共查询到20条相似文献,搜索用时 31 毫秒
1.
The catalytic activity of fresh Pd and Pt catalysts supported on γ-alumina in the complete oxidation of CH 4 traces under lean-burn conditions was studied in the presence or the absence of water or H 2S. Steam-aged catalysts were also studied in order to simulate long-term ageing in real lean-burn natural gas fuelled vehicles (NGVs) exhaust conditions. Without water or H 2S added to the feed, Pd catalysts exhibit a superior catalytic activity in methane oxidation compared to Pt ones, whatever the catalysts were fresh or aged. The addition of 10 vol.% water vapour to the feed strongly affects the activity of the fresh Pd catalyst, thus being only slightly more efficient than the fresh Pt one. H 2S has a strong poisoning effect on the catalytic activity of Pd catalysts, while Pt catalysts are more resistant. The fresh H 2S-poisoned Pd/Al 2O 3 catalyst was studied by TPD in O 2/He. Poisoning species decompose above 873 K as SO 2 and O 2 in relative concentrations consistent with the decomposition of surface sulphate species. However, a treatment in O 2/He at temperatures as high as 923 K does not allow the complete regeneration of the catalytic activity of H 2S-poisoned Pd/Al 2O 3. A mechanism involving the poisoning of PdO by sulphate species is proposed. Different diffusion processes by which these sulphate species can migrate back and forth between PdO and the support, depending on the experimental conditions, are suggested. 相似文献
2.
在工业二氧化碳加氢制甲醇过程中,硫化氢气体的引入将对该过程中使用的催化剂活性及稳定性带来负面的影响。基于此,采用微反应合成法成功制备了InZrO x和ZnZrO x锆基催化剂,并研究了在二氧化碳加氢反应中,硫化氢气体对锆基催化剂的结构性质及其催化性能的影响规律。结果表明,在T=573 K、p=3.0 MPa和GHSV=18 000 mL/(g cat·h)条件下,仅通入二氧化碳/氢气反应气时,InZrO x和ZnZrO x催化剂的二氧化碳转化率和甲醇选择性分别为7.2%、9.3%和93%、92%。在二氧化碳/氢气原料气中通入体积分数为5×10 -3硫化氢气体时,InZrO x和ZnZrO x催化剂的二氧化碳转化率和甲醇选择性都降为0,这主要是因为硫化氢气体占据了氧空位,导致锆基双金属氧化物催化剂硫中毒失活。当停止通硫化氢气体时,InZrO x和ZnZrO x催化剂的二氧化碳转化率和甲醇选择... 相似文献
3.
Hydrogenating catalysts were prepared by inserting Ru into the pores of mesoporous Al-MCM-41 materials by selective adsorption of [Ru(NH 3) 6] 3+. Ru/support catalysts were obtained after reduction with H 2. The activities of these catalysts in hydrogenation reactions were compared to those of Ru/HY and Ru/SiO 2. The catalytic properties in the absence of sulfur were tested in benzene hydrogenation, and the intrinsic activities of all the catalysts (either supported on mesoporous materials or on zeolites) were identical. It was concluded from this result that the dispersion of the Ru metallic phase was similar for all these catalysts. These samples were tested in the tetralin hydrogenation in pure H 2 and in the presence of H 2S (330 ppm of H 2S in H 2). They were found to be much less active than the zeolite-supported catalysts in the presence of H 2S. It is proposed that the lower activity of the catalysts supported on mesoporous materials is either due to their milder acidity, as evidenced by NH 3-TPD, cumene cracking and pyridine desorption experiments, or to the localization of the Ru nanoparticles on alumina islands. 相似文献
4.
