Temperature Water Gas Shift Catalysts Research Articles

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.

Comparison of a commercial water-gas shift catalyst and La modified Cu-based catalysts prepared by deposition-precipitation in methanol steam reforming.

Herein, a performance analysis of La-doped copper-based catalysts (CuO/ZrO2/La-Al2O3) in methanol steam reforming (MSR) was conducted and compared with a commercial low temperature water-gas shift catalyst (HiFUEL W220) to produce H2 with low CO selectivity. The physicochemical properties of as-obtained catalysts were characterized by N2 adsorption, XRD, and ICP-OES. Effect of calcination temperature (750 °C and 1000 °C) on the properties of mixed oxide support (La-Al2O3) were discussed based on catalytic activity. The optimum conditions of H2O/CH3OH ratio (1.0-3.0), space-time ratio (WFA0) (40-120 kg s mol-1), and reaction temperature (180-310 °C) were evaluated by a parametric study using the commercial catalyst (HF220). Additionally, thermodynamic equilibrium calculations of experimentally identified components by using Aspen HYSYS process simulation software were also performed to analyze MSR process. The results were indicated that the calcination temperature significantly affected the structural properties and the activity with respect to CO selectivity. An increasing trend in CO selectivity for catalysts with supports calcined at 750 °C and a decreasing trend for catalysts with supports calcined at 1000 °C were observed. Hence, CZ30LA750 and CZ30LA1000 catalysts were selected to attain low CO selectivity and comparable activity when compared to other catalysts and the simulated thermodynamic calculation results.

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.

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.

Preparation of high temperature water gas shift catalyst with coprecipitation method in microemulsion system

In this paper nanocrystalline mesoporous iron-based high temperature water gas shift catalysts were prepared by coprecipitation method in water-in-oil (W/O) microemulsion. The prepared samples were characterized by using X-ray diffraction (XRD), N2 adsorption (BET), temperature-programmed reduction (TPR), Fourier transform infrared spectroscopy (FTIR), transmission and scanning electron microscopies (TEM, SEM) techniques. The results revealed that the Fe2O3 possessed low specific surface area and catalytic activity in high temperature water gas shift reaction. The addition of copper to Fe2O3 favored the active phase formation and significantly decreased the reduction temperature of hematite to magnetite and consequently improved the catalytic activity of Fe2O3. The incorporation of chromium in hematite increased the surface area and catalytic activity of Fe2O3. The results also showed that the prepared Fe⿿Cr⿿Cu catalyst showed higher activity than the commercial catalyst. In addition, the effects of GHSV, steam/gas ratio, and calcination temperature were investigated on the catalytic performance of Fe⿿Cr⿿Cu catalyst.

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.

Applying Taguchi robust design to the optimization of the synthesis parameters of nanocrystalline Cr-free Fe–Al–Cu catalyst for high temperature water gas shift reaction

Nanocrystalline Cr-free Fe–Al–Cu catalysts with high surface area and mesoporous structure was prepared by coprecipitation method and employed in high temperature water gas shift reaction. Several parameters such as pH, aging temperature and aging time were optimized by the Taguchi method of experimental design. The sample prepared under optimized conditions showed a high surface area of 208m2g−1, pore size of 3.76nm and theoretical particle size of 5.47nm after calcination at 400°C for 4h. This catalyst illustrated the highest CO conversion compared to other prepared catalysts. These results confirmed that the Taguchi method is an effective method of determining the optimum parameters in preparation process of high temperature water gas shift catalyst. Moreover, the effect of calcination temperature, GHSV and steam/gas ratio on the catalytic performance of optimized Fe–Al–Cu catalyst was investigated.

Structure and activity of flame made ceria supported Rh and Pt water gas shift catalysts

A series of ceria-supported Rh and Pt catalysts was synthesized by flame spray pyrolysis for high temperature water gas shift (WGS) reactions in a membrane reactor. The structural and catalytic properties were compared with a Pt/CeO2 catalyst prepared conventionally by incipient wetness impregnation. BET results show that compared to conventionally prepared catalysts the specific surface area of the flame made catalysts is larger and decreases with increasing metal content. This is in line with X-ray diffraction (XRD) results uncovering a high nanocrystallinity of the ceria, whose crystallite size slightly increases with higher noble metal loading. Both Pt and Rh particles are not detected by XRD due to the small crystallite size. In fact, transmission electron microscopy (TEM) images of the flame made catalysts with high loading showed Pt and Rh particles with diameters of ca. 3nm which remained stable after catalytic testing. X-ray absorption near edge spectra (XANES) at the Rh K- and Pt L3-edge showed that both Pt and Rh were in an oxidized state after preparation. In situ XANES during temperature programmed reduction in 5% H2/He indicated a lower reduction temperature than for the conventional Pt/CeO2 catalyst. Hence, Rh and Pt species are located on the surface of the CeO2 particles. Extended X-ray absorption fine structure (EXAFS) spectra provide further evidence for oxidized Rh, Pt before reduction and full reduction after activation in hydrogen, and small particle sizes in agreement with the TEM and XRD results. The catalytic activity measurements were performed at atmospheric pressure in two different gas mixtures by measuring CO conversion as a function of temperature. In all cases the Pt/CeO2 catalysts prepared by flame spray pyrolysis showed high catalytic activity and much higher selectivity than the Rh/CeO2 catalyst, where methane formation is observed above 300°C. Furthermore, the reaction rate in terms of turnover frequencies is much higher on the Pt-based catalysts, which makes them promising candidates for high temperature WGS catalysts in membrane and microreactors.

