Steam reforming of ethanol over Co3O4–Fe2O3 mixed oxides

Co₃O₄, Fe₂O₃ and a mixture of the two oxides Co–Fe (molar ratio of Co₃O₄/Fe₂O₃ = 0.67 and atomic ratio of Co/Fe = 1) were prepared by the calcination of cobalt oxalate and/or iron oxalate salts at 500 °C for 2 h in static air using water as a solvent/dispersing agent. The catalysts were studied in the steam reforming of ethanol to investigate the effect of the partial substitution of Co₃O₄ with Fe₂O₃ on the catalytic behaviour. The reforming activity over Fe₂O₃, while initially high, underwent fast deactivation. In comparison, over the Co–Fe catalyst both the H₂ yield and stability were higher than that found over the pure Co₃O₄ or Fe₂O₃ catalysts. DRIFTS-MS studies under the reaction feed highlighted that the Co–Fe catalyst had increased amounts of adsorbed OH/water; similar to Fe₂O₃. Increasing the amount of reactive species (water/OH species) adsorbed on the Co–Fe catalyst surface is proposed to facilitate the steam reforming reaction rather than decomposition reactions reducing by-product formation and providing a higher H₂ yield.     

Ordered mesoporous MgO–Al2O3 composite oxides supported Ni based catalysts for CO2 reforming of CH4: Effects of basic modifier and mesopore structure

A series of ordered mesoporous MgO–Al₂O₃ composite oxides with various Mg containing were facilely synthesized via one-pot evaporation induced self-assembly strategy. These materials with advantageous structural properties and superior thermal stabilities were used as the supports of Ni based catalysts for CO₂ reforming of CH₄. These mesoporous catalysts behaved both high catalytic activities and long term stabilities toward this reaction. The effects of the mesopore structure and MgO basic modifier on catalytic performances were carefully studied. Specifically, their mesoporous frameworks could accommodate the gaseous reactants with more “accessible” Ni active centers; the “confinement effect” of the mesopores would effectively suppress the thermal sintering of the Ni nanoparticles; the modified MgO basic sites would enhance the chemisorption and activation of CO₂. Consequently, the catalytic activities and stabilities of these catalysts were greatly promoted. Therefore, the present materials were considered as promising catalyst supports for CO₂ reforming of CH₄.     

Plasma-reduced Ni/γ–Al2O3 and CeO2–Ni/γ–Al2O3 catalysts for improving dry reforming of propane

Pristine Ni/γ–Al₂O₃ and CeO₂–Ni/γ–Al₂O₃ catalysts were prepared by co-impregnation technique for dry reforming of propane. X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) were used to examine the structure and morphology of the catalysts before and after the reforming reactions. The excellent interaction between catalyst active phases was observed in both CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃ stabilized with polyethelene glycol (Ni/γ–Al₂O₃–PEG). Towards C₃H₈ and CO₂ conversion, the CeO₂–Ni/γ–Al₂O₃ and Ni/γ–Al₂O₃–PEG showed improved catalytic activity when compared to the pristine Ni/γ–Al₂O₃ catalyst. Interestingly, high H₂ concentration was achieved with the CeO₂–Ni/γ–Al₂O₃ and high CO concentration with the Ni/γ–Al₂O₃–PEG, which is due to the nanoconfinement of nickel particles within the support and favorable metal-support interaction as a result of plasma reduction. The CeO₂–Ni/γ–Al₂O₃ catalyst exhibited better stability for anti-sintering and coke resistance, thus exhibiting high reactivity and durability in the dry reforming.     

