Narkhede, V., Kumar, D., Cursetji, R., Siddiquie, T. et al., "VWT - SCR Catalyst to Meet BS-IV Emission Standards and Beyond," SAE Technical Paper 2013-26-0056, 2013, doi:10.4271/2013-26-0056.
Technologies for exhaust aftertreatment of diesel engines are driven by emission standards and Selective Catalytic Reduction (SCR) will play a key role in complying with the requirements, particularly for the heavy duty vehicles. Amongst the variety of catalysts for the SCR reaction, the Vanadium-Tungsten-Titanium-Based (VWT) system is preferred over the base metal doped zeolite because of the established advantages of wide temperature window, robust and durable performance and resistance to sulfur exposure.While the basic chemical reactions involved in ammonia-SCR are well known, the challenge lies in identifying the right combination of substrate and wash coat formulation to meet with customer specific requirements. An insight into the relevant materials properties of the substrates as well as the bulk surface properties of the wash coat such as its ammonia storage capacity, V2O5 dispersion and stability are important.Typically the VWT-SCR technology is operated upto a upper limit of 450°C. This paper reports the optimization of a VWT formulation which can be used upto > 500°C. The influence of different operating parameters such as NO2/NOx ratio, NH3/NOx ratio, oxygen content, space velocity has been studied. In addition, the suppression of the undesirable formation of N2O on an optimized catalyst formulation is also reported. Effects of poisonous elements such as Na, K, Zn, etc on the SCR performance are also studied. The database generated over a wide range of operating parameters forms the basis to evolve the design criteria for offering customer specific solutions with demonstrated performance and durability.