Catalysts For Partial Oxidation Of Methane Research Articles

ABO3 perovskite catalyst screening for chemical looping methane partial oxidation from descriptor-based microkinetic analysis

DFT calculations and descriptor-based microkinetic analysis have been performed to screen ABO3 perovskite catalysts for methane partial oxidation. The scaling relations indicate the adsorption energies of H@O and CH3@B have the capability of representing the energetics of methane oxidation, and bulk oxygen vacancy formation energy is identified to be a better single descriptor of the kinetics. The resultant volcano-shaped plot shows the catalytic activity varies in the order LaMnO3 > LaFeO3 > LaCoO3 ≈ LaCrO3, which agrees with the experimental findings and thus validates our theoretical predications. By screening 667 combinations of A- and B-cations based on electron neutrality, structural tolerance factors, and experimental verification, 77 ABO3 have been identified to be stable. Of them, SrRuO3, SmRhO3, LaIrO3, NdRhO3, and BaOsO3 are located at the summit of the volcano, which also exhibit satisfactory CO selectivity and enhanced carbon resistance compared to LaFeO3, and may act as the oxygen carrier candidates.

Active site for syngas production by direct partial oxidation of CH4 over ZrO2

ZrO2 is a promising catalyst for direct partial oxidation of methane. The reaction mechanism and active site for partial oxidation of methane over ZrO2 were proposed using kinetic analysis, in situ diffuse reflectance infrared Fourier transform spectroscopy, and DFT calculations.

Lanthanide modified Pt/CeO2-based catalysts for methane partial oxidation: Relationship between catalytic activity and structure

In most cases, reasonable design and construction of Pt/CeO2-based catalysts and detailed exploration of relationship between its structural characteristics and the catalytic activity are crucial to improve the catalytic performance and reduce the cost. In this work, a series of CeO2 doped with lanthanide metal ions (La, Nd, Er and Yb) has been successfully synthesized, and then Pt is introduced through impregnation. The morphology, structure and component analysis are characterized by SEM, TEM (HRTEM), EDS, XRD, ICP-AES, XPS, UV Raman, O2-TPD, H2-TPR and CO or O2-pulse chemisorption, and the corresponding catalytic performances are developed by partial oxidation of methane. On the basis of the analysis of the structural properties of various catalysts, it is found that the Pt/CeLa catalyst shows the best catalytic performance due to its low valence state of Pt, excellent oxygen migration capacity and oxygen storage capacity, T50 is 510 °C and the selectivity is superiority. What's more, the modification of CeO2 by lanthanide metal ions especially La3+ can effectively change the oxygen activity of supports, so that this catalyst can be used in various redox catalytic reactions.

A review on state-of-the-art catalysts for methane partial oxidation to syngas production

ABSTRACT The rapid and severe deactivation of methane partial oxidation catalysts remains a major hindrance restraining its potential in commercialization and industrialization for large-scale syngas production. It is imperative to provide an in-depth understanding discission about the intrinsic and synergistic interactions of catalyst components toward the catalyst efficiency during reforming reactions. This review presents a contemporary evaluation of recent works on synergistic relationship among catalyst components (support, active metals and catalyst structure) during methane partial oxidation using theoretical and state-of-the-art experimental procedures. Advancements achieved through this synergistic relationship not only enhance properties of existing catalysts but also leading to discovery and development of novel catalyst systems. Thermodynamics, reaction mechanisms, catalytic performances, catalyst deactivation induced by carbonaceous deposition and reaction kinetic modeling have been successfully explored and described using information from these essential interactive factors over these decades. This viewpoint explains the roles of the interactions and their functions toward exploration of efficient catalysts systems for industrial applications.

Single-Atom High-Temperature Catalysis on a Rh1O5 Cluster for Production of Syngas from Methane.