This study focuses on the loading of catalytic materials, e.g., palladium on the surface of supporting materials, with the aim to obtain catalysts with high activity for methane combustion. The catalyst PdO/CeO 2-Al 2O 3 was prepared by impregnation under ultrasonic condition. The effect of different activation methods on the activity of catalysts for methane catalytic combustion was tested. The properties of reaction and adsorption of oxygen species on catalyst surface were characterized by H 2-temperature programmed reduction (H 2-TPR), and O 2-temperature programmed desorption (O 2-TPD). Furthermore, the sulfur tolerance and sulfur poisoning mode were investigated. The results indicate that the catalyst PdO/CeO 2-Al 2O 3 activated with rapid activation shows higher activity for methane combustion and better sulfur tolerance. The result of sulfur content analysis shows that there is a large number of sulfur species on the catalyst’s surface after reactivation at high temperature. It proves that the activity of catalysts cannot be fully restored by high-temperature reactivation. 相似文献
5.
采用等体积浸渍法制备了1% AuCl 3/AC催化剂,探究了硫化氢(H 2S)为毒物对乙炔氢氯化反应中催化剂催化活性的影响及失活机理。催化活性测试结果表明,以H 2S为毒物可导致乙炔氢氯化反应中的AuCl 3/AC催化剂的失活,且是一个不可逆过程;程序升温还原(TPR)和X射线光电子能谱(XPS)分析结果表明,H 2S的加入可有效地加快Au 3+还原为Au 0;透射电镜能谱(TEM-EDX)观测分析形成的Au-S化合物也可导致催化剂失活,即随着H 2S量的增大,更多的Au 3+被还原为Au 0,且形成的Au-S化合物覆盖在活性位点,使有效的活性组分降低进而导致AuCl 3/AC催化剂失活。 相似文献
6.
Properties of the oxidized activated carbon KAU treated at different temperatures in inert atmosphere were studied by means of DTA, Boehm titration, XPS and AFM methods and their catalytic activity in H 2S oxidation by air was determined. XPS analysis has shown the existence of three types of oxygen species on carbon catalysts surface. The content of oxygen containing groups determined by Boehm titration is correlated with their amount obtained by XPS. Catalytic activity of the KAU catalysts in selective oxidation of hydrogen sulfide is connected with chemisorbed charged oxygen species (O 3.1 oxygen type with BE 536.8–537.7 eV) present on the carbons surface. Formation of dense sulfur layer (islands of sulfur) on the carbons surface and removal of active oxygen species are the reason of the catalysts deactivation in H2S selective oxidation. The treatment of deactivated catalyst in inert atmosphere at 300 °C gives full regeneration of the catalyst activity at low temperature reaction but only its partial reducing at high reaction temperature. The last case is connected with transformation of chemisorbed charged oxygen species into CO groups. The KAU samples treated in flow of inert gas at 900–1000 °C were very active in H2S oxidation to elemental sulfur transforming up to 51–57 mmol H2S/g catalyst at 180 °C with formation of 1.7–1.9 g Sx/g catalyst. 相似文献
7.
The direct synthesis of methanethiol, CH 3SH, from CO and H 2S was investigated using sulfided vanadium catalysts based on TiO 2 and Al 2O 3. These catalysts yield high activity and selectivity to methanethiol at an optimized temperature of 615 K. Carbonyl sulfide and hydrogen are predominant products below 615 K, whereas above this temperature methane becomes the preferred product. Methanethiol is formed by hydrogenation of COS, via surface thioformic acid and methylthiolate intermediates. Water produced in this reaction step is rapidly converted into CO 2 and H 2S by COS hydrolysis. Titania was found to be a good catalyst for methanethiol formation. The effect of vanadium addition was to increase CO and H2S conversion at the expense of methanethiol selectivity. High activities and selectivities to methanethiol were obtained using a sulfided vanadium catalyst supported on Al2O3. The TiO2, V2O5/TiO2 and V2O5/Al2O3 catalysts have been characterized by temperature programmed sulfidation (TPS). TPS profiles suggest a role of V2O5 in the sulfur exchange reactions taking place in the reaction network of H2S and CO. 相似文献
8.
