Effect of support preparation method on water-gas shift activity of copper-based catalysts

Reducing the effect of global warming and increasing the needs for fuel sources appoint hydrogen utilization in fuel cell technology a very promising demand. A step for required pure hydrogen production for this purpose is the water-gas shift (WGS) reaction and the design of well performing but cost effective WGS catalysts, the latter being of growing research interest. In the present study catalysts containing copper (3 wt%) supported on ceria/alumina (30 wt% ceria) and Y-doped ceria/alumina (1 wt% Y₂O₃ regarding ceria content) were prepared by impregnation (IM) and by mechanochemical mixing (MM). The effect of support synthesis methods on the performance in the WGS reaction was discussed based on catalyst characterization by means of XRD, HRTEM, XPS, and H₂-TPR methods. It was established that the effect of Y-doping was strongly dependent on the method of support preparation being positive for MM and unfavourable in the case of impregnation. The IM method caused the formation of a superficial phase with CuO, Y-dopant, and ceria in close location. Additionally, a higher amount of oxygen vacancies was related to non-reducible Y³⁺ ions that interrupted Cu–oxygen vacancy–Ce interaction thus leading to both lower reducibility and WGS activity. The presence of yttria phase located on ceria-free alumina in the case of MM support decreased the negative influence of Ce³⁺ replacement by Y³⁺ ions. A positive effect of separate Y₂O₃ could explain the best WGS performance observed. Long-term WGS tests showed good stability thus making this catalyst promising composed mainly of alumina and low amount of active phases. The study contributes to the development of an advantageous formulation of well-performing and economically profitable WGS catalysts for efficient improving of hydrogen purity for small-scale applications.     

Effects of Pt precursors on Pt/CeO2 to water-gas shift (WGS) reaction activity with Langmuir-Hinshelwood model-based kinetics

The crystallite size effects of Pt nanoparticles on the CeO₂ (Pt/CeO₂) prepared with four different Pt precursors were investigated in terms of their thermal stability and catalytic activity for a water-gas shift (WGS) reaction using the compositions of reformates after a typical steam reforming of propane. The Pt/CeO₂ prepared with a diamine dinitroplatinum (Pt(NO₂)₂(NH₃)₃) precursor, which forms the cationic Pt(NH₃)₂²⁺ species on the negatively-charged CeO₂ surfaces, revealed a superior catalytic activity and thermal stability by forming the partially oxidized smaller Pt nanoparticles decorated with metallic Pt surfaces as well as by forming the strongly interacted PtOx-CeO₂ interfaces. The stable preservation of the pristine smaller Pt nanoparticles with small aggregations even under the hysteresis test from 250 to 400 °C was mainly attributed to the strong metal-support interactions. The optimized Pt/CeO₂ was further studied to obtain kinetic equations derived by Langmuir-Hinshelwood (LH) model, and the optimal operating conditions of WGS reaction were found to be ~280 °C and H₂O/CO molar ratio of 9 with the activation energy of ~78.4 kJ/mol.     

Hydrogen production via water-gas shift reaction over gold supported on Ni-based layered double hydroxides

Co-precipitated NiAl and NiMgAl layered double hydroxides (LDHs) were prepared at M²⁺/Al³⁺ molar ratio of 2.5/1 and subsequently promoted with gold targeting to be studied as catalysts and supports of gold particles in the hydrogen production via water-gas shift (WGS) reaction. Powder X-ray diffraction and N₂ physisorption before and after WGS tests were applied to investigate the impacts of Mg and Au on the structure and catalytic behavior of the systems. Partial replacement of Ni by Mg resulted in moderate activity of NiMgAl and Au/NiMgAl catalysts than NiAl analogues due to: (i) smaller Ni amount that could not supply sufficient number catalytically active sites; (ii) higher thermal stability leading to the creation of the active Ni species at higher temperatures, and (iii) partial regeneration of the layered structure with the assistance of small Au particles, Mg, and the reaction medium as well. Favorable role of gold on Au/NiAl WGS activity was elucidated.     

