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The impact of operating parameters on H2S capture from a syngas mixture by a Mopromoted Mn-based high-temperature sorbent was investigated. The parameters investigated included temperature, space velocity, H2S concentration in the feed gas, and steam content. The H2S and SO2 concentrations in the gas after passing over a bed of the sorbent were analyzed and compared with thermodynamic calculations. The results confirmed that low temperature, low space velocity, low H2S concentration, and a dry feed were favorable for achieving a low residual concentration of sulfur compounds in the effluent gas. The sorbent was able to reduce the residual H2S concentration to below 1 ppm under all tested conditions. However, the unavoidable steam content in the gas phase had a significant adverse effect on sulfur removal from the gas. An empirical model, containing the three variables, i.e., temperature, space velocity, and H2S concentration in the feed, was developed and can be used to predict the effluent H2S residual concentration after treatment by the 15Mn8Mo sorbent. [ABSTRACT FROM AUTHOR]

A detailed kinetic model describing the consumption of key components and product distribution in the Fischer–Tropsch synthesis (FTS) over a 20%Co/0.5Re γ‐Al2O3 commercial catalyst is developed. The developed model incorporates the H2O‐assisted CO dissociation mechanism developed by Rytter and Holmen and a novel approach to product distribution modeling. The model parameters are optimized against an experimental dataset comprising a range of process conditions: total pressure 2.0–2.2 MPa, temperature 210–230°C, CO conversion range of 10%–75% and feed with and without added water. The quality of the model fit measured in terms of mean absolute relative residuals (MARR) value is 23.1%, which is comparable to literature reported values. The developed model can accurately describe both positive and negative effects of water on the rate kinetics, the positive effect of water on the growth factor, temperature and syngas composition on the kinetics and product distribution over a wide range of process conditions, which is critical for the design and optimization of the Fisher–Tropsch reactors. [ABSTRACT FROM AUTHOR]

Single‐metal high‐temperature solid sorbents for syngas cleaning using Mn, Ca, Fe, Cu, or Mo supported on γ‐Al2O3 were synthesized, characterized, and tested in a fixed‐bed reactor. H2S and SO2 concentrations in the gas after treatment at T = 400 to 700 °C were compared with thermodynamic calculations. The Mn‐based sorbent showed the best ability to achieve a low sulfur residual in the gas, especially at temperatures above 600 °C. Sorbents with Fe, Cu, and Mo gave SO2 formation in the initial phase, but this could be avoided by a pre‐reduction treatment of the sorbent material. [ABSTRACT FROM AUTHOR]

Cu‐CHA is the state‐of‐the‐art catalyst for the Selective Catalytic Reduction (SCR) of NOx in vehicle applications. Although extensively studied, diverse mechanistic proposals still stand in terms of the nature of active Cu‐ions and reaction pathways in SCR working conditions. Herein we address the redox mechanism underlying Low‐Temperature (LT) SCR on Cu‐CHA by an integration of chemical‐trapping techniques, transient‐response methods, operando UV/Vis‐NIR spectroscopy with modelling tools based on transient kinetic analysis and density functional theory calculations. We show that the rates of the Reduction Half‐Cycle (RHC) of LT‐SCR display a quadratic dependence on CuII, thus questioning mechanisms based on isolated CuII‐ions. We propose, instead, a CuII‐pair mediated LT‐RHC pathway, in which NO oxidative activation to mobile nitrite‐precursor intermediates accounts for CuII reduction. These results highlight the role of dinuclear Cu complexes not only in the oxidation part of LT‐SCR, but also in the RHC reaction cascade. [ABSTRACT FROM AUTHOR]

The defect plays a significant role in tuning the electronic structure of metal compounds such as oxides, chlorides, sulfides and nitrides, which is frequently used to explain the enhanced catalytic activity. However, the dynamic change of defect relating to the oxidation state change during the reaction is rarely addressed, and it is still not able to be appropriately predicted since the kinetic modeling of the redox reaction involving the in‐situ formation of defects is challenged by the dynamic evolution of the active sites and the complex kinetic phenomena. Here, for the first time, we present a general method to build a new kinetic model of the redox reaction cycle by combined kinetics of reduction‐ and oxidation steps to predict the time and spatially resolved formation of defects of solid catalysts and the reaction products in ethylene oxychlorination on CuCl2/Al2O3 catalyst. The defect concentration can be tuned by manipulating the relative rates of the reduction‐ and oxidation steps. [ABSTRACT FROM AUTHOR]

