Search Results (79)

Cu-based layered double hydroxides (LDH) have been extensively employed as catalyst precursors. However, due to the Jahn–Teller effect of copper ions, it is a challenge to synthesize well-crystallized LDH with a high Cu content, which usually contains considerable CuO impurity. By adding competitive ligands during the coprecipitation process, such as glycine, a well-crystallized Cu-rich LDH with less CuO impurity was successfully synthesized. The Cu-Mg-Al mixed oxides derived from the well-crystallized Cu-rich LDH have relatively high S_BET, large pore volume, and well dispersion of Cu nanoparticles. The derived catalyst exhibited unexpectedly high catalytic activity in the water–gas shift (WGS) reaction, and the mass-specific reaction rate was reached as high as 33.5 μmol_CO${·\mathrm{g}}_{\mathrm{cat}}^{-1}$·s⁻¹ at 200 °C. The high catalytic activity of this catalyst may originate from the high S_BET and well dispersion of Cu particles and metal oxides. Moreover, the derived catalyst also displayed outstanding long-term stability in the WGS reaction, which should benefit from the enhanced metal–support interaction. Full article

Unlike on Fe and Co catalysts, the CO conversion effect on Ru catalyst performance is little reported. This study is undertaken to explore the issue using a series of Ru/NaY catalysts under 200–230 °C, 2.0 MPa, H₂/CO = 2, and 10–60% CO conversion in a 1 L continuous stirred tank reactor (CSTR). The results are comparatively studied with those of Fe and Co catalysts reported previously. The NaY support and four 1.0%, 2.5%, 5.0%, and 7.5% Ru/NaY catalysts were characterized by BET, H₂ chemisorption, H₂O-TPD, XRD, HRTEM, and XANES/EXAFS techniques. The BET and XRD results suggest a high surface area (730 m²/g), high degree of crystallinity of the NaY support, and high dispersion of Ru, while an hcp Ru structure and well-reduced Ru were reflected in the HR-TEM FFT and XANES/EXAFS results. The reaction results indicate that the CO conversion effect on CH₄ and C₅₊ selectivities on the Ru is the same as that on the Fe and Co catalysts, with CH₄ selectivity decreasing and C₅₊ selectivity increasing with increasing CO conversion. However, the CO conversion effect on olefin formation for the Ru catalyst was found to be opposite to that of the Fe and Co; increasing CO conversion enhanced olefin formation but suppressed secondary reactions of 1-olefins. The H₂O cofeeding experiments showed that H₂O impacted olefin formation by suppressing hydrogen adsorption and hydrogenation. The H₂O-TPD experiment evidenced a much stronger H₂O adsorption capacity (6.8 mmol/g-cat) on Ru followed by Co (1 mmol/g-cat), and then Fe (0.2 mmol/g-cat)., which showed only a very low H₂O adsorption capacity.This finding may explain the opposite CO conversion effect on olefin formation observed on the Ru catalyst, and may also explain why low CH₄ selectivity (i.e., 3%) occurred on the Ru catalyst and high CH₄ selectivity (i.e., 6–8%) occurred on the Co catalyst, both of which possess low water gas shift (WGS) activity. Full article

A thermodynamic analysis of a compact hydrogen generation system for mobile fuel cell applications is presented. The system consists of a miniature autothermal steam reformer (ATR) and a water–gas shift (WGS) reactor, designed to produce hydrogen from hydrocarbon fuels for a 1 kW proton exchange membrane (PEM) fuel cell. Methane is used as the model fuel, and the study focuses on optimizing feed compositions and operational conditions to maximize hydrogen yield and purity. Feed compositions and operational conditions are optimized. In total, 0.7 Nm³ h⁻¹ H₂ is generated from 0.25 Nm³ h⁻¹ CH₄ with properly adjusted steam and air feeding. Issues with product purity and start-up procedures have been identified and discussed, along with feasible solutions. The system is suitable for remote and mobile applications. Full article

