Shift Catalysts Research Articles

Surface coverage effects on water gas shift activity of ZrO2 supported Mo sulfide catalysts

ZrO2-supported Mo sulfide water gas shift (WGS) catalysts were prepared by the incipient wetness impregnation method with varying MoO3 surface coverage. TEM, XRD, Raman spectroscopy and XPS characterization revealed the formation of a topmost Mo-S layer and Mo-O subsurface in the ZrO2-supported Mo sulfide catalysts above MoO3 monolayer surface coverage. The CO conversion during WGS reaction over the ZrO2-supported Mo sulfide catalysts increased with Mo content up to the monolayer coverage and correlated with the extent of Mo sulfidation.

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.

Accurate 3D Characterization of Catalytic Bodies Surface by Scanning Electron Microscopy

AbstractCatalytic bodies of millimetric dimensions are frequently used in industrial catalysis. The engineering process applied on the raw nanocatalyst during the fabrication and the working conditions affect the spatial and chemical relations of the exposed surface of the catalytic device. Hence, for improving their synthesis and for monitoring the evolution during its life cycle it is important understanding the actual heterogeneities of their surfaces. In this work scanning electron microscopy, photogrammetry and X‐Ray spectroscopy are combined to perform physico‐chemical characterization in three‐dimensions and with high resolution of the surface of commercial water gas shift catalyst bodies. By analyzing a phase of carbon present on their surface we show that the method provides measurements that are at the same time reliable, accurate and precise.

Strong Metal-Support Interactions between Copper and Iron Oxide during the High-Temperature Water-Gas Shift Reaction.

The commercial high-temperature water-gas shift (HT-WGS) catalyst consists of CuO-Cr2 O3 -Fe2 O3 , where Cu functions as a chemical promoter to increase the catalytic activity, but its promotion mechanism is poorly understood. In this work, a series of iron-based model catalysts were investigated with in situ or pseudo in situ characterization, steady-state WGS reaction, and density function theory (DFT) calculations. For the first time, a strong metal-support interaction (SMSI) between Cu and FeOx was directly observed. During the WGS reaction, a thin FeOx overlayer migrates onto the metallic Cu particles, creating a hybrid surface structure with Cu-FeOx interfaces. The synergistic interaction between Cu and FeOx not only stabilizes the Cu clusters, but also provides new catalytic active sites that facilitate CO adsorption, H2 O dissociation, and WGS reaction. These new fundamental insights can potentially guide the rational design of improved iron-based HT-WGS catalysts.

Strong Metal–Support Interactions between Copper and Iron Oxide during the High‐Temperature Water‐Gas Shift Reaction

AbstractThe commercial high‐temperature water‐gas shift (HT‐WGS) catalyst consists of CuO‐Cr2O3‐Fe2O3, where Cu functions as a chemical promoter to increase the catalytic activity, but its promotion mechanism is poorly understood. In this work, a series of iron‐based model catalysts were investigated with in situ or pseudo in situ characterization, steady‐state WGS reaction, and density function theory (DFT) calculations. For the first time, a strong metal‐support interaction (SMSI) between Cu and FeOx was directly observed. During the WGS reaction, a thin FeOx overlayer migrates onto the metallic Cu particles, creating a hybrid surface structure with Cu‐FeOx interfaces. The synergistic interaction between Cu and FeOx not only stabilizes the Cu clusters, but also provides new catalytic active sites that facilitate CO adsorption, H2O dissociation, and WGS reaction. These new fundamental insights can potentially guide the rational design of improved iron‐based HT‐WGS catalysts.

Oxide supported metal catalysts for the aldehyde water shift reaction: Elucidating roles of the admetal, support, and synergies

There is significant interest in the use of H2O as a reactant for production of commodity chemicals and fuels, in particular from water-laden biomass-derived feedstocks. In this paper, we describe results for the aldehyde water shift (AWS), a reaction where aldehydes are partially oxidized by water to produce the corresponding carboxylic acid and H2, over a series of CeO2-, Al2O3-, and SiO2-supported Cu, Pt, and Au catalysts. The effects of support were further investigated by evaluating the performances of a Cu-Zn-Al water gas shift catalyst and bulk Cu nanoparticles. The supported Cu catalysts were more active than the supported Pt and Au catalysts, and the reducible oxide (CeO2) supported Cu catalyst had the highest AWS activity. The high activity of the Cu/CeO2 catalyst is believed to derive from coupling H2O dissociation and aldehyde oxidation. The two major side reactions, aldol condensation and aldehyde disproportionation, appeared to be catalyzed by acid and Cu sites, respectively. The results indicate that both the admetal and support play critical roles in catalyzing the AWS reaction and provide guidance for the design of highly active AWS catalysts.

