Fourier-transform Infrared Spectroscopic Studies of the Reactivity of Vanadia Titania Catalysts Toward Olefins .1. Propylene

The adsorption and transformation of propylene and of several O-containing C3 organic molecules (namely isopropyl alcohol, acetone, allyl alcohol, acrolein, and acrylic acid) on vanadia-titania in the temperature range 150-673 K have been investigated by IR spectroscopy. At low temperatures (150-200 K), propylene adsorbs as such through pi-bonding and reacts later to give an adsorbed species identified tentatively as an allyl radical. Alternatively, it undergoes addition by a surface OH group to give an isopropoxy species. At least two main surface pathways for propylene transformation are active, leading to surface species functionalized at C2 (isopropoxy species and acetone) and at C1 (acrolein and acrylates) as well as products arising from coupling of the allyl radical. The results are discussed in relation to literature data concerning the heterogeneously catalyzed selective oxidation of propylene carried out on vanadia-titania as well as on bismuth-molybdate-based catalysts.