Water Gas Shift Research Articles

High-performance single-atom M/TiO2 catalysts in the reverse water-gas shift reaction: A comprehensive experimental and theoretical investigation

Single-atom catalysts (SACs) offer high efficiency and selectivity in chemical reactions but face challenges in converting CO2 to CO via the reverse water gas shift (RWGS) reactions. This study addresses these challenges by anchoring three noble metals (Ir, Pd, and Ru) onto titania (TiO2) and analyzing their performance. Comprehensive characterization techniques, including electron microscopy, confirmed the uniform dispersion of metal atoms on TiO2. Among the catalysts, Ir/TiO2 exhibited the best results, achieving an 84 % CO2 conversion rate and ∼98 % CO selectivity, surpassing Pd/TiO2 and Ru/TiO2, which gained 56 % and 52 % conversion, respectively. In-situ gas transmission electron microscopy revealed the catalytic behavior of Ir/TiO2, showing Ir atom mobility and the formation of ∼1 nm nanoclusters. Density functional theory (DFT) and in-situ diffuse reflectance infrared spectroscopy (DRIFTs) further explained that the atomically dispersed Ir sites in Ir/TiO2 follow a hydrogen-assisted mechanism, with the COOH* intermediate desorbing and dissociating into CO. These findings suggest SACs' potential to facilitate greener chemical processes and reduce greenhouse gas emissions.

Modelling of Biomass Gasification Through Quasi-Equilibrium Process Simulation and Artificial Neural Networks

In the past two decades, advancements in thermochemical technologies have improved biomass gasification for distributed power generation, enhancing efficiency, scalability, and emission control. This study aims to optimize syngas production from biomass gasification by comparing two computational models: a quasi-equilibrium thermodynamic model implemented in Aspen Plus and an artificial neural network (ANN) model. Operating at 850 °C with varying steam-to-biomass (S/B) ratios, both models were validated against experimental data. Results show that hydrogen concentration in syngas increased from 19.96% to 43.28% as the S/B ratio rose from 0.25 to 0.5, while carbon monoxide concentration decreased from 24.6% to 19.1%, consistent with the water–gas shift reaction. The ANN model provided rapid predictions, showing a mean absolute error of 3% for hydrogen and 2% for carbon monoxide compared to experimental data, though it lacks thermodynamic constraints. Conversely, the Aspen Plus model ensures mass and energy balance compliance, achieving a cold gas efficiency of 95% at an S/B ratio of 0.5. A Multivariate Statistical Analysis (MVA) further clarified correlations between input and output variables, validating model reliability. This combined modelling approach reduces experimental costs, enhances gasification process control and offers practical insights for improving syngas yield and composition.

Irreversible Lattice Expansion Effects in Nanoscale Indium Oxide for CO2 Hydrogenation Catalysis.

Thermal energy has been considered the exclusive driving force in thermochemical catalysis, yet associated lattice expansion effects have been overlooked. To shed new light on this issue, variable temperature in situ high-resolution (scanning) transmission electron microscopy (HR-(S)TEM) and electron energy-loss spectroscopy (EELS) were employed to provide detailed information on the structural changes of an archetype nanoscale indium oxide materials and how these effects are manifest in reverse water gas shift heterogeneous catalytic reactivity. It is found that with increasing temperature and vacuum conditions, an irreversible surface lattice expansion is traced to the formation and migration of oxygen vacancies. Together, these changes are believed to be responsible for the decreased activation energy and improved reaction rate observed for the reverse water gas shift reaction. Studies of this kind provide new insight into how thermal energy affects thermochemical heterogeneous catalysis.

Study on the reaction mechanism and kinetics of limestone hydrogenation by micro fluidized bed: Effect of H2 concentration and natural limestone

