Effects of electroless deposition conditions on microstructures of cobalt–phosphorous catalysts and their hydrogen generation properties in alkaline sodium borohydride solution

Cobalt–phosphorous (Co–P) catalysts with a high hydrogen generation rate in alkaline sodium borohydride (NaBH₄) solution are developed by electroless deposition. The microstructures of the Co–P catalysts and their catalytic activities for hydrolysis of NaBH₄ are analyzed as a function of the electroless deposition conditions such as the pH and temperature of the Co–P bath. The electroless-deposited Co–P catalysts are composed of nano-crystalline Co and amorphous Co–P. The size of the nano-crystalline Co particles dispersed in amorphous Co–P matrix depends largely on the electroless deposition conditions. Moreover, Co–P catalysts with finer crystalline Co exhibit a higher hydrogen generation rate. In particular, the Co–P catalysts formed in a pH 12.5 bath at 60–70 °C exhibit the best hydrogen generation rate of 3300 ml min⁻¹ g⁻¹-catalyst in 1 wt.% NaOH + 10 wt.% NaBH₄ solution at 30 °C, which is 60 times faster than that obtained with a Co catalyst.     

Steam reforming of iso-octane toward hydrogen production over mono- and bi-metallic Cu–Co/CeO2 catalysts: Structure-activity correlations

Τhe feasibility of tailoring the iso-octane steam reforming activity of Cu/CeO₂ catalysts through the use of Co as a second active metal (Cu_20−xCo_x, where x = 0, 5, 10, 15, 20 wt%), is investigated. Characterization studies, involving N₂ adsorption–desorption at −196 °C (BET), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS) and Temperature Programmed Reduction (H₂-TPR), were carried out to reveal the impact of the morphological, structural and surface properties of the catalysts on the reforming performance. The results showed that reforming activity was monotonically increased upon increasing cobalt loading. The Co/CeO₂ catalyst demonstrated the optimum performance with a H₂ yield of 70–80% in the 600–800 °C temperature interval. The Co/CeO₂ catalyst exhibited also excellent stability at temperatures above 700 °C, while Cu-based catalysts rapidly deactivated in long term stability tests. A close correlation between surface/redox properties and steam reforming efficiency was established. The lower reducibility of Co/CeO₂ catalysts, associated with the formation of Co³⁺ species, in Co₃O₄-like phase, can be accounted for the enhanced carbon tolerance of Co-based catalysts. Furthermore, the high concentration of surface oxygen species on Co/CeO₂ catalysts can be considered for their enhanced performance. On the other hand, the Cu-induced easier reducibility of bimetallic catalysts, in conjunction with carbon deposition and active phase sintering can be accounted for their inferior steam reforming performance. Irreversible changes in the redox properties of Cu-based catalysts, taking place under reaction conditions, could be resulted to ceria deactivation thus hindering the redox process to keep on.     

Hydrogen production by glycerol steam-reforming over nickel and nickel-cobalt impregnated on alumina

Hydrogen is a clean energy carrier, and its utilization will reduce environmental problems related to fossil fuels one. Biomass is an inexhaustible renewable source to generate biocompounds. Glycerol, obtained from a crescent biodiesel industry, is an abundant bio-substrate to produce hydrogen. The steam reforming of glycerol was studied employing 4Ni/Al₂O₃, 4Co–4Ni/Al₂O₃, and 12Co–4Ni/Al₂O₃ catalysts at 300, 500, and 700 °C, 1 atm, 10 h⁻¹ WHSV, 6:1 water:glycerol molar ratio (WGMR), 0.17 ml min⁻¹ glycerol solution feed flow rate and time-on-stream 8 h. The main product obtained was H₂, followed by CO₂, CO, and CH₄ in smaller proportion. Co promotes H₂ production and unfavors CO₂ generation when temperature decreases; CH₄ formation is observed at higher temperature. A low Co loading produces the largest H₂ and CO₂ amounts at the lowest temperature. A high Co loading improves H₂ production at lower temperature, but this does not occur at high temperature.     