The Implication of the Choice between Sour and Sweet Shift on Process Design and Operation of an IGCC Power Plant Integrated with a Dual-Stage Selexol Process

In this study, it was sought to design and evaluate two different process configurations of an IGCC integrated with a dual stage Selexol unit where they differ in that one is based on sour shift and the other is sweet shift (Fig. 1). Depending on the choice of the two water-gas shift reactors, the process configuration undergoes significant changes in steam cycle, syngas cooling and Selexol process, apart from the location of the H2S removal step around the shift reactor. Integrating an IGCC with a pre-combustion capture involves a significant energy penalty. The energy penalty associated with carbon capture integration was mainly due to the power plant demanding a greater heat input for running the same gas cycle. Also the syngas must undergo water-gas shift reaction (WGSR) in order to convert CO to CO2, as the ensuing separation process can capture only CO2 efficiently from the syngas. The WGSR needs a huge amount of steam. The syngas leaving the scrubber already contains some steam, as it leaves the scrubber saturated with water. However more steam has to be added to the syngas to have the water-to-CO ratio around 2, to make sure good CO conversion. The extra steam has to be sourced from the steam cycle. Adding new units of the pre-combustion capture process and CO2 compressors augments the total capital cost and the operation of the CO2 capture and compression units increases the auxiliary power consumption. In turn, the net plant efficiency of the IGCC drops significantly with the cost of electricity rising accordingly. In this study, the whole IGCC power plant was simulated by using Honeywell UniSim based on the DOE study. The IGCC simulation also include a dual-stage Selexol process for pre-combustion capture to estimate the energy consumption involved, similarly to the past researches carried out by the group. It turned out that the sweet shift would give rise to greater reduction of the net power efficiency than the sour shift (Table 1), mainly due to it requiring approximately 4.6 times more shift steam, most of which has to be sourced from the steam cycle. This substantial increase of the shift steam usage involves significant alternation to the steam cycle. From the perspective of the energy penalty, the adverse effect resulting from the need for vast shift steam outweighs the positive aspect of the AGR (Acid Gas Removal) unit of the sweet shift case spending less power. On the other hand, the sour shift catalyst (CoMo) was estimated to have a reaction rate much lower than the sweet shift catalyst (Cu-ZnO) by two orders of magnitude at the condition of the low temperature shift reactor. It was certain that the sweet shift case had to undergo significant energy penalty due to it having to source vast steam from the steam cycle. This is not only because the syngas loses almost all the steam while being cooled for H2S removal, but also it requires a steam-to-CO ratio of water-gas shift reaction greater than it would do in sour shift case. To alleviate these adverse effects, the sweet shift case was designed to generate additional LP steam by recovering the heats from the raw and shifted syngas. Also the auxiliary power expensed in the AGR unit was found to be slightly less, due to the H2S absorber also functioning as a H2S concentrator. The resultant net plant efficiencies of the two cases exhibited that the sour shift case would be more energy-efficient than the sweet shift case by 3.7% points as shown in Table 1. However, the advantage would be compromised to some extent, given that the low temperature sour shift reactor had to be sized larger than the equivalent sweet shift reactor, due to the sour shift catalysts exhibiting lower reaction rates than the sweet catalysts at the condition.

Towards the development of materials for chemically stable carbonate-ceramic membranes to be used for CO2 separation in water-gas-shift reactors

Synthesis gas with a CO/H2 ratio suitable for production of energy carriers, e.g. hydrogen, methanol, and gasoline, can be produced by gasification of solid fuels with subsequent water-gas-shift (WGS) reaction. The separation of CO2 using conventional absorption processes leads to high efficiency losses. In contrast, a membrane reactor containing a catalyst provides the opportunity for significantly reduced efficiency losses.The present work aims at developing a chemically stable membrane for separation of carbon dioxide in gasification atmosphere. The desired membrane consists of two phases, a porous ceramic oxygen ion conductor filled with molten carbonate. Both phases need to be stable under the relevant process conditions, i.e. syngas at up to 800 °C, and compatible with each other and the water gas shift catalyst. The potential oxygen ion conductor materials, e.g. cerium gadolinium oxide (Ce0.8Gd0.2O2-δ) and cerium samarium oxide (Ce0.8Sm0.2O2-δ), which are known from literature to be compatible with alkali carbonate melts, were exposed to different gasification-relevant gas atmospheres at 600–900 °C and subsequently investigated regarding chemical reactions. Furthermore thermodynamic properties of alkali and alkaline earth carbonate systems were studied to identify a mixture with suitable melting behavior and high chemical stability as well as low volatility under relevant syngas conditions.

