High Water Gas Shift Activity Research Articles

Au and Pt Remain Unoxidized on a CeO2-Based Catalyst during the Water-Gas Shift Reaction.

The active forms of Au and Pt in CeO2-based catalysts for the water-gas shift (WGS) reaction are an issue that remains unclear, although it has been widely studied. On one hand, ionic species might be responsible for weakening the Ce-O bonds, thus increasing the oxygen mobility and WGS activity. On the other hand, the close contact of Au or Pt atoms with CeO2 oxygen vacancies at the metal-CeO2 interface might provide the active sites for an efficient reaction. In this work, using in situ X-ray absorption spectroscopy, we demonstrate that both Au and Pt remain unoxidized during the reaction. Remarkable differences involving the dynamics established by both species under WGS atmospheres were recognized. For the prereduced Pt catalyst, the increase of the conversion coincided with a restructuration of the Pt atoms into cuboctahedrical metallic particles without significant variations on the overall particle size. Contrary to the relatively static behavior of Pt0, Au0 nanoparticles exhibited a sequence of particle splitting and agglomeration while maintaining a zero oxidation state despite not being located in a metallic environment during the process. High WGS activity was obtained when Au atoms were surrounded by oxygen. The fact that Au preserves its unoxidized state indicates that the chemical interaction between Au and oxygen must be necessarily electrostatic and that such an electrostatic interaction is fundamental for a top performance in the WGS process.

A new application of the commercial high temperature water gas shift catalyst for reduction of CO2 emissions in the iron and steel industry: Lab-scale catalyst evaluation

In this study, we present a detailed investigation of a commercial iron-based high temperature water gas shift (HTWGS) catalyst (Johnson Matthey KATALCOTM 71-6) in a new application: the production of hydrogen from blast furnace gas (BFG), which originates from iron and steel manufacturing. During the lab-scale catalytic testing under BFG conditions the catalyst demonstrated: 1) high water gas shift activity and stability; 2) minimal methanation at reduced steam to CO ratios; 3) high resistance towards H2S impurities present in the feed. The results of post-characterization of the discharged samples confirm the robustness of KATALCO 71-6 towards BFG process conditions: no over-reduction of the catalytically active Fe3O4 phase and no formation of a less active FeS phase. An in situ X-ray absorption spectroscopy study revealed no over-reduction of the iron phase under BFG conditions and the stabilization of the iron phase by diffusion of chromium into the iron oxide matrix. The findings of this study demonstrate the suitability of the iron-based HTWGS catalyst KATALCO 71-6 for the production of hydrogen from BFG streams. Knowledge gained in this study is an essential step in the development and scale up of carbon capture and storage as well as carbon capture and utilization technologies, such as the sorption enhanced water gas shift (SEWGS) technology, aimed at reducing the CO2 footprint during steel manufacturing.

Cu nanoparticles confined in TiO2 nanotubes to enhance the water-gas shift reaction activity

ABSTRACT It is of great significance to develop water-gas shift (WGS) catalyst with high catalytic activity in low-temperature operational regime. In this paper, we have prepared Cu confined in TiO2 nanotubes (TiO2NT, Cu-in-TiO2NT) catalyst via a vacuum-assisted impregnation method and subsequent calcination. The confined Cu-in-TiO2NT catalyst exhibits the higher CO conversion and H2 production rate than that of the Cu loaded on TiO2NT catalyst throughout the entire reaction temperature range. At the reaction temperature of 250°C and 300°C, the CO conversion of the confined catalyst is twofold and fourfold, respectively, higher than that of the supported catalyst, demonstrating superior catalytic activity toward WGS reaction. Due to the confinement effect of TiO2NT, the confined Cu-in-TiO2NT catalyst can enhance the concentration of the oxygen vacancies for H2O activation, contributing to the higher WGS activity.

