The Role of Alloying in Highly Selective and Stable Propane Dehydrogenation Catalysts based on Silica-Supported Pt-Mn Particles Prepared via SOMC
Light olefins, e.g. ethene/propene, are key intermediates for the production of a large number of bulk and fine chemicals as well as polymers. While these olefins were mostly produced from cracking of naphtha, the increasing availability of shale gas led to changes in cracking technology, resulting in decreased propene production despite an increased demand.1 Thus, the direct dehydrogenation of the corresponding alkane has become the dominating alternative approach for the production route of olefins in recent years. Two classes of catalysts are currently used industrially, based on either Cr or Pt. Both of them suffer from fast deactivation requiring constant regeneration and necessitate additional promoter metals to achieve high selectivity at high conversion as well as stability.2 The Pt-based catalysts, used in the Olefex (PtSn) and Dow Fluidized Catalytic Dehydrogenation (PtGa), are bimetallic, where the two metal components generate an alloy, improving the selectivity and the stability of the catalysts towards sintering and coke formation.3 Other metal dopants have also been investigated, where the formation of alloys has be shown to a key to high selectivity in Pt-based catalysts.
Here we report the preparation and characterization of a highly selective and stable silica-supported, Pt-Mn based Propane dehydrogenation catalyst using Surface Organometallic Chemistry.4 This involves a two-step approach with first the generation of Mn(II) single sites on the support surface and second, grafting of a Pt precursor followed by a reduction treatment under a flow of H2. Detailed multi-technique characterization, including microscopy, in-situ XAS, XPS and EPR show that this particularly robust and highly selective catalyst is best described as Pt-rich nanoparticles – resembling Pt3Mn – with a majority of Mn(II) sites on the support surface.
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