Single-atom catalysts are a relatively new type of catalyst active for numerous reactions but mainly for chemical transformations performed at low or intermediate temperatures. Here we report that singly dispersed Rh1O5 clusters on TiO2 can catalyze the partial oxidation of methane (POM) at high temperatures with a selectivity of 97% for producing syngas (CO + H2) and high activity with a long catalytic durability at 650 °C. The long durability results from the substitution of a Ti atom of the TiO2 surface lattice by Rh1, which forms a singly dispersed Rh1 atom coordinating with five oxygen atoms (Rh1O5) and an undercoordinated environment but with nearly saturated bonding with oxygen atoms. Computational studies show the back-donation of electrons from the dz2 orbital of the singly dispersed Rh1 atom to the unoccupied orbital of adsorbed CHn (n > 1) results in the charge depletion of the Rh1 atom and a strong binding of CHn to Rh1. This strong binding decreases the barrier for activating C-H, thus leading to high activity of Rh1/TiO2. A cationic Rh1 single atom anchored on TiO2 exhibits a weak binding to atomic carbon, in contrast to the strong binding of the metallic Rh surface to atomic carbon. The weak binding of atomic carbon to Rh1 atoms and the spatial isolation of Rh1 on TiO2 prevent atomic carbon from coupling on Rh1/TiO2 to form carbon layers, making Rh1/TiO2 resistant to carbon deposition than supported metal catalysts for POM. The highly active, selective, and durable high-temperature single-atom catalysis performed at 650 °C demonstrates an avenue of application of single-atom catalysis to chemical transformations at high temperatures.

Role of oxygen vacancies in dendritic fibrous M/KCC-1 (M = Ru, Pd, Rh) catalysts for methane partial oxidation to H2-rich syngas production

The fibrous M/KCC-1 (M = Ru, Pd, Rh) catalysts prepared by microwave-assisted hydrothermal approach were investigated for methane partial oxidation (MPO) reaction at stoichiometric CH4/O2 feed ratio and temperature of 500–800 °C. A drop in BET surface area with metal oxide addition suggesting the successful embedment of metal oxides on KCC-1. Low-angle XRD, FTIR and TEM analyses confirmed the formation of bicontinuous concentric lamellar morphologic structure, typical fingerprint of fibrous KCC-1. The H2-TPR and ESR studies revealed that oxygen vacancy (OV) of KCC-1 not only beneficial for the metal-support interactions of catalysts but also strongly and dissociately bind with O2, CO2 and H2O promoting the syngas formation rate. The post-reaction Raman spectroscopy measurement corroborated the M/KCC-1 catalysts hindered the graphitic carbon formation during reaction. The Rh/KCC-1 appeared to be the optimum catalyst as it exhibited the TOF of both CH4 consumption and H2 formation about 2-fold higher to other catalysts meanwhile achieving H2/CO ratio about 2.16 that applicable for industrial applications. Based on the experimental MPO evaluation, post-reaction Raman spectroscopy and the in-situ ESR studies, the synergistic effects of metals and OV from fibrous KCC-1, where metal dissociates CH bonds in CH4 molecules whilst OV generates activated O2− species from oxidants at the OV sites, are determined as the key factors for the enhancement in MPO activity.

(Ag)Pd-Fe3O4 Nanocomposites as Novel Catalysts for Methane Partial Oxidation at Low Temperature.

Nanostructured composite materials based on noble mono-(Pd) or bi-metallic (Ag/Pd) particles supported on mixed iron oxides (II/III) with bulk magnetite structure (Fe3O4) have been developed in order to assess their potential for heterogeneous catalysis applications in methane partial oxidation. Advancing the direct transformation of methane into value-added chemicals is consensually accepted as the key to ensuring sustainable development in the forthcoming future. On the one hand, nanosized Fe3O4 particles with spherical morphology were synthesized by an aqueous-based reflux method employing different Fe (II)/Fe (III) molar ratios (2 or 4) and reflux temperatures (80, 95 or 110 °C). The solids obtained from a Fe (II)/Fe (III) nominal molar ratio of 4 showed higher specific surface areas which were also found to increase on lowering the reflux temperature. The starting 80 m2 g−1 was enhanced up to 140 m2 g−1 for the resulting optimized Fe3O4-based solid consisting of nanoparticles with a 15 nm average diameter. On the other hand, Pd or Pd-Ag were incorporated post-synthesis, by impregnation on the highest surface Fe3O4 nanostructured substrate, using 1–3 wt.% metal load range and maintaining a constant Pd:Ag ratio of 8:2 in the bimetallic sample. The prepared nanocomposite materials were investigated by different physicochemical techniques, such as X-ray diffraction, thermogravimetry (TG) in air or H2, as well as several compositions and structural aspects using field emission scanning and scanning transmission electron microscopy techniques coupled to energy-dispersive X-ray spectroscopy (EDS). Finally, the catalytic results from a preliminary reactivity study confirmed the potential of magnetite-supported (Ag)Pd catalysts for CH4 partial oxidation into formaldehyde, with low reaction rates, methane conversion starting at 200 °C, far below temperatures reported in the literature up to now; and very high selectivity to formaldehyde, above 95%, for Fe3O4 samples with 3 wt.% metal, either Pd or Pd-Ag.

