Activity For Methane Conversion Research Articles

Small iridium clusters supported on TiO2 as catalysts for intensifying low-temperature methane activation and reforming

Hydrogen production via low-temperature (<550 °C) steam reforming of methane (SRM) has attracted increasing research attention due to its importance as an alternative, efficient, and environmentally benign energy carrier. The thermodynamic limitation of low-temperature SRM can be eased by process design such as using a membrane reactor or an adsorption-enhanced reforming process, and an active low-temperature SRM catalyst with high stability would be indispensable. Herein, we report a 2 wt% Ir/TiO2 catalyst that exhibits high methane conversion activity in low-temperature SRM with a relatively high turnover frequency (TOF) and a low activation energy in comparison with the literature. Long-term catalyst stability test demonstrates a good resistance to coking and sintering during low-temperature SRM reactions. In situ spectroscopy analyses and density functional theory (DFT) calculations reveal that the small Ir clusters and Ir single atoms (SAs) are both active for methane conversion, while the clusters exhibit higher activity than SAs for low-temperature SRM reaction. Microkinetic simulation based on DFT calculations shows consistent product formation temperatures and the simulation nicely reproduces the product distribution observed in experimental analysis, which confirms the superior SRM activity of the TiO2-supported Ir clusters in this work.

Performance and reaction mechanism of Mg-doped and Li-doped La2O3 catalysts in oxidative coupling of methane: DFT and experiment study

Lanthanum oxide (La2O3) catalyst is a promising catalytic system for oxidative coupling of methane (OCM) reaction, while low activity for methane dissociation restricts its widespread application. Low-value dopants can enhance methane conversion activity on La2O3 catalysts. This work systematically studied the mechanism and catalytic performance of OCM reaction on Mg-doped and Li-doped La2O3 catalysts using a combination of DFT and experimental methods. The results show that Mg-doped and Li-doped can significantly improve CH4 dissociation activity and C2H4 selectivity on La2O3(001) surface. The microscopic property analysis shows that the p-band center of lattice oxygen on Mg-doped and Li-doped La2O3(001) is closer to the Fermi level, compared with undoped La2O3(001), which is more conducive to the activation of methane. Furthermore, Mg-doped and Li-doped La2O3 catalysts are prepared and their OCM catalytic performance are investigated. The catalytic performance of Mg-doped La2O3 catalyst reaches its best at 750 °C, with a high CH4 conversion (above 30.9 %) and the highest C2+ hydrocarbons selectivity (about 47.5 %) and C2+ yield (about 14.7 %). However, Li-doped La2O3 shows poorer catalytic performance than undoped La2O3, primarily due to the loss of the doped Li during the OCM process. In addition, the OCM reaction cycle and the mechanism of action of oxygen species on Mg doped La2O3(001) have been studied. The results show that lattice oxygen and peroxide species are the major active oxygen species for activating methane.

Effect of different valence metals doping on methane activation over La2O3(001) surface

La2O3 as a catalyst is used for oxidative coupling of methane (OCM) reactions due to its excellent stability and high C2 selectivity, but poor activity on methane dissociation limits its wide application. Different valence metals are doped on the La2O3(001) surface to improve the methane conversion activity, and the activation of methane on metal-doped La2O3(001) surfaces has been investigated via the density functional theory (DFT) calculations. The relationship between the valence states of doped metals and the methane conversion activities shows that doping low valence metals (Li, Na, K, Mg, Ca, Sr and Ba) and equivalent metals (Al, Ga, In) can significantly improve the conversion activity of methane. Among them, the activation energy of methane on the Li-La2O3(001) surface is the lowest, which is only 13.0 kJ/mol. However, doping of high valence metals (Zr, Nb, Re and W) cannot improve the CH4 dissociation activity. Furthermore, the relationships between surface oxygen vacancy formation energies, acid-base properties and the activation energies of CH4 have also been investigated. The results show that with the increase of metal valence state, the oxygen vacancy formation energy increases, while the dissociation activity of CH4 decreases. The introduction of alkali and alkaline earth metals increases the alkalinity of La2O3(001) surface, and the alkalinity of La2O3(001) doped with the alkali metal is stronger than that with the alkaline earth metal, exhibiting higher dissociation activity of CH4. Our research may provide a guide for improving methane conversion activity on La2O3 catalysts.

