WGS Reaction Research Articles

A direct in situ observation of water-enhanced proton conductivity of Eu-doped ZrO2: Effect on WGS reaction

Eu-doped ZrO2 solid solutions have been synthesized in order to prepare proton conductors as water-enhancer additives for the WGS reaction. Elemental characterization has been carried out revealing homogeneous dopant distribution resulting in fluorite-type solid solutions for Eu2O3 contents up to ∼9 mol.%. Representative samples of the Eu-doped ZrO2 series have been analysed by Impedance Spectroscopy (IS) in inert, oxygen and wet conditions. The solid solution with 5 mol.% of Eu2O3 has presented the highest conductivity values for all tested conditions indicating an optimal amount of dopant. Moreover, the presence of vapour pressure results in an increment of the conductivity at temperatures lower than 300 °C, meanwhile at higher temperatures the conductivity is the same than that in inert conditions. To elucidate these results, in situ DRIFTS studies were carried out. These experiments evidenced the existence of water dissociation at oxygen vacancies (band at 3724 cm−1) as well as the presence of physisorbed water at temperatures up to ∼300 °C where the band at 5248 cm−1 characteristic of these species disappeared. These results points to a layer model where the physisorbed water interacts with surface hydroxyls generated by dissociated water that improves the proton conductivity through Grotthuss’ mechanism in the RT-300 °C temperature range. These samples were successfully tested in WGS reaction as additive to a typical Pt-based catalyst. The presence of the mixed oxide reveals an increase of the catalyst’ activity assisted by the proton conductor, since improves the water activation step.

Role of fixed carbon and metal oxides in char during the catalytic conversion of tar from RDF gasification

The catalytic activity of char (fixed carbon + metal oxides) recovered from a commercial waste gasification plant and char-derived ash (metal oxides only) from the oxidation of the char (i.e. the controlled oxidation of the amorphous carbon in the char) was investigated for the cracking and steam reforming of tar. The latter was obtained following the soxhet extraction of sludge collected during a cleaning process (water scrubbing) on primary syngas. The tar was evaporated along with water in an evaporator maintained at 650 °C and entrained by a nitrogen flow. Tar in the gas phase was sent to a reformer where cracking + reforming tests were carried-out at 900 °C and 1 bar using char and char-derived ash pellets as catalysts. These catalysts were characterized using TGA, AE, XRD, SEM, EDX, XRF, ICP-MS, BET and Matersizer. Char-derived ash and char both hold similar metals and mineral structures. Following a 2 h conditioning at 900 °C, the fixed carbon in the char exhibited a larger surface area and pore volume while the char-derived ash revealed larger particle from the merging of vicinal minerals. No metal evaporation was observed after 24 h at 900 °C. During cracking and reforming, the initial 2–6 rings tar mixture extracted from the gasification residues sludge, loaded in the stream of nitrogen + steam at 65 g/Nm3, was reduced to 173.3 and 90.2 mg/Nm3, when using char-derived ash and char respectively. Pure syngas (CO + H2) was produced as the only permanent gases while carbon deposition was noticed in the solid beds. Even though the extent and type of tar were essentially similar when char and char-derived ash were used, the kinetics to reach steady state were slower for the char-derived ash. Steam content did not seem to impact on the tar conversion. However WG and WGS reactions most probably occurred, which might contribute to modulate the H2/CO molar ratio in the produced gas according to its targeted downstream utilization.

Catalytic properties of cobalt-promoted Pd/HAP catalyst for CO-cleanup of H2-rich stream

The promoting effect of Co addition on the behaviour of the Pd/HAP system in WGS reaction has been investigated. Hydroxyapatite-supported bimetallic PdCo samples have been prepared by two consecutive impregnation steps with solutions of Co and Pd precursors, respectively. The resulting catalysts have been thoroughly characterised by BET, XRD, H2-TPR, XPS, OSCC and OSC techniques.The progressive addition of cobalt drives to an abundance of the Pd species exhibiting an intimate contact with Co and an eminent enhancement of the redox properties of the Pd/Co(x)/HAP catalysts. This results in an improvement of their performance in WGS reaction. The Pd species presenting an intimate contact with cobalt seems to be the responsible of the improvement of the CO conversion. However, this PdCo interaction leads to an increase in the methanation activity at the expense of WGS activity. When small amounts of O2 is added to the WGS mixture, the activity is exclusively enhanced in the presence of Co species exhibiting easier reducibility.

Pt/CePO4catalysts for the WGS reaction: influence of the water-supplier role of the support on the catalytic performance

CePO4supports enhance the WGS catalytic performance of Pt catalysts through the supplying of water, which depends on the crystallographic structure of the support.

