Nanocomposite Ni/ZrO2: Highly active and stable catalyst for H2 production via cyclic stepwise methane reforming reactions

This work investigates the catalytic performance of nanocomposite Ni/ZrO₂-AN catalyst consisting of comparably sized Ni (10–15 nm) and ZrO₂ (15–25 nm) particles for hydrogen production from the cyclic stepwise methane reforming reaction with either steam (H₂O) or CO₂ at 500–650 °C, in comparison with a conventional Ni/ZrO₂-CP catalyst featuring Ni particles supported by large and widely sized ZrO₂ particles (20–400 nm). Though both catalysts exhibited similar activity and stability during the reactions at 500 and 550 °C, they showed remarkably different catalytic stabilities at higher temperatures. The Ni/ZrO₂-CP catalyst featured a significant deactivation even during the methane decomposition step in the first cycle of the reactions at ≥600 °C, but the Ni/ZrO₂-AN catalyst showed a very stable activity during at least 17 consecutive cycles in the cyclic reaction with steam. Changes in the catalyst beds at varying stages of the reactions were characterized with TEM, XRD and TPO–DTG and were correlated with the amount and nature of the carbon deposits. The Ni particles in Ni/ZrO₂-AN became stabilized at the sizes of around 20 nm but those in Ni/ZrO₂-CP kept on growing in the methane decomposition steps of the cyclic reaction. The small and narrowly sized Ni particles in the nanocomposite Ni/ZrO₂-AN catalyst led to a selective formation of filamentous carbons whereas the larger Ni particles in the Ni/ZrO₂-CP catalyst a preferred formation of graphitic encapsulating carbons. The filamentous carbons were favorably volatilized in the steam treatment step but the CO₂ treatment selectively volatilized the encapsulating carbons. These results identify that the nature but not the amount of carbon deposits is the key to the stability of Ni/ZrO₂ catalyst and that the nanocomposite Ni/ZrO₂-AN would be a promising catalyst for hydrogen production via cyclic stepwise methane reforming reactions.     

Evaluation of Ni/Y2O3/Al2O3 catalysts for hydrogen production by autothermal reforming of methane

Ni/xY₂O₃–Al₂O₃ (x = 5, 10, 15, 20 wt%) catalysts were prepared by sequential impregnation synthesis. The catalytic performance for the autothermal reforming of methane was evaluated and compared with Ni/γ-Al₂O₃ catalyst. The physicochemical properties of catalysts were characterized by X-ray diffraction (XRD), Transmission electron microscope (TEM), X-Ray Photoelectron Spectrometer (XPS), Thermo Gravimetric Analyzer (TGA) and H₂-temperature programmed reduction techniques (TPR). The decrease of nickel particle size and the change of reducibility were found with Y modification. The CH₄ conversion increased with elevating levels of Y₂O₃ from 5% to 10%, then decreased with Y content from 10% to 20%. Ni/xY₂O₃–Al₂O₃ catalysts maintained high activity after 24 h on stream, while Ni/Al₂O₃ had a significant deactivation. The characterization of spent catalysts indicated that the addition of Y retarded Ni sintering and decreased the amount of coke.     

Effect of ZrO2 addition on Ni/Al2O3 catalyst to produce H2 from glycerol

In this work, ZrO₂ was employed as support and as Al₂O₃ modifier of Ni based catalysts due to its special interesting characteristics. The catalytic activity of these systems was studied in steam reforming of glycerol to produce H₂. As the activity results at 773 K and 873 K showed, the NiZ catalyst allowed low glycerol conversion and H₂ production when compared to the NiγA catalyst. Moreover, the NiZ catalyst was not able to reform intermediate liquid products into gaseous products.     

Thermodynamic and experimental study of combined dry and steam reforming of methane on Ru/ ZrO2-La2O3 catalyst at low temperature

Analysis of the effect of adding small amounts of steam to the methane dry reforming feed on activity and products distribution was performed from thermodynamic equilibrium calculations of the system based on the Gibbs free energy minimization method. This analysis is supported by new insights from the direct experimental investigation of the influence of co-feeding with H₂O over a Ru/ZrO₂-La₂O₃ catalyst. Activity measurements were carried out in a fixed-bed reactor but using the operating conditions applicable in a Pd membrane reactor, that is, at maximum reaction temperature below 550 °C. Experimental results were in good agreement with thermodynamics predictions. It was observed that the addition of H₂O into the dry reforming feed strongly affects activity and products distribution. The co-feeding of steam resulted in increasing methane conversion and hydrogen yield but decreasing carbon dioxide conversion and carbon monoxide yield. At a given temperature, syngas composition (H₂/CO ratio) can be tuned by changing the amount of H₂O co-fed. Interestingly the stability of the Ru/ZrO₂-La₂O₃ catalyst was improved by adding steam to the dry reforming reactant mixtures.     

