Low-temperature Water Gas Shift Reaction Research Articles

Impact of Incorporation of Active Nanoporous Components or Their Precursors in a CuAlO/CuAl Ceramometal Skeleton on the Properties in the Low-Temperature Water-Gas Shift Reaction

Enhanced activity in low-temperature water-gas shift (LT-WGS) reaction of some ceramometal catalysts compared to conventional Cu–Zn–Al oxide catalyst was demonstrated. Porous ceramometals were synthesized from powdered CuAl alloys prepared by mechanical alloying with the addition of either CuAlexp powders produced by current spark explosion of Cu+Al wires or CuZnAl oxide obtained by coprecipitation. Their structural, microstructural, and textural characteristics were examined by means of X-ray diffraction, scanning electron microscopy with energy-dispersive X-ray spectrometry, NMR, and adsorption methods, and catalytic properties were studied in the LT-WGS reaction. CuAlO/CuAl ceramometals were found to have mostly the egg-shell microstructure with the metallic cores (AlxCu1–x, Al2Cu, and Al4Cu9) and the oxide shell containing copper oxides and/or mixed oxides of copper and aluminum and, at same time, CuAlO/CuAl ceramometal with incorporated additives was found to create a more complicated microstructure. A large amount of X-ray amorphous oxides of copper and aluminum is typical for all composites. CuAl ceramometal was shown to be more active than the CuZnAl oxide catalyst in spite of a much lower specific surface area. The CuAl+CuZnAl catalyst consisting of prismatic granules showed a higher activity in comparison with CuZnAl oxide consisting of cylindrical granules. The activity of the composite granulated catalyst referred to its unit weight was more than 6-fold higher as compared to the oxide catalyst, while the activity per the surface area was found to be more than an order of magnitude higher due to much higher specific activity of small fraction and additively much lower diffusion limitation of granules.

Use of industrial and sol-gel catalysts in the removal of co from autonomous fuel cells

The low-temperature water-gas shift reaction (WGSR) is already used in several industrial chemical processes. However, interest in this reaction has increased significantly in the last few years because of the advances in fuel cell technology and the need to develop compact reformers for the production of pure hydrogen streams (free from CO). In the present work, the WGSR was carried out on copper-based supported catalysts, one of them already used in the industry and the other one prepared using the sol-gel method with the same composition as the industrial catalyst. The synthesized sol-gel catalyst presented excellent catalytic performance, with a very stable CO conversion of around 60%. The high activity and stability of the sol-gel catalyst were mainly attributed to its large metal surface area and high copper dispersion.

Unraveling the Origin of Ceria Activity in Water–Gas Shift by First-Principles Microkinetic Modeling

Water–gas shift (WGS) is a well-known reaction for production and purification of hydrogen from synthesis gas. Transition metals supported on ceria (CeO2) have received much attention as single-step catalysts for the low-temperature WGS reaction. The intrinsic WGS activity of the ceria support indicates that it might play an essential role in the catalytic process. However, there is still no consensus on the governing reaction mechanism at mild conditions. Thus, in this work self-consistent periodic density functional theory and microkinetic calculations were performed to investigate redox, formate-mediated, and carboxyl-mediated pathways on the CeO2(111) surface. Binding energies of reactants (H2O and CO), intermediates (OH, formate, and carboxyl), and products (CO2 and H2) were calculated, together with energy barriers associated with possible elementary reaction steps. These results were used as input in a mean-field microkinetic model. The analysis of degrees of rate control from microkinetic calculations shows the prevalence of a combined redox-associative route for WGS on pure ceria. Overall, these results provide insight into the WGS reaction on ceria and can contribute to experimental research of catalytic systems for low-temperature WGS.

Styrene Hydroformylation with In Situ Hydrogen: Regioselectivity Control by Coupling with the Low-Temperature Water-Gas Shift Reaction.

The hydroformylation of olefins is one of the most important homogeneously catalyzed industrial reactions for aldehyde synthesis. Various ligands can be used to obtain the desired linear aldehydes in the hydroformylation of aliphatic olefins. However, in the hydroformylation of aromatic substrates, branched aldehydes are formed preferentially with common ligands. In this study, a novel approach to selectively obtain linear aldehydes in the hydroformylation of styrene and its derivatives was developed by coupling with a water-gas shift reaction on a Rh single-atom catalyst without the use of ligands. Detailed studies revealed that the hydrogen generated in situ from the water-gas shift is critical for the highly regioselective formation of linear products. The coupling of a traditional homogeneous catalytic process with a heterogeneous catalytic reaction to tune product selectivity may provide a new avenue for the heterogenization of homogenous catalytic processes.

