Effect of preparation methods on the performance of Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol: Part I-catalytic activity

The effect of preparation method on the performance of Ni/Al₂O₃ catalysts for aqueous-phase reforming of ethanol (EtOH) has been investigated. The first catalyst was prepared by a sol–gel (SG) method and for the second one the Al₂O₃ support was made by a solution combustion synthesis (SCS) route and then the metal was loaded by standard wet impregnation. The catalytic activity of these catalysts of different Ni loading was compared with a commercial Al₂O₃ supported Ni catalyst [CM (10%)] at different temperatures, pressures, feed flow rates, and feed concentrations. Based on the product distribution, the proposed reaction pathway is a mixture of dehydrogenation of EtOH to CH₃CHO followed by C–C bond breaking to produce CO + CH₄ and oxidation of CH₃CHO to CH₃COOH followed by decarbonylation to CO₂ + CH₄. CH₄(C₂H₆ and C₃H₈) also can form via Fischer–Tropsch reactions of CO/CO₂ with H₂. The CH₄ (C₂H₆ and C₃H₈) reacts to form hydrogen and carbon monoxide through steam reforming, while CO converts to CO₂ mostly through the water–gas shift reaction (WGSR). SG catalysts showed poorer WGSR activity than the SCS catalysts. The activation energies for H₂ and CO₂ production were 153, 155 and 167 kJ/mol and 158, 160 and 169 kJ/mol for SCS (10%), SG (10%), and CM (10%) samples, respectively.     

Effects of modifying Ni/Al2O3 catalyst with cobalt on the reforming of CH4 with CO2 and cracking of CH4 reactions

Alumina supported nickel (Ni/Al₂O₃), nickel–cobalt (Ni–Co/Al₂O₃) and cobalt (Co/Al₂O₃) catalysts containing 15% metal were synthesized, characterized and tested for the reforming of CH₄ with CO₂ and CH₄ cracking reactions. In the Ni–Co/Al₂O₃ catalysts Ni–Co alloys were detected and the surface metal sites decreased with decrease in Ni:Co ratio. Turnover frequencies of CH₄ were determined for both reactions. The initial turnover frequencies of reforming (TOF_DRM) for Ni–Co/Al₂O₃ were greater than that for Ni/Al₂O₃, which suggested a higher activity of alloy sites. The initial turnover frequencies for cracking (TOF_CRK) did not follow this trend. The highest average TOF_DRM, H₂:CO ratio and TOF_CRK were observed for a catalyst containing a Ni:Co ratio of 3:1. This catalyst also had the maximum carbon deposited during reforming and produced the maximum reactive carbon during cracking. It appeared that carbon was an intermediate product of reforming and the best catalyst was able to most effectively crack CH₄ and oxidize carbon to CO by CO₂.     

Effect of Ce on 5 wt% Ni/ZSM-5 catalysts in the CO2 reforming of CH4 reaction

The aim of this study is to investigate the promotional effect of Ce on Ni/ZSM-5 catalysts in the CO₂ reforming of CH₄ reaction. The evaluation of the catalytic performances of the composite catalysts was conducted in a fixed-bed reactor at atmospheric pressure. The influencing factors, including temperature, Ni and Ce loadings, molar feed ratio of CO₂/CH₄, and time-on-stream (TOS), were investigated. The characteristics of the catalysts were checked with Brunauer-Emmett-Teller (BET) analysis, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). The reduction and the basic properties of the composite catalysts were elucidated by temperature-programmed reduction by H₂ (H₂-TPR) and temperature-programmed desorption of CO₂ (CO₂-TPD), respectively. The reactivity of deposited carbon was studied by sequential temperature-programmed surface reaction of CH₄ (CH₄-TPSR) and temperature-programmed oxidation using CO₂ and O₂ (CO₂-TPO and O₂-TPO). Results indicate that higher CH₄ conversion, H₂ selectivity, and desired H₂/CO ratio for 5 wt% Ni & 5 wt% Ce/ZSM-5 could be achieved with CO₂/CH₄ feed ratio close to unity over the temperature range of 500–900 °C. Moreover, the addition of Ce could not only promote CH₄ decomposition for H₂ production but also the gasification of deposited carbon with CO₂. The dispersion of Ni particles could be improved with Ce presence as well. A partial reduction of CeO₂ to CeAlO₃ was observed from XPS spectra over 5 wt% Ni & 5 wt% Ce/ZSM-5 after H₂ reduction and 24 h CO₂–CH₄ reforming reaction. Benefiting from the introduction of 5 wt% Ce, the calculated apparent activation energies of CH₄ and CO₂ over the temperature range of 700–900 °C could be reduced by 30% and 40%, respectively.     