CO2 formation mechanism in Fischer–Tropsch synthesis over iron-based catalysts: a combined experimental and theoretical study

Our investigation has unveiled that the Boudouard reaction rather than the WGS reaction plays a predominant role in CO2 formation over iron-based FTS catalysts.

CFD modeling of the influence of carrier thermal conductivity for structured catalysts in the WGS reaction

This work describes a CFD modeling study of the Water Gas Shift single stage process in adiabatic conditions, operated by COMSOL Multiphysics 5.0, by means of two different catalytic configurations; the real novelty was to show that the use of structured catalysts with high thermal conductivity could greatly improve the performances of the whole process. The simulations are then validated with kinetic data reported in a previous work, and provides a useful springboard for the design of a single stage process. It was demonstrated that the use of highly conductive carriers reduces the difference of temperature throughout the catalytic bed, under adiabatic conditions, by means of a backdiffusion of the heat of reaction from the output to the input of the bed. The redistribution allows to increase the inlet temperature, with a benefit for the kinetics, at the expence of the outlet temperature that, decreasing, promotes the thermodynamics. The use of a highly active catalytic formulation, at low temperatures, coupled with a conductive carrier, provides, in principle, the possibility to realize a strong intensification of the process.

Optimum operating conditions in ethanol steam reforming over a Ni/La2O3-αAl2O3 catalyst in a fluidized bed reactor

This manuscript analyzes the steam reforming of ethanol (SRE) over a Ni/La2O3-αAl2O3 catalyst in a fluidized bed reactor under a wide range of operating conditions (500–650°C, space time up to 0.35gcatalysth/gEtOH, and steam/ethanol (S/E) molar ratio in the feed between 3 and 9) in order to select optimum conditions for maximizing H2 production. The significance the individual reactions in the reaction mechanism have on products distribution and the role of the catalyst in the extent of these reactions has also been analyzed. Blank runs (without catalyst) have been performed to test the contribution of thermal routes to this mechanism. Ethylene and acetaldehyde are intermediate products in the kinetic scheme, whose presence is only observed when ethanol conversion is not full. The increase in temperature enhances the reforming and decomposition of ethanol and acetaldehyde and, when the catalyst is used, CH4 reforming and reverse WGS reactions are also promoted, so that the yield of H2 and CO increases, that of CH4 decreases and the one of CO2 remains almost constant with temperature. The increase in S/E molar ratio increases H2 yield, but attenuates the rate of some reactions involved in the process. 600°C, a space time of 0.35gcatalysth/gEtOH and S/E=6 are suitable conditions for maximizing ethanol conversion (100%) and H2 yield (82%) with high catalyst stability.

Membrane-based reactive separations for process intensification during power generation

We present here a study of the water gas shift membrane reactor (WGS-MR) in the context of its potential application in the IGCC process for power generation from coal. In our research, we use in the WGS-MR a sour-shift WGS catalyst and carbon molecular sieve (CMS) membranes, and show that the reactor displays higher conversions than a conventional packed-bed reactor (PBR) under the IGCC-relevant conditions, i.e., for temperatures up to 300°C and pressures up to 25bar. Our experimental results manifest the ability of the WGS-MR to operate under the desired conditions and to improve the efficiency of the WGS reaction. They demonstrate, in addition, the potential of the MR to carry out the in-situ separation of hydrogen using the CMS membranes. We conclude from our study, that the CMS-membrane-based WGS-MR is a good candidate technology for incorporation into IGCC power plants for environmentally-benign power generation.

Water–Gas Shift Reaction over Ni/CeO2 Catalysts

This paper reports the results of a study of a water–gas shift reaction over nickel–ceria catalysts with different metal loading. Within this study, the overall CO conversion and observed kinetic behavior were investigated over the temperature range of 250–550 °C in different reactor configurations (fixed-bed and microchannel reactors). The quasi-steady state kinetics of the CO water–gas shift reaction was studied for fractions of Ni-containing cerium oxide catalysts in fixed-bed experiments at lab-scale level using a very dilute gas (1% CO + 1.8% H2O in Не). A set of experiments with a microchannel reactor was performed using the feed composition (CO:H2O:H2:N2 = 1:2:2:2), representing a product gas from methane partial oxidation. The results were interpreted using computational models. The kinetic parameters were determined by regression analysis, while mechanistic aspects were considered only briefly. Simulation of the WGS reaction in the microreactor was also carried out by using the COMSOL Multiphysics program.

