Water-gas Shift Reaction Rate Research Articles

Electrochemical promotion of copper nanoparticles for the reverse water gas shift reaction

Copper nanoparticles deposited on YSZ provides an opportunity of altering the reverse water gas shift reaction rate by in situ controlling the oxidation states of a new copper nano-structured catalyst which is highly active and economic.

Water-gas shift reaction over supported Au nanoparticles

The water–gas shift (WGS) reaction rates per total mole of Au at 120 °C, 7% CO, 22% H2O, 8.5% CO2, 37% H2 decrease in the order Au/Anatase ∼ Au/Anatase001 (uniform anatase TiO2 single crystals with 64 per cent of the more {001} facets) ∼ Au/P25 ∼ Au/P25-WGC (obtained from the World Gold Council) ∼ Au/Rutile > Au/ZrO2 > Au/CeO2 > Au/ZnO when compared at the same number average Au particle size (d) and vary as ∼ d-3. From high resolution transmission electron microscopy images, the geometry of Au nanoparticles on these catalysts resembled truncated cubo-octahedra. A physical model of Au nanoparticles as truncated cubo-octahedra was used to calculate that the fractions of surface, perimeter and corner sites to the total Au sites vary as d-0.7, d-1.8 and d-2.9, respectively. Thus, the variation in the WGS reaction rate per total mole of Au (∼d-3) correlates well with the corner sites (d-2.9) allowing us to determine that the dominant active sites for these catalysts are the low coordinated metallic corner Au sites. In addition, as the apparent H2O order increases and the apparent activation energy decreases, the WGS reaction rate per total mole of Au systematically decreases for Au nanoparticles supported on anatase, anatase001, P25, rutile, ZrO2, CeO2, ZnO and Al2O3 at near 120 °C. Density functional theory calculations were carried out over Au nano-rods supported on rutile TiO2(100) and α-Al2O3(0001) surfaces to elucidate the differences in reactivity for the most reactive (Au/TiO2) and least reactive (Au/Al2O3) catalysts. Water preferentially adsorbs and dissociates at the Lewis acid- Lewis base Ti4+-Ob and Al3+-Ob site pairs at the Au/TiO2(110) and Au/α-Al2O3 interfaces with activation energies of 0.25 eV and 0.20 respectively. These barriers are significantly lower than those to activate water on the corner sites of unsupported Au nanoparticles (1.48 eV). The prediction that both the TiO2 and Al2O3 readily dissociate water supports the experimental findings that the support plays an important role in activating the water in the WGS reaction. The subsequent oxidation of CO appears to proceed at the Au/support interface via the reaction of CO adsorbed on Au with the OH on the support. DFT results indicate that OH binds 0.4 eV stronger to Al3+ sites at the Au/Al2O3 interface perimeter than to Ti4+ sites at the Au/TiO2 interface perimeter. As such, the barrier for OH to react with CO at an adjacent Au site is 0.52 eV higher for Au/Al2O3 (0.85 eV) than for Au/TiO2 (0.33 eV). The theoretical results suggest that the oxidation of CO is rate-limiting on Al2O3 whereas both the water dissociation as well as CO oxidation limit the rate on TiO2. This is consistent with the near first order CO dependence of the measured rates over both Au/TiO2 and Au/Al2O3 as well as the changes in the water reaction orders over Au/TiO2 (−0.2 to −0.5) and Au/Al2O3 (0.5 to 0.8).

Transient reaction phenomena of sorption-enhanced steam methane reforming in a fixed-bed reactor