Catalytic and DRIFTS study of the WGS reaction on Pt-based catalysts

The water–gas shift (WGS) activity of Pt/SiO₂, Pt/CeO₂ and Pt/TiO₂ catalysts was studied by in-situ diffuse reflection infrared Fourier transform spectroscopy (DRIFTS). Samples contained a similar amount of Pt, between 0.34 and 0.50%, and were characterized by employing a variety of physical and spectroscopic techniques. The catalyst activities were evaluated through both CO conversion versus temperature and CO conversion versus time tests. The DRIFTS spectra were obtained on stream during the WGS reaction at increasing temperatures, from 303 to 573 K. Reduced ceria was the only active support and promoted the WGS reaction on surface bridging OH groups that react with CO to form formate intermediates. Pt/SiO₂ was more active than CeO₂ and catalyzed the WGS reaction through a monofunctional redox mechanism on metallic Pt sites. The CO conversion turnover rate was more than one order of magnitude greater on Pt/CeO₂ than on Pt/SiO₂ showing that the reaction proceeds faster via a bifunctional metal-support mechanism. Platinum on Pt/CeO₂ increased the concentration of OH groups by increasing the ceria reduction extent and also provided a faster pathway for the formation of formate intermediates in comparison to CeO₂ support. Pt/TiO₂ catalysts were clearly more active than Pt/CeO₂. The WGS reaction on Pt/TiO₂ was catalyzed via a bifunctional metal-support mechanism, probably involving the activation of CO and water on the metal and the support, respectively. The role of platinum on Pt/TiO₂ was critical for promoting the reduction of Ti⁴⁺ ions to Ti³⁺ which creates oxygen vacancies in the support to efficiently activate water.     

Investigation on the effect of synthesizing temperature on the catalytic activity of nickel cobalt boron catalysts in sodium borohydride hydrolysis process

Hydrogen production through the reaction between sodium borohydride (NaBH₄) and water in presence of three different catalysts including; NiB, CoB and NiCoB is studied. The catalysts are synthesized by chemical reduction method at room and 0 °C temperature. The products are characterized by X-Ray Diffraction (XRD), High-Resolution Scanning Electron Microscopy (HRSEM) and Inductively Coupled Plasma-optical emission spectroscopy (ICP). The results showed that carrying out synthesizing process at low temperature, causes decreasing the nuclei size and reducing driving force for the growth stage, and results in a meaningful reduction in size of the produced catalysts particles. Furthermore, it leads to a recognizable change in particles shape to fine spherical with definite boundaries and slightly increase in boron content of each catalyst. These changes, especially in size and shape of the produced catalysts, results in an improvement in catalytic activity of the synthesized catalysts and the rate of hydrogen generation through using them. This achievement were successfully proved for all three NiB, CoB and NiCoB catalysts, although it was more pronounced for CoB so that it was possible to produce 1.4 lit hydrogen in less than 13 s (12,923 ml·min^?1.g^?1_catalyst) by using 0.5 g of CoB catalyst synthesized at 0 °C.     

Production of hydrogen by methane dry reforming: A study on the effect of cerium and lanthanum on Ni/MgAl2O4 catalyst performance

Hydrogen production from dry reforming of methane (DRM) was investigated on different Nickel based catalysts deposited on MgAl₂O₄. MgAl₂O₄ spinel was prepared using γ-Alumina supplied from different manufacturers (Sigma Aldrich, Alfa Aesar and Degussa) with low and high specific surface area. Moreover, the influence of different parameters on the catalytic activity on methane dry reforming was studied such as the effect of Ni content, the effect of commercial alumina and the effect of doping nickel with cerium and lanthanum.During this study, the catalytic activity was compared at atmospheric pressure at 750 °C during 4 h then 650 °C during 4 h toward methane dry reforming (DRM) reaction with a molar ratio CH₄/CO₂ = 1/1 and a Weight Hourly Space Velocity (WHSV) of 60.000 mL g⁻¹.h⁻¹. The results showed that among the different catalysts 1.5Ce–Ni5/MgAl₂O₄, synthesized with alumina from Alfa Aesar, exhibited the best catalytic activity for DRM.Furthermore, this catalyst showed the best performance during a stability test at 600 °C for 24 h under reacting mixture with a low carbon formation rate (2.71 mg_C/g_cat/h). Such superior activity is consistent with characterization results from BET, XRD, SEM, TPR and TPO analysis. Furthermore, it seems that the addition of Cerium on Ni/MgAl₂O₄ leads to an increase in catalyst efficiency. It can be due to an effective active oxygen transfer due to the redox properties of CeO_2, leading to the formation of oxygen vacancies offering a benefit for DRM reaction.     

