The influence of chemical transport via vapour phase on the properties of chloride and caesium doped V-Fe mixed oxide catalysts in the oxidation of butadiene to furan

Chloride and caesium doped V-Fe mixed oxides prepared by different methods and calcined under vapour-phase transport-restricted conditions showed a high initial furan yield of up to 40 mol-% in the oxidation of butadiene. However,after only a few hours on stream a significant loss of activity and selectivity was observed. The reason for this undesirable property was investigated using different bulk and surface-sensitive characterisation methods such as x-ray diffraction, x-ray photoelectron spectroscopy, ransmission electron microscopy and chemical methods. The data obtained for the structure, morphology, and composition of the fresh and used catalysts were correlated with their activity and selectivity properties. The presence of chloride ions was found to be surprisingly necessary for the origin of furan selectivity even up to 50 %, which was however stable only for a short period of time. Chemical transport via chlorides or bromides was observed to be essential for the formation as well as the maintenance of the activity and selectivity properties of the system. The results obtained are interpreted with an assumption that the formation of volatile halides is necessary to form disperse VOx species, which act as active and selective centres for the present reaction. Models for the formation and deactivation of these centres are discussed in this work. In addition, the possible roles of caesium and iron oxides in the catalytic system are also described and disputed

Structure–reactivity relationships in VOx/TiO₂ catalysts for the oxyhydrative scission of 1-butene and n-butane to acetic acid as examined by in situ-spectroscopic methods and catalytic tests

Different VOx/TiO2 catalyst have been catalytically tested and studied by in situ-spectroscopic methods (FT-IR, UV/vis, EPR) in the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid (AcOH). While 1-butene OHS follows the sequence butane → butoxide → ketone → AcOH/acetate with a multitude of side products also formed, n-butane OHS leads to AcOH, COx and H2O only. Water vapour in the feed improves AcOH selectivity by blocking adsorption sites for acetate. The admixture of Sb2O3 was found to improve AcOH selectivity which is due to deeper V reduction under steady state conditions and lowering of surface acidity. VOx/TiO2 catalysts with sulfate-containing anatase are the most effective ones. Covalently bonded sulfate at the catalyst surface causes specific bonding of VOx, stabilizes active V species and ensures their high dispersity

Structure-reactivity relationships in supported VOx catalysts for the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid: A comprehensive catalytic and in situ study

A pure and an antimony-modified VOx/TiO2 catalyst have been catalytically tested in a total pressure range of 1-17 bar and studied by in situ-FTIR, in situ-UV/vis and operando-EPR spectroscopy at normal pressure in the oxyhydrative scission (OHS) of 1-butene and n-butane to acetic acid (AA). While 1-butene OHS follows the sequence butene butoxide ketone acetate/AA with a multitude of trace side products also formed, n-butane OHS leads to AA, COx and H2O only. Adding water to the feed improves AA selectivity by favouring the hydrolysis of the ketone intermediate. Doping by Sb was found to improve AA selectivity being due, among other reasons, to deeper V reduction under steady state conditions. Activity in n-butane OHS decreases continuously with rising total pressure while both activity and selectivity in 1-butene OHS pass a maximum at 7 bar

Grundlagen der Selektivoxidation von n-C_4-Olefinen zu C_4-Oxygenaten Abschlussbericht

SIGLEAvailable from TIB Hannover: F02B1724 / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekBundesministerium fuer Bildung und Forschung, Berlin (Germany)DEGerman