Y2O3-promoted NiO/SBA-15 catalysts highly active for CO2/CH4 reforming

A series of Y₂O₃-promoted NiO/SBA-15 (9 wt% Ni) catalysts (Ni:Y weight ratio = 9:0, 3:1, 3:2, 1:1) were prepared using a sol–gel method. The fresh as well as the catalysts used in CO₂ reforming of methane were characterized using N₂-physisorption, XRD, FT-IR, XPS, UV, HRTEM, H₂-TPR, O₂-TPD and TG techniques. The results indicate that upon Y₂O₃ promotion, the Ni nanoparticles are highly dispersed on the mesoporous walls of SBA-15 via strong interaction between metal ions and the HO–Si-groups of SBA-15. The catalytic performance of the catalysts were evaluated at 700 °C during CH₄/CO₂ reforming at a gas hourly space velocity of 24 L g_cat⁻¹ h⁻¹(at 25 ^°C and 1 atm) and CH₄/CO₂molar ratio of 1. The presence of Y₂O₃ in NiO/SBA-15 results in enhancement of initial catalytic activity. It was observed that the 9 wt% Y–NiO/SBA-15 catalyst performs the best, exhibiting excellent catalytic activity, superior stability and low carbon deposition in a time on stream of 50 h.     

Pathways of ethanol steam reforming over ceria-supported catalysts

Ceria-supported Pt, Ir and Co catalysts are prepared herein by the deposition–precipitation method and investigated for their suitability in the steam reforming of ethanol (SRE) at a temperature range of 250–500 °C. SRE is tested in a fixed-bed reactor under an H₂O/EtOH molar ratio of 13 and 20,000 h⁻¹ GHSV. Possible pathways are proposed according to the assigned temperature window to understand the different catalysts attributed to specific reaction pathways. The Pt/CeO₂ catalyst shows the best carbon–carbon bond-breaking ability and the lowest complete ethanol conversion temperature of 300 °C. Acetone steam reforming over the Ir/CeO₂ catalyst at 400 °C promotes a hydrogen yield of up to 5.3. Lower reaction temperatures for the water–gas shift and acetone steam reforming are in evidence for the Co/CeO₂ catalyst, whereas the carbon deposition causes its deactivation at temperature over 500 °C.     

Study of partial oxidation reforming of methane to syngas over self-sustained electrochemical promotion catalyst

A self-sustained electrochemical promotion (SSEP) catalyst is synthesized for partial oxidation reforming (POXR) of CH₄ to produce syngas (H₂ and CO) at a relatively low temperature ranging from 350 to 650 °C. The SSEP catalyst is comprised of 4 components: microscopic Ni/Cu/CeO₂ anode, La_0.9Sr_0.1MnO₃ cathode, copper as electron conductor, and yttria-stabilized-zirconia as oxygen ion conductor, which form microscopic electrochemical cells to enable the self-sustained electrochemical promotion for the POXR process. The SSEP catalyst exhibited much better catalytic performance in POXR of CH₄ than a Ni–Cu–CeO₂ catalyst and a commercial Pt–CeO₂ catalyst. The CH₄ conversion over the SSEP catalyst is 29.4% at 350 °C and reaches 100% at 550 °C and the maximum selectivity to H₂ is on the level of 90% at 450–650 °C under a GHSV of 42,000 h⁻¹. The mechanism of the SSEP is discussed.     

Synthesis and characterization of non-noble nanocatalysts for hydrogen production in microreactors

Nanoscale Co and Ni catalysts in silica were synthesized using sol–gel method for hydrogen production from steam reforming of methanol (SRM) in silicon microreactors with 50 μm channels. Silica sol–gel support with porous structure gives specific surface area of 452.35 m² g⁻¹ for Ni/SiO₂ and 337.72 m² g⁻¹ for Co/SiO₂. TEM images show the particles size of Ni and Co catalysts to be <10 nm. The EDX results indicate Co and Ni loadings of 5–6 wt.% in silica which is lower than the intended loading of 12 wt.%. The DTA and XRD data suggest that 450 °C is an optimum temperature for catalyst calcination when most of the metal hydroxides are converted to metal oxides without significant particle aggregation to form larger crystallites. SRM reactions show 53% methanol conversion with 74% hydrogen selectivity at 5 μL min⁻¹ and 200 °C for Ni/SiO₂ catalyst, which is higher than that for Co/SiO₂. The activity of the metal catalysts decrease significantly after SRM reactions over 10 h, and it is consistent with the magnetization (VSM) results indicating that ∼90% of Co and ∼85% of Ni become non-ferromagnetic after 10 h.     