Kinetic Modeling of the Catalytic Steam Reforming of High-Density Polyethylene Pyrolysis Volatiles

The kinetics of the steam reforming of HDPE pyrolysis volatiles is studied on a Ni commercial catalyst in a fluidized bed reactor in-line with the pyrolysis reactor (a conical spouted bed reactor at 500 oC). Steam reforming reactions have been carried out under the following conditions: 600-700 oC and space time 0-16.7 gcat min gHDPE-1. Based on the composition of HDPE pyrolysis volatiles, a kinetic scheme is assumed with four reactions (C5+ hydrocarbon reforming, C2-C4 hydrocarbon reforming, CH4 reforming and WGS reaction). Moreover, the kinetics of the deactivation has been quantified with an expression dependant on C5+ hydrocarbon concentration (coke precursors). Calculation of the kinetic parameters is conducted by nonlinear multiple regression, fitting the experimental data to those calculated by the mass conservation equations for each component in the reaction medium. The overall kinetic model proposed describes accurately the evolution of the main products (H2, CO2, CO) with time on stream in the ...

Sulfur resistant WGS catalyst for hydrogen production based on CoMo supported by Nb modified MgAl mixed oxide

In this paper, CoMo supported on Nb modified MgAl mixed oxide by calcination of layered double hydroxides (LDHs) were prepared using wet impregnation method. The fresh calcined catalysts were further sulfided by H2S/H2 and tested for water-gas shift reaction (WGSR). The physicochemical properties of fresh calcined catalysts were characterized by various adsorption and bulk techniques like XRD, ICP, N2-physisorption, CO2-TPD, H2-TPR, H2S-TPS and HRTEM. It is found that the addition of Nb does not affect the formation of LDHs, but changes the reduction and sulfidation behavior of Mo species on oxidic catalyst as well as the dispersion of MoS2 phase on the sulfided catalyst. The CoMo/Nb(5%)MgAl catalyst shows the lowest apparent sulfidation activation energy, consumes the highest amount of H2S and thus has the highest catalytic activity in WGS reaction.

Transition metals supported on bone-derived hydroxyapatite as potential catalysts for the Water-Gas Shift reaction

Calcined pork bone which is mainly composed by hydroxyapatite (HAp) was used as catalytic support of transition metals (Ni, Cu, Co, Fe) for WGS reaction. The catalysts were characterised by TGA, ICP, XRD, FTIR, H2-TPR, H2 chemisorption, OSC, CO2-TPD and N2 adsorption. The activity and selectivity was investigated and correlated with the chemical, structural and textural properties of the catalysts. For comparison, the performance of Ni loaded onto synthetic HAp was also investigated. The catalytic activity followed this trend: Ni > Co > Cu > Fe. Interestingly, natural support decreased methanation activity of Ni and increased stability as compared to synthetic HAp.

Preparation and characterization of Ce1−xPrxO2 supports and their catalytic activities

In this work, the addition of praseodymium (Pr) into ceria as a mixed oxide support in a form of Ce1−xPrxO2 (x = 0.01, 0.025, 0.050, 0.075 and 0.10) was prepared using a co-precipitation method. The structural and textural properties of the synthesized supports were characterized by X-ray diffraction (XRD), N2 adsorption–desorption, Raman spectroscopy, H2-temperature programmed reduction (H2-TPR) and H2-chemisorption. Upon addition of Pr, XRD patterns and Raman spectra indicated an enlargement of ceria unit cell and the characteristics Raman broad peak at 570 cm−1 which was attributed to the existence of oxygen vacancies in the ceria lattice. This indicated that some Ce4+ ions in ceria were replaced by larger Pr3+ cations. To evidence the incorporation of Pr3+ cations into ceria lattice, X-ray absorption near edge structure (XANES) was employed. The results showed that the oxidation states of Ce in mixed oxide supports were slightly lower than 4+ while those of Pr were still the same as a precursor salt. Therefore, the incorporation of Pr3+ into ceria lattice would lead to strain and unbalanced charge and result in oxygen vacancies. The reducibility of Ce1−xPrxO2 mixed oxide supports was investigated by H2-TPR and temperature-resolved X-ray absorption spectroscopy experiment under reduction conditions. XANES spectra of Ce L3 edges showed a lower surface reduction temperature (Ce4+ to Ce3+) of Ce0.925Pr0.075O2 than that of CeO2 which agreed with H2-TPR results. H2-chemisorption indicated that Pr promoted the dispersion of the metal catalyst on the mixed oxide support and increased the adsorption site for CO. For WGS reaction, 1% Pd/mixed oxide support had higher WGS activity than 1% Pd/ceria. The increase of WGS activity was due to the increase of Pd dispersion on the support and the existence of oxygen vacancies produced from incorporation of Pr into the ceria lattice.