Thermodynamics of Cu/ZnO/Al2O3 water-gas shift catalyst poisoning on yellow phosphorus off-gas

The thermodynamics of copper-based water-gas shift catalyst for yellow phosphorus off-gas have been calculated according to the thermodynamic theory of heterogeneous reaction systems. The possible chemical reactions and products were analyzed and are discussed here. The results show that AsH3 and S-containing gaseous impurities (H2S, COS, CS2, and SO2) in the yellow phosphorus off-gas can preferentially lead to active CuO poisoning of the catalyst, and the poisoning products are Cu3As and Cu2S. Small amounts of PH3 and P4 were the main cause of the inactivation of the anti-toxic component (ZnO) and the support (Al2O3) in the catalyst. The inactive products were Zn3(PO4)2 and AlPO4, respectively. If yellow phosphorus off-gas is used as the raw material gas for water-gas shift reaction, the As-, S- and P-containing gaseous impurities should be removed to avoid catalyst poisoning.

Structure-activity relationship in water-gas shift reaction over gold catalysts supported on Y-doped ceria

The utilization of pure hydrogen as an energy source in fuel cells gave rise to renewed interest in developing active and stable water-gas shift catalysts. Gold catalysts have proven to be very efficient for water-gas shift reaction at low temperature. The aim of the present study was to investigate the effect of: (i) different preparation methods (impregnation and coprecipitation) to obtain a modified ceria support, and (ii) the amount of Y2O3 (1.0 wt%, 2.5 wt%, 5.0 wt% and 7.5 wt%) as dopant on the water-gas shift activity of Au/CeO2 catalysts. An extended characterization by means of SBET, XRD, HRTEM/HAADF, FTIR, H2-TPR and CO-TPR measurements in combination with careful evaluation of the catalyst behavior allowed to shed light on the parameters governing the water-gas shift activity. The catalysts show very high activity (>90% CO conversion) in the temperature range 180–220 °C, with a slightly better performance of the gold catalysts on supports prepared by impregnation. The decreased activity with increasing Y2O3 concentration is related to the hindering of oxygen mobility due to ordering of surface oxygen vacancies in vicinity of segregated Y3+. The effect of catalyst pre-treatments and the stability of the best performing samples were examined as well.

Two-train elevated-temperature pressure swing adsorption for high-purity hydrogen production

The trade-off between hydrogen recovery ratio (HRR) and hydrogen purity (HP) is one of the main drawbacks in normal temperature pressure swing adsorption (NT-PSA) for producing high-purity hydrogen from shifted gas. In this paper, a two-train elevated-temperature pressure swing adsorption (ET-PSA) process that achieved 99.999% HP and over 95% HRR is proposed, which has wide application potentials in fuel cells and chemical industries. Potassium-promoted layered double oxide (K-LDO), which shows reasonable working capacity and fast adsorption/desorption kinetics at elevated temperatures (200–450 °C), is adopted as the CO2 adsorbent. CO in the shifted gas is co-purified by high-temperature water gas shift (WGS) catalysts added to the columns. The first-train ET-PSA adopted an eight-column thirteen-step configuration with shorter step time to remove most of the CO/CO2 in the shifted gas, and the second-train ET-PSA adopted a double-column seven-step configuration with longer step time to purify the residual gas impurities. The introduction of co-current high-pressure steam rinse and counter-current low-pressure steam purge is the key to achieve both high HRR and HP. The high-temperature steam is the main energy consumption of ET-PSA rather than low HRR in NT-PSA, and the total steam consumption is reduced by adopting the tail gas from second-train ET-PSA as the purge gas for first-train ET-PSA. The optimal results achieved 97.51% HRR and 99.9994% HP with only 0.188 rinse-to-feed ratio and 0.263 purge-to-feed ratio, which are the highest values reported for PSAs producing high-purity hydrogen from carbon-based fuels.

Pd Doped La0.1Sr0.9TiO3 as High-Temperature Water-Gas Shift Catalysts: In-Situ Formation of Active Pd Phase

A series of La0.1Sr0.9Ti1−xPdxO3 with x up to 0.1 were prepared through a modified sol–gel method. Combining X-ray diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS) and Temperature programmed reduction (TPR), we proved that solid solutions formed with a Pd substitution (in the B-sites) of no more than 5 at.%. Further addition of Pd resulted in segregation of PdOx species. An in-depth analysis of in-situ CO adsorption confirmed that the metallic Pd, formed in-situ during the water-gas shift reactions (WGSR), was the major contributor for this reaction.

