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.     

Non-thermal plasma assisted synthesis and physicochemical characterizations of Co and Cu doped Ni/Al2O3 nanocatalysts used for dry reforming of methane

Ni/Al₂O₃ nanocatalysts doped with Co and Cu were prepared by co-impregnation and modified by non-thermal plasma. The nanocatalysts were characterized by XRD, FESEM, TEM, EDX dot-mapping, BET, FTIR, TGA-DTG, and XPS analysis. According to XRD and XPS results, good interaction between active phase and support can be observed in both Ni–Co/Al₂O₃ and Ni–Cu/Al₂O₃ nanocatalysts. A uniform morphology, high surface area, and well dispersed particles of active sites in Ni–Co/Al₂O₃ nanocatalyst were observed that shows the effect of cobalt in controlling Ni ensemble size. In contrast Ni–Cu/Al₂O₃ nanocatalyst had no homogenous dispersion of active phase due to sintering of copper particles. The activity measurements illustrated better Ni–Co/Al₂O₃ nanocatalyst activity in comparison to Ni/Al₂O₃ and Ni–Cu/Al₂O₃ in terms of CH₄ and CO₂ conversion. H₂ and CO yield were higher for Ni–Co/Al₂O₃ and higher H₂/Co ratio was obtained as well. Whereas Ni/Al₂O₃ and Ni–Co/Al₂O₃ did not experience deactivation, Ni–Cu/Al₂O₃ suffered from activity loss by ca. 22% and 16% for CH₄ and CO₂ conversion, respectively. Sintering most likely happened in Ni–Cu/Al₂O₃ nanocatalyst due to high temperature of calcination while cobalt by controlling the size of Ni particles, alternated the size of active sites to a size range in which carbon formation was suppressed. Ni/Al ratio from XPS analysis which signifies Ni dispersion on alumina support was 5.15, 9.16, and 6.35 for Ni/Al₂O₃, Ni–Co/Al₂O₃, and Ni–Cu/Al₂O₃ nanocatalysts respectively. The highest ratio of Ni/Al was for Ni–Co/Al₂O₃ nanocatalyst that shows the best coverage of support by Ni active phase in this nanocatalyst.     

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.     

Methanol steam reforming in an Al2O3 supported thin Pd-layer membrane reactor over Cu/ZnO/Al2O3 catalyst

In this experimental study, a membrane reactor housing a composite membrane constituted by a thin Pd-layer supported onto Al₂O₃ is utilized to perform methanol steam reforming reaction to produce high-grade hydrogen for PEM fuel cell applications. The influence of various parameters such as temperature, from 280 to 330 °C, and pressure, from 1.5 to 2.5 bar, is analyzed. A commercial Cu/Zn-based catalyst is packed in the annulus of the membrane reactor and the experimental tests are performed at space velocity equal to 18,500 h⁻¹ and H₂O:CH₃OH feed molar ratio equal to 2.5:1. Results in terms of methanol conversion, hydrogen recovery, hydrogen yield and products selectivities are given. As a best result of this work, 85% of methanol conversion and a highly pure hydrogen stream permeated through the membrane with a CO content lower than 10 ppm were reached at 330 °C and 2.5 bar. Furthermore, a comparison between the experimental results obtained in this work and literature data is proposed and discussed.     

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.     

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.     

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.     

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.     

Catalytic properties of Ag promoted ZnO/Al2O3 catalysts for hydrogen production by steam reforming of ethanol

Ag promoted ZnO/Al₂O₃ catalysts were prepared by using the incipient wetness impregnation method. The catalytic properties of steam reforming reaction for hydrogen production on the prepared catalysts were evaluated with H₂O:C₂H₅OH molar ratios of 3:1 at 450 °C and atmospheric pressure. Ag promoted ZnO/Al₂O₃ catalysts show higher SRE catalytic activity than ZnO/Al₂O₃ catalysts. H₂ and CH₃CHO are the major products on Ag promoted catalysts, and C₂H₄ is also produced probably due to acid sites on Al₂O₃. SRE mechanism on Ag promoted ZnO/Al₂O₃ catalysts, which contains C-C scission, is different from that on ZnO/Al₂O₃ catalysts. A method based on thermogravimetry (TG), differential scanning calorimetry (DSC) and mass spectrometry (MS) was used to analysis the coking behavior on catalyst surface. The surfaces of Ag promoted ZnO/Al₂O₃ catalysts show two different types of coking, and suffer higher coke deposition during the steam reforming reaction.     

