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Current NOx emission reduction systems, selective catalytic reduction (SCR) and NOx storage and reduction (NSR), function well after achieving their operation temperature (typically ca. 250 °C) but have unsatisfactory NOx conversion at lower exhaust temperatures encountered during cold start and low load operation. The reduced exhaust temperature of advanced diesel engines with higher fuel efficiency challenges the low-T NOx reduction. We report here a new concept of high low-T deNOx efficiency of up to 80% at a feed temperature of ca. 200 °C at relevant space velocities (70k h−1). It utilizes high-frequency hydrocarbon pulsing on a dual-layer LNT-SCR monolithic catalyst under lean conditions. This system has the potential to expand the operating temperature window of the conventional deNOx devices.

Monolithic catalysts consisting of a layer of SCR catalyst deposited on top of a LNT catalyst were optimized to provide high NOx conversion at both low and high temperatures with minimal precious group metal (PGM) loading for effective diesel NOx emission control. In this study we demonstrate the application of LNT & SCR zoning in dual-layer catalyst to improve NOx reduction efficiency and show the potential to reduce the expensive PGM loading by up to 40% from that of LNT only catalyst without degrading its deNOx performance under simulated diesel exhaust conditions. We investigated the NOx reduction pathway in the SCR layer of the dual-layer catalyst using simulated rich exhaust of C3H6/CO/H2 as reductants. The non-NH3 reduction pathway by N-containing organic intermediates via the synergy of LNT and SCR catalysts can play a major role in the incremental NOx conversion over SCR layer at low temperatures (<= 225 °C).

A Benchtop Engine System (BES) is described to evaluate the NOx emission characteristics of diesel fuels. The BES enables the efficient testing of the combustion and NOx emission features of alternative fuels and additives. The BES comprises a computer controlled single cylinder engine generator, fuel blending and feed system, and NOx analyzer. The engine can be operated at different loads using the programmable load control. NOx concentration are monitored and recorded to evaluate the impact of the diesel fuel and/or additive. Several commercial diesel fuels and one commercial fuel additive were tested in both the 500 HP Heavy Duty Chassis Dynamometer and the BES. The reported results demonstrate the BES capabilities, differences in the NOx emission features of several fuels and additives.

The mechanism for the purging of a lean NOx trap has been investigated. For realistic purge times (e.g., 2 to 5 seconds), the stored NOx species do not decompose simply from equilibrium considerations (i.e., from the drop in O2 and NO concentrations during the rich purge). Instead, the decomposition of stored NOx is promoted by the reductants in the exhaust by a process referred to as reductive elimination. H2 is far more effective than CO or C3H6 for promoting this reductive elimination, particularly at low temperatures (e.g., 250°C). As long as H2 is available in the feedgas, H2O does not participate in the reductive elimination. However, if CO is the only reductant, H2O is needed to convert some of the CO to H2 through the water-gas-shift reaction. H2O is also important for the efficient storage of NOx during lean operation, possibly by enhancing the spillover of NO2 from a precious metal site to a NOx storage site.

A one-dimensional two-phase model of an adsorptive catalytic monolith reactor is used to analyze the Lean NOx Trap (LNT). The model simulates the features of NOx storage and reduction (NSR), a periodic process involving the sequential trapping on a storage component and conversion of NOx to nitrogen on a precious metal catalyst under lean conditions found in the exhaust of lean burn and diesel vehicles. A detailed storage kinetic model is used for the simulations. The NOx storage phase on Pt/BaO/Alumina catalyst has been studied in detail with particular attention to the effect of fluid velocity, storage time and storage component loading. The reductive phase is also analyzed. The simulated results are compared with our lab experimental data. The model predictions are in good agreement with the experimental observations and trends reported in the literature.

A one-dimensional two-phase model of an adsorptive catalytic monolith reactor (used as Lean NOx Trap, LNT) is developed and analyzed. The model simulates the features of NOx storage and reduction (NSR), a periodic process involving the sequential trapping on a storage component and conversion of NOx to nitrogen under lean conditions found in the exhaust of lean burn and diesel vehicles. The effect of design and operating parameters, such as the lean and rich times and feed temperature, on NO2 conversion is examined. Using a relatively simple kinetic model and without any attempt to fit data, the LNT model predicts the dependencies of NO2 conversion on several feed parameters that are in good agreement with experimental observations.