FeOx supported single‐atom Pd bifunctional catalyst for water gas shift reaction

Water gas shift reaction on supported noble metal catalysts is an essential process for upgrading hydrogen source industrially. Here a series of Pd/FeO_x catalysts were detected for this reaction with Pd/Al₂O₃ as reference. It was found that Pd/FeO_x exhibited higher CO conversion than Pd/Al₂O₃ with a good stability even in the presence of CO₂ and H₂. Along the loading decreasing, the turnover frequency of exposed Pd atoms increased with the dispersion from subnanometer (～1 nm) to single atoms. Various characterizations suggested that Pd single atoms greatly enhanced the reducibility of FeO_x and facilitated the formation of oxygen vacancies, which served as sites to promote the dissociation of H₂O to form H₂ and atomic O. The atomic O was ready to react with the linear adsorbed CO species on Pd single‐atom sites through a redox mechanism, which resulted in low activation energy of ～30 kJ mol^?1. © 2017 American Institute of Chemical Engineers AIChE J, 63: 4022–4031, 2017     

The effect of La on Au-ceria catalyst for water gas shift reaction

For Au-ceria catalysts prepared by deposition-precipitation method, catalytic performance of water gas shift reaction was studied in different La loadings. In the complete doping range, ceria retains with its cubic fluorite structures. BET, XRD, H₂-TPR, HRTEM studies showed that La doping can improve the activity of Au-ceria catalyst by stabilizing ceria and modifying its morphology. In addition, the test of catalyst stability evaluation also proved a better stability performance of Au-ceria catalyst can be realized by appropriate La doping.     

Support‐dependent activity of noble metal substituted oxide catalysts for the water gas shift reaction

The water gas shift reaction was carried out over noble metal ion substituted nanocrystalline oxide catalysts with different supports. Spectroscopic studies of the catalysts before and after the reaction showed different surface phenomena occurring over the catalysts. Reaction mechanisms were proposed based upon the surface processes and intermediates formed. The dual site mechanism utilizing the oxide ion vacancies for water dissociation and metal ions for CO adsorption was proposed to describe the kinetics of the reaction over the reducible oxides like CeO₂. A mechanism based on the interaction of adsorbed CO and the hydroxyl group was proposed for the reaction over ZrO₂. A hybrid mechanism based on oxide ion vacancies and surface hydroxyl groups was proposed for the reaction over TiO₂. The deactivation of the catalysts was also found to be support dependent. Kinetic models for both activation and deactivation were proposed. © 2010 American Institute of Chemical Engineers AIChE J, 2010     

Pulse-response TAP studies of the reverse water–gas shift reaction over a Pt/CeO2 catalyst

The temporal analysis of products (TAP) technique was successfully applied for the first time to investigate the reverse water–gas shift (RWGS) reaction over a 2% Pt/CeO₂ catalyst. The adsorption/desorption rate constants for CO₂ and H₂ were determined in separate TAP pulse-response experiments, and the number of H-containing exchangeable species was determined using D₂ multipulse TAP experiments. This number is similar to the amount of active sites observed in previous SSITKA experiments. The CO production in the RWGS reaction was studied in a TAP experiment using separate (sequential) and simultaneous pulsing of CO₂ and H₂. A small yield of CO was observed when CO₂ was pulsed alone over the reduced catalyst, whereas a much higher CO yield was observed when CO₂ and H₂ were pulsed consecutively. The maximum CO yield was observed when the CO₂ pulse was followed by a H₂ pulse with only a short (1 s) delay. Based on these findings, we conclude that an associative reaction mechanism dominates the RWGS reaction under these experimental conditions. The rate constants for several elementary steps can be determined from the TAP data. In addition, using a difference in the time scale of the separate reaction steps identified in the TAP experiments, it is possible to distinguish a number of possible reaction pathways.     

Catalyst effectiveness in low-temperature water—gas shift reaction

A procedure has been developed for a priori prediction of intraparticle diffusion effects in low temperature water—gas shift reaction. Use is made of transport characteristics of the Cu/ZnO/A1₂O₃ pelleted catalyst determined independently by combination of diffusion and permeation results obtained under nonreactive conditions. The porous medium is described by the mean transport pore model and diffusional behaviour of the multicomponent reaction mixture by a modified Stefan-Maxwell equation. Using data from kinetic region obtained at 200°C, it was possible to predict the performance of a bench-scale reactor packed with pelleted catalyst at 200°C and 220°C satisfactorily.     