Effect of preparation conditions of CuO–CeO2–ZrO2 catalyst on CO removal from hydrogen-rich gas

The activities of CuO–CeO₂–ZrO₂ catalysts synthesized by four methods, e.g. sol–gel, co-precipitation, one-step impregnation, and two-step impregnation, were compared for CO removal from hydrogen-rich gas. The influence of the precipitant and calcination temperature on the catalytic activity was investigated, and a series of analytical methods, such as XRD, H₂-TPR, TG-DSC, and SEM, were used to characterize the catalysts. It was indicated that CuO–CeO₂–ZrO₂ catalyst prepared by co-precipitation method exhibits the widest operation temperature range with the 99% conversion of CO and relatively high selectivity. The optimized preparation conditions were confirmed using Na₂CO₃ as a precipitant, and calcining at 500 °C. It was proposed that the high activity and selectivity result from the high dispersion of copper and strong interaction among CuO, CeO₂, and ZrO₂. The effects of precipitants on the grain size and morphology of the catalyst is larger than that of calcination temperature.     

The effect of Ni:Pt ratio on oxidative steam reforming performance of Pt–Ni/Al2O3 catalyst

Oxidative steam reforming of propane was tested over four Pt–Ni/δ-Al₂O₃ bimetallic catalysts aiming to investigate the effect of metal loadings and Ni:Pt loading ratio on catalyst performance. A trimetallic Pt–Ni–Au/δ-Al₂O₃ catalyst was additionally studied aiming to understand the effect of Au presence. Reaction temperature, carbon to oxygen ratio, and residence time were taken as the reaction parameters. The effect of C/O₂ ratio on the hydrogen production and H₂/CO selectivity was found dependent on the Pt and Ni loadings. The results underlined the importance of C/O₂ ratio as an optimization parameter for product distribution. The highest hydrogen production and H₂/CO ratio levels were obtained for the highest C/O₂ ratio tested. An optimum Ni:Pt weight ratio was found around 50 due to suppressed methanation and enhanced hydrogen production activities of these catalysts. The presence of gold in the trimetallic catalyst caused poor activity and selectivity in comparison to bimetallic catalysts.     

The steam reforming of guaiacol for hydrogen via Ni/Al2O3: The influence of dispersion

In this paper, three Ni/Al₂O₃ catalysts with different structure were prepared by different methods. The differences between the catalysts had been compared by H₂ temperature program reduction (H₂-TPR), X-ray diffraction, thermogravimetric analysis, scanning electron microscope, transmission electron microscope, and X-ray photoelectron spectroscopy. The results showed that synthesis method had significant effect on the combination of Ni particle with carrier. The method of coprecipitation could help to improve the combination of Ni and Al₂O₃, and the effect was further enhanced after adding polyethylene glycol (PEG). Due to the enhanced interaction between the active metal and the carrier, the NiO could be easily deoxidized and hard to sinter, which could obtain smaller and more dispersed Ni particles. Moreover, the addition of PEG improved the Ni particle size and its dispersion, and promoted the formation of the unique acicular Al₂O₃. The performance of guaiacol steam catalytic reforming via different catalysts was further analyzed, and the results showed the catalyst obtained by coprecipitation method with PEG exhibited best activity with 73.8% guaiacol conversion and 23.1 wt% H₂ yield.     

Steam reforming of methanol over Cu/ZnO/ZrO2/Al2O3 catalyst

Steam reforming of methanol was investigated over Cu–ZnO–ZrO₂–Al₂O₃ catalysts at 473 and 573 K. The Cu:Zn:(Al + Zr) molar ratio was 3:3:4; however, the Zr:Al molar ratio was varied and the catalysts were pretreated at different calcination and reduction temperatures. The synthesized catalysts were characterized by N₂ physisorption, temperature-programmed reduction with H₂ (H₂-TPR), X-ray diffraction, oxidized surface TPR, and infrared spectroscopy after carbon monoxide chemisorption. The crystalline size of Cu decreased on increasing the calcination temperatures from 573 to 623 K and increased on increasing the reduction temperatures from 523 to 573 K. Among the tested catalysts, the Cu–ZnO–ZrO₂ catalyst exhibited the highest and lowest hydrogen-formation rates at 473 and 573 K, respectively. After the reaction at 573 K, all the tested catalysts exhibited an increase in the Cu crystalline size, causing the catalyst deactivation. Among the tested catalysts, the Cu–ZnO–ZrO₂–Al₂O₃ catalyst, where the Cu:Zn:Al:Zr molar ratio was 3:3:2:2, showed the highest and most stable catalytic activity at 573 K. Cu dispersion and catalyst composition affected the catalytic performance for steam reforming of methanol.     

