High Temperature Water-gas Shift Catalyst Research Articles

Design of Cr-Free Promoted Copper-Iron Oxide-Based High-Temperature Water-Gas Shift Catalysts.

The effect of Ce addition to the Cr-free Al-promoted Cu-Fe oxide-based catalysts is investigated. Catalyst characterization (X-ray diffraction (XRD), in situ Raman spectroscopy, high-sensitivity low-energy ion scattering (HS-LEIS), Brunauer-Emmett-Teller (BET) analysis), CO-temperature-programmed reduction chemical probing, and steady-state WGS activity reveal that (i) in the absence of Al, Ce addition via coprecipitation has a detrimental effect on the catalytic activity related to the poor thermostability and formation of less active Ce-Cu-O NPs, (ii) the addition of Ce via coprecipitation also does not improve the performance of the CuAlFe catalyst because of the formation of a thick CeOx overlayer on the active Cu-FeOx interface, and (iii) impregnation of Ce onto the CuAlFe catalyst exhibits significant improvement in catalytic performance due to the formation of a highly active CeOx-FeOx-Cu interfacial area. In summary, Al does not surface-segregate and serves as a structural promoter, while Ce and Cu surface-segregate and act as functional promoters in Ce/CuAlFe mixed oxide catalysts.

Water-gas shift reaction in ceramic-carbonate dual-phase membrane reactor at high temperatures and pressures

Water-gas-shift (WGS) reaction is a critical step in integrated gasification combined cycles (IGCC) power plants with CO2 capture. Membrane reactors made with a CO2-permselective ceramic-carbonate dual-phase (CCDP) membrane offers the potential to enhance hydrogen yield with simultaneous CO2 capture for WGS reaction. The present work studies operation of WGS reaction in a tubular membrane reactor made of samarium-doped ceria infiltrated with lithium/sodium molten carbonate mixture. The WGS reaction was performed in the membrane reactor with and without a high-temperature WGS catalyst at 800–850 °C, feed pressure of 7 bar, the space velocity of 150–3000 h−1, and a feed gas mixture of 45.7/13.1/41.3 mol% CO/CO2/N2 with steam to carbon ratio of 4. The results show that the catalyst-free membrane reactor can convert 92% of carbon monoxide into CO2 and H2 and recover 29% CO2 at 850 °C and a space velocity of 150 h−1. However, in the catalyst-free membrane reactor, a significant amount of unwanted carbon deposition is observed. The side reactions can be minimized by reducing the operating pressure and increasing the operating temperature and space velocity, and completely avoided using a high-temperature catalyst at space velocity>500 h−1. The membrane reactor with a WGS catalyst achieves CO conversion of about 85%, above the equilibrium conversion, and 40% CO2 recovery without carbon deposition at high temperature and pressure. The membrane remains in the same structure and gas-tightness after the WGS reaction tests.

Alkali promoted zinc-aluminum oxide as high temperature water gas shift catalyst

A new kind of high-temperature water gas shift catalyst based on K-promoted ZnO/ZnAl2O4, introduced by Haldor Topsøe as SK-501 Flex™, has begun to replace the well-known Fe/Cr oxide catalysts in the industry. In this research article, we focus on optimization of the catalyst system, especially on promotion with alkali metals and on structural characterization using X-ray diffraction. The promotional effect of the alkali metals increases in the order Li < < Na < < Cs < Rb < K. With K, a 20-fold increase of the mass-based intrinsic rate constant compared to an un-promoted sample is observed. The optimum in the K-content, 2.1 wt%, corresponds to a surface concentration of 0.0057 mmol/m2 or 0.0059 mmol/m2 if K only decorates the ZnAl2O4 spinel surface. This coverage coincides with the surface concentration of Al vacancies on the dominating spinel (111) facet, the so-called kagome layer, with a coverage of 0.00586 mmol/m2. Potassium decoration of the spinel surface is corroborated by FTIR studies of promoted and un-promoted samples in a CO atmosphere. The promotion by potassium is both structural, inhibiting growth of the spinel crystals as evidenced by XRD and BET surface area measurements, but also electronic since the activity per surface area strongly increases on K-promotion. Finally, our studies include long term tests of thermal stability and tolerance towards H2S.

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.

