Engineering HC-SCR: Improved Low Temperature Performance through a Cascade Concept

Abstract

A catalytic after treatment system for lean HC-SCR was constructed of two different catalyst beds, e.g. of a Ag/alumina and Cu-ZSM-5 catalyst (cascade concept). The improved activity especially at low temperature range was found to be due to the synergetic effect of the two catalysts, which combines the transformation of the feed gas over Ag/alumina to such compounds that are highly reactive towards N 2 over Cu-ZSM-5. The effluent coming from the Ag/alumina bed was analysed by GC-MS along with the NO to N 2 conversion over the whole system by GC. The results obtained from the GC-MS measurements revealed that hydrocarbon used as a reducing agent is oxidised and that besides oxygenates also various N-containing hydrocarbons are formed over the Ag/Al 2 O 3 .

Selective catalytic reduction of NO over supported silver catalysts—practical and mechanistic aspects

“…Arve et al carefully analysed the gas phase by-products in octane-SCR and toluene-SCR over Ag/Al 2 O 3 by GC-MS and detected various types of by-products such as amines, ketones, and cracking products. 78 They also demonstrated that a cascade reactor consisting of Ag/Al 2 O 3 and Cu-MFI is very effective for both the increase in NO conversion at lower temperatures and suppression of the formation of these byproducts.…”

NO reduction by hydrocarbons and oxygenated compounds in O2 excess over a Pt/Al2O3 catalyst

“…Numerous reducers have been investigated: hydrocarbons [5,6,7,8,9,10,11,12,13], oxygenated compounds (mainly alcohols, more rarely aldehydes, ketones, ethers,…) [13,14,15] and nitrogen containing compounds (ammonia, urea, nitrocompounds,…) [15,16,17,18,19].…”

Alternate Pathway to Ammonia Formation in NOx Reduction: Direct Reaction of Acetylene and Nitrogen Atoms on Pt (111)

“…Although ammonia has been used effectively as a reductant for stationary sources, the injection of a urea-water solution (UWS) for deNOx in mobile sources remains problematic because of deposit formation issues at low temperatures and the possibility of ammonia slip . A recent solution to this problem is the use of one catalyst that produces ammonia from NOx, either a lean NOx trap (when rich) or a hydrocarbon SCR (HC-SCR) catalyst (when lean) − followed by an ammonia-SCR catalyst to maximize N 2 formation These dual catalyst systems offer the distinct advantage of avoiding ammonia and urea handling, while achieving high levels of NOx reduction without significant generation of N 2 O or release of ammonia.…”