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The effect of phosphorus on a cobalt-based catalyst for Fischer-Tropsch Synthesis (FTS) has been investigated. Phosphorus is an impurity present in biomass and, in this work, its deposition on the catalyst during biomass to liquid (BTL) operation, based on gasification and FTS, has been mimicked. For this purpose, four different cobalt-manganese-rhenium catalysts supported on alumina were prepared by incipient wetness impregnation with different phosphorus loadings. The results showed that below 800 ppm of phosphorus, the catalysts performance was not significantly affected, possibly because the interaction of phosphorus mainly was with the alumina support. However, above this threshold, the effect of phosphorus was noticeable with a decrease in intrinsic activity. The reduced performance can be attributed to a physical blocking of cobalt sites. But, in all poisoned catalysts, the product distribution was affected and shifted towards less valuable products as methane and light paraffins. The electronegativity of phosphorus might be the cause for this effect, as the effective H2/CO ratio on the catalyst surface may be increased due to a weakened metal-CO bonding and consequently, the selectivity of the hydrogenated products increased. [ABSTRACT FROM AUTHOR]

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]

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 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]