steps. The first step is to decompose the TA model into several submodels by using decomposable condition. The second step is to combine individual solution of subproblems for the decomposed submodels by the penalty function method. A feasible solution for the entire model is derived through the iterated computation of solving the subproblem for each submodel. The proposed methodology is applied to solve flowshop and jobshop scheduling problems. Computational experiments demonstrate the effectiveness of the proposed algorithm compared with a conventional TA scheduling algorithm without decomposition. 相似文献
96.
过渡金属离子掺杂纳米TiO2的相变与光催化活性 总被引:4,自引:0,他引:4
采用溶胶-凝胶法制备了掺杂Mo6+、Cr3+、Fe3+的改性纳米TiO2光催化剂,并分别在550℃和580℃下对其进行了热处理,考察了热处理温度对掺杂纳米TiO2相变和光催化活性的影响.通过光催化降解染料罗丹明B实验,对在不同热处理温度下Mo6+、Cr3+、Fe3+改性以及不同Mo6+掺杂量的TiO2光催化活性进行了评价,发现掺杂离子对TiO2光催化活性的影响与其对TiO2相转变的作用是一致的,即抑制相转变的同时也提高了光催化活性.实验结果也进一步表明,Mo6+掺杂量为0.05%(摩尔分数)时的TiO2具有最佳光催化活性. 相似文献
97.
98.
针对海绵城市径流总量控制目标,提出一种在城市规划体系中控制性详细规划和修建性详细规划阶段分解落实年径流总量控制率的方法。在控制性详细规划阶段分解径流总量控制指标时,分步骤先后确定各项低影响开发措施的面积率和下沉深度;在修建性详细规划阶段,配合径流总量控制指标分解结果,给出适宜的各项低影响开发措施的技术实施导则,以保证各单项指标的正确实施,并以某项目为例介绍了技术实施导则的构建方法。 相似文献
99.
Platinum-based catalysts, for the electro-oxidation of methanol, have been made by thermal decomposition of chloride precursors onto titanium mesh. The catalysed electrodes were successfully operated in acidic methanol electrolytes. Electrochemical characterisation has been carried out using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic polarisations. A complete analysis of the electrochemical results showed that the preliminary performance of the catalysed titanium mesh was comparable to that achieved with carbon-supported PtRu catalysts. The catalysts formed on titanium mesh by thermal decomposition also exhibited dimensional stability. Catalysed titanium mesh therefore appears to be a promising alternative to carbon-supported catalysts for certain fuel cell applications. 相似文献
100.