Hydrogen production by steam reforming of ethanol over an Ir/CeO2 catalyst: Reaction mechanism and stability of the catalyst

Steam reforming of ethanol over an Ir/CeO₂ catalyst has been studied with regard to the reaction mechanism and the stability of the catalyst. It was found that ethanol dehydrogenation to acetaldehyde was the primary reaction, and acetaldehyde was then decomposed to methane and CO and/or converted to acetone at low temperatures. Methane was further reformed to H₂ and CO, and acetone was directly converted into H₂ and CO₂. Addition of CO, CO₂, and CH₄ to the water/ethanol mixture proved that steam reforming of methane and the water gas shift were the major reactions at high temperatures. The Ir/CeO₂ catalyst displayed rather stable performance in the steam reforming of ethanol at 650 °C even with a stoichiometric feed composition of water/ethanol, and the effluent gas composition remained constant for 300 h on-stream. The CeO₂ in the catalyst prevented the highly dispersed Ir particles from sintering and facilitated coke gasification through strong Ir–CeO₂ interaction.     

Flowerlike microspheres catalyst NiO/La2O3 for ethanol-H2 production

Catalysts of nano-sized nickel oxide particles based on flowerlike lanthanum oxide microspheres with high disperse were prepared to achieve simultaneous dehydrogenation of ethanol and water molecules on multi-active sites. XRD, SEM, 77K N₂ adsorption were used to analyze and observe the catalysts’ structure, morphology and porosity. Catalytic parameters with respect to yield of H₂, activity, selectivity towards gaseous products and stability with time-on-stream and time-on-off-stream were all determined. This special morphology NiO/La₂O₃ catalyst represented more than 1000 h time-on-stream stability test and 500 h time-on-off-stream stability test for hydrogen fuel production from ethanol steam reforming at 300 °C without any deactivation. During the 1000 h time-on-stream stability test, ethanol–water mixtures could be converted into H₂, CO, and CH₄ with average selectivity values of 57.0, 20.1, 19.6 and little CO₂ of 3.2 mol%, respectively, and average ethanol conversion values of 96.7 mol%, with H₂ yield of 1.61 mol H₂/mol C₂H₅OH. During the 500 h time-on-off-stream stability test, ethanol–water mixtures could be converted into H₂, CO, CH₄ and CO₂ with average selectivity values of 65.1, 17.3, 15.1 and 2.5 mol%, respectively, and average ethanol conversion values of 80.0 mol%. For the ethanol-H₂ and petrolic hybrid vehicle (EH–HV), the combustion value is the most important factor. So, it was very suitable for the EH–HV application that the low temperature ethanol steam reforming products’ distribution was with high H₂, CO, CH₄ and very low CO₂ selectivity over the special NiO/La₂O₃ flowerlike microspheres.     

Optimized mixed reforming of biogas with O2 addition in spark-discharge plasma

Adding O₂ into biogas to achieve partial oxidation and CO₂ mixed reforming can not only increase H₂ + CO concentration, but also reduce energy cost for H₂ production. In this study, optimized mixed reforming of biogas with O₂ addition in spark-discharge plasma was pursued in combination with thermodynamic-equilibrium calculation. With respect to mixed reforming of biogas with O₂ addition in spark-discharge plasma, combination coefficients of independent reactions were given to quantitatively evaluate the mixed extent at various O₂/(CH₄–CO₂) ratios. Compared thermodynamic-equilibrium with experimental results, it can be concluded that the optimal O₂/(CH₄–CO₂) ratio for optimized mixed reforming of biogas in spark-discharge plasma was about 0.7. When total-carbon conversion was relatively high (>75%), H₂ + CO concentration on wet basis was the highest and energy cost for H₂ production was the lowest at O₂/(CH₄–CO₂) = 0.7, and their experimental results were closest to their thermodynamic-equilibrium values.     