Identifying the adsorbed active intermediates on Pt surface and promotion of activity through the redox CeO2 in preferential oxidation of CO in H2

A series of non- and modified with niobia and ceria alumina-supported Pt catalysts with different Pt content (0.3–2wt%) were prepared by wetness impregnation method and characterized by N2 adsorption-desorption isotherms, XRD, TPR, DRIFT, in situ EXAFS and ΔXANES. The effect of the content of Pt and promoter on the change of catalyst electronic structure and behaviors in the reaction of preferential oxidation of CO in the presence of H2 was studied. A strong interaction of Pt with CO and O2 in atmospheres of H2/CO and H2/CO/O2 mixtures was detected by ΔXANES. Different steps of activation of reagents molecules were observed. The increase of activity with increasing the Pt content was related to the presence of Pt nanoparticles with high electron density. While, the highest metal dispersion of the low metal-loaded Pt catalyst was responsible for its high CO oxidation selectivity. Addition of ceria to Pt catalysts caused significantly increase of activity and CO oxidation selectivity at lower reaction temperatures. Niobia addition did not improve the catalysts behaviors. The promotion effect of ceria was related to the oxygen mobility at PtOCe interface. The ceria-promoted Pt catalysts with the highest ceria loading of 12wt% exhibited the highest activity and CO oxidation selectivity, but at higher reaction temperatures of about 110°–130°C it was begin slowly to decrease. This was attributed to going on the reverse of WGS reaction and high O2 consumption to H2 oxidation during the PROX-CO reaction on ceria alumina-supported Pt catalysts at high temperatures.

Sorption-enhanced water gas shift reaction for high-purity hydrogen production: Application of a Na-Mg double salt-based sorbent and the divided section packing concept

Hydrogen is considered a promising environmentally benign energy carrier because it has high energy density and produces no pollutants when it is converted into other types of energy. The sorption-enhanced water gas shift (SE-WGS) reaction, where the catalytic WGS reaction and byproduct CO2 removal are carried out simultaneously in a single reactor, has received considerable attention as a novel method for high-purity hydrogen production. Since the high-purity hydrogen productivity of the SE-WGS reaction is largely dependent on the performance of the CO2 sorbent, the development of sorbents having high CO2 sorption capacity is crucial. Recently, a Na-Mg double salt-based sorbent has been considered for high-temperature CO2 capture since it has been reported to have a high sorption capacity and fast sorption kinetics. In this study, the SE-WGS reaction was experimentally demonstrated using a commercial catalyst and a Na-Mg double salt-based sorbent. However, the SE-WGS reaction with a one-body hybrid solid, a physical admixture of catalyst and sorbent, showed poor reactivity and reduced CO2 sorption uptake. As a result, a divided section packing concept was suggested as a solution. In the divided section packing method, the degree of mixing for the catalyst and sorbent in a column can be controlled by the number of sections. High-purity hydrogen (<10ppm CO) was produced directly from the SE-WGS reaction with divided section packing, and the hydrogen productivity was further improved when the reactor column was divided into more sections and packed with more sorbent.

Glycerol Steam Reforming for Hydrogen Production over Nickel Supported on Alumina, Zirconia and Silica Catalysts

The aim of the work was to investigate the influence of support on the catalytic performance of Ni catalysts for the glycerol steam reforming reaction. Nickel catalysts (8 wt%) supported on Al2O3, ZrO2, SiO2 were prepared by the wet impregnation technique. The catalysts’ surface and bulk properties, at their calcined, reduced and used forms, were determined by ICP, BET, XRD, NH3-TPD, CO2-TPD, TPR, XPS, TEM, TPO, Raman, SEM techniques. The Ni/Si sample, even if it was less active for T <600 °C, produces more gaseous products and reveals higher H2 yield for the whole temperature range. Ni/Zr and Ni/Si catalysts facilitate the WGS reaction, producing a gas mixture with a high H2/CO molar ratio. Ni/Si after stability tests exhibits highest values for total (70%) and gaseous products (45%) glycerol conversion, YH2 (2.5), SH2 (80%), SCO2 (65%), H2/CO molar ratio (6.0) and lowest values for SCO (31%), SCH4 (3.1%), CO/CO2 molar ratio (0.48) among all samples. The contribution of the graphitized carbon formed on the catalysts follows the trend Ni/Si (I D /I G = 1.34) < Ni/Zr (I D /I G = 1.08) < Ni/Al (I D /I G = 0.88) and indicates that the fraction of different carbon types depends on the catalyst’s support nature. It is suggested that the type of carbon is rather more important than the amount of carbon deposited in determining stability. It is confirmed that the nature of the support affects mainly the catalytic performance of the active phase and that Ni/SiO2 can be considered as a promising catalyst for the glycerol steam reforming reaction.

