Catalytic Partial Oxidation Of CH4 Research Articles

Catalytic partial oxidation of CH4 to H2 over cobalt catalysts at moderate temperatures

Catalytic partial oxidation (CPO) of methane has been investigated over Co/Al 2 O 3 catalysts with different metal (0.1 wt.% of Ni, Pt, Rh, Ru or Pd) and oxide (<4 wt.% Fe 3 O 4 /Cr 2 O 3 , La 2 O 3 , SnO 2 or K 2 O) promoters. A comparison with Ni- and Fe-based catalysts was performed. Methane conversions and selectivities were determined in the temperature range 200–750 °C at atmospheric pressure in a continuous fixed-bed quartz reactor. Catalytic partial oxidation (CPO) of methane has been investigated over Co/Al 2 O 3 catalysts with different metal (0.1 wt.% of Ni, Pt, Rh, Ru or Pd) and oxide (<4 wt.% Fe 3 O 4 /Cr 2 O 3 , La 2 O 3 , SnO 2 or K 2 O) promoters. A comparison with Ni- and Fe-based catalysts was performed. Methane conversions and selectivities were determined in the temperature range 200–750 °C at atmospheric pressure in a continuous fixed-bed quartz reactor. The scope was to identify factors for control of product selectivity and investigate the potential of low temperature operation. The unpromoted 10 wt.% Co/Al 2 O 3 catalyst showed stable steady-state performance at 650 °C in the gas hourly space velocity range 15–180 N l CH 4 /g cat h. Equilibrium behaviour was observed during ramping (−1 °C/min) until a sudden extinction occurred around 450 °C, seemingly coinciding with O 2 breakthrough. Addition of 0.1 wt.% metal promoter, particularly Pt and Rh, caused the activity to be maintained to lower temperatures. While Rh maintained H 2 formation, Pt promoted combustion at low temperatures. Addition of 0.1 wt.% Ni by co-impregnation promoted carbon formation and deactivation. Addition of surface oxides typically promoted instability, deactivation and combustion. While the performance of Ni catalysts was superior to Co catalysts at low temperatures, Fe-based catalysts showed combustion activity in the whole temperature range. A hydrogen yield according to equilibrium predictions seems to be the best possible achievement.

Catalytic properties of nanostructured Pt and Ru metal clusters over alumina promoted by CeO 2

0.5%Pt-0.5%Ru/2%Ce/(θ + α)-Al 2O 3, reduced by H 2 at 1173 K, presents a mixture of Pt and Ru (3–30 nm) nanoparticles in reduced and partially oxidised condition surrounded by larger formations of surface compound CeAlO 3 with perovskite structure and oxide Ce 6O 11 (15–80 nm). High conversion of CH 4 and selectivity for CO and H 2 (close to 100%) at short contact times (2.35–8 × 10 −3 s) are observed by using that catalyst in catalytic partial oxidation of CH 4 to synthesis-gas at 1173 K and atmospheric pressure. Methane is activated on Pt and Ru metal clusters while oxygen is activated on Ce oxide nanostructures.

Mechanism of [formula omitted] and CO formation in the catalytic partial oxidation of [formula omitted] on Rh probed by steady-state spatial profiles and spatially resolved transients