The role of chromium in iron-based high-temperature water-gas shift catalysts under industrial conditions

Chromium promotion of iron oxide based water-gas shift (WGS) catalysts prepared via co-precipitation/calcination was investigated. Mössbauer spectroscopy and XRD evidence that chromium is incorporated in the calcined hematite (α-Fe2O3) precursor irrespective of the doping level (0−12 wt.%). CO-TPR shows chromium delays the reduction of hematite and the active magnetite (Fe3O4) phase. WGS activity was evaluated under realistic conditions for 4 days. Enhanced CO conversion was observed with increased chromium doping. Mössbauer spectra indicate that chromium incorporates into octahedral sites of magnetite and prevents reduction of Fe3+ to Fe2+ during formation of the active phase, leading to an increased Fe3+/Fe2+ ratio in octahedral sites. The higher Fe3+/Fe2+ ratio did not affect the high CO conversion associated with the structural stabilization mechanism of Cr-doping. Interpretation of the Mössbauer spectra was supported by computational modelling of various chromium and vacancy-doped magnetite structures. The bulk structure of an in situ prepared chromium-doped high-temperature WGS catalyst is best described as a partially oxidized chromium-doped magnetite phase. No surface effects of Cr-doping were found.

Ecofriendly K-decorated ZnO/Zn(Al,La)2O4 catalyst for hydrogen production – Effect of heterostructure on catalyst activity at steam‐lean process gas

The effect of ZnAlLa-LDHs calcinations temperature on physicochemical and catalytic properties of K-decorated Zn-Al-La mixed oxides for water-gas shift reaction was investigated. The fresh and spent catalysts were characterized using various methods including XRF, N2 adsorption, TG/DTG/MS, XRD, FT-IR, STEM-EDS and HRTEM. Catalysts activity tests were carried out in high-temperature water-gas shift (HT-WGS) reaction in kinetic regime within the temperature range of 330–400 °C and H2O/dry gas molar ratio in the range of 0.5–1. The relationship between the structural, surface morphology of catalysts and the activity in the HT-WGS reaction was studied. The presence of ZnO-Zn(AlLa)2O4 heterostructure decorated with potassium species enhances HT-WGS activity. Calcinations of ZnAlLa-LDH precursor at mild conditions creates a favorable morphology of the surface and results in relatively high activity similar to the standard HT-WGS catalyst (Fe-Cr-Cu). The highest activity in the HT-WGS reaction at lower steam/dry gas ratios was obtained for the ZnAlLa_600_K.

High Temperature Water Gas Shift Reactivity of Novel Perovskite Catalysts

High temperature water-gas shift (HT-WGS) is an industrially highly relevant reaction. Moreover, climate change and the resulting necessary search for sustainable energy sources are making WGS and reverse-WGS catalytic key reactions for synthetic fuel production. Hence, extensive research has been done to develop improved or novel catalysts. An extremely promising material class for novel highly active HT-WGS catalysts with superior thermal stability are perovskite-type oxides. With their large compositional flexibility, they enable new options for rational catalyst design. Particularly, both cation sites (A and B in ABO3) can be doped with promoters or catalytically active elements. Additionally, B-site dopants are able to migrate to the surface under reducing conditions (a process called exsolution), forming catalytically active nanoparticles and creating an interface that can strongly boost catalytic performance. In this study, we varied A-site composition and B-site doping (Ni, Co), thus comparing six novel perovskites and testing them for their HT-WGS activity: La0.9Ca0.1FeO3-δ, La0.6Ca0.4FeO3-δ, Nd0.9Ca0.1FeO3-δ, Nd0.6Ca0.4FeO3-δ, Nd0.6Ca0.4Fe0.9Ni0.1O3-δ and Nd0.6Ca0.4Fe0.9Co0.1O3-δ. Cobalt and Nickel doping resulted in the highest activity observed in our study, highlighting that doped perovskites are promising novel HT-WGS catalysts. The effect of the compositional variations is discussed considering the kinetics of the two partial reactions of WGS-CO oxidation and water splitting.

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.

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.

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 (&lt;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.

