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 has been 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 were as follows: poor thermal endurance (deteriorates at 550°-600°C), volatilization of harmful vanadium into environment and 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) was its low thermal/hydrothermal stability. In the current study, it has been attempted to overcome this by various zeolites and metals combinations. Various combinations of metallic 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 etc. The active transition metals were also selected based on its affinity to react and attach with the zeolytic framework elements. It has been observed that when the selected transition metal is substituted in small pore zeolites, the resultant Z-SCR gains high thermal and hydrothermal stability. It was also observed that, in addition to the selection of the zeolites & transition metals, the choice of binder, plays a vital role in achieving the required DeNOx activity in the wide temperature range (180°C - 650°C).

Z-SCR washcoat derived from above combinations were coated on a ceramic substrate. And the developed new technology washcoats have been undergone proprietary treatment. The washcoats 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 (SGTB) for its DeNOx activity and it was found that the total NOx conversion reaches higher than benchmark and meeting BS VI norms. The catalysts have been tested again as aged on the simulated gas test bench for its DeNOx activity and it has been found that the total NOx conversion has been substantially enhance ed.