The texture of Fe 2O 3 support and Ru/Fe 2O 3 catalysts supported on iron oxides obtained from β-FeOOH (B) or δ-FeOOH (D) and their catalytic activity in WGSR were studied. Also their susceptibilities to reduction and reoxidation, were studied by TPR, using H 2 or CO and TPO methods. In the case of TPR CO the composition of the reducing mixture containing traces of H 2O enabled investigation of water gas shift reaction (WGSR). The catalysts from series D were found more readily reducible and oxidised than those from series B. The supported ruthenium enhanced the redox effects and caused the appearance of additional effects related directly to its presence. Depending on the kind of support and on ruthenium presence considerable differences in temperatures of WGSR onset were found. It is suggested that the susceptibility of the catalysts to reduction and oxidation is responsible for their activity in the WGSR. 相似文献
9.
The influence of the addition of 5 vol.% of carbon monoxide, hydrogen, carbon dioxide or water to the feed of partial oxidation of methane was investigated over Ni/γ-Al 2O 3 and Rh/γ-Al 2O 3 catalysts. In addition to catalytic tests, thermodynamic calculations were performed to predict the effect of these gas co-feeds. Compared to the thermodynamic trends, differences in the influence of the co-feeding on catalytic performances were observed between both catalysts. Co-feeding of CO, H 2, CO 2 or H 2O can modify the oxidation state and dispersion of the metal component of the catalysts during reaction, and as a consequence, their performances. Changes in catalysts can be due to dynamic processes occurring during reaction. It is suggested to take these processes into account in a more complex kinetic equation for the reactions involved. 相似文献
10.
Cobalt-based catalysts doped with different amounts of ruthenium supported on Zr-MSU type materials were studied in the hydrogenation and hydrogenolysis/hydrocracking of tetralin at different temperatures. The catalytic tests were carried out in a high-pressure fixed-bed continuous-flow stainless steel catalytic reactor operating at a pressure of 6.0 MPa. Textural, structural, acidic and metallic properties were studied by XRD, XPS, H 2-TPR, NH 3-TPD and Elemental Chemical Analysis. Five catalysts were prepared with 10 wt% of cobalt and a ruthenium loading ranging from 0.5 to 5 wt%, along with a monometallic ruthenium catalyst with 3 wt% of metal, for comparison. From catalysts characterization, no interaction between cobalt and ruthenium can be established, however, the presence of ruthenium influences the reducibility of cobalt. Ruthenium-doped catalysts not only improve the catalytic activity of monometallic cobalt and ruthenium ones, but also ruthenium acts as a trap for sulphur organic molecules, preserving cobalt particles from sulphur poisoning and thus maintaining their high hydrogenation activity. The catalyst with a ruthenium loading of 3 wt% is found to be the most active, both, with or without sulphur in the feed. The most striking improvement of ruthenium-doped catalyst properties is their greater resistance to sulphur molecules than in the case of monometallic cobalt catalysts, which are otherwise rapidly deactivated under the same experimental conditions. 相似文献
11.
氰化氢(HCN)、羰基硫(COS)、二硫化碳(CS 2)广泛共存于黄磷尾气、焦炉煤气、碳一化工等化工行业废气中,目前大多数研究局限于3种气体的单独脱除,3种气体同时脱除的研究鲜有报道,而3种气体的协同脱除势在必行。催化水解法能够将HCN转化成NH 3,COS和CS 2水解成H 2S。NH 3和H 2S可以分别被催化氧化为N 2及S,S可以回收利用。一步法实现HCN、COS和CS 2的水解及水解产物NH 3和H 2S的催化氧化的催化剂开发是该技术的核心问题,本文针对近几年3种气体水解催化剂的相关研究成果进行了综述,包括负载型催化剂和非负载型催化剂,与此同时,针对水解产物NH 3和H 2S的催化氧化的协同净化技术进行了分析,旨在为后续3种气体同时催化水解及协同净化其水解产物催化剂的开发提供理论指导,为低温环境下协同催化水解HCN、COS和CS 2,并利用原料气中的氧一步法净化水解产物技术的未来发展及应用提供参考。 相似文献
12.
