Showing papers on "Partial oxidation published in 1992"

Role of oxygen in selective reduction of nitrogen monoxide by propane over zeolite and alumina-based catalysts

Abstract: The role of coexisting oxygen in the selective reduction of nitrogen monoxide by propane on H-zeolites, alumina, Cu-ZSM-5 zeolite and Pt/Al2O3 catalysts was investigated. In the case of H-zeolites and alumina, oxidation of NO to NO2 played an important role for the overall selective reduction of NO. On the other hand, the initial reaction step was considered to be partial oxidation of propane over Cu-ZSM-5 and Pt/Al2O3.

Physical and chemical characterization of surface vanadium oxide supported on titania : influence of the titania phase (anatase, rutile, brookite and B)

Abstract: Different phases of titania were prepared and used to support ca. 1 wt.-% V 2 O 5 . The different titania phases prepared were: anatase (A22), rutile (R28), brookite (BT110) and B-phase (B18). Physical characterization of the various vanadia-titania catalysts was performed using X-ray photoelectron spectroscopy (XPS), in situ Raman and 51 V solid state nuclear magnetic resonance (NMR) spectroscopy. The XPS results reveal that the all the catalysts contain various levels of impurities. In situ dehydration Raman shows, for all the samples, the stretching vibration of the terminal VzO bond at ca. 1030 cm −1 . Solid state 51 V NMR spectra of all the samples in the dehydrated state show basically the same powder pattern with a peak maximum around −660 to −670 ppm. The combined Raman and NMR results indicate that the same surface vanadium oxide species is present on all the titania supports irrespective of the crystal structure of the bulk titania phase. Partial oxidation of methanol show similar activity and selectivity for the various vanadia-titania catalysts. The reaction selectivity was primarily to formaldehyde and methyl formate (92–96%). The turnover number for methanol oxidation was essentially the same for all the vanadia-titania catalysts and ranged from 1.4 to 2.8 s −1 . These results indicate that the type of titania phase used as the support is not critical for partial oxidation over vanadia-titania catalysts as long as other parameters (e.g. surface impurities ) are similar. Thus, the structure-reactivity studies of the different vanadia-titania catalysts suggest that the specific titania phase is not a critical parameter in determining the physical or chemical nature of the surface vanadia phase.

Low temperature oxidative conversion of methane to syngas over NiO-CaO catalyst

Abstract: Catalytic partial oxidation of methane over NiO-CaO (with or without its prereduction by H2) at low temperatures (⩽ 973 K) under non-equilibrium conditions yields syngas (H2/CO ratio ≈ 2.0) with high conversion/selectivity and extremely high productivity. If required, the H2/CO ratio can be increased by adding water vapour to the feed. Product selectivity is controlled by the process kinetics and also the reaction path is different from that observed for the high-temperature non-catalytic and catalytic processes operating at equilibrium.

Catalytic partial oxidation of methane over a monolith supported catalyst

Abstract: The catalytic partial oxidation of methane over a monolithic supported catalyst to produce synthesis gas was investigated in pilot plant experiments conducted at commercially feasible operating conditions. It was demonstrated that, with air as the oxidant, an equilibrium synthesis gas could be produced at very high space velocity. Measured axial composition and temperature profiles provided some evidence that the oxidation step was a near total oxidation step producing carbon monoxide, carbon dioxide, and water. No carbon was found on the catalyst under the conditions investigated, and the process condensate was clean.

Role of F centers in the oxidative coupling of methane to ethane over lithium-promoted magnesium oxide catalysts

Abstract: We report a study of the partial oxidation of methane to ethane over a model MgO catalyst prepared under well-controlled, ultrahigh vacuum (UHV) conditions using a combination of surface science techniques and elevated pressure kinetics measurements.

Light Emission from Microcrystalline Si Confined in SiO2 Matrix through Partial Oxidation of Anodized Porous Silicon

Abstract: Optical properties of microcrystalline Si embedded in a SiO2 matrix through a partial oxidation of anodized porous silicon using a wet process have been studied. Thick (~30 µm) films thus obtained were dark red to light yellow in color, depending on the oxidation condition. The fundamental edge of the absorption spectra shifted to the higher energy side with increasing oxide fractions in the colored specimen. Visible light emissions from these specimens were observed at room temperature with photoexcitations using a He-Cd laser. All of the data, including the broadening effect in X-ray diffraction peaks, can be explained in terms of the size reduction effect of the Si islands confined in the SiO2 matrix.

Process for the transformation of vanadium/phosphorus mixed oxide catalyst precursors into active catalysts for the production of maleic anhydride

Abstract: Vanadium/phosphorus mixed oxide catalysts comprising vanadyl pyrophosphate, optionally containing a promoter component, are transformed from vanadium/phosphorus mixed oxide catalyst precursors comprising vanadyl hydrogen phosphate, optionally containing a promoter component, by subjecting the catalyst precursors to elevated temperatures in three stages: (a) an initial heat-up stage in an atmosphere selected from the group consisting of air, steam, an inert gas, and mixtures thereof, (b) a rapid heat-up stage at a programmed heat-up rate in a molecular oxygen/steam-containing atmosphere, and (c) a maintenance/finishing stage, first in a molecular oxygen/steam-containing atmosphere, and thereafter in a nonoxidizing, steam-containing atmosphere. Such catalysts are useful for the production of maleic anhydride via the partial oxidation of nonaromatic hydrocarbons, particularly n-butane, in the vapor phase with molecular oxygen or a molecular oxygen-containing gas.