Spatially resolved species and temperature profiles have been measured for the catalytic partial oxidation of CH 4 on autothermally operated Rh-coated α - Al 2 O 3 foams in both steady state and transient mode. A probe consisting of a thin quartz capillary and a thermocouple was moved with sub-mm resolution through the catalyst/heat shield stack to sample the gases into a mass spectrometer and measure temperature. The probe was also used to follow the relaxation of the system upon perturbation by stepping the stoichiometry of the reactants periodically. The spatial profiles in steady state show that H 2 and CO are formed in presence of gas phase oxygen (oxidation zone) and after total oxygen conversion by steam reforming (reforming zone). The stepwise change of the reactant stoichiometry in the transient experiments allowed decoupling chemistry (ms timescale) and temperature (s timescale). By exposing a catalyst, initially operating very hot at C / O = 0.6 , suddenly to a CH 4 rich feed ( C / O = 1.4 ) , it was possible to follow how the integral H 2 and CO production rates decrease with decreasing temperature of the catalyst. The reverse switch from C / O = 1.4 to 0.6 showed how the integral H 2 and CO production rates increased with increasing temperature of the catalyst. Differential reaction rates were obtained by performing these transients spatially resolved at two adjacent points in the catalyst. For C / O = 0.6 → 1.4 , H 2 and CO formation show a strict linear Arrhenius behavior over the entire temperature range from ∼ 1100 to ∼ 600 ∘ C . For C / O = 1.4 → 0.6 , the Arrhenius plots show two straight segments, a steep increase in the formation rate from ∼ 630 to ∼ 710 ∘ C and a weak increase from ∼ 725 to ∼ 1000 ∘ C . In both cases, H 2 formation is more activated than CO formation indicating two different rate determining steps.

Syngas by catalytic partial oxidation of methane on rhodium: Mechanistic conclusions from spatially resolved measurements and numerical simulations

The mechanism for the catalytic partial oxidation of CH 4 on Rh-coated α-Al 2O 3 foam monoliths was investigated by measuring species and temperature profiles along the catalyst axis and comparing them with numerical simulations. A thin quartz capillary connected to a quadrupole mass spectrometer was moved through the catalyst with a spatial resolution of ∼0.3 mm. Profiles were measured under autothermal operation for C/O ratios of 0.7, 1.0 and 1.3. The influence of the flow rate (5 vs. 10 l min −1) was studied for syngas stoichiometry (C/O = 1). Numerical simulations were performed with a 38 step surface mechanism using both a porous 2D-model with mass and heat transfer and a simple plug-flow model. The experimental profiles reveal complete O 2 conversion within 2 mm of the catalyst entrance for all C/O ratios and flows. H 2 and CO are formed partly in the oxidation zone and partly after O 2 is fully converted by steam reforming. CO 2 is formed in small amounts in the oxidation zone and remains constant thereafter, except for C/O = 0.7, where some water gas shift is observed. CO 2 reforming does not occur under the experimental conditions. Based on the experimental findings, a two-zone picture of the reaction mechanism is proposed. The 2D numerical simulations and the measured profiles agree qualitatively for all experimental conditions. Quantitative agreement is best for syngas stoichiometry (C/O = 1.0) at 5 and 10 l min −1 flow rate. Some quantitative differences are observed for C/O = 0.7 and 1.3. The plug flow model is for all conditions inferior to the 2D model. The importance of spatial profiles for mechanism and reactor model validation is highlighted.

Comparison among structured and packed-bed reactors for the catalytic partial oxidation of CH 4 at short contact times

Three types of catalyst support (foams, honeycomb monoliths with square channels and spheres with approximately equal values of specific geometric surface a v) were examined and compared by simulation with a 1D, dynamic heterogeneous mathematical model for application to the autothermal partial oxidation of methane. Both cold start-up and steady-state behaviours were investigated. It was found that mass and, particularly, heat transfer properties markedly affect the reactor behaviour, both at start up and at steady state. Thus, the choice of the catalyst support can lead to greatly different reactor performances. Concerning the reactor start-up, simulations revealed that better interphase heat transport properties and lower bed heat capacity are useful to minimize the total start-up time; on the other hand, more favourable transport properties reduce the maximum flow rate which allows to achieve and maintain an ignited steady state. At steady state, oxygen conversion is strictly governed by interphase mass transfer, while methane conversion depends on a more complex, mixed chemical-diffusional regime.