High metal loaded Cu(i)N3 single-atom catalysts: superior methane conversion activity and selectivity under mild conditions

With a high-metal loading of 17.7 wt%, a single-atom Cu(i)N3 catalyst was prepared using a Cu–benzimidazole complex, exhibiting high reactivity (6.1 mmol g−1 h−1) and ∼90% selectivity in methane partial oxidation.

(Invited, Digital Presentation) Methane Conversion to High Value Chemicals By Photocatalysis

As underlined in the COP26, methane as a greenhouse gas is nearly 80 time more potent than CO2 while its reserve is much more than the sum of coal, oil and natural gas. Thus methane conversion not only involves the environmental issue but also is related to high-value chemical production /clean energy supply, which has been attracting substantial interest over the last decades. However CH4 activation is energy intensive and kinetically very challenging so that methane activation is regarded as the “holy grail” in the catalytically chemical process. [1] Photocatalysis provides a cost efficient potential to activation of such small molecule under very mild conditions, while to achieve the potential is a huge challenge.[2]Stimulated by our research outcomes on the charge dynamics in inorganic semiconductor photocatalysis, which reveal that the low reaction efficiency is due to both fast charge recombination and large bandgap of an inorganic semiconductor [3,4], together with the recent findings on atomic catalysis [5], we developed novel material strategies for photocatalytic methane conversion to methanol. Highly dispersed atomic level iron species immobilised on a TiO2 photocatalyst show an excellent activity for methane conversion, resulting into ~97% selectivity towards alcohols operated under ambient conditions by a one-step chemical process [6]. Such photocatalyst is also very stable, promising an attractive industrial process of methane upgrade. The dominating function of the iron species has also been investigated in detail. Furthermore, we designed a flow system for relatively efficient methane to C2, achieving the benchmark results in this area.[7] In addition, C1 oxygenates can be produced with nearly 100% by photocatalytic methane conversion due to the synergy between Au and Cu cocatalysts loaded on ZnO.[8] References ： Li, X. Wang, C., Tang, J. Nature Reviews Materials , 2022, Doi: 1038/s41578-022-00422-3.Wang Y., Suzuki H., Xie, J., Tomita, O., Martin, D. J., Higashi, M., Kong, D., Abe R. Tang, J., Chem. Rev., 2018, 118: 5201-5241.Tang, J. Durrant J. R., Klug, R ., J. Am. Chem. Soc ., 2008, 130(42) : 13885-13891.Miao, T., Wang, C., Xiong, L., Li, X., Xie, X., Tang, J., ACS Catalysis , 2021, 11, 8226-8238.Wang, A. Li J., Zhang. T., Nat . Rev. Chem ., 2018, 2; 65-81.Xie, J., Jin, R. ,Li, A., Bi, Y., Sankar, G. , Ma , Tang, J. Nature Catalysis , 2018, 1: 889-896.Li, X., Xie J.,Rao, H., Wang, , Tang, J., Angewandte Chemie International Edition , 2020, 132: 19870-19875.Luo, L., Gong, Z., Xu, Y., Ma, J., Liu, H., Xing, J., Tang, J., Journal of the American Chemical Society , 2022, 144, 2, 740–750.

Spinel oxides as coke-resistant supports for NiO-based oxygen carriers in chemical looping combustion of methane