Synthesis gas production

Abstract: Synthesis gas production comprising primary catalytic steam reforming (20) a first stream (c) of desulphurised hydrocarbon feedstock, optionally followed by secondary reforming using an oxygen-containing gas, and then cooling; adiabatically low temperature steam reforming (76) a second stream (u) of the feedstock, preferably adding a hydrogen-containing gas (v), and then subjecting the product to partial oxidation (82) with an oxygen-containing gas, and then cooling; and mixing the cooled products. For methanol production, the partial oxidation step pressure may be greater than the primary reforming pressure, and the hydrogen-containing gas is taken from the methanol synthesis loop: if the partial oxidation step is non-catalytic and in the absence of steam, the pre-reforming stage can be omitted. Methanol can be synthesised from the reformed first and/or second streams in an auxiliary synthesis stage at an intermediate pressure before the relevant stream is added to the synthesis loop.

Selective reduction of nitrogen oxides under oxidising exhaust-gas conditions

Abstract: Temperature-programmed reaction traces for Cu/ZSM-5 heated under an oxidising exhaust-gas are not consistent with the hydrocarbon acting as a direct reductant of NO Steady-state kinetic studies eliminate another possible mechanism (catalytic decomposition of NO), but reveal a near first order dependence of NO conversion on propene partial pressure The results are reconciled by a surface mechanism in which the hydrocarbon generates a reactive intermediate capable of reducing NO, but which itself can be depleted by oxidation This intermediate may be a partial oxidation product of the hydrocarbon, or deposited coke; it does not appear to be CO

Partial oxidation of hydrocarbons and oxygenated compounds on perovskite oxides

Abstract: Research of perovskite oxide catalysts (AB03) with a rare-earth ion as an A-site and a transition metal ion as a B-site has been concentrated on the complete oxidation of hydrocarbons, particularly related to exhaust control, and revealed that they are potential catalysts for deep combustion of hydrocarbons (1). The complete oxidation activities have been reported to be mainly controlled by the physicochemical property of the B-site metal cations such as the electronic configuration of d-electron (2), the binding energy of B-0 bond (3) and the stabilization energy of the crystal field (4), rather than the relatively small and less important effect of the rare-earth ion of the A-site (5) and also improved by the substitution of other metal cations for A- or B-site (6,7). Although it is difficult to find many investigations on the application of perovskite-type oxides to partial oxidation, in this chapter, the movement to the partial oxidation of hydrocarbons and oxygenated compounds using various ...

Calorimetric study of vanadium pentoxide catalysts used in the reaction of ethane oxidative dehydrogenation

Abstract: Vanadium pentoxide catalysts have been studied in the partial oxidation reaction of ethane in the 723-843 K temperature range. The relationship between the acid-base properties and the catalytic behavior was investigated. The number and character of acidic sites of V{sub 2}O{sub 5} catalysts were determined by studying the adsorption of a basic molecule using microcalorimetry. The reducibility level and the evolution of the surface state, as well as the heat evolved, were studied by using a pulse method with pure ethane only. The reaction of ethane oxidative dehydrogenation was studied by a continuous flow method and the activation energies for the formation of C{sub 2}H{sub 4} and CO were calculated. The selectivity of the catalyst was interpreted in connection with the acid-base properties. The strong sites were observed to decrease rapidly with time on stream, although the catalysts were still active. Temperature-programmed reduction of V{sub 2}O{sub 5} using a TG-DSC coupling was also investigated with hydrogen, ethylene, or ethane as reducers. The different heats of reduction are given. It was observed that C{sub 2}H{sub 4} is a much more efficient reducing agent than H{sub 2} and C{sub 2}H{sub 6}. Following each reduction, reoxidation studies by oxygen were performed in the more » same equipment showing clearly different step in the reoxidation process. 20 refs., 8 figs., 1 tab. « less

Selective oxidation of methane with air over silica catalysts

Abstract: Partial oxidation of methane by oxygen to form formaldehyde, carbon oxides, and C2 products (ethane and ethene) has been studied over silica catalyst supports (fumed Cabosil and Grace 636 silica gel) in the 630–780 °C temperature range under ambient pressure. The silica catalysts exhibit high space time yields (at low conversions) for methane partial oxidation to formaldehyde, and the C2 hydrocarbons were found to be parallel products with formaldehyde. Short residence times enhanced both the C2 hydrocarbons and formaldehyde selectivities over the carbon oxides even within the differential reactor regime at 780 °C. This suggests that the formaldehyde did not originate from methyl radicals, but rather from methoxy complexes formed upon the direct chemisorption of methane at the silica surface at high temperature. Very high formaldehyde space time yields (e.g., 812 g/kg cat h at the gas hourly space velocity = 560 000 l(NTP)/kg cat h) could be obtained over the silica gel catalyst at 780 °C with a methane/air mixture of 1.5/1. These yields greatly surpass those reported for silicas earlier, as well as those over many other catalysts. Low CO2 yields were observed under these reaction conditions, and the selectivities to formaldehyde and C2 hydrocarbons were 28.0 and 38.8%, respectively, at a methane conversion of 0.7%. A reaction mechanism was proposed for the methane activation over the silica surface based on the present studies, which can explain the product distribution patterns (specifically the parallel formation of formaldehyde and C2 hydrocarbons).

