Catalytic Water Gas Shift Research Articles

A comparative study of water-gas-shift reaction over ceria supported metallic catalysts

Water-gas-shift (WGS) reaction rates have been measured on Pd/ceria, Ni/ceria, Fe/ceria, Co/ceria, ceria, and Pd/silica. Pd/ceria exhibited much higher activities than either ceria alone or Pd/silica, demonstrating a cooperative effect between Pd and ceria. Pd/ceria and Ni/ceria showed essentially the same activities and were much more active than either Co/ceria or Fe/ceria. Reaction orders on Pd/ceria were approximately zeroth-order in CO, half-order in H 2O, inverse-half-order in CO 2 and inverse-first-order in H 2. Diffuse reflectance, FTIR measurements on Pd/ceria indicate the ceria exists in a reduced state under WGS conditions and is covered by carbonate species that are removed only by reoxidation of ceria. The implications of these results for improved WGS catalysis are 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.

98/01184 Producer gas as a superior cooking fuel: results of emission and efficiency tests: Uma, R. et al. Biomass Energy Syst., Proc. Int. Conf., 1996 (Pub. 1997), 270–275. Edited by Ramana, P. V. and Srinivas, S. N., Tata Energy Research Institute, New Delhi, India

The water-gas shift (WGS) reaction is central to a spectrum of industrially important catalytic processes, ranging from the manufacture of hydrogen to the processing of biomass-derived feedstocks. Recently, oxide-supported Au catalysts have attracted attention for low-temperature WGS reactions, but the role of the Au/oxide interface in promoting this chemistry remains under debate. In this contribution, we combine periodic Density Functional Theory (DFT) calculations, detailed microkinetic modeling, and rigorous kinetic measurements to elucidate the impact of this interface on the molecular-level features of WGS chemistry of a gold nanowire supported on a MgO(1 0 0) substrate. The results demonstrate that the barrier to activate water, which is prohibitively high (∼2 eV) on a clean Au(1 1 1) surface, is decreased to essentially zero at the Au/MgO interface. From the DFT-calculated energetics, a dual-site microkinetic model of the Au/MgO interface is constructed. Rate and thermodynamic control analysis demonstrate both the high degree of kinetic control of COOH formation at the interface and a strong influence of competitive adsorption between CO and H. A procedure to refine the microkinetic predictions by iterative replacement of the energies of kinetically sensitive steps with a higher accuracy hybrid HSE06 prediction is introduced, and the determined effective activation barriers and reaction orders agree well with the results of detailed kinetic measurements on Au nanoparticles on MgO substrates. The results clearly show the critical role that the metal/oxide interface plays in WGS catalysis, and the approach introduced to predict kinetics at the metal/oxide interface should be applicable to a variety of catalytic processes on oxide-supported metal nanoparticles.

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.

A simple model for a water gas shift membrane reactor

A simplified process model was developed to simulate a catalytic membrane water gas shift (WGS) reactor. A number of computer simulations were conducted to determine the potential of increased carbon monoxide (CO) conversion in WGS reaction due to simultaneous separation of product hydrogen (H2) from the reactant mixture. Gas separation factors based on Knudsen diffusion were used in these simulations to assess the feasibility of inorganic and ceramic membranes in a high-temperature, high-pressure (HTHP) coal gasification environment. The simulations indicated that although the increase in CO conversion and hydrogen concentration in a single membrane reactor stage was significant, a multistage membrane separation system would be needed to increase the hydrogen product concentration above 90%. As expected, increasing the feed pressure to permeate pressure ratio was found to increase the CO conversion and the product hydrogen concentration. At low feed to permeate pressure ratios, the model predicted a much better membrane reactor performance with a countercurrent feed and permeate flow scheme when compared with a concurrent flow scheme. The membrane performance, of course, depends strongly on the gas separation factors. With gas separation factors lower than the ideal Knudsen diffusion separation factors (e.g. H2 to CO2 separation factor of 2 instead of the ideal Knudsen value of 4.7), the model simulation predicted a much smaller increase in CO conversion and product hydrogen concentration.

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.

Kinetics of the water gas shift reaction catalyzed by rhodium(III) chloride in aqueous picoline studied by use of a continuous-flow stirred reactor

Described is a kinetics investigation of the homogeneous water gas shift catalysis by rhodium(III) chloride in aqueous picoline solution. These investigations were carried out under flow conditions using a continuous-flow stirred reactor, which allowed the systematic variation of the reaction conditions (P[sub CO], T, flow rate, P[sub tot], [Rh][sub tot]). The catalysis rates proved to be nonlinear in [Rh][sub tot] over the range 3-20 mM, a result which was interpreted in terms of the system having dinuclear and mononuclear rhodium species present, both types of species being catalytically active but the mononuclear cycles being the more reactive. The rates also displayed a nonlinear dependence on P[sub CO] over the range 0.3-1.8 atm, although this was independent of [Rh]. The kinetics behavior with respect to P[sub CO] leads to the proposal of the reversible addition of CO to the catalytically active species prior tothe rate-limiting step in both the mono- and dinuclear catalytic cycles.