Hydroprocessing of Jatropha oil over NiMoCe/Al2O3 catalyst

The non-sulfided NiMoCe/Al₂O₃ catalyst was developed to produce green diesel from the hydroprocessing of Jatropha oil. The NiMoCe/Al₂O₃ catalysts were prepared by impregnation and characterized by N₂-BET, SEM, XRD and TPD-H_ads techniques. The straight chain alkanes ranging from C15 to C18 were the main components in product oil. The maximum yield of C15-C18 alkanes of 80%, selectivity of 90% and conversion of 89% were obtained at 370 °C, 3.5 MPa and 0.9 h⁻¹. Influence of reaction temperature (280–400 °C) and reaction time (10–163 h) on the composition of product oil were discussed. The experimental results demonstrated that a suitable amount of metal Ce doping on the NiMo/Al₂O₃ catalyst presented stable catalytic performance and enhanced Jatropha oil conversion as well as C15-C18 fraction selectivity.     

Fuel cell grade hydrogen production via methanol steam reforming over CuO/ZnO/Al2O3 nanocatalyst with various oxide ratios synthesized via urea-nitrates combustion method

Hydrogen production via steam reforming of methanol has been studied over a series of CuO/ZnO/Al₂O₃ catalysts synthesized by the combustion method using urea as fuel. Furthermore, the effect of alumina loading on the properties of the catalyst has been investigated. XRD analysis illustrated the crystallinity of the Cu and Zn oxides decreases by enhancing alumina loading. BET showed the surface area improvement and FESEM images revealed lower size distribution by increasing the amount of alumina. EDX results gave approximately the same metal oxide compositions of primary gel for the surface of the nanocatalysts. Catalytic performance tests showed the well practicability of catalysts synthesized by the combustion method for steam reforming of methanol process. Alumina addition to the CuO/ZnO catalyst caused the higher methanol conversion and the lower CO generation. Among different compositions the sample with molar component of CuO/ZnO/Al₂O₃ = 4/4/2.5 showed the best performance which without CO generation at 240 °C its methanol conversion decreased from 90 to 60% after 90 h.     

Nanocrystallites-forming hierarchical porous Ni/Al2O3–TiO2 catalyst for dehydrogenation of organic chemical hydrides

Dehydrogenation of organic chemical hydrides has been improved by reconstructing the catalyst in the form of hierarchical porous structure nanocatalyst, in which the economical Ni was adopted as catalytic component and nano Al₂O₃–TiO₂ hybrid composite as support. The Al₂O₃–TiO₂ composite was prepared by spontaneous self-assembly of nano Al₂O₃ and TiO₂ aggregates by hydrolysis of tetra-n-butyl-titanate under continuous agitation. The multi-scaled distribution of Al₂O₃–TiO₂ aggregates with hierarchy could be observed in dynamic light scattering spectrometer. The aggregates are comprised of nano-sized γ-Al₂O₃ and anatase TiO₂ crystallites with sizes of about 5 and 7 nm, respectively. The surface modulation by TiO₂ could be verified in FTIR Spectra. The migration of Ti species and crystallite growth were hindered by the Al₂O₃ skeleton and the hierarchical porous structure was sustained during the thermal related process. The multi-scaled distributed pores were confirmed by both TEM analysis and N₂ adsorption results. The results of dehydrogenation experiments showed that the hierarchical porous structure nano Ni/Al₂O₃–TiO₂ exhibited superior catalytic performance to Ni/Al₂O₃ with the optimum conversion of 99.9% at 400 °C, while the catalyst of Ni/Al₂O₃ exhibited only 16.5% under the same condition.     