Limestone decomposition is the first step in cement production, which produces a significant amount of CO2 and poses a significant challenge to achieve carbon neutrality. Hydrogenation of limestone can produce CO or CH4 instead of CO2, which can be considered as a new way of carbon capture, making it a promising method for carbon emission reduction. In this work, pure CaCO3 and several natural limestone samples were hydrolyzed under varying H2 concentration using a micro fluidized bed (MFB) reactor combined with online mass spectrometry to reveal the mechanism and kinetics of limestone hydrogenation.The main gases produced by hydrogenation at 1 atm are CO and CO2. The CO2 comes from the calcination of CaCO3. The CO comes from 2 steps: the first step is the in-situ hydrogenation of CaCO3 and the second step is the Reverse Water Gas Shift (RWGS) reaction. The activation energy (Ea) of CO2 formation in H2 atmosphere is lower than in Ar atmosphere. However, there is no obvious effect of different H2 concentrations on the Ea of CO2 formation. The Ea of CO in situ formation is 72.70 KJ/mol, 54.53 KJ/mol, 71.34 KJ/mol and 60.29 KJ/mol in 10%, 30%, 50% and 70% H2 atmosphere, respectively. The H2 concentration also has no significant effect on the in-situ CO evolution. However, the H2 concentration can affect the Ea of CO produced by RWGS. The Ea is 75.67 KJ/mol, 167.59 KJ/mol and 221.47 KJ/mol in 10%, 30% and 50% H2 atmosphere, and this reaction doesn't occur in 70% H2 atmosphere. Compared with the pure CaCO3, the hydrogenation of limestone can produce more CO and less CO2. In limestone, impurity elements are the main factor affecting the reaction kinetics. Transition metals can increase the rate of CO2 production, but have no apparent effect on CO. The CO2 yield of high impurity limestone is higher than that of limestone with low impurities. Transition metals can also reduce the Ea of CO2 formation and the RWGS reaction. In the 50% H2 atmosphere, the Ea of CO2 formation is 88.87 KJ/mol and the Ea of CO from RWGS is 137.60 KJ/mol. However, under the same conditions, the Ea of pure CaCO3 is 126.91 KJ/mol and 221.47 KJ/mol.

Silicalite-1 Zeolite Enables Graphitic Carbon Nitride High Selectivity toward CO2 Photoreduction

Carbon monoxide (CO) constitutes a pivotal chemical feedstock, extensively applied in diverse industrial processes such as the Fischer–Tropsch synthesis and the water-gas shift reaction, among others, underscoring its significant role in the chemical industry. Photocatalytic CO2 reduction to produce CO provides an appealing route to consume useless greenhouse gases to valuable chemical feedstock. Regarding the poor selectivity of photocatalytic CO2 conversion and the separation complexity for mixed products, integrating zeolite with semiconductor photocatalyst is first presented to achieve highly selective CO2 photoreduction. Herein, silicalite-1 zeolite with high surface area and excellent CO2 affinity is selected to construct a graphitic carbon nitride/silicalite-1 (CN/S-1) composite via a facile thermal polymerization procedure. The introduced S-1 zeolite enables extended visible light response, enhanced CO2 adsorption, promoted separation and transportation of photoexcited charge carriers for the as-synthesized CN/S-1 composite. The resulting CN/S-1 composite shows significantly improved photocatalytic CO2 reduction activity, yielding CO and CH4 of 452.8 and 11.63 μmol·h-1, respectively. The CO selectivity of the CN/S-1 composite achieves 97.5%, which is maximal so far among the CN-based photocatalysts. In-situ Fourier transformed infrared (in-situ FTIR) spectra characterization reveals the composite prefer to dissociate COOH* to CO upon the incorporation of S-1 zeolite rather than protonation into hydrogenation products.

Water–Gas Shift over Pt Nanoparticles Dispersed on CeO2 and Gadolinium-Doped Ceria (GDC) Supports with Specific Nano-Configurations

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 CeO2,NRs and GDCNRs supports presented a higher specific surface area, lower primary crystallite size and enhanced reducibility at lower temperatures compared to the corresponding irregular faceted CeO2,IRFP and GDCIRFP supports, leading to up to 5-fold higher WGS activity of the Pt particles supported on them. The Pt/GDCNRs 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 CeO2,NRs and GDCNRs 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.

Light-Assisted Catalysis and the Dynamic Nature of Surface Species in the Reverse Water Gas Shift Reaction over Cu/γ-Al2O3.

The reverse water gas shift (RWGS) reaction converts CO2 and H2 into CO and water. We investigated Cu/γ-Al2O3 catalysts in both thermally driven and light-assisted RWGS reactions using visible light. When driven by combined visible light and thermal energy, the CO2 conversion rates were lower than in the dark. Light-assisted reactions showed an increase in the apparent activation energy from 68 to 87 kJ/mol, indicating that light disrupts the energetically favorable pathway active in the dark. A linear correlation between irradiance and decreasing reaction rate suggests a photon-driven phenomenon. In situ diffuse reflectance infrared Fourier transform spectroscopy and TD-DFT analyses revealed that catalyst illumination causes significant, partly irreversible surface dehydroxylation, highlighting the importance of OH groups in the most favorable RWGS pathway. This study offers a novel approach to manipulate surface species and control activity in the RWGS reaction.