The transient chemical reaction phenomena of the sorption-enhanced steam methane reforming (SE-SMR) by using Ni/Al2O3 catalyst and CaO sorbent in a tubular fixed-bed reactor were numerically investigated by an experimentally verified unsteady 2D model. Four chemical reactions are involved in SE-SMR including steam reforming (SR), water gas shift (WGS), global steam reforming (GSR), and CO2 sorption. The reaction process in time is divided into period 1, transient period, and period 2. The high-purity H2 is produced in period 1 which is defined as the outlet molar fractions of H2 ≥ 90% and CO ≤ 1% (dry basis) in this work. In the first half of period 1, the endothermic reaction rates of SR and GSR are dominant in the entrance region of catalyst/sorbent bed. The WGS and CO2 sorption reactions are triggered by SR and GSR reactions. The heat transfer from the wall plays an important role. Higher CaO conversion, temperature, and reaction rates appear first near the wall region, then they gradually expand to the central region.In the second half of period 1, a sharp wave-shaped curve of strong CO2 sorption reaction occurred in downstream becomes dominant and it moves to downstream almost at a constant speed, as time progresses. The peak value of the CO2 sorption reaction is more than twice larger than that of SR or WGS. The SR and WGS reaction rates are significantly enhanced by CO2 sorption reaction. The great sorption, WGS, and SR reactions result in a high-purity H2 production with the outlet molar fractions of 95.8% H2, 0.998% CO, and 0.73% CO2 at the end of period 1, based on the parameters used in this work such as reactor temperature of 600 °C. The maximum CaO conversion is about 76% in end of period 1 and the average CaO conversion in the reactor is 51%. The 2D distributions of CaO conversion, temperature, and reaction rates are also presented and discussed.

Water-gas shift reaction over platinum/strontium apatite catalysts

Platinum supported on calcium hydroxy (CaHAP) and fluoroapatite (CaFAP) exhibits excellent water-gas shift (WGS) activity comparable to the best Pt WGS catalysts on reducible oxides. The high activity of these unusual WGS catalysts is attributed to the parallel activation of CO on the noble metal and H2O on the ionic phosphates with formate species apparently being the major reaction intermediates. We have studied Pt supported on strontium hydroxy and fluoroapatites with varying cation and noble metal contents now in order to elucidate the role of the apatite cations and anions on WGS activity. Initial Pt dispersions approached 100% for loadings up to 3% (weight) with mean particle sizes of 1–2nm according to H2 chemisorption and EXAFS results (coordination number of 6.6). TEM analyses show further that the Pt aggregates grew slightly during catalytic testing up to 723K with 1.5–2.5nm particles being most abundant afterwards. Moreover, Ptn+ reduction is much facilitated on these apatites as revealed by temperature programmed reduction coupled with in situ X-ray absorption spectroscopy (XAS). The WGS reaction rates in a reformate-type gas mixture increased strongly with Sr/P ratio in the apatite, with the rates over the most active Pt/SrHAP and Pt/SrFAP catalysts being among the highest reported to date. In particular, Pt/SrHAP and Pt/SrFAP rates surpassed the rates over analogous Ca2+ substituted catalysts by ca. 30% at 573K. This demonstrates that apatite cations have a strong impact on WGS conversion over these systems opening a route to catalysts with potentially even higher WGS activity.

Comparison of steam-gasification characteristics of coal char and petroleum coke char in drop tube furnace

The steam-gasification reaction characteristics of coal and petroleum coke (PC) were studied in the drop tube furnace (DTF). The effects of various factors such as types of carbonaceous material, gasification temperature (1100–1400°C) and mass ratio of steam to char (0.4:1, 0.6:1 and 1:1 separately) on gasification gas or solid products were investigated. The results showed that for all carbonaceous materials studied, H2 content exhibited the largest part of gasification gaseous products and CH4 had the smallest part. For the two petroleum cokes, CO2 content was higher than CO, which was similar to Zun-yi char. When the steam/char ratio was constant, the carbon conversion of both Shen-fu and PC chars increased with increasing temperature. When the gasification temperature was constant, the carbon conversions of all char samples increased with increasing steam/char ratio. For all the steam/char ratios, compared to water gas shift reaction, char-H2O and char-CO2 reaction were further from the thermodynamic equilibrium due to a much lower char gasification rate than that of water gas shift reaction rate. Therefore, kinetic effects may play a more important role in a char gasification step than thermodynamic effects when the gasification reaction of char was held in DTF. The calculating method for the equilibrium shift in this study will be a worth reference for analysis of the gaseous components in industrial gasifier. The reactivity of residual cokes decreased and the crystal layer (L002/d002) numbers of residual cokes increased with increasing gasification temperature. Therefore, L002/d002, the carbon crystallite structure parameter, can be used to evaluate the reactivity of residual cokes.

