Partial oxidation of methane over nickel-added strontium phosphate

It was found that nickel-added strontium phosphate exhibited high activity and selectivity in partial oxidation of methane. The optimum nickel content could be determined. Over the optimum catalyst, methane conversions and H₂ and CO concentrations in excess of those predicted by the thermodynamic equilibrium were observed. It is believed that the catalytically active species is metallic nickel. This metallic nickel is considered to come from nickel-substituted strontium phosphate under reducing environment, giving highly dispersed nickel metal particles.     

Fuel processor integrated H2S catalytic partial oxidation technology for sulfur removal in fuel cell power plants

H₂S catalytic partial oxidation technology with an activated carbon catalyst was found to be a promising method for the removal of hydrogen sulfide from fuel cell hydrocarbon feedstocks. Three different fuel cell feedstocks were considered for analysis: sour natural gas, sour effluent from a liquid middle distillate fuel processor and a Texaco O₂-blown coal-derived synthesis gas. The H₂S catalytic partial oxidation reaction, its integratability into fuel cell power plants with different hydrocarbon feedstocks and its salient features are discussed. Experimental results indicate that H₂S concentration can be removed down to the part-per-million level in these plants. Additionally, a power law rate expression was developed and reaction kinetics compared to prior literature. The activation energy for this reaction was determined to be 34.4 kJ/g mol with the reaction being first order in H₂S and 0.3 order in O₂.     

Partial oxidation of light paraffins on supported superacid catalytic membranes

Superacid-supported catalytic membranes were found to be active and very selective in the partial oxidation of light paraffins (C₁–C₂) with H₂O₂ under mild conditions (T_R: 80–110°C; P_R: 1.4 bar) in a three-phase catalytic membrane reactor (3PCMR). Among different catalytic membranes investigated, Nafion-based ones showed the best performance in terms of both activity and selectivity. Addition of Fe²⁺ ions in the liquid phase enhances the reaction rate, however, a volcano-shaped trend between reaction rate and concentration of Fe²⁺ was observed. Reaction temperature drastically affects both reaction rate and product distribution. A reaction pathway based on the electrophilic hydroxylation of the C–H bond on superacid sites and subsequent reaction of the activated paraffin with OH radicals has been proposed.     

Partial oxidation of13C-labeled ethylene in methane over Ca/Ni/K catalysts

The relative reactivity of ethane and ethylene compared to methane over the Ca/Ni/K catalyst was determined. The reactivities are in the order of ethylene > ethane methane. The catalyst was also studied using temperature-programmed reaction, desorption and decomposition.     

A review of catalytic partial oxidation of methane to synthesis gas with emphasis on reaction mechanisms over transition metal catalysts

Catalytic partial oxidation of methane has been reviewed with an emphasis on the reaction mechanisms over transition metal catalysts. The thermodynamics and aspects related to heat and mass transport is also evaluated, and an extensive table on research contributions to methane partial oxidation over transition metal catalysts in the literature is provided.Presented are both theoretical and experimental evidence pointing to inherent differences in the reaction mechanism over transition metals. These differences are related to methane dissociation, binding site preferences, the stability of OH surface species, surface residence times of active species and contributions from lattice oxygen atoms and support species.Methane dissociation requires a reduced metal surface, but at elevated temperatures oxides of active species may be reduced by direct interaction with methane or from the reaction with H, H₂, C or CO.The comparison of elementary reaction steps on Pt and Rh illustrates that a key factor to produce hydrogen as a primary product is a high activation energy barrier to the formation of OH. Another essential property for the formation of H₂ and CO as primary products is a low surface coverage of intermediates, such that the probability of O–H, OH–H and CO–O interactions are reduced.The local concentrations of reactants and products change rapidly through the catalyst bed. This influences the reaction mechanisms, but the product composition is typically close to equilibrated at the bed exit temperature.     

Partial oxidation and combined reforming of methane on Ce-promoted catalysts

Pt/ZrO₂ and Pt/Ce_0.14Zr_0.86O₂ catalysts containing 0.5 and 1.5 wt.% Pt were studied in order to evaluate the effect of the support reducibility and metal dispersion on the catalyst stability for the partial oxidation and the combined partial oxidation and CO₂ reforming of methane. The Pt/Ce_0.14Zr_0.86O₂ catalysts proved to be more active, stable and selective than Pt/ZrO₂ catalysts during the partial oxidation reaction. No increase in deactivation was observed when the CH₄:O₂ feed ratio was increased from 2:1 to 4:1. In addition, no water formation was observed at the high CH₄:O₂ ratios. The activity of the catalyst is dependent upon both the dispersion and the ability of the catalyst to resist carbon deposition.