Dolomite-derived catalyst-free dual function materials pellets for integrating calcium-looping and reverse–water–gas–shift reaction

Integrated CO2 capture and utilization via reverse water–gas shift reaction (ICCU-RWGS) for syngas production is a promising step contributing to carbon neutrality. Naturally occurring Ca-rich ores are potential candidates of dual function materials (DFMs) for ICCU-RWGS, while the practical circulating operation in twin fluidized-bed reactors necessitates DFMs pellets with high reactivity and good mechanical properties, to overcome powder elutriation and to withstand particle attrition. Dolomite (DM)-derived catalyst-free DFMs pellets are synthesized via the extrusion-spheronization (ES) and graphite-casting (GC) methods. Pelletization will result in pore structure blockage while the decline in textural properties has been remedied to some extent, due to the decomposition of CaMg(CO3)2. The hydration activation of Ca species in molding has benefited the DFMs pellets with uniform dispersion of CaO with smaller grain size. The dolomite-derived DFMs pellets outperform the pristine dolomite and the calcined dolomite DFMs regarding the ICCU-RWGS performance. Promoters such as Al2O3, ZrO2 or aluminate cement (AC) are incorporated to enhance the mechanical strength of the DM-GC pellets. The formed Ca3Al2O6, CaAl2O4, CaZrO3, and Ca2Al2SiO7 due to the interaction between CaO and the promoter, act as supporting skeleton for reinforced mechanical strength and physical barrier for retarding crystal sintering and particle agglomeration. Upon doping 10 wt% ZrO2, the compressive strength of the DM-GC pellets increases remarkably from 0.13 to 1.35 MPa. The desired DM-GC-Zr5 DFMs pellets exhibit excellent ICCU-RWGS performance with high and stabilized CO2 capture capacity (6.01 mmol CO2/g) and CO yield (5.01 mmol CO/g) within 10 cycles, demonstrating as a good DFMs candidate for cost-effective CO2 capture and conversion.

Exploring the impact of cobalt and H2 to CO ratios on catalytic performance of FeKAl and FeCoKAl catalysts in CO hydrogenation to light olefins

This study explores the CO hydrogenation to light olefins over FeKAl catalysts, examining how varying H2 to CO ratios (from 1:1 to 7:1) and the introduction of cobalt (Co) influence catalytic performance. Our investigation reveals that Co addition significantly enhances the reducibility of iron oxide species and increases sites favorable for moderate hydrogen adsorption and weak to moderate basicity. We discovered that without Co (FeKAl), increasing the H2 to CO ratio progressively lowers CO2 space–time yield (STY), shifting the reaction’s preference from the water–gas shift reaction towards hydrogenation. The STY of light olefins reaches a peak at an H2 to CO ratio of 3:1, indicating optimal conditions for their production before decreasing at higher ratios. Incorporation of Co (FeCoKAl) maintains this trend but with marked improvements in CO conversion and olefin STY, especially notable at a ratio of 1:1 due to enhanced hydrocarbon product desorption. The findings underscore the critical role of Co and H2 to CO ratios in modulating catalyst stability and activity, with specific ratios significantly reducing catalyst deactivation through diminished wax and carbon fiber formation, and Co presence aiding in the maintenance of steady CO2, hydrocarbon, and light olefin yields by preventing the excessive transformation of iron carbide to Fe3O4.

Iron sulfide-catalyzed gaseous CO2 reduction and prebiotic carbon fixation in terrestrial hot springs

Understanding abiotic carbon fixation provides insights into early Earth’s carbon cycles and life’s emergence in terrestrial hot springs, where iron sulfide (FeS), similar to cofactors in metabolic enzymes, may catalyze prebiotic synthesis. However, the role of FeS-mediated carbon fixation in such conditions remains underexplored. Here, we investigate the catalytic behaviors of FeS (pure and doped with Ti, Ni, Mn, and Co), which are capable of H2-driven CO2 reduction to methanol under simulated hot spring vapor-zone conditions, using an anaerobic flow chamber connected to a gas chromatograph. Specifically, Mn-doped FeS increases methanol production five-fold at 120 °C, with UV−visible light (300–720 nm) and UV-enhanced light (200–600 nm) further increasing this activity. Operando and theoretical investigations indicate the mechanism involves a reverse water-gas shift with CO as an intermediate. These findings highlight the potential of FeS-catalyzed carbon fixation in early Earth’s terrestrial hot springs, effective with or without UV light.