Synergistic promotion effect of MgO and CeO2 on nanofibrous Ni/Al2O3 catalysts for methane partial oxidation

Ni/Al2O3 catalysts are formed via NiAl2O4 reduction while inactive NiAl2O4 is readily re-formed in the presence of oxidant agent during reactions, such as oxygen in methane partial oxidation. MgO has demonstrated promotion effect through securing Al2O3 to form MgAl2O4 during catalyst calcination so as to diminish NiAl2O4 formation. However, the promotion effect is limited by the formation of NiO-MgO solid solution with low reducibility. CeO2 promotes NiAl2O4 reduction via forming CeAlO3 and therefore prevents NiAl2O4 re-formation during the reaction. This study, for the first time, demonstrates the synergistic promotion effect of MgO and CeO2 on the Ni/Al2O3 catalysts for methane partial oxidation through optimizing MgO and CeO2 contents in the MgO-CeO2-Ni/Al2O3 catalyst system. The thermally stable structure of fibrous catalysts prepared by one-step electrospinning enables the investigation of the synergistic promotion.

La1-xSrxFeO3 perovskite-type oxides for chemical-looping steam methane reforming: Identification of the surface elements and redox cyclic performance

We report a family of perovskite-type oxides La1-xSrxFeO3 (x = 0.1, 0.3, 0.5, 0.7, 1.0) prepared by combustion method as effective redox catalysts for methane partial oxidation and thermochemical water splitting in a cyclic redox scheme. The effect of Sr-doping on the characterizations and properties of these perovskite-type oxides were studied by means of X-ray diffraction (XRD), hydrogen temperature-programmed reduction (H2-TPR), X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM). All the as-prepared and regenerated samples with various Sr substitutions exhibited pure crystalline perovskite structure. The oxygen carrying capacity of the La1-xSrxFeO3 perovskites was improved by doping Sr into the La-site. Besides, Sr-substitution has obvious effects on the valences of the Fe cations in the B-site and the oxygen species distribution of the La1-xSrxFeO3 perovskites. We recommend La0.7Sr0.3FeO3 as the optimal oxygen carrier in the series because it gives the maximum Ola/Oad (Ola and Oad stand for lattice oxygen and adsorbed oxygen species, respectively.) ratio of 3.64:1, which can be regarded as a criterion for the reactivity and selectivity of partial oxidation of methane into syngas of the oxygen carriers. Up to 80% CH4 conversion in the methane partial oxidation step and 96% of H2 concentration in the water splitting step were achieved in ten successive redox tests conducted in a fixed bed reactor at 850 °C with La0.7Sr0.3FeO3 as a redox catalyst. The electronic properties of the original LaFeO3 cell and its lattice substituted by Sr were calculated based on the density functional theory method. Electronic structure analysis demonstrates that doping of Sr makes LaFeO3 more electric conductive and its electron is prone to be excited. This is in agreement with the test results that La0.7Sr0.3FeO3 exhibited better performance in chemical looping reactions.

Ni/CeO2 catalysts for methane partial oxidation: Synthesis driven structural and catalytic effects

Catalytic partial oxidation of methane (CPO) to synthesis gas was performed over differently prepared CeO2 supported nickel catalysts with 6wt% Ni content. The samples were synthesized by microwave assisted procedures and by hydrothermal deposition procedure. Differences in the catalyst structural properties of the prepared catalysts were detected by XRD, TPR and XPS measurement. When tested at atmospheric pressure with feed gas mixture containing methane and oxygen in molecular ratio CH4/O2=2, all the samples reached 98% conversion with CO selectivity values >95% in the 700–800°C temperature range. The samples exhibited different behavior towards carbon formation during the tests. Moreover, according to XRD, XPS and TGA results, when the carbon was formed it did not cause catalyst deactivation. TPR profiles confirmed different degree of chemical interaction between NiO and CeO2 support, depending on the preparation method. The building up or the easy removal of carbon during the CH4 temperature programmed surface reaction (TPSR), substantiate the role of the CeO2 lattice oxygen mobility, enhanced by metal-support interaction, in the removal of the deposited carbon through CO evolution. Structure-activity relationship established a close dependence of the CPO performance on the combination of NiO and CeO2 crystallite sizes and the interaction between the two.

