Catalysis Of Water Gas Shift Reaction Research Articles

Catalysts for water–gas shift processing of coal‐derived syngases

AbstractAlthough the gasification of coal is an efficient means of producing syngas, the carbon content of coal is such that gasification produces significantly higher ratios of carbon oxides to hydrogen than those obtained by the steam reforming of natural gas. The CO:H2 ratio can be adjusted, and more hydrogen produced, by the subsequent application of the water–gas shift (WGS) reaction. This article presents a review of technologies associated with the catalytic WGS reaction in a fixed‐bed reactor that might be incorporated into a coal gasification‐based system for H2 production with CO2 capture. The main output from this review is the identification of key project areas requiring further research. The performance of existing, commercially available catalysts—designed for use in natural gas reforming processes—with coal‐derived syngases is an important aspect of developing technologies for coal‐based H2 production. This article presents an experimental assessment of the performance of selected commercially available WGS catalysts, two high‐temperature catalysts (HT01 and HT02) and a sour shift catalyst (SS01), with such syngases. For the three commercial catalysts investigated in this study, CO reaction order is found to be in a range of 0.75–1. The effect of changes in H2O concentration over HT01 is insignificant, whereas H2O reaction orders determined using HT02 and SS01 are found to be significantly positive even at high H2O:C ratios. The CO conversion rate is significantly reduced by increasing CO2 concentration, whereas increasing H2 concentration also causes a slight reduction in CO conversion rate for the three commercial catalysts investigated. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Investigation of the effect of total pressure on performance of the catalytic water–gas shift reaction using simulated coal-derived syngases

Abstract The effect of operating pressure on the water–gas shift (WGS) reaction rate over an iron-based high-temperature catalyst, and a Co–Mo based sour-shift catalyst, was investigated using simulated coal-derived syngas at 450 °C. For both catalysts, it was found that the CO conversion rate depends linearly upon total operating pressure. The apparent reaction orders used in a power-law rate expression, where the reaction orders were derived from experimental results at atmospheric pressure, are valid at elevated pressures up to at least 11 bar.

Hydrogen generation from a catalytic water gas shift reaction under microwave irradiation

A new device with microwave irradiation has been developed to trigger hydrogen generation from a water gas shift reaction (WGSR) in this study. In the experiments, the effect of a high-temperature catalyst on the WGSR is investigated. The results indicate that the increase of hydrogen generation tends to slow down once the gas hourly space velocity (GHSV) decreases and approaches 28,000 h −1. When the steam/CO ratio is low, for example, steam/CO = 1, a concave up curve of CO concentration, characterized by conventional heating methods, is not observed a microwave irradiation environment. This comparison shows that the performance of the WGSR with microwave irradiation is better. It is noted, however, that cracks may occur on the catalyst surface as a result of less water to relieve the high thermal gradient, stemming from the microwave radiation on the catalyst bed. With an increase in the reaction temperature or steam/CO ratio, a smoother increase in CO conversion is observed, as opposed to those observed in conventional heating methods. This is attributed to the fact that the energy absorption by steam and the catalyst is more efficient under the effects of microwave radiation. As a whole, this study shows that the microwave reactor heats faster, provides more efficient energy transfer to reactants and minimizes the space needed to achieve the desired results.

H2 enrichment from synthesis gas by Desulfotomaculumcarboxydivorans for potential applications in synthesis gas purification and biodesulfurization

Desulfotomaculum carboxydivorans, recently isolated from a full-scale anaerobic wastewater treatment facility, is a sulfate reducer capable of hydrogenogenic growth on carbon monoxide (CO). In the presence of sulfate, the hydrogen formed is used for sulfate reduction. The organism grows rapidly at 200 kPa CO, pH 7.0, and 55 degrees C, with a generation time of 100 min, producing nearly equimolar amounts of H(2) and CO(2) from CO and H(2)O. The high specific CO conversion rates, exceeding 0.8 mol CO (g protein)(-1) h(-1), makes this bacterium an interesting candidate for a biological alternative of the currently employed chemical catalytic water-gas shift reaction to purify synthesis gas (contains mainly H(2), CO, and CO(2)). Furthermore, as D. carboxydivorans is capable of hydrogenotrophic sulfate reduction at partial CO pressures exceeding 100 kPa, it is also a good candidate for biodesulfurization processes using synthesis gas as electron donor at elevated temperatures, e.g., in biological flue gas desulfurization. Although high maximal specific sulfate reduction rates (32 mmol (g protein)(-1) h(-1)) can be obtained, its sulfide tolerance is rather low and pH dependent, i.e., maximally 9 and 5 mM sulfide at pH 7.2 and pH 6.5, respectively.

