Catalysts For Partial Oxidation Research Articles

A simple preparation method of eggshell Ni/MgO-Al2O3 catalyst for partial oxidation of methane

A simple method to prepare eggshell Ni/MgO-Al2O3 catalyst was developed. In partial oxidation of methane, eggshell Ni/MgO-Al2O3 showed better reactivity and stability than the uniform one, even than eggshell Ni/Al2O3.

Supported Rh catalysts for methane partial oxidation prepared by OM-CVD of Rh(acac)(CO)2

Abstract The organometallics chemical vapour deposition (OM-CVD) technique, using Rh(acac)(CO) 2 as a precursor, was employed for the preparation of heterogeneous Rh catalysts supported on low surface area refractory oxides (α-Al 2 O 3 , ZrO 2 , MgO and La 2 O 3 ). Prepared systems were tested in the methane catalytic partial oxidation (CH 4 -CPO) reaction in a fixed bed reactor and compared to a reference catalyst prepared from impregnation of Rh 4 (CO) 12 . Catalysts supported on Al 2 O 3 , ZrO 2 and MgO show better or comparable performances with respect to the reference system. Complete decomposition of Rh precursor during formation of the metal phase under reductive conditions was investigated by TPRD and confirmed by infrared and mass spectrometry data. Supported Rh phase was characterized by CO and H 2 chemisorption, CO-DRIFT spectroscopy and HRTEM microscopy in fresh and aged selected samples. Rh(I) isolated sites and Rh(0) metal particles were found on fresh catalysts; after ageing an extensive reconstruction occurs mainly consisting in a sintering of Rh isolate sites to metal particles but without large increase in mean particles size. Catalytic performances and Rh species balance were found to be dependent on the support material.

Supported nanocomposite catalysts for high-temperature partial oxidation of methane

In order to utilize the vast potential of nanoparticles for industrial catalysis, it is necessary to develop methods to stabilize these particles at realistic technical conditions and to formulate nanoparticle-based catalysts in a way that facilitates handling and reduces health and safety concerns. We have previously demonstrated that metal nanoparticles can be efficiently stabilized by embedding them into a high-temperature stable nanocomposite structure. Building onto these results, we report here on the next step towards a simple, hierarchically structured catalyst via supporting platinum barium-hexaaluminate (Pt-BHA) nanocomposites onto a range of different conventional and novel support structures (monoliths, foams, and felts). The catalysts were characterized via SEM, TEM, XRD, porosimetry, chemisorption, and reactive tests in catalytic partial oxidation of methane to synthesis gas (CPOM), and compared to conventionally prepared Pt-catalysts. In particular silica felt supported Pt-BHA showed excellent activity and selectivity combined with good stability and very low noble metal requirement at the demanding high-temperature conditions of short-contact time CPOM. Overall, we see great potential for these supported nanocomposite catalysts for use in demanding environments, such as high-temperature, high-throughput conditions in fuel processing and similar energy-related applications.

Silicon nitride supported nickel catalyst for partial oxidation of methane to syngas

Abstract Silicon nitride supported nickel catalyst prepared by impregnation was employed for the partial oxidation of methane to syngas. The Ni/Si 3 N 4 catalyst was tested in a fixed-bed quartz reactor at 800 °C for 200 h. The experimental results show that the catalyst exhibits not only high activity but also remarkable resistance to coke formation. The conversion of CH 4 remained almost constant at about 92%. Temperature jump in the catalyst bed was not detected during the test. The structure and properties of fresh and used catalysts were further analyzed by X-ray diffraction, transmission electron microscopy, temperature programmed reduction and elemental analysis.

Flexible ligand synthesis, characterization and catalytic oxidation of cyclohexane with host (nanocavity of zeolite-Y)/guest (Mn(II), Co(II), Ni(II) and Cu(II) complexes of tetrahydro-salophen) nanocomposite materials

Transition metal (M = Mn(II), Co(II), Ni(II) and Cu(II)) complexes with tetrahydro-salophen (salophen = N, N-bis-(salycilidene)-1,2-phenylenediamine; H 2[H 4salophen] = 2-({2-[(2-hydroxybenzyl)amino]anilino}methyl)phenol) have been encapsulated in nanopores of zeolite-Y; [M(H 4salophen)]-NaY; with Flexible Ligand Method for the first time. The new Host–Guest Nanocomposite Materials (HGNM) was characterized by several techniques: chemical analysis, spectroscopic methods (DRS, FTIR and UV/Vis), BET technique, conductometric and magnetic measurements. The catalytic activities for oxidation of cyclohexane with HGNM complexes are reported. Zeolite-encapsulated tetrahydro-salophen copper(II) complexes; [Cu(H 4salophen)]-NaY; was found to be more active than the corresponding cobalt(II), manganese(II) and nickel(II) complexes for cyclohexane oxidation. The catalytic properties of the complexes are influenced by their geometry and by the steric environment of the active sites. HGNM are stable enough to be reused and are suitable to be utilized as partial oxidation catalysts. The encapsulated catalysts systems; [M(H 4salophen)]-NaY; were more active than the corresponding neat complexes; [M(H 4salophen)].