Sorption-enhanced water gas shift reaction by sodium-promoted calcium oxides

The water gas shift reaction was evaluated in the presence of novel carbon dioxide (CO₂) capture sorbents, both alone and with catalyst, at moderate reaction conditions (i.e., 300-600 °C and 1-11.2 atm). Experimental results showed significant improvements to carbon monoxide (CO) conversions and production of hydrogen (H₂) when CO₂ sorbents are incorporated into the water gas shift reaction. Results suggested that the performance of the sorbent is linked to the presence of a Ca(OH)₂ phase within the sorbent. Promoting calcium oxide (CaO) sorbents with sodium hydroxide (NaOH) as well as pre-treating the CaO sorbent with steam appeared to lead to formation of Ca(OH)₂, which improved CO₂ sorption capacity and WGS performance. Results suggest that an optimum amount of NaOH exists as too much leads to a lower capture capacity of the resultant sorbent. During capture, the NaOH-promoted sorbents displayed a high capture efficiency (nearly 100%) at temperatures of 300-600 °C. Results also suggest that the CaO sorbents possess catalytic properties which may augment the WGS reactivity even post-breakthrough. Furthermore, promotion of CaO by NaOH significantly reduces the regeneration temperature of the former.     

改性铝土矿负载Ni-Mn-K一氧化碳高温变换催化剂的研究

以改性后铝土矿石为载体,采用两步浸渍法,制备Ni-Mn-K一氧化碳高温变换催化剂。采用活性评价、低温N₂吸附、XRD和TPR等表征方法,考察催化剂的结构和性能。结果表明,改性后的铝土矿本身具有一定的变换活性,用该载体负载多组分制得的催化剂具有较好的变换活性。XRD和TPR结果表明,催化剂中具有明显的晶相NiO和K₂CO₃的特征衍射峰, MnO₂与铝土矿载体中的Fe₃O₂和SiO₂形成非晶态复合氧化物。比表面积和孔容减小主要因负载引起,负载活性组分后使耗氢量增大,还原峰温降低。     

Hydrodenitrogenation reaction of quinoline with nascent hydrogen generated from water gas shift reaction

The HDN of quinoline was investigated for the purpose of utilizing the hydrogen which could be generated from the water gas shift reaction (WGSR). The optimum concentration of hydrogen were produced under 1.5 of water to carbon monoxide mole ratio and 6 hr^-1 of space velocity at 390°C of temperature during WGSR over Co-Mo/γ-Al₂O₃ catalyst. The HDN reactions were compared by using the pure hydrogen and the nascent hydrogen which was produced by a WGSR. The pure hydrogen gave much higher activity in the overall HDN reaction than the nascent hydrogen. However, kinetic study on the hydrogenation, hydrogenolysis and cracking reaction steps showed that only at the cracking reaction step the nascent hydrogen gave the superiority to the pure hydrogen. This inferiority of the nascent hydrogen in overall HDN reaction could be resulted from the negative effect of water which should be accompanied during WGSR. The conversion of the HDN reaction was maximized at the water pressure of 150 kpa.     

Kinetic study on the hydrodesulfurization reaction of thiophene by water gas shift reaction

The in-situ hydrodesulfurization (HDS) reaction of thiophene was performed by using hydrogen which was generated by a water gas shift reaction (WGSR) in a same catalyst bed. The catalyst used was commercial CoMo/γ-Al₂O₃ and it was used after presulfiding. The activity in the conversion of thiophene by using hydrogen generated in-situ from a WGSR was inferior to that by the pure hydrogen. The lower efficiency in the in-situ HDS with WGSR was attributed to water, carbon monoxide and carbon dioxide which were mixed after WGSR. The following rate equation, which was revised from that of Satterfield, was proposed for this in-situ HDS reaction of thiophene with WGSR to explain the observed phenomena.     

Study of the reverse water gas shift (RWGS) reaction over Pt in a solid oxide fuel cell (SOFC) operating under open and closed-circuit conditions

The (electro-)kinetics of the reverse water gas shift (RWGS) reaction was studied in a solid oxide fuel cell (SOFC) of the type Pt/YSZ/Pt. The effect of imposed potentials, cell temperature (650–800 °C), H₂ (1–10 kPa) and CO₂ (1–10 kPa) partial pressures on the kinetics and mechanism of the catalytic and electrocatalytic RWGS reaction, were systematically examined. The apparent catalytic activation energy was found equal to 15.6 kcal/mol, while H₂ and CO₂ apparent reaction orders were equal to 0.5 and 0.7, respectively. At both open and closed circuit operation, the associative formate decomposition reaction mechanism was considered to describe kinetics. Under closed circuit operation, rate enhancement factor, |Λ|, values up to 10 were achieved. Finally, current density–voltage and current density–power density characteristics of the cell were recorded at various temperatures and gas mixtures of CO₂ and H₂. It was found that electrical power output of the cell was optimized by increasing temperature and decreasing CO₂/H₂ feed ratio. Maximum power density obtained was 9 mW/cm² (at 520 mV cell voltage and a current density of 17.3 mA/cm², at 800 °C and P_CO2/P_H2=0.16).     

