Selective catalytic reduction of NO.sub.x in combustion gases, especially
from diesel engines, utilizes a system incorporating an oxidation catalyst
to convert at least a portion of NO to NO.sub.2, a particulate filter
downstream of the oxidation catalyst, a source of reductant such as
NH.sub.3 or urea for injection downstream of the particulate filter, and
an SCR catalyst located downstream of the point of injection of the
reductant. Considerable improvements in NO.sub.x conversion are observed.