The addition of CO₂ resulted in a decrease in the methane conversion and a decrease in the H₂/CO ratio for the Ce_0.14Zr_0.86O₂ and ZrO₂ supported catalysts. Small increases in the temperature of the bed have been recorded during the partial oxidation reaction. However, within a few minutes the temperature stabilizes below the furnace temperature providing indirect evidence for the combined combustion and reforming mechanisms previously proposed. The 1.5 wt.% Pt/CeZrO₂ catalyst shows promise for the autothermal reforming reaction based on the stability during transient operation.     

Partial oxidation of methane over rhodium catalysts for power generation applications

The partial oxidation of methane (POM) to syngas, i.e. H₂ 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 H₂ 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 H₂-stabilized homogeneous combustion.     

Partial oxidation of methane using a microscale non-equilibrium plasma reactor

A flow-type, microscale, non-equilibrium plasma reactor was developed for partial oxidation of methane without a catalyst. A wide range of oxygen and methane mixtures was directly processed without dilution or explosion at ambient temperature because the microscale plasma reactor removes excess heat generated by partial oxidation, thereby maintaining a reaction field at temperatures near room temperature. Consequently, the least reactive methane was excited by high-energy electrons, whereas successive destruction of reactive oxygenates was minimized simultaneously within the extremely confined environment. A highly reactive and quenching environment is thereby obtained within a single reactor: these are paradoxical conditions in conventional thermochemical processes. A major product among liquid oxygenates was methanol, whose selectivity reached 34% at 30% of methane conversion. Selectivity of oxygenates such as methanol and formaldehyde depends strongly on the fragmentation pattern of methane dissociation by electron impact. Maximum selectivity of oxygenates, which is estimated from numerical simulation of a filamentary microdischarge, reaches 60% when the applied electric field corresponds to the breakdown field of methane (80 Td, 1 Td = 10⁻¹⁷ V cm²). The discharge current increases markedly with an applied electric field, but the selectivity of oxygenates decreases as the field strength increases.     

Complete and partial catalytic oxidation of methane over substrates with enhanced transport properties

The development of improved substrate properties for catalytic combustion has been an area of much interest in recent years. Towards this end, Precision Combustion Inc. has developed novel short channel length, high cell density substrates (trademarked Microlith^®) and high surface area ceramic coatings for them. These substrates avoid substantial boundary layer buildup and greatly enhance heat and mass transfer rates in reactors. The high cell density of these substrates results in high amount of the catalyst per unit of reactor volume. In this paper we examine the performance of these substrates coated with precious metal catalysts for the catalytic combustion and reforming of methane.

Under fuel-lean operating conditions the surface temperature of Pd-based catalyst supported on Microlith^® substrate and the temperature of the gas exiting the reactor remain stable at 800 °C over a wide range of inlet conditions. This is attributed to combination of enhanced transport properties and characteristics of Pd–PdO transformation. Preheating of the gas mixture in the Microlith^® reactor was sufficient to stabilize a downstream premixed flame with NO_x, CO, and UHC emissions in the single digit ppm range.

Microlith^® substrates were also examined for partial oxidation of methane under fuel-rich conditions. The enhanced transport properties of the Microlith^® substrate allowed complete conversion of methane with surface temperature not exceeding material limits at 93% selectivity to partial oxidation products. High flow rate of reactants result in extremely high power densities and syngas output. The catalyst performance was observed to be stable over 500 h of operation.     

Steady-state and dynamic modeling of indirect partial oxidation of methane in a wall-coated microchannel

