Structured NSR-SCR hybrid catalytic technology: Influence of operational parameters on deNOx activity

Abstract An intermediate approximation using structured reactors between the study of deNOx catalysts at laboratory scale and in motor bench has been addressed. The hybrid NSR (NOx Storage and Reduction) and SCR (Selective Catalytic Reduction) technology has been analyzed for Pt-Ba-K/Al2O3 and Cu-SAPO-34 catalysts structured in monolithic form. In order to analyze the influence of the way of driving on deNOx efficiency, operational parameters such as NO inlet concentration, space velocity in terms of total flow rate, temperature, and the concentration of reductant agent, using H2 and C3H6, have been modified. The coupled NSR-SCR configuration is more efficient than the single NSR alternative, since the former used the ammonia produced in NSR monolith to reduce the non-adsorbed NOx through the SCR process over the system placed downstream. However, NH3 production depended on NO concentration, temperature, and reductant agent content in the process, limiting the promoting effect at high temperatures and NO concentrations, and low hydrogen concentration. N2 selectivity increased when temperature increased, and NO concentration and hydrogen content decreased. On the other hand, NOx to N2 reduction efficiency of the combined NSR-SCR system was not affected by variations in space velocity, with a maximum range studied up to 90,000 h-1. Based on these results, the location of the catalytic system should be adjusted in order to work in the 250-350 oC temperature range, where conversion and N2 selectivity values were around 70 and 95%, respectively. On the other hand, the hydrogen concentration of 2 and 3% can be suitable for the efficient operation of the system, since as reductant agent increased the ammonia formation and the surface regeneration also increased. The substitution of H2 by propylene as reducing agent caused a decrease in the amount of ammonia produced in the NSR configuration, which limits the improvement of deNOx activity of the double NSR-SCR configuration, and overproduces CO2, CO and N2O through parallel reactions as reverse water gas shift or C3H6 oxidation, which could poison the system and require emission control through other technologies.