Catalysts For Partial Oxidation Research Articles

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.

The study on the source of Te and the dispersion of TeO 2 in fabricating Mo–V–Te and Mo–V–Te–Nb mixed metal oxide catalysts for propane partial oxidation

The effects of the source of Te and the dispersion of TeO 2 on fabricating Mo–V–Te and Mo–V–Te–Nb mixed metal oxide (MMO) catalysts for propane partial oxidation to acrylic acid (AA) were systematically studied. In order to modify the dispersion of TeO 2 in the preparation medium, wet-milling and ultrasonic-assisted dispersion of TeO 2 were adopted. The selected samples were characterized by means of BET, XRD, ICP/XRF, XPS, SEM, H 2- and C 3H 8-TPR and calorimetric NH 3 adsorption. It was clearly demonstrated that different sources of Te and dispersion of TeO 2 in preparation showed significant impact on the physicochemical properties (phase composition, bulk/surface elemental concentration, reactivity of lattice oxygen, and surface acidity) and catalytic activity of the MMO catalysts. The employment of ultrasonic treatment was proved to be effective for making more active and selective Mo–V–Te/Mo–V–Te–Nb catalysts for the target action.

Gas phase partial oxidation of toluene over modified V2O5/TiO2 catalysts in a microreactor

The influence of different additives to V2O5/TiO2 catalyst for the gas phase partial oxidation of toluene was investigated in a microchannel reactor, where well-controlled reaction conditions were provided without heat and mass transfer influence. It was found that K-doping decreased the catalyst selectivity for benzaldehyde and benzoic acid. The addition of Sb promoted the selectivity but inhibited the catalyst activity greatly. The modification with Ag remarkably improved the catalyst performance in terms of increasing benzaldehyde and benzoic acid selectivity along with an increased activity. With Ag modified V2O5/TiO2 as catalyst and pure oxygen as oxidant, the total selectivity of benzaldehyde and benzoic acid reached over 80% with the toluene conversion above 10%. The maximum space–time yield of 4.82 kg h−1 L−1 has been achieved, calculated on the basis of the channel volume.

Synthesis of carbon nanotubes by catalytic conversion of methane: Competition between active components of catalyst

Catalytic growth of carbon nanotubes from methane was studied as competitive catalytic process in situ of both oxidative (partial oxidation) and non-oxidative (pyrolysis) conversion. Ni and Fe may act as either competing or cooperative catalyst components in the process of carbon nanotubes growth. The competition between Ni and Fe in the process of carbon nanotube growth on Ni–Fe based stainless steel alloy during partial oxidation of methane results in suppression of Ni catalytic activity in favor of Fe. The discrimination is so strong that iron is segregated from Ni–Fe based stainless steel alloy leaving characteristic Ni-enriched corrosion caverns. Interaction between Ni and Fe during non-oxidative conversion, in contrast to the oxidative conversion, leads to cooperative effect; the activity of bimetallic catalyst increases as compared with monometallic one. Depending on particular catalyst bed composition, the nanotubes of various morphologies may occur. In particular, the use of perovskite-type catalyst for partial oxidation of methane leads to formation of “olive-branch”-like peculiar carbon nanostructures.

Methane Oxidation at Redox Stable Fuel Cell Electrode La0.75Sr0.25Cr0.5Mn0.5O3-δ

Because of its widespread availability, natural gas is the most important fuel for early application of stationary fuel cells, and furthermore, methane containing biogases are one of the most promising renewable energy alternatives; thus, it is very important to be able to efficiently utilize methane in fuel cells. Typically, external steam reforming is applied to allow methane utilization in high temperature fuel cells; however, direct oxidation will provide a much better solution. Recently, we reported good electrochemical performance for an oxide anode La0.75Sr0.25Cr0.5Mn0.5O3 (LSCM) in low moisture (3% H2O) H2 and CH4 fuels without significant coking in CH4. Here, we investigate the catalytic activity of this oxide with respect to its ability to utilize methane. This oxide is found to exhibit fairly low reforming activity for both H2O and CO2 reforming but is active for methane oxidation. LSCM is found to be a full oxidation catalyst rather than a partial oxidation catalyst as CO2 production dominates CO production even in CH4-rich CH4/O2 mixtures. X-ray adsorption spectroscopy was utilized to confirm that Mn was the redox active species, clearly demonstrating that this material has the oxidation catalytic behavior that might be expected from a Mn perovskite and that the Cr ion is only present to ensure stability under fuel atmospheres.