A bifunctional catalyst comprising CuCl2/Al2O3 and nitrogen‐doped carbon was developed for an efficient one‐pot ethylene oxychlorination process to produce vinyl chloride monomer (VCM) up to 76 % yield at 250 °C and under ambient pressure, which is higher than the conventional industrial two‐step process (≈50 %) in a single pass. In the second bed, active sites containing N‐functional groups on the metal‐free N‐doped carbon catalyzed both ethylene oxychlorination and ethylene dichloride (EDC) dehydrochlorination under the mild conditions. Benefitting from the bifunctionality of the N‐doped carbon, VCM formation was intensified by the surface Cl*‐looping of EDC dehydrochlorination and ethylene oxychlorination. Both reactions were enhanced by in situ consumption of surface Cl* by oxychlorination, in which Cl* was generated by EDC dehydrochlorination. This work offers a promising alternative pathway to VCM production via ethylene oxychlorination at mild conditions through a single pass reactor. [ABSTRACT FROM AUTHOR]

A numerical comparison of the pseudo-homogeneous, conventional heterogeneous, and simplified heterogeneous reactor models is performed for the steam methane reforming process. The pseudo-homogeneous reactor model consists of a set of partial differential equations, where the diffusional limitations are accounted for by considering the effectiveness factor. The heterogeneous model is divided into two categories: conventional and simplified heterogeneous models. In the conventional heterogeneous model, there are separate equations for the fluid phase species mass balance, the fluid inside the catalyst pores. This is type of reactor model is needed when there is a considerable amount of inter-phase mass transfer resistance present in the process. However, in the simplified heterogeneous reactor model the mass transport phenomenon is accounted for by accounting the efficiency factors. The model is validated against literature data. Several closures for the intra-particle mass diffusion fluxes, the Maxwell-Stefan, Wilke, dusty gas, and Wilke-Bosanquet models, have been compared on the level of the catalyst pellet and the impacts of the different particle flux closures on the reactor performance are investigated. The simulations show that the conventional heterogeneous reactor model is necessary for the SMR process, because the effectiveness factor values of different reactions of the SMR process vary along the reactor axis. The maximum deviation between the pseudo-homogeneous and the conventional heterogeneous reactor model is less than 38 %, whereas between the conventional and simplified heterogeneous reactor models it is less than 21 %. A parametric study of the transport phenomena on the pellet level is recommended prior to any large-scale reactor simulation to determine what the rate determining transport mechanisms are. [ABSTRACT FROM AUTHOR]

[Display omitted] • Polyethylenimine over mesoporous carbon spheres solid sorbent for CO 2 capture. • CO 2 capture capacity (3.22 mmol/g) was achieved on 62.5PEI/MCS-1.1. • PEI /MCS will be one of the ideal candidates for CO 2 capture in the future. A novel low-concentration CO 2 capture material (PEI/MCS) was developed by loading polyethylenimine (PEI) over mesoporous carbon spheres (MCS) with high porosity. The effects of pore structure, PEI loading, capture temperature, and promoters on CO 2 capture of PEI/MCS were studied. The MCS with perfect spherical morphology was successfully synthesized by a hard-template assisted reverse emulsion method. The pore structure of MCS was adjusted by tuning the ratio of silica to carbon (Si/C) in the precursors. With increasing the Si/C from 0.8 to 1.1, the pore volume of MCS increased from 1.25 to 2.68 cm3/g. The optimal PEI loadings depending on the pore volume of MCS were 45, 62.5, and 65 wt.% for MCS-0.8, MCS-1.1, and MCS-1.5, respectively. The highest CO 2 capture capacity (3.22 mmol/g) was achieved on 62.5PEI/MCS-1.1 at CO 2 partial pressure of 0.05 bar (5 vol.%, a typical concentration of the tail gas from natural gas power plant and natural gas processing plant) and temperature of 75 °C, outperforming most of the solid amine sorbents reported at similar condition. However, the cycling stability of PEI/MCS is poor at the capture-regeneration temperature of 75 °C. The promoters Span 80 and 1,2-epoxybutane did not show remarkable effect on the cycling stability of PEI/MCS at 75 °C. Decreasing the capture-regeneration temperature can significantly improve the stability of PEI/MCS and there is almost no CO 2 capacity loss (regeneration >99.5 %) when the temperature decreased to 50 °C. As a result of high CO 2 capacity and excellent regenerability and stability, PEI /MCS will be one of the ideal candidates for CO 2 capture in the future. [ABSTRACT FROM AUTHOR]