Role of the composition and preparation method in the activity of hydrotalcite-derived Ru catalysts in the catalytic partial oxidation of methane

Hydrotalcite-derived Ru catalysts were tested in the catalytic partial oxidation of CH₄ to produce syngas. The effect of Ru content, oxidic matrix composition, and preparation procedure on chemical–physical properties and performances of catalysts was studied. Bulk catalysts (0.25 and 0.50 wt.% Ru) were obtained via Ru/Mg/Al hydrotalcite-type (HT) precursors with carbonates or silicates as interlayer anions. A supported catalyst was prepared by impregnation on a calcined Mg/Al–CO₃ HT. Ru/γ-Al₂O₃ was evaluated for comparison. Both the Ru dispersion and the interaction with the support decreased as the Ru loading increased and when silicates were present due to RuO₂ segregation. Regardless of the Ru loading, carbonate-derived catalysts performed better than those containing silicates. The increased Ru loading improved the initial activity, but deactivation occurred after high temperature tests. Stability tests for shorter contact times over a 0.25 wt.% bulk sample obtained from Ru/Mg/Al HT with carbonates showed a tendency to deactivate at 750 °C.     

Effect of boron doping and preparation method of Ni/Ce0.5Zr0.5O2 catalysts on the performance for steam reforming of ethanol

Ce_0.5Zr_0.5O₂ supported Ni-based catalysts with a Ni loading of 10 wt% and a B loading of 0.5 wt% were prepared by co-precipitation (assigned as NiCeZr(C) and BNiCeZr(C), respectively) and impregnation (assigned as NiCeZr(I) and BNiCeZr(I), respectively) procedures to evaluate the effects of fabrication methods and B-doped on the catalytic performance for steam reforming of ethanol (SRE). These catalysts were characterized with XRD, TPR, TPO, TEM, BET, TG and EA. The well dispersed active species that can be obtained through co-precipitation and formation of a NiB alloy come from a B-doped catalyst, which can promote catalysis performance and reaction pathway. Further, it can improve the selectivity of hydrogen for a SRE reaction. Also, the B-doped catalysts possess a high oxygen storage capacity (OSC) via formation of CeBO₃ under SRE ambience, which is the factor for removal of the carbonaceous species. TG and EA analyses demonstrate that there are fewer carbon deposits for the B-doped catalysts. The performance of the BNiCeZr(C) catalyst was preferential among these catalysts.     

The synergistic effect of Ca(OH)2 on the process of lignite steam gasification to produce hydrogen-rich gas

The synergistic effect of Ca(OH)₂ prepared by the wet-mixing method on lignite steam gasification process at different temperatures (700–900 °C) was analyzed in a spout-fluid bed reactor. Firstly, to avoid disturbance of volatile and tar, active carbon was used as a model compound. On the one hand, Ca(OH)₂ effectively catalyzed the water-gas shift (WGS) reaction to improve H₂ concentration, but the performance was weaker at higher temperature due to the enhancement of boudouard reaction and the weakening of WGS reaction. On the other hand, it was found that the (CO+2CO₂)/H₂ ratio of syngas produced at 700 °C in the presence of Ca(OH)₂ was 0.82, which was much lower than that of the other cases, owning to the absorption of CO₂. The synergistic effect was observed at this temperature, for the adsorption of CO₂ altered equilibrium of the WGS reaction and further improved H₂ concentration. Then two kinds of Chinese lignite (HLH and XM) were selected to further study the performance of Ca(OH)₂ on optimizing the lignite steam gasification process. In the presence of Ca(OH)₂, tar and char yields greatly reduced at the same reaction temperature, whereas the gas yields significantly increased. As a catalyst, Ca(OH)₂ can not only promote solid–gas reaction to decrease char yield, but also accelerate tar decomposition to reduce its yield in syngas. Based on GC–MS data, it can be deduced that Ca(OH)₂ has different catalytic activity on the steam reforming of tar with different molecular structures. Contrast to Class 4, tars of aliphatic hydrocarbons, Class 2 and Class 5 were clearly catalytic reformed. Hydrogen-rich gas can be produced at 800 °C and 900 °C owning to the catalytic effect of Ca(OH)₂, but the highest H₂ concentration was found at 700 °C due to the additional effect of CO₂ absorption, which was supported by the results of thermogravity experiments.     