Hydrogen production by biomass gasification in supercritical water over Ni/γAl2O3 and Ni/CeO2-γAl2O3 catalysts

Hydrogen production by supercritical water gasification (SCWG) is a promising technology for wet biomass utilization. Ni catalyst can realize the high gasification efficiency of biomass near the critical temperature of water. In this paper, Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts were prepared by an impregnation method. The catalyst performance for glucose gasification in supercritical water was tested in autoclave reactor. All experiments were carried out in the autoclave at 673 K, 24.5 MPa, and the concentration of glucose was 9.09 wt.%. The catalysts before and after reaction were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurements, X-ray fluorescence spectrum (XRF) and Thermo-gravimetric analyses (TGA) in order to investigate on the chemical property and catalytic mechanism. The experimental results showed that hydrogen yield and hydrogen selectivity increased sharply with addition of Ni/γAl₂O₃ and Ni/CeO₂-γAl₂O₃ catalysts. The catalytic activity and H₂ selectivity of Ni/CeO₂-γAl₂O₃ was higher than that of Ni/γ-Al₂O₃ catalyst. The results revealed that carbon deposition and coking led to the deactivation of the catalysts. Ce in the Ni/CeO₂-γAl₂O₃ catalyst had a certain role in the inhibition of carbon deposition and coking.     

Autothermal syngas production from model gasoline over Ni,Rh and Ni–Rh/Al2O3 monolithic catalysts

On-board reforming of liquid fuels is attractive for fuel cell-powered auxiliary power units in vehicles. In this work, monometallic Ni/Al₂O₃/cordierite, Rh/Al₂O₃/cordierite and bimetallic Ni–Rh/Al₂O₃/cordierite monolithic catalysts were prepared, characterized and tested in ATR of isooctane for syngas production. Compared to monometallic formulations, the bimetallic Ni–Rh/Al₂O₃ catalyst was active for ATR at lower temperature and H₂ production already reached the equilibrium composition in 400–550 °C temperature range. The Ni–Rh/Al₂O₃ catalyst exhibited stable performances for 140 h in ATR of isooctane at 700 °C, and was unaffected by oxidizing conditions at 700 °C. Thermoneutral reactions conditions at H₂O/C = 2 were obtained with O/C = 0.66. Carbon deposition was marginal during ATR of isooctane and no carbons whiskers were detected. Post-reaction characterizations showed that the Ni particles were small enough to prevent filamentous carbon formation, while Rh also prevented carbon film deposition by improving the gasification of adsorbed C with steam.     

Hydrogen production by steam reforming of ethanol over P123-assisted mesoporous Ni–Al2O3–ZrO2 xerogel catalysts

A series of mesoporous Ni–Al₂O₃–ZrO₂ xerogel (denoted as X-NAZ) catalysts were prepared by a P123-assisted epoxide-driven sol–gel method under different P123 concentration (X, mM), and they were applied to the hydrogen production by steam reforming of ethanol. The effect of P123 concentration on the physicochemical properties and catalytic activities of X-NAZ catalysts was investigated. All the catalysts retained a mesoporous structure. Pore volume of the catalysts increased with increasing P123 concentration. Ni surface area and ethanol adsorption capacity of X-NAZ catalysts exhibited volcano-shaped trends with respect to P123 concentration. The trend of hydrogen yield was well matched with the trend of Ni surface area and ethanol adsorption capacity. Thus, Ni surface area and ethanol adsorption capacity of the catalysts served as important factors determining the catalytic performance. Among the catalysts tested, 12-NAZ catalyst with the highest Ni surface area and the largest ethanol adsorption capacity showed the best catalytic performance in the steam reforming of ethanol. In conclusion, an optimal P123 concentration was required for maximum production of hydrogen in the steam reforming of ethanol over X-NAZ catalysts.     

Characterization and activity test of commercial Ni/Al2O3, Cu/ZnO/Al2O3 and prepared Ni–Cu/Al2O3 catalysts for hydrogen production from methane and methanol fuels

