Testing zeolite SCR catalysts under protocol conditions for NOx abatement from stationary emission sources (original) (raw)
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NOx abatement in lean exhaust gas conditions over metal substrated zeolite catalysts
Catalysis Today, 1996
Metal substrated ZSM-5 zeolites ion-exchanged with copper are effective catalysts in the elimination of nitrogen oxides from lean automotive exhaust gases when propene works as a reductant. Some co-cations improve the catalytic activity of Cu-ZSM-5. The critical temperature for the deactivation of Cu-ZSM-5 catalysts is around 700°C where the state of copper begins to change resulting in the decrease of the catalytic activity. The structure of the Cu-ZSM-5 zeolite collapses after thermal aging at temperatures above 800°C. However, the coexistence of chromium in the zeolite increases the thermal stability of Cu-ZSM-5 considerably. -5861 (95) 00207-3 ratio, ion-exchange procedure, role of different reductants (C3H 6 or CO), cation and co-cation, and aging were used as variables in the experiments.
Selective Catalyst Reduction (SCR) using Zeolite for Reduction of NOx Emissions in C.I. Engines
2021
The current study is aimed for reduction of NOx emission (oxides of nitrogen) from a direct injection CI engine by SCR (selective catalytic reduction) technology. The SCR system was developed originally at the (CAER) Centre for alternate and renewable energy in which zeolite was used as a catalyst. The developed SCR system was integrated with a single chamber direct injection CI engine of 3.7 kW rated power at 1500 rpm. Experimental tests results revealed the significant reduction of NOx emission with SCR system at all engine loads. Experimental design of the investigation typified obtaining standard behaviour of the engine i.e., without SCR followed by engine's information after the presentation of SCR framework. It is investigated from the exploratory tests results that hydrocarbon (HC) emission was highest about 20ppm at 10kg load yet at 4kg load it decreased to 16ppm. Carbon monoxide (CO) emission was moderately increased with SCR system. NOx emission are minimum with SCR at...
Applied Catalysis B: Environmental, 1996
Ambient temperature SCR of NO was studied over Ti, V and B silicalite-I, silicalite-1 and H-ZSM-5 catalysts. It was observed that even at 0°C sihcalite-1 possesses some activity which falls off sharply with increasing temperature. An enhanced activity could be correlated to the titanium content in the Ti and Ti-V silicalite samples. H-ZSM-5 and H-BS-1 show an unusually high transient activity probably due to weakly adsorbed ammonia species. These would not be adsorbed at higher temperature thus explaining the decreased activity as temperature is raised. Indeed with these catalysts no transient high activity was observed when the reaction was carried out at decreasing temperatures.
Selective Catalytic Reduction of NO x over H-ZSM-5 Under Lean Conditions Using Transient NH 3 Supply
Topics in Catalysis, 2004
The selective catalytic reduction (SCR) of NO x over zeolite H-ZSM-5 with ammonia was investigated using in situ FTIR spectroscopy and flow reactor measurements. The adsorption of ammonia and the reaction between NO x , O 2 and either preadsorbed ammonia or transiently supplied ammonia were investigated for either NO or equimolar amounts of NO and NO 2 . With transient ammonia supply the total NO reduction increased and the selectivity to N 2 O formation decreased compared to continuous supply. The FTIR experiments revealed that NO x reacts with ammonia adsorbed on Brønsted acid sites as NH 4 + ions. These experiments further indicated that adsorbed -NO 2 ) is formed during the SCR reaction over H-ZSM-5.
Journal of Catalysis, 2015
A comparative study was carried out on a small-pore Cu-CHA and a large-pore Cu-BEA zeolite catalyst to understand the lower N 2 O formation on small-pore zeolite supported Cu catalysts in the selective catalytic reduction (SCR) of NOx with NH 3. On both catalysts, the N 2 O yield increases with an increase in the NO 2 /NOx ratios of the feed gas, suggesting N 2 O formation via the decomposition of NH 4 NO 3. Temperature-programmed desorption experiments reveal that NH 4 NO 3 is more stable on Cu-CHA than on Cu-BEA. In situ FTIR spectra following stepwise (NO 2 + O 2) and (15 NO + NH 3 + O 2) adsorption and reaction, and product distribution analysis using isotope-labelled reactants, unambiguously prove that surface nitrate groups are essential for the formation of NH 4 NO 3. Furthermore, Cu-CHA is shown to be considerably less active than Cu-BEA in catalyzing NO oxidation and the subsequent formation of surface nitrate groups. Both factors, i.e., (1) the higher thermal stability of NH 4 NO 3 on Cu-CHA, and (2) the lower activity for this catalyst to catalyze NO oxidation and the subsequent formation of surface nitrates, likely contribute to the higher SCR selectivity with less N 2 O formation on this catalyst as compared to Cu-BEA. The latter is determined as the primary reason since surface nitrates are the source that leads to the formation of NH 4 NO 3 on the catalysts.