Oxygen effect on the selectivity of ketone hydrogenation reaction on Pt and Pd catalysts

An oxygen deactivated metal catalyst that exhibits less catalytic activity can catalyze an extensive ketone hydrogenation reaction which results in the formation of alkanes, but a fully reduced metal catalyst that exhibits stronger catalytic activity only catalyzes a mild hydrogenation reaction which results in the formation of alcohols.     

Temperature control of the water gas shift reaction in microstructured reactors

Microchannel reactors offer unique possibilities for temperature control of chemical reactions due to the strong coupling of channel and wall temperatures. This may be applied to all chemical reactions which require a certain temperature profile to achieve an optimum yield. For the reformation of hydrocarbons for fuel cell applications a low CO concentration of the product gas is desired. In conventional systems, this is achieved by sequentially processing the reformate through a high and low temperature water gas shift reactor because increased temperature enlarges the reaction rate while lower temperature shifts the equilibrium to the desired small CO concentrations. However, for every gas composition arising during the reaction process an optimum temperature exists at which the reaction rate is highest. We will demonstrate that this optimum temperature profile to a good approximation can be achieved in a single step WGS reactor by controlling the temperature via cooling gas flowing in counter current to the reformate. Furthermore, the effect of water addition (steam injection) is analysed for a conventional two-step adiabatic reactor system and the possible size reduction in an integrated heat-exchanger reactor under comparable conditions is validated. Finally, the effect of diffusion limitations at various channel dimensions is investigated applying a two-dimensional model which allows a trade-off between pressure drop or respective reactor size and performance when dimensioning a real system in future.     

Methanol formation in the water gas shift reaction over copper-containing catalysts

In ammonia and hydrogen production, methanol formation takes place mainly at the low-temperature (second) WGS stage, where the gas composition, catalysts, and operating conditions are similar to those in methanol synthesis. The methanol formation reaction consumes hydrogen, an expensive gas, and causes a number of technological and environmental problems. This raises the problem of reducing the methanol formation rate. To do this, it is necessary to analyze the kinetics, thermodynamics, and technological features of methanol formation at the low-temperature shift stage. Here, we report the equilibrium methanol concentrations calculated for CO conversion under near-industrial conditions. Systematizing the relevant experimental data available from the literature, we demonstrate how methanol formation depends on WGS conditions. The methanol formation rate can be reduced by lowering the CO concentration in the feed gas and employing low-methanol catalysts. Another favorable factor for methanol reduction is the aging of the catalyst during its operation.     

Water-gas shift reaction over supported Pt and Pt-CeOx catalysts

A comparison study was performed of the water-gas shift (WGS) reaction over Pt and ceria-promoted Pt catalysts supported on CeO₂, ZrO₂, and TiO₂ under rather severe reaction conditions: 6.7 mol% CO, 6.7 mol% CO₂, and 33.2 mol% H₂O in H₂. Several techniques—CO chemisorption, temperature-programmed reduction (TPR), and inductively coupled plasma-atomic emission spectroscopy (ICP-AES)—were employed to characterize the catalysts. The WGS reaction rate increased with increasing amount of chemisorbed CO over Pt/ZrO₂, Pt/TiO₂, and Pt-CeO _x /ZrO₂, whereas no such correlation was found over Pt/CeO₂, Pt-CeO _x /CeO₂, and Pt-CeO _x /TiO₂. For these catalysts in the absence of any impurities such as Na⁺, the WGS activity increased with increasing surface area of the support, showed a maximum value, and then decreased as the surface area of the support was further increased. An adverse effect of Na⁺ on the amount of chemisorbed CO and the WGS activity was observed over Pt/CeO₂. Pt-CeO _x /TiO₂ (51) showed the highest WGS activity among the tested supported Pt and Pt-CeO_x catalysts. The close contact between Pt and the support or between Pt and CeO _x , as monitored by H₂-TPR, is closely related to the WGS activity. The catalytic stability at 583K improved with increasing surface area of the support over the CeO₂- and ZrO₂-supported Pt and Pt-CeO _x catalysts.     

