On the Transformation of Vanadyl Hydrogenphosphate Hemihydrate

The tribomechanical treatment of vanadyl hydrogenphosphate hemihydrate (VHP) has been proven to be a valuable tool to enhance the catalytic performance of vanadyl pyrophosphate (VPP) catalysts for the oxidation of n butane to maleic anhydride. It was demonstrated that tribomechanically improved catalytic properties are mainly caused by decreased particle sizes and increased internal micro strain in the VHP precursor. This altered VHP microstructure is transferred to the VPP catalyst in a topotactic reaction, which is described as 2 VOHPO4 • 0.5H2O  (VO)2P2O7 + 2 H2O (1) Untreated and tribomechanically treated VHP’s, milled in different laboratory mills, were investigated by thermo analysis (TG/DSC/MS) to gain more information on the thermal decomposition of VHP concerning the dynamic release of water from the crystal lattice. The VHP precursors studied were prepared by the alcoholic route (VHPROH) and by the aqueous route (VHPH2O)

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

Identifizierung der Realstrukturen im System VOHPO4 x 0.5 H2O - (VO)2P2O7

Vanadylpyrophosphate werden seit langer Zeit in der selektiven Partialoxidation von n-Butan zu Maleinsäureanhydrid (MSA) eingesetzt. Entscheidend für die katalytische Aktivität sowie Selektivität gegenüber MSA ist der Syntheseweg des Precursors VOHPO4 x 0.5 H2O sowie des durch Kalzinierung erhaltenen Vanadylpyrophosphates (VO)2P2O7 [1, 2]. Ziel dieser Untersuchungen ist es, einen Beitrag zum fundamentalen Verständnis der Struktur – Wirkungsbeziehung dieser Katalysatoren in der Partialoxidation zu liefern. Hierzu wurde eingehend die Realstruktur, d.h. Defektarten wie Atompositionen und Besetzungszahlen sowie Kristallitmorphologien und Mikrospannungen in der Verbindung (VO)2P2O7 untersucht