Development and performance evaluation of NOx reduction catalysts for lean-burn engines
13th, March 2019, Thursday, 4:00‐4:30 pm, ChE Seminar hall
Abstract:- Air pollution caused by mobile sources (such as vehicles) has become a major concern nowadays. The major pollutants include COx, NOx, unburnt HC’s and SOx. NOx being one of the major pollutants is responsible for causing acid rain, photochemical smog, acidification of soils and waters. All of these phenomena affect plants, animals and human health directly or indirectly. With the introduction of BS-VI emission norms in the upcoming future, stringent norms for NOx emissions have been introduced for light-duty vehicles and two-wheelers. According to a report issued by International Council on Clean Transportation, NOx emission limit for both light and heavy-duty diesel vehicles has been reduced below 0.1 g/km. This corresponds to NOx reduction of 68-76% in case of light-duty CI vehicles and 89% reduction in case of heavy-duty CI vehicles from BS IV to BS VI emission limits. The two major de-NOx technologies used are LNT and SCR. SCR utilizes a reductant such as ammonia (a product of hydrolysis of urea), hydrocarbon or hydrogen. Ammonia is considered best reductant for SCR unit so far. In order to provide ammonia to the SCR unit, an additional space is required to store urea solution which produces NH3 on hydrolysis. This is one of the disadvantages of using SCR as an after-treatment device. On the other side, LNT comprises of noble metal (Pt, Rh, Pd and Ru), NOx storage component (alkali or alkaline earth metal) and a high surface area support. The NOx storage and reduction catalyst works under alternating cycles of lean and rich conditions. Thermal degradation, limited resistance to sulfur poisoning and formation of carbon deposits are the issues faced by the basic configuration of NSR catalyst (i.e. Pt/BaO/γ-Al2O3). Considering the limitations of the base configuration of the LNT catalyst (Pt/Ba/γ-Al2O3), there is a need to develop an efficient catalyst that can overcome these problems. The objective of the present work is to develop an efficient LNT catalyst that is highly active for the reduction of NOx for temperatures higher than 400 0 C. Recently, mixed transition-metal oxides derived from hydrotalcite-like compounds have been identified as a potential candidate for NSR catalyst. In the current work, a spinel-structured Pt/K/MgAl2O4 and a base Pt/Ba/γ-Al2O3 catalyst are synthesized. The storage-reduction behavior of the developed catalysts is studied at different temperatures ranging from 200-500 o C. The activity of the catalysts is also tested for cyclic lean-rich reaction conditions. From the experiments performed, it is observed that even though the storage-reduction activity of Pt/K/MgAl2O4 is significantly high, the conversion obtained during transient experiments is very low over the entire temperature range due to poor reduction activity of the catalyst. In future, the work will be focussed on the inclusion of Rh into existing Pt/K/MgAl2O4 catalyst and optimization of the composition for maximum NOx conversion.