Techno-economic analysis and process simulation of alkoxylated surfactant production in a circular carbon economy framework

Successfully transitioning to a net-zero and circular carbon economy requires adopting innovative technologies and business models to capture CO2 and convert it into valuable chemicals and materials. Given the high economic costs and limited funding available for this transition, robust economic modelling of potential circular carbon pathways is essential to identify economically viable routes. This study introduces a novel techno-economic analysis (TEA) of producing alcohol ethoxylate (AE7), a valuable surfactant, from industrial flue gas. Traditionally, AE7 is produced by reacting fatty alcohols with ethylene oxide derived from fossil or bio-based sources. This research explores a method using CO2 captured from steel industry flue gas to produce AE7, addressing a notable gap in the literature. It evaluates a thermo-catalytic pathway involving Fischer-Tropsch (FT) synthesis with syngas generated by the reverse-water gas-shift reaction, where CO2 reacts with H2. CO2 conversion rates range around 3% across processing capacities of 25 kt/a, 100 kt/a, and 1000 kt/a. The study finds that the CO2 mass fraction concentration in the process emission is 2.47 × 10–5, compared to 0.13 in the incoming flue gas, highlighting the system's positive environmental impact. A radial basis function neural network was built to forecast the long-term average price of fossil-based and bio-based surfactants to benchmark the results against. Economic analysis reveals that the cost of green hydrogen significantly impacts the minimum selling price (MSP), making cost parity with existing fossil-based surfactants challenging. The lowest MSP of $8.77/kg remains above the long-term forecasted price of $3.75/kg for fossil-based C12–14 AE7. However, Monte Carlo simulations show a 21% probability of achieving a positive net present value (NPV) compared to leading bio-based surfactant alternatives. Sensitivity analyses identify capital costs, the price of low-carbon hydrogen (LCOH), and diesel prices as the most influential factors affecting the MSP. Continued advancements in Fischer-Tropsch catalyst technologies, reductions in green hydrogen costs and growing consumer demand for environmentally friendly products could significantly enhance the economic feasibility of this sustainable approach, paving the way for broader adoption and contributing to a circular carbon economy.

Highly stable Co/CeO2 catalyst for high-temperature water–gas shift reaction using a CeO2 support with an optimized precipitant ratio

We report hydrogen production from waste through waste gasification and the water–gas shift reaction using highly stable Co/CeO2 catalysts. Here, careful control of the KOH:K2CO3 precipitant ratio during CeO2 support synthesis yielded highly active and stable Co/CeO2 catalysts. Crucially, the precipitant ratio affects the Co dispersion, oxygen vacancies, crystallinity, and Co-CeO2 interactions, and the Co dispersion increases with increase in KOH content. Further, the oxygen storage capacity improves at the optimal KOH:K2CO3 ratio. In addition, the Co-CeO2 interaction is enhanced when catalysts are synthesized using CeO2 with a large amount of K2CO3. All prepared Co/CeO2 catalysts show high CO conversion, even at extremely high gas hourly space velocities: the Co/CeO2 (λ = 2:1 and 1:1.5) catalysts exhibit stable performance because of robust Co-CeO2 interactions, high oxygen storage capacities, and effective Co dispersions. These findings aid hydrogen production from waste and CeO2 support design for various catalytic reactions.

Minimizing CoxMn1-xO content in a Co2C catalyst for low CO2 selectivity in Fischer-Tropsch synthesis to olefins

The Co2C-based catalyst is a promising candidate for the Fischer-Tropsch to olefins reaction. However, it consistently exhibits high CO2 selectivity (∼40 %), and the origin of the high activity in the water–gas-shift reaction is not well-understood. In this study, Co2C catalysts constructed with the same elemental compositions but using the melting and co-precipitation methods resulted in drastic differences in CO2 selectivity − one at 3.8 % and the other at 35.3 %. A detailed structural study revealed that the presence of CoxMn1-xO instead of Co2C is responsible for the elevated CO2 selectivity. Interestingly, CoxMn1-xO alone demonstrates limited CO2 selectivity, but when promoted with Na, its WGSR activity is greatly enhanced. Conversely, the catalysts maintained consistently low CO2 selectivity even with improved Na content, as long as a high fraction of Co2C is present. This finding is important for designing Co2C-based catalysts that can achieve high olefin selectivity while minimizing undesirable CO2 emissions.