Partial oxidation of methane: the role of surface reactions

Abstract: The gas-phase partial oxidation of methane with molecular oxygen, to methanol and formaldehyde, has been studied in a flow reactor at 2 MPa and 400-650°C. The influence of reactor surface area on the reaction was examined both experimentally and by using the model developed by Bedeneev et al. Increasing the surface to volume ratio in a quartz-lined reactor was found to significantly decrease both the reaction rate and the selectivity to methanol. Under favorable conditions, combined methanol/formaldehyde selectivities of over 60% were obtained, although at methane conversions of below 1%. The implications of these results for both previous and future work are discussed

Direct partial oxidation of benzene to phenol on zeolite catalysts

Abstract: The partial oxidation of benzene to phenol at 330°C over various silica/alumina zeolite catalysts, using nitrous oxide as the oxidising agent, has been studied. An initial phenol yield of around 28% (based on benzene converted) was obtained over the protic form of ZSM-5 type zeolites, although this decreased to about 16% over a period of 24 h: no phenol at all was detected over Na-ZSM-5. An amorphous silica/alumina, and EU-1 type zeolites were also tested and were found to be much less active than the H-ZSM-5 materials. It is concluded that a zeolite possessing both Bronsted acidity and a particular internal structure is required to produce active and selective catalysts.

Conversion of methane to methanol by catalytic supercritical water oxidation

Abstract: Selective conversion of methane to methanol has been accomplished by catalytic partial oxidation over Cr2O3 in supercritical water (SCW). The presence of water in high concentration inhibits the methane conversion but promotes the yield of methanol. The methane oxidation reaction was observed to be slightly negative order in oxygen concentration; increasing oxygen concentration produced a small decrease in methane conversion. Methanol oxidation was positive order in oxygen concentration; thus, increasing oxygen concentration dramatically reduced the yield of methanol. A consistent set of reaction pathways are developed and rate constants, which accurately model the experimental results, are calculated.

Steam reforming analyzed

Abstract: This paper reports that maximum steam reformer operation without excessive coking reactions requires careful control of thermodynamic and kinetic conditions. Regardless of the syngas-based feedstock composition, carbon formation problems can be avoided while increasing reformer CO or H{sub 2} production. Steam reforming technology is best understood via: Primary steam reformer developments, Kinetics of methane steam reforming, Simulation of an industrial steam/CO{sub 2} reformer, Example conditions (steam/CO{sub 2} reforming), Thermodynamic approach (minimum to steam ratio). Hydrogen and carbon monoxide are two of the most important building blocks in the chemical industry. Hydrogen is mainly used in ammonia and methanol synthesis and petroleum refining. Carbon monoxide is used to produce pains, plastics, foams, pesticides and insecticides, to name a few. Production of H{sub 2} and CO is usually carried out by the following processes: Steam reforming (primary and secondary) of hydrocarbons, Partial oxidation of hydrocarbons, Coal gasification. Coal gasification and partial oxidation do not use catalysts and depend on partial combustion of the feedstock to internally supply reaction heat. Secondary (autothermal) reforming is a type of steam reforming that also uses the heat of partial combustion but afterwards uses a catalyst of promote the production of hydrogen and CO.

Deep oxidation of hydrocarbons

Abstract: The activity of two commercial oxidation catalysts was investigated for the oxidation of a humidified air stream containing 500 ppm of a mixture of C5 to C9 hydrocarbons over an extended period of time (ten months). The composition of the feed stream was similar to that obtained from air-strippers used for groundwater clean-up. The reaction was conducted continuously in fixed bed reactors at constant total conversion (> 99%). The temperature was increased, when needed, to compensate for the catalyst deactivation and maintain a constant conversion. A 0.1% Pt/3% Ni/Al2O3 catalyst (G-43A, United Catalysts, Inc., Louisville, KY) did not lose any activity at 430 ° C when used continuously for 253 days-on-stream. On the other hand, a ceria-promoted hopcalite catalyst suffered considerable deactivation and required a temperature increase of 85° C over 297 days-on-stream to maintain the total conversion above 99%. However, the final temperature (400 ° C) required to maintain > 99% conversion over the hopcalite catalyst was still lower than the initial temperature required for the operation of the Pt/Ni catalyst (430° C). No partial oxidation products were formed over either of the catalysts. Also, the only total carbon oxidation product was carbon dioxide. A simple first order deactivation model fits the time-temperature relationship over the hopcalite catalyst and predicts a hopcalite catalyst lifetime of 362 days for a maximum operating temperature of 500° C.