Reaction and oxygen permeation studies in Sm 0.4Ba 0.6Fe 0.8Co 0.2O 3 − δ membrane reactor for partial oxidation of methane to syngas

A disk-type Sm 0.4Ba 0.6Co 0.2Fe 0.8O 3 − δ perovskite-type mixed-conducting membrane was applied to a membrane reactor for the partial oxidation of methane to syngas (CO + H 2). The reaction was carried out using Rh (1 wt%)/MgO catalyst by feeding CH 4 diluted with Ar. While CH 4 conversion increased and CO selectivity slightly decreased with increasing temperature, a high level of CH 4 conversion (90%) and a high selectivity to CO (98%) were observed at 1173 K. The oxygen flux was increased under the conditions for the catalytic partial oxidation of CH 4 compared with that measured when Ar was fed to the permeation side. We investigated the reaction pathways in the membrane reactor using different membrane reactor configurations and different kinds of gas. In the membrane reactor without the catalyst, the oxygen flux was not improved even when CH 4 was fed to the permeation side, whereas the oxygen flux was enhanced when CO or H 2 was fed. It is implied that the oxidation of CO and H 2 with the surface oxygen on the permeation side improves the oxygen flux through the membrane, and that CO 2 and H 2O react with CH 4 by reforming reactions to form syngas.

Pulse study on the partial oxidation of methane over Ni/ θ-Al 2O 3 catalyst

Pulse reactions of CH 4, O 2 and mixed gas (CH 4/O 2=2) over fresh, partially reduced and well reduced Ni/ θ-Al 2O 3 catalysts have been carried out at 923 and 1023 K to study the mechanism of CH 4 activation and the catalytic partial oxidation of CH 4. The fresh catalyst showed high activity for the dissociation of CH 4, and CO rather than CO 2 was the main carbon-containing gaseous product while H 2 being detected for the first CH 4 pulse, suggesting that CH 4 can be partially oxidized to CO and H 2 by the lattice oxygen of NiO. The bond strength of Ni–O seems to be favorable to the partial oxidation of CH 4, which is due to the strong interaction between NiO and θ-Al 2O 3. The results of CH 4/O 2 pulses indicate that both metallic nickel and NiO x ( x<1.0) are active phases for partial oxidation of CH 4. It has been demonstrated that both the reaction temperature and the C/O ratio are critical to the selectivities to CO and CO 2. The mechanisms of the oxidation of CH 4 over fresh and reduced catalysts have been proposed.

Catalytic partial-oxidation of methane on a ceria-supported platinum catalyst for application in fuel cell electric vehicles

Fuel cell developers are investigating the generation of hydrogen from light hydrocarbons, such as methane or natural gas, for fuelling polymer electrolyte fuel cells (PEFCs). This study demonstrates generation of H 2 and CO by catalytic partial-oxidation of CH 4 in air at atmospheric pressure on a ceria-supported platinum catalyst prepared by a novel solution–combustion method where platinum is present in ionically-substituted form. These catalysts at different platinum loadings showed methane conversion and hydrogen selectivity of 90 and 97%, respectively. Interestingly, there is little carbon deposition in the catalytic reactor even after prolonged reaction time.

Partial Oxidation of Methane to Syngas over Calcined Ni–Mg/Al Layered Double Hydroxides

The catalytic partial oxidation of CH4 to syngas was carried out over an Ni–Mg/Al mixed-oxide catalyst prepared from layered double hydroxide-type precursors. The catalysts were characterized by XRD, TPR, UV-DRS, XRF, BET and CHNS analysis. The effects of the catalyst composition and the calcination temperature on the catalytic performance and the extent of catalyst deactivation were investigated. Ni–Mg/Al oxide catalysts converted CH4 into syngas efficiently with high selectivity. The catalyst performance was strongly related to the Ni particle size and the calcination temperature. The catalysts that were calcined at higher temperature exhibited a better catalytic performance. In conclusion, the NiAl2O4 spinel phase had a positive effect on the stability of the catalyst.

