Browse Publications Technical Papers 2019-26-0130
2019-01-19

Thermally Durable Zeolite Based SCR Catalysts for Controlling NOx Emissions in Diesel Exhaust to Meet BS VI Norms 2019-26-0130

From the recent past, automotive exhaust emission management strategies are progressing towards an alternative for vanadia based selective catalytic reduction (V-SCR) of NOx in diesel powered vehicles. Some of the major inadequacies of existing V-SCR technology are as follows: • Poisoning tendency of V-SCR • Poor thermal endurance (deteriorates at 550°-600°C) • Volatilization of harmful vanadium into environment • Inadequate NO2 conversion. Metal incorporated zeolite systems, (the metals being preferably selected from transition metal elements), has gained momentum for commercial DeNOx applications. However, the major challenge with this zeolite SCR (Z-SCR) is its low thermal /hydrothermal stability. In the current study, it has been attempted to overcome this by various synthetic combinations. In present study, various combinations of mono metallic & bimetallic Z-SCR were extensively studied for their low and high temperature activities. The host zeolites were selected on the basis of various properties such as surface area, crystallinity, crystal size and pore opening. The active transition metals were selected based on its affinity to react and attach with the zeolytic framework elements. It is observed that when the selected transition metal is substituted in small pore zeolites, the resultant Z-SCR gains high thermal and hydrothermal stability. It is also observed that, in addition to the selection of the zeolites & transition metals, the choice of silica/alumina binder, plays a vital role in achieving the required DeNOx activity in the wide temperature range (180°C - 650°C). The Z-SCR washcoat derived from above combinations were coated on a ceramic substrate. The catalysts were evaluated for physical properties as well as its DeNOx activity. It was found to have excellent adhesion, high surface area and optimal NH3 adsorption capacity. The coated ceramic substrates were tested on Simulated Gas Test Bench for its DeNOx activity and it was found that the total NOx conversion reaches higher than benchmark. The catalysts was tested again as hydrothermally treated on the Simulated Gas Test Bench for its DeNOx activity and it was found that the total NOx conversion surprisingly improved.

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