Role of dispersion of vanadia on SBA-15 in the oxidative dehydrogenation of propane

A series of vanadia catalysts supported on the mesoporous silica SBA-15 are synthesized using an automated laboratory reactor The catalysts contain from 06 up to 13 6V atoms/nm(2) and are structurally characterized by various techniques (BET XRD SEM TEM Raman IR UV/Vis) Samples containing up to 3 IV/nm(2) are structurally rather similar They all contain a mixture of tetrahedral (VOx)(n) species both monomeric and oligomeric The ratio of monomeric and oligomeric species depends on the vanadia loading At the highest loading of 13 6V/nm(2) in addition to tetrahedral (VOx)(n) also substantial amounts of three-dimensional bulk-like V2O5 are present in the catalyst The structural similarity of the low-loaded catalysts is reflected in their alike catalytical activity during the oxidative dehydrogenation (ODH) of propane between 380 and 480 C Propene CO and CO2 are formed as reaction products while neither the formation of ethene nor acrolein or acrylic acid is observed in other than trace amounts The activation energy for ODH of propane is similar to 140 kJ/mol The catalyst with the highest loading yields varying activation energies for different reaction conditions which is probably related to rearrangements between bulk-like and dispersed two-dimensional (VOx)(n) Rather than the monomer to oligomer ratio the ratio of two-dimensional to three-dimensional vanadia seems to be crucial for the catalytic properties of silica supported vanadia in the ODH of propane (C) 2010 Elsevier B V All rights reserved