Excess of nio loading - key for catalyst activity decline prevention

The activity of co-precipitated NiO-Al2O3 catalyst for partial oxidation of methane in a steel flow reactor was investigated. The catalyst samples loaded with 5, 10 and 20 wt.% nickel before use were thermally treated at 400, 700 and 1100oC. The feed gas for catalytic oxidation was prepared by dilution of natural gas with air, and had approximately the following volume composition: CH4: O2: N2 = 5: 2: 8. The reaction was carried out over 100 mg unreduced NiO-Al2O3 catalyst at gas flow rate of 50 cm3/min at 650oC and atmospheric pressure. The catalyst activity with 5 and 10 wt.% of nickel was very similar, decreasing with enhance of previous heat treatment. Further nickel loading did not increase significantly the catalyst activity compared to low level nickel samples. However, high nickel content has a levelling effect on catalyst activity, suppressing the undesired effect of previous heat treatment at high temperature

Selective Hydrocarbon Oxidation in Zeolites

Zeolites are highly selective catalysts for partial oxidation of hydrocarbons, but practical applications require faster release of the products.

Co-generation of energy and synthesis gas by partial oxidation of methane

Catalytic partial oxidation (CPO) of methane was carried out over a Rh/γ-Al 2O 3 foam monolith catalyst at pressures up to 1.5 MPa and normal gas flow rates of up to 35 L/min. It was shown that the reaction took place autothermally once the reaction had lit off. Maintenance of short catalyst contact time and reactor cooling was necessary to prevent coke formation at elevated pressures. The concept of obtaining both syngas and energy from the partial oxidation of methane was tested using two geometries. In the first, the hot exit gases from partial oxidation catalysts were used to drive a turbine. In the second, a partial oxidation catalyst was deposited on turbine blade materials, converting ca. 55% of feed methane to syngas. The novelty in generating energy by this method lies in the combination of CPO, the catalyst configuration and the ability to capture energy via the turbine without further processing of valuable syngas product. Based on the conditions of pressure, conversion and gas composition used in this study, it has been calculated that up to 60 MW of power could be generated from 2500 tonnes per day (TPD) methane feed when the combination of CPO for syngas generation and a turbine are used.

MoVW mixed metal oxides catalysts for acrylic acid production: from industrial catalysts to model studies

(MoVW)5O14-type oxides were identified as the active and selective components in industrial acrylic acid catalysts. Tungsten is suggested to play an important role as a structural promoter in the formation and stabilization of this oxide. Vanadium is responsible for high catalytic activities but is detrimental for the stability of this oxide at the necessary high concentrations for optimum catalytic performance. The activity of mixed MoVW oxide catalysts for methanol, propene, and acrolein partial oxidation could be considerably improved, when the amount of the (MoVW)5O14-type oxide was increased by thermal annealing. A model is proposed on the basis of the correlation between Raman wavenumber and bond order and degree of reduction, which explains the observed different selectivities of MoO3−x and the (MoVW)5O14-type oxides in terms of metal–oxygen bond strengths, i.e. oxygen basicity and oxygen lability, respectively. According to this model, the (MoVW)5O14 mixed oxide catalyses partial oxidation because of its intermediate C–H activation and oxygen releasing oxygen functionalities. However, these (MoVW)5O14-type industrial oxidation catalysts are heterogeneous and highly complex systems. Their physicochemical characterization also revealed that their chemical bulk and surface compositions vary with thermal activation and oxygen potential. A core-shell model is suggested to describe the active catalyst state, the shell providing a high number of active centers, the core high electronic conductivity and ion mobility. The fact that the surface composition of such catalysts is considerably different from their bulk compositions, most probably implies that the “molecular structure” at their surface differs too considerably from their bulk crystal structure. Hence, the posed question about the active catalyst structure and its relation to its catalytic performance cannot unambiguously be explained by the crystallographic structure, but still remains unsolved.

Design of one-component ceramic membrane-reactor for natural gas conversion

One-component ceramic membrane-reactor, constituting of the same type of Ca 0.8Sr 0.2Ti 1− x Fe x O 3− α perovskite-type oxide for the catalyst involving support oxides, i.e., Ni/Ca 0.8Sr 0.2Ti 0.9Fe 0.1O 3− α , and the oxide ionic and electronic mixed conductor, i.e., Ca 0.8Sr 0.2Ti 0.7Fe 0.3O 3− α , has been investigated for the partial oxidation of methane into synthesis gas in natural gas conversion process. Unique point of the membrane reactor is that the products formed between catalyst and membrane material should have no influence as a blocking layer against the oxygen pumping since catalyst and membrane material are consisted of same component, leading long time operation at the process of natural gas. Ni/Ca 0.8Sr 0.2Ti 0.9Fe 0.1O 3− α used as a catalyst for partial oxidation of methane into synthesis gas shows the excellent activity for the anti-coking performance by the insertion of mixed conduction into the perovskite support. From the relationship between the amount of carbon deposited on the catalyst and the mixed conduction property in the support, it is suggested that a self-migration of lattice oxygen inside the support regulated the balance of the conductivities of oxide ion and electron plays an important role to prevent accumulation of carbon deposition. Ca 0.8Sr 0.2Ti 1− x Fe x O 3− α performed as an oxygen separator from air chamber to reaction chamber, and its oxygen pumping property enhanced with increase in the Fe partial substitution. In addition, we demonstrated the one-component ceramic membrane-reactor for the methane conversion into synthesis gas at 1173 K. Methane conversion was drastically accelerated by the electrochemical oxygen pumping with one component membrane reactor. An addition of cathodic catalyst brought about further acceleration of methane conversion, and highly level of methane conversion (50%) and CO selectivity (95%) was reached. It is suggested that oxygen permeation was dependent on the cathodic process when the Ca 0.8Sr 0.2Ti 0.7Fe 0.3O 3− α was used as a mixed conducting oxide in the membrane system.