In this study, methane and methanol steam reforming reactions over commercial Ni/Al₂O₃, commercial Cu/ZnO/Al₂O₃ and prepared Ni–Cu/Al₂O₃ catalysts were investigated. Methane and methanol steam reforming reactions catalysts were characterized using various techniques. The results of characterization showed that Cu particles increase the active particle size of Ni (19.3 nm) in Ni–Cu/Al₂O₃ catalyst with respect to the commercial Ni/Al₂O₃ (17.9). On the other hand, Ni improves Cu dispersion in the same catalyst (1.74%) in comparison with commercial Cu/ZnO/Al₂O₃ (0.21%). A comprehensive comparison between these two fuels is established in terms of reaction conditions, fuel conversion, H₂ selectivity, CO₂ and CO selectivity. The prepared catalyst showed low selectivity for CO in both fuels and it was more selective to H₂, with H₂ selectivities of 99% in methane and 89% in methanol reforming reactions. A significant objective is to develop catalysts which can operate at lower temperatures and resist deactivation. Methanol steam reforming is carried out at a much lower temperature than methane steam reforming in prepared and commercial catalyst (275–325 °C). However, methane steam reforming can be carried out at a relatively low temperature on Ni–Cu catalyst (600–650 °C) and at higher temperature in commercial methane reforming catalyst (700–800 °C). Commercial Ni/Al₂O₃ catalyst resulted in high coke formation (28.3% loss in mass) compared to prepared Ni–Cu/Al₂O₃ (8.9%) and commercial Cu/ZnO/Al₂O₃ catalysts (3.5%).     

Oxidative steam reforming of ethanol over Ni/Al2O3 catalysts promoted by CeO2, ZrO2 and CeO2–ZrO2

Oxidative steam reforming of ethanol at low oxygen to ethanol ratios was investigated over nickel catalysts on Al₂O₃ supports that were either unpromoted or promoted with CeO₂, ZrO₂ and CeO₂–ZrO₂. The promoted catalysts showed greater activity and a higher hydrogen yield than the unpromoted catalyst. The characterization of the Ni-based catalysts promoted with CeO₂ and/or ZrO₂ showed that the variations induced in the Al₂O₃ by the addition of CeO₂ and/or ZrO₂ alter the catalyst's properties by enhancing Ni dispersion and reducing Ni particle size. The promoters, especially CeO₂–ZrO₂, improved catalytic activity by increasing the H₂ yield and the CO₂/CO and the H₂/CO values while decreasing coke formation. This results from the addition of ZrO₂ into CeO₂. This promoter highlights the advantages of oxygen storage capacity and of mobile oxygen vacancies that increase the number of surface oxygen species. The addition of oxygen facilitates the reaction by regenerating the surface oxygenation of the promoters and by oxidizing surface carbon species and carbon-containing products.     

Hydrogen production from oxidative steam-reforming of n-propanol over Ni/Y2O3–ZrO2 catalysts

Oxidative steam reforming (OSR) of n-propanol was studied over new Ni catalysts (ca. 7% Ni wt/wt) supported on Y₂O₃–ZrO₂ oxides with different yttrium content (2–41 % Y₂O₃ wt/wt). Materials were characterized by X-ray diffraction, temperature-programmed reduction, X-ray photoelectron and Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray analysis and high resolution transmission electron microscopy. Samples were used in calcined form and tested in the temperature range 673–773 K using a reactant feed of n-propanol/water/O₂ at a molar ratio 1/9/0.5. Hydrogen production is related with the support composition and Ni dispersion.     

Hydrogen production by steam reforming of ethanol over mesoporous Ni–Al2O3–ZrO2 xerogel catalysts: Effect of nickel content

Hydrogen production by steam reforming of ethanol over mesoporous Ni–Al₂O₃–ZrO₂ xerogel catalysts (denoted as XNiAZ) with different nickel content (X, wt%) was studied. A single-step epoxide-driven sol–gel method was employed for the preparation of the catalysts. The effect of nickel content of XNiAZ catalysts on their physicochemical properties and catalytic activities was investigated. All the XNiAZ catalysts exhibited a well-developed mesoporous structure and they dominantly showed an amorphous NiO–Al₂O₃–ZrO₂ composite phase, leading to high dispersion of NiO. Nickel surface area and reducibility of XNiAZ catalysts showed volcano-shaped trends with respect to nickel content. Nickel surface area of XNiAZ catalysts played a key role in determining the catalytic performance in the steam reforming of ethanol; an optimal nickel content was required for maximum production of hydrogen. Among the catalysts tested, 15NiAZ catalyst with the highest nickel surface area exhibited the best catalytic performance in the steam reforming of ethanol. In addition, 15NiAZ catalyst showed high and stable hydrogen yields under different total feed rate, demonstrating its potential applicability in large-scale hydrogen production.     