Kinetics of Water Gas Shift Reaction on Au/CeZrO4: A Comparison Between Conventional Heating and Dielectric Barrier Discharge (DBD) Plasma Activation

The kinetics of the low-temperature forward water gas shift (LT-WGS) reaction have been studied over a 2 wt% Au/CeZrO4 (Au/CZO) catalyst using both thermal and dielectric barrier discharge plasma heterogeneous catalyst systems. Using the energy density (e), the apparent activation energy has been calculated under plasma and thermally activated conditions. A substantially lower apparent activation energy is observed in the plasma activated system (9.5 kJ/mol) compared with the thermal-catalysed reaction (132.9 kJ/mol). Different kinetic isotope effect (KIE) values for water were found in thermal (1.43) and plasma (1.89) activated catalytic systems which infer different mechanisms between the two activation processes and also shows the importance of water activation. Furthermore, negative and positive reaction orders with respect to CO and H2O are found for both conditions which are − 1.30, 0.28 under thermal and − 1.53, 0.35 under plasma processes, respectively. The reaction order with respect to H2O and KIE studies demonstrate that the bond cleavage in H2O molecule is a rate determining step in the plasma-assisted LT-WGS, similar to that in the thermal-assisted reaction.

The optimization of Nb loading amount over Cu–Nb–CeO2 catalysts for hydrogen production via the low-temperature water gas shift reaction

The effect of Nb promotion over a Cu–CeO2 catalyst was investigated in the low-temperature water gas shift reaction. The Nb loading amount was systematically varied from 0 to 5 wt% for the Cu–Nb–CeO2 catalyst, and the 1 wt% Nb promoted Cu–Nb–CeO2 catalyst exhibited the highest catalytic performance even at extremely high GHSV of 72,152 h−1. The catalysts were characterized through various techniques such as Brunauer-Emmet-Teller measurements, X-ray diffraction, N2O-chemisorption, H2-temperature programmed reduction, X-ray photoelectron spectroscopy, and transmission electron microscopy. It was found that the superior performance of the 1 wt% Nb promoted Cu–Nb–CeO2 catalyst was due to its enhanced reducibility, high BET surface area, small metallic Cu crystallite size, and high number of oxygen vacancies.

Highly efficient copper-manganese oxide catalysts with abundant surface vacancies for low-temperature water-gas shift reaction

Efficient and low-cost water-gas shift (WGS) catalysts have aroused much attention for the purification of H2-rich syngas in the application of fuel cell. In this study, combustion of ethylene glycol and methanol (EGM), fractional precipitation (FP) and template growth (TG) methods have been utilized to synthesize copper-manganese oxide (CMO) catalysts. The prepared CMO catalysts are consisted of spinel Cu1.5Mn1.5O4 and Mn2O3 phases and exhibit porous, polyhedral nanoparticle and nanorod morphologies for EGM, FP and TG, respectively. The low-temperature WGS reaction activities of prepared catalysts follow the sequence: CMO-EGM > CMO-FP > CMO-TG, which are higher than that of CMO catalyst prepared by traditional co-precipitation method. Among them, CMO-EGM catalyst exhibits the highest reaction rate of 122.72 μmolCO gcat.−1 s−1 at 200 °C, which is much higher than that of commercial Cu/ZnO/Al2O3 (73.62 μmolCO gcat.−1 s−1). CO-TPSR and DRIFTS analysis reveal the superior activity of CMO-EGM is attributed to the larger amounts of active hydroxyl groups on the surface of catalysts, which correlate well with the high reducibility and abundant surface oxygen vacancies of CMO-EGM catalyst.

Activation of Gold on Metal Carbides: Novel Catalysts for C1 Chemistry.

