Dimensionality reduction for predicting CO conversion in water gas shift reaction over Pt-based catalysts using support vector regression models

Removal of CO in fuel cell applications is an important issue. In this study, models based on support vector regression (SVR) along with several dimensionality reduction methods are utilized for predicting the CO conversion in water–gas shift (WGS) reaction. SVR model parameters are determined with a two-stage grid search method and for dimensionality reduction, principal component analysis (PCA), backward feature elimination (BFE) and simulated annealing (SA) methods are used. PCA reduces the dimension by mapping the input data to a lower dimensional feature space. On the other hand, BFE and SA methods finds a subset of features leading to a higher prediction performance. Influence of these methods on prediction performance is investigated by testing the SVR models with and without reducing the dimension. It is observed that all of these methods reduce the prediction error when an appropriate threshold for final number of features is set. Moreover, identical feature subsets are output by BFE and SA methods. In conclusion, it has been shown that some of the features for CO conversion in WGS reaction are more important and using only these features may improve the prediction performance.     

Study of activity and effectiveness factor of noble metal catalysts for water–gas shift reaction

Platinum on ceria-zirconia (CZO) catalysts for the water–gas shift (WGS) reaction were prepared with various platinum loadings. In addition, the activity of Pt/CZO catalysts was tested preliminarily at gas hourly space velocity (GHSV) of 5000 h⁻¹. Activity tests were also conducted at GHSV of 200,000 h⁻¹ with limited conversions, and activation energies and pre-exponential factors for rate equations were obtained by fitting the data. The effectiveness factors were estimated on the basis of the intra-particle mass transfer. Moreover, with this estimation, an attempt was made to calculate the utilization of the Pt loading with an eggshell morphology.     

Syngas production from oxidative methane reforming and CO cleaning with water gas shift reaction

Fuel cell based heat and power cogeneration is considered to be well qualified for a distributed energy system for residential and small business applications. A fuel processing unit including an oxidative steam methane reformer, a high temperature shift reactor and a low temperature shift reactor is under development in South China University of Technology. Performance of the unit is experimentally investigated in a bench-scale experimental setup. Processor performance under typical operating conditions is tested. The influence of reaction temperature, methane space velocity in the oxidative steam methane reformer, and air to carbon molar ratio on unit performances is experimentally studied. It is found that under the typical operating conditions, the total energy efficiency reaches 88.3%. The efficiency can further be improved by utilizing the sensible heat of the reformate gas. The current study has been focused on the chemical performances such as methane conversion of the reformer and CO concentration in the synthesis gas downstream water gas shift reactors. Heat integration of the unit will be further implemented in future to improve energy efficiency.     

DFT study of the enhancement on hydrogen production by alkaline catalyzed water gas shift reaction in supercritical water

Supercritical water gasification (SCWG) is hopefully to be an acceptable choice for hydrogen production, the hydroxide ion assisted water gas shift reaction (WGSR) has been regarded as the most important reaction to generate hydrogen during the process. However, the principle of practical OH^? catalyzed reaction is not possible to acquire by experiments. Thus, density functional theory (DFT) is utilized to investigate the reaction mechanism theoretically in this work. Through first principle calculations, every species and energy barrier for elementary steps are achieved, and formate ion is determined as the important intermediate. Besides, HCOO^? + H₂O → HCO₃^? + H₂ is the dominant path to generate hydrogen, as well as the rate-determining step with 47.94 kcal/mol energy barrier. Furthermore, the reaction rate constant is calculated to be k_catalytic(s^?1) = 2.34 × 10¹²exp(?1.80 × 10⁵/RT) using transition state theory with Wigner transmission coefficient (TST/w). Lastly, supercritical water condition is demonstrated to be a favored media for WGSR, because it may dissociate, dissolve or hydrolyze more hydroxide anion than conventional steam. The results are expected to benefit the control of reaction process and the design of SCWG reactor.     

Performance of copper–ceria catalysts for water gas shift reaction in medium temperature range

A series of copper–ceria catalysts with copper loading in the range of 20–90 at% Cu (=100 × Cu/(Cu + Ce)) were prepared by the method of coprecipitation, and their performance was tested for water gas shift (WGS) reaction in medium temperature condition (150–360 °C). Both fresh and used catalysts were characterized using XRD, H₂-TPR and BET surface area measurements. After the first run, the catalysts stabilized in terms of activity and BET surface area. XRD results of used catalysts confirmed the formation of metallic Cu species during WGS reaction. The WGS activity of ceria catalysts increased with copper loading, and the synergy of copper and ceria was confirmed. Results showed 80 at% copper–ceria had the best performance. The catalysts showed stable activities at 360 °C.     