Hydrogen production by steam reforming of model bio-oil using structured Ni/Al2O3 catalysts

This study focuses on hydrogen production from the steam reforming of model bio-oil over Ni/Al₂O₃ catalysts prepared in two different geometries (monolith and pellet) using the dip-coating and wet impregnation methods and characterized using Powder X-Ray diffraction, Temperature Programmed Reduction, Scanning Electron Microscopy (SEM) and BET Surface area analysis. The effects of the catalyst geometry and reforming temperatures were studied by carrying out experiments at the optimal conditions of T = (823, 923, 1023) K and S/C ratio = 13 determined from the thermodynamic analysis of the process prior to the experiments using the process simulator PRO-II. The experimental results showed high steady state H₂ yield corresponding to 2.58 and 1.73 mol (out of 5.13 mol) using monolithic and the pelletized catalysts respectively. The product distribution achieved with the monolithic catalyst was closer to the thermodynamic results suggesting a higher selectivity to hydrogen production.     

Hydrogen production by oxidative steam reforming of methanol over Ni/CeO2–ZrO2 catalysts

Single ZrO₂ and mixed CeO₂-ZrO₂ oxides with different CeO₂/ZrO₂ ratios were prepared by the sol-gel method and the CeO₂ by precipitation. The prepared support were impregnated with an aqueous solution of NiCl₂·6H₂O at an appropriate concentration to yield 3 wt.% of nickel respectively in the catalysts. Catalytic materials were characterized by BET (N₂ adsorption-desorption), SEM-EDS, XRD and TPR. The oxidative steam reforming of methanol (OSRM) reaction was investigated on these catalysts for H₂ production as a function of temperature. Depending of the CeO₂/ZrO₂ ratio; the catalysts composition has a significant influence on the surface area (BET), reduction properties and methanol conversion. XRD patterns of the Ni-base catalysts showed well defined diffraction peaks of the metallic Ni except on the Ni/CeO₂ catalyst, suggesting that on this sample all of the active phase was highly dispersed. Ni/Ceria-rich catalysts were vastly active for OSRM, giving a total CH₃OH conversion at 325 °C with GHSV = 0.3 × 10⁵ h⁻¹. They also showed close selectivity toward H₂, with high selectivity to CO₂ in all range of temperatures, this suggests that the reverse WGS reaction does not occur on these samples. It seems that the nickel is the phase mainly responsible of hydrogen production although the CeO₂/ZrO₂ support reduces the CO formation.     

Two-step steam pretreatment of softwood by dilute H2SO4 impregnation for ethanol production

Fuel ethanol can be produced from softwood through hydrolysis in an enzymatic process. Prior to enzymatic hydrolysis of the softwood, pretreatment is necessary. In this study two-step steam pretreatment by dilute H₂SO₄ impregnation to improve the overall sugar and ethanol yield has been investigated. The first pretreatment step was performed under conditions of low severity (180°C, 10 min, 0.5% H₂SO₄) to optimise the amount of hydrolysed hemicellulose. In the second step the washed solid material from the first pretreatment step was impregnated again with H₂SO₄ and pretreated under conditions of higher severity to hydrolyse a portion of the cellulose, and to make the cellulose more accessible to enzymatic attack. A wide range of conditions was used to determine the most favourable combination. The temperatures investigated were between 180°C and 220°C, the residence times were 2, 5 and 10 min and the concentrations of H₂SO₄ were 1% and 2%.

The effects of pretreatment were assessed by both enzymatic hydrolysis of the solids and with simultaneous saccharification and fermentation (SSF) of the whole slurry, after the second pretreatment step. For each set of pretreatment conditions the liquid fraction was fermented to determine any inhibiting effects. The ethanol yield using the SSF configuration reached 65% of the theoretical value while the sugar yield using the SHF configuration reached 77%. Maximum yields were obtained when the second pretreatment step was performed at 200°C for 2 min with 2% H₂SO₄. This form of two-step steam pretreatment is a promising method of increasing the overall yield in the wood-to-ethanol process.     