Nickel catalyst prepared via glycine nitrate process for partial oxidation of methane to syngas

Nickel/alumina catalyst promoted by Li2O and La2O3 was prepared via glycine nitrate process (GNP) for the first time. The catalyst was characterized by BET specific surface area measurement, powder X-ray diffraction (XRD), H2 temperature programmed reduction (H2-TPR), scanning electronic microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and catalytic performance measurements for partial oxidation of methane, comparison between the catalysts with the same composition while prepared via different methods and initial catalyst stability were also investigated. The results indicated that there was a strong interaction between the NiO and Al2O3 phase in the catalyst prepared via GNP. Alumina existed in mainly in a γ form, while spinel phase of nickel aluminate also occurred. The catalyst showed superior catalytic performances, e.g. higher methane conversion and selectivity to CO under similar working conditions over the one with same composition prepared by sol–gel and incipient-to-wetness impregnation method. Thus, an alternative method for preparing catalyst for methane partial oxidation was developed, which may find application to develop composite anodes for direct hydrocarbon fuelled solid oxide fuel cells.

Effects of preparation methods of ZrO2 support on catalytic performances of Ni/ZrO2 catalysts in methane partial oxidation to syngas

Abstract ZrO 2 was prepared by hydrothermal method (denoted as HT method), the method of drying and calcinating of alcogel in N 2 (denoted as AN method) and conventional precipitation method (denoted as CP method). And 14%Ni/ZrO 2 catalysts were prepared by impregnation method. The physico-chemical properties of supports and catalysts were characterized by XRD, TEM, N 2 -adsorptioin. The effects of preparation methods of ZrO 2 support on the catalytic performances of 14%Ni/ZrO 2 in methane partial oxidation (POM) at 700 °C, 1.0 × 10 5 ml/(g cat h) and ambient pressure were investigated. The experimental results showed that ZrO 2 particles prepared by HT method were uniform and spindle-like with the size of 100 nm × 400 nm, while ZrO 2 particles prepared by AN method were spheric and small with the size of 20–40 nm. As for ZrO 2 prepared by CP method, its particles were un-uniform and the size distribution of its particles was wide from 20 to 100 nm. The reaction results of POM illustrated that the 14%Ni/ZrO 2 catalysts in which ZrO 2 was prepared by HT and AN methods, had small Ni particles and showed high ability of resistance to carbon deposit and high stability of time on-stream (TOS). The 14%Ni/ZrO 2 -CP catalyst had large Ni particles and showed an serious deactivation within 50 h of TOS due to the formation of large amount of carbon deposit on the surface of catalyst. The results from TEM and TPO showed that encapsulated carbon deposit was formed on small Ni particles and was active for oxidation, while carbon nano-tube was mainly formed on large Ni particles and was inert for oxidation.

Stability of Pt particles on ZrO 2 support during partial oxidation of methane: DRIFT studies of adsorbed CO

In this work, diffuse reflectance infrared Fourier transformation (DRIFT) spectroscopy of adsorbed CO was studied to investigate the stability of Pt/ZrO 2 catalysts for partial oxidation of methane. The studies confirmed that the preparation method has a significant effect on the catalyst performance and the catalyst treatment using argon glow discharge plasma improves the catalyst stability. TG analysis showed that coke formation is not significant on both samples with and without glow discharge plasma treatment, indicating the coke formation is not responsible for the catalyst deactivation. The IR band intensity of adsorbed CO decreases remarkably with increasing calcination temperature, suggesting the sintering of Pt particles in the presence of O 2. The sintering of plasma treated sample is slower than that of the untreated sample, especially at higher temperature, which indicates that the plasma treated sample is more resistant to sintering under the oxidizing atmosphere.

Effect of Relative Bed Lengths on a Platinum/Nickel Stratified Dual Bed Catalyst for the Catalytic Partial Oxidation of Methane at Millisecond Contact Times

Stratified, dual bed catalysts composed of platinum followed by nickel have shown reactant conversions and product selectivities similar to rhodium, which has shown the highest activity for the mil...