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.

A newly proposed cycle for the water gas shift reaction homogeneously catalyzed by platinum and tin chloride

Data previously reported by Cheng and Eisenberg for catalysis of the water gas shift (WGS) reaction by platinum and tin chlorides have been reviewed. A new catalytic cycle for the WGS catalysis that is consistent with more recent studies and the experimental data for the Pt-Sn system is presented. It appears to be likely that the platinum intermediates have the trichlorotin ligand, but the exact nature of the catalytic intermediates is still unknown. 16 refs., 2 figs.

The chemisorption and coadsorption of water and oxygen on Cs-dosed Cu(110)

The adsorption of H 2O and the coadsorption of oxygen and H 2O on Cu(110) containing overlayers of Cs have been studied with thermal desorption mass spectroscopy (TDS), X-ray photoelectron spectroscopy, Auger electron spectroscopy, and work function measurements. On clean Cu(110), H 2O adsorbs at 110 K and desorbs intact at 175 K, with no measurable dissociation probability (< 0.5%). In the presence of Cs a, the heat of adsorption of H 2O is increased by ∼ 50%, and the cleavage of OH bonds during TDS becomes highly probable when θ Cs * exceeds ∼ 0.5 monolayers (i.e., the work-function minimum). In this case, hydrogen adatoms are produced which associatively desorb as H 2 at ∼ 440 K (or ∼ 200 K for Cs multilayers). In addition, a CsOH a species is produced which decomposes at ∼ 510 K., probably via the evolution of gaseous (CsOH) 2 dimers. When Cs a and O a are both present on the surface, the cleavage of OH bonds to produce surface hydroxyl species proceeds already at 110 K, considerably colder than in the presence of either Cs a or O a alone. In addition, Cs a allows the production of approximately twice as much OH a than with O a alone. This OH a desorbs as H 2O at ∼ 350–420 K via the disproportionation reaction 20H a→ H 2O g+O a, considerably warmer than in the absence of Cs. It is postulated that this Cs-induced stabilization of OH a may be responsible for the promotional effect of Cs in water-gas shift catalysis over Cu. While H 2O a has a dipole pointing toward the surface, OH a creates a substantial dipole moment pointing away from the Cu. Upon dosing H 2O to Cs/O/Cu(110), the CsOH a species is also produced, and it decomposes at a slightly higher temperature than in the absence of O a (∼ 500–580 K).

Chemisorption studies on Cs/Cu(110): Model studies of cesium promoters on copper-based catalysts

The adsorption of CO, CO2, and H2 O, the coadsorption of oxygen and H2 O, and the coadsorption of CO and surface hydroxyl (OHa) on clean and cesium-covered Cu(110) surfaces have been studied with thermal desorption mass spectroscopy, x-ray photoelectron spectroscopy, Auger electron spectroscopy, and work function measurements. We review here results which show that the presence of preadsorbed cesium dramatically affects the adsorption behavior and surface chemistry of CO, CO2, and H2 O on Cu(110). We also present new results which show that surface formate (HCOOa) is not produced in any observable amount upon heating coadsorbed COa and OHa on clean or Cs-dosed Cu(110). The implication of these results to Cs promotion of the catalytic water–gas shift and methanol synthesis reactions over Cu will be discussed.

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.

Development of a Catalytic Water Gas Shift Reactor for Fusion Fuel Exhaust Streams

Catalytic reactors based on the water gas shift reaction were designed, built and tested to provide data for the design of a prototype reactor as an alternative to the uranium hot metal beds in a F...

Development of a catalytic water gas shift reactor for fuel exhaust streams

Catalytic reactors based on the water gas shift reaction were designed, built and tested to provide data for the design of a prototype reactor as an alternative to the uranium hot metal beds in a F...

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

Kinetic studies with a sulfur-tolerant water gas shift catalyst

Experimental measurements have demonstrated high water gas shift (WGS) activity for molybdenum sulfide-based catalyst in the presence of hydrogen sulfide. The defect structure of the catalyst, controlled by the sulfur activity in the gas phase, has a dominant effect on the reaction rate. The reaction kinetics are interpreted in terms of Langmuir-Hinshelwood surface reaction. The mechanism is shown to involve a redox cycle with Mo(V) as an important species in WGS catalysis. XPS measurements provide information on the reductive sulfidation of the catalysts from the Mo(VI)-oxide state.

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.

Design, Simulation, and Operation of a Laboratory Recycle Reactor with Controlled Gas Concentrations

TU Braunschweig has designed a relatively simple control system for operating a laboratory recycle reactor so as to establish and maintain specified gas concentrations. This system will enable researchers to perform kinetic investigations using selected values of partial pressures and to uncouple the effects of gas concentrations and catalytic activity upon reaction rates. The design has proved efficient in simulation and in experimental studies of a multiple-reaction system: the simultaneous catalytic methanation and water gas shift reaction. Through this novel experimental approach, some interesting insights into reaction kinetics were obtained and, for the first time, selectivity changes became evident.