Effect of preparation method on structural characteristics and propane steam reforming performance of Ni–Al2O3 catalysts

Propane steam reforming was studied over Ni–Al₂O₃ catalysts that were prepared by a conventional impregnation (IM) method and a one-step sol–gel (SG) technique. Both Ni–Al₂O₃ catalysts showed similar initial activity. However, IM-Ni–Al₂O₃ deactivated severely with time-on-stream of propane steam reforming. The catalyst prepared using a SG technique demonstrated stable catalytic performance. The two catalysts also showed major differences in product distribution, with SG catalyst giving much higher yields of hydrogen. Catalysts were characterized with temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), temperature-programmed oxidation (TPO), transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. It was revealed that, with sol–gel preparation, highly dispersed small Ni crystallites are formed with a strong interaction with the support. This is shown to be important for coke suppression and catalyst stability.     

Surface Reaction Kinetics of the Oxidation and Reforming of CH4 over Rh/Al2O3 Catalysts

An 48‐step sur face reaction mechanism with thermodynamic consistent kinetic data is presented for the catalytic conversion of the gaseous chemical system H₂/O₂/H₂O/CO/CO₂/CH₄ over Rh/Al₂O₃ catalysts. Total and partial oxidation as well as steam reforming and dry reforming of methane over Rh catalysts is studied experimentally and numerically at varying temperature and composition. The results are used to extend the kinetic schemes we developed for H₂ oxidation, CO oxidation kinetics, and the water‐gas‐shift reactions in former studies. Aside from the experiments in a stagnation‐flow reactor presented here, we modeled a number of experiments from the literature to test the newly established kinetic scheme.     

Methane steam reforming over rhodium promoted Ni/Al2O3 catalysts

The effect of Rh addition upon catalyst characteristics and performance in methane steam reforming was investigated using Rh-promoted Ni/Al₂O₃ catalysts. The number of reduced metal atoms exposed on the surface increased for the Rh-promoted catalysts. Rh-promoted catalysts showed an increase in CH₄ reforming activity; however, constant turnover frequencies for promoted and unpromoted catalysts suggest that the increase in the number of metal surface atoms caused the activity enhancement. Rh also facilitated reduction of Ni/Al₂O₃.     

Effect of Pt and Pd additives on the state of the surface layer and catalytic activity of niobium oxides in the oxidation of hydrogen

Catalysts prepared by the hydrogen reduction of Nb₂O₅ in the presence of Pt or Pd have specific surface much greater than for the starting oxide and their catalytic activity in the oxidation of hydrogen is much greater than the activity of Pt/Al₂O₃ or Pd/Al₂O₃. X-ray phase analysis and X-ray photoelectron spectroscopy were used to establish the existence of Nb₂O_5–x nonstoichiometric oxides in the catalyst, which enhances the catalytic activity of the surface. The kinetic behavior of the oxidation of hydrogen on these catalysts is explained in the framework of the Eley–Riedel mechanism.     

MgO纳米晶负载镍催化剂用于甲烷蒸汽重整反应(英文)

Nanocrystalline MgO with a relatively high surface area and mesoporous structure was synthesized by a surfactant assisted precipitation method for use as the support of nickel catalysts for steam reforming of methane. The samples were characterized by X‐ray diffraction, N2 adsorption, temperature‐programmed reduction, temperature‐programmed oxidation, scanning electron microscopy, and transmission electron microscopy. The catalysts showed high catalytic activity and good stability in the steam reforming of methane. Increasing the nickel loading up to 10 wt% gave increased activity. Catalysts with higher nickel loadings showed more deposited carbon after reaction. The excellent anti‐coking performance of the catalysts was attributed to the formation of a nickel‐magnesia solid solution, basicity of the support surface, and nickel‐support interaction.     