Water-treated Rh/γ-Al2O3 catalyst for methane partial oxidation

A water treatment technique, using H2 as a reducing agent in a wet environment, was applied to a conventional Rh/γ-Al2O3 catalyst. Both standard- and water-treated Rh/γ-Al2O3 catalysts were prepared and their catalytic performances were tested in methane partial oxidation reaction. The water-treated Rh/γ-Al2O3 catalyst shows higher CO selectivity and lower CO2 selectivity between 300 and 600 °C, compared with the standard-treated catalyst. The enhancement is attributed to the formation of well-dispersed smaller Rh nanoparticles.

Synthesis of single-site copper catalysts for methane partial oxidation.

Cu-Exchanged zeolites are known as active materials for methane oxidation to methanol. However, understanding of the formation of Cu active species during synthesis, dehydration and activation is fragmented and rudimentary. We show here how a synthesis protocol guided by insight in the ion exchange elementary steps leads to highly uniform Cu species in mordenite (MOR).

Effect of core and shell compositions on MeOx@LaySr1−yFeO3 core–shell redox catalysts for chemical looping reforming of methane

The chemical looping reforming (CLR) process converts methane into syngas through cyclic redox reactions of an active lattice oxygen (O2−) containing redox catalyst. In CLR, methane is partially oxidized to CO and H2 using the active lattice oxygen of a redox catalyst. In a subsequent step, the oxygen-deprived redox catalyst is regenerated by air. Such a process can eliminate the need for steam and/or oxygen in reforming, thereby improving methane conversion efficiency. A number of perovskite-structured mixed metal oxides are known to be active for CLR. However, the oxygen storage capacity of perovskites tends to be low, limiting their practical application in chemical looping. In contrast reducible metal oxides such as cobalt and iron oxides can store up to 30wt.% lattice oxygen but are less selective for syngas generation. We explore oxygen carriers that utilize the advantages of both perovskites and first-row transition metal oxides by integrating a transition metal oxide core with a mixed ionic–electronic conductive (MIEC) perovskite support/shell. MIEC perovskites facilitate countercurrent conduction of O2− and electrons, allowing facile O2− transport though the solid. It is proposed that this conduction allows rapid oxygen transport to and from the transition metal oxide cores irrespective of the porosity of the redox catalyst. In this work, we show that MeOx@LaySr1−yFeO3 can be an excellent model catalyst system for CLR. The activity, selectivity, and coke resistance of the core–shell system can be tuned by changing the ratio of La to Sr in the perovskite shell and the type of transition metal oxide in the core. Our studies indicate that lower Sr loadings can improve activity and selectivity of the catalyst for methane partial oxidation, but make the LSF shell less resistant to decomposition during the reduction step.

Effects of alkaline-earth strontium on the performance of Co/Al2O3 catalyst for methane partial oxidation

A series of Sr-Co/Al2O3 catalysts were prepared by co-impregnation method using γ-Al2O3 as the support. The effect of strontium promoter on the catalytic performance of Co/Al2O3 catalyst for partial oxidation of methane (POM) to synthesis gas was studied. The catalysts were characterized by some physicochemical characterizations such as N2 physical adsorption, X-ray diffraction (XRD), H2-temperature programmed reduction (H2-TPR) and thermogravime try (TG). The results show that both Co/Al2O3 calcined at 700°C and Sr-Co/Al2O3 calcined at 800°C exhibit low activity and deactivate at the initial stage of POM reaction. The addition of above 2% mass fraction of strontium will greatly enhance the activity and stability of Co/Al2O3. Two types of Co species were identified on the fresh calcined catalysts. One is Co3O4 which weakly interacts with Al2O3 (easily reduced by H2) and the other is the spinel CoAl2O4 (non-catalytic performance) which strongly interacts with the support. During the course of calcination, strontium can react with Al2O3 to form Sr4Al14O25 which will restrain the generation of the CoAl2O4 species and promote the stability and activity of catalysts. Without strontium promoter, CoAl2O4 is easy to be formed over Co/Al2O3 in the POM reaction. However, the formation of CoAl2O4 cannot be avoided with the addition of limited strontium when the calcination temperature is over 800°C.