Elevated temperature pressure swing adsorption process for reactive separation of CO/CO2 in H2-rich gas

Purification of CO and CO2 to the ppm level in H2-rich gas without losing H2 is one of the technical difficulties for fuel cell power systems. In this work, a two-column seven-step elevated temperature pressure swing system with high purification performance was proposed. The concept of reactive separation by adding water gas shift catalysts into the columns filled with elevated temperature CO2 adsorbents was adopted. The H2 recovery ratio and H2 purity were greatly improved by the introduction of steam rinse and steam purge, which could be realized due to the increasing operating temperature (200–450 °C). An optimized operating region to both achieve high efficiency and low energy consumption was proposed. The optimized case with 0.09 purge-to-feed ratio and 0.15 rinse-to-feed ratio could achieve 99.6% H2 recovery ratio and 99.9991% H2 purity at a stable state for a feed gas containing 1% CO, 1% CO2, 10% H2O, and 88% H2. No performance degradation was observed for at least 1000 cycles. The proposed (ET-PSA) system possessed self-purification ability while the columns were penetrated by CO2. It is however suggested that periodical heat regeneration should be adopted to accelerate performance recovery during long-term operation.

Easy alloying on flat carbides

Reactive metal–support interactions are generally considered characteristic of oxide supports. Now, two-dimensional niobium carbide, a member of the MXenes family, has been used as a platinum support providing an active water-gas shift catalyst via reduction-induced formation of stable, catalytically active Nb–Pt nanoparticles.

Revealing structure-activity relationships in chromium free high temperature shift catalysts promoted by earth abundant elements

Finding a replacement for the toxic hexavalent chromium oxide in commercial iron oxide-based high temperature water-gas shift (HT-WGS) catalyst is of current environmental concern. Previous studies in developing Cr-free catalysts mainly focus on ex-situ characterization on catalysts bulk structure. In the present study, CuO/MOx-Fe2O3 catalysts promoted by Si, Al, Cr or Mg were studied with XRD, in situ Raman, HS-LEIS, BET, transient C16O2 → C18O2 isotopic switch, steady-state WGS activity test and CO-TPR to elucidate their structure-activity relationships. The Mg and Al are homogeneously distributed within both fresh and activated catalysts as texture promoters, while the Si exists as discrete SiO2 that is covered by iron oxides. During the HT-WGS reaction, the Mg promoter resulted in the poorest thermally stability and least amount of metal-metal oxide interface, and the Si promoter inhibited the reducibility of surface oxygen. Only the Al promoter was found to yield a catalyst that possessed similar catalyst structure, comparable thermostability and activity with the Cr-promoted catalyst. This work demonstrates the importance of in situ characterization to the rational design of Cr-free iron oxide based HT-WGS catalysts.

In Situ UV-Visible Assessment of Iron-Based High-Temperature Water-Gas Shift Catalysts Promoted with Lanthana: An Extent of Reduction Study

The extent of reduction of unsupported iron-based high-temperature water-gas shift catalysts with small (<5 wt %) lanthana contents was studied using UV-visible spectroscopy. Temperature- programmed reduction measurements showed that lanthana content higher than 0.5 wt % increased the extent of reduction to metallic Fe, while 0.5 wt % of lanthana facilitated the reduction to Fe3O4. In situ measurements on the iron oxide catalysts using mass and UV-visible spectroscopies permitted the quantification of the extent of reduction under temperature-programmed reduction and high-temperature water-gas shift conditions. The oxidation states were successfully calibrated against normalized absorbance spectra of visible light using the Kubelka-Munk theory. The normalized absorbance relative to the fully oxidized Fe2O3 increased as the extent of reduction increased. XANES suggested that the average bulk iron oxidation state during the water-gas shift reaction was Fe+2.57 for the catalyst with no lanthana and Fe+2.54 for the catalysts with 1 wt % lanthana. However, the UV-vis spectra suggest that the surface oxidation state of iron would be Fe+2.31 for the catalyst with 1 wt % lanthana if the oxidation state of iron in the catalyst with 0 wt % lanthana were Fe+2.57. The findings of this paper emphasize the importance of surface sensitive UV-visible spectroscopy for determining the extent of catalyst reduction during operation. The paper highlights the potential to use bench-scale UV-visible spectroscopy to study the surface chemistry of catalysts instead of less-available synchrotron X-ray radiation facilities.