Steady and dynamic characteristics of catalytic indirect partial oxidation (combined total oxidation and steam reforming) of methane to hydrogen in a wall-coated microchannel are investigated using computational techniques. Steady-state behavior is initially modeled using a two-dimensional axisymmetrical wall-coated reactor model. Considering the small channel diameter, adiabatic operation and negligible transport resistances, response of the microchannel is also investigated using a one-dimensional pseudohomogeneous tubular reactor model. Simulations of the microchannel are carried out using both models for different feed conditions ranging between 1.89 and 2.24 for CH₄/O₂ and 1.17–2.34 for H₂O/CH₄. Outcomes from both models are found to be close, allowing the use of the low-cost one-dimensional model in dynamic simulations. Analysis of transients during the system start-up indicate that steady state is reached between 100 and 120 s depending on the feed composition. Product temperature and flow rates obtained from steady-state and dynamic simulations are found to be close with some differences arising from the finite difference-based numerical method used to solve partial differential equations of the dynamic model. Dynamic responses of the microchannel to several disturbances in the feed are analyzed. The response to a step increase in the inlet oxygen flow rate (decrease of CH₄/O₂ from 2.24 to 1.89) is the elevation of temperature by ca. 100 K, which in turn leads to ca. 33% in hydrogen yield, and the time to reach the new steady state is around 90 s. If the disturbance involves an increase in inlet steam flow, temperature and hydrogen yield decrease in time to a local minimum within 10 s and then gradually increase to the subsequent steady state within 50 s ending up with net reductions of ca. 1.6% and 9%, respectively.     

Partial oxidation of methane to synthesis gas:: Elimination of gas phase oxygen

The reaction between methane and cerium oxide to produce syngas has been studied at 700°C in a pulse apparatus. The cerium oxide was supported on γ-Al₂O₃ and promoted by re-impregnation with Pt or Rh. The promoters drastically enhanced the conversion of methane. TPR with hydrogen shows that Pt and Rh also lowered the temperature necessary to reduce the cerium oxide. Studies of the reaction between methane and promoted cerium oxide showed that the selectivity to syngas depends on the degree of reduction of the cerium oxide. The promoters also led to some carbon formation. Regeneration of the reduced oxide was studied both with oxygen and carbon dioxide.     

Partial oxidation of methane to synthesis gas over iridium–nickel bimetallic catalysts

Partial oxidation of methane to synthesis gas was carried out using supported iridium–nickel bimetallic catalysts, in order to reduce loading levels of iridium and nickel, and to avoid carbon deposition on nickel-based catalysts by adding iridium. The performance of supported iridium–nickel bimetallic catalysts in synthesis gas formation depended strongly upon the support materials. La₂O₃ gave the best performance among the support materials tested. Ir(0.25 wt%)–Ni(0.5 wt%)/La₂O₃ afforded 36% conversion of methane (CH₄/O₂=5) to give CO and H₂ with the selectivities of above 90% at 800°C, and those at 600°C were 25.3% conversion of methane and CO and H₂ selectivities of about 80%, respectively. Reduced monometallic Ir(0.25 wt%)/La₂O₃ and Ni(0.5 wt%)/La₂O₃ catalysts did not produce synthesis gas at 600°C. A higher conversion of methane was obtained by synergistic effects. The product concentrations of CO, H₂, and CO₂, and CH₄ conversion were maintained in high values, even increasing the space velocity of feed gas over Ir–Ni/La₂O₃ catalyst, indicating that rapid reaction takes place. As a by-product, a small amount of carbon deposition was observed, but carbon formation decreased with increasing the space velocity. On the other hand, with reduced monometallic Ni(10 wt%)/La₂O₃ catalyst, yield of synthesis gas and carbon decreased with increasing the space velocity.     

Contributions of heterogeneous and homogeneous chemistry in the catalytic partial oxidation of octane isomers and mixtures on rhodium coated foams

Catalytic partial oxidation experiments with n-octane, 2,2,4-trimethylpentane (i-octane), and an n-octane:i-octane (1:1) mixture were performed on 80 and 45 ppi Rh-coated α-alumina foam supports at 2, 4, and 6 SLPM total flow rate in order to explore the effects of chemical structure for single components and binary mixtures on fuel reactivity and product distribution. When reacted as single components, the conversion of i-octane is greater than n-octane at C/O>1.1 (both fuel conversions are 100% for C/O<1.1). However, when reacted in an equimolar mixture, the conversion of n-octane is greater than i-octane. All three fuels give high selectivity to syngas (H₂ and CO) on 80 ppi supports for C/O<1. For C/O>1, n-octane produces high selectivity to ethylene while i-octane makes i-butylene and almost no ethylene. The fuel mixture produces these species proportional to the mole fractions of n-octane and i-octane within the reacting mixture. Increasing the support pore diameter decreases the selectivity to syngas and increases H₂O and olefin selectivity.The reforming of all three fuels is modeled using detailed chemistry by decoupling the heterogeneous and homogeneous chemistry in a two-zone plug flow model. Detailed homogeneous reaction mechanisms with several thousand elementary reactions steps and several hundred species are used to simulate experimentally observed olefin selectivities for all three fuels on 80 and 45 ppi monoliths at 2, 4, and 6 SLPM quite well. These results support the hypothesis that a majority of the observed olefins are made through gas-phase chemistry.     