Surface and structural features of Pt/CeO2-La2O3-Al2O3 catalysts for partial oxidation and steam reforming of methane

Mixed xCeO2-yLa2O3-Al2O3 oxides (where x+y=12wt%) were prepared by sol–gel method. It was shown that the mixed oxides are suitable carriers for supported Pt catalysts. The catalytic performances of the catalysts were evaluated in the reaction of stem methane reforming (SMR) and partial oxidation of methane (POM). The effect of the support kind on the surface and structural properties, as well as on the redox and catalytic behavior of the catalyst was studied. It was shown that the coexistence of the Pt0/Ptδ+ and Ce4+/Ce3+ redox couples leads to the increase of the CH4 conversion and carbon resistance over Pt catalysts. The CeO2-containing catalysts showed the highest TOFCH4 values in SMR in spite of the low metal dispersion that is related to the high capacity of the surface to carbon cleaning caused by the highest oxygen mobility at metal–support interface. The strong initial deactivation of alumina-supported Pt catalyst in POM was related to Pt sintering.

A new Gd-promoted nickel catalyst for methane conversion to syngas and as an anode functional layer in a solid oxide fuel cell

The effect of lanthanide promoters on a Ni–Al 2O 3 catalyst for methane partial oxidation, steam reforming and CO 2 reforming at 600–850 °C is systematically investigated. The promoters include La 2O 3, CeO 2, Pr 2O 3, Sm 2O 3 and Gd 2O 3. GdNi–Al 2O 3 shows comparable catalytic activity to LaNi–Al 2O 3 and PrNi–Al 2O 3 but higher activity than CeNi–Al 2O 3 and SmNi–Al 2O 3 for all three reactions. The O 2-TPO results show that GdNi–Al 2O 3 possesses the best coke resistance among those tested. It also displays good stability at 850 °C for 300 h. Raman spectroscopy indicates that the addition of lanthanide promoters can reduce the degree of graphitization of the carbon deposited on Ni–Al 2O 3. The GdNi–Al 2O 3 is further applied as an anode functional layer in solid-oxide fuel cells operating on methane. The cell yields peak power densities of 1068, 996 and 986 mW cm −2 at 850 °C, respectively, for operating on methane–O 2, methane–H 2O and methane–CO 2 gas mixtures, which is comparable to operating on hydrogen fuel. GdNi–Al 2O 3 is promising as a highly coking-resistant catalyst layer for solid-oxide fuel cells.

The Effect of Support on Sulphur Tolerance of Rh Based Catalysts for Methane Partial Oxidation

The presence of sulphur containing compounds, naturally occurring in natural gas or added as odorants, can adversely affect the performance of noble metals based catalysts for the partial oxidation of methane to syngas. In this paper the effect of SO2 addition on the catalytic partial oxidation of methane was investigated on Rh (1 wt.%) catalysts prepared by incipient wetness impregnation method on two different commercially available high temperature γ-alumina supports stabilized either with 10% SiO2 or 3% La2O3. Based on the results of catalytic activity measurements and in-situ FT-IR spectroscopic characterisation, as well as TPR/TPD studies, it has been shown that the presence of sulphur can severely suppress the formation of synthesis gas by inhibiting the reforming reactions during the catalytic partial oxidation of methane. The results also demonstrated that the support plays a crucial role in the partial oxidation reaction. In the presence of a sulphating support such as La2O3–Al2O3 the partial oxidation reaction was much less inhibited than a less sulphating support such as SiO2–Al2O3. The sulphating support acts as a sulphur storage reservoir, which minimises the poison from adsorbing on or near the active Rh sites where reactions take place.

Methane partial oxidation using Ni/Ce 0.9Zr 0.1O 2 catalysts

The development of active and selective catalysts for methane partial oxidation is one of today's challenges, because these catalysts could be used either for hydrogen production purposes or as anode materials in single-chamber solid oxide fuel cells (SOFCs). In this work, the synthesis of ceria–zirconia solid solutions of nominal composition Ce 0.9Zr 0.1O 2 through the gel-combustion route is presented. The solids obtained were impregnated with nickel solutions to achieve contents of 9% and 50% (m/m), characterized texturally and structurally, and their catalytic behavior in the methane partial oxidation reaction was assessed. The synthesis method was effective, leading to solids with good morphological properties. Likewise, the Ni/Ce 0.9Zr 0.1O 2 catalysts proved to be active and showed a stable behavior during the working period, with methane conversion levels of 90% at temperatures above 550 °C, being hydrogen and carbon monoxide the main products.

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.

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.