Revisiting the synthesis of Au/TiO2 P25 catalyst and application in the low temperature water–gas shift under realistic conditions

The performance of Au/TiO2 P25 synthesized at different pH's (8, 9 and 10) is studied over time-on-stream in low temperature water–gas shift (WGS) at 21bar under semi-industrial conditions. Furthermore, their performance is compared with a commercial CuO/ZnO/Al2O3 low temperature WGS catalyst and AUROlite 1wt.% Au/TiO2 as a reference. Sulfur severely poisons the Au/TiO2 catalyst, which is irreversible over time-on-stream under high pressure (21bar) WGS conditions.The Au/TiO2 P25 catalysts are synthesized using deposition precipitation to a targeted loading of gold close to 1wt.% and are carried at three different pH (8, 9 and 10) under controlled conditions. The influence of parameters such as final pH, rate of addition of basic solution, type of basic solution are discussed. A higher final pH resulted in smaller gold particles deposited on TiO2-P25. The Au/TiO2-P25 catalyst prepared at the higher final pH (pH 10) showed higher WGS activity which relates to the averaged smaller particle size of the gold on TiO2-P25. The Au/TiO2-P25 catalyst prepared at lower final pH (pH of 8) is stable, while the catalysts prepared at pH of 9 and 10 deactivate over 130h timeon stream.

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.

Rapid synthesis of magnetite catalysts incorporated with M (Cu, Ni, Zn, and Co) promoters for high temperature water gas shift reaction

A rapid one step direct synthesis of high temperature water gas shift (HT-WGS) catalysts, magnetite incorporated with various promoters like Cu, Ni, Zn, and Co, has been shown. The key achievements in this work, in terms of catalyst preparation, are as follows: (1) direct synthesis of magnetite, a catalytically active phase in HT-WGS reaction, (2) easy incorporation of various transition metal promoters like Cu, Ni, Zn, and Co, (3) rapid preparation without any washing step by using an ample amount of solvent, and (4) a simplified procedure by avoiding longer digestion time and any specific pH value. To achieve this, an amino acid, glycine, was used as a complexing agent as well as a fuel for the auto-combustion process. The zwitterionic nature of glycine favors the easy incorporation of the promoter metal ions. In addition, the reducing atmosphere created by glycine during its burning makes it possible to prepare magnetite directly. During the HT-WGS reaction, the activity follows the order Cu-FAG > Ni-FAG > Zn-FAG > Co-FAG. The optimization of the Cu promoter is also carried out. At 12.5 mol% of Cu loading the catalytic activity reached a CO conversion value of 87% at 400 °C.

A kinetic study on the structural and functional roles of lanthana in iron-based high temperature water–gas shift catalysts

The structural and functional roles of varying amounts of lanthana in co-precipitated high temperature Fe2O3/Cr2O3/CuO water–gas shift catalysts were studied at 1 atm and 350–425 °C temperature range.Addition of 0.5 wt% of lanthana enhanced the reducibility of the catalyst, increased its surface area and its WGS activity from 24 to 31 mmol CO/(gcat min), and reduced the deactivation rate at 400 °C from 23% to 11% relative to a similar catalyst with no lanthana. XRD results suggested that 0.5 wt% of lanthana stabilized the iron–chromium cubic spinel structure most efficiently under the operating conditions; however, further additions appeared to disrupt the spinel structure and degrade the performance of the catalysts.The power-law and Langmuir–Hinshelwood models provided much better fits to the rate data than either the redox or the Eley–Rideal models, suggesting that the reaction tends to follow an adsorptive mechanism. The CO adsorption equilibrium constant was largest for the catalyst with 0.5 wt% lanthana, indicating that the addition of lanthana might facilitate CO adsorption. Water inhibited the reaction as it strongly adsorbed on the catalyst surface.

Ceria-based palladium zinc catalysts as promising materials for water gas shift reaction

The production of hydrogen for fuel cell applications requires several fuel processing steps, including CO removal by means of the water gas shift (WGS) and CO preferential oxidation reactions. In this work we investigate the behavior of palladium–zinc supported on CeO2, Ce0.5Zr0.5O2 and ZrO2 as a promising alternative to low temperature WGS catalysts for fuel processing. WGS activity is optimized when the PdZn alloy is formed. Ceria-containing materials show little deactivation during startup–shutdown cycles in reformate gas and for palladium–zinc supported on pure ceria the activity can be fully recovered by an in situ reduction treatment.