Determining the effect of trace elements on biohydrogen production from fruit and vegetable wastes

Trace elements are one of the important parameters for dark fermentative H₂ production because they work as co-factors in H₂ formation biochemistry. Lack or excess of trace element and its concentrations could be an important reason for the low yield of H₂ production. In this study, the effects of 11 different trace elements (Fe, Ni, Zn, Co, Cu, Mn, Al, B, Se, Mo and W) were tested at two levels in terms of biohydrogen production from Fruit and Vegetable Wastes (FVW) with Biochemical Hydrogen Potential (BHP) Tests using Plackett-Burman statistical design. 1.1–2.8 times enhancement of biohydrogen production was determined with its addition. The most effective trace elements were found as Zn and Ni. In order to reveal the resident microbial flora, Denaturing Gradient Gel Electrophoresis (DGGE) analysis was carried out on all BHP effluent samples. Results of DGGE analysis, four microbial sequences evaluated as Clostridium sp., Clostridium baratii, Uncultured bacterium, Uncultured Streptococcus sp., and their similarity rates were 99%, 100%, 89%, 98%, respectively.     

An evaluation of hydrogen production from the perspective of using blast furnace gas and coke oven gas as feedstocks

Blast furnace (BF) is a large-scale reactor for producing hot metal where coke and coal are consumed as reducing agent and fuel, respectively. As a result, a large amount of CO₂ is liberated into the atmosphere. The blast furnace gas (BFG) and coke oven gas (COG) from the ironmaking process can be used for H₂ production in association with carbon capture and storage (CCS), thereby reducing CO₂ emissions. In this study thermodynamic analyses are performed to evaluate the feasibility of H₂ production from BFG and COG. Through the water gas shift reaction (WGSR) of BFG, almost all CO contained in BFG can be converted for H₂ production if the steam/CO (S/C) ratio is no less than unity and the temperature is at 200 °C, regardless of whether CO₂ is captured or not. The maximum H₂ production from WGSR is around 0.21 Nm³ (Nm³ BFG)⁻¹. Regarding H₂ production from COG, a two-stage reaction of partial oxidation (POX) followed by WGSR is carried out. It is found the proper conditions for syngas formation from the POX of COG is at the oxygen/fuel (O/F) ratio of 0.5 and the temperature range of 1000-1750 °C where the maximum syngas yield is 2.83 mol (mol hydrocarbons)⁻¹. When WGSR is subsequently applied, the maximum H₂ production from the two-stage reaction can reach 0.83 Nm³ (Nm³ COG)⁻¹.     

Effect of Ce on the structural features and catalytic properties of La(0.9−x)CexFeO3 perovskite-like catalysts for the high temperature water-gas shift reaction

La_(0.9−x)Ce_xFeO₃ perovskite-like catalysts were investigated for the production of hydrogen from simulated coal-derived syngas via the water-gas shift reaction in the temperature range 450-600 °C and at 1 atm. These catalysts exhibited higher activity at high temperatures (T ≥ 550 °C), compared to that of a commercial high temperature iron-chromium catalyst at 450 °C. Addition of a low Ce content (x = 0.2), has little influence on the formation of the LaFeO₃ perovskite structure, but enhances catalytic activity especially at high temperatures with 19.17% CO conversion at 550 °C and 40.37% CO conversion at 600 °C. The LaFeO₃ perovskite structure and CeO₂ redox properties play an important role in enhancing the water-gas shift activity. Addition of a high Ce content (x = 0.6) inhibits the formation of the LaFeO₃ perovskite structure and decreases catalyst activity.