Hydrogen production from catalytic steam reforming of bio-oil aqueous fraction over Ni/CeO2–ZrO2 catalysts

A series of composite catalysts Ni/CeO₂–ZrO₂ were prepared via impregnation method with Ni as the active metal. A laboratory-scale fixed-bed reactor was employed to investigate the catalyst performance during hydrogen production by steam reforming bio-oil aqueous fraction. Effects of water-to-bio-oil ratio (W/B), reaction temperature, and the loaded weight of Ni and Ce on the hydrogen production performance of Ni/CeO₂–ZrO₂ catalysts were examined. The obtained results were compared with commercial nickel-based catalysts (Z417). The best performance of Ni/CeO₂–ZrO₂ catalyst was observed when the Ni and Ce loaded weight were 12% and 7.5% respectively. At W/B = 4.9, T = 800 °C, H₂ yield reaches the highest of 69.7% and H₂ content of 61.8% were obtained. Under the same condition, H₂ yield and H₂ content were higher than commercial nickel-based catalysts (Z417).     

Ni/YSZ and Ni–CeO2/YSZ anodes prepared by impregnation for solid oxide fuel cells

In this paper, Ni/YSZ and Ni–CeO₂/YSZ anodes for a solid oxide fuel cell (SOFC) were prepared by tape casting and vacuum impregnation. By this method, the Ni content in the anode could be reduced compared to the traditional tape casting method. It was found that adding CeO₂ into the Ni/YSZ anode by a Ni(NO₃)₂ and Ce(NO₃)₃ mixed impregnation could further enhance cell performance. This was investigated in H₂ at 1073 K. XRD patterns indicated that CeO₂ and Ni were separate phases, and the CeO₂ addition could enhance the Ni dispersion on the YSZ framework surface which was observed by SEM images. It was shown that adding CeO₂ into the Ni anodes could decrease the cell polarization resistance. The maximum power density for cells with 25 wt.% Ni, 5 wt.% CeO₂–25 wt.% Ni/YSZ, or 10 wt.% CeO₂–25 wt.% Ni/YSZ anode was 230 mW cm⁻², 420 mW cm⁻² and 530 mW cm⁻², respectively, in H₂ at 1073 K. The OCV for these cells was 1.05–1.09 V, indicating that a dense electrolyte film was obtained by co-firing porous YSZ layer and dense YSZ layer.     

Co–B nanoparticles supported on carbon film synthesized by pulsed laser deposition for hydrolysis of ammonia borane

Thin films of Carbon-supported Co–B nanoparticles were synthesized by using Pulsed Laser Deposition (PLD) and used as catalysts in the hydrolysis of Ammonia Borane (AB) to produce molecular hydrogen. Amorphous Co–B-based catalyst powders, produced by chemical reduction of cobalt salts, were used as target material for nanoparticles-assembled Co–B film catalysts preparation through PLD. Various Ar pressures (10–50 Pa) were used during deposition of carbon films to obtain extremely irregular and porous carbon support with high surface area prior to Co–B film deposition. Surface morphology of the catalyst films was studied using Scanning Electron Microscopy, while structural characterization was carried out using X-Ray diffraction. The hydrogen generation rate attained by carbon-supported Co–B catalyst film is significantly higher as compared to unsupported Co–B film and conventional Co–B powder. Almost complete conversion (95%) of AB was obtained at room temperature by using present film catalyst. Morphological analysis showed that the Co–B nanoparticles produced after the laser ablation process act as active catalytic centers for hydrolysis while the carbon support provides high initial surface area for the Co–B nanoparticles with better dispersion and tolerance against aggregation. The efficient nature of our carbon-supported Co–B film is well supported by the obtained very low activation energy (∼29 kJ (mol)⁻¹) and exceptionally high H₂ generation rate (13.5 L H₂ min⁻¹ (g of Co)⁻¹) by the hydrolysis of AB.     