Effect of the precursor on the activity of high temperature water gas shift catalysts

The conventional catalysts used for high temperature water gas shift reaction are composed of Fe3O4–Cr2O3–CuO. The synthesis method to prepare them affects to their properties and catalytic activity. Moreover, the raw material used during the synthesis has also influence on their performance. In this work, the effect of the precursor on the activity of magnetite-based catalysts prepared by oxidation–precipitation method was studied. Ferrous sulfate and chloride were the precursors selected and the addition of Cu and Co as activity promoters was also studied. The materials prepared with sulfate showed larger crystallite sizes and lower specific surface areas but they were more active and selective than those obtained from chloride. This could be due to a decrease of the surface basicity that improves the reducibility and affects to the hydrogen adsorption and CO chemisorption. Addition of Cu or Co increased the CO conversion for the materials prepared with chloride but not for those prepared with sulfate. In the former case, Cu improved the reducibility of the samples. Cobalt was incorporated into magnetite lattice improving the covalency of Fe2+ ↔ Fe3+ redox couple of magnetite.

A Comparative Density Functional Theory Study of Water Gas Shift Over PdZn(111) and NiZn(111)

PdZn catalysts have been proposed as an alternative to Cu low temperature water gas shift (WGS) catalysts due to their similar reactivity but higher thermal stability. Unfortunately, Pd based alloys are likely to be considerably more expensive than Cu catalysts. Therefore, we explore NiZn as a potentially cheaper alternative to PdZn. Both PdZn(111) and NiZn(111) have similar potential energy surfaces for WGS as previous work on Cu(111) suggesting that they may be effective WGS catalysts. However, unlike PdZn (and Cu), the primary mechanism for WGS shifts from the carboxyl mechanism to a redox mechanism over NiZn(111) (although they are similar in magnitude).

Effect of alkali cations on the CuZnOAl2O3 low temperature water gas-shift catalyst

Low temperature water gas-shift catalysts containing 1.0% by weight of alkali elements (Li, K, Rb and Cs) were prepared by impregnation of a ternary Cu/ZnO/Al2O3 (CZA) base catalyst. The calcined precursors were characterized by different physical and chemical techniques such as X-ray diffraction, X-ray fluorescence, N2O chemisorption, N2 adsorption at low temperature and X-ray photoelectron spectroscopy. Then these precursors were activated and tested in the low temperature water gas-shift reaction (LT-WGS). It was shown that the K-containing CZA catalyst exhibited the highest CO conversion level at reaction temperature within the range 450–530K. In addition, the alkali promoters were found to prevent methanol production at temperatures higher than 480K.

Kinetics of the water-gas shift reaction over a La 0.7Ce 0.2FeO 3 perovskite-like catalyst using simulated coal-derived syngas at high temperature

The kinetics of the water-gas shift (WGS) reaction over a novel La 0.7Ce 0.2FeO 3 perovskite-like catalyst is investigated using simulated coal-derived syngas at temperatures of 550 °C and 600 °C which are higher than the maximum operating temperature limit for conventional high temperature WGS catalysts. The influences of CO, CO 2, H 2O and H 2 concentration on WGS reaction rate are determined using selected gas compositions that might be encountered in a coal-based gasification system. An empirical power-law rate model used in this study is found to correlate well with experimental data with good accuracy. Kinetics parameters over La 0.7Ce 0.2FeO 3 obtained in this study are mostly in agreement with those previously measured using Fe–Cr based commercial catalysts in a range of relatively lower temperatures (300–500 °C).

High temperature water gas shift catalysts with alumina

Alumina (Al 2O 3) was added as a component of conventional iron oxide-based high temperature water gas shift (WGS) catalysts. The catalysts contained Fe–Al–Cr–Cu–O and were synthesized by coprecipitation. A series of catalysts were prepared with 5–50 wt% Al 2O 3, 8 wt% Cr 2O 3, 4 wt% CuO, and the balance Fe 2O 3. One catalyst was prepared in which the chromia was replaced by alumina. All of the catalysts were compared to a reference WGS catalyst (88 wt% FeO x, 8 wt% Cr 2O 3, and 4 wt% CuO) with no alumina. The catalysts were characterized using temperature programmed reduction (TPR), surface area analysis using nitrogen physisorption, and scanning electron microscopy (SEM) with compositional analysis. The catalysts were also tested kinetically under WGS conditions. Addition of 10–15 wt% alumina increased the catalyst activity and thermal stability, with approximately 15 wt% alumina addition being optimum, as this catalyst produced a reaction rate (normalized per mass) 74% higher than the reference catalyst. The effect of alumina addition was greater than the surface area increase alone, which suggests that alumina alters the activity of the iron oxide domains, likely through an increase in reducibility, as shown by the TPR results. This synergistic effect was only observed when both alumina and chromia were present. Alumina alone (as a replacement for chromia) was not as an effective stabilizer as chromia. Although both the alumina-containing catalyst (without chromia) and the reference with chromia had similar initial surface areas (∼160 m 2/g), the alumina-containing catalyst retained only 74% as much surface area after reaction. Results from the catalysts with 50 wt% alumina suggest that the loss of catalytic activity is also due to the formation of aluminates.