Catalysis for efficient low-temperature hydrogen production and storage

Hydrogen, an energy-intensive and clean power source, has been treated as an ideal energy carrier to replace the coal and oil based global energy system for the more sustainable economic development. Especially, with the increasing finical support from worldwide in the researching of renewable energy both for the public and military using. Generally, hydrogen cycling includes three steps: (1) the continuously large scale hydrogen generation; (2) the safe and efficient hydrogen storage and transportation; (3) the efficient conversion of hydrogen to electricity or other forms of energy. For the using of hydrogen, a representative example is polymer electrolyte membrane fuel cells (PEMFCs) which has been widely studied. However, the bottle-neck for the bursting of hydrogen economy besides the effective using of hydrogen lies in the efficient generation and safe storage of hydrogen. Recently, our research group developed α-molybdenum carbide (α-MoC) supported Au and Pt catalysts for the low temperature water-gas shift (WGS) reaction and aqueous-phase reforming of methanol, respectively, both were essential reactions for industrial hydrogen generation. The WGS reaction (where carbon monoxide plus water yields hydrogen and carbon dioxide) is an important process for hydrogen generation and carbon monoxide removal in various energy-related chemical operations. This equilibrium-limited reaction is favored at a low working temperature. However, the reported catalysts by now always show unsatisfied performance under low operating temperatures and no catalysts ever reported reaching the activity of 0.1 molCO molmetal−1 s−1 below 150°C. Meanwhile, potential application in fuel cells also requires a WGS catalyst to be highly active, stable, and energy-efficient to match the working temperature of on-site hydrogen generation and consumption units. Concerning this problem, we synthesized layered gold clusters on a molybdenum carbide (Au/α-MoC) substrate to create an interfacial catalyst system for the ultralow-temperature WGS reaction. Water was activated over α-MoC at 30°C, whereas carbon monoxide adsorbed on adjacent Au sites was apt to react with surface hydroxyl groups formed from water splitting, leading to a high WGS activity reaching 1.05 molCO molmetal−1 s−1 under 120°C which is one order of magnitude higher than the early reported catalysts. Beside the Au/α-MoC for robust WGS reaction, we also developed highly distributed single atom Pt supported by molybdenum carbide (Pt/α-MoC) for aqueous-phase reforming of methanol. With the reforming of methanol and water, hydrogen with a high gravimetric density of 18.8% by weight can be in situ released. The average turnover frequency of Pt/α-MoC can reach 18046 mol of hydrogen per mole of platinum per hour at 190°C, which is two order of magnitude higher than the traditional catalysts. Based on the X-ray absorption fine structure (XAFS) and single atom resolution electron microscopy characterization results, Pt was determined to be atomic dispersed over α-MoC support at the low metal loadings, which maximized the exposure of Pt atom. Based on reaction mechanism investigation and DFT calculation, Pt/α-MoC was proved to be a bifunctional catalyst, with α-MoC support dissociating the O−H bond of H2O and methanol at low temperature, atomic dispersion of Pt scissoring C−H bond of CH3OH. The effectively reforming of intermediates with surface hydroxyls generate CO2 at the interface of Pt/α-MoC. The excellent performance of our catalytic system provide a new strategy for the efficient low-temperature hydrogen production and storage. In this short perspective, we introduce the new findings by our group and also summarize the recently developed representative catalysts involving the low temperature water-gas shift reaction and aqueous-phase reforming of methanol. We hope it can provide a reference for the future designing of catalysts in the field of hydrogen production and storage.

Water-gas shift reaction over platinum/strontium apatite catalysts

Platinum supported on calcium hydroxy (CaHAP) and fluoroapatite (CaFAP) exhibits excellent water-gas shift (WGS) activity comparable to the best Pt WGS catalysts on reducible oxides. The high activity of these unusual WGS catalysts is attributed to the parallel activation of CO on the noble metal and H2O on the ionic phosphates with formate species apparently being the major reaction intermediates. We have studied Pt supported on strontium hydroxy and fluoroapatites with varying cation and noble metal contents now in order to elucidate the role of the apatite cations and anions on WGS activity. Initial Pt dispersions approached 100% for loadings up to 3% (weight) with mean particle sizes of 1–2nm according to H2 chemisorption and EXAFS results (coordination number of 6.6). TEM analyses show further that the Pt aggregates grew slightly during catalytic testing up to 723K with 1.5–2.5nm particles being most abundant afterwards. Moreover, Ptn+ reduction is much facilitated on these apatites as revealed by temperature programmed reduction coupled with in situ X-ray absorption spectroscopy (XAS). The WGS reaction rates in a reformate-type gas mixture increased strongly with Sr/P ratio in the apatite, with the rates over the most active Pt/SrHAP and Pt/SrFAP catalysts being among the highest reported to date. In particular, Pt/SrHAP and Pt/SrFAP rates surpassed the rates over analogous Ca2+ substituted catalysts by ca. 30% at 573K. This demonstrates that apatite cations have a strong impact on WGS conversion over these systems opening a route to catalysts with potentially even higher WGS activity.