The Effect of Nb Loading on Catalytic Properties of Ni/Ce 0.75Zr 0.25O 2 Catalyst for Methane Partial Oxidation

In this study, the effect of Nb loading on the catalytic activity of Ce 0.75Zr 0.25O 2-supported Ni catalysts was studied for methane partial oxidation. The catalysts were characterized by BET, H 2 chemisorption, XRD, TPR, TEM and tested for methane partial oxidation to syngas in the temperature range of 400–800 °C at atmospheric pressure. The results showed that the activity of methane partial oxidation on the catalysts was apparently dependent on Nb loading. It seemed that the addition of Nb lowered the catalytic activity for methane partial oxidation and increased the extent of carbon deposition. This might be due to the strong interaction between NiO and Nb-modified support and reduction of surface oxygen reducibility.

Asymmetric Tubular Oxygen-Permeable Ceramic Membrane Reactor for Partial Oxidation of Methane

We report a successful paradigm of implementing the nickel catalyst for partial oxidation of methane (POM) in an oxygen-permeable ceramic membrane reactor (OPCMR). With using air feed, the OPCM (or the cathode of O2 reaction) was completely gastight but presented a desirable oxygen anion flux, which is required by POM in the anodic side. An almost 100% of CH4 conversion with high selectivity of CO and H2 was achieved in the anode, which was initially a composite of YSZ and NiO. It is also found that a mutual diffusion of Ni2+ and Zr4+ ions happens between the YSZ and NiO phases, which affected performance of POM. Besides experimental work, a new activation pathway was proposed to describe cleavage of the first C−H bond of methane. This activation pathway was simulated using the density function-theory and the computed activation energy for breaking up the first C−H bond falls in the experimental measurement range.

Influence of Supports on Catalytic Performance and Carbon Deposition of Palladium Catalyst for Methane Partial Oxidation

The catalytic performance of methane partial oxidation was investigated on Pd/CeO 2-ZrO 2 and Pd/α-Al 2O 3 catalysts. The catalysts were characterized by XRD, Raman spectra, and TG-DTA techniques. The results show that CeO 2-ZrO 2 support is more advantageous for the catalytic activity and stability of catalysts compared to α-Al 2O 3. TG-DTA and Raman spectra results indicated that carbon deposited on the catalysts was in the form of graphite, which is the main reason for the deactivation of catalysts after a 24-hour reaction. Moreover, CeO 2-ZrO 2 had positive effect on inhibiting carbon deposition.

Experimental and numerical investigation of supported rhodium catalysts for partial oxidation of methane in exhaust gas diluted reaction mixtures

The partial oxidation of methane/oxygen mixtures with large exhaust gas dilution (46.3 vol% H 2 O and 23.1 vol% CO 2 ) has been investigated experimentally and numerically over Rh / CeO 2 – ZrO 2 , Rh / ZrO 2 and Rh / α - Al 2 O 3 catalysts. Experiments were carried out in a short-contact-time ( ∼ 8 ms ) reactor at 5 bar and included exhaust gas analysis, temperature measurements along the reactor, and catalyst characterization. Additional experiments were performed in an optically accessible channel-flow reactor and involved in situ Raman measurements of major gas-phase species concentrations over the catalyst boundary layer and laser-induced fluorescence (LIF) of formaldehyde. A full elliptic two-dimensional numerical code that included elementary hetero-/homogeneous chemical reaction schemes and relevant heat transfer mechanisms in the solid was used in the simulations. The employed heterogeneous reaction mechanism, including only active Rh sites, reproduced the experiments with good accuracy. The ratio of active to geometrical surface area, deduced from hydrogen chemisorption measurements, was the single model parameter needed to account for the effect of different supports. This indicated that water activation occurring on support sites, resulting in inverse OH spillover from the support to the noble metal sites, could be neglected under the present conditions with high water dilution. An evident relationship between noble metal dispersion and catalytic behavior, in terms of methane conversion and synthesis gas yields, could be established. Both measurements and predictions indicated that an increasing Rh dispersion (in the order Rh / α - Al 2 O 3 , Rh / ZrO 2 , and Rh / CeO 2 – ZrO 2 ) resulted in higher methane conversions, lower surface temperatures, and higher synthesis gas yields.

Effects of MgO promoter on properties of Ni/Al2O3 catalysts for partial oxidation of methane to syngas

The effects of MgO promoter on the physicochemical properties and catalytic performance of Ni/Al2O3 catalysts for the partial oxidation of methane to syngas were studied by means of BET, XRD, H2-TPR, TEM and performance evaluation. It was found that the MgO promoter benefited from the uniformity of nickel species in the catalysts, inhibited the formation of NiAl2O4 spinel and improved the interaction between nickel species and support. These results were related to the formation of NiO-MgO solid solution and MgAl2O4 spinel. Moreover, for the catalysts with a proper amount of MgO promoter, the nickel dispersiveness was enhanced, therefore making their catalytic performance in methane partial oxidation improved. However, the excessive MgO promoter exerted a negative effect on the catalytic performance. Meanwhile, the basicity of MgO promoted the reversed water-gas shift reaction, which led to an increase in CO selectivity and a decrease in H2 selectivity. The suitable content of MgO promoter in Ni/Al2O3 catalyst was ∼7 wt-%.