A novel formulation representation of the equilibrium constant for water gas shift reaction

In order to meet prominent disagreement for the water gas shift reaction (WGSR) equilibrium constant values obtained from various conventional empirical correlations and mitigate the strong dependence on plenty of experimental data points, here, we report a novel WGSR equilibrium constant formulation representation approach with direct algebraic operation, which only involves experimental data of 3–6 molecular constants for each reactants and products and does not contain the fitting of any experimental equilibrium constant data. The reliability of the developed approach is demonstrated by comparing the predicted values with experimentally measured data and the calculated results with other previous WGSR equilibrium constant correlations. The average absolute deviations between the theoretical values predicted from the developed technique and the directly measured data reported in the literature are 3.993%, 5.970%, 2.418%, 2.083%, 8.659%, 3.733%, and 3.755% for 7 experimental data sets, respectively.     

Influence of group IIA metals on the performance of the NiCu/CeO2Al2O3 catalysts in high-temperature water gas shift reaction

In this research, the effect of alkaline earth promoters (Mg, Sr, Ca and Ba) on the catalytic performance of the 7 wt%Ni-7.5 wt%Cu/CeO₂Al₂O₃ catalyst in high-temperature water gas shift (HTWS) reaction was studied. The mesoporous support was prepared via a simple solid-state method with the BET surface area of 94.46 m² g⁻¹. The results indicated that among the prepared catalysts, the Ba-promoted catalyst demonstrated a high CO conversion (68.9% at 450 °C) and a low decline in BET area after the reaction. The maximum methane production for this catalyst was lower than that observed for the unpromoted catalyst that could be related to the higher concentration of basic sites in the Ba-promoted catalyst. Although, a higher amount of Ba can improve the selectivity toward water gas shift reaction, increasing the Ba content from 4 wt% to 6 wt% had a negative effect on the activity. Moreover, the addition of Ba to 7Ni-7.5Cu/CeO₂Al₂O₃ improved the long-time stability of the catalyst.     

Multi-scale model based design of membrane reactor/separator processes for intensified hydrogen production through the water gas shift reaction

This work aims to first quantify the impact of various diffusion models (Maxwell-Stefan, Wilke, Dusty-Gas) on the predictions of a multi-scale membrane reactor/separator mathematical model, and to then demonstrate this model's use for the design and process intensification of membrane reactor/separator systems for hydrogen production. This multi-scale model captures velocity, temperature and species' concentration profiles along the catalyst pellet's radial direction, and along the reactor's axial direction, by solving the momentum, energy, and species transport equations, accounting for convection, conduction, reaction, and diffusion mechanisms. In the first part of work, the effect of pellet-scale design parameters (mean pore diameter, volumetric porosity, tortuosity factor, etc.) and various species' flux models on the model predictions is studied. In the second part, the study focuses on the comparison, in terms of their process intensification characteristics, of various hydrogen production processes. These include a conventional high-temperature shift reactor (HTSR)/low-temperature shift reactor (LTSR) sequence, a novel HTSR/membrane separator (MS)/LTSR/MS sequence, and a process that involves low-temperature shift membrane reactors-LTSMR in a series.     

Preparation of highly dispersed Cu/SiO2 doped with CeO2 and its application for high temperature water gas shift reaction

Highly dispersed Cu/SiO₂ catalysts doped with CeO₂ have been successfully prepared via in-situ self-assembled core-shell precursor route. The prepared catalysts were characterized by XRD, SEM, TPR, chemisorption and XPS techniques. The results showed that our newly developed method could not only prepare highly dispersed supported metal catalysts but also highly dispersed supported CeO₂ on silica. The highly dispersed CeO₂ showed strong interaction with highly dispersed Cu. The synergy between the highly dispersed CeO₂ and the highly dispersed Cu exhibited high catalytic activity for high temperature water gas shift reaction compared to the catalysts prepared with the routine method of incipient impregnation.     