Magnesium-aluminum mixed metal oxide supported copper nanoparticles as catalysts for water-gas shift reaction

Mg(Al)O mixed metal oxide (MMO) supported Cu nanoparticles catalysts have been prepared by calcination and reduction of Cu-Mg-Al layered double hydroxides (LDHs). By adjusting the chemical compositions of LDHs precursors, various catalysts with 10–40wt% Cu content and molar ratio of (Cu+Mg)/Al=1–4 were prepared. The catalysts were characterized by ICP, N2 physical adsorption, XRD, TEM, H2-TPR, and N2O chemisorption, and tested for the water-gas shift (WGS) reaction. The characterization results suggested that upon calcination Cu-Mg-Al LDHs were converted to Mg(Cu, Al)O MMOs, where both Cu2+ and Al3+ were incorporated into the MgO framework to form a solid solution; reduction of Mg(Cu, Al)O gave highly dispersed and uniform Cu metal nanoparticles. The Cu metal dispersion was as high as 22–78% and the particle size varied from 1.5 to 5nm depending on the chemical compositions. The WGS activity of the Cu catalysts increased with the increase of Cu0 surface area. Among the prepared catalysts, the 30%Cu/Mg2Al catalyst exhibited the highest Cu surface area and the highest WGS activity. The optimized catalyst also showed superior activity, thermal stability, and steady-state stability than a commercial Cu/ZnO/Al2O3 catalyst under the present reaction conditions. The characterization on the spent catalysts showed that the LDHs-derived Cu nanoparticles remained highly dispersed, suggesting that the Mg(Al)O supported Cu nanoparticles were stable and possessed good resistance against sintering.

Platinum/Apatite Water-Gas Shift Catalysts

Water-gas shift (WGS) micro and membrane reactors are interesting components for compact H2 production and purification devices, but they require catalysts with very high activity for optimum efficiency to minimize catalyst bed thickness and mass transfer limitations. On the other hand, activation of H2O is known to be more challenging than CO in this reaction. Catalysts comprising ca. 2 nm large Pt particles on hydrophilic apatites are found to have very high WGS activity, with specific reaction rates exceeding those of a highly active Pt/CeO2 catalyst by up to 50% at 573 K. These apatite-supported catalysts exhibit stable CO conversions at 673 K without showing any CH4 formation tendencies up to 723 K. WGS activity increases with Ca/P ratio in the apatite, leveling off around Ca/P ≈ 1.75, and formate has been identified as the main reaction intermediate. The outstanding WGS performance is attributed to the superior activation of H2O on these ionic oxides due to coordination of H2O to Lewis acidic Ca2+ i...

Characterization of palladium/copper/ceria electrospun fibers for water–gas shift catalysis

Nano-fibers of palladium–copper (Pd/Cu) in ceria for water–gas-shift (WGS) catalysis were prepared by electrospinning solutions containing polyvinylpyrrolidone (PVP) and soluble salts of cerium, palladium, and copper in a water/ethanol co-solvent. Catalyst precursors were mixed in a single pot, electrospun, and calcined to produce ceramic fibers with 88wt% CeO2, 2% Pd, and 10% Cu. Slowing the rate of polymer removal with controlled heating during calcining did not significantly change fiber diameters (∼200nm) but did lower the ceria crystallite to typically less than 10nm and produce longer fibers that formed non-woven mats with structural integrity. The resulting catalyst materials were characterized for WGS activity by temperature-programmed and time-on-stream reactor tests. X-ray photoelectron spectroscopy, Raman spectroscopy, and transmission electron microscopy analysis indicated that for different precursor salts, much of the Cu and Pd are incorporated into the ceria lattice before testing. For the Pd/Cu/ceria nano-fiber catalysts, time-on-stream testing at 400°C showed high WGS activity, that asymptotically decayed with time. Post-testing XPS and Raman spectroscopy indicated that reduced Pd and Cu segregate to the surface during time-on-stream testing, which lowers activity. Exposure to intermittent oxidizing environments, particularly with O2, partially reverses the metal segregation and restores catalyst activity. Adding surfactant to the synthesis solution increases catalyst surface area without significantly improving activity or slowing its asymptotic decay, which suggests that activity is not limited strictly by surface area, but rather by metal/ceria interactions, for these catalysts.

