High coke-resistance of K-Ca-promoted Ni/a-Al2O3 catalyst for ch4 reforming with CO2

Summary  K-Ca-promoted Ni/&agr;-Al2O3 catalyst exhibited higher activity better coke-resistance than Ni/&agr;-Al2O3 for CH4 reforming with CO2 under different reaction conditions. Temperature-programmed activation process of CH4 reforming with CO2 was investigated on these catalysts.     

Methane steam reforming over rhodium promoted Ni/Al2O3 catalysts

The effect of Rh addition upon catalyst characteristics and performance in methane steam reforming was investigated using Rh-promoted Ni/Al₂O₃ catalysts. The number of reduced metal atoms exposed on the surface increased for the Rh-promoted catalysts. Rh-promoted catalysts showed an increase in CH₄ reforming activity; however, constant turnover frequencies for promoted and unpromoted catalysts suggest that the increase in the number of metal surface atoms caused the activity enhancement. Rh also facilitated reduction of Ni/Al₂O₃.     

Combination of CO2 reforming and partial oxidation of CH4 over Ni/Al2O3 catalysts using fluidized bed reactor

The effects of the Ni loading, total feed flow rate, prereduction temperature, reaction temperature and feed gas ratio for combination of CO₂ reforming and partial oxidation of CH₄ over Ni/Al₂O₃ were investigated using a fluidized bed reactor. Methane conversion to syngas was drastically enhanced using a fluidized bed reactor over Ni/Al₂O₃ catalyst calcined at high temperature. The fluidized bed and the fixed bed reactor were compared and a promoting mechanism of the fluidized bed reactor was proposed. This revised version was published online in August 2006 with corrections to the Cover Date.     

The influence of La2O3 and TiO2 on NiO/MgO/α-Al2O3

Summary The effect of La₂O₃ and TiO₂ on product selectivity, methane conversion and coke formation over NiO/MgO/ α -Al₂O₃ catalyst were studied in a simultaneous steam and CO₂ reforming of methane to syngas. La₂O₃ and TiO₂ were added to the catalyst via incipient wetness impregnation and bulk precipitation techniques and catalyst activity was tested in a fixed bed quartz reactor. Results reveal that although the addition of these oxides has no effect on the product selectivity and methane conversion, but can reduce coke formation on the surface of the catalysts as it can enhance the mobility of lattice oxygen anions. The results further show that the catalysts prepared by bulk precipitation technique decrease the coke formation more effectively.     

Improvement of stability of a Fe/Mg/Al2O3 catalyst for the decomposition of methane in the presence of O2/CO2

The stability of an Fe/Al₂O₃ catalyst in the methane decomposition in the presence of O₂/CO₂ was found to be improved by the addition of Mg into the catalyst (Mg/Fe=1/1 wt ratio), probably due to suppression of carbon deposition even under CH₄/ O₂/CO₂ (80/10/5 vol. ratio) conditions. This revised version was published online in June 2006 with corrections to the Cover Date.     

Carbon dioxide reforming of methane over Ni/Mo/SBA-15-La2O3 catalyst: Its characterization and catalytic performance

The Ni/Mo/SBA-15 catalyst was modified by La2O3 in order to improve its thermal stability and carbon deposition resistance during the CO2 reforming of methane to syngas. The catalytic performance, thermal stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were comparatively investigated by many characterization techniques such as N2 adsorption, H2-TPR, CO2-TPD, XRD, FT-IR and SEM. It was found that the major role of La2O3 additive was to improve the pore structure and inhibit carbon deposition on the catalyst surface. The La2O3 modified Ni/Mo/SBA-15 catalyst possessed a mesoporous structure and high surface area. The high surface area of the La2O3 modified catalysts resulted in strong interaction between Ni and Mo-La, which improved the dispersion of Ni, and retarded the sintering of Ni during the CO2 reforming process. The reaction evaluation results also showed that the La2O3 modified Ni/Mo/SBA-15 catalysts exhibited high stability.     

Effect of Transition Metals (Cu, Co and Fe) on the Autothermal Reforming of Methane over Ni/Ce0.2Zr0.1Al0.7Oδ Catalyst

The transition metals (Cu, Co, and Fe) were applied to modify Ni/Ce0.2Zr0.1 Al0.7Oδcatalyst. The effects of transition metals on the catalytic properties of Ni/Ce0.2Zr0.1 Al0.7Oδautothermal reforming of methane were investigated. The Ni-supported catalysts were characterized by XRD, TPR and XPS. Tests in autothermal reforming of methane to hydrogen showed that the addition of transition metals (Cu and Co) significantly increased the activity of catalyst under the conditions of lower reaction temperature, and Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδwas found to have the highest conversion of CH4 among all catalysts in the operation temperatures ranging from 923 K to 1023 K. TPR, XRD and XPS measurements indicated that the cubic phases of CexZr1-xO2 solid solution were formed in the preparation process of catalysts. Strong interaction was found to exist between NiO and CexZr1-xO2 solid solution. The addition of Cu improved the dispersion of NiO, inhibited the formation of NiAl2O4, and thus significantly promoted the activity of the catalyst Ni/Cu0.05Ce0.2Zr0.1Al0.65Oδ.     