Iron-containing heterogeneous catalysts for partial oxidation of methane and epoxidation of propylene

Mesoporous molecular sieves containing iron sites with different dispersions and environments were studied for the partial oxidation of methane and the epoxidation of propylene. The tetrahedral Fe(III) sites incorporated inside the framework of SBA-15 showed higher HCHO selectivity under a similar CH 4 conversion than the oligomeric FeO x clusters located in the mesopores in the partial oxidation of CH 4 by O 2. HCHO selectivity of the FeO x clusters in SBA-15 could be improved by the modification with either an acidic group (e.g., phosphate) or an alkali metal ion, which increased the dispersion or changed the local coordination environment of iron species. The catalyst containing FePO 4 clusters formed by the modification with phosphate exhibited the best catalytic performances for HCHO formation. This catalyst also showed uniquely high selectivities to HCHO and CH 3OH as N 2O was used as the oxidant for the partial oxidation of CH 4. For the epoxidation of propylene to propylene oxide (PO), the modification of the FeO x /SBA-15 with an alkali metal salt typified by KCl was effective. Among many SBA-15-supported transition metal oxides modified by KCl, the KCl-FeO x /SBA-15 showed the best catalytic performances for the epoxidation of propylene by N 2O. The comparative studies using N 2O and O 2 as the oxidant revealed that N 2O was necessary for PO formation over the KCl-FeO x /SBA-15 catalyst.

Lanthanum Modified Ni/γ-Al 2O 3 Catalysts for Partial Oxidation of Methane

La modified Ni/γ-Al 2O 3 catalysts prepared by co-precipitation method using NaOH-Na 2CO 3 as a precipitator show high activity and selectivity for the partial oxidation of methane (POM). Meanwhile, the addition of La is beneficial for the formation of an active component and stability of support. We investigated some factors including calcining temperature, nickel content, and space velocity, which turned out to have a strong influence on catalytic activity and selectivity. By XRD and TPR, it is concluded that Ni 0 reduced from amorphous NiAl 2O 4 is the major active component for POM.

Large scale electronic structure calculations in the study of the condensed phase

We consider the role that large-scale electronic structure computations can now play in the modelling of the condensed phase. To structure our analysis, we consider four distinct ways in which today's scientific targets can be re-scoped to take advantage of advances in computing resources: 1. Time to solution—performing the same calculation, with delivery of the simulation in shorter elapsed time; 2. Size—applying today's methods to a more extensive problem; 3. Accuracy—replacing current physical models with more accurate ones. 4. Sampling—simultaneously studying more chemical or conformational states. Each of these offer some scientific rewards, but all present technological challenges and it is likely that a mixture of approaches will be needed to make the best use of capability computing. We discuss some aspects of our work in each of these areas, including replicated and distributed data parallel implementations of GAMESS-UK, and approaches incorporating multi-level parallelism. Examples of the latter include pathway optimization using replica methods and task farming approaches to global optimization problems. We consider a typical application of GAMESS-UK to heterogeneous catalysis, and the role that large-scale DFT vibrational frequency calculations have played in the study of partial oxidation catalysts incorporating supported VO x species.