H2 and CO production over a stable Ni–MgO–Ce0.8Zr0.2O2 catalyst from CO2 reforming of CH4

Ni–Ce_0.8Zr_0.2O₂ and Ni–MgO–Ce_0.8Zr_0.2O₂ catalysts were investigated for H₂ production from CO₂ reforming of CH₄ reaction at a very high gas hourly space velocity of 480,000 h⁻¹. Ni–MgO–Ce_0.8Zr_0.2O₂ exhibited higher catalytic activity and stability (CH₄ conversion >95% at 800 °C for 200 h). The outstanding catalytic performance is mainly due to the basic nature of MgO and an intimate interaction between Ni and MgO.     

Hydrogen production from steam reforming of ethanol using a ceria-supported iridium catalyst: Effect of different ceria supports

Catalytic activity of a ceria-supported Iridium (Ir/CeO₂) catalyst was investigated for steam reforming of ethanol within a temperature range of 300–500 °C. Three types of ceria were chosen to prepare the catalyst: commercial [assigned as CeO₂(C)] and prepared [using a simple reduction–oxidation method, CeO₂(R), and another combined with ultrasonic irradiation, CeO₂(U)] ceria. The Ir/CeO₂ catalyst with Ir loading of 2 wt.% was prepared by deposition–precipitation using iridium chloride (IrCl₃) as a precursor at 75 °C and pH = 9 (adjusted with 0.25 M Na₂CO₃). Catalytic activities toward the steam reforming of ethanol (SRE) were tested in a fixed-bed reactor. In order to better understand the effect of activation conditions of a catalyst on the reforming of ethanol, reduction pretreatment at 200 and 400 °C (assigned as H₂ and H₄) were conducted. The results indicated that only less sintering influences the catalytic activities for high temperature reduction. The ethanol conversion approached completion around 450 °C via reduction pretreatment for Ir/CeO₂(U) and Ir/CeO₂(C) samples under H₂O/EtOH molar ratio of 13 and 22,000 h⁻¹ GHSV. Not only was a high dispersion of both catalysts present but also no impurities (e.g., boron) interfered with the catalytic activities. The hydrogen yield (H₂ mole/EtOH mole) exceeds 5.0 with less content of CO and CH₄ (<2%).     

Development of highly effective supported nickel catalysts for pre-reforming of liquefied petroleum gas under low steam to carbon molar ratios

The pre-reforming of commercial liquefied petroleum gas (LPG) was investigated over Ni–CeO₂ catalysts at low steam to carbon (S/C) molar ratios less than 1.0. It was found that the catalytic activity and selectivity depended strongly on the nature of the support and the interaction between Ni and CeO₂. The Ni–CeO₂/Al₂O₃ catalysts, which were prepared by impregnating boehmite (AlOOH) with an aqueous solution of cerium and nickel nitrates, exhibited the optimal catalytic activity and remarkable stability for the steam reforming of LPG in the temperature range of 275–375 °C. The effects of CeO₂ loading, reaction temperature and S/C ratio on the catalytic behavior of the Ni–CeO₂/Al₂O₃ catalysts were discussed in detail. The results showed that the catalysts with 10 wt.% CeO₂ had the highest catalytic activity, and higher S/C ratios contributed to LPG reforming and the methanation of carbon oxides and hydrogen. The XRD and H₂-TPR analyses revealed that the strong interaction between Ni and CeO₂ resulted in the formation of CeAlO₃ in the Ni–CeO₂/Al₂O₃ catalysts reduced. The stability tests of 15Ni–10CeO₂/Al₂O₃ catalyst at 350 °C indicated that the catalyst was stable, and the stability could be enhanced by increasing S/C ratio.     

Hydrogen production from low temperature WGS reaction on co-precipitated Cu–CeO2 catalysts: An optimization of Cu loading

Low temperature water–gas shift (WGS) reaction has been carried out at the gas hourly space velocity of 72,152 h⁻¹ over Cu–CeO₂ catalyst prepared by a co-precipitation method. Cu loading was optimized to obtain highly active co-precipitated Cu–CeO₂ catalysts for low temperature WGS. 80 wt% Cu–CeO₂ exhibited the highest CO conversion as well as the most stable activity (X_CO > 46% at 240 °C for 100 h). The excellent catalytic performance is mainly due to a strong metal to support interaction, resulting in the prevention of Cu sintering.     