Catalytic Steam Reforming of Methane: New Data on the Contribution of Homogeneous Radical Reactions in the Gas Phase: II. A Ruthenium Catalyst

The kinetics of methane steam reforming and pyrolysis on Ru/Al₂O₃(T= 650–750°C, = 0.001–0.030 MPa) is studied. The values of the rates and activation energies are compared with the kinetic parameters for nickel catalysts. It was shown that steam reforming can occur on the ruthenium catalyst both heterogeneously and heterogeneously–homogeneously depending on the reaction conditions. Comparative activities of the Ru/Al₂O₃and Ni–Al₂O₃catalysts are discussed under the conditions of purely heterogeneous and heterogeneous–homogeneous steam reforming.     

在Ni/HZSM-5催化剂上低温水蒸汽重整生物油制氢

We investigated high catalytic activity of Ni/HZSM-5 catalysts synthesized by the impregna-tion method, which was successfully applied for low-temperature steam reforming of bio-oil. The influences of the catalyst composition, reforming temperature and the molar ratio of steam to carbon fed on the stream reforming process of bio-oil over the Ni/HZSM-5 catalysts were investigated in the reforming reactor. The promoting effects of current passing through the catalyst on the bio-oil reforming were also studied using the electrochemical catalytic re-forming approach. By comparing Ni/HZSM-5 with commonly used Ni/Al₂O₃ catalysts, the Ni₂₀/ZSM catalyst with Ni-loading content of about 20% on the HZSM-5 support showed the highest catalytic activity. Even at 450 oC, the hydrogen yield of about 90% with a near complete conversion of bio-oil was obtained using the Ni₂₀/ZSM catalyst. It was found that the performance of the bio-oil reforming was remarkably enhanced by the HZSM-5 supporter and the current through the catalyst. The features of the Ni/HZSM-5 catalysts were also investigated via X-ray diffraction, inductively coupled plasma and atomic emission spectroscopy, hydrogen temperature-programmed reduction, and Brunauer-Emmett-Teller methods.     

Hydrogen Production by Steam Reforming of Ethanol Over Mesoporous Ni–Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–ZrO<Subscript>2</Subscript> Catalysts

This review paper reports the recent progress concerning the application of nickel–alumina–zirconia based catalysts to the ethanol steam reforming for hydrogen production. Several series of mesoporous nickel–alumina–zirconia based catalysts were prepared by an epoxide-initiated sol–gel method. The first series comprised Ni–Al₂O₃–ZrO₂ xerogel catalysts with diverse Zr/Al molar ratios. Chemical species maintained a well-dispersed state, while catalyst acidity decreased with increasing Zr/Al molar ratio. An optimal amount of Zr (Zr/Al molar ratio of 0.2) was required to achieve the highest hydrogen yield. In the second series, Ni–Al₂O₃–ZrO₂ xerogel catalysts with different Ni content were examined. Reducibility and nickel surface area of the catalysts could be modulated by changing nickel content. Ni–Al₂O₃–ZrO₂ catalyst with 15 wt% of nickel content showed the highest nickel surface area and the best catalytic performance. In the catalysts where copper was introduced as an additive (Cu–Ni–Al₂O₃–ZrO₂), it was found that nickel dispersion, nickel surface area, and ethanol adsorption capacity were enhanced at an appropriate amount of copper introduction, leading to a promising catalytic activity. Ni–Sr–Al₂O₃–ZrO₂ catalysts prepared by changing drying method were tested as well. Textural properties of Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst produced from supercritical drying were enhanced when compared to those of xerogel catalyst produced from conventional drying. Nickel dispersion and nickel surface area were higher on Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst, which led to higher hydrogen yield and catalyst stability over Ni–Sr–Al₂O₃–ZrO₂ aerogel catalyst.     

Decomposition of methane over alumina supported Fe and Ni–Fe bimetallic catalyst: Effect of preparation procedure and calcination temperature

Catalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al₂O₃ catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N₂ physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500 °C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34 nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al₂O₃ oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results.     