Hydrogen production by steam reforming of ethanol over mesoporous Ni–Al2O3–ZrO2 aerogel catalyst

A mesoporous Ni–Al₂O₃–ZrO₂ aerogel (Ni–AZ) catalyst was prepared by a single-step epoxide-driven sol–gel method and a subsequent supercritical CO₂ drying method. For comparison, a mesoporous Al₂O₃–ZrO₂ aerogel (AZ) support was prepared by a single-step epoxide-driven sol–gel method, and subsequently, a mesoporous Ni/Al₂O₃–ZrO₂ aerogel (Ni/AZ) catalyst was prepared by an incipient wetness impregnation method. The effect of preparation method on the physicochemical properties and catalytic activities of Ni–AZ and Ni/AZ catalysts was investigated. Although both catalysts retained a mesoporous structure, Ni/AZ catalyst showed lower surface area than Ni–AZ catalyst. From TPR, XRD, and H₂–TPD results, it was revealed that Ni–AZ catalyst retained higher reducibility and higher nickel dispersion than Ni/AZ catalyst. In the hydrogen production by steam reforming of ethanol, both catalysts showed a stable catalytic performance with complete conversion of ethanol. However, Ni–AZ catalyst showed higher hydrogen yield than Ni/AZ catalyst. Superior textural properties, high reducibility, and high nickel surface area of Ni–AZ catalyst were responsible for its enhanced catalytic performance in the steam reforming of ethanol.     

Influence of the acid–base properties over NiSn/MgO–Al2O3 catalysts in the hydrogen production from glycerol steam reforming

In this work we have investigated the hydrogen production from glycerol steam reforming. The effect of the acid–base properties was evaluated using four catalysts based in an alloy Ni–Sn as active phase supported over γ-Al₂O₃ with different content in MgO, varying between 0 and 30 wt.% The incorporation of MgO results in the formation of MgAl₂O₄ spinel, which modifies the acid–base properties of the catalyst. Addition of MgO favored the glycerol conversion into gas, and the catalyst loaded with 10 wt.% MgO exhibited better catalytic performance and higher stability. A blank test with quartz was performed indicating that pyrolysis of glycerol takes place in the quartz.     

Production of hydrogen via steam reforming of biofuels on Ni/CeO2–Al2O3 catalysts promoted by noble metals

The catalytic activity of Ni/CeO₂–Al₂O₃ catalysts modified with noble metals (Pt, Ir, Pd and Ru) was investigated for the steam reform of ethanol and glycerol. The catalysts were characterized by the following techniques: Energy-dispersive X-ray, BET, X-ray diffraction, temperature-programmed reduction, UV–vis diffuse reflectance spectroscopy and X-ray absorption near edge structure (XANES). The results showed that the formation of inactive nickel aluminate was prevented by the presence of CeO₂ dispersed on alumina. The promoting effect of noble metals included a decrease in the reduction temperatures of NiO species interacting with the support, due to the hydrogen spillover effect. It was seen that the addition of noble metal stabilized the Ni sites in the reduced state along the reforming reaction, increasing the ethanol and glycerol conversions and decreasing the coke formation. The higher catalytic performance for the ethanol steam reforming at 600 °C and glycerol steam reforming was obtained for the NiPd and NiPt catalysts, respectively, which presented an effluent gaseous mixture with the highest H₂ yield with reasonably low amounts of CO.     

Power-law type rate equation for propane ATR over Pt–Ni/Al2O3 catalyst

Kinetics of autothermal reforming (ATR) of propane on bimetallic Pt–Ni catalyst supported over δ-Al₂O₃ is investigated at 673 K with the purpose of obtaining an easy-to-implement power-law type rate equation. The rate expression is proposed for conditions extending up to 20% propane conversion and has reaction orders of 1.64, 2.44 and −0.59 in propane, oxygen and steam partial pressures, respectively. Parameters estimated by non-linear regression analysis in the MATLAB™ environment can be reliably used for propane ATR in the steam-to-carbon ratio range of 2.0–3.0 and carbon-to-oxygen ratio range of 3.0–5.4. The apparent activation energy is calculated as 46 ± 4 kJ mol⁻¹ in the 653–693 K interval.     