Char-Supported Nano Iron Catalyst for Water-Gas-Shift Reaction: Hydrogen Production from Coal/Biomass Gasification

This paper reports a novel char-supported nano iron catalyst prepared from the pyrolysis and gasification of iron-loaded Victorian brown coal. The catalyst samples were examined using X-ray diffraction and TEM. Iron is highly dispersed in the char matrix as magnetite with a particle size smaller than 50 nm. The catalyst is found experimentally to be very active for the water–gas-shift reaction at temperatures as low as 300°C. A conceptual process is proposed for the integrated catalytic production of hydrogen based on the gasification of solid fuels such as coal and biomass. Within the proposed process, the char-supported nano Fe catalyst in a moving-bed reactor has the potential to carry out integrated functions of chemical heat pumping, hot gas cleaning, pollutant (particularly NH3 and H2S) abatement and water–gas-shift reaction catalysis.

Theoretical Study of the Gas-Phase Fe(CO)5 Catalyzed Water Gas Shift Reaction: A New Mechanism Proposed

A novel mechanism for the gas-phase Fe(CO)(5) and base catalyzed water gas shift reaction has been examined. The reaction pathway described here is predicted at the B3LYP/6-31++G(d,p) level to be energetically competitive with the classic mechanism. The reaction path explored here involves the energetically barrierless formation of (CO)(4)FeCOOH(-) (the catalyst of the system) decarboxylation induced by the addition of CO to give (CO)(4)FeCHO, and evolution of H(2) upon addition of H(2)O to the (CO)(4)FeCHO intermediate. The energetic barriers predicted for the last two steps are 21.2 and 42.0 kcal/mol, respectively, using the B3LYP method.

English

Hydrogen has been considered a potential fuel for the future since it is carbon-free and oxidized to water as a combustion product. Bioconversion of synthesis gas to hydrogen was demonstrated in a continuous fermentation utilizing malate as a carbon source.Rhodospirillum rubrum, an anaerobic photosynthetic bacterium catalyzed water gas shift reaction which was used in this research. The synthesis gas (CO) was used as a source of energy along with tungsten light supplied for growth and bioconversion of the photosynthetic bacteria. The microbial process in fermentation media was carried out in continuous culture to observe the effect of light intensity, agitation and liquid dilution rate on hydrogen production. The maximum hydrogen yield at 500 rpm was 0.65 mmol H2/mmol CO. Desired media flow rate was preferable for high hydrogen production. At 0.65 ml/min media, hydrogen was produced at 7.2 mmol/h. This new approach, use of biocatalyst, can be considered as an alternative method to the conventional Fischer Tropsch synthetic reactions, which were able to convert synthesis gas into hydrogen.   Key words: Hydrogen, syngas, continuous bioreactor, Rhodospirillum rubrum, light intensity, agitation rate and flow rate.