Oxidative conversion of methane and methanol on M/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/cordierite structured metal oxide catalysts (m = Ni,Cu, Zn)

A study was carried out on the properties of Ni/Al₂O₃ and Cu-ZnO/Al₂O₃ composites supported on ceramic honeycomb monoliths made from synthetic cordierite in the carbon dioxide conversion of methane and the partial oxidation of methanol. The structured nickel-alumina catalysts are significantly more efficient than the conventional granulated catalysts. The improved working stability of these catalysts was achieved by adjusting the acid-base properties of the surface by introducing sodium and potassium oxides, which leads to inhibition of surface carbonization. The hydrogen yield was close to 90% in the partial oxidation of methanol with a stoichiometric reagent ratio in the presence of the Cu-ZnO/Al₂O₃/cordierite catalyst. A synergistic effect was found, reducing the selectivity of CO formation in the presence of the Cu-ZnO catalyst relative to samples derived from the individual components Cu and ZnO. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 43, No. 5, pp. 299–306, September–October, 2007.     

Influence of Support Type and Metal Loading in Methane Decomposition over Iron Catalyst for Hydrogen Production

Natural gas resources, stimulate the method of catalytic methane decomposition. Hydrogen is a superb energy carrier and integral component of the present energy systems, while carbon nanotubes exhibit remarkable chemical and physical properties. The reaction was run at 700 °C in a fixed bed reactor. Catalyst calcination and reduction were done at 500 °C. MgO, TiO₂ and Al₂O₃ supported catalysts were prepared using a co‐precipitation method. Catalysts of different iron loadings were characterized with BET, TGA, XRD, H₂‐TPR and TEM. The catalyst characterization revealed the formation of multi‐walled nanotubes. Alternatively, time on stream tests of supported catalyst at 700 °C revealed the relative profiles of methane conversions increased as the %Fe loading was increased. Higher %Fe loadings decreased surface area of the catalyst. Iron catalyst supported with Al₂O₃ exhibited somewhat higher catalytic activity compared with MgO and TiO₂ supported catalysts when above 35% Fe loading was used. CH₄ conversion of 69% was obtained utilizing 60% Fe/Al₂O₃ catalyst. Alternatively, Fe/MgO catalysts gave the highest initial conversions when iron loading below 30% was employed. Indeed, catalysts with 15% Fe/MgO gave 63% conversion and good stability for 1 h time on stream. Inappropriateness of Fe/TiO₂ catalysts in the catalytic methane decomposition was observed.     

Activities of δ-Al2O3-supported bimetallic Pt?NiO and Co?NiO catalysts for methane autoreforming: Oxidation studies

The methane oxidation activities of Pt−NiO and Co−NiO bimetallic catalysts have been investigated as part of a larger research program on the autothermal reforming of methane (combined methane oxidation and steam reforming) in a fluidized bed reactor. Experiments at atmospheric pressure and 783–1023 K for both catalysts showed that the reaction was more selective towards H₂ production at CH₄∶O₂ ratios greater than unity. Light-off temperature increased with decreasing CH₄∶O₂ ratios, but increase in gas velocity (beyond minimum fluidization) increased the light-off temperature. Co−NiO was as promising as the more expensive Pt−NiO catalyst for the oxidation.     

Preparation of supported metal catalysts starting from hydrotalcites as the precursors and their improvements by adopting “memory effect”