This work outlines the commissioning and initial experiments from a new pilot plant at Arcelor Mittal Gas Lab (Asturias, Spain) designed to decarbonize up to 300 Nm³/h of blast furnace gas (BFG). This investigation intends to demonstrate for the first time at TRL7 the calcium-assisted steel-mill off-gas hydrogen (CASOH) process to decarbonize blast furnace gases. The CASOH process is carried out in packed-bed reactors operating through three main reaction stages: (1) H₂ production via the water–gas shift (WGS) of the CO present in the BFG assisted by the simultaneous carbonation of CaO; (2) oxidation of the Cu-based catalyst with air, and (3) reduction of CuO with a fuel gas to regenerate CaO and produce a concentrated CO₂ stream. The first experimental campaign used 200 kg of commercial Ca- and Cu-based solids mixed to create a 1 m reactive bed, which is sufficient to validate operations and confirm the process’s effectiveness. A product gas with 40% of H₂ is obtained with CO₂ capture efficiency above 95%. Demonstrating at TRL7 the ability to convert BFG into H2-enriched gas with minimal CO/CO₂ enables remarkable decarbonization in steel production while utilizing existing blast furnaces, eliminating the need for less commercially developed production processes. Full article

A multiparametric study was conducted on a hydrogen (H₂) production rig designed to process 0.25 Nm³·h⁻¹ of syngas. The rig consists of two Pd-Ag membrane permeator units and two Pd-Ag membrane reactor units for the water–gas shift (WGS) reaction, enabling a detailed and comprehensive analysis of its performance. The aim was to find the optimal conditions to maximize hydrogen production by WGS and its separation in a pure stream by varying the temperature, pressure, and steam-to-CO ratio (S/CO). Two syngas mixtures obtained from an updraft gasifier using different gasification agents (air–steam and oxy–steam) were used to investigate the effect of gas composition. The performance of the rig was investigated under nine combinations of temperature, pressure, and S/CO in the respective ranges of 300–350 °C, 2–8 bar, and 1.1–2 mol·mol⁻¹, as planned with the help of design of experiment (DOE) software. The three parameters positively affected performance, both in terms of capacity to separate a pure stream of H₂, reported as moles permeated per unit of surface area and time, and in producing new H₂ from WGS, reported as moles of H₂ produced per volume of catalyst unit and time. The highest yields were obtained using syngas from oxy–steam gasification, which had the highest H₂ concentration and was free of N₂. Full article

Hydrogen production from ethanol steam reforming (ESR) was performed using the synthesized LaNi_xCu_1−xO_3−λ perovskite-type catalysts in a continuous two-stage fixed-bed reactor from 450 to 700 °C under atmospheric pressure. The elemental analysis (EA), XRD, SEM, BET, and TGA-DTG technologies were used to characterize the structures and properties of the synthesized catalysts. The thermodynamic equilibrium model, based on the minimization of Gibbs free energy using a non-stoichiometric methodology, was carried out and compared with experimental data. The results demonstrated that the catalytic activity of the perovskite-type catalysts for ESR can be improved after modification with a certain amount of copper (about 0.67 mmol/g) and decreased further with an increase in copper content (about 3.41 mmol/g). The most active catalyst was found to be LaNi_0.9Cu_0.1O_3−λ, with an ethanol conversion value of 96.0% and hydrogen selectivity of 71.3%. The perovskite-type catalysts with an appropriate amount of Cu promoter improved coking resistance and presented excellent stability with no loss of activity over 101 h at 700 °C. Based on the power-law kinetic model with the first reaction order, the activation energy and the frequency factor for ethanol steam reforming by perovskite-type catalysts were calculated. Our studies indicated the enhanced effects of Ni and Cu on the small Ni-Cu bimetallic particles in the water gas shift (WGS) reaction, which could also contribute to the activity and stability of the LaNi_xCu_1−xO_3−λ perovskite-type catalysts in hydrogen production. Full article