CuO/ZrO2 catalysts for water–gas shift reaction: Nature of catalytically active copper species

A series of CuO/ZrO2 catalysts with different Cu loadings (4.1, 6.1 and 8.4 wt.%) were synthesized by a deposition-precipitation method and evaluated with the water–gas shift (WGS) reaction. In order to distinguish the different supported copper oxide species, (NH4)2CO3-leaching process was conducted on the three CuO/ZrO2 catalysts. The parent and leached catalysts were characterized by ICP-OES, XPS, XRD, N2-physisorption, N2O titration, UV–Vis DRS, H2-TPR and CO-TPR. The results reveal that three types of copper oxide species are present on the parent CuO/ZrO2 catalysts: (α) highly dispersed CuO that is weakly bound with ZrO2; (β) strongly bound Cu-[O]-Zr species, which can not be leached by (NH4)2CO3 solution and is possibly associated with the surface oxygen vacancy of ZrO2; (γ) crystalline CuO. The XRD and TEM results of the freshly reduced catalysts disclose that the three types of CuO species are transformed into their corresponding metallic states after the H2-pretreatment. It is found that the reaction rate correlates well with the amount of Cu-[O]-Zr species, indicating the metallic Cu derived from this species should be the catalytically active copper species for the WGS reaction. Moreover, CO-TPR results disclose that the Cu-[O]-Zr species play a significant role in promoting the reactivity of the surface hydroxyl groups, as is thought to be responsible for the high WGS activity of the CuO/ZrO2 catalysts.

Fischer–Tropsch Synthesis: Effect of K Loading on the Water–Gas Shift Reaction and Liquid Hydrocarbon Formation Rate over Precipitated Iron Catalysts

The effect of K loading on the water–gas shift (WGS) reaction and hydrocarbon formation rate during Fischer–Tropsch synthesis (FTS) was studied over 100 Fe/5.1 Si/2 Cu/x K (x = 1.25 or 3) precipitated catalysts using a 1-L continuously stirred tank reactor. The catalysts were tested over a wide range of experimental conditions: 260–270 °C, 1.3 MPa, H2/CO = 0.67 and 20–90 % CO conversions. On the low K loading (1.25 % K) Fe catalyst, the H2 deficiency required for the FTS reaction was made up by the WGS reaction only at high CO conversion level, i.e. >70 %; however, increasing potassium loading to 3 % dramatically improved the WGS reaction rate which provided enough hydrogen for the FTS reaction even at low CO conversion level, i.e. 30 %. Kinetic analysis suggests that increasing K loading resulted in significant increases in the WGS rate constant relative to that of FTS, which is a major cause of the high WGS activity on the high K loading catalyst. Both the low and high potassium containing iron catalysts have high liquid oil and solid wax formation rates, i.e. 0.78–0.93 g/g-cat/h at 260 °C, 1.3 MPa, H2/CO = 0.67 and 50 % CO conversion, but increasing potassium loading from 1.25 to 3 % shifted the primary product to wax (70 %) from oil (73.5 %). The wax fraction increased with increasing CO conversion for both iron catalysts. The effect of K loading on initial FTS activity and hydrocarbon distribution/selectivity of the Fe catalysts was also studied. High K loading, i.e. 3 % K, increased the iron carburization rate and significantly shortened the induction period of the FTS reaction. Secondary reactions of olefins were remarkably suppressed and the olefin content was greatly enhanced with increasing K loading from 1.25 to 3 %, consistent with a number of studies in the open literature.

Hydrogen production from oxidative steam reforming of ethanol over rhodium catalysts supported on Ce–La solid solution

The catalytic behaviors of Rh catalysts supported on Ce–La solid solution in H2 production from the oxidative steam reforming (OSR) of ethanol were studied for the first time. 1%Rh/Ce0.7La0.3Oy exhibits 100% ethanol conversion at 573 K with H2 yield rate 214 μmol g-cat−1 s−1, which is 150 K lower than that required for comparable performance with 1%Rh/CeO2. La doping also enhanced the stability by accelerating CH3COCH3 conversion and gave low CO selectivity due to the high water gas shift activity. X-ray diffraction and Raman spectroscopy characterizations indicate the formation of Ce–La solid solutions and oxygen vacancies. H2 temperature-programmed reduction and thermo-gravimetric measurement results confirmed that the redox properties of Rh/CeO2 were greatly enhanced by La doping, which accelerated ethanol conversion, promoted H2 yield, and maintained good long–term activity for the OSR reaction.