The effect of treatment with different mineral acids (H 2SO 4, H 3PO 4, HNO 3 and HCl) on the activity of monolithic CoO x/γ-Al 2O 3 catalysts in the reduction of nitric oxide with methane in the presence of oxygen (CH 4-SCR of NO x) was studied. Their behaviour in the methane oxidation reaction in both the presence and absence of NO x was determined in order to interpret the results in terms of intrinsic activity and competition between both processes. Depending on the nature of the acid used, significant differences were observed in the catalytic activities which were related to the textural states, surface acidities and the nature of the detected species. The best results were obtained after treatment with H 2SO 4, which increased the activity towards NO x elimination compared to the other catalysts. This behaviour was attributed not only to an increase in surface acidity but also to the stabilisation of the active Co 2+ species, thus avoiding the formation of Co 3O 4 spinel that is responsible for the strongly adsorbed NO x species that lead to NO 2 formation which increase the rate of the undesired methane oxidation reaction at high temperatures. 相似文献
13.
Water formed during hydrotreating of oxygen-containing feeds has been found to affect the performance of sulphided catalysts in different ways. The effect of water on the activity of sulphided NiMo/γ-Al 2O 3 and CoMo/γ-Al 2O 3 catalysts in hydrodeoxygenation (HDO) of aliphatic esters was investigated in a tubular reactor by varying the amount of water in the feed. In additional experiments, H 2S was added to the feed, alone and simultaneously with water. Under the same conditions, the NiMo catalyst exhibited a higher activity than the CoMo catalyst. The ester conversions decreased with increase in the amount of added water. When H2S and water were added simultaneously, the conversion increased to the same level as without water addition on the NiMo catalyst and reached a higher value on the CoMo catalyst. The conversions were highest, however, when only H2S was added. Unfortunately, the conversions decreased with time under all conditions. On both catalysts, the total yield of the C7 and C6 hydrocarbons decreased with the amount of added water, while the concentrations of the oxygen-containing intermediates increased. The presence of H2S improved the total hydrocarbon yield and shifted the main products towards the C6 hydrocarbons. Thus, the addition of H2S effectively compensated the inhibition by water. 相似文献
14.
Phosphate of transition elements A 3M 4(PO 4) 6 (A=Fe, Ni, Zn, Mg, Cu, Cr and M=Fe, V, Cr) are prepared by solid methods, at 1223 K. Their activity in H 2S selective oxidation are compared. In spite of their low specific area, the catalysts develop a good activity (up to 17% of H 2S conversion for surface area lower than 1 m 2 g −1) and an excellent sulphur selectivity (always higher than 95%). Screening experiments show that the best systems always contain Fe as element and, in these cases, Mössbauer characterisations evidence the establishment of Fe 2+/Fe 3+ mixed valency during the reaction. As shown by XANES and XRD results, the ability of the element in the divalent A site to promote the redox mechanism between M 2+/M 3+and H 2S/S 0 and to prevent sulphidation determines the catalytic activity. 相似文献
15.
The partial oxidation of methane (POM) to syngas, i.e. H 2 and CO, over supported Rh catalysts was investigated at atmospheric pressure. The influence of support material, Rh loading and the presence of water vapor on the methane conversion efficiency and the product gas composition was studied. The catalysts containing ceria in the support material showed the highest activity and formation of H 2 and CO. By increasing the Rh loading, a decrease of the ignition temperature was obtained. The addition of water vapor to the reactant gas mixture was found to increase the ignition temperature and the formation of hydrogen, which is favorable for combustion applications where the catalytic POM stage is followed by H 2-stabilized homogeneous combustion. 相似文献
16.