Hydrotalcite-like compounds (HTlcs) can be used as the catalysts as it is since they contain various transition metal cations as the catalytically active species well dispersed on the basic support materials. Moreover, increasing numbers of the applications of HTlcs after the heat treatment have been found since the oxides with very small crystal size, stable to thermal treatments, are obtained after the calcination. The oxides possess interesting properties such as high surface area, basic properties and further form small and thermally stable metal crystallites by reduction. Moreover, the calcined oxides show a unique property, i.e., “memory effect,” which allows the reconstitution of the original hydrotalcite structure. We have developed the catalytic applications of hydrotalcites as it is and moreover the mixed oxides derived from hydrotalcites for various catalytic reactions, i.e., oxidation, dehydrogenation and reforming of hydrocarbons, and even for the reforming of methanol and the CO shift reaction. Aerobic oxidation of alcohols, Baeyer−Villiger oxidation of ketones and O₃ oxidation of oxalic acid have been successfully carried out with the Mg−Al hydrotalcites containing Ni, Fe and Cu, respectively, as the catalysts in liquid phase. In the O₃ oxidation of oxalic acid, the catalytic activity was enhanced by the “memory effect,” i.e., Mg(Cu)–Al hydrotaclite was reconstituted on the surface of Mg(Cu,Al)O periclase particles and oxalic acid was incorporated as anions in the hydrotalcite layer, resulting in an enhanced oxidation of oxalic acid. As the catalysts in the vapor phase reactions, Mg/Fe/Al mixed oxides prepared from Mg–Al(Fe) hydrotalcites and effectively catalyzed the dehydrogenation of ethylbenzene. Supported Ni metal catalysts have been prepared from Mg(Ni)–Al hydrotalcites and successfully used in the steam reforming and the oxidative reforming of methane and propane. Moreover, the Ni catalysts have been improved by combining a trace amount of noble metals by adopting the “memory effect” and used in the production of hydrogen for the PEFC under the daily startup and shutdown operation. Also starting from aurichalcite or hydrotalcite precursor as the precursor, Cu/Zn/Al catalysts with high Cu metal surface area have been prepared and successfully applied in the steam reforming of methanol and dimethyl ether, and moreover in the CO shift reaction.     

The effect of the nature of the support on catalytic properties of ruthenium supported catalysts in partial oxidation of methane to syn-gas

The effect of the carrier on catalytic properties of ruthenium supported catalysts in partial oxidation of methane (POM) was investigated. A variety of supports differed in texture and reducibility (Al₂O₃, SiO₂, TiO₂, Cr₂O₃, CeO₂ and Fe₂O₃) were used. The catalyst activity is governed by ruthenium phase formation (RuO₂ → Ru⁰), and it depends on redox properties of the support as well as support-ruthenium phase interaction. The activity of Ru supported catalysts decreases in the order Al₂O₃ ≈ SiO₂ > Cr₂O₃ > TiO₂ > CeO₂ > Fe₂O₃. No significant effects of the specific surface area and porosity of catalysts on the methane conversion and selectivity of CO formation were found. The selectivity of CO₂ formation (total oxidation of CH₄) under conditions of POM (a ratio of CH₄/O₂ = 2) is associated with the contribution of reducible support oxides into the catalytic performance.     

Methane-fueled SOFC with traditional nickel-based anode by applying Ni/Al2O3 as a dual-functional layer

Novel γ-Al₂O₃ supported nickel (Ni/Al₂O₃) catalyst was developed as a functional layer for Ni–ScSZ cermet anode operating on methane fuel. Catalytic tests demonstrated Ni/Al₂O₃ had high and comparable activity to Ru–CeO₂ and much higher activity than the Ni–ScSZ cermet anode for partial oxidation, steam and CO₂ reforming of methane to syngas between 750 and 850 °C. By adopting Ni/Al₂O₃ as a catalyst layer, the fuel cell demonstrated a peak power density of 382 mW cm^?2 at 850 °C, more than two times that without the catalyst layer. The Ni/Al₂O₃ also functioned as a diffusion barrier layer to reduce the methane concentration within the anode; consequently, the operation stability was also greatly improved without coke deposition.     