Bimetallic Ni–Cu catalyst supported on CeO2 for high-temperature water–gas shift reaction: Methane suppression via enhanced CO adsorption

The formation of methane as the undesired side product is one of the major issues in the water–gas shift (WGS) reaction, particularly for nickel-based catalysts. A detailed study of Ni–Cu bimetallic catalyst supported on nanopowder CeO2 is extensively investigated to suppress the methanation reaction as well as maintain high WGS reaction rate. XRD, EXAFS, H2-TPR and XPS reveal the formation of Ni–Cu alloy, while CO-TPR-MS, CO-TPD-MS and in situ DRIFTS show the enhancement of CO adsorption on Ni–Cu alloy at high temperature. The Ni–Cu/CeO2 catalyst with Ni/Cu ratio of 1 exhibits high reaction rate with the least methane formation due to the formation of Ni–Cu alloy phase. The Ni–Cu alloy phase is found to be the active site for WGS reaction with methane suppression as Ni–Cu alloy can enhance CO adsorption which prevents CO dissociation during high-temperature WGS reaction. Kinetic studies performed reveal that one-site carboxyl mechanism could be the main reaction pathway with formate as spectator. However, there could be other possibilities for the real reaction mechanism on Ni–Cu/CeO2 catalyst.

Investigating the production of liquid fuels from synthesis gas (CO + H2) in a bench-scale packed-bed reactor based on Fe–Cu–La/SiO2 catalyst: experimental and CFD modeling

A computational fluid dynamic (CFD) and experimental study of Fischer–Tropsch Synthesis (FTS) process in a fixed-bed reactor is presented. The reactor was a 1.2 cm diameter and 80 cm length steel tube in which ceramic particles were employed to dilute the catalyst bed and thus prevent the emergence of hot spot in it. An axi-symmetric CFD model with an optimized mesh of 22,016 square cells was developed to model hydrodynamics, chemical reaction, and heat and mass transfer in the reactor. Thermodynamic non-ideal behavior of the gas mixture was modeled using Peng–Robinson equation of state. Kinetic models for FTS and water–gas-shift reaction rates based on Langmuir–Hinshelwood type for each of the species were employed. Good agreement was achieved between the bench experimental data and the model. Performing reactions inside packed-bed reactor due to high pressure and temperature is very difficult and expensive, and CFD simulations are considered as numerical experiments in many cases. A sensitivity analysis was run to find the effect of temperature, pressure, GHSV and H2/CO ratio on the reactor performance. It was concluded that the obtained results from CFD analysis give precise guidelines for further studies on optimization of FTS fixed-bed reactor performance.

Water–Gas Shift Reaction on Pt/Ce1–xTixO2−δ: The Effect of Ce/Ti Ratio

Pt nanoparticles (1.2–2.0 nm size) supported on Ce1–xTixO2−δ (x = 0, 0.2, 0.5, 0.8, and 1.0) carriers synthesized by the citrate sol–gel method were tested toward the water–gas shift (WGS) reaction in the 200–350 °C range. A deep insight into the effect of two structural parameters, the chemical composition of support (Ce/Ti atom ratio), and the Pt particle size on the catalytic performance of Pt-loaded catalysts was realized after employing in situ X-ray diffraction (XRD), high-resolution transmission electron microscopy (HR-TEM) and HAADF/STEM, scanning electron microscopy (SEM), in situ Raman and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies under different gas atmospheres, H2 temperature-programmed reduction (H2-TPR), and temperature-programmed desorption (NH3-TPD and CO2-TPD) techniques. The 0.5 wt % Pt/Ce0.8Ti0.2O2−δ solid (dPt = 1.7 nm) was found to be by far the best catalyst among all the other solids investigated. In particular, at 250 °C the CO conversion over Pt/Ce0.8Ti0.2O2−δ was increased by a factor of 2.5 and 1.9 compared to Pt/TiO2 and Pt/CeO2, respectively. The catalytic superiority of the Pt/Ce0.8Ti0.2O2−δ solid is the result of the support’s (i) robust morphology preserved during the WGS reaction, (ii) moderate acidity and basicity, and (iii) better reducibility at lower temperatures and the significant reduction of “coking” on the Pt surface and of carbonate accumulation on the Ce0.8Ti0.2O2−δ support. Several of these properties largely influenced the reactivity of sites (k, s–1) at the Pt–support interface. In particular, the specific WGS reaction rate at 200 °C expressed per length of the Pt–support interface (μmol CO cm–1 s–1) was found to be 2.2 and 4.6 times larger on Pt supported on Ce0.8Ti0.2O2−δ (Ti4+-doped CeO2) compared to TiO2 and CeO2 alone, respectively.