Effect of Ce-doping on Rh/ZrO2 catalysts for partial oxidation of methane

The partial oxidation of methane over supported (ZrO2, CeO2-ZrO2) rhodium catalysts was investigated at atmospheric pressure. The effect of temperature, CH4/O-2 ratio, catalyst composition and pr ...

Time-resolved studies on correlations between dynamic electronic structure and selectivity of a H 5[PV 2Mo 10O 40] partial oxidation catalyst

Time-resolved in situ X-ray absorption spectroscopy studies on an activated H 5[PV 2Mo 10O 40] oxidation catalyst were performed to obtain correlations between the dynamic structure and the catalytic selectivity of the material. Both the geometric and electronic structures of the vanadium and molybdenum metal centers of the catalyst change dynamically under the reaction conditions used. Moreover, the selectivity of the catalyst exhibits a pronounced correlation with the degree of reduction and the solid-state kinetics of the reoxidation process. The corresponding extent of reoxidation curve can be simulated with a solid-state kinetic model assuming three-dimensional diffusion as the rate-limiting step. Thus, the partially reduced catalyst exhibits a rate constant of the bulk-diffusion limited reoxidation, coinciding with the temporal evolution of the selectivity of the catalyst.

High performance of Ni-substituted calcium aluminosilicate for partial oxidation of methane into syngas

Newly synthesized calcium aluminosilicate, in which oxide anions were occluded, was tested as a catalyst for partial oxidation of CH 4 into CO and H 2 . Substitution of a part of Ca 2+ with Ni 2+ resulted in a marked increase in CH 4 conversion (93% at 800 °C) and in CO and H 2 selectivities (94% and 95%, respectively), while Cr 3+ , Co 3+ , Fe 3+ and Cu 2+ slightly increased CH 4 conversion with a considerable decrease in CO and H 2 selectivities. Such a high performance may be attributed to the ability of Ni-substituted sample for CH 4 steam reforming appearing during CH 4 partial oxidation.

Preparation of La 2NiO 4 catalyst and catalytic performance for partial oxidation of methane

The performance of La 2NiO 4 perovskite catalysts, prepared using a citric acid complexation method, for the partial oxidation of methane to synthesis gas has been studied. The catalysts were characterized by X-ray diffraction (XRD), specific surface area measurements, thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). The experimental studies show that the calcination temperature and the amount of citric acid (CA) have a significant influence on the characteristics of the catalysts and their catalytic activity. Among the catalysts tested, the La 2NiO 4 catalyst calcined at 850 °C with a molar ratio of La:Ni:CA = 2:1:3 exhibited the best activity and excellent stability as well as very low coke formation.

Selective Hydrocarbon Oxidation in Zeolites

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A surface science approach to ambient pressure catalytic reactions

Recent advances in the preparation and characterization of planar model catalysts and in ambient pressure surface spectroscopy enable us to investigate well-defined supported metal nanoparticles under working conditions, approaching the conditions of applied catalysis. The reactivity of Pd–Al 2O 3/NiAl(1 1 0) model catalysts for CO hydrogenation and methanol partial oxidation were examined by sum frequency generation (SFG) vibrational spectroscopy and by polarization-modulation infrared reflection absorption spectroscopy (PM-IRAS) at pressures ranging from ultrahigh vacuum to ∼1 bar. Kinetic measurements were performed by on-line gas chromatography. A comparison with Pd(1 1 1) revealed the inherent differences between Pd nanoparticles and Pd single crystals. Apart from differences in surface structure, the small volume (or finite size) of Pd nanoparticles strongly affected their properties, in particular for hydrogen absorption. Methanol oxidation proceeded via dehydrogenation to formaldehyde CH 2O, which either desorbed or further dehydrogenated to CO, which was subsequently oxidized to CO 2. Carbonaceous overlayers that were present during the reaction were shown to favourably affect the selectivity towards CH 2O. During methanol oxidation Pd particles were more easily oxidized than Pd(1 1 1), which reduced their activity. Deactivation of Pd nanoparticles supported on Nb 2O 5/Cu 3Au(1 0 0), a support less inert than alumina, originated from the formation of mixed “Pd–NbOx” sites. 1,3-butadiene hydrogenation is known to be particle size dependent but when a realistic structural model of Pd nanoparticles on alumina was used for rate normalization, the reaction turned out to be particle size independent, even though the reaction is structure-sensitive, as corroborated by reactivity studies on Pd single crystals.