Molybdenum oxide based partial oxidation catalyst

Abstract

A new Mo-based structure was detected by high resolution transmission electron microscopy (HRTEM) and electron diffraction techniques in a molybdenum based mixed oxide catalyst after operation in the partial oxidation of acrolein at temperatures between 533 and 573 K for 9 h. This new crystalline phase has an orthorhombic crystal system. The structure has presumably a space group of Pban, but Pmmn cannot be excluded. XRD analysis was further used to refine this new Mo2O5 structure. The lattice constants were estimated to be a=1217.5, b=374.7 and c=404.4 pm, respectively. The elemental composition of the crystal was determined by the EDAX system attached to the electron microscope to be about (Mo0.6V0.3W0.1)2O5-x. This new structure is discussed in relation to earlier reports on a comparable composition and with respect to its possible role for partial oxidation catalysis.

Heterogeneously catalysed partial oxidation of acrolein to acrylic acid—structure, function and dynamics of the V–Mo–W mixed oxides

“…The data at 382 1C show only a very slight decrease in oxidation state from 5.6 to 5.3, coupled with small structural changes around the Mo centres. This is compatible with the proposals of Andrushkevich 14 and Schlo¨gl et al 15,16 for possible active phases in the catalyst. At temperatures above 400 1C, the change of oxidation state is much more drastic, and average minimum oxidation states close to Mo 4+ are reached.…”

“…In the SSITKA experiments, 16 O 2 in the feed gas was abruptly exchanged against 18 O 2 under steady state reaction conditions. A fast exchange reaction of the carbonylic oxygen of ACR involving lattice oxygen from the catalyst was observed.…”

“…The total oxidation products appear with all kinds of isotopomers ( 16 CO, 18 The slope of the other transient responses is characterised by a rapid decrease of the unlabelled components followed by a very slow decrease which is not terminated after 10 min. This phenomenon can be described by the fast replacement of the unlabelled intermediates on the catalyst's surface and a slow depletion of 16 O from the catalyst's bulk. By calculating the mass balance of the isotopic distribution the quantification of the oxygen released by the catalyst is possible.…”

“…After switching from 16 O 2 to 18 O 2 the formation of 18 O-labelled ACR was observed. This is due to a fast exchange reaction of the carbonylic oxygen of ACR involving lattice oxygen from the catalyst.…”

In Situ Investigations of Structureactivity correlations of Mixed Molybdenum Oxide Catalysts

“…In the mixed oxide system little is known about the cooperation of the different metal centers and their role for the stabilization of the active phase [1,2,3]. Here we report in situ X-ray absorption spectroscopy (XAS) and in situ X-ray diffraction (XRD) studies on the structural evolution of a precursor for bulk (MoVW) 5 O 14 during calcination and under propene oxidation conditions…”