The water–gas shift (WGS) reaction is one of the most significant reactions in hydrogen technology since it can be used directly to produce hydrogen from the reaction of CO and water; it is also a side reaction taking place in the hydrocarbon reforming processes, determining their selectivity towards H₂ production. The development of highly active WGS catalysts, especially at temperatures below ~450 °C, where the reaction is thermodynamically favored but kinetically limited, remains a challenge. From a fundamental point of view, the reaction mechanism is still unclear. Since specific nanoshapes of CeO₂-based supports have recently been shown to play an important role in the performance of metal nanoparticles dispersed on their surface, in this study, a comparative study of the WGS is conducted on Pt nanoparticles dispersed (with low loading, 0.5 wt.% Pt) on CeO₂ and gadolinium-doped ceria (GDC) supports of different nano-morphologies, i.e., nanorods (NRs) and irregularly faceted particle (IRFP) CeO₂ and GDC, produced by employing hydrothermal and (co-)precipitation synthesis methods, respectively. The results showed that the support’s shape strongly affected its physicochemical properties and in turn the WGS performance of the dispersed Pt nanoparticles. Nanorod-shaped CeO_2,NRs and GDC_NRs supports presented a higher specific surface area, lower primary crystallite size and enhanced reducibility at lower temperatures compared to the corresponding irregular faceted CeO_2,IRFP and GDC_IRFP supports, leading to up to 5-fold higher WGS activity of the Pt particles supported on them. The Pt/GDC_NRs catalyst outperformed all other catalysts and exhibited excellent time-on-stream (TOS) stability. A variety of techniques, namely N₂ physical adsorption–desorption (the BET method), scanning and transmission electron microscopies (SEM and TEM), powder X-ray diffraction (PXRD) and hydrogen temperature programmed reduction (H₂-TPR), were used to identify the texture, structure, morphology and other physical properties of the materials, which together with the in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) and detailed kinetic studies helped to decipher their catalytic behavior. The enhanced metal–support interactions of Pt nanoparticles with the nanorod-shaped CeO_2,NRs and GDC_NRs supports due to the creation of more active sites at the metal–support interface, leading to significantly improved reducibility of these catalysts, were concluded to be the critical factor for their superior WGS activity. Both the redox and associative reaction mechanisms proposed for WGS in the literature were found to contribute to the reaction pathway. Full article

The ability of Parageobacillus thermoglucosidasius to produce H₂ from CO via the water–gas shift (WGS) reaction makes it a compelling microorganism for biofuels research. Optimizing this process requires evaluating parameters such as pressure. This study aimed to understand how H₂ production is affected by increasing CO, N₂, and H₂ partial pressures to 1.0, 2.0, and 3.0 bar. Increasing CO partial pressure can improve the solubility of the gas in the liquid phase. However, raising CO partial pressure to 3.0 bar had an inhibitory effect, delaying and reducing H₂ production. By contrast, increasing N₂ and H₂ partial pressures to 3.0 bar had positive effects, reaching a H₂ production of 9.2 mmol and 130 mmol, respectively. Analysis of the electron balance at the end of the fermentation process showed that the selectivity toward H₂ production reached 95%, with the remainder of electrons deriving from CO and glucose directed at organic acid production, mainly acetate, followed by formate. Full article

The role of dopants (Sm, Tb and Pr) on the water–gas shift performance of CeO₂-based materials was studied. Modification of CeO₂ with Sm significantly improved the water–gas shift performance. The catalytic activities of doped CeO₂ were increased when compared with the catalytic activities of pure ceria (65% conversion at 600 °C for Ce5%SmO and 50% conversion at 600 °C for CeO₂). The key factors driving the water–gas shift performance were reduction behavior and oxygen vacancy concentration. In the redox mechanism of the WGS reaction, CeO₂ plays a crucial role in transferring oxygen to CO through changes in the oxidation state. Therefore, Sm is effective in catalyzing the water–gas shift activity because the addition of Sm into CeO₂ decreases the surface reduction temperature and alters the oxygen transportation ability through the redox mechanism. XRD results suggested that Mⁿ⁺ (M = Sm, Tb and Pr) incorporate into ceria lattice to form a solid solution resulting in unit cell enlargement. The defect structure inside the CeO₂ lattice generates a strain on the oxide lattice and facilitates the generation of oxygen vacancies. XANES analysis revealed that Sm reduced CeO₂ easily by transporting its electron into the d-orbitals of Ce, thus giving rise to more Ce³⁺ at the CeO₂ surface. The presence of Ce³⁺ is a result of oxygen vacancy. Therefore, the high content of Ce³⁺ provides more oxygen vacancies. The oxygen vacancy formation results in easy oxygen exchange. Thus, reactive oxygen species can be generated and easily reduced by CO reactant, which enhances the WGS activity. Full article