Effect of Al2O3 content on the adsorptive properties of Cu/ZnO/Al2O3 for removal of odorant sulfur compounds

Cu/ZnO/Al₂O₃ adsorbents for removal of odorant sulfur compounds were prepared with various Al/Cu molar ratios by co-precipitation method. The sulfur removing ability as a function of Al/Cu molar ratio of the adsorbents for t-butyl mercaptan (TBM), tetrahydro thiophene (THT), dimethyl disulfide (DMS) and H₂S were investigated at 250 °C and 6000 h⁻¹ space velocity. Based on the results of adsorption capacity and characterization by various techniques, the optimum Al/Cu ratio for maximum sulfur removal capacity is found to be at Al/Cu molar ratio of 0.15 which possesses the well-dispersed Cu species with high reducibility. The adsorption capacity is highest for H₂S followed by TBM, DMS and THT. The main role of Al₂O₃ component is to provide the dispersion of CuO species homogeneously with small particle formation and high reducibility.     

Effect of Pr addition on the properties of Ni/Al2O3 catalysts with an application in the autothermal reforming of methane

Ni/xPr-Al₂O₃ (x = 5, 10, 15, 20 wt%) catalysts with an application in autothermal reforming of methane were prepared by sequential impregnation synthesis; its catalytic performance was evaluated and compared with that of Ni/γ-Al₂O₃ catalyst; the physicochemical properties of the 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 results showed that Pr addition promoted the reduction of nickel particle size on the surface. TPR experiments suggested a heterogeneous distribution of nickel oxide particles over xPr-Al₂O₃ supports and the promotion of NiO reduction by Pr modification. The CH₄ conversion increased with elevating levels of Pr addition from 5% to 10%, then decreased with Pr content from 10% to 20%. For the stability catalytic tests, Ni/xPr-Al₂O₃ catalysts maintained the high activity after 48 h while Ni/Al₂O₃ had a significant deactivation.     

Solution combustion synthesized cobalt oxide catalyst precursor for NaBH4 hydrolysis

In this paper we report the solution combustion synthesis of cobalt oxide nanofoam from solutions of cobalt nitrate and glycine and subsequent use as an effective catalyst precursor for NaBH₄ hydrolysis. The catalytic activity results show that the hydrogen generation rate (HGR) at room temperature was much higher for the solution combustion synthesized material than for commercial Co₃O₄ nanopowder, though their specific surface areas were comparable (∼26–32 m²/g). Using a 0.6 wt.% aqueous solution of NaBH₄ at 20 °C and a 5 wt.% catalyst precursor loading, a HGR of 1.93 L min⁻¹ g_cat⁻¹ was achieved for solution combustion synthesized Co₃O₄. In contrast, at the same conditions, for commercial Co₃O₄ and elemental Co powders HGRs of 0.98 and 0.49 L min⁻¹ g_cat⁻¹ were achieved respectively. This type of synthesis is amenable to many complex metal oxide catalysts as well, such as LiCoO₂, which have also been shown to be good catalyst precursors for hydrolysis of NaBH₄.     

Photocatalytic hydrogen production from aqueous methanol solution with CuO/Al2O3/TiO2 nanocomposite

The photocatalytic hydrogen production from aqueous methanol solution was investigated with ZnO/TiO₂, SnO/TiO₂, CuO/TiO₂, Al₂O₃/TiO₂ and CuO/Al₂O₃/TiO₂ nanocomposites. A mechanical mixing method, followed by the solid-state reaction at elevated temperature, was used for the preparation of nanocomposite photocatalyst. Among these nanocomposite photocatalysts, the maximal photocatalytic hydrogen production was observed with CuO/Al₂O₃/TiO₂ nanocomposites. A variety of components of CuO/Al₂O₃/TiO₂ photocatalysts were tested for the enhancement of H₂ formation. The optimal component was 0.2 wt% CuO/0.3 wt% Al₂O₃/TiO₂. The activity exhibited approximately tenfold enhancement at the optimum loading, compared with that with pure P-25 TiO₂. Nano-sized TiO₂ photocatalytic hydrogen technology has great potential for low-cost, environmentally friendly solar-hydrogen production to support the future hydrogen economy.     