硫化铜精矿催化氧化氨浸工艺研究

提出了硫化铜精矿催化氧化氨浸提铜方法。在ＮＨ＋４ 浓度为３００ｇ／Ｌ、氧化剂ＳＮ２２ 浓度为６０ｋｇ／ｔ、催化剂ＡＮ３１ 用量为０－２ｋｇ／ｔ、液固比为５ 的条件下,常温搅拌４ｈ,铜的浸出率可达８０－２５ ％ 。     

Investigation on the structure and the oxidation activity of the solid carbon produced from catalytic decomposition of methane

The structure and the oxidation activity of the solid carbon produced from catalytic decomposition of methane at different temperatures were investigated using TEM, XRD, Raman and TPO techniques. The results show that the graphitization degree of the solid carbon is increased with decomposition reaction temperature. The addition of ethylene or acetylene to methane can change the growth way of the solid carbon and decrease their graphitization degree. The average oxidation temperature of the solid carbon has a close relationship with the corresponding graphitization degree. The addition of ethylene or acetylene to methane can decrease the average oxidation temperature of the solid carbon.     

甲烷部分氧化制甲醇及甲醛

综述了甲烷部分氧化制甲醇及甲醛工艺在催化剂、载体、选择反应条件及氧化反应机理等方面的研究进展。建议研制开发新型的复合型催化剂。     

甲烷部分氧化制合成气反应中床层热点问题研究进展

综述了甲烷部分氧化制合成气反应中催化剂床层热点问题,包括热点产生的原因,热点位置的测定,热点温度的影响因素,以及热点问题的解决方法,对于保护催化剂和反应器,降低反应的危险性起到借鉴作用.     

Selective oxidation of H2S to elemental sulfur over chromium oxide catalysts

CrO_x and CrO_x supported on SiO₂ have been found to be active for the selective oxidation of hydrogen sulfide to elemental sulfur. The catalysts show maximum sulfur yield at a stoichiometric ratio of O₂/H₂S, 0.5. Amorphous Cr₂O₃ exhibits higher yield of sulfur and has stronger resistance against water than supported Cr/SiO₂, especially at low temperatures. At high temperatures above 300°C, the sulfur yield over the supported catalyst becomes similar to amorphous Cr₂O₃ because the Claus reaction occurring on the silica support removes SO₂ to increase the sulfur yield. Active sites are the amorphous monochromate species that can be detected as a strong temperature programmed reduction (TPR) peak at 470°C. Catalytic activity can be correlated with the amount of labile lattice oxygen and the strength of Cr–O bonding. The reaction proceeds via the redox mechanism with participation of lattice oxygen.     

基于Ba-Ce-Co-Fe-O膜反应器的甲烷部分氧化反应研究

为开发稳定性和透氧量俱佳并适用于甲烷部分氧化反应(POM)的透氧膜材料,采用溶胶凝胶工艺合成了具有纯相钙钛矿结构的BaCe0.1Co0.4Fe0.5O3-δ混合导体陶瓷材料。POM操作结果表明:BaCe0.1Co0.4Fe0.5O3-δ膜反应器透氧量高于同类材料,875℃时透氧量达到了8.9 mL/(cm2.m in)。在1 000 h寿命实验中,膜反应器各项反应指标没有出现任何衰减,反应性能稳定,甲烷转化率和CO的选择性都在97%以上。SEM表征表明,反应后膜片表面微观结构的变化虽然不可避免,但是其仍然保持比较完整的结构。因此,该材料良好的透氧量和稳定性说明其具有较好的应用前景。     

Partial oxidation of methane towards hydrogen production over a promising class of catalysts: Rh supported on Ti-modified MgO

The partial oxidation of methane over the supported Rh (0.8 wt.%) catalysts was investigated. Two kinds of supports were used, MgO and Ti-modified MgO (prepared by grafting technique). Among the Ti-modified MgO supports, two different compounds were used as source of Ti: inorganic (chloride) and organic (alkoxide). The catalytic performance of Rh-supported catalysts depends on the support and varies in the sequence: Ti-MgO/I > Ti-MgO/O > MgO. Ti-containing catalysts exhibited higher activity and selectivity compared to MgO, which is especially noticeable at low temperature. Possible explanations for the phenomena observed were proposed on the basis of characterization results.