This article presents a review of recent uses of Au-carbide interfaces as catalysts for C1 Chemistry (CO oxidation, low-temperature water-gas shift, and CO2 hydrogenation). The results of density-functional calculations and photoemission point to important electronic perturbations when small two-dimensional clusters of gold are bounded to the (001) surface of various transition metal carbides (TiC, ZrC, VC, Ta C, and δ-MoC). On these surfaces, the C sites exhibited strong interactions with the gold clusters. On the carbide surfaces, the Au interacts stronger than on oxides opening the door for strong metal-support interactions. So far, most of the experimental studies with well-defined systems have been focused on the Au/TiC, Au/δ-MoC, and Au/β-Mo2C interfaces. Au/TiC and Au/δ-MoC are active and stable catalysts for the low-temperature water-gas shift reaction and for the hydrogenation of CO2 to methanol or CO. Variations in the behavior of the Au/δ-MoC and Au/β-Mo2C systems clearly show the strong effect of the metal/carbon ratio on the performance of the carbide catalysts. This parameter substantially impacts the chemical behavior of the carbide and its interaction with supported metals, up to the point of modifying the reaction rate and mechanism of C1 processes.

The catalytic mechanism of the Au@TiO2−x/ZnO catalyst towards a low-temperature water-gas shift reaction

A redox mechanism towards the water-gas shift reaction was certified based on in situ/operando experiments and density functional theory calculation studies.

A low-temperature water-gas shift reaction catalyzed by hybrid NiO@NiCr-layered double hydroxides: catalytic property, kinetics and mechanism investigation.

The realization of a high efficiency water gas shift reaction (WGSR) at low temperatures has always been a research hotspot and is difficult to achieve. Based on NiCr layered double hydroxides (NiCr-LDHs), a hybrid NiO@NiCr-LDH was prepared by intercalation and surface complexing. The above materials were applied to WGSR at low temperatures, and the catalytic activity and reaction mechanism of WGSR with NiCr-LDHs and LDHs intercalated with organic metal ligands (NiCr-Ni/SB-LDHs) were compared. It was found that the activity of NiO@NiCr-LDHs was about 4 and 2 times higher than that of NiCr-LDHs and NiCr-Ni/SB-LDHs, respectively. At 150 °C, the CO conversion of NiO@NiCr-LDHs is 35.2%, the reaction rate is 19.71 μmol gcat-1 s-1, the TOF value is 0.225 s-1, and the activation energy is 77.4 kJ mol-1. In addition, the complexing NiO content has a great influence on the activity of NiO@NiCr-LDHs for WGSR. In addition, DFT calculations were used to compare the differences in the performance and catalytic mechanism of different nickel containing LDH catalysts for WGSR. According to the calculated results of relative energy barrier and activation energy, a possible reaction pathway and mechanism are discussed. The results show that compared with NiCr-LDHs and NiCr-Ni/SB-LDHs, NiO@NiCr-LDHs can effectively reduce the activation energy of the H2O dissociation step, which is the rate determining step of WGSR.

Carboxyl intermediate formation via an in situ-generated metastable active site during water-gas shift catalysis

Definitive experimental proof for catalytic pathways and active sites during the low-temperature water-gas shift reaction remains elusive. Herein, we combine spectroscopic, kinetic and computational analyses to address the decades-long mechanistic controversy by studying the reverse water-gas shift over Pd/Al2O3. Isotopic transient kinetic analysis established the minor role of the formate intermediate, whereas hydrogen titration experiments confirmed the intermediacy of carboxyl. The ability to decouple the parallel formate and carboxyl pathways led to the identification of a distinct active site that exhibits regio- and chemoselective hydrogen addition to CO2 to yield the carboxyl intermediate. The metastable active site is formed in situ, resulting in hydroxylation of the metal–support interface and electronic restructuring. Atomistic simulations of the active site electronic structure and mechanistic landscape provided a framework that is consistent with experimental observations. Our study highlights the dynamic creation of a coordinatively unsaturated metal site caused by substrate adsorption on an adjacent support site. Due to its importance, the water-gas shift reaction has been the subject of numerous studies; however, a unifying mechanistic picture has not yet emerged. Now, a combination of spectroscopic, kinetic and computational methods reveal the crucial role of carboxyl intermediate for this centuries-old process.

Enhanced Activity and Stability of Gold/Ceria-Titania for the Low-Temperature Water-Gas Shift Reaction.