Kinetics of the water–gas shift reaction on Pt catalysts supported on alumina and ceria

We report the kinetic parameters for the water–gas shift (WGS) reaction on Pt catalysts supported on ceria and alumina under fuel reformer conditions for fuel cell applications (6.8% CO, 8.5% CO₂, 22% H₂O, 37.3% H₂, and 25.4% Ar) at a total pressure of 1 atm and in the temperature range of 180–345 °C. When ceria was used as a support, the turnover rate (TOR) for WGS was 30 times that on alumina supported Pt catalysts. The overall WGS reaction rate (r) on Pt/alumina catalysts as a function of the forward rate (r_f) was found to be: r = r_f(1 − β), where r_f = k_f[CO]^0.1[H₂O]^1.0[CO₂]^−0.1[H₂]^−0.5, k_f is the forward rate constant, β = ([CO₂][H₂])/(K_eq[CO][H₂O]) is the approach to equilibrium, and K_eq is the equilibrium constant for the WGS reaction. The negative apparent reaction orders indicate inhibition of the forward rate by CO₂ and H₂. The surface is saturated with CO on Pt under reaction conditions as confirmed by diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The small positive apparent reaction order for CO, in concert with the negative order for H₂ and the high CO coverage is explained by a decrease in the heat of adsorption as the CO coverage increases. Kinetic models based on redox-type mechanisms can explain the observed reaction kinetics and can qualitatively predict the changes in CO coverage observed in the DRIFTS study.     

Reaction and characterization studies of an industrial Cr-free iron-based catalyst for high-temperature water gas shift reaction

Activity and stability of an industrial Cr-free iron-based catalyst (NBC-1) for high-temperature water gas shift (WGS) reaction were studied in a fixed-bed reactor under 350 °C, 1 atm, H₂O:gas = 1:1 and 3000 h⁻¹ (dry-gas basis). Physical properties of the NBC-1 catalyst before and after the WGS reaction, the desorption behavior of H₂O, CO, CO₂ and H₂, and surface reaction over the catalyst were characterized by BET, X-ray diffraction (XRD), Mössbauer emission spectroscopy (MES), temperature programmed desorption (TPD) and temperature programmed surface reaction (TPSR). The NBC-1 catalyst is active and has excellent thermo-stability even after pretreatment at a high temperature of 530 °C. Its activity and thermo-stability are comparable to those of an UCI commercial Fe-Cr catalyst, C12-4. XRD and MES studies show that iron in the fresh NBC-1 catalyst is present as γ-Fe₂O₃, most of which is converted to Fe₃O₄ during reduction and reaction. Results of TPD demonstrate that adsorbed CO₂ and CO cannot exist on the NBC-1 surface beyond the temperature of 300 °C while higher temperatures (>400 °C) are required to completely desorb H₂O. A redox mechanism of WGS on the NBC-1 surface is proposed based on the TPD and TPSR observations.     

A facile method for preparation of iron based catalysts for high temperature water gas shift reaction

Nanocrystalline Fe₃O₄ based catalysts with theoretical particle size of 31–78 nm were synthesized by a facile direct pyrolysis method and employed in high temperature water gas shift reaction. XRD analysis showed that this method led to obtaining the catalysts directly in the active phase with chromium and copper incorporated into magnetite lattice. The results showed that the addition of chromium significantly increases the BET surface area of the pure iron oxide from 14.87 to 35.42 m² g⁻¹. Among the catalysts evaluated, Fe–Cr–Cu catalyst revealed higher activity compared to commercial catalyst and showed high stability during 10 h time on stream.     

生物质合成气甲烷化与变换反应串联偶合新工艺

以模拟生物质合成气为原料,在固定床反应器中,对合成气甲烷化反应工艺条件进行优化,并在此反应中串联偶合水煤气变换反应,以此提高生物质合成气中碳氢的比例,从而弥补生物质合成气碳氢比较低的不足,使生物质合成气甲烷化反应更彻底,进而提高甲烷的收率。实验结果表明,在水煤气变换空速为15 000 h~(-1)、进水量0.02 m L·min~(-1)和还原温度为450℃条件下,甲烷化催化剂的性能最优,CO转化率100%,甲烷选择性对于整个偶合反应为50%,但就单一甲烷化反应高达99%。