The Effect of Preparation Method on Ni/Ce/Al Catalyst for High Temperature Water-Gas Shift Reaction

High temperature water gas shift (HT-WGS) is an important catalytic process connected with reforming process in hydrogen production. Ni/CeO2-Al2O3 (or Al2O3) catalysts were studied in this work on the effect of catalyst preparation method toward the physicochemical properties and the HT-WGS activity. Ni/CeO2-Al2O3 were prepared by sol-gel and impregnation methods whereas Ni/Al2O3 was prepared by impregnation method. The catalyst samples were characterized by XRD, H2-TPR and H2-TPD techniques. The catalytic activities of HT-WGS catalysts was demonstrated at 550°C, GHSV of 2x105 mLh-1gcat-1and steam-to-CO ratio of 3. Nickel was detected as a nickel aluminate phase in the calcined catalyst. Ni strongly interacted with support in the calcined catalyst prepared by sol-gel method. The strong metal-support interaction can be resisted by preparing catalyst via impregnation and CeO2 can promote the H2O dissociation in HT-WGS mechanism. The highest metal dispersion, largest metal surface area and greatest HT-WGS activity were consequently achieved by Ni/CeO2-Al2O3 prepared from impregnation method.

A perspective on chromium-Free iron oxide-based catalysts for high temperature water-gas shift reaction

Recent efforts to replace toxic hexavalent chromium oxide in commercial copper-chromium-iron oxide catalysts for the High-Temperature Water-Gas Shift (HT-WGS) reaction are reviewed. Advances in understanding the fundamentals of the HT-WGS reaction catalyzed by copper-chromium-iron oxide reveal that the role of chromium is to act as textural promoter to stabilize the surface area of the iron oxide phase towards sintering. The lack of in situ/operando spectroscopic characterization of the bulk and surface phases of the newly designed promoted catalysts, however, severely hampers a thorough understanding of the chemical states as well as the exact role of the non-Cr promoters. Future research studies will need to perform in situ/operando spectroscopy studies to fill this void to allow for the rational design of advanced HT-WGS catalysts.

Promotion Mechanisms of Iron Oxide-Based High Temperature Water–Gas Shift Catalysts by Chromium and Copper

The Cr and Cu promotion mechanisms of high temperature water–gas shift (HT-WGS) iron oxide catalysts, synthesized by coprecipitation, were investigated as a function of reaction conditions. XRD and in situ Raman characterization showed that the initial calcined catalysts consisted of the Fe2O3 (hematite) bulk phase and transformed to the Fe3O4 (magnetite) phase during the HT-WGS reactions. In situ NAP-XPS and HS-LEIS surface analysis revealed that Cr was surface enriched as Cr6+ for the initial catalyst and reduced to Cr3+ during the HT-WGS reactions, with the Cr3+ dissolving into the bulk iron oxide lattice forming a solid solution. In situ NAP-XPS, XANES, and HS-LEIS characterization indicated that Cu was initially present as Cu2+ cations dissolved in the Fe2O3 bulk lattice and reduced to metallic Cu0 nanoparticles (∼3 nm) on the external surface of the iron oxide support during the HT-WGS reactions. In situ HS-LEIS surface analysis also suggests that ∼1/3 of the surface of the Cu nanoparticles was cove...

Chromium free high temperature water–gas shift catalyst for the production of hydrogen from waste derived synthesis gas

A comparative study between monometallic (Me−CeO2, Me=Zn, Cu, Fe and Co) and Ni-doped bimetallic (Me−Ni−CeO2) catalysts has been performed in the high temperature water-gas shift (HT−WGS) reaction using waste derived synthesis gas. Experimental results revealed that Me−Ni−CeO2 exhibited higher catalytic performance than simple Me−CeO2 catalysts. Within the Me−Ni−CeO2 series, Co−Ni−CeO2 exhibited excellent and stable catalytic performance (CO conversion>90%) at a very high GHSV of 143,000h−1. The existence of high concentration of Ce3+ ions and oxygen vacancies on the catalyst surface were responsible for the increased WGS activity of Co−Ni−CeO2. In addition, Co−Ni−CeO2 maintains a stable performance for 50h. However, commercial Fe2O3-Cr2O3 catalyst showed a steep decline from their initial CO conversion values 15–10% within 5h.

