(670c) Using Aberration-Corrected STEM Imaging to Explore Chemical and Structural Variations in the MoVNbTeO Oxidation Catalyst
Selective oxidation catalysis is used in production of roughly 25% of all important organic chemicals and intermediates used for making consumer and industrial products . Current processes used to produce high-demand C3 derivatives, namely acrylic acid and acrylonitrile, make use of multicomponent bismuth molybdate catalysts with propene feeds [1-2]. Significant cost savings exist if propene can be replaced by propane as the feedstock. The dominant candidate for this process is based on the multiphase MoVTeNbO complex oxide system [1-3]. The best MoVTeNbO catalysts with respect to selectivity and activity are two-phase mixtures comprised of an orthorhombic network bronze phase (M1) and a hexagonal tungsten bronze (HTB)-type phase (M2) [2-3]. Structural models currently exist for both phases based on simultaneous Rietveld refinement of high-resolution synchrotron X-ray and neutron powder diffraction data . Recently, we have used aberration-corrected STEM methods to image M1 and M2 phase preparations. Structural models based on HAADF images are developed and compared to the Rietveld-refined model developed by DeSanto et al.[2-5].
As an extension of this work, we have characterized a number of compositional and structural variants. These include omission of Te and/or Nb, replacement of Nb with Ta [6,7], Te with Sb , and changing the basic framework structure. Understanding the relationship between crystal chemistry, stucture, and catalyst performance is central to the development of these catalysts.
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