The inhibition of propane oxidation by nitric oxide on a Pt/SiO2 catalyst

The effect of nitric oxide on the oxidation of alkanes over Pt/SiO2 under stoichiometric conditions has been investigated. With propane, 1000 ppm NO lowers the rate by a factor of more than 20 and the effect remains substantial with <1 ppm of NO. The response to the introduction and removal of NO is near instantaneous. Nitric oxide is very weakly adsorbed with similar to0.03% coverage under reaction conditions with 1 ppm NO present. Some NO2 is formed concurrently with alkane oxidation and the oxidation of propane is much slower with NO2 than with a NO/O-2 mixture. Inhibition by trace NO is best explained in terms of the repeated oxidation of NO to NO2 and subsequent NO2 dissociation which induces filling of the empty sites required for alkane oxidation on a largely oxygen covered surface. Inhibition is less with isobutane, which is oxidised at a lower temperature where less NO2 is formed. It is also less during ethane oxidation which proceeds at a higher temperature where surface and gaseous oxygen equilibrate faster, thus restricting any increase in oxygen coverage due to NO2 formation. (C) 2002 Elsevier Science B.V. All rights reserved.