Gold supported on ceria-zirconia is one of the most active low temperature water-gas shift catalysts reported to date but rapid deactivation occurs under reaction conditions. In this study, ceria-titania was evaluated as an alternative catalyst support. Materials of different Ce:Ti compositions were synthesized using a sol-gel methodology and gold was supported onto these using a deposition-precipitation method. They were then investigated as catalysts for the low-temperature water-gas shift reaction. Au/Ce0.2Ti0.8O2 exhibited superior activity and stability to a highly active, previously reported gold catalyst supported on ceria-zirconia. High activity and stability was found to be related to the support comprising a high number of oxygen defect sites and a high specific surface area. These properties were conducive to forming a highly active catalyst with well-dispersed Au species.

An electronic perturbation in TiC supported platinum monolayer catalyst for enhancing water–gas shift performance: DFT study

The water–gas shift (WGS) reaction behaviors over the TiC(0 0 1) supported Pt monolayer catalyst (PtML/TiC(0 0 1)) are investigated by using the spin-unrestricted density functional theory calculations. Importantly, we find that the PtML/TiC(0 0 1) system exhibits a much lower density of Pt-5d states nearby the Fermi level compared with that for Pt(1 1 1), and the monolayer Pt atoms undergo an electronic perturbation when in contact with TiC(0 0 1) support that would strongly improve the WGS activity of supported Pt atoms. Our calculations clearly indicate that the dominant reaction path follows a carboxyl mechanism involving a key COOH intermediate, rather than the common redox mechanism. Furthermore, through the detailed comparisons, the results demonstrate that the strong interactions between the monolayer Pt atoms and TiC(0 0 1) support make PtML/TiC(0 0 1) a highly active catalyst for the low-temperature WGS reaction. Following the route presented by Bruix et al (2012 J. Am. Chem. Soc. 134 8968–74), the positive effect derived from strong metal-support interaction in the metal/carbide system is revealed.

An important parameter for synthesis of Al2O3 supported Cu-Zn catalysts in low-temperature water-gas shift reaction under practical reaction condition

Herein, we investigated the effects of aging time and temperature on the performance of co-precipitation–prepared Cu-Zn-Al catalysts in the low-temperature water-gas shift (LT-WGS) reaction. The highest CO conversion within the employed temperature range as well as very stable activity over 200 h were observed for the catalyst prepared at 80 °C and aged for 72 h, which was ascribed to its high surface area and close-to-100% degree of CuO reduction. Conversely, catalysts aged at temperatures below 80 °C had poor physical properties, while aging for <72 h resulted in the formation of bulk copper oxide, which was hardly reduced under the low-temperature conditions.

Production of Bio-hydrogen Using Bio-oil as a Potential Biomass-derived Renewable Feedstock

The bio-oil derived from pyrolysis of straw can be selectively converted into high-purity hydrogen by coupling three steps: (i) steam reforming(SR) of different bio-oils, (ii) water-gas shift(WGS), and (iii) the removal of CO2. The catalytic SR reaction over the NiLaTiAl catalyst, coupled with a low-temperature WGS reaction with the CuZnAl catalyst, promoted the conversion of various oxygen-containing organic compounds in the bio-oil into hydrogen and carbon dioxide. Under the optimized condition, light bio-oil achieved the highest conversion(99.8%, molar fraction), with a high hydrogen yield of 16.4%(mass fraction) and a H2 purity of 99.94%(volume fraction). The carbon deposition on the NiLaTiAl catalyst was the main factor caused catalyst deactivation. Production of hydrogen from different bio-oil model compounds was also investigated in detail.

Generation and extraction of hydrogen from low-temperature water-gas-shift reaction by a ZIF-8-based membrane reactor

Abstract In this study, for the first time, a membrane reactor (MR) was constructed with a crystalline metal-organic framework (MOF) membrane and Cu/Zn/Al2O3 catalysts, and utilized for hydrogen production and purification through a low-temperature water gas shift reaction (LT-WGSR). Compared with the existing metal and zeolite membranes, the as-synthesized zeolitic imidazolate framework-8 (ZIF-8) membrane showed a pure hydrogen permeance of 9.2 × 10−7 mol/m2 s Pa, which is orders of magnitude higher than those of metal membranes, and a considerable H2/CO ideal selectivity of 6.13 at room temperature without any post-treatment, making it a more practical option for producing hydrogen with a MR process from a WGSR from the perspectives of productivity and scalability. Significantly enhanced CO conversions and hydrogen purities were achieved when the LT-WGSR was conducted in this ZIF-8-based MR system compared to those achieved with traditional packed-bed reactors (PBRs) under the operating conditions of interest in the present study, i.e. temperature of 120–220 °C and space velocity of 20–80 L/g·h. An improvement of ∼13.5% in the CO conversion was achieved with the MR at 220 °C and a space velocity of 80 L (STP)/g-cat·h, whereas a higher temperature and lower space velocity favoured a higher H2 recovery. The feasibility of using this ZIF-8-based MR for long-term LT-WGSRs was assessed; the structural stability of the ZIF-8 membrane must be enhanced to achieve a ZIF-8-based MR in the future.