Preferential CO oxidation on Pt–Cu/Al2O3 catalysts with low Pt loadings

This work demonstrates that a small loading of Pt (0.2–0.5 wt.%) selectively located at the top of the Cu/Al₂O₃ solid is enough to obtain active catalysts for the COPrOx reaction. The characterizations of the catalysts prepared in this work using different Pt:Cu ratios show that the phases formed strongly depend on the Cu and Pt loadings. For the samples with 4 wt.% of Cu, the formation of defective CuAl₂O₄-like species is predominant, with Cu²⁺ occupying distorted sites in the alumina surface. For the samples with 8 wt.% of Cu, CuO and metallic Cu in the form of small crystals are observed besides Cu²⁺. For both 0.2 and 0.5 wt.% of Pt, some proportion of Cu–Pt alloy is found which increased with the Cu content. Metallic Pt particles are only observed by EXAFS for the samples with a higher loading of the noble metal.     

Hydrogen production from CH4 dry reforming over bimetallic Ni–Co/Al2O3 catalyst

Bimetallic 5%Ni–10%Co/Al₂O₃ catalyst was synthesized using impregnation method and evaluated for methane dry reforming reaction at different reaction temperatures. NiO, Co₃O₄ and spinal metal aluminates, namely, CoAl₂O₄ and NiAl₂O₄ phases were formed on γ-Al₂O₃ support surface during calcination process. 5%Ni–10%Co/Al₂O₃ catalyst exhibited reasonable surface area of 86.93 m² g^?1 with small crystallite dimension of less than 10 nm suggesting that both Co₃O₄ and NiO phases were finely dispersed on the surface of support in agreement with results from scanning electron microscopy (SEM) measurement. Temperature-programmed calcination measurement indicates the complete thermal decomposition and oxidation of metal precursors, viz. Ni(NO₃)₂ and Co(NO₃)₂ to metal oxides and metal aluminates at below 700 K. Both CH₄ and CO₂ conversions were stable over a period of 4 h on-stream and attained an optimum at about 67% and 71%, respectively at 973 K whilst H₂ selectivity and yield were higher than 49%. The ratio of H₂/CO was always less than unity for all runs indicating the presence of reverse water–gas shift reaction. The activation energy for CH₄ and CO₂ consumption was computed as 55.60 and 40.25 kJ mol^?1, correspondingly. SEM micrograph of spent catalyst detected the formation of whisker-like carbon on catalyst surface whilst D and G bands characteristic for the appearance of amorphous and graphitic carbons in this order were observed on surface of used catalyst by Raman spectroscopy analysis. Additionally, the percentage of filamentous carbon was greater than that of graphitic carbon.     

Production of hydrogen by methane catalytic decomposition over Ni–Cu–Fe/Al2O3 catalyst

Catalysts with high nickel concentrations 75%Ni–12%Cu/Al₂O₃, 70%Ni–10%Cu–10%Fe/Al₂O₃ were prepared by mechanochemical activation and their catalytic properties were studied in methane decomposition. It was shown that modification of the 75%Ni–12%Cu/Al₂O₃ catalyst with iron made it possible to increase optimal operating temperatures to 700–750 °C while maintaining excellent catalyst stability. The formation of finely dispersed Ni–Cu–Fe alloy particles makes the catalysts stable and capable of operating at 700–750 °C in methane decomposition to hydrogen and carbon nanofibers. The yield of carbon nanofibers on the modified 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst at 700–750 °C was 150–160 g/g. The developed hydrogen production method is also efficient when natural gas is used as the feedstock. An installation with a rotating reactor was developed for production of hydrogen and carbon nanofibers from natural gas. It was shown that the 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst could operate in this installation for a prolonged period of time. The hydrogen concentration at the reactor outlet exceeded 70 mol%.     

