Typical diesel engine-out emissions consist of hydrocarbons
(HC), carbon monoxide (CO), particulate matter (PM) & oxides of
nitrogen (NOx). The HC and CO emissions are oxidized by a diesel
oxidation catalyst (DOC), placed upstream, closer to the exhaust
manifold. The DOC is often followed by a diesel particulate filter
(DPF), which entraps and combusts PM. The NOx is often controlled
by a selective catalytic reduction (SCR) catalyst. An SCR catalyst
commonly uses NH3 to reduce the NOx to N2. Vanadium-based SCR
catalysts have been widely used for many years. More recently,
Cu-Zeolite based SCR (Cu-ZSCR) has gained much attention primarily
due to the potential environmental hazards of vanadium and a wider
temperature window of effective operation. The SCR reaction is
facilitated by the presence of NO2 at lower exhaust gas
temperatures by means of the so-called "fast" reaction.
However, this is only advantageous up to about 300°C. At higher
temperatures, the contribution of NO2 is insignificant, since mass
transfer & diffusion phenomenon become dominant in NOx
conversion enabling the "standard" SCR reaction. In this
study, Full Useful Life (FUL) performance was evaluated for a novel
Cu-ZSCR catalyst placed downstream of a DOC & DPF in a
DOC+DPF+SCR catalyst system. The Cu-ZSCR catalyst performance was
tested as fresh and as high temperature aged (>800°C) on an
engine test bed using 0.7 L diesel engine and Non-Road Steady-state
Cycle (NRSC). The efficiency of the catalyst during alpha (NH3/NOx)
changes, NO2/NOx ratio changes and space velocity changes was
established. In order to evaluate FUL durability, including high
temperature durability with multiple active DPF regeneration events
(≥ 650°C) and sulfation/desulfation events, the system was exposed
to a customized cycle for 450 cycles, equivalent to the FUL thermal
load and sulfur exposure of a vehicle over 180K km. The performance
of the novel Cu-ZSCR was tested using the NRSC test cycle at
increments of 50 cycles. The results show that the novel Cu-ZSCR
catalyst has excellent NOx reduction performance over a wide
temperature range, as well as excellent durability to FUL.