Electrochemical promotion of Rh catalyst in gas-phase reduction of NO by propylene

The concept of non-faradaic electrochemical modification of catalytic activ ity (NEMCA) has been applied for the in situ control of catalytic activity of a rhodium film deposited on YSZ (yttria stabilized zirconia) solid elect rolyte towards reduction of 1000 ppm NO by 1000 ppm C3H6 in presence of exc ess (5000 ppm) O-2 at 300 degreesC. A temporary heating at this feed compos ition results in a long-lasting deactivation of the catalyst under open cir cuit conditions due to partial oxidation of the rhodium surface. Positive c urrent application (5 muA) over both the active and the deactivated catalys ts gives rise to an enhancement of N-2 and CO2 production, the latter excee ding several hundred times the faradaic rate. While active rhodium exhibits a reversible behaviour, electrochemical promotion on the deactivated catal yst is composed of a reversible and an irreversible part. The reversible pr omotion results from the steady-state accumulation of current-generated act ive species at the gas exposed catalyst surface whereas the irreversible ef fect is due to the progressive reduction of the catalyst resulting in an in creased recovery rate of lost catalytic activity. The results are encouragi ng with respect to application of rhodium for the catalytic removal of NO f rom auto-exhaust gases under lean-burn conditions.