Showing papers on "Syngas published in 1998"

Role of CeO2 in Ni/CeO2–Al2O3 catalysts for carbon dioxide reforming of methane

Abstract: Ni catalysts supported on gamma-Al2O3, CeO2 and CeO2-A1(2)O(3) systems were tested for catalytic CO2 reforming of methane into synthesis gas. Ni/CeO2-Al2O3 catalysts showed much better catalytic performance than either CeO2- or gamma-Al2O3-supported Ni catalysts. CeO2 as a support for Ni catalysts produced a strong metal-support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO2 had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/gamma-Al2O3 catalysts for this reaction. A weight loading of 1-5 wt% CeO2 was found to be the optimum. Ni catalysts with CeO2 promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO2-promoted catalysts are attributed to the oxidative properties of CeO2. (C) 1998 Elsevier Science B.V. All rights reserved.

CO2 reforming of methane on Ni catalysts: Effects of the support phase and preparation technique

Abstract: The effects of the support phase and catalyst preparation methods on catalytic activity and carbon deposition were systematically investigated over nickel catalysts supported on Al2O3, SiO2 and MgO for the reforming reaction of methane with carbon dioxide. It is found that the pore structure of the support and metal-support interaction significantly affected the catalytic activity and coking resistance. Catalyst with well-developed porosity exhibited higher catalytic activity. Strong interaction between metal and the support made the catalyst more resistant to sintering and coking, thus resulting in a longer time of catalyst stability. (C) 1998 Elsevier Science B.V.

Modeling the partial oxidation of methane in a short‐contact‐time reactor

Abstract: Partial oxidation of methane in monolithic catalysts at very short contact times offers a promising route to convert natural gas into syngas (H2 and CO), which can then be converted to higher alkanes or methanol. Detailed modeling is needed to understand their complex interaction of transport and kinetics in these systems and for their industrial application. In this work, the partial oxidation of methane in noble-metal (Rh and Pt)-coated monoliths was studied numerically as an example of short-contact-time reactor modeling. A tube wall catalytic reactor was simulated as a model for a single pore of the monolithic catalyst using a 2-D flow field description coupled with detailed reaction mechanisms for surface and gas-phase chemistry. The catalytic surface coverages of adsorbed species are calculated vs. position. The reactor is characterized by competition between complete and partial oxidation of methane. At atmospheric pressure, CO2 and H2O are formed on the catalytic surface at the entrance of the catalytic reactor. At higher pressure, gas-phase chemistry becomes important, forming more complete oxidation products downstream and decreasing syngas selectivity by about 2% at 10 bar. Temperature (from 300 to ∼ 1,200 K), velocity, and transport coefficients change very rapidly at the catalyst entrance. The dependence of conversion and selectivity on reactor conditions was examined.

Rhodium-Catalyzed Hydroformylation in Supercritical Carbon Dioxide

Abstract: Supercritical carbon dioxide (scCO2) is an environmentally benign reaction medium for highly efficient rhodium-catalyzed hydroformylation reactions. Olefinic substrates can be hydroformylated in scCO2 at 40−65 °C to give the corresponding aldehydes in practically quantitative yields. The reaction course of the hydroformylation of 1-octene in scCO2 was analyzed in detail by online-GC monitoring. The influence of reaction parameters such as temperature, synthesis gas pressure, and [P]/Rh ratio on reaction rates and selectivities is grossly similar to the effects observed in conventional solvents. Maximum turnover frequencies of 1375, 500, and 115 h-1 were determined as lower limits for the catalytic activities under the present conditions for the unmodfied, phosphine-modified, and phosphite-modified systems, respectively. With unmodified catalysts, the hydroformylation rates are considerably higher in scCO2 than in organic solvents or liquid CO2 under otherwise identical conditions. Modified catalytic syste...

Comparative study at low and medium reaction temperatures of syngas production by methane reforming with carbon dioxide over silica and alumina supported catalysts

Abstract: Two series of transition metals (Co, Ni, Ru, Rh, Ir, Pt) based catalysts have been prepared using silica and γ-alumina. Their activity and stability for the dry reforming of methane in the temperature interval from 673 up to 1023 K have been examined and compared. The obtained results show that the support exerts a great influence on the turnover frequency of a given metal but deactivation occurring under reaction conditions mainly depends on the nature of the active metallic phase. Some of the catalysts suffer deactivation processes at temperatures close to 1023 K, that can be ascribed to sintering, and in only some cases, also to carbon deposition. At low reaction temperatures, i.e. 723 K, deactivation was only observed over supported iridium. Among all tested catalysts, those based on nickel, cobalt and rhodium appear to be the most resistant to deactivation processes under our experimental conditions and for the whole temperature range up to 1023 K. Among them, supported rhodium catalysts show an excellent stability, though alumina supported rhodium exhibits a much higher turnover frequency.