LaNiO3@SiO2 core–shell nano-particles for the dry reforming of CH4 in the dielectric barrier discharge plasma

LaNiO₃@SiO₂ core–shell nano-particles were prepared by coating LaNiO₃ nano-particles with SiO₂ and then employed to catalyze the dry reforming of CH₄ to produce syngas (CO + H₂) in a coaxial dielectric barrier discharge (DBD) plasma reactor under ambient conditions. Compared to the traditional Ni-based catalysts (Ni/SiO₂, LaNiO₃/SiO₂ and LaNiO₃), LaNiO₃@SiO₂ exhibited better catalytic performance in the dry reforming of CH₄ in DBD plasma reactor, such as higher reactant conversion and product selectivity, and excellent catalytic stability. The conversions of CH₄ and CO₂ reached 88.31% and 77.76%, and selectivities of CO and H₂ were 92.43% and 83.65%, respectively. Results manifested the core–shell structure endowed LaNiO₃@SiO₂ with excellent catalytic performance because the SiO₂ shell was capable of preventing Ni from sintering and mitigating carbon deposition during the reaction.     

Catalytic CO2 reforming of CH4 over Cr-promoted Ni/char for H2 production

The objective of the study is to investigate the catalytic performance of Cr-promoted Ni/char in CO₂ reforming of CH₄ at 850 °C. The char obtained from the pyrolysis of a long-flame coal at 1000 °C was used as the support. The catalysts were prepared by incipient wetness impregnation methods with different metal precursor doping sequence. The characterization of the composite catalysts was evaluated by XRD, XPS, SEM-EDS, TEM, H₂-TPR, CO₂-TPD, CH₄-TPSR, and CO₂-TPO. The results indicate that the catalyst prepared by co-impregnation of Ni and Cr possess higher activity than those by sequential impregnation. The optimal loading of Cr on 5 wt% Ni/char is 7.8 wt‰. Moreover, the molar feed ratio of CH₄/CO₂ has a considerable effect on both the stability and the activity of Cr–Ni/char. The main effect of Cr is the great enhance of the adsorption to CO₂. It is interesting that the conversions of CH₄ and CO₂ over Cr-promoted Ni/char and Ni/char decrease initially, following by a steady rise as the reaction proceeds with time-on-stream (TOS). In addition, cyclic tests were conducted and no distinct deterioration in the catalytic performance of the catalysts was observed. On the basis of the obtained results, nickel carbide was speculated to be the active species which was formed during the CO₂ reforming of CH₄ reaction.     

Dry and steam reforming of biomass pyrolysis gas for rich hydrogen gas

Biomass pyrolysis gas (including H₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ and etc.) reforming for hydrogen production over Ni/Fe/Ce/Al₂O₃ catalysts was presented in this study. This study investigated how the operating conditions, such as the calcinations temperature of catalysts, the reaction temperature, the gas hourly space velocity (GHSV) and the ratio of H₂O/C, affect the conversion of CH₄ and CO₂ and the selectivity of hydrogen from dry and steam reforming of pyrolysis gas. The experimental results indicated that, under the conditions: the reaction temperature of 600 °C, the GHSV of 900 h⁻¹ and H₂O/C of 0.92, the reaction efficiency is the optimal. Especially, the concentration of H₂, CO, CH₄, CO₂, and C₂H_n (C₂H₄ and C₂H₆) were 36.80%, 10.48%, 9.61%, 42.62%, 0.49% respectively. The conversion of CH₄ and CO₂ reached 45.9% and 51.09%, respectively. There were all kinds of reactions during the processing of reforming of pyrolysis gas. And the main reactions changed with the operation condition. It was due to the promoting or inhibiting interaction among different constituents in the pyrolysis gas and the different activity of catalysts in the different operation condition.     

Hydrogen production from methane dry reforming over nickel-based nanocatalysts using surfactant-assisted or polyol method

In this study, two series of Ni-based nanocatalysts were synthesized successfully by the polyol and surfactant-assisted methods and subsequently tested for hydrogen production from CO₂–CH₄ reforming. Surfactant-assisted catalysts were prepared by using cetyl trimethyl ammonium bromide (CTAB) as a surfactant, whereas polyol catalysts were prepared in ethylene glycol (EG) medium with polyvinylpyrrolidone (PVP) as a nucleation-protective agent. The catalytic performance of each catalyst, in terms of H₂ yield and selectivity, was evaluated at different temperatures (500–800 °C). In order to clarify and explain the differences in catalytic activities of catalysts, the prepared samples were characterized by various techniques, such as BET, H₂-TPR, CO₂-TPD, XRD, TGA, SEM, HRTEM and CO pulse chemisorption. The results demonstrated that the method of preparation had a significant effect on the catalytic performance of tested catalysts. Overall, polyol catalysts showed high activity and selectivity for hydrogen production, while surfactant-assisted catalysts exhibited a fairly high resistance towards carbon deposition under similar reaction conditions of dry reforming of methane. Moreover, due to the reverse water gas shift reaction (RWGS), surfactant-assisted catalysts always produced smaller values of H₂/CO product ratio than their corresponding polyol catalysts.     