Due to their high activity for methane conversion under a cyclic redox scheme, supported nickel oxides are among the most extensively investigated oxygen carrier materials for chemical looping combustion (CLC) and reforming (CLR) of methane. However, coke formation remains as a key challenge for Ni-containing oxygen carriers. The current study investigates the effect of reducible, spinel-structured supports to enhance coke resistance of NiO-based oxygen carriers. It was hypothesized that reducible supports capable of continued yet slow lattice oxygen donation in the presence of methane can actively retard coke formation on the surface of the oxygen carriers. To evaluate such effects, NiFe2O4, MgFe2O4, and BaFe2O4 are investigated as coke-resistant, reducible supports for NiO using mass spectrometry (MS) and thermogravimetric analysis (TGA) during chemical looping cycles. All three reducible supports were capable of continuous oxygen donation over an extended period of time (>40 min) without signs of coke formation. When used as supports for NiO, the resulting oxygen carriers showed no sign of carbon deposition under typical methane CLC environments. In comparison, NiO supported on inert MgAl2O4 exhibited significant coke formation after only 2.5 min. Moreover, NiO supported on NiFe2O4 and BaFe2O4 exhibited faster redox activity and higher oxygen carrying capacity when compared to the inert MgAl2O4-supported NiO. Detailed investigation of the reduction behavior of NiFe2O4-supported NiO revealed extensive solid-state reactions and Ni/Fe exchanges among the support, NiO, and newly formed phases. Specifically, initial weight loss in NiFe2O4-supported NiO was associated with reduction of the oxygen carrier to metallic Ni and Fe3O4 phases. Subsequent coke inhibition was attributed to the slow reduction of Fe3O4 and FeO phases. Multi-cyclic redox studies indicated that NiFe2O4-supported NiO gradually lost its redox activity. In comparison, both MgFe2O4- and BaFe2O4-supported NiO exhibited satisfactory redox stability, activity, and coke resistance.

Enhanced performance of chemical looping combustion of methane by combining oxygen carriers via optimizing the stacking sequences

Combination of different types of oxides is a general strategy to prepare high performance oxygen carriers (OCs) for chemical looping combustion (CLC) technology. However, the possible chemical interactions among different components during the long-term redox cycling may reduce the stability of OCs. In the present work, we physically combine different types of OC sticks (i.e., CuO/SiO2, Fe2O3/Al2O3, Mn2O3/ZrO2 and NiO/ZrO2) in particular stacking sequences in a fixed bed reactor to improve the CLC performance. The reaction between methane and CuO is exothermic and the CuO/SiO2 OC exhibits very high activity for methane oxidation and superior resistance to carbon deposition. It is suitable to place the CuO/SiO2 in the front of the sequence which can sufficiently convert methane, and the heat releasing from this reaction will promote the following endothermic reactions. NiO/ZrO2 OC also represents very high activity for CH4 oxidation but results in serious carbon deposition. Since the reduced metallic Ni is an active catalyst for methane activation, it is suggested to place NiO/ZrO2 in the middle of the sequence to enhance the further conversion of methane and to provide enough space to remove the carbon deposition via the gasification by CO2 or H2O generated from the front reaction. Mn2O3/ZrO2 OC possesses poor activity for methane conversion but high resistance to carbon deposition, which can be used to convert unreacted methane in the end of the sequence. Fe2O3/Al2O3 OC is not an important issue due to the low activity and reaction rate. As a result, the combined OCs with a stacking sequence of CuNiFeMn or FeCuNiMn show high performance in CH4 conversion (>97%), CO2 selectivity (>96%), redox stability and resistance to carbon deposition. These results make a certain reference for using the combined OCs in the large-scale CLC system.

Non-oxidative methane dehydroaromatization on Mo/HZSM-5 catalysts: Tuning the acidic and catalytic properties through partial exchange of zeolite protons with alkali and alkaline-earth cations

