3.1. Catalyst performance
3.1.1. Effect of sulphur on NOx interconversions
Before discussing the performance of the catalyst, it is important
to address the issue of the catalyst temperature. Catalyst heating
was achieved by contact with the exhaust gases, which in turn
depends on the combustion temperature and therefore engine
load. The catalyst used in the present study was rather large and,
as outlined in the experimental section, it was divided into two
sections: in principle, a consequence of this situation could be
catalyst temperature inhomogeneity during tests. We monitored
catalyst temperature both at the engine outlet (before the catalyst)
and after the catalyst to obtain indications on potential variations
in catalyst temperature along its length. The presence of gas–solid
heat transfer effects cannot be discounted, nevertheless, as shown
in Fig. 4, significant variations in catalyst temperature were not
observed, indicating that there were not significant temperature
gradients along the catalyst beds. Finally, it is worth noting that
on increasing the load and, hence the reaction temperature, GHSV
increases nearly linearly, which clearly affects the conversions
(vide infra).