Is steam addition necessary for the landfill gas fueled solid oxide fuel cells?

Landfill gas in Hong Kong – a mixture of about 50% (by volume) CH₄ and 50% CO₂ – can be utilized for power generation in a solid oxide fuel cell (SOFC). Conventional way of utilizing CH₄ in a SOFC is by adding H₂O to CH₄ to initiate methane steam reforming (MSR) and water gas shift reaction (WGSR). As the methane carbon dioxide reforming (MCDR: CH₄ + CO₂ ↔ 2CO + 2H₂) is feasible in the SOFC anode, it is unknown whether H₂O is needed or not for landfill gas fueled SOFC. In this study, a numerical model is developed to investigate the characteristics of SOFC running on landfill gas. Parametric simulations show that H₂O addition may decrease the performance of short SOFC at typical operating conditions as H₂O dilute the fuel concentration. However, it is interesting to find that H₂O addition is needed at reduced operating temperature, lower operating potential, or in SOFC with longer gas channel, mainly due to less temperature reduction in the downstream and easier oxidation of H₂ than CO. This preliminary study could help identify strategies for converting landfill gas into electrical power in Hong Kong.     

Production of CO-rich hydrogen gas from glycerol dry reforming over La-promoted Ni/Al2O3 catalyst

Dry reforming of glycerol has been carried out over alumina-supported Ni catalyst promoted with lanthanum. The catalysts were characterized using EDX, liquid N₂ adsorption, XRD technique as well as temperature-programmed reduction. Significantly, catalytic glycerol dry reforming under atmospheric pressure and at reaction temperature of 1023 K employing 3 wt%La–Ni/Al₂O₃ catalyst yielded H₂, CO and CH₄ as main gaseous products with H₂:CO < 2.0. Post-reaction, XRD analysis of used catalysts showed carbon deposition during glycerol dry reforming. Consequently, BET surface area measurement for used catalysts yielded 10–21% area reduction. Temperature-programmed gasification studies with O₂ as a gasification agent has revealed that La promotion managed to reduce carbon laydown (up to 20% improvement). In comparison, the unpromoted Ni/Al₂O₃ catalyst exhibited the highest carbon deposition (circa 33.0 wt%).     

Thermodynamic analysis of glycerol-steam reforming in the presence of CO2 or H2 as carbon gasifying agent

This paper deals with the thermodynamic analysis of glycerol-steam reforming with H₂ or CO₂ co-fed as carbon gasifying agents in order to mitigate carbon deposition. Thermodynamic calculations were carried out at temperatures from 500 to 800 K and steam-to-glycerol ratios of 0:1–20:1 at atmospheric pressure. Carbon deposition was significant (1.0–1.7 mol C/mol C₃H₈O₃) at low steam-to-glycerol ratio (<4.0) within the reaction temperature range (500–800 K). Carbon-free regime can only be achieved at temperatures above 700 K at steam-to-glycerol ratio of 3:1. Beyond the steam-to-glycerol ratio of 4:1, carbon deposition is essentially zero. The addition of H₂ (as co-reactant) reduced the carbon deposition (down to 0.58 mol C/mol C₃H₈O₃ from 1.70 mol C/mol C₃H₈O₃) even at steam-to-glycerol ratio of 0:1 and reaction temperature of 500 K. Above 5 mol H₂/mol C₃H₈O₃, thermodynamic analysis showed undetectable carbon deposition. Significantly, this could be attributed to the H₂-gasification of carbon species to produce CH₄ and hence, the concomitant increase in the latter. The introduction of CO₂ into the glycerol-steam system, however, led to increased carbon deposition at all temperatures considered in this study due to the reaction between CO₂ and CH₄ in forming carbon deposits. Nevertheless, the carbon yield can be reduced through reforming at higher temperatures. It was further concluded from the current work that H₂ co-feeding linearly increased the exothermicity of reforming system.     