Metal foam-supported Pd–Rh catalyst for steam methane reforming and its application to SOFC fuel processing

Pd–Rh/metal foam catalyst was studied for steam methane reforming and application to SOFC fuel processing. Performance of 0.068 wt% Pd–Rh/metal foam catalyst was compared with 13 wt% Ni/Al₂O₃ and 8 wt% Ru/Al₂O₃ catalysts in a tubular reactor. At 1023 K with GHSV 2000 h⁻¹ and S/C ratio 2.5, CH₄ conversion and H₂ yield were 96.7% and 3.16 mol per mole of CH₄ input for Pd–Rh/metal foam, better than the alumina-supported catalysts. In 200 h stability test, Pd–Rh/metal foam catalyst exhibited steady activity. Pd–Rh/metal foam catalyst performed efficiently in a heat exchanger platform reactor to be used as prototype SOFC fuel processor: at 983 K with GHSV 1200 h⁻¹ and S/C ratio 2.5, CH₄ conversion was nearly the same as that in the tubular reactor, except for more H₂ and CO₂ yields. Used Pd–Rh/metal foam catalyst was characterized by SEM, TEM, BET and CO chemisorption measurements, which provided evidence for thermal stability of the catalyst.     

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

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

Amorphous cobalt–boron/nickel foam as an effective catalyst for hydrogen generation from alkaline sodium borohydride solution

Low cost and catalytically effective transition metal catalysts are of interest for the development of on-board hydrogen generation systems for fuel-cell vehicles. In the present study a modified electroless plating method was developed for the preparation of amorphous Co–B catalyst supported on Ni foam. Compared to the conventional electroless plating method, the newly developed method is more effective and produces Co–B catalyst with much higher catalytic activity. The catalytic activity of the supported Co–B catalyst was found to be highly dependent on the plating times and calcination conditions. Through optimization of these preparation conditions we were able to prepare a catalyst capable of a hydrogen generation rate of 11 l (min g)⁻¹ (catalyst) in a 20 wt.% NaBH₄ + 10 wt.% NaOH solution. Preliminary phase analyses and microstructure characterization were performed to understand the effects of preparation conditions on the catalytic activity of the Co–B catalyst.     

Hydrogen-rich gas production from ethanol steam reforming over Ni/Ga/Mg/Zeolite Y catalysts at mild temperature

In order to reduce the coke formation over a conventional Ni/γ-Al₂O₄ catalyst and increase the activity at low temperature, we used the impregnation approach to synthesize MgO (30.0 wt.%)/Zeolite Y catalysts loaded with bimetallic Ni(10.0 wt.%)/Ga(10.0–30.0 wt.%) and study the steam-reforming reactions of ethanol. The Ga-loaded catalyst impregnated between the Ni and Mg components exhibits significantly higher reforming reactivity compared to the conventional Ni/Mg/Zeolite Y catalyst. The main products from steam reforming over the Ni/Ga/Mg/Zeolite Y catalyst are only H₂ and CH₄ at above 550 °C, and the catalytic performances differ according to the amount of Ga. The H₂ production and ethanol conversion are maximized at 87% and 100%, respectively, over Ni(10)/Ga(30)/Mg(30)/Zeolite Y at 700 °C for 1 h at CH₃CH₂OH:H₂O = 1:3 and a gas hourly space velocity (GHSV) of 6740 h⁻¹, and the high performance is maintained for up to 59 h.     

Carbon-resistant Ni-YSZ/Cu–CeO2-YSZ dual-layer hollow fiber anode for micro tubular solid oxide fuel cell

A NiO-YSZ/porous YSZ dual-layer hollow fiber with an asymmetric structure was fabricated by a co-spinning-sintering method. A dense YSZ electrolyte film was prepared on NiO-YSZ layer by dip-coating method and calcined at 1450 °C; subsequently a porous cathode was dip-coated on the dense YSZ electrolyte film using LSM-YSZ (in the weight ratio 4:1) ink to fabricate a micro tubular solid oxide fuel cell (MT-SOFC). Cu–CeO₂ catalyst was impregnated into the porous YSZ layer to form the second anode composition. The power output of the MT-SOFC with Ni-YSZ/Cu–CeO₂-YSZ graded anode was up to 242 mW cm⁻² operated at 850 °C using CH₄ as fuel and air as oxidant. Little carbon deposition was observed on the double anode using methane as the fuel after 60 h' stable operation.