The effect of different components of gasification gas on sulphur poisoning of nickel catalysts were studied. In addition, the sulphur distribution and content of nickel catalyst beds were analysed to account the poisoning effect of sulphur on the activity of catalysts to decompose tar, ammonia and methane. The desorption behaviour of chemisorbed sulphur from the bed materials was monitored by temperature programmed hydrogenation (TPH). It was established that bulk nickel sulphide was active in decomposing ammonia in high-temperature gasification gas-cleaning conditions. The decomposing activity of methane was not affected by bulk nickel sulphide formation, but that of toluene was decreased. The activity of the catalyst regained rapidly when H 2S was removed from the gas. However, the conversion of ammonia was not regained at as high a level as before sulphur addition, most probably due to irreversible sulphur adsorption on the catalyst. The temperature increase could also be used to regenerate the catalyst performance especially in respect to methane and toluene. Sulphur adsorbed on nickel catalysts in different chemical states depends on the process conditions applied. At >900°C the sulphur adsorbed on the catalyst formed an irreversible monolayer on the catalyst surfaces, while at <900°C the adsorbed sulphur, probably composed of polysulphides (multilayer sulphur), was desorbed from the catalyst in sulphur-free hydrogen containing atmosphere. However, a monolayer of sulphur still remained on the catalyst after desorption. The enhanced effect of high total pressure on sulphur-poisoning of nickel catalysts could be accounted for the increased amount of sulphur, probably as a mode of polysulphides, adsorbed on the catalyst. 相似文献
17.
锰基催化剂在低温氨选择性催化还原(NH3-SCR)脱硝反应中表现出良好的催化活性。讨论H_2O和SO_2对锰基催化剂活性的影响,综述通过制备方法改性、添加助剂和优化载体改善锰基催化剂抗H_2O和抗SO_2性能的研究进展,并对锰基低温SCR催化剂的研究方向进行展望。 相似文献
18.
The room temperature wet catalytic oxidation was conducted in a batch reactor with Fe/MgO catalyst. Fe/MgO catalyst was prepared by the dissolution–precipitation method. XRD and temperature-programmed reductions (TPR) indicate that Fe oxide in the Fe/MgO is finely dispersed in the MgO support. The high H 2S removal capacities of Fe/MgO can be explained by the finely dispersed iron oxide MgO. The H 2S removal capacities of Fe/MgO are dependent on oxygen partial pressure (1.0 g H 2S/g cat in air and 2.6 g H 2S/g cat in oxygen). The valence state analysis of Fe/MgO catalyst suggests that the H 2S oxidation on Fe/MgO can occur by a redox couple reaction, reducing Fe 3+ into Fe 2+ by H 2S and oxidizing Fe 2+ to Fe 3+ by O 2. 相似文献
19.
考察过渡金属Ni对Pd/Al_2O_3催化剂甲烷催化燃烧活性的影响以及过渡金属负载量及循环条件对甲烷降解性能的影响,采用扫描电镜、N_2吸附-脱附以及H_2程序升温还原技术对催化剂进行表征。结果表明,过渡金属Ni的添加对催化剂在(375~475)℃下的甲烷催化燃烧活性产生影响。催化剂经多次重复使用后,催化燃烧活性提高。分析原因为经过渡金属Ni改性后,可与载体形成NiAl_2O_4尖晶石,促进活性组分形成较小晶粒,并改善活性组分分散度,提高催化剂催化活性。 相似文献
20.
采用共沉淀法合成一系列具有不同Ce/Zr物质的量比的铈锆固溶体Ce xZr 1-xO 2,考察Ce/Zr比例对H 2S选择氧化反应催化活性的影响。通过XRD、BET、Raman、XPS、CO 2-TPD、O 2-TPD、H 2-TPR等手段对铈锆固溶体的晶体结构、表面性质、碱性位以及氧化还原性等进行表征。结果表明,所有的铈锆固溶体催化剂均可以在化学计量比的氧气下具有优良的低温催化活性,催化活性随着Ce/Zr比例的提高而增加,其中Ce 0.9Zr 0.1O 2活性最高,(160~260) ℃转化率均保持在95%以上,在180 ℃时硫收率可达到97%,这主要是因为Ce 0.9Zr 0.1O 2具有最多的中度碱性位、活性位数量和强的氧化还原性。同时推测Ce 4+为催化反应的活性位,并遵循氧化还原机理。此外,催化剂的失活主要是由于催化剂表面生成硫酸盐物种,消耗了活性组分Ce 4+。 相似文献
|