The water–gas shift (WGS) performance of 10%Ni/Al₂O₃, 20%Ni/Al₂O₃ and 10%Ni/CaO-Al₂O₃ catalysts was studied to reduce CO concentration and produce extra hydrogen. Ni was added onto the Al₂O₃ support by an impregnation method. The physicochemical properties of nickel catalysts that influence their catalytic activity were examined. The most influential factors in increasing the CO conversion for the water–gas shift reaction are Ni dispersion and surface acidity. Ni metal sites were identified as the active sites for CO adsorption. The main effect of nickel metal was reducing the adsorbed CO amount by reducing the active site concentration. The 10%Ni/Al₂O₃ catalyst was more active for the WGS reaction than other catalysts. This catalyst presents a high CO conversion rate (75% CO conversion at 800 °C), which is due to its high Ni dispersion at the surface (6.74%) and surface acidity, thereby favoring CO adsorption. A high Ni dispersion for more surface-active sites is exposed to a CO reactant. In addition, favored CO adsorption is related to the acidity on the catalyst surface because CO reactant in the WGS reaction is a weak base. The total acidity can be evaluated by integrating the NH₃-Temperature-Programmed Desorption curves. Therefore, an enhancement of surface acidity is identified as the favored CO adsorption. Full article

To develop customized sulfur–resistant catalysts for the water gas shift (WGS) reaction in the waste–to–hydrogen process, the effects of changing the nucleation conditions of the CeO₂ support on catalytic performance were investigated. Supersaturation is a critical kinetic parameter for nuclei formation. The degree of supersaturation of the CeO₂ precipitation solution was controlled by varying the cerium precursor concentration from 0.02 to 0.20 M. Next, 2 wt.% of Pt was impregnated on those various CeO₂ supports by the incipient wetness impregnation method. The prepared samples were then evaluated in a WGS reaction using waste–derived synthesis gas containing 500 ppm H₂S. The Pt catalyst supported by CeO₂ prepared at the highest precursor concentration of 0.20 M exhibited the best sulfur resistance and catalytic activity regeneration. The sulfur tolerance of the catalyst demonstrated a close correlation with its oxygen storage capacity and easier reducibility. The formation of oxygen vacancies in CeO₂ supports is promoted by the formation of small crystals due to a high degree of supersaturation. Full article

The water–gas shift (WGS) performance was investigated over 5%Ni/CeO₂, 5%Ni/Ce_0.95Pr_0.05O_1.975, and 1%Re4%Ni/Ce_0.95Pr_0.05O_1.975 catalysts to decrease the CO amount and generate extra H₂. CeO₂ and Pr-doped CeO₂ mixed oxides were synthesized using a combustion method. After that, Ni and Re were loaded onto the ceria support via an impregnation method. The structural and redox characteristics of monometallic Ni and bimetallic NiRe materials, which affect their water–gas shift performance, were investigated. The results show that the Pr addition into Ni/ceria increases the specific surface area, decreases the ceria crystallite size, and improves the dispersion of Ni on the CeO₂ surface. Furthermore, Re addition results in the enhancement of the WGS performance of the Ni/Ce_0.95Pr_0.05O_1.975 catalyst. Among the studied catalysts, the ReNi/Ce_0.95Pr_0.05O_1.975 catalyst showed the highest catalytic activity, reaching 96% of CO conversion at 330°. It was established that the occurrence of more oxygen vacancies accelerates the redox process at the ceria surface. In addition, an increase in the Ni dispersion, Ni surface area, and surface acidity has a positive effect on hydrogen generation during the water–gas shift reaction due to favored CO adsorption. Full article