Reforming of methane with carbon dioxide over Ni/Al2O3 catalysts : Effect of nickel precursor

Abstract: The catalytic activities of Ni/gamma-Al2O3 catalysts prepared using different nickel precursor compounds were studied for the reaction of methane reforming with CO2. It is found that the nickel precursor employed in the catalyst preparation plays an important role. The catalyst based on nickel nitrate exhibited higher catalytic activity and stability over a 24-h test period than the other two catalysts derived from nickel chloride and nickel acetylacetonate. A comprehensive characterisation of the catalysts showed that the weak interaction between Ni particles and gamma-Al2O3 resulted in more active sites on Ni nitrate-derived Ni/gamma-Al2O3 catalyst. Coking studies showed that carbon deposition on Ni catalysts derived from inorganic precursors (nitrate and chloride) were more severe than on the organic precursor-derived catalyst. However, the Ni nitrate-derived catalyst was found to have the highest stability (or lowest deactivation rate) mainly due to the active carbon species (-C-C-) of the resulting graphitic structure and their close contact with the metal particles. In contrast, the carbon formed on Ni-AA catalyst (from Ni acetylacetonate) is dominated by inactive -CO-C- species, thus leading to a rapid accumulation of carbon in this catalyst and more severe deactivation. (C) 1998 Elsevier Science B.V.

Nonequilibrium Plasma Reforming of Greenhouse Gases to Synthesis Gas

Abstract: The use of dielectric-barrier discharges (DBDs) is a mature technology originally developed for industrial ozone production. In this article, it is demonstrated that DBDs are also an effective tool to convert the greenhouse gases CH4 and CO2 to synthesis gas (syngas, H2/CO) at low temperature and ambient pressure. The synthesis gas produced in this system can have an arbitrary H2/CO ratio, mainly depending on the mixing ratio of CH4/CO2 in the feed gas. Specific electric energy, gas pressure, and temperature hardly influence syngas composition. The amount of syngas produced strongly depends on the electric energy input. CO2-rich mixtures prevent carbon and wax formation. At fixed specific input energies, the maximum amount of syngas with low H2/CO molar ratio is produced from a mixture of CH4:CO2 = 20:80. In a mixture of CH4:CO2 = 80:20, as high as 52 mol of H2 and 14 mol of CO have been obtained from 100 mol of feed gas at a specific input energy of 87 kW h/(N m3). CH4 conversion reaches 64%, and CO2 con...

Bifunctional catalysts for conversion of synthesis gas to dimethyl ether

Abstract: The effects of preparation methods and dehydration components on catalytic properties and the structures of bifunctional catalysts were investigated. Catalytic synthesis of dimethyl ether from synthesis gas was evaluated in a fixed-bed flow microreactor at a pressure of 4.0 MPa and a GHSV of 1500 h −1 . Characterization of catalysts has been carried out using XRD, TPR, Pyridine-TPD, CO 2 -TPD and XPS. The experimental results show that CuO ZnO Al 2 O 3 /HZSM-5 and CuO ZnO Al 2 O 3 /HSY catalysts, which were prepared by a coprecipitating sedimentation method, exhibit the highest catalytic activity for direct synthesis of dimethyl ether from synthesis gas with 89% CO conversion and 99% selectivity of dimethyl ether (in organic products). In addition, the results indicate that the dehydration step of the reaction occurs on the weak acidic sites and there is a ‘synergistic effect’ between the two kinds of active components in bifunctional catalysts.

Simultaneous steam and CO2 reforming of methane to syngas over NiO/MgO/SA-5205 in presence and absence of oxygen

Abstract: Steam reforming, CO 2 reforming and simultaneous steam and CO 2 reforming reactions of methane for its conversion into syngas (H 2 and CO) over NiO/MgO/SA-5205 catalyst (prepared by depositing NiO on MgO precoated SA-5205 support) have been investigated at different process conditions. In some cases O 2 was present in the feed, while in other cases it was not. The catalyst has been characterised by its temperature programmed reduction and also, after its reduction, by temperature programmed desorption of hydrogen. It showed high activity and selectivity in the above methane-to-syngas conversion reactions at low contact times. The H 2 /CO product ratio in the simultaneous methane conversion reactions showed a strong dependence on the feed composition; such dependence is increased by increasing the concentration of steam relative to that of O 2 and/or CO 2 in the feed. In the oxy-steam and/or CO 2 reforming reactions, there is a direct coupling of the exothermic and endothermic reactions and hence these processes over the catalyst occur in the most energy efficient and safe manners, requiring little or no external energy. The net heat of reactions in these processes is strongly influenced by the reaction temperature and/or CH 4 /O 2 ratio in the feed. In the simultaneous steam and CO 2 reforming of methane in both the presence and absence of O 2 , it is possible to convert methane into syngas with high conversion (above 97%) and 100% selectivity for both CO and H 2 .

Partial oxidation of methane to syngas over Ni/MgO, Ni/CaO and Ni/CeO2

Abstract: Partial oxidation of methane to syngas at atmospheric pressure and 750°C was examined over Ni/MgO, Ni/CaO and Ni/CeO2 catalysts with nickel loading of 13 wt%. All catalysts had similar high conversion of methane and high selectivity to syngas, which nearly approached the values predicted by thermodynamic equilibrium. However, only Ni/MgO showed high resistance to carbon deposition under thermodynamically severe conditions (CH4/O2 = 2.5, a higher CH4 to O2 ratio than the stoichiometric ratio). Its catalytic activity remained stable during 100 h of reaction, with no detectable carbon deposition. The oxidation of carbon deposited from pure CH4 decomposition and from pure CO disproportionation was investigated by in situ TPO-MS study which showed that both were effectively inhibited over Ni/MgO. In addition, the catalysts were characterized by TPR, XRD and XPS. It was revealed that the excellent performance of Ni/MgO resulted from the formation of an ideal solid solution between NiO and MgO.