Photoacoustic measurements of water–gas shift reaction on ferric oxide catalyst

A photoacoustic spectroscopic (PAS) technique was applied to the kinetic study of the water–gas shift reaction in the presence of α-Fe 2O 3 catalyst. The catalytic reaction was performed in the temperature range from 523 to 673 K at various partial pressures of carbon monoxide and water–vapor in a closed-circulation reactor system using a differential photoacoustic cell. The variation of CO 2 photoacoustic signal with the concentration of CO 2 produced during the reaction was recorded as a function of time. The time-resolved photoacoustic spectra obtained for the early reaction stage provided precise data of CO 2 formation rate. The results of CO 2 photoacoustic spectra indicated that the catalytic water–gas shift reaction over α-Fe 2O 3 occurred when α-Fe 2O 3 was partially reduced to Fe 3O 4 by heating it in vacuum. The vacuum-pretreated α-Fe 2O 3 catalyst showed catalytic activity for the water–gas shift reaction and its rate of CO 2 formation increased with increasing temperature in this temperature range. The rate of CO 2 formation on the vacuum-activated α-Fe 2O 3 catalyst was highly enhanced when the catalyst was treated in situ with H 2O(g) prior to the admittance of CO(g)/H 2O(g) reaction mixture. The reaction orders determined from the initial reaction rates of CO 2 formation were found to be 0.80 and 0.08 with respect to CO and H 2O, respectively. From the experimental results, the active sites and the reaction mechanism for the water–gas shift reaction on the vacuum-activated α-Fe 2O 3 catalyst could also be discussed.

Ferrofluid catalyzed water gas shift reaction to give carbon-dioxide and hydrogen

A ferrofluid consisting of colloidally dispersed magnetite particles in water was found to be an efficient selective catalyst for water gas shift reaction at 15–25 atmosphere of CO pressure in the temperature range of 423–553 K where the products obtained were only CO2 and H2. The reaction was studied as a function of variation of the concentration of catalyst, pressure of CO gas and temperature. Kinetic parameters suggested a mechanism involving first order dependence in CO and catalyst concentrations.

Synthesis of arylacetic acid derivatives from mandelic acid derivatives by hydrogen transfer from H 2OCO catalyzed by a [formula omitted] system

A Pd CHCl catalytic system is highly active and selective in the hydrogen transfer from H 2OCO to ArCHOHCOOH for the synthesis of ArCH 2COOH (Ar is para substituted with a OH group). Typical reaction conditions are: temperature 50–70°C; P CO 20–80 atm; solvent; acetonitrile; substrate/Pd/HCl/H 2O = 200–400/1/25–100/500–2000; [Pd] = 0.6−1.2 mmol·l −1. The reaction rate is approximately of the first order with respect to ArCHOHCOOH. The yield increases with the increasing of P CO and of the temperature, as expected, and passes through a maximum with the increasing of the concentration of H 2O and of HCl. The proposed catalytic cycle proceeds through the following steps. (i) H 2O and CO interact with the metal giving rise to an intermediate having a PdCOOH moiety, which, upon β-hydride abstraction, gives off CO 2 with formation of a PdH species. (ii) The starting substrate is in equilibrium, in the presence of HCl, with the corresponding chloride ArCHClCOOH, which adds to the metal forming an intermediate having a PdCH(Ar)COOH moiety. (iii) This species interacts with the hydride yielding the product ArCH 2COOH and regenerating the catalyst. The reaction is compared to the closely related catalyzed water gas shift reaction.

Reactant-Promoted Reaction Mechanism for Water-Gas Shift Reaction on Rh-Doped CeO 2

Reactant-promoted reaction mechanism for catalytic water-gas shift reaction (WGSR) on Rh-doped CeO 2, including the activation of intermediate by a reactant, has been investigated by FT-IR. The intermediate of WGSR on Rh/CeO 2 is bidentate formate produced from CO and terminal (on-top) surface OH groups on Ce ions: 65% of the surface formates decomposed to -OH + CO (backward decomposition) and only 35% of them decomposed to H 2 + CO 2 (forward decomposition) in vacuum. In the coexistence of second-adsorbed water molecules, almost 100% of the formate decomposed to H 2 + CO 2. Besides the direct change of decomposition selectivity, the rate constant of the forward decomposition and the activation energy were surprisingly affected by water coadsorption. The rate constant increased one hundred times and the activation energy decreased from 55.6 to 33.3 kJ mol −1. The rate-determining step for catalytic WGSR on Rh/CeO 2 is the decomposition of the bidentate formate to H 2 and unidentate carbonate. The desorption of CO 2 by the decomposition of unidentate carbonate was also promoted by H 2O coexistence. The phenomena observed on Rh/CeO 2 are entirely different from those on pure CeO 2 and similar to the case of ZnO surface. The reactant-promoted reaction mechanism for WGSR is illustrated.