Nickel catalysts supported on ZrO2, Y2O3-stabilized ZrO2 and CaO-stabilized ZrO2 for the steam reforming of ethanol: Effect of the support and nickel load

Catalysts with various nickel loads were prepared on supports of ZrO₂, ZrO₂–Y₂O₃ and ZrO₂–CaO, characterized by XRD and TPR and tested for activity in ethanol steam reforming. XRD of the supports identified the monoclinic crystalline phase in the ZrO₂ and cubic phases in the ZrO₂–Y₂O₃ and ZrO₂–CaO supports. In the catalysts, the nickel impregnated on the supports was identified as the NiO phase. In the TPR analysis, peaks were observed showing the NiO phase having different interactions with the supports. In the catalytic tests, practically all the catalysts achieved 100% ethanol conversion, H₂ yield was near 70% and the gaseous concentrations of the other co-products varied in accordance with the equilibrium among them, affected principally by the supports. It was observed that when the ZrO₂ was modified with Y₂O₃ and CaO, there were big changes in the CO and CO₂ concentrations, which were attributed to the rise in the number of oxygen vacancies, permitting high-oxygen mobility and affecting the gaseous equilibrium. The liquid products analysis showed a low selectivity to liquid co-products during the reforming reactions.     

The effect of Ni content on a highly active Ni-Al2O3 catalyst prepared by the homogeneous precipitation method

Highly active Ni-Al₂O₃ catalysts were prepared by the homogeneous precipitation method with a variety of high nickel contents ranging from 30 to 70 wt.%. The effects of nickel content on the physicochemical properties and catalytic activities of the Ni-Al₂O₃ catalysts were investigated. XRD measurements showed that the catalyst with 30 Ni wt.% only had a diffraction peak corresponding to NiAl₂O₄, whereas the catalysts of 50, 60 and 70 Ni wt.% had diffraction peaks corresponding to NiO and NiAl₂O₄. Hydrogen chemisorption results showed that the nickel surface area increased with increasing nickel content in the order: 30 < 40 < 50 < 60 < 70 Ni wt.%. Specifically, the nickel surface area increased steadily from 11 to 22 m²/g with increasing the nickel content from 30 to 50 wt.%, after which it stayed nearly constant at 22 m²/g despite the increase in nickel content from 50 to 70 wt.%. TEM images of the reduced Ni-Al₂O₃ catalysts revealed that the average sizes of the Ni particles were 12, 13 and 16 nm for the catalysts with 30, 50 and 70 Ni wt.%, respectively, suggesting that a higher nickel content yielded a larger Ni particle. The catalytic performance of methane steam reforming showed that the catalytic reaction rate increased steadily with increasing nickel content from 30 to 50 wt.%, after which it stayed nearly constant despite that the nickel content increased to over 50 wt.%. As a result, about 50 wt.% of nickel was found to be a reasonable nickel content to obtain the maximum catalytic activity.     

Steam reforming and oxidative steam reforming of methanol over CuO–CeO2 catalysts

Steam reforming (SRM) and oxidative steam reforming of methanol (OSRM) were carried out over a series of coprecipitated CuO–CeO₂ catalysts with varying copper content in the range of 30–80 at.% Cu (= 100 × Cu/(Cu + Ce)). The effects of copper content, reaction temperature and O₂ concentration on catalytic activity were investigated. The activity of CuO–CeO₂ catalysts for SRM and OSRM increased with the copper content and 70 at.% CuO–CeO₂ catalyst showed the highest activity in the temperature range of 160–300 °C for both SRM and OSRM. After SRM or OSRM, the copper species in the catalysts observed by XRD were mainly metallic copper with small amount of CuO and Cu₂O, an indication that metallic copper is an active species in the catalysis of both SRM and OSRM. It was observed that the methanol conversion increased considerably with the addition of O₂ into the feed stream, indicating that the partial oxidation of methanol (POM) is much faster than SRM. The optimum 70 at.% CuO–CeO₂ catalyst showed stable activities for both SRM and OSRM reactions at 300 °C.     

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.     