Hydrogen produced sustainably has the potential to be an important energy source in the short term. Biomass gasification is one of the fastest-growing technologies to produce green hydrogen. In this work, an air-blown gasification model was developed in Aspen Plus^®, integrating a water–gas shift (WGS) reactor to study green hydrogen production. A sensitivity analysis was performed based on two approaches with the objective of optimizing the WGS reaction. The gasifier is optimized for carbon monoxide production (Case A) or hydrogen production (Case B). A CO₂ recycling stream is approached as another intensification process. Results suggested that the Case B approach is more favorable for green hydrogen production, allowing for a 52.5% molar fraction. The introduction of CO₂ as an additional gasifying agent showed a negative effect on the H₂ molar fraction. A general conclusion can be drawn that the combination of a WGS reactor with an air-blown biomass gasification process allows for attaining 52.5% hydrogen content in syngas with lower steam flow rates than a pure steam gasification process. These results are relevant for the hydrogen economy because they represent reference data for further studies towards the implementation of biomass gasification projects for green hydrogen production. Full article

The water–gas shift (WGS) reaction (CO + H₂O ↔ CO₂ + H₂) plays an important role in the hydrogen economy because it is an effective way to reduce the carbon release to net-zero CO₂ emissions. The general goal of this research is to develop nanosized oxo-rhenium catalyst formulations promoted by K and Co components for the WGS process. Rhenium, as a low-cost catalyst component, is a good choice compared to platinum group metals. A surface density of 2 Re atoms/nm² on a γ-Al₂O₃ support as well as cobalt (3 wt.% CoO) and potassium (5 wt.% K₂O) amounts were chosen to match the composition of our own active sour WGS KCoRe catalyst developed some years ago. An initial evaluation of the impact of replacing half of the rhenium with molybdenum, which is more affordable, was also studied. The purpose of this study is to explore the catalytic ability of CoRe, K-CoRe, CoReMo, and K-CoReMo formulations in the WGS reaction and elucidate the effect of a CO/Ar reaction mixture used in an activation–reduction pretreatment to form active catalyst structures. Oxo-K-Co-Re(Mo) entities formed in synthesized samples and their reducibility were analyzed via several physicochemical methods, such as N₂ physisorption, PXRD, UV-vis DRS, and H₂-TPR. In summary, the selected potassium- and cobalt-promoted Re-containing formulations have potential as catalysts for the classical WGS reaction. The selection of an appropriate procedure for activation–reduction, involving the reducing gas (CO or H₂), temperature, and duration, was needed for tuning the K-CoRe catalyst’s high activity for the WGS reaction with structural stability and longevity. Full article

Water–gas shift (WGS) reaction was performed over 5% Ni/CeO₂, 5% Ni/Ce-5% Sm-O, 5% Ni/Ce-5% Gd-O, 1% Re 4% Ni/Ce-5% Sm-O and 1% Re 4% Ni/Ce-5% Gd-O catalysts to reduce CO concentration and produce extra hydrogen. CeO₂ and M-doped ceria (M = Sm and Gd) were prepared using a combustion method, and then nickel and rhenium were added onto the mixed oxide supports using an impregnation method. The influence of rhenium, samarium and gadolinium on the structural and redox properties of materials that have an effect on their water–gas shift activities was investigated. It was found that the addition of samarium and gadolinium into Ni/CeO₂ enhances the surface area, reduces the crystallite size of CeO₂, increases oxygen vacancy concentration and improves Ni dispersion on the CeO₂ surface. Moreover, the addition of rhenium leads to an increase in the WGS activity of Ni/CeMO (M = Sm and Gd) catalysts. The results indicate that 1% Re 4% Ni/Ce-5% Sm-O presents the greatest WGS activity, with the maximum of 97% carbon monoxide conversion at 350 °C. An increase in the dispersion and surface area of metallic nickel in this catalyst results in the facilitation of the reactant CO adsorption. The result of X-ray absorption near-edge structure (XANES) analysis suggests that Sm and Re in 1% Re 4% Ni/Ce-5% Sm-O catalyst donate some electrons to CeO₂, resulting in a decrease in the oxidation state of cerium. The occurrence of more Ce³⁺ at the CeO₂ surface leads to higher oxygen vacancy, which alerts the redox process at the surface, thereby increasing the efficiency of the WGS reaction. Full article