Effect of Engine Exhaust Parameters on the Hydrothermal Stability of Hydrocarbon-Selective Catalytic Reduction (SCR) Catalysts for Lean-Burn Systems

Abstract

A dual-catalyst bed composed of a reduction catalyst, Pd-sulfated zirconia, and an oxidation catalyst, CoO x /CeO 2 , was investigated for selective catalytic reduction (SCR) of NO x (NO and NO 2 ) by hydrocarbons for use in lean-burn natural gas engines. The primary focus of this submission is to examine the hydrothermal stability of the dual-catalyst bed and improve its hydrothermal durability by studying the effect of the engine exhaust parameters. The main parameters investigated were the concentration and nature of the hydrocarbons and the reaction temperature. Both cyclic as well as time-on-stream experiments were conducted under various engine exhaust compositions and different reaction temperatures to establish the conditions that could improve the water tolerance of the dual-catalyst bed. The higher concentration of the hydrocarbon mixture in the simulated engine exhaust was seen to assist the water tolerance of the dual-catalyst bed. Experiments were performed to isolate and identify the primary component in the hydrocarbon mixture that contributed more toward water tolerance. This study revealed that ethane had a more prominent effect than methane or propane for improving the hydrothermal stability of the catalyst bed. Moreover, the effect of the reaction temperature confirmed a shift in the operating temperature window in the presence of water vapor, as higher reaction temperatures were seen to significantly improve the hydrothermal stability of the dual-catalyst bed.

Pt-Rh/CeO2-Al2O3 for Controlling Emissions from Natural Gas Engines: Three-Way Catalytic Activity at Low Temperatures and Effects of SO2 Aging

“…This imposes a further challenge for controlling emissions from natural gas engines. The selective catalytic reduction of NO x with methane (CH 4 -SCR) coupled with lean combustion can be an alternative solution and has been studied extensively [10][11][12][13][14][15]. However, activities of the reported catalysts are not sufficient to obtain NO x and CH 4 conversions required in practical applications.…”

In-situ incorporation of binder during sol-gel preparation of Pd-based sulfated zirconia for reduction of nitrogen oxides under lean-burn conditions: Effect on activity and wash-coating characteristics

“…Previously we have demonstrated the hydrothermal stability of the dual-catalyst bed under simulated lean-burn engine exhaust conditions [12]. As a first step towards selection of a suitable binder, the binder-free and the binder-incorporated Pd/SZ catalysts have been tested under the same feed conditions to ensure that addition of binder to the reduction catalyst does not deteriorate its catalytic activity and consequently, impact the performance of the dual-catalyst bed.…”

“…Time-on-stream experiments were conducted for over 40 hours on the aluminaincorporated Pd/SZ containing dual-catalyst bed to test how it compares with the hydrothermal stability test previously conducted on the binder-free Pd/SZ containing mixed bed at 450 o C [12].…”

“…This dual catalyst system has three functions: (i) NO oxidation to NO2 (ii) NO2 reduction to N2 (iii) oxidation of unutilized hydrocarbons and CO to CO2. In this scheme, NO gets oxidized to NO2 over the oxidation catalyst (CoOx /CeO2) [11][12][13][14][15]. This step is important because NO2 has a stronger oxidizing potential when compared to NO and hence gets reduced more easily.…”

Reduce NOx Emissions by Adsorber-Reduction Catalyst on Lean Burn Engine

“…Although the Ricardo developed an variable tumble CCVS system [3] and good exhaust stratified combustion was obtained with high EGR rate of 70%, The structure of this system was complicated and NOx emission was also hard to satisfied the request of stricter emission regulation. For the methods of NOx decomposing [14] and selective catalyst reduction (SCR) [15] using for vehicle exhaust, the NOx catalyst conversion rate and the thermal stability of the catalyst are all hard to satisfied the practical request. Compared with these methods of reducing lean burn NOx, The NOx adsorber reduction catalyst combined with TWC can purify the NOx high efficiently within wide temperature scope.…”