Effect of Ce modification on the structural and catalytic property of Co-Mo/Mg(Al)O catalyst for water-gas shift reaction

A series of Mg-Al-Ce mixed oxides with (nMg2+)/(nCe3+ + nAl3+) = 5 and nCe3+/(nCe3+ + nAl3+) = 0 ∼ 7% were synthesized by co-precipitation method based on a hydrotalcite route and used as support to prepare Co-Mo sulfur-resistant water-gas shift (WGS) catalysts. The supports and catalysts were characterized by XRD, ICP, N2-physisorption, CO2-TPD, H2-TPR, H2S-TPS, TEM, and CO-IR. It is found that the catalytic performance and physicochemical property of the Co-Mo/Mg(Al)O catalyst are significantly influenced by the Ce modification. The addition of Ce effectively enhances the WGS activity and the highest activity is obtained on the Co-Mo/Mg(Al)O-CeO2 (5%) catalyst, where the activity at 623 K increases about 2.5 times. The results of H2S-TPS investigation show that in the presence of Ce, the H2S consumption peak shifts to lower temperatures and there is decrease of Mo sulfidation activation energy. Furthermore, HRTEM analysis shows that the addition of Ce (5%) results in decrease of MoS2 slab length and stacking number, and those of CO-IR characterization indicate increased exposure of surface MoS2 sites. It is suggested that the addition of Ce promotes the formation of MoS2 slabs that are smaller in size, leading to higher exposure of surface active sites and hence higher activity.

Hydrogen-Etched TiO2−x as Efficient Support of Gold Catalysts for Water–Gas Shift Reaction

Hydrogen-etching technology was used to prepare TiO2−x nanoribbons with abundant stable surface oxygen vacancies. Compared with traditional Au-TiO2, gold supported on hydrogen-etched TiO2−x nanoribbons had been proven to be efficient and stable water–gas shift (WGS) catalysts. The disorder layer and abundant stable surface oxygen vacancies of hydrogen-etched TiO2−x nanoribbons lead to higher microstrain and more metallic Au0 species, respectively, which all facilitate the improvement of WGS catalytic activities. Furthermore, we successfully correlated the WGS thermocatalytic activities with their optoelectronic properties, and then tried to understand WGS pathways from the view of electron flow process. Hereinto, the narrowed forbidden band gap leads to the decreased Ohmic barrier, which enhances the transmission efficiency of “hot-electron flow”. Meanwhile, the abundant surface oxygen vacancies are considered as electron traps, thus promoting the flow of “hot-electron” and reduction reaction of H2O. As a result, the WGS catalytic activity was enhanced. The concept involved hydrogen-etching technology leading to abundant surface oxygen vacancies can be attempted on other supported catalysts for WGS reaction or other thermocatalytic reactions.

THE TRANSMISSION AND CIRCULATION OF WESTERN OPERA IN THE NETHERLANDS EAST INDIES, 1835-1869: PRELIMINARY OBSERVATIONS

In October-November 1835 eight French professional performers directed by Ferdinand Minard completed six vaudeville shows in Batavia. The shows were highly acclaimed as they enlivened Batavia’s cultural life dominated by productions and performances by amateur artists. Inspired by the novel experience, local dilettantes were now calling for more professional shows, especially opera. Much to their delight, Minard and his ten some performers returned to Batavia in October 1836, specifically for operas. The second residency of Minard and his troupe marked the first known season of Théâtre-Français (French Theatre) that would continue into the 1860s and beyond under the successor series Théâtre Français de Batavia (French Theatre of Batavia). The arrival of Minard and his performers was a catalyst for a few important shifts in Batavia’s cultural life among European residents. It set in motion a tradition of annual professional and commercial productions by visiting performing artists. Minard’s engagement in 1836 included select performances of Italian opera, which placed Batavia within the emerging world culture of Italian opera. The journeys of Minard and his performers also saw early uses of steamboat and hotels that were antecedent to the age of steam to usher in globally with the opening of the Suez Canal in 1869. By focusing on Batavia, this article makes a fresh contribution to the global study on the transmission and circulation of Western opera in Southeast Asia.

Pr3+ surface fraction in CePr mixed oxides determined by XPS analysis

CePr mixed oxides were previously studied as supports for Water Gas Shift catalysts, considering their promising textural and redox properties arising from the presence of a non-stoichiometric oxide. A very small Ce3+ fraction was observed on those oxides, suggesting that Pr3+ion could be responsible for the enhanced activity. Therefore, in-depth XPS analysis is conducted in the present work in order to determine the Pr3+ fraction by fitting the XPS Pr 3d region. Much higher values of reduced Pr ions than Ce ions were observed, confirming the promoter role of the former.