Plasmon-enhanced hydrogen production from photocatalytic methanol aqueous-phase reforming over novel nickel-tin intermetallic compounds photocatalyst

Hydrogen production from the aqueous phase reforming (APR) of methanol is promising to reduce the global carbon dioxide emission, but it is still a great challenge for hydrogen production with high catalytic efficiency at low reaction temperature. Here we report that Al2O3 supported Ni3Sn1 intermetallic compounds nanoparticles as new class of plasmonic photocatalyst and enables low temperature (150–190 °C), efficient hydrogen production (277μmol g−1 min−1) and low CO and CH4 selectivity (≤ 0.1 %) through APR with the help of light irradiation. The hydrogen production rate of Ni3Sn1/Al2O3 is 8 times higher than that of conventional noble metal 3 wt% Pt/Al2O3 catalyst under the same optimized reaction conditions. The exceptional photocatalytic performance for hydrogen production can be attribute to higher efficiency of “hot electron” transference into the reactant due to the higher energy level of “hot electron” and the lower energy level of metal-reactant adsorption bond induced by Sn doping in Ni3Sn1 under light irradiation, which not only improve the reactivity via enhanced methanol dissociation and the sequential water–gas shift (WGS) reaction, but also suppressed catalyst poisoning via accelerated CO2 desorption over the Ni sites.

Atomically dispersed nickel in CeO2 aerogel catalysts completely suppresses methanation in the water-gas shift reaction.

Nickel-based catalysts are widely studied for water-gas shift (WGS), a key intermediate step in hydrogen production from carbon-based feedstocks. Their viability under practical conditions is limited at high temperatures when Ni aggregates and converts CO to methane, an undesirable side product. Because experimental and computational studies identify undercoordinated Ni step sites as most active toward CH4 formation, we eliminate Ni step sites by atomically dispersing Ni into networked, nanoparticulate CeO2 aerogels. The mesoporous catalyst with 2.5 atomic % Ni in CeO2 is highly active for WGS, converting near-equilibrium levels of CO at 350°C, while no CH4 is detected at the limit of detection (<2 parts per million). In contrast, supporting low weight percentages of Ni clusters or nanoparticles on CeO2 aerogels leads to methanation. The CH4 yield produced by the atomically dispersed Ni-substituted CeO2 aerogel is over an order of magnitude lower than previously reported Ni-based catalysts claiming methane suppression, marking an important advance in the development of WGS catalysts.

Unraveling the role of EPOC during the enhancement of RWGS reaction in a Pt/YSZ/Au single chamber reactor

The hydrogenation of CO2 remains one of the most intriguing and effective strategies for addressing the continuous increase of CO2 emissions in the atmosphere. At the same time, it serves as an effective pathway for the formation of value-added products. This work explores the Electrochemical Promotion of Catalysis (EPOC) phenomenon on the CO2 hydrogenation reaction, utilizing a single chamber reactor with a Pt/YSZ/Au electrochemical cell. Experiments were conducted under ambient pressure conditions, within a temperature range of 200–400 °C, for a reactant flow rate of 100 cm3/min under reducing (PCO2: PH2 = 1:7) and oxidizing (PCO2: PH2 = 2:1) conditions. The effect of reactant ratio, reactor temperature, and applied current/potentials on the reaction rate were thoroughly investigated. The only observed product was carbon monoxide through the Reverse Water Gas Shift Reaction (RWGS). Under purely catalytic operation of the cell (open circuit), reducing conditions were found to be more favorable for the RWGS reaction as compared to oxidizing ones. The imposition of negative potential values under reducing environment resulted in a 2.3-fold increase in the RWGS reaction rate (rCO = 21 × 10−9 mol/s) as compared to open circuit values (rCO = 9 × 10−9 mol/s). On the other hand, application of positive potentials had no profound effect on the catalytic rate, which was attributed to competing electrochemical and surface processes taking place on the catalyst electrode. The kinetic results are discussed in conjunction with the physicochemical and the morphological characteristics of the catalytic film.

