Showing papers on "Partial oxidation published in 1998"

Propylene Oxidation on Copper Oxide Surfaces: Electronic and Geometric Contributions to Reactivity and Selectivity

Abstract: Cu2O is an efficient catalyst in the partial oxidation of propylene to acrolein, while propylene oxidation on CuO leads to complete combustion. The interaction of propylene at elevated temperature (>300 K) and elevated pressure (5 Torr) with cuprous and cupric oxide has been investigated with core level XPS, resonant photoemission, and temperature-programmed desorption. Reduction of the copper oxide surfaces was examined as a function of temperature and revealed that cupric oxide has a greater reactivity toward propylene oxidation than cuprous oxide (Ea = 5.9 versus 11.5 kcal/mol for cuprous oxide (24.7 and 48.1 kJ/mol)). This variable temperature oxidation of propylene was also monitored via core level and resonant photoemission and was found to occur by a similar mechanism on both surfaces. Reaction at lower temperature produces a surface intermediate which exhibits carbon 1s XPS peaks at 284.0 and 285.5 eV binding energy in a 2:1 intensity ratio. This is consistent with an allyl alkoxide surface specie...

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.

Partial oxidation of methanol over supported palladium catalysts

Abstract: Hydrogen production by partial oxidation of methanol (CH 3 OH+1/2 O 2 ⇄2 H 2 +CO 2 ) was studied over ZnO- and ZrO 2 -supported Pd catalysts. Catalyst performance was investigated under feed ratios O 2 /CH 3 OH (molar) of 0.3 and 0.5 at 503–543 K. Irrespective of the large difference in BET area of Pd/ZnO and Pd/ZrO 2 catalysts, significant differences were observed when comparing H 2 selectivities. For the 1% Pd/ZnO catalyst, reaction occurs through consecutive oxidation → reforming steps. However, the behavior of catalyst 1% Pd/ZrO 2 approached that expected for Group 8 metals, that is, although the oxidation products are observed as for the catalyst 1% Pd/ZnO, the decomposition reaction seems to occur to a greater extent. Catalyst characterization by TPR, X-ray diffraction and XPS revealed that PdZn alloys can be formed upon reduction of Pd/ZnO catalysts at moderate temperatures.

Selective oxidation of propylene over gold deposited on titanium-based oxides

Abstract: Gold supported on titanium-based metal oxides can assist the selective partial oxidation of propylene at temperatures from 313 K to 573 K in a gas containing both H2 and O2 The preparation method was found to be crucial in controlling the selectivities In general, impregnation and chemical vapor deposition methods do not produce selective catalysts Only the deposition-precipitation method makes gold selective to propylene oxide or propanal, suggesting that a strong contact between the gold particles and the titanium ion sites on the support is important The effect of changing the support was also dramatic; the use of the anatase form of TiO2 and Ti-MCM-41 results in propylene oxide production, while the rutile structure of TiO2 caused complete oxidation to CO2 Microporous crystalline titanium silicates such as TS-1, TS-2, and Ti-β zeolite make gold relatively selective to propanal and of the three TS-1 gives the highest selectivity These results indicate that the oxidation of propylene in the copresence of H2 must involve the surface of the supports and that the reaction takes place at the interface perimeter around the gold particles

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.

Catalytic hydrodesulfurization of dibenzothiophene through partial oxidation and a water-gas shift reaction in supercritical water

Abstract: We conducted a comparative study of catalytic hydrodesulfurization of dibenzothiophene (DBT) with NiMo/Al2O3 at 673 K and 30 MPa, in various atmospheres (H2−SCW, CO−SCW, CO2−H2−SCW, and HCOOH−SCW), using a tube bomb reactor Higher conversion of DBT was obtained in CO−SCW, CO2−H2−SCW, and HCOOH−SCW than in H2−SCW These results clearly indicate that a water−gas shift reaction in supercritical water (SCW) produces species which can hydrogenate DBT more effectively than H2 gas We also conducted another experiment for the partial oxidation of a DBT−hexylbenzene mixture in SCW Even in the presence of oxygen, effective hydrogenation of DBT took place This result is probably because CO forms through the partial oxidation of hexylbenzene and converts to the hydrogenating species through a water−gas shift reaction We think the catalytic desulfurization of heavy oils in SCW will be a promising new technology, since even by introducing oxygen or air instead of hydrogen, an excellent hydrogenating atmosphere can

Partial oxidation of methane to methanol with oxygen or air in a nonequilibrium discharge plasma

Abstract: The partial oxidation of methane to methanol with oxygen or air was investigated experimentally and theoretically in a dielectric-barrier discharge (DBD). The predominant parameters of specific electric energy, oxygen content, flow rate, temperature, and gas pressure were determined in CH 4 /O 2 and CH 4 /air mixtures. Optimum selectivities toward methanol formation were found at an oxygen concentration of about 15% in both feed gas mixtures. Low specific energy favors the selectivity toward methanol and suppresses the formation of carbon oxides. The experiments indicate that high methanol selectivities can be obtained at high methane conversion. The highest methanol yield of 3% and the highest methanol selectivity of about 30% were achieved in CH 4 /O 2 mixtures. In CH 4 /air mixtures, as high as 2% methanol yield was also obtained. In addition, other useful products, like ethylene, ethane, propane, and ethanol, were detected. Experiment and numerical simulations show that the formation of H 2 O and CO has a strong negative influence on methanol formation.