Fischer–Tropsch Synthesis: Effect of K Loading on the Water–Gas Shift Reaction and Liquid Hydrocarbon Formation Rate over Precipitated Iron Catalysts

The effect of K loading on the water–gas shift (WGS) reaction and hydrocarbon formation rate during Fischer–Tropsch synthesis (FTS) was studied over 100 Fe/5.1 Si/2 Cu/x K (x = 1.25 or 3) precipitated catalysts using a 1-L continuously stirred tank reactor. The catalysts were tested over a wide range of experimental conditions: 260–270 °C, 1.3 MPa, H2/CO = 0.67 and 20–90 % CO conversions. On the low K loading (1.25 % K) Fe catalyst, the H2 deficiency required for the FTS reaction was made up by the WGS reaction only at high CO conversion level, i.e. >70 %; however, increasing potassium loading to 3 % dramatically improved the WGS reaction rate which provided enough hydrogen for the FTS reaction even at low CO conversion level, i.e. 30 %. Kinetic analysis suggests that increasing K loading resulted in significant increases in the WGS rate constant relative to that of FTS, which is a major cause of the high WGS activity on the high K loading catalyst. Both the low and high potassium containing iron catalysts have high liquid oil and solid wax formation rates, i.e. 0.78–0.93 g/g-cat/h at 260 °C, 1.3 MPa, H2/CO = 0.67 and 50 % CO conversion, but increasing potassium loading from 1.25 to 3 % shifted the primary product to wax (70 %) from oil (73.5 %). The wax fraction increased with increasing CO conversion for both iron catalysts. The effect of K loading on initial FTS activity and hydrocarbon distribution/selectivity of the Fe catalysts was also studied. High K loading, i.e. 3 % K, increased the iron carburization rate and significantly shortened the induction period of the FTS reaction. Secondary reactions of olefins were remarkably suppressed and the olefin content was greatly enhanced with increasing K loading from 1.25 to 3 %, consistent with a number of studies in the open literature.

A Novel Method for Measuring Active Sites of Fe3O4 for WGS Reaction

Phase transformation among iron oxides was investigated. Pure magnetite material was obtained by reducing iron oxide with diluted hydrogen in a narrow temperature window and with steam to prevent over-reduction. A pulse chromatographic method with N2O decomposition over magnetite surface to determine active sites of iron oxide based catalysts for water gas shift reaction has been developed. N2O decomposes over activated Fe3O4 surface to N2 and leaves oxygen species at oxygen vacancy on the catalyst surface, which is the same site for water gas shift reaction. Lower temperature for N2O decomposition is required to avoid magnetite bulk oxidation. An oxygen coverage on the active sites θ = 1 corresponded to a surface stoichiometry of N2O/Fe2+ = 0.5 was estimated. A linear correlation between water gas shift reaction rate and the quantity of decomposed N2O over the corresponded catalysts was observed.

Water–gas shift modeling in coal gasification in an entrained-flow gasifier – Part 2: Gasification application