[Display omitted] • Using UV–vis-NIR to analyze the kinetics of ethylene oxychlorination. • Co-promoter effect of alkali and alkali earth metals on ethylene oxychlorination. • Methods to design and predict the reaction rate and Cu2+ concentration for the steady-state. The comprehensive kinetic study for CuCl 2 /γ-Al 2 O 3 -based catalysts was performed to elucidate the co-promoter effect in the ethylene oxychlorination, one of the most significant industrial processes to produce vinyl chloride monomer. Kinetic analysis was performed separately by transient kinetic studies, taking account of the reduction and oxidation steps in the catalytic cycle. The promoter effects on ethylene oxychlorination were ascribed to their influence on the Cu2+ reduction or Cu+ oxidation in the catalytic cycle. The reaction rate-diagram was gained and used to predict the steady-state reaction rate and Cu oxidation state by an operando setup combing MS and UV–vis-NIR spectroscopy. The results indicated that the K-doped catalyst could greatly increase the reaction rate of the oxidation step, which gave rise to higher Cu2+ concentration on the catalyst. Mg-doped catalyst had a great effect on enhancing the reaction rate for the reduction step. K and Mg co-doped catalyst had the dual effect, both the reaction rate and Cu oxidation state were located between K and Mg mono-doped catalyst. The results of steady-state reactions indicated that the reaction rates were quite close with that predicated by the rate-diagram. Byproduct analysis during the steady-state was also performed, the results demonstrated that the co-promoted catalysts can also reduce the byproduct formation. The current study is expected to provide one way for exploring the potential benefits of co-promotion on CuCl 2 /γ-Al 2 O 3 -based industrial oxychlorination catalysts to improve the catalytic performance and understand the reaction further. [ABSTRACT FROM AUTHOR]

The evaluation of the Fischer-Tropsch experiment with H 2 /CO = 2.13 at 210 °C with changes in CO conversion and water addition. [Display omitted] • Co-based catalyst developed WGS activity at low H 2 /CO ratio. • Water has a positive effect on C 5+ selectivity for all H 2 /CO ratios. • Re-oxidation of cobalt is proposed as the main deactivation mechanism caused by water. Fischer-Tropsch synthesis has been investigated over a commercial type cobalt-based catalyst (20 %Co/0.5 %Re/γ-Al 2 O 3) by varying the H 2 /CO ratio (2.55–1.12), CO conversion (15–75 %), reaction temperature (210 °C, 230 °C), and by adding water to the syngas. The experiments were conducted in a fixed bed reactor with the main purpose of obtaining experimental data to be used in the development and fitting of a mechanistic model. A positive effect of water on the catalyst activity was found for experiments with a H 2 /CO ratio higher than 1.7. Water was found to always increase the C 5+ selectivity regardless of the H 2 /CO ratio. Increasing conversion led to increased C 5+ selectivity. The selectivity to CO 2 was significantly enhanced at higher conversions (high water partial pressure), particularly with the lowest H 2 /CO = 1.12, interpreted as the emergence of water-gas shift activity. Re-oxidation of cobalt, probably limited to small cobalt particles, is proposed as the main deactivation mechanism caused by water while a steeper deactivation curve was found for higher temperature, indicating that sintering also may play a role. [ABSTRACT FROM AUTHOR]