Hydrogen-Rich Syngas Production Based on a Co-Gasification Process Coupled to a Water–Gas Shift Reactor Without Steam Injection

Future decarbonized applications that rely on renewable and carbon-dioxide-neutral hydrogen production could benefit from the gasification of waste to produce hydrogen. In the current study, an Aspen Plus® model was developed by coupling a co-gasification model to a water–gas shift (WGS) model. The feedstock employed in the simulations was a blend of municipal solid waste (MSW) and biomass from Morocco. A parametric assessment was conducted to analyze the effect of the steam-to-feedstock ratio (SFR) on the syngas composition and the WGS reactor temperature. This study also presents a comparison between the results of the gasification process before and after the WGS reactor, using air and steam as the gasifying agent. The results show an increase in hydrogen volumetric percentage for higher steam-to-feedstock ratios in the gasifier. Moreover, the inclusion of a WGS reactor enhances hydrogen and carbon dioxide while reducing the amount of carbon monoxide in the syngas for both air and steam as the gasifying agents. It can be concluded that a co-gasification process can be intensified by coupling it to a WGS reactor without steam injection to produce hydrogen-rich syngas with reduced operational expenditures.

Methanol steam reforming using Ce and La modified low-Cu catalysts for On-board hydrogen production

Methanol steam reforming (MSR) combined with simultaneous hydrogen purification using palladium membranes offers an advanced method for on-board hydrogen utilization in fuel cell vehicles. However, commercial Cu-Zn-Al catalysts typically operate around 300 °C, significantly lower than palladium membranes. In this study, a series of γ-Al2O3 supported and CeO2 and La2O3 modified low-copper catalysts (n%Cu-CL-Al, n% = 2∼6 wt.%) were synthesized and compared with a commercial 45 %Cu-Zn-Al catalyst at 1.1 MPa. The Cu-CL-Al catalysts exhibited higher hydrogen yields (Y [H2]) at temperatures above 400 °C. This performance is attributed to a limited reverse water-gas shift (R-WGS) reaction, facilitated by the strong CO2 absorption properties of rare earth oxides. During long-term stability tests, the activity of the 4 %Cu-CL-Al catalyst significantly decreased after 50 h but rapidly recovered upon oxygen introduction. As no significant carbon deposition was observed on the catalyst surface, and nearly all Cu species in the used catalyst were reduced to Cu0, suggesting that deactivation was due to the over-reduction of Cu species by the generated H2. The presence of O2 accelerated the oxidation rate of Cu0, maintaining an appropriate Cu0/Cu+ ratio for MSR reaction. At 450 °C, Y [H2] was constrained only by the equilibrium of R-WGS reaction, independent of the Cu loading and contact time. This indicates that for on-board hydrogen production using Cu-based catalysts, it is crucial to regulate Cu loading and catalyst quantity to achieve Y [H2] that surpass the equilibrium limit of the chemical reaction.

Effect of Different Partial Pressures on H2 Production with Parageobacillus thermoglucosidasius DSM 6285

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.

Effectively regulating Ni distribution on CeO2 through formation of Ce1−xNixO2−y solid solution to enhance the selectivity in RWGS reaction

Nickel-based catalysts frequently encounter significant challenges in achieving both high CO2 conversion and superior CO selectivity during reverse water gas shift (RWGS) reactions. To address this issue, we developed a facile strategy to prepare highly dispersed Ni/CeO2 catalysts by forming Ce1−xNixO2−y solid solutions. Under conditions of 300–600 °C, 0.1 MPa, and a gas hourly space velocity (GHSV) of 40,000 mL gcat−1 h−1, the 5Ni/CeO2-A catalyst exhibited outstanding selectivity, approaching 100 %. The RWGS reaction rate reached 1332 μmolCO gNi−1 s−1 and maintained stable for 50 h almost without deactivation. The formation of Ce1−xNixO2−y solid solution uniformly disperses numerous Ni species in the CeO2 lattice, effectively inhibiting Ni aggregation. This highly dispersed Ni weakens CO adsorption and facilitates its direct desorption without excessive hydrogenation. Moreover, the catalyst remains well-dispersed state even after reduction. The formed Ce1−xNixO2−y solid solution generates abundant oxygen vacancies on the catalyst surface, enhancing H2 dissociation. The catalyst’s pore size distribution is also modified, creating stacked pores that favor reactant diffusion and expose more active centers. In-situ DRIFTS experiments demonstrate that Ce-OH plays a pivotal role in CO2 adsorption on the 5Ni/CeO2-A catalyst, while the stabilization of bicarbonate and formate intermediates by the highly dispersed Ni further promotes catalytic performance. This study introduces a novel preparation method and provides valuable insights for designing Ni-based catalysts with exceptional CO selectivity.