Effect of CaO hydration and carbonation on the hydrogen production from sorption enhanced water gas shift reaction

Sorption enhanced water gas shift reaction (SEWGS) based on calcium looping is an emerging technology for hydrogen production and CO₂ capture. SEWGS involves mainly two reactions, the catalytic WGS reaction and the bulk carbonation of CaO with CO₂, and the solid product is CaCO₃, and the Ca(OH)₂ may be formed from the reaction of CaO with H₂O with the presence of steam in gas phase. The effect of Ca(OH)₂ and CaCO₃ on the catalytic WGS reaction and carbonation reaction was studied in a fluidized bed reactor. It was found that the hydrated sorbent and CaCO₃ did not show any catalytic reactivity toward WGS reaction at 400 °C. When the temperature was increased to 500 °C and 600 °C, the catalytic reactivity of hydrated sorbent was recovered partially, but this will depend on the steam fraction in gas phase, the recovery of fresh CaO surface from dehydration of Ca(OH)₂ may be the reason of catalytic reactivity recovery. CaCO₃ can catalyze the WGS reaction at the high-temperature (>600 °C), this may due to the CaCO₃ decomposition and recarbonation processes in which the CaO is transiently formed. The possible mechanism was discussed.     

Activity,stability and deactivation behavior of Au/CeO2 catalysts in the water gas shift reaction at increased reaction temperature (300 °C)

The effect of increasing the reaction temperature to 300 °C on the activity, stability and deactivation behavior of a 4.5 wt.% Au/CeO₂ catalyst in the water gas shift (WGS) reaction in idealized reformate was studied by kinetic and spectroscopic measurements at 300 °C and comparison with previously reported data for reaction at 180 °C under similar reaction conditions [A. Karpenko, Y. Denkwitz, V. Plzak, J. Cai, R. Leppelt, B. Schumacher, R.J. Behm, Catal. Lett. 116 (2007) 105]. Different procedures for catalyst pretreatment were used, including annealing at 400 °C in oxidative, reductive or inert atmospheres as well as redox processing. The formation/removal of stable adsorbed reaction intermediates and side products (surface carbonates, formates, OH_ad, CO_ad) was followed by in situ IR spectroscopy (DRIFTS), the presence of differently oxidized surface species (Au⁰, Au^0′, Au³⁺, Ce³⁺) was evaluated by XPS. The reaction characteristics at 300 °C generally resemble those at 180 °C, including (i) significantly higher reaction rates, (ii) comparable apparent activation energies (44 ± 1/50 ± 1 kJ mol⁻¹ vs. 40 ± 1 kJ mol⁻¹ at 180 °C), (iii) a correlation between deactivation of the catalyst and the build-up of stable surface carbonates, and (iv) a decrease of the initially significant differences in activity after different pretreatment procedures with reaction time. Different than expected, the tendency for deactivation did not decrease with higher temperature, due to enhanced carbonate decomposition, but increases.     

Thermodynamic analysis of hydrogen production from methane via autothermal reforming and partial oxidation followed by water gas shift reaction

Reaction characteristics of hydrogen production from a one-stage reaction and a two-stage reaction are studied and compared with each other in the present study, by means of thermodynamic analyses. In the one-stage reaction, the autothermal reforming (ATR) of methane is considered. In the two-stage reaction, it is featured by the partial oxidation of methane (POM) followed by a water gas shift reaction (WGSR) where the temperatures of POM and WGSR are individually controlled. The results indicate that the reaction temperature of ATR plays an important role in determining H₂ yield. Meanwhile, the conditions of higher steam/methane (S/C) ratio and lower oxygen/methane (O/C) ratio in association with a higher reaction temperature have a trend to increase H₂ yield. When O/C ≤ 0.125, the coking behavior may be exhibited. In regard to the two-stage reaction, it is found that the methane conversion is always high in POM, regardless of what the reaction temperature is. When the O/C ratio is smaller than 0.5, H₂ is generated from the partial oxidation and thermal decomposition of methane, causing solid carbon deposition. Following the performance of WGSR, it suggests that the H₂ yield of the two-stage reaction is significantly affected by the reaction temperature of WGSR. This reflects that the temperature of WGSR is the key factor in producing H₂. When methane, oxygen and steam are in the stoichiometric ratio (i.e. 1:0.5:1), the maximum H₂ yield from ATR is 2.25 which occurs at 800 °C. In contrast, the maximum H₂ yield of the two-stage reaction is 2.89 with the WGSR temperature of 200 °C. Accordingly, it reveals that the two-stage reaction is a recommended fuel processing method for hydrogen production because of its higher H₂ yield and flexible operation.     