In this work, partial exchange of protons in H-ZSM-5 zeolite with alkali (Na+, Cs+) and alkaline-earth (Ca2+, Mg2+) cations was applied as a simple means of modulating the density and strength of the zeolite Brønsted acid sites with the aim of depressing the coke-forming tendency and, hence, of improving the stability of Mo/ZSM-5 catalysts (3wt% Mo, Si/Al=15) for methane dehydroaromatization (MDA). The materials were characterized by ICP-OES, XRD, N2 physisorption, 27Al MAS NMR, H2-TPR, DRS UV–vis, XPS, FTIR-pyridine, and NH3-TPD. Coke in spent catalysts was characterized by TGA and TPO. The MDA experiments lasted about 8h and were performed at the standard conditions of 700°C, 1bar, and GHSV of 1500cm3/(gcath). The preferential neutralization of the most acidic OH groups (likely associated to “isolated Al” atoms in the zeolite framework) by Na+ reduced both the amount and the average strength of the remaining Brønsted acid sites. The reduction in the acid site density decreased the amount of (Mo2O5)2+ and/or (MoO2)2+ species anchored to the zeolite framework (precursors of the active MoCx/MoCxOy nanoclusters) and, consequently, the methane conversion rate. However, an optimum exchange level (corresponding to a Na/Al atomic ratio of 0.1) was found for which the derived catalyst (Mo/Na10HZ5) exhibited an unusually low coke selectivity of ca. 10% (on a C basis) as compared to the selectivity of ca. 36% obtained for the parent Mo/HZ5 catalyst. Concomitantly, the selectivity to benzene raised from 42% for Mo/HZ5 to 66% for Mo/Na10HZ5 and the decay rates for both methane conversion and benzene formation (at TOS>6h) decreased by about one order of magnitude for Mo/Na10HZ5 with respect to Mo/HZ5. The increased benzene selectivity and stability lead to higher and more sustained benzene formation rates during the last reaction stages (TOS>6h) for Mo/Na10HZ5 in spite of its lower activity for methane conversion in comparison to Mo/HZ5. Similar trends, though less pronounced, were observed for the catalyst comprising the zeolite exchanged with Cs+ at the optimum exchange level of M+/Al=0.1. On the other hand, the exchange with divalent Ca2+ and Mg2+ cations (at an equivalent exchange level of M2+/Al=0.05) produced zeolites having similar amount of Brønsted acid sites but with a higher average strength than those of the zeolites exchanged with Na+ and Cs+. Despite an alike density of Brønsted acid sites, the migration of Mo and formation of exchanged divalent Mo cationic precursors within the zeolite channels were restrained in the catalysts comprising the Ca2+ and Mg2+ exchanged zeolites as part of the sites required to accommodate the (Mo2O5)2+/(MoO2)2+ species (those associated to the so-called “Al pairs”) were already balanced by the alkaline-earth cations. Consequently, lower methane conversion rates were obtained for the Mo/Ca5HZ5 and Mo/Mg5HZ5 catalysts. In turn, the reduction in Brønsted acidity upon partial exchange with Ca2+ and Mg2+ also decreased the selectivity to coke and increased that to benzene of the corresponding catalysts with respect to the reference Mo/HZ5 sample, though the changes were much less notorious than for the catalysts based on the zeolites exchanged with alkali cations. However, differently from the later, the reduction in coke selectivity did not translate into an enhanced stability of the Mo/Ca5HZ5 and Mo/Mg5HZ5 catalysts with respect to Mo/HZ5 which, according to TPO, was ascribed to the more inert nature (higher deactivating power) of their carbon deposits.

Methane oxidation over Pt, Pt:Pd, and Pd based catalysts: Effects of pre‐treatment

This paper presents a comparison of the activity for methane oxidation of selected commercial platinum, palladium, and platinum‐palladium supported catalysts. Precious metal loadings are typical of those found in the catalytic converters for lean‐burn natural gas engines. Experiments are presented for de‐greened as well as hydrothermally aged catalysts, both in the presence and the absence of water. For the platinum catalyst, fraction conversion of methane is shown to be independent of methane concentration, while for the palladium‐containing catalysts a dependence of conversion on methane partial pressure is observed. For catalysts containing palladium, reduction in hydrogen gives an increase in methane conversion activity, although the increase is subsequently lost in the oxidizing atmosphere. Hydrothermal aging of the platinum catalyst causes a relatively large and permanent loss in methane oxidation activity, while the palladium‐based catalysts showed more resistance to deactivation. Adding a small amount of palladium to the platinum catalyst provides an overall improvement in performance.

