Activity For Partial Oxidation Research Articles

Methane oxidation over nanocrystalline Ce0.45Zr0.45La0.10O2-δ/Pt and Ce0.9Sm0.1O2-δ/Pt anodes

The electrocatalytic activity of composite anodes, comprising metallic platinum and nanocrystalline Pt-modified Ce0.45Zr0.45La0.10O2-δ and Ce0.9Sm0.1O2-δ , was evaluated for the oxidation of dry methane in a solid oxide fuel cell (SOFC) – type reactor with yttria-stabilized zirconia solid electrolyte. At 923–1073 K, the total combustion is dominant, whilst above 1100 K the composite anodes exhibit significant catalytic activity towards the partial oxidation of methane (POM). At 1223 K and for a O2:CH4 ratio equal to 0.5, stoichiometric for the POM reaction, CO selectivity and CH4 conversion over Ce0.9Sm0.1O2-δ /Pt achieves 55% and 41%, respectively. Under these conditions, Ce0.45Zr0.45La0.10O2-δ /Pt anodes possess higher catalytic activity for partial oxidation, associated with the lower lattice oxygen mobility and instability of the Ce0.45Zr0.45La0.10O2-δ cubic fluorite structure, and provide 54% conversion efficiency with 73% selectivity to carbon monoxide. Further increase in CH4 conversion and CO selectivity can be achieved by packing the reactor with an additional catalyst, such as Pt-promoted Ce0.45Zr0.45La0.10O2-δ or LaNiO3-δ / Al2O3 .

Promoted partial oxidation activity of alkali metal added-Co catalysts supported on NaY and NaUSY zeolites in the gas-phase catalytic oxidation of benzyl alcohol

A study on the oxidation activity of cobalt (Co) catalysts ion-exchanged and impregnated on NaY and NaUSY (ultra stable Y) zeolites and their alkali metal added counterpart, and the nature of the active supported Co species was carried out using the gas-phase catalytic oxidation of benzyl alcohol. The main oxidation products over the supported Co catalysts used in this study were benzaldehyde and CO 2. The partial oxidation activity increased with increasing the amount of Co in the Co catalyst (Co/NaUSY imp) impregnated on NaUSY zeolite, although the degree of the increase in the benzaldehyde yield tended to decrease in the region of the higher amount of Co. The yield of benzaldehyde over the Co catalyst (Co/NaY imp) impregnated on NaY zeolite had a maximum at a comparatively lower amount of Co. The addition of an alkali metal to the impregnated and ion-exchanged Co catalysts with a low amount of Co (1 wt.%) effectively promoted the partial oxidation activity. The redox property of the supported Co catalysts was investigated using UV–vis diffuse reflectance (DR) spectra. The role of the added alkali metal was inferred to be assistance for Co 2+ to be oxidized to Co 3+ to form Co 3O 4 [Co 2+(Co 3+) 2O 4] which was assumed to be active species for the partial oxidation of benzyl alcohol.

Preparation and properties of sodium iron orthooxomolybdates, Na xFe y(MoO 4) z

Five different crystalline phases are established in the quaternary system Na–Fe–Mo–O with isolated MoO 4 tetrahedra: NaFe(MoO 4) 2, Na 3Fe 2(MoO 4) 3, α- and β-NaFe 2(MoO 4) 3 and NaFe 4(MoO 4) 5. The optimized conditions for sample preparation are described together with structural analyses by X-ray and neutron powder diffraction. The observed crystal structures are compared with known structure types. The high-temperature behaviour, thermal expansion, decomposition or congruent melting, is reported together with some preliminary characterisation of oxygen release as requested for catalytic activity in partial oxidation of hydrocarbons. Magnetic properties and antiferromagnetic ordering have been studied by magnetisation measurements and neutron diffraction.

Effect of zeolite geometry for propane selective oxidation on cation electrostatic field of Ca 2+ exchanged zeolites

The effects of zeolite geometry on propane selective oxidation were studied by in situ infrared spectrometry on Ca 2+ exchanged Y, MOR and ZSM5 zeolites. Oxygen and propane adsorption at room temperature, revealed that the electrostatic field of Ca 2+ increased in the order CaY < CaMOR < CaZSM5. The electrostatic field of Ca 2+ cations in CaY and CaZSM5 was observed to correlate with propane selective oxidation activity and selectivity. At 353 K, low activity but high selectivity to acetone was observed for propane oxidation on CaY zeolite, while high activity and a 2:1 mixture of 2-propanol and acetone was observed on CaZSM5. CaMOR showed the lowest activity for oxygenates formation of propane oxidation, but deep oxidation to CO and CO 2 was found. The results convincingly show that the geometrical structure of a zeolite determines activity and selectivity of propane partial oxidation on Ca 2+ exchanged zeolites to a large extent.