Reforming of CH4 with CO2and O2to produce syngas over CaO modified Ni/SiO2 catalysts in a fluidized bed reactor

Methane reforming by carbon dioxide and oxygen was investigated over 5 wt.%Ni/CaO-SiO₂ catalyst in a fluidized-bed reactor. The catalyst exhibited high activity and good stability at stoichiometric methane, carbon oxide and oxygen feed. Effects of calcium loading, space velocities, reaction temperatures and the feed gas compositions for this combined reaction were investigated. These results indicated that Ni/CaO-SiO₂ is more effective and stable. The catalyst performance, stability, structure, dispersion of nickel and carbon deposition of the modified and unmodified catalysts were investigated by a series of characterization techniques. Results showed that catalysts modified with CaO improved their stability better than the pure nickel-based catalysts. This revised version was published online in June 2006 with corrections to the Cover Date.     

Computational fluid dynamics study of the dry reforming of methane over Ni/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalyst in a membrane reactor. Coke deposition

This work investigates the dry reforming of CH₄ as an important process for the conversion of greenhouse gases to synthesis gas. The mixture of methane and CO₂ is readily available in the greenhouse gas which makes realization of dry reforming of methane process more convenient. The paper is an attempt to numerically analyse by computational fluid dynamics (CFD) the coking and gasification mechanisms in the lab-scale membrane module with a fixed-bed supported nickel catalyst (Ni/Al₂O₃). The concentrations and molar fluxes obtained by the simulation are compared with the experimental profiles to validate the CFD model. It was found that working in a catalytic fixed-bed membrane reactor, in the case of the dry reforming of methane and under specific conditions, was not critical, from the point of view of catalyst deactivation.     

The Mechanistic Study of Methane Reforming with Carbon Dioxide on Ni/α-Al2O3

The reactions of oxidized and reduced 6 wt % NiO/-Al₂O₃ with H₂, CH₄, CO₂, O₂, and their mixtures are studied in flow and pulse regimes using a setup equipped with a differential scanning calorimeter DSC-111 and a system for chromatographic analysis. It is shown that treatment with hydrogen at 700° results in the partial reduction of NiO to Ni. Methane practically does not react with oxidized Ni/-Al₂O₃ but it does react actively with the reduced catalyst to form H₂ and surface carbon. The latter is capable of reacting with lattice oxygen of Ni/-Al₂O₃ (slowly) and with adsorbed oxygen (rapidly). Carbon dioxide also reacts with surface carbon to form CO (rapidly) and with metallic Ni to yield CO and NiO (slowly). Thus, the main route of methane reforming with carbon dioxide on Ni/-Al₂O₃ is the dissociative adsorption of CH₄ to form surface carbon and H₂ and the reaction of this carbon with CO₂ resulting in the formation of CO by the reverse Boudouard reaction. Side routes are the interaction of the products of methane chemisorption with catalyst oxygen and the dissociative adsorption of CO₂ on metallic nickel. A competitive reaction of surface carbon with adsorbed oxygen results in a decrease in the CO₂ conversion in methane reforming with carbon dioxide. Therefore, the presence of gaseous oxygen in the reacting mixture decelerates methane reforming (catalyst poisoning by oxygen).     

Properties of internal heat supply with carbon dioxide reforming of methane over a Ni/Al2O3 catalyst.

An addition of 6%-oxygen into a reactant of CH₄/CO₂(1/1) gave lower operating temperature of carbon dioxide reforming of methane by 130 K in obtaining 0.029 MPa of H₂, accompanied by a more endothermic atmosphere in the catalyst bed than in the absence of oxygen. This revised version was published online in June 2006 with corrections to the Cover Date.     

Enhanced photocatalytic activity of thin TiO2 films dotted with ZnS nanoparticles

The effect of Ni loading on the catalytic activity of Ni/ZrO₂ catalyst for methane steam reforming was investigated. The sample containing 15 wt.% Ni exhibited the highest activity as well as stability at 600°C. An erratum to this article is available at .     

The Catalytic Dehydrogenation of c2h6 to c2h4 under non-Oxidative Conditions over the 6cr/g-al2o3Catalyst

In the present paper, the catalytic dehydrogenation of C₂H₆ to C₂H₄ under non-oxidative conditions was investigated in a fixed-bed micro-reactor under ambient pressure at 823 - 923 K. The 6Cr/g-Al₂O₃ catalyst was found to be the best catalyst among the g-Al₂O₃, SiO₂, MCM41, MgO and Si-2 supported chromium oxide catalysts. The features of the 6Cr/g-Al₂O₃ catalyst for the reaction could be listed as follows: (1) At 823 - 923 K, the C₂H₄ selectivity of 92.5-78.6% at a C₂H₆ conversion of 9.5-29.8% could be obtained. (2) The catalyst had the good regeneration performance, i.e., could be regenerated by air repeatedly. (3) The main products were C₂H₄, CH₄, H₂ and coke. No carbon oxides were identified.     