Plasma-Enhanced Methane Direct Conversion over Particle-Size Adjusted MOx/Al2O3 (M = Ti and Mg) Catalysts

Non-oxidative methane activation over particle-size adjusted alumina catalysts loaded with metal oxide (Al2O3, MgO/Al2O3, and TiO2/Al2O3) was investigated with a dielectric barrier discharge reactor using 10 % CH4 in Ar at plasma induced temperature. Plasma-assisted catalytic activity for direct conversion of methane over the catalysts was compared with that using plasma only. Catalyst hybrid reaction in a non-thermal discharge showed that MgO/Al2O3 had the highest activity for methane conversion. C2, C3, and C4 hydrocarbons were formed as products; ethane, ethylene, and acetylene were predominant over all catalysts. The effect of varying particle size of the MgO/Al2O3 catalyst was also examined. The conversion of methane over MgO/Al2O3 dramatically increased with decreasing catalyst particle size from 1.70 to 0.25 mm. It is interesting to note that distribution of C2 hydrocarbons was tuned by changing the particle size of the catalyst. It was also observed that the gas flow rate, frequency, and power supplied affected direct conversion of methane and selectivity of products significantly.

Low metal content Co and Ni alumina supported catalysts for the CO2 reforming of methane

Low metal content Co and Ni alumina supported catalysts (4.0, 2.5 and 1.0 wt% nominal metal content) have been prepared, characterized (by ICP-OES, TEM, TPR-H2 and TPO) and tested for the CO2 reforming of methane. The objective is to optimize the metal loading in order to have a more efficient system. The selected reaction temperature is 973 K, although some tests at higher reaction temperature have been also performed. The results show that the amount of deposited carbon is noticeably lower than that obtained with the Co and Ni reference catalysts (9 wt%), but the CH4 and CO2 conversions are also lower. Among the catalysts tested, the Co(1) catalyst (the value in brackets corresponds to the nominal wt% loading) is deactivated during the first minutes of reaction because CoAl2O4 is formed, while Ni(1) and Co(2.5) catalysts show a high specific activity for methane conversion, a high stability and a very low carbon deposition.

Application of BaTiO3 as anode materials for H2S-containing CH4 fueled solid oxide fuel cells

Undoped BaTiO3 perovskite oxide is more effective than SrTiO3 and La2Ti2O7 oxide as anode catalyst in SOFC fueled with H2S-containing methane. Electrochemical performance, impedance spectroscopy and other characterizations show that pure BaTiO3 is a good anode catalyst for conversion of methane in SOFC, especially in H2S-containing atmospheres. Compared with SrTiO3 and La2Ti2O7 samples, the BaTiO3−based fuel cell has higher resistance to carbon deposition, better electrochemical performance and much higher stability during long term operation. A maximum power density of 135 mW cm−2 was achieved at 900 °C with 0.5% H2S–CH4 in a fuel cell having a 300 μm thick YSZ electrolyte. High catalytic activity for methane conversion, mixed electronic and ionic conductivity, and the surface basicity of BaTiO3 unexpectedly provides promising performance as anodes in SOFC.

Mechanistic aspects of the Andrussow process over Pt–Rh gauzes. Pathways of formation and consumption of HCN

Reaction pathways governing HCN selectivity in the oxidative coupling of methane and ammonia were investigated over three commercial Pt–Rh gauzes (fresh, activated, and spent) in the temporal analysis of products reactor with submillisecond-time resolution using isotopic traces. These gauzes differed in the extent of reaction-induced restructuring as well as impurity content. The ability of the gauzes to form HCN in the dual interactions of CH 4 with NH 3 or NO was compared considering the morphological differences of the gauzes. It was found that the progressive structural changes increased the gauze activity for methane conversion and facilitate the stabilization of methane fragments on the catalyst surface, but did not influence significantly the surface residence time of N-containing species. The well-known increase in HCN selectivity within first hours on-stream in the Andrussow process was suggested to be likely due to restructuring-induced stabilization of surface methane fragments. The decrease in the HCN selectivity after a stable phase of operation is mainly related to consecutive oxidation of HCN over iron oxide accumulated on the catalyst surface under industrial conditions of the Andrussow process.