Selective Combinatorial Studies on Ce and Zr Promoted Cu/Zn/Pd Catalysts for Hydrogen Productio via Methanol Oxidative Reforming

The activity and selectivity for partial oxidation of methanol to H2 and CO2 on Zr, Ce, promoted Cu/Zn/Pd catalysts, have been studied using a high-throughput method of screening and analysis. In this work, infrared thermography was first used as a descriptor of overall catalytic activity. Then, activity and selectivity of samples with high infrared signal were measured in a flow reactor and characterized by BET, XRD, and XPS. Catalysts promoted with 10% Zr and showed H2 selectivity >95% with methanol conversion approaching 100% at ~200 °C.

Promotion effects of ceria in partial oxidation of methane over Ni-calcium hydroxyapatite

Effects of ceria added as a promoter to a nickel-calcium hydroxyapatite catalyst, which has recently been reported to exhibit high activity and selectivity in partial oxidation of methane, were investigated. The ceria-promoted catalyst exhibited higher activity and stability than the unpromoted one. This is considered due to the oxygen storage capacity of ceria, which promotes easier removal of the deposited carbon. The optimum content of ceria was determined to lie in the range of the Ce/Ni ratio from 0.1/2.5 to 0.2/2.5.

Promoted partial oxidation activity of supported Ag catalysts in the gas-phase catalytic oxidation of benzyl alcohol

The gas-phase catalytic oxidation of benzyl alcohol was carried out using Ag catalysts impregnated on a SiO 2 or CaO support, as well as a potassium-added counterpart (K/Ag/SiO 2), to clarify the surface state of the Ag species active in the oxidation reaction, the effect of the basic support and the added alkali metal. Benzaldehyde was obtained as the main oxidation product. The effects of the calcination temperature of the Ag/SiO 2 catalyst and the reaction temperature on oxidation activity were investigated. The benzaldehyde yield markedly increased between 553 and 593 K. Increasing the calcination temperature from 773 to 1173 K also caused a significant increase in partial oxidation activity. Both a CaO support for the Ag species and potassium added to the Ag/SiO 2 catalyst promoted partial oxidation at a comparatively low reaction temperature. X-ray diffraction and extended X-ray absorption fine structure demonstrated that a high calcination temperature, a basic support, and addition of an alkali metal led to a more ready reduction of the supported Ag to metallic Ag. Oxidized surface Ag species on the metallic Ag were inferred to be the active Ag components for the partial oxidation of benzyl alcohol based on the amount of O 2 uptake and the diffuse reflectance spectra of the supported Ag catalysts.

Promotion Effect of Alkali Metal Added to Impregnated Cobalt Catalysts in the Gas-Phase Catalytic Oxidation of Benzyl Alcohol

The effect of the addition of alkali metals on the catalytic activity of cobalt catalysts (Co/NaY, Co/SiO2, etc.) impregnated on inorganic oxides including NaY and SiO2 was studied using the gas-phase catalytic oxidation of benzyl alcohol. The partial oxidation activities, measured by the yield of benzaldehyde, of the supported Co catalysts were selectively promoted by adding alkali metal, with keeping the yield of CO2 low. The amount of added alkali metal under a constant amount of the impregnated cobalt had an optimal value for the catalytic activity of the benzaldehyde formation. The influences of the supporting method of Co, the inorganic oxide support, the amount of supported Co, and the kind of the added alkali metal on the partial oxidation activity were investigated to explore the supported Co catalysts for high catalytic activity. The sorpted oxygen species, rather than gaseous oxygen, were suggested to participate in the formation of benzaldehyde on the basis of a transient response experiment. ...

Nickel-calcium phosphate/hydroxyapatite catalysts for partial oxidation of methane to syngas: Effect of composition

Nickel-calcium phosphate/hydroxyapatite catalysts have recently been reported to exhibit high activity and selectivity in partial oxidation of methane (POM). In this work the optimum composition was determined. The optimum mole ratio of Ca/PO4 was around 10/6 and that of Ni/PO 4 was in a range from 1.0/6 to 3.0/6 with the optimum Ca/PO4, and the activity could be related with the amount of metallic nickel. In a temperature range from ca. 400 to 700 K, an apparent autothermal reaction was observed to occur in some cases. This is due to the fact that the actual catalyst temperature is higher than the measured temperature, which comes from the exothermic nature of the reaction. The mixing sequence of the precursors during the catalyst preparation does little affect the catalyst activity and char- acteristics. Deactivation of the catalyst occurred slowly, but the catalyst could easily be regenerated. Moreover, the nickel-calcium phosphate/hydroxyapatite catalyst showed higher activity than the nickel-strontium phosphate catalyst.