Partial oxidation of n-hexadecane at short contact times: Catalyst and washcoat loading and catalyst morphology

Rhodium supported on alumina foam is an exceptionally active catalytic partial oxidation catalyst, giving high selectivities to syngas or olefins by changing reaction stoichiometry or catalyst properties such as rhodium loading and washcoat loading. Rhodium catalyst loading and γ-alumina washcoat loading were varied systematically on α-alumina foams to investigate resulting microstructure and products of the partial oxidation of n-hexadecane. At conditions favorable for producing syngas, varying rhodium loading between 0.05 and 10.0 wt.% (a factor of 200) had little affect on H 2 and CO selectivities or fuel conversions. However, non-washcoated catalysts gave low selectivities to syngas. Increasing washcoat loading results in high selectivities of olefins, while varying rhodium loading has little affect on production of olefins. Selectivitiy data from multi-metallic catalysts, Rh–Ce and Rh–Pt, was also investigated. The morphology of catalysts was examined using scanning electron microscopy. The micrographs indicate that increasing rhodium loading above a few percent led to the formation of a rhodium film on the catalyst support. The presence of washcoat seems to keep rhodium spread on the surface at high reaction temperatures enhancing heterogeneous products. Very high washcoat loadings (10 wt.%) decrease pore diameters, increasing the likelihood of reactant contact with the rhodium surface, leading to increased H 2 and decreased olefin selectivities.

Catalytic performance of supported Ni catalysts in partial oxidation and steam reforming of tar derived from the pyrolysis of wood biomass

Activity test of Ni/Al 2O 3, Ni/ZrO 2, Ni/TiO 2, Ni/CeO 2 and Ni/MgO catalysts in the partial oxidation (POT) and steam reforming of tar (SRT) derived from the pyrolysis of cedar wood was performed. In these activity tests, the order of the performance in both reactions was similar. Catalyst characterization was also carried out by means of H 2 adsorption, TPR and XRD. From the combination of catalyst characterization with the results of the activity tests, it is suggested that the conversion of tar in POT and SRT is mainly controlled by the number of surface Ni metal. In addition, Ni/CeO 2 showed smaller amount of coke than other catalysts in the POT and SRT. From the TGA profiles of active carbon mixed with catalysts, it is found that Ni/CeO 2 promoted the reaction of active carbon with O 2 and steam. The function of the fluidized bed reactor in the POT with respect to coke and tar amount was discussed.

Metal oxides as combustion catalysts for a stratified, dual bed partial oxidation catalyst

Bimetallic, dual bed catalysts made up of metal oxides were investigated in the millisecond catalytic partial oxidation of methane to synthesis gas. A metal oxide combustion catalyst containing manganese, chromium, or copper was coupled with a nickel reforming catalyst to carry out the partial oxidation of methane. These catalysts produce hydrogen yields that compare to a platinum/nickel dual bed catalyst at a fraction of the cost. The high space velocity of the millisecond reactor improves performance by giving high rates of heat convection from the exothermic, upstream combustion catalyst to the downstream, endothermic reforming catalyst. Additionally, over a 10 h experiment, the catalyst activity did not decrease.

혼합가스 주입형 연료전지를 위한 전지 디자인

In this study, we fabricated honeycomb type Mixed-Gas Fuel Cell (MGFC) which has advantages of stacking to the axial direction and increasing volume power density. Honeycomb-shaped anode with four channels was prepared by dry pressing method. Two alternative channels were coated with electrolyte and cathode slurry in order to make cathodic reaction sites and the others were filled with partial oxidation (POX) catalyst to increase fuel conversion. Furthermore we employed the sol-gel technique which can increase cell performance and decrease carbon coking.

Plasma treatment of Ni and Pt catalysts for partial oxidation of methane

In this work DBD (dielectric barrier discharge) plasma treatments of 10%Ni/Al2O3and 1%Pt/Al2O3catalysts have been conducted to study the principles of plasma treatment of supported catalysts. It was found that 10%Ni/Al2O3and 1%Pt/Al2O3catalysts treated by plasma exhibit a higher catalytic activity and a better stability than the catalysts prepared without plasma treatment. Methane conversion over the plasma treated catalyst is 3-5% higher than on untreated catalysts. The metal species dispersion also increased after plasma treatment, which leads to improvement of the interaction between active species and supports, the catalytic activities and the resistance to carbon deposition.

Synthesis and functional verification of the unsupported active phase of V xO y catalysts for partial oxidation of n-butane

We studied unsupported V x O y nanoparticles prepared by a novel nonaqueous route in the selective oxidation of n-butane to maleic anhydride. The evolution of the electronic and geometric structure of the material was characterized by X-ray photoemission spectroscopy, electron energy-loss spectroscopy, transmission electron microscopy, and electron diffraction before and after the reaction at different temperatures. A change from a water-mediated C C bond cracking functionality of the catalyst forming acetic acid to an oxidizing functionality resulting in maleic anhydride was observed. It was found that the particles underwent a radical modification of the geometric and electronic structure that finally resulted in V 2O 5 crystals. Experimentally derived conclusions are related to some conceptual claims from the literature.

05/02474 Highly active and coking resistant Ni/CeO 2-ZrO 2 catalyst for partial oxidation of methane

05/02474 Highly active and coking resistant Ni/CeO 2-ZrO 2 catalyst for partial oxidation of methane