The reaction of nitric oxide with carbon monoxide on a catalyst of 0.5
wt% Pt-3.4 wt% MoO3 supported on alpha-Al2O3 has been investigated in
different reactors at atmospheric pressure. A fixed-bed reactor with
external recycle loop exhibited bistability and hysteresis as CO conce
ntration or temperature were varied. In a tubular fixed-bed reactor no
n-isothermal periodic oscillations (Delta T-max=40 K) were found in a
specific pressure-concentration-temperature region (p-c-T region). The
amplitude and period time of the oscillations changed smoothly inside
the p-c-T region and died out suddenly at the borders of the region.
The oscillations were of a relaxation type and lasted for more than 48
h. With fresh catalyst, a new quartz reactor and a specific pretreatm
ent they were reproducible. It was shown that oscillations had kinetic
origins and that the changes of the temperature synchronised the elem
entary oscillators. An autocatalytic model is proposed to explain the
experimentally observed phenomena.