Water–gas-shift (WGS) reaction is one of the major reactions in the industrial gasification process. Using an adequate WGS reaction rate is vital to predicting correctly syngas composition in a gasification process. In Part 1, three different WGS reaction rates from Jones, Wade, Sato were modified to match the experimental data of raw syngas undergoing water quench process. It is not clear if these calibrated WGS reaction rates are adequate in a gasification process. Hence, the objective of this study in Part 2 is to apply both the three original published WGS rates and the calibrated rates derived in Part 1 to simulate experiments performed in the Japanese CRIEPI research gasifier. The CFD model incorporates 3-D Navier–Stokes equations and nine species transport equations with seven global gasification reactions (three heterogeneous and four homogeneous,) and a two-step thermal cracking model for volatiles. The Chemical Percolation Devolatilization (CPD) model is used for the devolatilization process. Similar to the result in Part 1 for water quench process, the result in this study further shows that the three originally published rates cannot be directly applied to the simulation of coal gasification process, due to different temperature and pressure range. Even the modified rates obtained from a water quench process in Part 1 also appear faster in the gasification process. The pre-exponential rate constant value (A) of each reaction rate is therefore further slowed down, while the activation energy is kept the same as the original value to match the experimental data. The results show that all three WGS reaction rates can be modified to match the experimental data reasonably well. The exit temperature can be matched within 2% (20K). The mole fractions of CO and H2O can be matched fairly well within 4 percentage points (or 10%); however, the simulated H2 mole fractions are always 7–9 percentage points higher than the experimental data. It needs to be emphasized that the calibrated WGS reaction rates in this study can only be applied in the range of water quench and gasification operating conditions for which they have been validated.

Water–gas shift modeling in coal gasification in an entrained-flow gasifier. Part 1: Development of methodology and model calibration

Most of the reaction rates for the water–gas shift (WGS) reaction were obtained from experiments under simplified laboratory conditions with specific catalysts. A few of the reaction rates without catalysts were obtained under supercritical (water) conditions with the pressure much higher than those in a typical gasifier. In either case, it is not clear how the published reaction rates can be used reliably to predict the actual WGS reaction rate in a gasifier without the presence of a catalyst and under different temperature and pressure conditions than those in the laboratory. Part 1 of this study focuses first on reviewing the published WGS reaction rates with and without the presence of catalysts, followed by calibrating the WGS reaction rate to match the experimental data taken from the quench section of an actual gasifier. Three different WGS reaction rates from Jones, Wade, and Sato are employed for calibration. The result shows that all of these published rates cannot work well in simulating the water quench process due to different ranges of temperature and pressure. The calibration is performed by adjusting the pre-exponential rate constant value (A) of each of the three reaction rates to match the experimental data. The advantage of this methodology is to obtain a global WGS reaction rates under water quench condition in less computational intensive way. However, it needs to be emphasized that the calibrated WGS reaction rates can only be applied in the range of water quench operation parameters for which it has been validated in this study. The calibrated results show that all three WGS reaction rates can be modified to match the experimental data within 2% points (or 6%) in both CO conversion rate and H2 generation. After calibrated rates are developed, complete gasification process is simulated, and the results are compared to experimental data taken from Japanese CRIEPI gasifier in Part 2.

The effect of La3+-doping of CeO2 support on the water-gas shift reaction mechanism and kinetics over Pt/Ce1−xLaxO2−δ

Platinum nanoparticles (dPt=1.0–1.2nm) supported on single CeO2 and La2O3 metal oxides and Ce0.8La0.2O2−δ solid solution were prepared to investigate for the first time the effect of La3+-doping of ceria on important mechanistic and kinetic aspects of the water-gas shift (WGS) reaction, namely: (i) the concentration and chemical structure of active adsorbed reaction intermediates present in the C-path and H-path of WGS at 250 and 300°C, (ii) the chemical nature of inactive species formed during WGS, and (iii) the prevailing mechanistic path among “redox” and “associative” both proposed in the literature. For this, steady-state isotopic transient kinetic analysis (SSITKA) experiments coupled with in situ DRIFTS and mass spectrometry were performed to follow the H-path (use of D2O) and C-path (use of 13CO) of the WGS. In addition, other transient isotopic experiments using operando methodology (use of DRFTS and mass spectrometry) were designed to follow with time on stream the reactivity toward water of the various adsorbed species formed under WGS. It is proposed that on Pt/Ce1−xLaxO2−δ (x=0.0, 0.2 and 1.0) the WGS reaction follows both the “redox” and “associative” mechanisms but the extent of participation of each mechanism to the overall WGS reaction rate depends on the support chemical composition. The WGS kinetic rate (μmol COg−1s−1) increased by a factor of 2.0 and 2.8 at 300°C on 0.5wt% Pt supported on Ce0.8La0.2O2−δ compared to CeO2 and La2O3, respectively. This was explained by (i) the larger concentration of active surface intermediates formed around each Pt nanoparticle (larger extent of reactive zone) and (ii) the higher reactivity of sites (k, s−1) responsible for CO2 and H2 formation on Pt/Ce0.8La0.2O2−δ compared to Pt/CeO2 and Pt/La2O3. Active OH groups is suggested to be formed on defect sites (Ce3+□s) of Ce0.8La0.2O2−δ as a consequence of the introduction of La3+ into the ceria lattice, the latter enhancing the concentration of labile oxygen and its surface mobility, important characteristics of the “redox” mechanism.