Design of Multiple Metal Doped Ni Based Catalyst for Hydrogen Generation from Bio-oil Reforming at Mild-temperature

A new kind of multiple metal (Cu, Mg, Ce) doped Ni based mixed oxide catalyst, synthesized by the co-precipitation method, was used for efficient production of hydrogen from bio-oil reforming at 250–500 °C. Two reforming processes, the conventional steam reforming (CSR) and the electrochemical catalytic reforming (ECR), were performed for the bio-oil reforming. The catalyst with an atomic mole ratio of Ni:Cu:Mg:Ce:Al=5.6:1.1:1.9:1.0:9.9 exhibited very high reforming activity both in CSR and ECR processes, reaching 82.8% hydrogen yield at 500 °C in the CSR, yield of 91.1% at 400 °C and 3.1 A in the ECR, respectively. The influences of reforming temperature and the current through the catalyst in the ECR were investigated. It was observed that the reforming and decomposition of the bio-oil were significantly enhanced by the current. The promoting effects of current on the decomposition and reforming processes of bio-oil were further studied by using the model compounds of bio-oil (acetic acid and ethanol) under 101 kPa or low pressure (0.1 Pa) through the time of flight analysis. The catalyst also shows high water gas shift activity in the range of 300–600 °C. The catalyst features and alterations in the bio-oil reforming were characterized by the ICP, XRD, XPS and BET measurements. The mechanism of bio-oil reforming was discussed based on the study of the elemental reactions and catalyst characterizations. The research catalyst, potentially, may be a practical catalyst for high efficient production of hydrogen from reforming of bio-oil at mild-temperature.

Effect of preparation method on the performance of the Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol: Part II-characterization

In the first part of this paper [1], we have discussed the effect of preparation method on the performance of Ni/Al2O3 catalysts for aqueous-phase reforming of ethanol (EtOH). One catalyst was synthesized using a sol–gel method (SG). The other was synthesized by adding nickel nitrate to a solution combustion synthesized alumina support (SCS). Based on the product distribution, we proposed the reaction pathway as a mixture of dehydrogenation of EtOH to acetaldehyde followed by C–C bond breaking to produce CO and CH4 and oxidation of acetaldehyde to acetic acid followed by decarbonylation to CO2 and CH4. CH4 (C2H6 and C3H8 also) can form via Fischer–Tropsch reactions of CO/CO2 with H2. The CH4 (C2H6 and C3H8) reacts to form hydrogen and carbon monoxide through steam reforming, while CO converts to CO2 mostly through the water-gas shift reaction (WGSR). The SG catalysts showed poorer WGSR activity than the SCS catalysts. The difference of the metal particle size distribution governed by preparation method appeared to be the key factor of controlling catalytic efficiency, but some contradictory results could not be explained.In this paper, we report the microstructural and phase compositional differences of the catalysts imposed by the variation of the preparation methods. The XRD analysis, TEM characterization, and H2-pulse chemisorptions showed that the SG samples sintered and metal particles grew during heat treatment and catalytic reaction, but for the SCS samples these changes are much less severe under similar conditions. N2 adsorption/desorption analysis showed that the used SCS(10%) catalyst contained a mesoporous structure of higher pore volume and the SG(%10) catalyst contained macro pores of smaller pore volume. The X-ray photoelectron spectroscopy (XPS) analysis of the used samples demonstrated less coke deposition and less bulk spinel formation on the SCS(10%) sample than that on the SG(10%) sample. These factors may be responsible for higher water gas shift activity in the SCS(10%) sample than that in the SG(%10) catalyst. For the CM(10%) sample, the large particle size and low dispersion of metal on the support were responsible for lower EtOH conversion, H2 & CO2 selectivity, and TOF values. Additionally, the XPS data showed that the SCS(2%) and SG(2%) catalysts have more bulk spinel than the 10% Ni samples and for SCS(2%) sample this is the highest. This diminishes the advantages of smaller Ni particle sizes and less C deposition for them, and explains the apparently anomalous kinetic results observed in the first part of the paper.