Influence of molar ratio on Pd–Pt catalysts for methane combustion

The catalytic oxidation of methane was investigated over six catalysts with different palladium and platinum molar ratios. The catalysts were characterised by TEM, EDS, XPS, PXRD and temperature-programmed oxidation. The results suggest that in the bimetallic catalysts, an alloy between Pd and Pt was formed in close contact with the PdO phase, with an exception for the Pt-rich catalyst, where no PdO was observed. It was found that the molar ratio between palladium and platinum clearly influences both the activity and the stability of methane conversion. By adding small amounts of platinum into the palladium catalyst, improved activity was obtained in comparison with the monometallic palladium catalyst. However, higher amounts of platinum are required for stabilising the methane conversion. The most promising catalysts with respect to both activity and stability were Pd 67Pt 33 and Pd 50Pt 50. The platinum-rich catalyst showed very poor activity for methane conversion.

CO2 Reforming of Methane to Syngas over CoOx/MgO Supported on Low Surface Area Macroporous Catalyst Carrier: Influence of Co Loading and Process Conditions

The effect of Co loading (5−30 wt %) and process parameters (reduction pretreatment, reaction temperature, and space velocity) have been investigated over CoOx/MgO(5%)/SA-5205 catalyst for the CO2 methane reforming process. The Co loading had a profound effect on the methane conversion and the hydrogen selectivity (initial and time-on-stream activity) for the unreduced catalysts. While negligible methane conversion was observed for the 5 and 10 wt % Co loading catalyst, methane conversions >95% were obtained over the high Co loading (20 and 30 wt %) catalysts; hydrogen selectivity followed the same trend as methane conversion. The Co loading level had a relatively smaller influence in the case of the reduced catalysts. While the 5 wt % Co catalyst showed low methane conversion activity (<30%), the 10 wt % Co catalyst showed methane conversion levels comparable to those of the high Co loading catalysts. The high Co loading catalysts showed an excellent time-on-stream performance for the CO2 methane reformi...

Stability Improvement of Rh/γ-Al2O3Catalyst Layer by Ceria Doping for Steam Reforming in an Integrated Catalytic Membrane Reactor System

Significant improvement over the equilibrium methane conversion level was achieved by performing the reforming of methane in a catalytic membrane reactor, which was prepared by integrating a microporous silica membrane with a sandwiched-type Rh/γ-Al2O3 catalyst layer. However, the methane conversion activity decreased progressively owing to the deactivation of the intermediate catalyst layer under the reaction environments. On the other hand, addition of CeO2 as a promoter for the Rh/γ-Al2O3 catalyst significantly improved the catalyst stability. The improvement was achieved probably by the kinetic and oxidative stabilization of the catalyst matrix with CeO2. However, compared to the nonpromoted system, the ceria-promoted systems displayed lower catalytic activities based on the Rh/Ce ratios. The results led to the conclusion that a controlled interplay of the catalytic potentiality of Rh and the stabilization effect of Ce are essential to obtain an acceptable system. The membrane quality and its performance decreased especially with high Ce incorporation in the catalyst layer, possibly as a result of the observed microstructural variations in the catalyst layer with the Ce addition. Therefore, a consensus between the activity and stability of the material as a catalyst and the textural characteristics of the catalyst layer as a support layer for the silica membrane is considered to be an important factor that decides the success of the approach. A possible mechanism has been suggested to explain the role of ceria as a promoter in the Rh/γ-Al2O3 system.

Development of anodes for direct electrocatalytic oxidation of methane in solid oxide fuel cells

Gold-doped nickel/zirconia and nickel/ceria cermet anodes incorporating different levels of gold have been prepared and studied as potential anodes for the direct electrocatalytic oxidation of methane in solid oxide fuel cells. The methane conversion activity and selectivity towards synthesis gas products of these anodes have been determined over a range of SOFC operating temperatures and methane/oxidant ratios, and compared with the corresponding undoped nickel cermet. The amount of carbon deposition has been determined using post-reaction temperature programmed oxidation. The influence of gold loading on the methane conversion activity, product selectivity and amount of carbon deposition has been determined. The addition of small amounts of gold to nickel cermets results in a dramatically increased tolerance to carbon deposition and a reduction in the activity of the anode and the selectivity towards partial oxidation compared to the corresponding undoped nickel cermet.