Numerical analysis of gasification performance via finite-rate model in a cross-type two-stage gasifier

The gasification process of a pressurized, oxygen-blown, entrained-flow E-Gas like gasifier through numerical modeling is investigated by solving the 3-D, steady-state Navier–Stokes equations with the Eulerian–Lagrangian method. Eight chemical reactions are solved via the Finite-Rate/Eddy-Dissipation Model. The preliminary gasification process is successfully modeled and the global chemical reactions are proved to be strongly affected by the finite rates. The results of parametric study show that the increasing O2/Coal ratio results in a decrease of CO, but an increase of CO2 and exit temperature. With a modified water–gas-shift reaction rate, a more reasonable trend is obtained that as the coal slurry concentration decreases, the mass flow rate of H2, CO2, and H2O increase while that of CO decreases. As the amount of coal slurry mass flow in the first stage increases, the exit temperature and the mole fraction of H2 and CO2 increase, while that of CO decreases. However, different fuel distributions do not provide notable influence on gasification performance due to the large space inside the E-Gas gasifier allowing complete reaction. The overall results show that the present CFD model can adequately capture the gasification behavior and analyze gasification performance inside the gasifier.

CO2 Selective Water Gas Shift Membrane Reactor : Modeling and Simulation

The concept of a CO2 selective water gas shift (WGS) membrane reactor has been modeled and simulated by a one-dimensional reactor and transport process in the membrane. The model was used to investigate the effect of temperature, total pressure, membrane thickness and area on the reactor performance. A Silicalite-1 membrane was considered to be integrated with the WGS reactor. The mass transport through the membrane was described by surface diffusion. Air was used as sweep gas on the permeate side of the membrane. The catalytic WGS kinetics were for a commercial Cu/ZnO catalyst for the lower-temperature WGS reaction. The WGS membrane reactor was sized to produce H2 sufficient for the production of 10 kW electrical power from a fuel cell. The modeling and simulation results showed that the WGS membrane reactor with a silicalite-1 membrane was capable of decreasing the CO concentration to about 675 ppm which is 70% less than that achievable at equilibrium conversion, but it would come at the cost of unacceptable H2 loss. Based on a minimum target of H2 loss, the optimum outlet CO concentration achieved by the silicalite-1 membrane reactor was about 1310 ppm, under a range of limited conditions. The modeling study showed that both the WGS reaction rate and the CO2/H2 selective permeation played an important role on the overall reactor performance.

Counting Au catalytic sites for the water–gas shift reaction

We have developed various techniques to count catalytic sites of Au/TiO2 catalysts for the water–gas shift (WGS) reaction. Addition of Br in an amount that is only 16% of the moles of the surface Au on a 2.3wt.%Au/TiO2 catalyst decreases the majority of its WGS reaction rate per total mole of Au but does not result in an appreciable change in the average Au particle size, Au particle shape, apparent activation energy, or reaction orders. From transient isotopic switch experiments, the WGS turnover frequency (TOF) for Au/TiO2 catalysts with and without Br, based on the operating active sites counted in the experiment, is 1.6±0.5s−1 under 6.8% CO, 8.5% CO2, 11.0% H2O, 37.4% H2 at 120°C. The estimated number of potential active sites, ∼2% of the total amount of Au on the 2.3wt.%Au/TiO2 catalyst, best correlates with the Au corner atoms (∼2%) of the cubo-octrahedral particles. From operando FTIR spectroscopy, the normalized IR peak area of CO adsorbed on Au0 near 2100cm−1 is proportional to the WGS reaction rate for Au/TiO2 catalysts with and without Br. Thus, the dominant active sites on Au/TiO2 catalysts for the WGS reaction are taken to be the metallic corner Au sites with Au–Au coordination number of 4.

