Site isolation based design of selective oxidation catalysts

• Behavior of selective oxidation catalysts was improved by adding low active elements.
• Active species were separated with low active ones within the same or different phases.
• Diluted oxydehydrogenation catalyst was further improved by decreasing surface acidity.
• Diluted (amm)oxidation catalysts were further improved by increasing surface acidity.

The paper summarizes results of using “dilution” approach for isolation of active sites in metal oxide catalysts. It is shown that the incorporation of catalytic inert elements, such as Mg, Al, Zr, Si, Hf, Ti and Nb, to the bulk of VSb and VMo oxides substantially increased their selectivity in partial oxidations of lower paraffins due to the structural isolation of V, Sb and Mo species. Herein the behavior of diluted oxides was dependent on the nature and amount of diluent material. The performance of diluted catalysts was further improved by tuning their surface properties. In particular, the selectivity of propane oxidative dehydrogenation to propylene was increased by making catalyst surface less acidic. On the contrary, the selectivity of propane ammoxidation to acrylonitrile was higher on more acidic surface built up by loading VSbAl oxide catalyst with tungsten. Phosphorus addition to the VMoNb oxide catalyst essentially improved selectivity of ethane oxidation to acetic acid also as a result of increasing surface acidity.

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