The second test reaction is the aldol condensation of

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Unformatted text preview: he catalyst and to propene by acidic sites. The second test reaction is the aldol condensation of acetone leading to α,β -unsaturated carbonyl compounds over basic and to hydrocarbons over acid site [116]. The basicity of the catalysts can be scaled by the selectivity of the products formed over basic sites to the ones formed over acidic sites. In order to study the influence of the catalyst composition on conversion, selectivity, stability and the tendency towards coke formation and to find the best catalyst for further studies, all Ni containing catalysts were reduced in-situ at 800°C and tested for 240 minutes time on stream. The reduction temperature was chosen on the basis of the TPR results, 240 min time on stream were chosen for two reasons. Firstly, because it was found to be long enough to analyse the catalytic performance under steady state conditions. Secondly, because it resulted in sufficient amounts of carbon deposits in order to study the catalyst tendency towards coking by temperature programmed combustion (TPC) of the carbon deposits using TG-MS. The results were compared with a conventional steam reforming catalyst Ni/Al2O3 (20% NiO, 2% K2O) tested under the same reaction conditions. The catalytic tests were performed at 700 and 800°C as these were reported to be suitable reaction temperatures in the related reactions. The reaction was performed in 25% O2 surplus compared to the stoichiometric value in order to avoid excessive coke formation, which could lead to the complete deactivation of the catalysts and the disintegration of the catalyst particles as reported for the partial oxidation of CH4. In order to improve the heat transfer necessary to minimise possible overheating of the catalyst surface He was used as a diluent because of its high thermal conductivity. Most of the catalytic tests were repeated to verify the reproducibility of the results. 1. Introduction 50 Additional catalytic tests were performed in order to quantify the effectiveness of the reduced catalysts using the empty reactor, SiO2 wool (used to hold the catalyst) and the not reduc...
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