Syngas production by CO2 reforming of coke oven gas over Ni/La2O3–ZrO2 catalysts

Syngas production by CO₂ reforming of coke oven gas (COG) was studied in a fixed-bed reactor over Ni/La₂O₃–ZrO₂ catalysts. The catalysts were prepared by sol–gel technique and tested by XRF, BET, XRD, H₂-TPR, TEM and TG–DSC. The influence of nickel loadings and calcination temperature of the catalysts on reforming reaction was measured. The characterization results revealed that all of the catalysts present excellent resistance to coking. The catalyst with appropriate nickel content and calcination temperature has better dispersion of active metal and higher conversion. It is found that the Ni/La₂O₃–ZrO₂ catalyst with 10 wt% nickel loading provides the best catalytic activity with the conversions of CH₄ and CO₂ both more than 95% at 800 °C under the atmospheric pressure. The Ni/La₂O₃–ZrO₂ catalysts show excellent catalytic performance and anti-carbon property, which will be of great prospects for catalytic CO₂ reforming of COG in the future.     

Combination of CO2 reforming and partial oxidation of methane to produce syngas over Ni/SiO2 and Ni–Al2O3/SiO2 catalysts with different precursors

Ni/SiO₂ and Ni–Al₂O₃/SiO₂ catalysts were prepared by incipient wetness impregnation using citrate and nitrate precursors and tested with a reaction of combination of CO₂ reforming and partial oxidation of methane to produce syngas (H₂/CO). The catalytic activity of Ni/SiO₂ and Ni–Al₂O₃/SiO₂ greatly depended on interaction between NiO and support. NiO strongly interacted with support formed small nickel particles (about 4 nm for NiSC which is abbreviation of Ni/SiO₂ prepared with Nickel citrate precursor) after reduction. The small nickel particles over NiSC catalysts exhibited a good catalytic performance.     

Autothermal reforming of iso-octane and gasoline over Rh-based catalysts: Influence of CeO2/γ-Al2O3-based mixed oxides on hydrogen production

Autothermal reforming (ATR) of iso-octane in the presence of Rh-based catalysts (0.5 wt% of Rh) supported onto γ-Al₂O₃, CeO₂, and ZrO₂ were initially carried out at 700 °C with a S/C ratio of 2.0, an O/C ratio of 0.84, and a gas hourly space velocity (GHSV) of 20,000 h⁻¹. The activity of Rh/γ-Al₂O₃ was found to be higher than Rh/CeO₂ and Rh/ZrO₂, with H₂ and (H₂ + CO) yields of 1.98 and 2.48 mol/mol C, respectively, after 10 h. This Rh/γ-Al₂O₃ material, however, was potentially susceptible to carbon coking and produced 3.5 wt% of carbon deposits following the reforming reaction, as evidenced by C, H, N, and S elemental analysis. In contrast, Rh/CeO₂ catalyst exhibited lower activity but higher stability than Rh/γ-Al₂O₃, with nearly no carbon being formed within 10 h. To combine the superior activity originated from Rh/γ-Al₂O₃ with high stability from Rh/CeO₂, Rh/CeO₂/γ-Al₂O₃ catalysts with different CeO₂ contents were synthesized and examined for the ATR reactions of iso-octane. Compared to Rh/γ-Al₂O₃, the newly prepared Rh/CeO₂/γ-Al₂O₃ catalysts (0.5 wt% of Rh and 20 wt% of CeO₂) showed even enhanced activity during 10 h, and H₂ and (H₂ + CO) yields were calculated to be 2.08 and 2.62 mol/mol C, respectively. In addition, as observed with Rh/CeO₂, the catalyst was further found to be stable with less than 0.3 wt% of carbon deposition after 10 h. The Rh/γ-Al₂O₃ and Rh/CeO₂/γ-Al₂O₃ catalysts were eventually tested for ATR reactions using commercial gasoline that contained sulfur, aromatics, and other impurities. The Rh/γ-Al₂O₃ catalyst was significantly deactivated, showing decreased activity after 4 h, while the Rh/CeO₂/γ-Al₂O₃ catalyst proved to be excellent in terms of stability against coke formation as well as activity towards the desired reforming reaction, maintaining its ability for H₂ production for 100 h.