Direct gas-phase epoxidation of propene with nitrous oxide over modified silica supported FeOx catalysts

Vapour phase epoxidation of propene with nitrous oxide over alkaline containing silica supported iron oxide catalysts was experimentally investigated. A reaction network is deduced from the trends of product selectivities as function of propene conversion using different catalysts. Important side reactions are parallel propanal formation and consecutive isomerisations of propylene oxide (PO) to propanal, acetone and allyl alcohol. Rates of these reactions were affected by catalyst composition, which influenced acid-base properties, number of silanol groups and surface area. A PO selectivity of similar to 75% and PO space-time yields of 0.02-0.03 g(PO) g(cat)(-1) h(-1) were obtained with a cat catalyst containing ironoxo-species and caesium ions/-oxides. These results can only be obtained at a high surplus of N2O versus propene concentration in the reactor feed. Likely reasons for that is an inhibition of propylene oxide's formation rate by propene and propylene oxide itself. (C) 2004 Elsevier Ltd. All rights reserved.