Development of a new bi-functional steam reforming/water-gas shift catalyst for production of hydrogen in a membrane reactor

Two bi-functional catalysts were developed and experimentally tested at 550 °C and atmospheric pressure to determine the activity for both steam reforming of methane (SRM) and water-gas shift (WGS) reactions. The compositions of the catalysts are 0.8wt%Cu-3.0wt%Ni (CR1) and 2.4wt%Cu-1.5wt%Ni (CR2) supported on CeO2–La2O3 (Ce/La = 2.33). The feed gases consist of CH4/H2O = 1:2.8 for SRM and CO/H2O = 1:3 for WGS reaction. The catalysts used in this study have been more active for both reactions on an active site basis than their counterpart commercial catalysts. The CH4 conversion rate increases by 128% over CR1 and by 36.7% over CR2 respectively, compared with that of the commercial reforming catalyst (RR) for SRM. Also, the CO conversion rate increases by a factor of 8.4 over CR1 and 3.7 over CR2 respectively, compared with that of the commercial high temperature water-gas shift catalyst (HT2) for WGS. The good dispersion of Cu and Ni species in the CeO2–La2O3 support and their interaction with the support could contribute to their enhanced performance.

ChemInform Abstract: Iron‐Based Catalysts for the High‐Temperature Water‐Gas Shift (HT‐WGS) Reaction: A Review

AbstractReview: 173 refs.

Iron-Based Catalysts for the High-Temperature Water–Gas Shift (HT-WGS) Reaction: A Review

This article critically reviews the literature on iron-based catalysts for the high-temperature water–gas shift (HT-WGS) reaction. The reaction mechanism, reaction intermediates, rate-determining step, kinetics, active site, and promoters are covered. Unlike the low-temperature water–gas shift (LT-WGS) reaction by Cu/ZnO catalysts that has received intensive analysis with modern in situ and operando spectroscopy and DFT studies, the corresponding HT-WGS reaction by Fe-based catalysts still lacks a fundamental understanding because of the absence of modern catalysis studies of this important catalytic system. Given the role of the WGS catalysts on production of H2 for a hydrogen economy, it is imperative that the fundamental molecular-level understanding of the HT-WGS catalyst be advanced.

High-temperature Water–Gas Shift catalysts for hydrogen enrichment of a gas produced by biomass steam gasification

To improve the hydrogen content of a biomass steam gasification syngas, Water–Gas Shift Fe/CeO 2 catalysts supported on ceramic foams were developed. The impregnation of ceria as washcoat led to an increase in the support surface area (BET) and to the formation of well-dispersed iron particles (XRD and TPR) by iron oxide impregnation. Catalytic tests were performed at atmospheric pressure with minor pressure drops, under a gas mixture similar to that produced at the gasifier outlet. A satisfactory CO conversion and a large increase in H 2 content were reached by adjusting the operating parameters of the WGS and the catalysts’ composition. After-test characterizations indicated in situ catalysts activation with no over-reduction and a positive action of ceria on iron dispersion and sintering prevention. Des catalyseurs de Water–Gas Shift Fe/CeO 2 supportés sur mousses céramiques ont été développés afin d’améliorer la teneur en hydrogène d’un gaz de synthèse produit par vapogazéification de la biomasse. L’imprégnation d’un washcoat de cérine a conduit à une augmentation de la surface spécifique du support (BET) et à la formation de particules de fer bien dispersées (DRX et TPR) par imprégnation d’oxyde de fer. Des tests catalytiques ont été réalisés à pression atmosphérique avec des pertes de charge minimes sous un mélange gazeux similaire à celui produit dans le gazéifieur. Une bonne conversion du CO et une large augmentation de la teneur en H 2 ont été atteintes en ajustant les paramètres opératoires du WGS et la composition des catalyseurs. Les caractérisations après test ont indiqué une activation in situ du catalyseur sans sur-réduction et une action positive de la cérine sur la dispersion du fer et la prévention du frittage.

Synthesis of copper promoted high temperature water–gas shift catalysts by oxidation–precipitation

Copper promoted high temperature water–gas shift catalysts were directly synthesized in the active phase (Fe3O4) through an oxidation–precipitation (oxiprecipitation) method, avoiding the usual reduction step used to activate the catalyst in the conventional method based on coprecipitation. They were characterized using X-ray diffraction, X-ray fluorescence, infrared spectroscopy, adsorption–desorption of N2 at 77 K, transmission electron microscopy and temperature programmed reduction. Their catalytic activity was also studied. The results indicated that the materials obtained through this new synthesis method exhibited higher catalytic activity than the commercialized catalysts. Furthermore, the addition of copper improved the catalytic performance of oxiprecipitated Fe–Cr materials, increasing the reducibility of the sample and its stability under reaction conditions.