Homogeneous catalysis of water-gas shift reaction in emulsions

The homogeneous catalysis of the water-gas shift reaction, H 2O + COH 2 + CO 2,has been demonstrated for a number of metal carbonyl complexes under alkaline conditions in toluene-water emulsions. Mo(CO) 6, W(CO) 6 and Ru 3(CO) 12 were found to be effective catalysts at temperatures below 200 °C. Activity of Ru 3(CO) 12 is about 20 times higher than Mo(CO) 6 and W(CO) 6. The effect of process parameters on hydrogen production catalysed by Mo(CO) 6 was studied in some detail. Hydrogen production was found to increase with increasing KOH concentration. Also, hydrogen production increased with increasing Mo(CO) 6 concentration up to 0.04 M and then decreased. Hydrogen turnover number increased with increasing CO loading pressure in the range of 1–3.1 MPa, remained practically constant in the range of 3.1–4.1 MPa and decreased with increasing CO loading pressure from 4.1 to 6.2 MPa. The effect of CO on hydrogen production could be explained by a postulated mechanism involving equilibrium formation of formate ion which reacts with Mo(CO) 5 in a rate determining step to generate a metalloformate, Mo(CO) 5HCOO −. Hydrogen production increased with increasing solvent polarity. Solvent effect is attributed to the stabilization of charged intermediate species.

Reactant-promoted reaction mechanism for water-gas shift reaction on ZnO, as the genesis of surface catalysis

The behavior of reaction intermediates in the catalytic water-gas shift reaction (WGSR) on ZnO surfaces has been studied by means of FT-IR spectroscopy, and a reactant-promoted mechanism including intermediate-reactant interaction is proposed. On-top (terminal) hydroxyl groups on Zn ions which are formed by the first-adsorbed water molecules react with CO to produce bidentate and bridge formates. Seventy percent of them were decomposed to original CO and surface hydroxyls and only 30% of them were converted to Hz and CO 2 (adsorbed) under vacuum. On the contrary, 100% of the formates were converted to the WGSR products, H2, and CO, in coexistence with second-adsorbed water molecules. The rate of the formate decomposition was promoted by a factor of more than 10 by the presence of a second water molecule. The activation energy of the decomposition of the surface formates decreases in the presence of water; 155 kJ mol −1 under vacuum and 109 kJ mol −1 with ambient water. The rate-determining step of the decomposition is the scission of the C-H bond of the formates according to isotope effects. In the absence of ambient water vapor, adsorbed CO, species exist as unidentate carbonate and carboxylate on ZnO surface. At room temperature most of CO 2 (ad) exist as carboxylate, and the population of unidentate carbonate increases with an increase in temperature. When the second water molecule coexists on the surface, carboxylate converts into unidentate carbonate. The surface carbonate and carboxylate were thermally stable even at 680 K by themselves, whereas they begin to desorb at room temperature in the coexistence of the adsorbed water. Steady-state rate of catalytic WGSR agree with the decomposition rates of the bidentate formate and the unidentate carbonate; the two decomposition rates are balancing during the steady-state WGSR on ZnO. Water molecules not only act as a reactant to form the formate, but also activate the bidentate formate(ad) to decompose to H 2 and unidentate carbonate(ad) and promote the desorption of the carbonate as CO 2.

Reactant-promoted reaction mechanism for catalytic water-gas shift reaction on MgO

The behavior of reaction intermediates in the catalytic water-gas shift reaction (WGSR) on the MgO surface was studied by means of FT-IR spectroscopy. The hydroxyl groups on top of coordinatively unsaturated Mg atoms reacted with CO to produce three kinds of surface formates of unidentate, bidentate, and bridge types in the order bridge > unidentate > bidentate. Unidentate-type formate was produced at room temperature and decomposed at ca. 450 K. The formation and decomposition of bridge- and bidentate-type formates proceeded at higher temperatures (ca. 400 and 550 K, respectively). In the presence of adsorbed water, unidentate-type formate changed into bridge-type formate and hence most formates are bridge type under reaction conditions. Contrary to previous reports, formate intermediates were never converted to HZ and CO 2 in the absence of H 2O. While all the formates decompose to CO and surface OH by themselves, adsorbed water promoted the decomposition of formates to the WGSR products HZ and CO 2 through electronic interaction between the adsorbed water and the formate. The reaction rate of WGSR at steady state agreed with the decomposition rate of the bridge-type formate intermediate to HZ and CO 2 in the presence of water.