Effect of alkali metal added to supported La catalysts on the catalytic activity in the gas-phase catalytic oxidation of benzyl alcohol

The oxidation activities of lanthanum (La) catalyst supported on both crystalline and amorphous oxides including NaZSM-5 zeolite and the alkali metal-added counterparts were studied using a gas-phase catalytic oxidation of benzyl alcohol. The main oxidation products were benzaldehyde and carbon dioxide, together with a trace amount of benzene and/or toluene under certain reaction conditions. The addition of alkali metal to the lanthanum catalysts supported on NaZSM-5 and SiO2 promoted the catalytic activity of the partial oxidation in the benzyl alcohol oxidation. The influences of the oxide supports, the amount of La supported on the catalyst, the added alkali metal/La atomic ratio, and the catalyst preparation on the catalytic activity in the benzyl alcohol oxidation were investigated. The amount of adsorbed ethanol on the La-supported catalyst, the O2 uptake amount, the transient response experiment of the oxidation reaction, together with the BET surface area and the X-ray powder diffraction (XRD) pattern of the catalysts, were measured in order to determine the crucial factors in the partial oxidation activity. A promotion scheme for the alkali metal added to the La/NaZSM-5 catalyst is proposed.

Plasma treatment of Ni catalyst via a corona discharge

In this paper, plasma treatment of Ni catalyst for partial oxidation of methane to syngas was investigated by using plate–plate discharge model via a corona discharge by flowing argon under atmospheric pressure and room temperature. The catalytic activity and stability for partial oxidation of methane (POM) process were measured for the catalyst before and after plasma treatment. It was found that after plasma treatment, methane conversion increased 5–10% and the syngas selectivity kept the same as before treatment. Also, these catalysts were characterized by thermogravimetric analysis and XPS measurement. It was found that the argon plasma treatment can improve the catalytic stability by preventing the carbon deposition on the Ni catalyst.

Characterization of a nickel-strontium phosphate catalyst for partial oxidation of methane

A nickel-strontium phosphate catalyst was recently reported to exhibit high activity and selectivity in partial oxidation of methane (POM). Further characterizations have been performed in the present work in order to better understand the characteristics of this catalyst. TEM showed that very fine nickel particles of a few nanometers of the size were present in the needle shape in the sample after the reaction. TPR showed the presence of three nickel species, confirming that the nickel in the strontium hydroxyapatite and phosphate structures comes out as fine particles and is reduced during the reaction. As the calcination time during the preparation increased, the total re-oxidation temperature became higher. This is considered due to larger crystallite size owing to the longer calcination, which results in a smaller amount of nickel coming out of the matrix to the surface.

The Relationship Between Structural and Catalytic Activity of α and γ-Bismuth-Molybdate Catalysts for Partial Oxidation of Propylene to Acrolein

Bismuth-molybdate catalysts are known to be effective for catalytic partial oxidation of propylene to acrolein. Their properties and the kinetics and reaction mechanisms for acrolein production have been extensively studied, especially in their basic forms, such as α, β, and γ-bismuth-molybdate. Although the reaction mechanisms have been reported widely in the literature, a general agreement has not been reached, especially from a catalyst-structure point of view. The present contribution reports an effort to understand the structural changes of α and γ-bismuth-molybdate catalysts at varying temperatures as examined using high temperature XRD and to relate the catalyst performance (activity and selectivity) for propylene partial oxidation to acrolein. The XRD analysis was performed at temperature between 250 and 450°C in ambient atmosphere and the Rietveld refinement method was used to extract unit cell parameters. The results showed a distinct similarity between the shapes of the thermal expansion of the catalysts and their activity and selectivity curves, indicating a significant role that the catalyst interatomic structure plays in the overall reaction mechanism.

Partial oxidation of methane over Ni catalysts based on hexaaliminate- or perovskite-type oxides

Ni/Al 2O 3, hexaaluminate-type BaNi x Al 12− x O 19− α and perovskite-type LaAl 5/6Ni 1/6O 3 were investigated for partial oxidation of methane (POM). The hexaaluminate-type BaNiAl 11O 19− α calcined at 1400 °C demonstrated more stable and higher activity than Ni/Al 2O 3 calcined at 1000 °C. The BaNiAl 11O 19− α catalyst reduced at 1000 °C was more active than the catalyst reduced at 800 °C. The results from XPS analysis revealed that the hexaaluminate-type catalysts calcined and reduced at higher temperature had Ni-rich surfaces and highly dispersed Ni species derived from hexaaluminate crystal, resulting in high activity for partial oxidation of methane.

