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Abstract: The performance of a 0.5wt.% Pd on alumina catalyst used for the hydrodechlorination of tetrachloroethylene, in presence of model organosulphur (thiophene and butanethiol) organonitrogen (quinoline and n-butylamine) and organooxygen (tetrahydrofurane, isobutanol) compounds, was studied in this work. Experiments were carried out in a continuous fixed bed reactor (space time of 1.8ming/mmol of TTCE) at a pressure of 0.5MPa and a temperature range of 200–300°C. Concentrations of heteroatomic molecules in the range 0.5–5% were used in this study. Organosulphur compounds produce strong inhibition on the TTCE hydrodechlorination, decreasing the conversion and increasing the selectivity for partially dechlorinated compounds (trichloroethylene). However, this effect is shown to be highly reversible, the catalyst almost recovering its initial activity when the sulphur source is removed from the feed. Organonitrogen compounds cause a fast and fatal deactivation of the catalysts, being this effect completely irreversible. Different regeneration procedures were tested, being the treatment with hydrogen at 400°C the only way to partially recover catalytic activity. Finally, organooxygen compounds hardly affect catalyst performance. [Copyright &y& Elsevier]

Open-cell foams are solid structures formed by an intricate network of macroporous interconnected channels. The high porosity and tortuosity of the channels results in high external surface area, so open-cell foams are very efficient for promoting phase contact, e.g. in gas–liquid packed-bed reactors. In addition, the tortuous path of the channels breaks up the flow and enhances mass transfer with respect to other structured beds, such as honeycomb monoliths, and pressure drop is comparatively low. The liquid hold-up (system water–air), and the mass transfer coefficient (oxygen from water to nitrogen), have been measured for a ceramic foam, specifically a 20 ppi alumina foam bed of 50 mm diameter and 100 mm length (average pore diameter 1.25 mm and strut diameter 0.42 mm), for co-current down flow. Gas and liquid flow rates have been varied in the range corresponding to 0–8.5·10 −2 and 0–3.2·10 −3 m/s superficial velocities, respectively. At these conditions, the bed operates at trickle flow regime. The dynamic liquid hold-up and the mass transfer coefficient have been correlated as a function of relevant dimensionless numbers. [ABSTRACT FROM AUTHOR]

Abstract: The deactivation of carbon- and alumina-supported palladium catalysts used for trichloroethylene (TCE) hydrodechlorination in wastewaters at mild conditions is studied in this work. TCE concentrations are in the interval of industrial wastewaters (200–900ppm, corresponding to 1.54–6.92mmol/L). Reaction studies have been performed in both batch slurry reactor and continuous fixed bed reactor. In both cases, a deactivation model (considering first-order kinetics for the main reaction, first-order deactivation kinetics, and the residual activity of the deactivated catalyst) has been proposed and experimentally validated. In general terms, carbon-supported catalysts are the most stable. Deactivation behavior can be explained in terms of the aqueous-phase redox and complexation equilibria of the active phase. The effect of different operation approaches, such the modification of the pH or the addition of alkalinity sources has been tested, being observed that the addition of sodium carbonate largely increases the catalyst stability. [Copyright &y& Elsevier]

Abstract: The deactivation of a 0.5wt.% Pd on alumina catalyst used for the hydrodechlorination of tetrachloroethylene (TTCE), chlorobenzene (CBZ) and dichloromethane (DCM) in organic matrix in gas phase has been studied in this work. Experiments were carried out in a continuous fixed bed reactor, at a pressure range of 0.1–2MPa. It was found that the reactivity and stability of the catalyst increases as pressure increases. Different compounds present quite different deactivation patterns: fast initial deactivation followed by a plateau for DCM and CBZ, continuous moderate deactivation for TTCE. The effect of hydrogen chloride was studied by adding to the reactor feed different amounts of hydrogen chloride, working at 225–300°C. Fresh and used catalysts were characterised by nitrogen porosimetry, X-ray diffraction, transmission electronic microscopy, scanning electronic microscopy, thermogravimetry and temperature-programmed oxidation. Results indicate that carbonaceous deposits play a key role in the catalyst deactivation, being this phenomenon promoted by the presence of HCl. [Copyright &y& Elsevier]

Abstract: The performance of four different alumina-supported noble metal catalysts (0.5% of Pd, Pt, Rh and Ru, respectively) for the deep oxidation of trichloroethene (1000–2500ppmV, WHSV=55h−1) in air was studied in this work. Experiments were carried out at both dry and wet (20,000ppm of H2O) conditions. Catalysts were compared in terms of activity, selectivity for the different reaction products (CO2, HCl, Cl2, C2Cl4, CCl4 and CHCl3), and stability at reaction conditions. As general trend, the activity of the catalysts decreases in the order Ru≫Pd>Rh>Pt. Concerning to the effect of the water addition, no important effect on the catalyst activity was observed, except in the case of Pt, for which an increase of the catalytic activity was observed. Reaction mechanism (and hence product distribution) is very similar for Rh, Pd and Pt, being in these cases C2Cl4 the only organochlorinated by-product detected. In the case of Ru, the reaction mechanism seems to be quite different, CCl4 and CHCl3 being the main organic by-products. Simple power-law kinetic expressions (first order on trichloroethene concentration for Pd, Rh and Ru, and zeroth order for Pt) provide fairly good fits for catalytic performance of the studied catalysts. Finally, deactivation studies show that both formation of active metal chlorides (especially in the case of Rh) and fouling (especially for Pd and Pt) are the main deactivation causes. [Copyright &y& Elsevier]

Abstract: The scope of this work is to compare systematically the performance of particle beds and monolithic beds in catalytic reverse flow reactors used for combustion of lean methane/air mixtures, using alumina-supported palladium as catalyst. Different values of gas surface velocity (0.1–0.3m/s), particle diameter (3–6mm, for particle bed), cell density (200–400 cpsi, for structured bed) and catalyst/inert ratio (0.4–1) were used for the simulation of the combustion of 3500ppm methane in both kinds of reverse flow reactor. An unsteady one-dimensional heterogeneous model has been developed and solved using a MATLAB code. The model, physical parameters and transport properties used had been experimentally validated in a previous work, operating with a particle bed reverse flow reactor. Results obtained indicate that the reverse flow reactor is more stable when the catalyst particle beds are use, although the difference with the monolith bed decreases as surface velocity increases. In contrast, pressure drops in the bed are higher for the particle bed. [Copyright &y& Elsevier]