Carbon Deposits Formed on the Surface of Ru–Ni Catalysts During the Mixed Reforming of Methane Process

Monometallic nickel and bimetallic ruthenium–nickel catalysts supported onto aluminum oxide without additives and aluminum oxide modified with MgO and CaO were prepared by an impregnation method. The catalysts were tested in the process of the mixed reforming of methane, and their properties were characterized by thermogravimetry, scanning electron microscopy, and X-ray diffractometry. The total organic carbon content of the catalysts was also measured. The promoting effect of ruthenium and structural promoters on the catalytic activity of Ni/Al₂O₃ was confirmed. The Ru–Ni/MgO–Al₂O₃ catalyst exhibited the highest stability and activity; this fact can be explained by the increased adsorption of methane on the surface of ruthenium–nickel clusters.     

Comparison of two preparation methods of supported Li?Ni catalyst on alumina for selective oxidation of methane

Lithium-added nickel catalysts on alumina were prepared for CO₂ reforming of methane by two methods, precipitation and impregnation. Performances of the catalysts were investigated by TG, CO-adsorption and SEM analysis. The catalyst with ratio of Li/Ni=1.0 prepared by precipitation method has high nickel dispersion, catalytic activity and stability for CO₂ reforming of methane.     

The influence of La2O3 and TiO2 on NiO/MgO/α-Al2O3

Summary The effect of La₂O₃ and TiO₂ on product selectivity, methane conversion and coke formation over NiO/MgO/ α -Al₂O₃ catalyst were studied in a simultaneous steam and CO₂ reforming of methane to syngas. La₂O₃ and TiO₂ were added to the catalyst via incipient wetness impregnation and bulk precipitation techniques and catalyst activity was tested in a fixed bed quartz reactor. Results reveal that although the addition of these oxides has no effect on the product selectivity and methane conversion, but can reduce coke formation on the surface of the catalysts as it can enhance the mobility of lattice oxygen anions. The results further show that the catalysts prepared by bulk precipitation technique decrease the coke formation more effectively.     

Steam reforming of ethylene glycol over Ni-based catalysts: the effect of K

The effect of K on the activities of Ni/Al₂O₃ catalysts in steam reforming of ethylene glycol was investigated. Ni/Al₂O₃ catalysts were prepared by incipient wetness impregnation and co-precipitation methods. The addition of K was achieved using an incipient wetness impregnation method. The prepared catalysts were characterized by N₂ physisorption, inductively coupled plasma-atomic emission spectroscopy, X-ray diffraction, temperature-programmed reduction, and scanning electron microscopy. Irrespective of the preparation method, the promotional effect of K was observed and the optimum K content (~5 wt%) was verified for K-promoted Ni/Al₂O₃ catalysts. The addition of K to the Ni–Al₂O₃ catalyst prepared by co-precipitation led to higher catalytic activity than addition of K to the Ni/Al₂O₃ catalyst prepared by incipient wetness impregnation.     

Effect of the oxidation state of manganese in the manganese oxides used in the synthesis of Mn-substituted cordierite on the properties of the product

Catalysts based on Mn-substituted cordierite 2MnO · 2Al₂O₃ · 5SiO₂ have been synthesized using different manganese oxides (MnO, Mn₂O₃, and MnO₂) at a calcination temperature of 1100°C. The catalysts differ in their physicochemical properties, namely, phase composition (cordierite content and crystallinity), manganese oxide distribution and dispersion, texture, and activity in high-temperature ammonia oxidation. The synthesis involving MnO yields Mn-substituted cordierite with a defective structure, because greater part of the manganese cations is not incorporated in this structure and is encapsulated and the surface contains a small amount of manganese oxides. This catalyst shows the lowest ammonia oxidation activity. The catalysts prepared using Mn₂O₃ or MnO₂ are well-crystallized Mn-substituted cordierite whose surface contains different amounts of manganese oxides differing in their particle size. They ensure a high nitrogen oxides yield in a wide temperature range. The product yield increases with an increasing surface concentration of Mn³⁺ cations. The highest NO_x yield (about 76% at 800–850°C) is observed for the MnO₂-based catalyst, whose surface contains the largest amount of manganese oxides.