On the mechanism of the chromium carbonyl photocatalyzed watergas shift reaction

The chromium hexacarbonyl catalyzed watergas shift reaction is accelerated by UV irradiation and inhibited by increased CO pressure. An activation energy of 30 kJ mol −1 has been determined for the photochemical and one of 145 kJ mol −1 for the thermal reaction. Light accelerates the conversion of Cr(CO) 6 into [Cr(CO) 5 formate] −, which is thermally activated, as evidenced by in situ IR and UV spectroscopy.

Kinetics of the chromium hexacarbonyl and tungsten hexacarbonyl catalyzed water gas shift reaction: photoinitiated formate decomposition as a probe of the catalytic cycle

Kinetics of the chromium hexacarbonyl and tungsten hexacarbonyl catalyzed water gas shift reaction: photoinitiated formate decomposition as a probe of the catalytic cycle

Activation of water molecule. 5. Rhodium(I) hydride catalyzed water gas shift reaction. Identification of the elemental reactions comprising the catalytic cycles

Rhodium(I)-hydrido compounds serve as catalyst precursors for the water gas shift (wgs) reaction active under relatively mild conditions (> 50/sup 0/C). The key intermediates appear to be trans-RhH(CO)L/sub 2/ (L = P(i-Pr)/sub 3/) and trans-Rh(OH)(CO)L/sub 2/ (L = P(c-C/sub 6/H/sub 11/)/sub 3/) which in pyridine is in equilibrium with the solvated form (trans-Rh(CO)(py)L/sub 2/)OH (L = P(i-Pr)/sub 3/; L = P(c-C/sub 6/H/sub 11/)/sub 3/). The formation of the solvated forms was shown to proceed through oxidative addition of H/sub 2/O to give (RhH/sub 2/(py)/sub 2/L/sub 2/)OH (step 1) and subsequent reaction of the adduct with CO releasing H/sub 2/ (step 2). H/sub 2/ evolution from the water adduct (RhH/sub 2/(PEt/sub 3/)/sub 3/)OH requires more drastic conditions (80/sup 0/C) and takes place through an intermediate (RhH/sub 2/(CO)(PEt/sub 3/)/sub 3/)/sup +/. Alternatively, the catalyst precursors may react first with CO to give a Rh(0) compound such as Rh/sub 2/(CO)/sub 3/(P(i-Pr)/sub 3/)/sub 3/ and Rh/sub 2/(CO)/sub 4/L/sub 2/ (step 3). Then, these carbonyl compounds react with H/sub 2/O with concomitant evolution of H/sub 2/ (step 4). Under a CO atmosphere trans-RhH(CO)L/sub 2/ is produced through a nucleophilic attack of OH/sup -/ to the coordinated CO to give Rh(CO/sub 2/H)(CO)L/sub 2/ as a transientmore » species (step 5), followed by decarboxylation (step 6). As the wgs reaction proceeds, another cycle becomes important. The cycle is comprised of the reaction with CO/sub 2/-H/sub 2/O to give Rh(OCO/sub 2/H)(CO)(P(i-Pr)/sub 3/)/sub 2/ and H/sub 2/ (step 7), transformation into Rh/sub 2/(..mu..-OCO/sub 2/)(CO)/sub 2/(P(i-Pr)/sub 3/)/sub 4/ (step 8), and hydrolysis.« less

Oxidation of Carbon Monoxide by Metal Ions and Homogeneous Catalysis of the Water Gas Shift Reaction and Related Processes

Abstract A variety of metal ions and complexes oxidize CO in aqueous solution through mechanisms that differ in detail but have in common the involvement of an intermediate hydroxycarbonyl complex (MCOOH). Such oxidation reactions can also be incorporated into various catalytic cycles including the homogeneously catalyzed water gas shift reaction.