Partial oxidation of methane into syngas with oxygen permeating ceramic membrane reactors

Partial oxidation of methane (CH4 +1/2O2 ⇌ CO + 2H2) is considered as an alternative reforming reaction to steam reforming for production of syngas. This reaction is a slightly exothermic reaction and produces syngas of H2/CO = 2, which is suitable for the synthesis of hydrocarbon or methanol. In this paper, the catalytic partial oxidation of CH4 with a membrane reactor using oxygen permeating ceramic, in particular, LaGaO3-based oxide, is reported. Supported Ni or Rh catalysts are active and selective for this reaction. On the other hand, a mixed ionic and electronic conducting (MIEC) ceramic membrane is useful for obtaining pure oxygen from air when the gradient in oxygen partial pressure is obtained. As for a MIEC membrane, mixed electronic–oxide ionic conductors of Fe- or Co-based perovskite oxides are widely investigated. However, the improvement in stability in a reducing atmosphere is critically required for the MIEC membrane for the application to the membrane reactor for CH4 partial oxidation. Perovskite oxides of LaGaO3 doped with Sr for a La site and a Fe, Co, or Ni for a Ga site, respectively, are promising as the oxygen-separating membrane for CH4 partial oxidation because of high stability in a reducing atmosphere as well as high permeability of oxygen. The partial oxidation of CH4 with solid oxide fuel cells (SOFCs) is also described. Simultaneous generation of electrical power and syngas is demonstrated by the fabricated fuel cell type reactor using a LaGaO3-based oxide electrolyte.

98/04320 Simulation of dynamic technical systems for gas utilisations

Fuel cell developers are investigating the generation of hydrogen from light hydrocarbons, such as methane or natural gas, for fuelling polymer electrolyte fuel cells (PEFCs). This study demonstrates generation of H2 and CO by catalytic partial-oxidation of CH4 in air at atmospheric pressure on a ceria-supported platinum catalyst prepared by a novel solution–combustion method where platinum is present in ionically-substituted form. These catalysts at different platinum loadings showed methane conversion and hydrogen selectivity of 90 and 97%, respectively. Interestingly, there is little carbon deposition in the catalytic reactor even after prolonged reaction time.

98/04326 System for continuous in-situ measurement of carbon in fly ash

Fuel cell developers are investigating the generation of hydrogen from light hydrocarbons, such as methane or natural gas, for fuelling polymer electrolyte fuel cells (PEFCs). This study demonstrates generation of H2 and CO by catalytic partial-oxidation of CH4 in air at atmospheric pressure on a ceria-supported platinum catalyst prepared by a novel solution–combustion method where platinum is present in ionically-substituted form. These catalysts at different platinum loadings showed methane conversion and hydrogen selectivity of 90 and 97%, respectively. Interestingly, there is little carbon deposition in the catalytic reactor even after prolonged reaction time.

A Sustainable Catalyst for the Partial Oxidation of Methane to Syngas: Ni/Ca1‐xSrxTiO3, Prepared In Situ from Perovskite Precursors

High activity and negligible coke formation in the course of the catalytic partial oxidation of CH4 to syngas are characteristics of the Ni/Ca4‐xSrxTiO3 catalyst, which is readily accessible by the citrate method from nickel nitrate, alkaline earth metal carbonates, and tetraisopropoxidotitanium. The properties and efficiency of the catalyst are normally only associated with catalysts that contain considerably more expensive metals such as Rh, Ir, and Ru.

Partial oxidation of methane to carbon monoxide and hydrogen over NiO/La 2O 3/γ-Al 2O 3 catalyst

The production of H 2 and CO by catalytic partial oxidation of CH 4 at atmospheric pressure has been examined over NiO γ- Al 2O 3 and NiO/La 2O 3/γ-Al 2O 3 catalysts. When NiO loading increased to 17.5 wt.-%, the syngas production over NiO γ- Al 2O 3 is found to increase consistently. In that case, the addition of La 2O 3 can improve the catalytic activity significantly, with a NiO content of more than 17.5 wt.-%, a very small extent of change in the catalytic activity and the selectivity for the methane oxidation to syngas as well as a little effect of La 2O 3 on the activity and the selectivity are observed. Under the condition of high space velocity, the CO 2 and H 2O reforming of CH 4 occurs to a very small extent over reduced 12.5 wt.-% NiO/0.5 wt.-% La 2O 3 γ- Al 2O 3 catalyst. This fact and the results of the effect of space velocity on the methane partial oxidation to syngas suggest that both H 2, CO and CO 2, H 2O are the primary products of the methane oxidation. The results of characterizing 12.5 wt.-% NiO/0.5 wt.-% La 2O 3 γ- Al 2O 3 catalyst reveal that the active form of catalyst is metallic Ni and the promoter La 2O 3 facilitate the reduction of the oxidative nickel.