Stable carbon dioxide reforming of methane over modified Ni/Al2O3 catalysts

Abstract: CO2 reforming of methane was studied over modified Ni/Al2O3 catalysts. The metal modifiers were Co, Cu, Zr, Mn, Mo, Ti, Ag and Sn. Relative to unmodified Ni/Al2O3, catalysts modified with Co, Cu and Zr showed slightly improved activity, while other promoters reduced the activity of CO2 reforming. Mn-promoted catalyst showed a remarkable reduction in coke deposition, while entailing only a small reduction in catalytic activity compared to unmodified catalyst. The catalysts prepared at high calcination temperatures showed higher activity than those prepared at low calcination temperature. The Mn-promoted catalyst showed very low coke deposition even in the absence of diluent gas and the activity changed only slightly during 100 h operation.

Syngas production using superadiabatic combustion of ultra-rich methane-air mixtures

Abstract: Two common methods for the production of synthesis gas (syngas) are: (1) methane partial oxidation and (2) methane steam re-forming. This paper discusses the experimental results obtained from the partial oxidation of “ultrarich,” (=4), methane-air mixtures in a new type of chemical reactor based on filtration combustion. Experimental results show that the reciprocal flow burner (RFB), due to its high heat recuperation efficiency (approximately 90%), can support self-sustained combustion of ultrarich methane-air mixtures up to an equivalence ratio of 8, well beyond the conventional flammability associated with a methane-air flame in free space. For the range of equivalence ratios (2 Parametric studies demonstrate that the maximum temperature in the combustion zone, which varies from 1100 to 1400°C, is a function of the equivalence ratio, filtration velocity, reactor pressure, and porous body diameter. Kinetic simulations reveal that methane partial oxidation occurs in a two-stage process: (1) ignition, a fast process that accounts for approximately 60% of the total hydrogen conversion relative to thermodynamic equilibrium and (2) steam reformation, a slow process where the remaining conversion of hydrogen occurs when water reacts with unburned methane.

Combination of CO2 Reforming and Partial Oxidation of Methane over NiO/MgO Solid Solution Catalysts

Abstract: To overcome the explosions that can occur during the partial oxidation of methane, the latter exothermic reaction is coupled with an endothermic one, namely, the CO 2 reforming of CH 4 . These combined reactions have been carried out over NiO/MgO solid solution, NiO/Al 2 O 3 , and NiO/SiO 2 catalysts. About 90% conversion of CH 4 and about 98% selectivities to CO and H 2 were obtained at 790°C and a GHSV (gas hourly space velocity) of 90000 cm 3 /g.h (O 2 /CO 2 /CH 4 =14.5/26.9/58.6), over a reduced NiO/MgO solid solution catalyst. Almost no change in activity and selectivity occurred during 50 h of reaction. Compared to the reduced NiO/MgO, the reduced NiO/SiO 2 and NiO/Al 2 O 3 catalysts provided lower activities and stabilities. The effects of the reaction temperature, space velocity, and feed gas composition for a ratio CH 4 /(CO 2 +2O 2 )=1 were investigated. The increase in O 2 in the feed gas resulted in a higher conversion of CH 4 , but the apparent conversion of CO 2 passed through a maximum. The CH 4 conversion decreased with increasing space velocity, while during the partial oxidation, because of the hot spots, it would have increased. This means that the coupling can, indeed, control the thermal behavior of the reactor.

Catalytic Activities and Coking Characteristics of Oxides-Supported Ni Catalysts for CH4 Reforming with Carbon Dioxide

Abstract: Catalytic activities and deactivation characteristics of oxides-supported nickel catalysts for the reaction of methane reforming with carbon dioxide were investigated. The dynamic carbon deposition on various nickel catalysts was also studied by a thermogravimetric method. Among the catalysts prepared, Ni/La2O3, Ni/alpha-Al2O3, Ni/SiO2, and Ni/CeO2 showed very high CH4 and CO2 conversions and moderate deactivation whereas Ni/MgO and Ni/TiO2 had lower conversions when the Ni reduction was conducted at 500 degrees C. When Ni/MgO catalyst was reduced at 800 degrees C, it exhibited not only comparable conversions of CH4 and CO2 with other active catalysts but also much longer period of stability without deactivation. The amount of carbon deposited in Ni-based catalysts varied depending on the nature of support and followed the order of Ni/La2O3 > Ni/alpha-Al2O3 > Ni/SiO2 > Ni/MgO > Ni/CeO2 at 700 degrees C. The carbons formed on the catalyst surface showed different structural and chemical properties, and these in turn affected the catalytic activity of the catalysts.