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.

New sulfonated engineering polymers via the metalation route. II. Sulfinated/sulfonated poly(ether sulfone) PSU Udel and its crosslinking

Abstract: New mixed sulfinated/sulfonated polysulfone PSU Udel has been produced by partial oxidation of sulfinated PSU with NaOCl. From the mixed sulfinated/sulfonated PSU, thin crosslinked polymer films have been produced by S-alkylation of the residual sulfinate groups with α,ω-diiodoalkanes having 4–10 (CH2) units. The advantages of the partial oxidation process using NaOCl are as follows: (1) The desired oxidation degree can be adjusted finely. (2) No side reactions take place during oxidation. (3) The partially oxidized polymers is stable at ambient temperature. By variation of the oxidation degree of the sulfinated/sulfonated prepolymer and by variation of the chain length of the diiodo crosslinker, crosslinked membranes with a large range of properties in terms of ionic conductivity, swelling, and permselectivity have been produced. The partially oxidized polymers have been characterized by redox titration, 1H-NMR, and FTIR. The crosslinked membranes have been characterized in terms of ionic conductivity (resistance), permselectivity, and swelling in dependence on ion-exchange capacity and oxidation degree of the prepolymers. In addition, the thermal stabilities of the membranes have been determined by TGA, and FTIR spectra have been recorded on the crosslinked films. Selected membranes show low ionic resistances, low swelling, and good temperature stability which makes them promising candidates for application in (electro)membrane processes. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1441–1448, 1998

Catalytic partial oxidation reforming of hydrocarbon fuels.

Abstract: The polymer electrolyte fuel cell (PEFC) is the primary candidate as the power source for light-duty transportation systems. On-board conversion of fuels (reforming) to supply the required hydrogen has the potential to provide the driving range that is typical of today's automobiles. Petroleum-derived fuels, gasoline or some distillate similar to it, are attractive because of their existing production, distribution, and retailing infrastructure. The fuel may be either petroleum-derived or other alternative fuels such as methanol, ethanol, natural gas, etc. [1]. The ability to use a variety of fuels is also attractive for stationary distributed power generation [2], such as in buildings, or for portable power in remote locations. Argonne National Laboratory has developed a catalytic reactor based on partial oxidation reforming that is suitable for use in light-duty vehicles powered by fuel cells. The reactor has shown the ability to convert a wide variety of fuels to a hydrogen-rich gas at less than 800 C, temperatures that are several hundreds of degrees lower than alternative noncatalytic processes. The fuel may be methanol, ethanol, natural gas, or petroleum-derived fuels that are blends of various hydrocarbons such as paraffins, olefins, aromatics, etc., as in gasoline. This paper will discuss the results obtainedmore » from a bench-scale (3-kWe) reactor., where the reforming of gasoline and natural gas generated a product gas that contained 38% and 42% hydrogen on a dry basis at the reformer exit, respectively.« less

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 reduction system of NOx in exhaust gases from diesel engines with secondary fuel injection

Abstract: Catalytic NOx reduction system with secondary fuel injection was studied not only in a laboratory scale, but also in a large bench scale. Diesel fuel was injected before the catalyst bed, and the activity and durability of the catalyst for the NOx reduction were tested. Using the fuel as a reductant, silver aluminate supported on alumina was selected as the most active and suitable catalyst. The resistance of the silver aluminate catalyst to SOx was enhanced by the addition of a small amount of WO3, MoO3 and Pt. It was found from the engine bench test that NOx conversion increased in proportion to the amount of aldehydes formed from the injected fuel in the exhaust gas. Thus, the secondary fuel injection into exhaust gas through a partial oxidation catalyst enhanced the NOx conversion. At 450°C, the engine bench test exhibited maximum NOx conversion of 75% and 45% at the SV of 15 000 and 70 000 h−1, respectively.

Gas-Phase Photooxidation of Trichloroethylene on TiO2 and ZnO: Influence of Trichloroethylene Pressure, Oxygen Pressure, and the Photocatalyst Surface on the Product Distribution

Abstract: Transmission Fourier transform infrared spectroscopy has been used to identify gas-phase and surface-bound products and intermediates formed during the gas-phase photooxidation of trichloroethylene (TCE) on TiO2 and ZnO. Several factors are found to influence the gas-phase product distribution for this reaction. On clean TiO2 and ZnO surfaces and at high TCE and O2 pressures, gas-phase CO, CO2, COCl2, CCl2HCOCl, CHCl3, C2HCl5, and HCl are produced, whereas at low TCE and O2 pressures, TCE is converted to gas-phase CO and CO2 only. In addition to TCE and O2 pressure, the product distribution of the photooxidation of TCE is strongly dependent upon the coverage of adsorbed species on the surface of the photocatalyst. It is shown here that the complete oxidation of adsorbed TCE can occur on clean photocatalytic surfaces whereas only partial oxidation of adsorbed TCE occurs on adsorbate-covered surfaces. The role of adsorbed surface products in TCE photooxidation is discussed.