Recent Advances in the Gold-Catalysed Low-Temperature Water–Gas Shift Reaction

The low-temperature water–gas shift reaction (LTS: CO + H2O ⇌ CO2 + H2) is a key step in the purification of H2 reformate streams that feed H2 fuel cells. Supported gold catalysts were originally identified as being active for this reaction twenty years ago, and since then, considerable advances have been made in the synthesis and characterisation of these catalysts. In this review, we identify and evaluate the progress towards solving the most important challenge in this research area: the development of robust, highly active catalysts that do not deactivate on-stream under realistic reaction conditions.

Solubility Limit of Cu and Factors Governing the Reactivity of Cu–CeO2 Assessed from First-Principles Defect Chemistry and Thermodynamics

Cu–CeO2 is a promising material system for low-temperature water gas shift reactions. The solubility and oxidation state of Cu in Cu–CeO2 is important for these reactions, but these values have been unclear from the literature to date. We used first-principle calculations and statistical thermodynamics to assess Cu defect configurations and oxidation states in bulk ceria, at both equilibrium and non-equilibrium conditions. Cu solubility was found to be very low, lower than ppm level at equilibrium, indicating that the nanoparticles with high Cu content reported in experimental literature are, in fact, in non-equilibrium states. Thus, these non-equilibrium states were also assessed by fixing the Cu content from 0.001 to 1%. Under oxygen-rich conditions, Cu takes 3+, serving as an acceptor substitutional dopant. Increasing Cu content increases the concentrations of oxygen vacancies and Ce3+ polarons, which can induce a higher catalytic activity compared to undoped ceria. In addition, with reducing condition...

The alcohol-modified CuZnAl hydroxycarbonate synthesis as a convenient preparation route of high activity Cu/ZnO/Al2O3 catalysts for WGS

The influence of the hydroxycarbonate precursors precipitation environment on the physico-chemical properties and catalytic activity in low-temperature water-gas shift (LT-WGS) reaction of Cu/ZnO/Al2O3 system has been studied. With the use of co-precipitation three precursors were obtained, which differed in the reactive medium, i.e. the solvent composition. Water, glycol aqueous solution or ethanol aqueous solution were used as the reactive medium. The prepared materials were characterized by means of XRF, XRD, BET, TG/MS, TPR, N2O titration techniques as well as SEM method and their catalytic activity was compared in LT-WGS reaction in the kinetic regime and differential conditions. It was shown that Cu/ZnO/Al2O3 system of higher activity can be obtained by means of alcohol-assisted technique rather than using a conventional method. Precursor synthesis performed in ethanol aqueous solution contributes to obtaining highly active and stable catalysts.

Confined Pt1 1+ Water Clusters in a MOF Catalyze the Low-Temperature Water-Gas Shift Reaction with both CO2 Oxygen Atoms Coming from Water.

The synthesis and reactivity of single metal atoms in a low-valence state bound to just water, rather than to organic ligands or surfaces, is a major experimental challenge. Herein, we show a gram-scale wet synthesis of Pt1 1+ stabilized in a confined space by a crystallographically well-defined first water sphere, and with a second coordination sphere linked to a metal-organic framework (MOF) through electrostatic and H-bonding interactions. The role of the water cluster is not only isolating and stabilizing the Pt atoms, but also regulating the charge of the metal and the adsorption of reactants. This is shown for the low-temperature water-gas shift reaction (WGSR: CO + H2 O → CO2 + H2 ), where both metal coordinated and H-bonded water molecules trigger a double water attack mechanism to CO and give CO2 with both oxygen atoms coming from water. The stabilized Pt1+ single sites allow performing the WGSR at temperatures as low as 50 °C.