Partial oxidation of p-tert butyl toluene to p-tert butyl benzaldehyde

In this paper, studies of V-Cs-Cu and V-Cs-Cu-Tl catalysts used in the partial oxidation of p-tert butyl toluene to p-tert butyl benzaldehyde are reported. The two series of catalysts are prepared by an impregnation method. The effects of temperature, space velocity, concentration, ratio of O 2/ p-tert butyl toluene and the stability of catalysts are examined. The results indicate that both the catalysts show good catalytic activity in partial oxidation of p-tert butyl toluene to p-tert butyl benzaldehyde; but the series of V-Cs-Cu-Tl catalysts exhibit more excellent catalytic activity. Under the reaction conditions of space velocity at 10,000 h −1 and temperature at 440 °C, the conversion of p-tert butyl toluene can reach 12 mol% and the selectivity of p-tert butyl benzaldehyde is 85 mol%. In addition, the good stability in the series of V-Cs-Cu-Tl catalysts is another important character: the catalytic activity still remained significant after stability test for 365 h.

Mesoporous titanium phosphates and related molecular sieves: Synthesis, characterization and applications

Titanium (IV) phosphates TCM-7 and -8 with mesoporous cationic framework topologies using both cationic and anionic surfactants have been synthesized. Experimental data suggest the stabilization of the tetrahedral state of Ti in TCM-7/8 (O-P-O-Ti-O-, at Ti/P = 1:1)vis-à-vis the most stable octahedral state of Ti in the rutile/anatase or pure mesoporous TiO2. Mesoporous TCM-7 and-8 show anion exchange capacity due to the framework phosphonium cation and cation exchange capacity due to defective P-OH groups. Grafting the organic functionality in the surface or bridging the organic moiety in between the inorganic phosphorus precursors can enhance hydrophobicity of these materials similar to that of mesoporous silica materials. The high catalytic activity in the liquid phase partial oxidation of cyclohexene over such organically surface modified mesoporous titanium phosphate using a dilute H2O2 oxidant supports the tetrahedral coordination of Ti in these materials. These materials also show excellent photocatalytic activity in the production of H2 by photo-reduction of water under UV light irradiation.

Partial Oxidation of Methane over Ni/SiO2

Ni catalyst (Ni: 15 wt%) supported on precalcined SiO2 has been investigated in reforming reactions of methane to synthesis gas. The catalyst exhibited fairly good activity and stability in partial oxidation of methane (POM), whereas it deactivated in steam reforming of methane (SRM). Pulse reaction results of CH4, O2, and CH4/O2 revealed that Ni/SiO2 has high capability to dissociate methane. The results also revealed that both CH4 and O2 are activated on the surface of metallic Ni, and then surface carbon species react with adsorbed oxygen to produce CO and CO2 depending on the bond strength of the oxygen species on the catalyst surface.

An in-situ modified sol–gel process for monolith catalyst preparation used in the partial oxidation of methane

An in-situ modified sol–gel method for the preparation of a Ni-based monolith-supported catalyst is reported. With the presence of a proper amount of plasticizer and binder, and at an optimized pH value, the stable boehmite sol was modified with metal ions (Ni, Li, La) successfully without distinct growth of the particle size. Monolith-supported Ni-based/γ-Al2O3 catalysts were obtained using the modified sol as the coating medium with several cycles of dip-coating and calcination. Combined BET, SEM–EDS, XRD and H2-TPR investigations demonstrated that the derived monolith catalysts had a high specific surface area, a relatively homogeneous surface composition, and a high extent of interaction between the active component and the support. These catalysts showed relatively stable catalytic activities for partial oxidation of methane (POM) to syngas under atmospheric pressure. The monolith catalysts prepared by this sol–gel method also demonstrated an improved resistance to sintering and loss of the active component during the reaction process.

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 H 2 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.

Effects of catalyst heating rates upon the activity of silica-supported silicomolybdic acid catalysts for methane partial oxidation

Silica-supported silicomolybdic acid (SMA) catalysts showed a very high activity for partial oxidation of methane into formaldehyde at 873 K in the presence of an excess amount of water vapor in feed. However, the high activity was observed only when the catalysts were heated to 873 K with very high heating rates such as 100 K min-1. In this article, the reason why these high heating rates are necessary to exhibit the higher catalytic activity into formaldehyde will be discussed based on the structural changes in SMA during heating the catalysts to 873 K.