Reforming of bioethanol over Ni/Al2O3 and Ni/CeZrO2/Al2O3 catalysts in supercritical water for hydrogen production

Bioethanol was reformed in supercritical water (SCW) at 500 °C and 25 MPa on Ni/Al₂O₃ and Ni/CeZrO₂/Al₂O₃ catalysts to produce high-pressure hydrogen. The results were compared with non-catalytic reactions. Under supercritical water and in a non-catalytic environment, ethanol was reformed to H₂, CO₂ and CH₄ with small amounts of CO and C2 gas and liquid products. The presence of either Ni/Al₂O₃ or Ni/CeZrO₂/Al₂O₃ promoted reactions of ethanol reforming, dehydrogenation and decomposition. Acetaldehyde produced from the decomposition of ethanol was completely decomposed into CH₄ and CO, which underwent a further water-gas shift reaction in SCW. This led to great increases in ethanol conversion and H₂ yield on the catalysts of more than 3-4 times than that of the non-catalytic condition. For the catalytic operation, adding small amounts of oxygen at oxygen to ethanol molar ratio of 0.06 into the feed improved ethanol conversion, at the expense of some H₂ oxidized to water, resulting in a slightly lower H₂ yield. The ceria-zirconia promoted catalyst was more active than the unpromoted catalyst. On the promoted catalyst, complete ethanol conversion was achieved and no coke formation was found. The ceria-zirconia promoter has important roles in improving the decomposition of acetaldehyde, the enhancement of the water-gas shift as well as the methanation reactions to give an extremely low CO yield and a tremendously high H₂/CO ratio. The SCW environment for ethanol reforming caused the transformation of gamma-alumina towards the corundum phase of the alumina support in the Ni/Al₂O₃ catalyst, but this transformation was slowed down by the presence of the ceria-zirconia promoter.     

Steam reforming of ethanol over nickel-tungsten catalyst

Ni-W/Al₂O₃ catalysts were synthesized, characterized and tested for the steam reforming of ethanol from 300 to 600 °C. Addition of Ni and W on the alumina, decreased the surface area and increased the pore volume of the mesoporous materials synthesized. The reaction products obtained were: H₂, CO₂, C₂H₄, CH₄, CO₂, CO and CH₃CHO. A promoting effect of Ni-W was observed in the conversion of ethanol to H₂ from 15 to 30 wt.% Ni and 1 wt.% W. The selectivity to H₂ on the alumina with Ni-W, was between 66.53 and 68.53% at 550 °C, appearing some undesirable products, with low ratio of CO/CO₂. Reaction was studied on a fixed bed reactor at atmospheric pressure with an ethanol/water molar ratio of 1:4, from 300 to 600 °C. The catalysts were characterized by the thermal gravimetric analysis (TGA)-Differential thermal analysis (DTA), N₂ physisorption (BET and BJH methods), X-ray diffraction (XRD) and scanning electron microscopy (SEM), these techniques were used for characterization, before and after of the steam reforming.     

Modifying perovskite-type oxide catalyst LaNiO3 with Ce for carbon dioxide reforming of methane

Perovskite-type oxide catalysts LaNiO₃ and La_1−xCe_xNiO₃ (x ≤ 0.5) were prepared by the Pechini method and used as catalysts for carbon dioxide reforming of methane to form synthesis gas (H₂ + CO). The gaseous reactants consisted of CO₂ and CH₄ in a molar ratio of 1:1. At a GHSV of 10,000 hr⁻¹, CH₄ conversion over LaNiO₃ catalyst increased from 66% at 600 °C to 94% at 800 °C, while CO₂ conversion increased from 51% to 92%. The achieved selectivities of CO and H₂ were 33% and 57%, respectively, at 600 °C. To prevent the deposition of carbon and the sintering nickel species, some of the Ni in perovskite-type oxide catalyst was substituted by Ce. Ce provided lattice oxygen vacancies, which activated C–H bonds, and increased the selectivity of H₂ to 61% at 600 °C. XRD analysis indicates that the catalyst exhibited a typical perovskite spinel structure and formed La₂O₂CO₃ phases after CO₂ reforming. The FE-SEM results reveal carbon whisker of the LaNiO₃ catalyst and the BET analysis indicates that the specific surface area increases after the reforming reaction. The H₂-TPR results confirm that Ce metals can store and provide oxygen.     