Evidence of composition deviation of metal particles of a Ni–Cu/Al2O3 catalyst during methane decomposition to COx-free hydrogen

A coprecipitated Ni–Cu/Al₂O₃ catalyst was examined in a fluidized bed reactor for the decomposition of methane to CO_x-free hydrogen and carbon nanofibers using two different reaction temperature schemes, i.e. constant temperature and pre-induction operation. At constant temperatures, the catalyst showed quasi-stable activity below 913 K for a notable time period, while its performance decayed fast above this temperature and a quick deactivation was observed at 1013 K. However, for reaction at 1013 K, the durability was improved if the catalyst was induced for 10 min at 823 K in the reaction atmosphere. A detailed examination of the metal particles after reaction with EDS revealed that the composition of the metal particle depended strongly on the reaction temperature and the induction scheme. The metal particles in the reduced catalyst showed a composition deviation also. The HRTEM micrographs of the carbon–metal interface and the EDS results support the surface migration and ensemble mechanism for carbon formation and give evidence for the reconstruction of the metal particles during the induction period.     

Effect of preparation method on the performance of the Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol: Part II-characterization

In the first part of this paper [1], we have discussed the effect of preparation method on the performance of Ni/Al₂O₃ catalysts for aqueous-phase reforming of ethanol (EtOH). One catalyst was synthesized using a sol–gel method (SG). The other was synthesized by adding nickel nitrate to a solution combustion synthesized alumina support (SCS). Based on the product distribution, we proposed the reaction pathway as a mixture of dehydrogenation of EtOH to acetaldehyde followed by C–C bond breaking to produce CO and CH₄ and oxidation of acetaldehyde to acetic acid followed by decarbonylation to CO₂ and 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). The SG catalysts showed poorer WGSR activity than the SCS catalysts. The difference of the metal particle size distribution governed by preparation method appeared to be the key factor of controlling catalytic efficiency, but some contradictory results could not be explained.     

Selective CO oxidation on Cu promoted Pt/Al2O3 and Pt/Nb2O5 catalysts

Pt–Cu catalysts supported on Al₂O₃ and Nb₂O₅ were studied for use in selective CO oxidation. The addition of copper enhanced the activity and selectivity of Pt–Cu/Nb₂O₅ at lower temperatures when compared to Pt/Nb₂O₅. On the other hand, copper addition was not beneficial in the case of Al₂O₃ supported catalysts.     

Nickel on a macro-mesoporous Al2O3@ZrO2 core/shell nanocomposite as a novel catalyst for CO methanation

A novel nickel catalyst supported on Al₂O₃@ZrO₂ core/shell nanocomposites was prepared by the impregnation method. The core/shell nanocomposites were synthesized by depositing zirconium species on boehmite nanofibres. This contribution aims to study the effects of the pore structure of supports and the zirconia dispersed on the surface of the alumina nanofibres on the CO methanation. The catalysts and supports were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR), nitrogen adsorption–desorption, and thermogravimetry and differential thermal analysis (TG-DTA). The catalytic performance of the catalysts for CO methanation was investigated at a temperature range from 300 °C to 500 °C. The results of the characterization indicate that the metastable tetragonal zirconia could be stably and evenly dispersed on the surface of alumina nanofibres. The interlaced nanorods of the Al₂O₃@ZrO₂ core/shell nanocomposites resulted in a macropore structure and the spaces between the zirconia nanoparticles dispersed on the alumina nanofibres formed most of the mesopores. Zirconia on the surface of the support promoted the dispersion and influenced the reduction states of the nickel species on the support, so it prevented the nickel species from sintering as well as from forming a spinel phase with alumina at high temperatures, and thus reduced the carbon deposition during the reaction. With the increase of the zirconia content in the catalyst, the catalytic performance for the CO methanation was enhanced. The Ni/Al₂O₃@ZrO₂-15 exhibited the highest CO conversion and methane selectivity at 400 °C, but they decreased dramatically above or below 400 °C due to the temperature sensitivity of the catalyst. Ni/Al₂O₃@ZrO₂-30 exhibited a high and constant rate of methane formation between 350 °C and 450 °C. The excellent catalytic performance of this catalyst is attributed to its reasonable pore structure and good dispersion of zirconia on the support. This catalyst has great potential to be further studied for the future industrial use.