Synthesis gas formation by catalytic oxidation of methane in fluidized bed reactors

The production of synthesis gas (CO + H 2) by the catalytic partial oxidation of CH 4 in air or O 2 in static fluidized beds at atmospheric pressure has been examined over Pt, Rh, and Ni catalysts coated on 100-μm α-Al 2O 3 beads. With CH 4/air feeds, CO and H 2 selectivities as high as 95% with >90% CH 4 conversion were obtained on Rh and Ni catalysts at contact times of 0.1–0.5 sec. Pt catalysts were found to have significantly lower selectivities and conversions, which may be due to more H 2O forming reactions or the slow steam reforming behavior of Pt. The optimal selectivities for all the three catalysts were improved by heating the reaction mixture above the autothermal reactor temperature and using O 2 instead of air. The selectivities and conversions were fairly constant over the range of contact times used. Probable reaction pathways for CH 4 oxidation in fluidized beds are discussed.

Synthesis gas formation by direct oxidation of methane over Rh monoliths

The production of H2 and CO by catalytic partial oxidation of CH4 in air or O2 at atmospheric pressure has been examined over Rh-coated monoliths at residence times between 10−4 and 10−2 s and compared to previously reported results for Pt-coated monoliths. Using O2, selectivities for H2 ( $$S_{H_2 }$$ ) as high as 90% and CO selectivities (S CO) of 96% can be obtained with Rh catalysts. With room temperature feeds using air, Rh catalysts give $$S_{H_2 }$$ of about 70% compared to only about 40% for Pt catalysts. The optimal selectivities for either Pt or Rh can be improved by increasing the adiabatic reaction temperature by preheating the reactant gases or using O2 instead of air. The superiority of Rh over Pt for H2 generation can be explained by a methane pyrolysis surface reaction mechanism of oxidation at high temperatures on these noble metals. Because of the higher activation energy for OH formation on Rh (20 kcal/mol) than on Pt (2.5 kcal/mol), H adatoms are more likely to combine and desorb as H2 than on Pt, on which the O+ H→ OH reaction is much faster.

Synthesis gas formation by direct oxidation of methane over Pt monoliths

The production of H 2 and CO by catalytic partial oxidation of CH 4 in air at atmospheric pressure has been examined over Pt and Pt-Rh coated monoliths at residence times between 10 −4 and 1 −2 sec. With these short contact times, the direct oxidation reaction can be studied independent of reforming reactions. We observe high conversions to H 2 and CO, which strongly suggests that the primary surface reaction is methane pyrolysis, CH 4 → C + 4H, from which H 2 desorbs and C is oxidized to CO. With room-temperature feeds using air, the optimal feed composition for H 2 and CO occurs between 15 and 20% CH 4 with optimal selectivities of up to S H 2 ≈ 0.5 and S co ≈ 0.95 at 80% conversion of the CH 4 at ≈100°C. Increasing the adiabatic reaction temperature by preheating the reactant gases or by using O 2 instead of air improves S H 2 to as much as 0.7 for a Pt catalyst and shifts the optimal feed composition toward the stoichiometric feed composition for H 2 and CO production. By examining several catalyst configurations, including Pt-10% Rh woven gauzes and Pt-coated ceramic foam and extruded monoliths, several reaction and reactor variables in producing H 2 and CO have been examined. These experiments show that the selectivity is improved by operating at higher gas and catalyst temperatures, by maintaining high rates of mass transfer through the boundary layer at the catalyst surface, and by using catalysts with high metal loadings. At flow rates high enough to minimize mass-transfer limitations, the gauze, foam monoliths, and extruded monoliths all give similar selectivities and conversions, but with important differences resulting from different catalyst geometries and thermal conductivities.