ACo_2O_4/HZSM-5催化剂上N_2O的直接分解

分别采用柠檬酸络合燃烧法和低温络合浸渍法制备尖晶石型复合金属氧化物催化剂ACo2O4(A=Mg,Ni,Zn)和分子筛负载尖晶石型复合金属氧化物催化剂ACo2O4/HZSM-5(A=Mg,Fe,Ni,Cu,Zn,Zr,La).采用X射线衍射(XRD)、氨程序升温脱附(NH3-TPD)、扫描电子显微镜(SEM)和X射线能谱(EDS)等手段对催化剂进行表征,并在固定床微型反应器中评价其催化分解N2O活性.实验结果表明,A位离子种类影响ACo2O4/HZSM-5催化剂活性,以Ni、Fe、Zr或La为A位离子时,催化剂的活性较好,N2O分解温度低.ACo2O4/HZSM-5催化剂的活性高于ACo2O4尖晶石型复合氧化物,一方面是ACo2O4在分子筛HZSM-5载体上高度分散,使其以超细颗粒形态存在,另一方面ACo2O4/HZSM-5催化剂具有适宜的酸性,可提高催化剂的活性.     

Catalytic Performance and Characterization of Pt‐Co/Al2O3 Catalysts for CO2 Reforming of CH4 to Synthesis Gas

Pt‐Co/Al₂O₂ catalyst has been studied for CO₂ reforming of CH₄ to synthesis gas. It was found that the catalytic performance of me catalyst was sensitive to calcination temperature. When Co/Al₂O₃ was calcined at 1473 K prior to adding a small amount of Pt to it, the resulting bimetallic catalyst showed high activity, optimal stability and excellent resistance to carbon deposition, which was more effective to the reaction than Co/Al₂O₃ and Pt/Al₂O₃ catalysts. At lower metal loading, catalyst activity decreased in the following order: Pt‐Co/ Al₂O₃ > Pt/Al₂O₃ > Co/Al₂O₃. With 9% Co, the Co/Al₂O₃ calcined at 923 K was also active for CO₂ reforming of CH₄, however, its carbon formation was much more fast man that of the Pt‐Co/Al₂O₃ catalyst. The XRD results indicated that Pt species well dispersed over the bimetallic catalyst. Its high dispersion was related to the presence of CoAl₂O₄, formed during calcining of Co/Al₂O₃ at high temperature before Pt addition. Promoted by Pt, Co/Al₂O₄ in the catalyst could be reduced partially even at 923 K, the temperature of pre‐reduction for the reaction, confirmed by TPR. Based on these results, it was considered that the zerovalent platinum with high dispersion over the catalyst surface and the zerovalent cobalt resulting from Co/Al₂O₄ reduction are responsible for high activity of the Pt‐Co/Al₂O₃ catalyst, and the remain Co/Al₂O₄ is beneficial to suppression of carbon deposition over the catalyst.     

TPR studies on steam reforming of 2-propanol on Rh/Al2O3, Ru/Al2O3 and Pd/Al2O3

Reaction pathways for steam reforming of 2-propanol (isopropyl alcohol, IPA) on Rh/Al₂O₃, Ru/Al₂O₃ and Pd/Al₂O₃ have been studied by temperature-programmed reactions (TPRs) of IPA and acetone in the presence of steam. The results of TPRs suggest that that of IPA on Rh/Al₂O₃ and Ru/Al₂O₃ proceeds via acetone, while the steam reforming of IPA on Pd/Al₂O₃ takes place via propene from acetone. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of ceria loading on the carbon formation during low temperature methane steam reforming over a Ni/CeO2/ZrO2 catalyst

The characterization and catalytic activity of a Ni/CeO₂/ZrO₂ catalyst for methane steam reforming at 600°C were investigated. The addition of ceria increased the surface area and basicity of the catalysts. The redox reaction capability of the ceria increased the hydrogen yield and carbon monoxide selectivity, and inhibited carbon formation.     

Influence of MgO in the CO2 – steam reforming of methane to syngas by NiO/MgO/ α-Al2O3 catalyst

Simultaneous steam and CO₂ reforming of methane to syngas (H₂and CO) over NiO/MgO/a-Al₂O₃ catalyst have been investigated at different MgO wt.%. The catalyst has been characterized by temperature-programmed reduction and XRD techniques. Addition of MgO reduced the carbon deposition and energy consumption. The stability and less coking on MgO-promoted catalysts are attributed to the lewis basicity of MgO.