A Durable and Efficient Cu Zeolite based SCR Catalyst for Cold Start and High Temperature DeNOx Applications 2021-26-0190
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 (CuZ-SCR) is gaining 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 to proceed.
In this study, the CuZ-SCR catalyst performance was tested as fresh and as high temperature aged (>800°C) on an engine test bed using a 0.7 L diesel engine and Non-Road Steady-state Cycle (NRSC). The NOx conversion efficiency of the CuZ-SCR catalyst during alpha (NH3/NOx) changes, NO2/NOx ratio changes and space velocity changes was established. Entire Full Useful Life (FUL) NOx emission control performance was evaluated for a novel CuZ-SCR catalyst placed downstream of a DOC & DPF in a DOC+DPF+SCR catalyst system. In order to evaluate FUL durability, including high temperature durability (exotherm functions) with multiple active DPF regeneration events (≥600°C) and sulfation/desulfation events, the catalyst system was exposed to a customized cycle for continuous 450 aging cycles, equivalent to the FUL thermal load and sulfur exposure of a vehicle over 160000 km. The performance of the novel CuZ-SCR catalyst was tested using the NRSC 8-mode test cycle after every continuous 50 cycles in 450 aging cycles. The results show that the novel Cu-ZSCR catalyst has excellent NOx reduction performance over a wide temperature range from low to high, as well as excellent durability to FUL.