Kinetic study of the catalytic reforming of biomass pyrolysis volatiles over a commercial Ni/Al2O3 catalyst

An original kinetic model has been proposed for the reforming of the volatiles derived from biomass fast pyrolysis over a commercial Ni/Al₂O₃ catalyst. The pyrolysis-reforming strategy consists of two in-line steps. The pyrolysis step is performed in a conical spouted bed reactor (CSBR) at 500 °C, and the catalytic steam reforming of the volatiles has been carried out in-line in a fluidized bed reactor. The reforming conditions are as follows: 600, 650 and 700 °C; catalyst mass, 0, 1.6, 3.1, 6.3, 9.4 and 12.5 g; steam/biomass ratio, 4, and; time on stream, up to 120 min. The integration of the kinetic equations has been carried out using a code developed in Matlab. The reaction scheme takes into account the individual steps of steam reforming of bio-oil oxygenated compounds, CH₄ and C₂-C₄ hydrocarbons, and the WGS reaction. Moreover, a kinetic equation for deactivation has been derived, in which the bio-oil oxygenated compounds have been considered as the main coke precursors. The kinetic model allows quantifying the effect reforming conditions (temperature, catalyst mass and time on stream) have on product distribution.     

CO2 reforming of methane combined with steam reforming or partial oxidation of methane to syngas over NdCoO3 perovskite-type mixed metal-oxide catalyst

CO₂ reforming with simultaneous steam reforming or partial oxidation of methane to syngas over NdCoO₃ perovskite-type mixed metal oxide catalyst (prereduced by H₂) at different process conditions has been investigated. In the simultaneous CO₂ and steam reforming, the conversion of methane and H₂O and also the H₂/CO product ratio are strongly influenced by the CO₂/H₂O feed-ratio. In the simultaneous CO₂ reforming and partial oxidation of methane, the conversion of methane and CO₂, H₂ selectivity and the net heat of reaction are strongly influenced by the process parameters (viz. temperature, space velocity and relative concentration of O₂ in the feed). In both cases, no carbon deposition on the catalyst was observed. The reduced NdCoO₃ perovskite-type mixed-oxide catalyst (Co dispersed on Nd₂O₃) is a highly promising catalyst for carbon-free CO₂ reforming combined with steam reforming or partial oxidation of methane to syngas.     

Syngas production via CO2 reforming of methane over plasma assisted synthesized Ni‐Co/Al2O3‐ZrO2 nanocatalysts with different Ni‐loadings

Ni‐Co/Al₂O₃‐ZrO₂ nanocatalysts with 5, 10 and 15 wt.% nominal Ni content have been prepared by impregnation followed by a non‐thermal plasma treatment, characterized and tested for dry reforming of methane. For nanocatalysts characterization the following techniques have been used: XRD, FESEM, TEM, EDX dot‐mapping, BET, FTIR and XPS. The dry reforming of methane was carried out at different temperatures (550‐850 °C) using a feed mixture of CH₄:CO₂ (1:1). Among the nanocatalysts studied, the catalyst with the medium Ni content (10 wt.%) was the most active in dry reforming of methane. This higher activity exhibited by Ni‐Co/Al₂O₃‐ZrO₂ catalyst with medium Ni content (10 wt.% ) can be attributed to small and well dispersed particles of Ni within the catalyst. Apart from the narrow surface particle size distribution in the case of Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂, the presence of small active components with average size of 7.5 nm is proposed to be the reason for the superior performance of the catalyst. Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂ nanocatalyst had maximum surface area and the lower surface area was observed in the case of Ni(5 wt.%)‐Co/Al₂O₃‐ZrO₂ and Ni(15 wt.%)‐Co/Al₂O₃‐ZrO₂ due to the formation of the larger agglomeration and higher mean particle size of nickel particles, respectively. Although, GHSV enhancment had inverse effect on product yield but yield reduction for Ni‐Co/Al₂O₃‐ZrO₂ catalyst with 10 wt.% Ni was less drastic at high GHSVs. According to XRD and XPS, existence of NiAl₂O₄ confirms strong interaction between Ni and support but higher loadings of Ni resulted in less NiAl₂O₄; loser interaction between support and active phase. Small particles of active components and well‐defined dispersion of them in Ni(10 wt.%)‐Co/Al₂O₃‐ZrO₂ nanocatalyst resulted in stability of the catalyst for either feed conversion or H₂/CO molar ratio. Copyright © 2013 John Wiley & Sons, Ltd.     

Autothermal reforming of methane over Ni/γ-Al2O3 catalysts: the enhancement effect of small quantities of noble metals

The effect of introducing small amounts of Pt, Pd and Ir (<0.3% by weight) into Ni/γAl₂O₃ catalysts (15% Ni w/w) for the autothermal reforming of methane (ATR) was investigated. While the unpromoted catalyst took the partial oxidation of methane to equilibrium, the promoted ones increased the methane conversion in ATR. No electronic modifications of nickel sites were observed with the addition of noble metals, but they did cause an increase in metal surface area. The effect of noble metals on this reaction, under these conditions, was assigned to this expansion of the metal surface.     

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.