Ru4 + ion in CeO2 (Ce0.95Ru0.05O $_{\bf 2-\boldsymbol\delta})$ : A non-deactivating, non-platinum catalyst for water gas shift reaction

Hydrogen is a clean energy carrier and highest energy density fuel. Water gas shift (WGS) reaction is an important reaction to generate hydrogen from steam reforming of CO. A new WGS catalyst, Ce1 − xRuxO2 − δ (0 ≤ x ≤ 0.1) was prepared by hydrothermal method using melamine as a complexing agent. The Catalyst does not require any pre-treatment. Among the several compositions prepared and tested, Ce0.95Ru0.05O2 − δ (5% Ru4 + ion substituted in CeO2) showed very high WGS activity in terms of high conversion rate (20.5 μmol.g − 1.s − 1 at 275°C) and low activation energy (12.1 kcal/mol). Over 99% conversion of CO to CO2 by H2O is observed with 100% H2 selectivity at ≥ 275°C. In presence of externally fed CO2 and H2 also, complete conversion of CO to CO2 was observed with 100% H2 selectivity in the temperature range of 305–385°C. Catalyst does not deactivate in long duration on/off WGS reaction cycle due to absence of surface carbon and carbonate formation and sintering of Ru. Due to highly acidic nature of Ru4 + ion, surface carbonate formation is also inhibited. Sintering of noble metal (Ru) is avoided in this catalyst because Ru remains in Ru4 + ionic state in the Ce1 − xRuxO2 − δ catalyst. A novel Ru ion substituted CeO2, Ce0.95Ru0.05O2-δ, synthesized by hydrothermal method showed, nearly 100% CO conversion in the WGS reaction with conversion rate 20.5 μ mol.g-1.s-1 at 275°C and activation energy 12.1 kcal/mol.

Sour water–gas shift reaction over Pt/CeO 2 catalysts

Ceria-supported catalysts with 0.38–2.0 wt.% Pt have been studied under high-temperature water–gas shift (WGS) conditions with and without 20 ppm H 2S present, which is a typical level in feed streams for WGS reactors in IGCC power plants. The effect of H 2S on CO conversion decreased with increasing temperature in the range 573–723 K and also with increasing Pt content. A 1 wt.% Pt catalyst exhibited excellent stability during a 300 h test at 673 K and GHSV = 7500 l kg −1 h −1 in an H 2S-charged feed with steam-to-CO ratio 2 as CO conversion remained stable around 73%. This was still close to the corresponding thermodynamic limit of 78.8%, which was reached under sulfur-free conditions. The Pt ionization degree in WGS-tested catalysts increased only slightly with the H 2S addition as the Pt 2+ fraction grew from ca. 40% to 50% and the Ce oxidation states remained similar too. The bimodal pore structure of the mesoporous CeO 2 was also retained after WGS experiments although the effective surface area had declined by nearly 20% following the 300 h test in sour syngas. This and the concomitant decline of surface OH groups were likely caused by adsorption of H 2S and subsequent formation of surface sulfates and thus responsible for lowering the WGS activity of the ceria surface in the presence of H 2S. We propose that Pt centers can mitigate this effect through hydrogen spillover in their vicinity thus maintaining a high WGS activity of these catalysts in sour syngas.

Chemical Reaction Engineering and Catalysis Issues in Distributed Power Generation Systems

Three issues are most critical in fuel processors which are integrated with polymer electrolyte membrane (PEM) fuel cells for power generation: the steam reformer configuration, which must ensure very rapid heat transfer to the reformation zone, the development of highly active catalysts for the water−gas shift (WGS) reaction and the development of highly selective catalysts for the methanation reaction. The heat-integrated wall reactor (HIWAR), in either the tubular or the plate form, which offers very rapid heat exchange between a combustion and a reformation zone, is proposed. This configuration results in high efficiency and compact design. Platinum catalysts supported on a “reducible” metal oxide such as TiO2 exhibit high WGS activity, which can be further improved with the addition of alkali or alkaline earth promoters. Titania-supported ruthenium catalysts are capable of completely and selectively methanate CO in the presence of excess CO2, provided that catalyst characteristics are optimized and operating conditions are properly selected. Integration of the three developments can result in efficient power generation systems.