Facile hydrothermal procedure to synthesize sheet-on-sheet reduced graphene oxide (RGO)/CuxO[sbnd]CeO2 nanocomposites for preferential oxidation of carbon monoxide

The sheet-on-sheet reduced graphene oxide (RGO)/CuxOCeO2 catalysts were synthesized by a facile hydrothermal procedure and systematically characterized by X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy, hydrogen temperature-programmed reduction, X-ray photoelectron spectroscopy and N2 adsorption–desorption techniques. It is found that there is a large amount of reduced copper species in the RGO/CuxOCeO2 catalysts, and the addition of RGO was beneficial for the dispersion of particles and the improvement of textural properties. The spherical nanoparticles of copper species can be served as spacers to prevent the stacking of RGO. Copper and cerium species are homogenously distributed on the surface of RGO sheets. The introduction of RGO improves the formation of high Ce3+ concentration and oxygen vacancies. Therefore, the RGO/CuxOCeO2 catalysts show higher catalytic activity than the CuOCeO2 catalyst at low temperature (below 135 °C). Moreover, good resistance to H2O and CO2 of the RGO/CuxOCeO2 may be from for the formation of hydroxyl groups by dissociative adsorption of H2O on the surface of RGO, which can improve the WGS reaction and the decomposition of carbonates.

Hydrogen from glycerol steam reforming with a platinum catalyst supported on a SiO2-C composite

This work studies 2 wt% Pt catalysts. The support is a SiO2-C composite whose main features are a high specific surface due to its mesoporosity, a higher thermal stability than the C support, and the absence of surface acid sites which could promote the dehydration reactions that produce coke precursors. The Pt/SiO2-C catalyst has very small metallic particles (dva = 1.37 nm) that favor the CC bond cleavage reactions which allow obtaining total gas conversion at 450 °C. With this catalyst, it is possible to obtain high yields to H2, between 4 and 5, which indicates that the active sites promote the WGS reaction, even with glycerol concentrations of 30 and 50%. Pt/SiO2-C is a very stable catalyst since it loses only 10% of its initial activity after 66 h on stream and is resistant to sintering and coke deposition.

Zinc and platinum co-doped ceria for WGS and CO oxidation

This study presents the synthesis and application of zinc and platinum co-doped ceria for CO oxidation and water gas shift reaction (WGS). To synthesize the catalyst, novel combustion synthesis procedure at pH=10 has been employed, yielding the catalyst in single step without further purification procedures. The catalyst was found to be active under high temperature conditions (>350°C) thus asserting the functionality of the catalyst as single stage WGS catalyst. In this study, we have also developed a dual site redox mechanism to understand the intrinsic kinetics of WGS reaction. For the proposed mechanism, a plausible microkinetic model has been developed for WGS and CO oxidation reactions, respectively. In line with the application of reaction route (RR) analysis to the microkinetic models developed for single site pathway for WGS. In this study, we have extended the RR approach to dual site redox mechanism. From the above analysis, the surface dissociation of OH surface species was found to be rate determining step of the mechanism. The rate expression developed using RR analysis was validated through isothermal plug flow reactor (PFR) model. The PFR simulations predicted the experimental trend for wider range of temperature conditions thus portraying the significance of the microkinetic model developed in this study.

Understanding Active Sites in the Water–Gas Shift Reaction for Pt–Re Catalysts on Titania

Pt–Re clusters supported on titania have shown promise as catalysts for the low temperature water–gas shift reaction. However, the enhanced activity of the bimetallic Pt–Re catalyst versus pure Pt is not well understood. In this work, exclusively bimetallic clusters were grown on TiO2(110) by vapor-deposition of Pt on 2 ML Re clusters and Re on 2 ML Pt clusters. Temperature programmed desorption experiments with CO were used to determine the concentration of Re at the surface, given that CO dissociates on Re but not on Pt. Deposition of 2 ML Pt on 2 ML Re resulted in Re core–Pt shell structures, whereas deposition of low coverages (<0.5 ML) of Re on 2 ML Pt resulted in complete diffusion of Re into the Pt clusters. Both of these Pt on Re bimetallic clusters are thermodynamically favored by the lower surface free energy of Pt compared to Re, and both are also more active than pure Pt clusters in the WGS reaction. Postreaction XPS experiments indicate that Re in the Pt on Re clusters is not oxidized under W...