Cu/Fe3O4 catalyst for water gas shift reaction: Insight into the effect of Fe2+ and Fe3+ distribution in Fe3O4

Two precursors, namely, p-CFO-T (tetragonal) and p-CFO-C (cubic), were fabricated by a sol-gel method via citric acid and poly(vinyl alcohol) complexation, respectively. After H₂-reduction, the two were converted to Cu/Fe₃O₄ catalysts of different complexions, which are named as CFO-CA and CFO-PVA, respectively. The distribution of Fe²⁺ and Fe³⁺ in the Cu/Fe₃O₄ catalysts was studied by Raman and XPS techniques. It was disclosed that the distribution of Fe²⁺ and Fe³⁺ in Fe₃O₄ has an effect on Cu–Fe₃O₄ interaction and catalyst surface basicity. Compared to CFO-PVA, CFO-CA has a larger amount of Fe³⁺, which mostly sits at the octahedral sites, leading to stronger Cu–Fe₃O₄ interaction, and a larger amount of catalyst surface sites that are of weak basicity. As a result, the critical elementary steps of WGS reaction, viz. water dissociation, –COOH decomposition and CO₂ desorption are promoted as reflected in the lower E_a and higher catalytic activity of CFO-CA.     

Hydrogen production from methane under the interaction of catalytic partial oxidation,water gas shift reaction and heat recovery

Hydrogen production from the combination of catalytic partial oxidation of methane (CPOM) and water gas shift reaction (WGSR), viz. the two-stage reaction, in a Swiss-roll reactor is investigated numerically. Particular emphasis is placed on the interaction among the reaction of CPOM, the cooling effect due to steam injection and the excess enthalpy recovery with heat recirculation. A rhodium (Rh) catalyst bed sitting at the center of the reactor is used to trigger CPOM, and two different WGSRs, with the aids of a high-temperature (Fe–Cr-based) shift catalyst and a low-temperature (Cu–Zn-based) shift catalyst, are excited. Two important parameters, including the oxygen/methane (O/C) ratio and the steam/methane (S/C) ratio, affecting the efficiencies of methane conversion and hydrogen production are taken into account. The predictions indicate that the O/C ratio of 1.2 provides the best production of H₂ from the two-stage reaction. For a fixed O/C ratio, the H₂ yield is relatively low at a lower S/C ratio, stemming from the lower performance of WGSR, even though the cooling effect of steam is lower. On the contrary, the cooling effect becomes pronounced as the S/C ratio is high to a certain extent and the lessened CPOM leads to a lower H₂ yield. As a result, with the condition of gas hourly space velocity (GHSV) of 10,000 h⁻¹, the optimal operation for hydrogen production in the Swiss-roll reactor is suggested at O/C = 1.2 and S/C = 4–6.     

The development and evaluation of microstructured reactors for the water gas shift and preferential oxidation reactions in the 5 kW range

5 kW_el One-Stage Water Gas Shift (WGS) and Preferential Oxidation (PROx) reactors were designed and evaluated for the clean-up of surrogate diesel reformate. For the WGS reactor, CO conversions of up to 95% were attained using typical surrogate synthetic diesel reformate. The PROx reactor was capable of converting a feed concentration of 1.0 mol% CO to 20 ppm. Load changes for both reactors could be carried out without significant overshoots of carbon monoxide.     

Facile synthesis of M-CuFe2O4 (M= Al2O3, CeO2, La2O3, ZrO2, Mn2O3) catalysts using a one-pot method and their applications in high-temperature water gas shift reaction

Water gas shift reaction is an essential process of hydrogen production and carbon monoxide removal from syngas. In this study, the promotional effect of ZrO₂, CeO₂, La₂O₃, Al₂O₃, and Mn₂O₃ was investigated on the CO conversion and thermal stability of the copper ferrite in high-temperature water gas shift reaction (HTSR) and hydrogen purification. The powders were synthesized by a simple solid-state route and characterized by XRD, H2-TPR, SEM, FT-IR, TG-DTA, and BET analyses. Promoters (ZrO₂, CeO₂, La₂O₃, Al₂O3, and Mn₂O₃) could affect the WGSR performance in activity and stability. In the M-CuFe2O4 catalyst, alumina acts as a texture promoter and aids in the fine dispersion of copper ferrite. The results indicated that the surface area of the Al₂O₃–CuFe₂O₄ (210 m²/g) catalyst was higher than the other samples. This catalyst presented higher CO conversion in HTSR and had higher stability at 1000 min on stream. It was found that the incorporation of different contents of alumina had a significant influence on the textural and catalytic properties of the CuFe₂O₄-based catalysts. The 30%Al₂O₃–70%CuFe₂O₄ catalyst exhibited the highest CO conversion of 65% at 350 °C, uniform pore size distribution, and intense interaction between copper ferrite and alumina, causing the effective stabilization of the active phase in the catalyst structure. The findings of this study represent that the solid-state method, due to its simplicity and creation of a mesoporous structure, can also be applied for the preparation of many heterogeneous metal oxide catalysts.     