Energy efficient conversion of methane to syngas over NiO–MgO solid solution

Methane-to-CO and H 2 conversion reactions, involving partial oxidation by O 2, oxy-steam reforming, oxy-CO 2 reforming, CO 2 reforming, simultaneous steam and CO 2 reforming, over a NiO–MgO solid solution (Ni/Mg =0.5) have been investigated. The calcination (up to 1200°C) temperature of the catalyst has a small but significant effect on its activity/selectivity in the oxidative conversion of methane to syngas. The reduction (by H 2) temperature of the catalyst has no significant effect on the catalyst's performance. The catalyst shows high activity and selectivity in the oxy-steam reforming and oxy-CO 2 reforming reactions, at 800–850°C and high space velocity [(40–50)×10 3 cm 3 g −1 h −1]. These two processes involve coupling of the exothermic oxidative conversion and endothermic steam or CO 2 reforming reactions, making both the processes highly energy efficient and also safe to operate. The catalyst also shows high methane conversion activity (nearly 95% conversion) with 100% selectivity for both CO and H 2 in the simultaneous steam and CO 2 reforming of methane at (800–850°C) at a high space velocity (3.6×10 3 cm 3 g −1 h −1).

Catalytic combustion of gasified biomass over hexaaluminate catalysts: influence of palladium loading and ageing

Catalytic combustion of a low-heating value synthetic gas, that resembles the gas from air-blown fluidised bed gasification, was studied over palladium-impregnated lanthanum hexaaluminate catalyst washcoated on 400 cpsi cordierite monoliths. Some of the prepared samples were aged in humidified air at 1000°C up to 30 days. The effects of varied palladium loading, gas hourly space velocity, and fuel composition (ethene, water and ammonia concentrations) were studied by statistical evaluation of the temperatures needed for 10%, 50% and 95% conversion, respectively. The palladium series was compared to manganese-substituted and platinum-impregnated hexaaluminate samples. The results showed that gas hourly space velocity and palladium loading were the two most important factors influencing the ignition temperature of carbon monoxide, hydrogen and methane over palladium catalysts. The activity for methane conversion drops substantially over an aged palladium catalyst compared to a fresh one. A similar drop in methane conversion is observed when comparing the activity of a fresh sample with a high loading of palladium to fresh samples with lower loading of palladium. On the other hand, both the aged catalyst with an initial high loading of palladium and all fresh catalysts, both with high and low loading of palladium, have a high activity for conversion of carbon monoxide and hydrogen.

Simultaneous oxidative conversion and CO 2 or steam reforming of methane to syngas over CoO–NiO–MgO catalyst

CO2 reforming, oxidative conversion and simultaneous oxidative conversion and CO2 or steam reforming of methane to syngas (CO and H2) over NiO–CoO–MgO (Co: Ni: Mg=0·5: 0·5:1·0) solid solution at 700–850°C and high space velocity (5·1×105 cm3 g−1 h−1 for oxidative conversion and 4·5×104 cm3 g−1 h−1 for oxy-steam or oxy-CO2 reforming) for different CH4/O2 (1·8–8·0) and CH4/CO2 or H2O (1·5–8·4) ratios have been thoroughly investigated. Because of the replacement of 50 mol% of the NiO by CoO in NiO–MgO (Ni/Mg=1·0), the performance of the catalyst in the methane to syngas conversion process is improved; the carbon formation on the catalyst is drastically reduced. The CoO–NiO–MgO catalyst shows high methane conversion activity (methane conversion >80%) and high selectivity for both CO and H2 in the oxy-CO2 reforming and oxy-steam reforming processes at ⩾800°C. The oxy-steam or CO2 reforming process involves the coupling of the exothermic oxidative conversion and endothermic CO2 or steam reforming reactions, making these processes highly energy efficient and also safe to operate. These processes can be made thermoneutral or mildly exothermic or mildly endothermic by manipulating the process conditions (viz. temperature and/or CH4/O2 ratio in the feed). © 1998 Society of Chemistry Industry