Interactions of dienes and alkynes with rutile (titanium dioxide)

Abstract

The catalytic properties of titanium dioxide (rutile) have been examined for a number of reactions involving dienes (propadiene and buta-1,3-diene) or alkynes (ethyne, propyne and but-2-yne) with hydrogen, deuterium or deuterium oxide.

The isomerization of propadiene to propyne and the exchange of the methine hydrogen atom of the latter with deuterium oxide occur below 370 K.

The main reaction with all the compounds, but particularly the alkynes, was a loss of hydrocarbon to the surface at 470 K or above to form a residue which was probably oligomeric. This process was accompanied by some formation of alkenes from buta-1,3-diene and to a much smaller extent from the alkynes; the reaction was not affected by the presence of gas phase hydrogen or deuterium and was essentially a self-hydrogenation of the unsaturated compounds. Water inhibited the formation of residue and the self-hydrogenation of buta-1,3-diene, and an exchange reaction occurred if deuterium oxide was used.

The influence of various pretreatments on the catalytic properties of titanium oxide were examined and possible intermediates for some of the reactions are proposed.