A CeO2–La2O3-based Cu catalyst for the processing of coal-derived syngases via high-temperature water–gas shift reaction

A CeO2–La2O3-based Cu catalyst (referred to as CE09) has been tested in a differential reactor to measure its kinetics for the water–gas shift (WGS) reaction at temperatures of 550°C and 600°C which can be described by an empirical power-law rate model. The effects of CO, CO2, H2O and H2 concentration on WGS reaction rate are determined using selected gas compositions that might be encountered in a coal based gasification system. The rates of the WGS reaction (in molgcatalyst-1s-1) over CE09 at a reaction temperature between 550°C and 600°C can be expressed by the a power-law rate expression which correlates well with experimental data with good accuracy: R=100.724exp-92350R′TPCO0.95PCO2-0.06PH2-0.0851-1KPCO2PH2PCOPH2OThe temperature range tested in this study is well beyond the maximum operating temperature of commercially available shift catalysts. To demonstrate the application of CE09 under practical reaction conditions, its performance has been tested with a wide range of steam-to-carbon ratios in an integral reactor operating mode at an inlet pressure of 20bar. This catalyst is shown to work well at relatively low steam-to-carbon gas ratios which could provide some practical benefits for a full-scale commercial process.

철 촉매를 이용한 Fischer-Tropsch 합성 반응과 수성 가스 전환 반응에 대한 반응 속도 연구

철 촉매를 이용한 Fischer-Tropsch 합성 반응과 수성 가스 전환 반응에 대한 반응 메커니즘과 반응 속도식을 5 채널 고정층 반응기를 이용하여 조사하였다. 실험 조건은, 반응물 합성가스 <TEX>$H_2$</TEX>/CO 비 0.5~2, 반응물 공급 유량 60~80 ml/min, 반응 온도 <TEX>$255{\sim}275^{\circ}C$</TEX>로서 반응 압력은 1.5 MPa을 유지하였다. F-T 합성 반응의 반응 속도식(<TEX>$r_{FT}$</TEX>)은 반응 속도 결정 단계로서 분자로 흡착된 CO와 기상의 수소 분자와의 반응을 바탕으로 하는 Eley-Rideal 반응 메카니즘을 통해 계산되었고, WGS 반응의 반응 속도식(<TEX>$r_{WGS}$</TEX>)은 formate 중간체 생성 반응을 반응 속도 결정 단계로 가정하여 결정되었다. 실험 결과, F-T 합성 반응의 반응 속도식과 WGS 반응의 반응 속도식은 각각 탄화수소 생성과 <TEX>$CO_2$</TEX> 생성에 대한 반응 속도 실험값을 잘 모사하였고, 또한 power law에 근거한 CO 전환 반응에 대한 반응 속도식도 실험값과 잘 일치하였다. 이처럼, 각각의 반응 메카니즘을 바탕으로 도출된 반응 속도식(<TEX>$r_{FT}$</TEX>, <TEX>$r_{WGS}$</TEX>, <TEX>$-r_{CO}$</TEX>)은 실험값과 여러 가지 기존 문헌에서 보고된 반응 속도식 모델과 잘 일치하였다. The kinetics of the Fischer-Tropsch synthesis and water gas shift reactions over a precipitated iron catalyst were studied in a 5 channel fixed-bed reactor. Experimental conditions were changed as follows: synthesis gas <TEX>$H_2$</TEX>/CO feed ratios of 0.5~2, reactants flow rate of 60~80 ml/min, and reaction temperature of <TEX>$255{\sim}275^{\circ}C$</TEX> at a constant pressure of 1.5 MPa. The reaction rate of Fischer-Tropsch synthesis was calculated from Eley-Rideal mechanism in which the rate-determining step was the formation of the monomer species (methylene) by hydrogenation of associatively adsorbed CO. Whereas water gas shift reaction rate was determined by the formation of a formate intermediate species as the rate-determining step. As a result, the reaction rates of Fischer-Tropsch synthesis for the hydrocarbon formation and water gas shift for the <TEX>$CO_2$</TEX> production were in good agreement with the experimental values, respectively. Therefore, the reaction rates (<TEX>$r_{FT}$</TEX>, <TEX>$r_{WGS}$</TEX>, <TEX>$-r_{CO}$</TEX>) derived from the reaction mechanisms showed good agreement both with experimental values and with some kinetic models from literature.