Catalysts for H2 production using the ethanol steam reforming (a review)

This review aims to provide an overview of the main catalytic studies of H₂ production by ethanol steam reforming (ESR). The reaction is endothermic and produces H₂, CO₂, CH₄, CO and coke. The conversion and H₂ selectivity of these products depended greatly of the physicochemical properties of the catalysts, active metal, promoters, temperature, long-term reaction, water/ethanol ratio, space velocity, contact time, and presence of O₂. Initial total conversion has been reported in all catalysts evaluated between 300 and 850 °C. The noble catalysts with high selectivity to H₂ (more than 80%) were: Rh, Ru, Pd and Ir and non-noble metal catalysts were: Ni, Co and Cu. The support materials include CeO₂, ZnO, MgO, Al₂O₃, zeolites-Y, TiO₂, SiO₂, La₂O₂CO₃, CeO₂–ZrO₂ and hydrotalcites. The impregnation method produced the best noble metal catalysts in terms of selectivity and conversion. The decrease of coke was related with the presence of basic sites on the support.     

The effect of impregnation strategy on methane dry reforming activity of Ce promoted Pt/ZrO2

Dry reforming of methane has been studied over Pt/ZrO₂ catalysts promoted with Ce for different temperatures and feed compositions. The influence of the impregnation strategy and the cerium amount on the activity and stability of the catalysts were investigated. The results have shown that introduction of 1 wt.% Ce to the Pt/ZrO₂ catalyst via coimpregnation method led to the highest catalytic activity and stability. 1 wt.%Ce–1 wt.%Pt/ZrO₂ catalyst prepared by sequential impregnation displayed inferior CH₄ and CO₂ conversion performances with lowest H₂/CO production ratios. 1 wt.%Ce–1 wt.%Pt/ZrO₂ catalyst prepared by coimpregnation showed the highest activity even for the feed with high CH₄/CO₂ ratio. The reason for high activity was explained by the intensive interaction between Pt and Ce phases for coimpregnated sample, which had been verified by X-ray photoelectron spectroscopy and Energy Dispersive X-Ray analyses. Strong and extensive Pt–Ce surface interaction results in an increase in the number of Ce³⁺ sites and enhances the dispersion of Pt.     

Synthesis gas production from dry reforming of methane over Ce0.75Zr0.25O2-supported Ru catalysts

Ce_0.75Zr_0.25O₂ solid solution supported Ru catalysts were prepared and tested for CH₄–CO₂ reforming. The effect of Ru content on the properties of the catalysts was investigated by means of N₂ adsorption–desorption, H₂-TPR/MS, XRD, XPS, CO chemisorption and H₂-TPD/MS. It was found that the highly dispersed Ru species favored the interaction between Ru and Ce_0.75Zr_0.25O₂. The reduced Ce_0.75Zr_0.25O₂ was able to store hydrogen, while Ru promoted the reduction of Ce_0.75Zr_0.25O₂. Under the identical conditions, the CH₄ and CO₂ conversions of the catalysts increased with the increase of Ru content, however, the turnover frequencies of CH₄ and CO₂ were higher for the catalysts with lower Ru contents, which may be resulted from the strong interaction between Ru and Ce_0.75Zr_0.25O₂. The Ru catalyst exhibited good stability and excellent resistance to carbon deposition. Remarkably, zirconium and cerium hydrides were detected in the used catalyst, which may participate in the elimination of the carbon deposit. Apart from the nature of metallic Ru and the redox property of Ce_0.75Zr_0.25O₂, we suggest that the excellent resistance of the catalyst to carbon deposition is also attributed to the hydrogen storage of the reduced Ce_0.75Zr_0.25O₂.     

Combined catalytic partial oxidation and CO2 reforming of methane over ZrO2-modified Ni/SiO2 catalysts using fluidized-bed reactor

Nickel on zirconium-modified silica was prepared and tested as a catalyst for reforming methane with CO₂ and O₂ in a fluidized-bed reactor. A conversion of CH₄ near thermodynamic equilibrium and low H₂/CO ratio (1<H₂/CO<2) were obtained without catalyst deactivation during 10 h, in a most energy efficient and safe manner. A weight loading of 5 wt% zirconium was found to be the optimum. The catalysts were characterized using X-ray diffraction (XRD), H₂-temperature reaction (H₂-TPR), CO₂-temperature desorption (CO₂-TPD) and transmission election microscope (TEM) techniques. Ni sintering was a major reason for the deactivation of pure Ni/SiO₂ catalysts, while Ni dispersed highly on a zirconium-promoted Ni/SiO₂ catalyst. The different kinds of surface Ni species formed on ZrO₂-promoted catalysts might be responsible for its high activity and good resistance to Ni sintering.