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1.
TPD/Exchange from CO/Re(001) in a gas ambience showed that the absolute rate of desorption depends on the gas pressure and has a first plus second order rate law. It is proposed that desorption is a two step process from the adsorbed state to a stable intermediate which is itself weakly adsorbed.  相似文献   
2.
The adsorption and the decomposition of methanol on an oxygen precovered polycrystalline silver surface were characterized by high resolution electron energy loss spectroscopy. A stable methoxy species and subsequently two new intermediates related to the decomposition of methoxy have been isolated and identified by temperature profiled ELS.  相似文献   
3.
Methane activation without using oxidants over Mo/HZSM-5 zeolite catalysts   总被引:1,自引:0,他引:1  
The effect of Mo loading, calcination temperature, reaction temperature and space velocity on the catalytic performance of methane dehydrogenation and aromatization without using oxidants over Mo/HZSM-5 has been studied. The XRD and BET measurements show that Mo species are highly dispersed in the channels of the HZSM-5 zeolite, resulting from the interaction between the Mo species and the zeolite, which also leads to a decrease in its crystallinity. The Brønsted acidity, the channel structure and the state and location of Mo species in the zeolite seem to be crucial factors for its catalytic performance. It was found that 2% Mo/HZSM-5 calcined at 773 K showed the best aromatization activity among the tested catalysts, the methane conversion being 9% at 1013 K with the selectivity to aromatics higher than 90%. The experimental results obtained from the variation of space velocity gave evidence that ethylene is an initial product. On the basis of these results a possible mechanism for methane dehydrogenation and aromatization has been proposed in which both the heterolytic splitting of methane in a solid acid environment and a molybdenum carbene-like complex as an intermediate are of significance.  相似文献   
4.
通过单泡浮选、吸附量测定、X射线光电子能谱(XPS)分析以及溶液化学计算研究了低碱环境下氯化铵抑制黄铁矿硫酸铜活化浮选的机理。单矿物和混合矿浮选结果表明,低碱条件下氯化铵能够有效抑制黄铁矿的铜活化浮选、提高锌硫分离效果。黄铁矿表面产物分析以及溶液化学计算结果表明,氯化铵抑制黄铁矿的铜活化浮选主要通过以下两个途径实现:在低碱性环境下,加入氯化铵后产生的酸碱缓冲对NH3-NH4+能够维持体系pH值,从而维持黄铁矿表面的羟基化程度,使黄铁矿被亲水抑制;NH3(aq)与Cu2+发生配合反应生成铜氨配合物的趋势很大,其能够与黄铁矿表面竞争消耗铜离子,削弱黄铁矿表面的铜离子吸附活化过程。为实现低碱锌硫浮选分离工艺提供了新思路,为在工业中实现低碱锌硫分离工艺奠定了理论基础。  相似文献   
5.
Room temperature adsorption of propene on ruthenium (001) was studied by HREELS and UPS. Adsorption was mainly dissociative, with cleavage of both C-H and C-C bonds, and resulted in a mixture of surface species: naked carbon atoms, CH fragments, metal carbynes, ethylidyne, di- adsorbed alkene, and -adsorbed alkene in order of their relative abundance.  相似文献   
6.
The reactions of dry (CO2) reforming and partial oxidation of methane have been investigated in a membrane reactor. The membrane is composed of a dense thin silica (SiO2) film supported on porous Vycor tubes and was synthesized by chemical vapor deposition. The hydrogen permeance of the membrane was 0.2–0.3 cm3/(cm2 min atm) at 600°C combined with a H2/N2 selectivity of 200–300. Significant increases in methane conversion were attained in both reactions at 500–750°C, albeit at very low space velocities. The membrane permeance declined by 50% after exposure to feeds containing H2O, but otherwise exhibited excellent stability under reaction conditions.  相似文献   
7.
Three magnesium vanadate phases, i.e., MgV2O6 (metavanadate), -Mg2V2O7 (pyrovana-date) and Mgs V2O8 (orthovanadate), have been successfully prepared with high purity by the citrate method at a relatively low temperature (550°C). FT-IR, LRS, XRD and SEM techniques have been used to characterize these vanadate phases. The effect of calcination temperature has also been investigated. It was found that the particle size and morphology of the MgV2O6 phase, which is a function of calcination temperature, appear to have a strong effect on the infrared spectra. Furthermore, the catalytic properties of the three phases were examined in the oxidative dehydrogenation of propane. The propene selectivity follows the order: -Mg2V2O7 > Mg3 Vg2O8 > MgV2O6, which is consistent with their redox properties. This fact suggests that there is some correlation between the catalytic and redox properties of these magnesium vanadate phases.  相似文献   
8.
Isotopic switching technique has been used to study the exchange of gaseous CO* with chemisorbed CO molecules on metal surface. The kinetic curves observed on Re(0001) exhibit a nonlinear dependence of desorption rate on the surface coverage of CO. However, the desorption rate for CO on Rh(111) in the same temperature range is strictly linear with the coverage of CO. A concerted adsorption-desorption mechanism is postulated which emphasizes that the desorption of CO in enhanced by the pressure of gas phase CO* on the one hand, and may be retarded by the screening effect of the CO* molecule chemisorbed on the surface on the other hand. It is pointed out that the adsorption of CO* (or CO) and the desorption of CO (or CO*) on a surface at high coverage, i.e. the molecular exchange processes, are primarily taking place simultaneously and concertedly.  相似文献   
9.
Atmospheric hydroformylation of ethylene was studied under differential conditions over Rh4(CO)12-derived Rh/SiO2 catalysts. The specific activities as functions of Rh dispersions show that ethylene hydroformylation is structure sensitive and ethylene hydrogenation structure insensitive. These structural dependences and in situ IR observations show that Rh0 is the unique active site for catalytic ethylene hydroformylation on Rh/SiO2. The reactions of Rh0-coordinated CO and Rh0-adsorbed CO with C2H4 + H2 at 293 K were monitored by IR spectroscopy. The linear CO adsorbed on Rh0/SiO2 is consumed with formation of propanal, whereas the coordinated CO in Rh6(CO)16/SiO2 and its derivative do not participate in CO insertion. IR study of the thermal decomposition of Rh6(CO)16/SiO2 indicates that the cluster can be stabilized on the surface up to 548 K by gaseous CO under hydroformylation conditions. Moreover, the Rh6(CO)16/SiO2 system exhibits increased catalytic hydroformylation activity with reducing coordinated CO. These results show that coordinative unsaturation on the Rh0 surface is necessary for heterogeneously rhodium-catalyzed hydroformylation and that totally decarbonylated Rh0/SiO2 is most effective. In addition, the oxidation of Rh0 by surface OH? is discussed.  相似文献   
10.
添加镧的羟基铝柱化粘土的合成与表征   总被引:2,自引:0,他引:2  
报道了添加镧的羟基铝拄化粘土(Pillared Clays,简称PILC)的合成。用~(27)Al-NMR、XRD、DTA、IR、吡啶吸附-IR、正丁胺吸附-TPD等手段表征了柱结构、热稳定性和表面酸性。利用脉冲反应技术,考察了异丙苯裂化和重芳烃1,2,4-三甲苯的转化。试验表明,利用取代法和共聚法,都可以合成出高底面间距(d_(001)=1.8nm)的添加镧的羟基铝柱化粘土(LaAl-PILC),并且未破坏其热稳定性。LaAl-PILC具有较高的裂解活性(76.8%)和1,2,4-三甲苯转化活性(74.9%)。镧的引入,使其表面酸性有所降低,裂解活性和偏三甲苯的歧化选择性却有所增加。  相似文献   
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