Analysis of chemical, electrochemical reactions and thermo-fluid flow in methane-feed internal reforming SOFCs: Part I – Modeling and effect of gas concentrations

Direct internal reforming solid oxide fuel cells (DIR SOFCs) have complicated distributions of temperature and species concentrations due to various chemical and electrochemical reactions. The details of these properties are studied by a 3-D numerical simulation in this work. The simulation modeling used governing equations (mass, momentum, energy and species balance equations) generally suitable to porous medium with porosity variable of zero (solid), 0.3 (porous medium) and 1.0 (fluid). Chemical kinetics equations for the internal reforming and shift reactions based on the Langmuir–Hinshelwood model were incorporated. Hydrogen and carbon monoxide oxidations were considered both participating in electrochemical reactions. The experimentally measured current density–potential curves were compared with the simulation data to validate the code, which revealed that the simulation model was able to predict the dilution effect of nitrogen and the mass transfer under high current densities. It is found that the temperature dramatically declined near the fuel inlet with strong endothermic reactions, but it increased along the fluid flow with electrochemically exothermic reactions. A low steam-to-carbon ratio (SCR) led to high steam reforming and water gas shift reaction rates, which generated a greater amount of hydrogen. Therefore, current density increased with low SCR. The average current density due to carbon monoxide electrochemical oxidation varies from 205.3 A/m2 under an SCR of 2.0 to 47.6 A/m2 under an SCR of 4.0. The average current density due to hydrogen electrochemical oxidation was 5535.4 A/m2 under an SCR of 2.0, which was 27 times higher than that of carbon monoxide. The total current density ranged from 5740.8 A/m2 under an SCR of 2.0 to 2268.9 A/m2 under an SCR of 4.0.

Low-temperature conversion of phenol into CO, CO2 and H2 by steam reforming over La-containing supported Rh catalysts

The steam reforming of phenol in the low-temperature range of 350–550°C was studied over 0.5wt% Rh supported on Ce0.15Zr0.85O2, Zr0.93La0.07O2, and Ce0.13Zr0.83La0.04O2 mixed metal oxides. The reforming specific activity (per gram of catalyst basis) was found to depend on (a) Rh dispersion, (b) the concentration (μmolg−1) of labile oxygen species of support, as determined by “oxygen storage capacity” measurements, and (c) the promotion of the water–gas shift (WGS) reaction rate, all of which largely influenced by the support chemical composition. The addition of 4atom% La3+ into the Ce0.15Zr0.85O2 crystal structure was found to largely promote the dispersion of Rh, to increase significantly (by a factor of 1.75) the concentration of surface basic sites (μmolm−2) of Ce0.13Zr0.83La0.04O2 compared to Ce0.15Zr0.85O2 support, to prevent to a large extent the inhibiting role of hydrogen in the rate of WGS reaction, and to influence significantly the concentration and structure of surface reaction intermediates of the WGS, namely: formate (HCOO–) and –OH groups formed on the support, and adsorbed CO formed on the Rh metal. The 0.5wt% Rh/Ce0.13Zr0.83La0.04O2 catalyst led to a significantly better performance towards steam reforming of phenol in terms of phenol conversion, H2-yield, and CO/CO2 product ratio in the 350–450°C range compared to a commercial Ni-based catalyst (44wt% Ni) used for steam reforming reactions. At 400°C, the 0.5wt% Rh/Ce0.13Zr0.83La0.04O2 catalyst exhibited approximately 54% and 50%, respectively, higher phenol conversion and hydrogen yield, compared to the Ni-based industrial catalyst. The significantly lower CO/CO2 product ratio obtained in the case of Rh/Ce0.13Zr0.83La0.04O2 compared to that obtained in the other supported-Rh catalysts is in agreement with the higher kinetic rate for the WGS reaction observed in the former catalyst.