Hydrogen production from water gas shift reaction in a high gravity (Higee) environment using a rotating packed bed

Hydrogen production via the water gas shift reaction (WGSR) was investigated in a high gravity environment. A rotating packed bed (RPB) reactor containing a Cu–Zn catalyst and spinning in the range of 0–1800 rpm was used to create high centrifugal force. The reaction temperature and the steam/CO ratio ranged from 250 to 350 °C and 2 to 8, respectively. A dimensionless parameter, the G number, was derived to account for the effect of centrifugal force on the enhancement of the WGSR. With the rotor speed of 1800 rpm, the induced centrifugal force acting on the reactants was as high as 234 g on average in the RPB. As a result, the CO conversion from the WGSR was increased up to 70% compared to that without rotation. This clearly revealed that the centrifugal force was conducive to hydrogen production, resulting from intensifying mass transfer and elongating the path of the reactants in the catalyst bed. From Le Chatelier’s principle, a higher reaction temperature or a lower steam/CO ratio disfavors CO conversion; however, under such a situation the enhancement of the centrifugal force on hydrogen production from the WGSR tended to become more significant. Accordingly, a correlation between the enhancement of CO conversion and the G number was established. As a whole, the higher the reaction temperature and the lower the steam/CO ratio, the higher the exponent of the G number function and the better the centrifugal force on the WGSR.     

Monolithic Pt/Ce0.8Zr0.2O2/cordierite catalysts for low temperature water gas shift reaction in the real reformate

Monolithic catalysts were prepared by washcoating Ce_0.8Zr_0.2O₂ slurries and then impregnating platinum or rhenium onto cordierite substrates, and characterized by Brunauer–Emmett–Teller (BET), X-ray diffraction (XRD), inductively coupled plasma (ICP), temperature-programmed-reduction (TPR) and temperature-programmed deposition of CO (CO-TPD) techniques. The effects of preparation parameters on the catalytic performance for water gas shift (WGS) reaction were investigated in details, including different Ce_0.8Zr_0.2O₂ powder as washcoat, coat loadings, metal loadings, Pt/Re weight ratio and impregnation sequences. In addition, pyrophoricity (exposure to oxygen stream) and long-term stability were carried out over monolithic catalysts with the optimized composition. The results showed that Ce_0.8Zr_0.2O₂ prepared by microemulsion methods was the preferred washcoat, and that 50 wt% Ce_0.8Zr_0.2O₂ coat loading and 0.68 wt% Pt loading were required to reduce CO content to ca. 1%. The optimal catalytic performance was achieved over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst. Pyrophoricity tests indicated that no obvious activity loss was observed over 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst after three exposures to oxygen; while 17% of the initial activity was lost over industrial B206 after one exposure. Monolithic 0.11 wt% Re/0.34 wt% Pt/50 wt% Ce_0.8Zr_0.2O₂–M/cordierite catalyst exhibited good stability during 80 h on-stream test.     

Preparation of nanocrystalline metal (Cr,Al, Mn,Ce, Ni,Co and Cu) modified ferrite catalysts for the high temperature water gas shift reaction

Water gas shift reaction is an essential process of hydrogen production and carbon monoxide removal from syngas. Fe–Cr–Cu catalysts are typical industrial catalysts for high temperature water gas shift reaction but have environmental and safety concerns related to chromium content. In this work nanocrystalline metal (M)-modified ferrite catalysts (M = Cr, Al, Mn, Ce, Ni, Co and Cu) for replacement of chromium were prepared by coprecipitation method and the effects of promoters on the structural and catalytic properties of the iron based catalysts were studied. Prepared catalysts were characterized using X-ray diffraction (XRD), N₂ adsorption (BET), temperature-programmed reduction (TPR) and transmission electron microscopies (TEM) techniques. Temperature-programmed reduction measurements inferred that copper favors the active phase formation and significantly decreased the reduction temperature of hematite to magnetite. In addition, water gas shift activity results revealed that Fe–Al–Cu catalyst with Fe/Al = 10 and Fe/Cu = 5 weight ratios showed the highest catalytic activity among the prepared catalysts. Moreover, the effect of calcination temperature, GHSV and steam/gas ratio on the catalytic performance of this catalyst was investigated.