Structural effects of Na promotion for high water gas shift activity on Pt–Na/TiO 2

Sodium (1–10 wt.%)-promoted 1 wt.% Pt/TiO 2 catalysts were prepared by a co-impregnation method and tested for the water gas shift (WGS) reaction under differential reaction conditions. Significantly higher intrinsic activity is achieved with 2–4 wt.% Na addition, when 2–4 layers of NaO x are deposited on the support and the Pt particles are partially covered by NaO x , with moderate surface basicity and exposed Pt surface areas. In addition to the physical coverage, XPS data suggest that interactions between Pt and NaO x may occur by Pt electron donation to O in NaO x through Pt–O–Na. The strong metal–promoter interactions provide highly active sites for the WGS reaction at the periphery of the Pt–NaO x interface and also inhibit Pt particles from sintering. Optimal 4 wt.% Na (Na/Pt = 34) improves the intrinsic reaction rate and turnover frequency of Pt/TiO 2 at 300 °C by 8 and 11 times, respectively, and appears to be significantly higher than reported in the literature. The catalysts were characterized by X-ray diffraction, N 2 adsorption, CO chemisorption, transmission electron microscopy, H 2 temperature-programmed reduction, CO 2 temperature-programmed desorption, and X-ray photoelectron spectroscopy.

Ultra‐Low‐Temperature Water–Gas Shift Catalysis using Supported Ionic Liquid Phase (SILP) Materials*

Ultra‐Low‐Temperature Water–Gas Shift Catalysis using Supported Ionic Liquid Phase (SILP) Materials*

Hydrogen production by water–gas shift reaction over bimetallic Cu–Ni catalysts supported on La-doped mesoporous ceria

Water–gas shift reaction was investigated over a series of Ni, Cu and Cu–Ni bimetallic catalysts supported on La-doped mesoporous ceria. The catalysts were characterized by powder X-ray diffraction (XRD), high-temperature XRD (HTXRD), transmission electron microscopy (TEM), N 2 adsorption analysis, and H 2 temperature-programmed reduction (TPR). Combined results of powder XRD, HTXRD and TPR studies provided evidence of the formation of CuNi alloys in the CuNi/CeLaO x bimetallic catalysts. The catalytic activity of supported Cu–Ni catalysts was evaluated in the water–gas shift (WGS) reaction at 150–400 °C. The effects of the Cu/Ni ratio on the physicochemical properties and the catalytic performance were examined. The presence of copper in bimetallic catalysts resulted in suppression of undesirable methanation side-reaction, while the Ni component was important for high WGS activity. These findings strongly suggested that the bimetallic Cu–Ni compositions are highly promising as WGS catalysts.

Effect of ceria on the desulfation characteristics of model lean NO x trap catalysts

Using model powder catalysts and fully formulated monolithic lean NO x trap (LNT) catalysts, the effect of ceria on LNT desulfation behavior was investigated. TPR experiments performed on the model catalysts showed that each of the oxide phases present (BaO, CeO 2, and Al 2O 3) is able to store sulfur and that they possess distinct behavior in terms of the temperatures at which desulfation occurs. For a Pt/BaO/Al 2O 3 catalyst, addition of ceria was found to reduce the degree of sulfur accumulation on the BaO phase, particularly at high sulfur loadings, by contributing to sulfur capture. The importance of maintaining the Pt and Ba phases in close proximity for efficient LNT desulfation was also demonstrated; physically separating the Pt and Ba sites resulted in a shift of the desulfation temperature of the surface BaSO 4 by 20–40 °C towards higher temperature, i.e., towards the position characteristic of bulk BaSO 4. From the monolith studies, it was found that relative to a sample containing no ceria, samples containing La-stabilized CeO 2 or CeO 2–ZrO 2 showed a greater resistance to deactivation during sulfation (as reflected by the NO x storage efficiency), and required lower temperatures to restore the NO x storage efficiency to its pre-sulfation value. In addition to the ability of ceria to store sulfur and release it at relatively low temperatures under reducing conditions, these findings can be attributed to the high water–gas shift activity displayed Pt/CeO 2, which result in increased intra-catalyst concentrations of H 2 under rich conditions. The results also showed that precious metal loadings can significantly impact desulfation efficiency and that both high Rh and Pt loadings are beneficial for catalyst desulfation.