Lean burn engines combine a high fuel economy with noticeable durability and low maintenance costs, therefore, used on a large scale for transportation, power generation, farming, army security, etc. However, their NOx and soot emissions are accountable for severe environmental and health problems. Recently, the emission regulations for diesel light duty and heavy duty vehicles are becoming more and more strict, e.g. there is a marginal reduction of 10% for PM, whereas; reduction of NOx emissions is relatively too much 55.56% from Euro-5 to Euro-6 for light duty vehicles. Soot can be efficiently reduced to 99.00 % by diesel particulate filter. Reducing NOx is more complicated than soot for diesel engine emissions. A variety of techniques are available for NOx abatement such as catalytic decomposition of NOx, NSCR, EGR, SCR, LNT, etc. Out of these concepts, SCR is the best for NOx reduction in terms of removal efficiency and safety constraints. In this method, various types of catalysts and reductants are invested and to reduce NOx emissions. Therefore, research in the field of NOx abatement has grown significantly in order to develop low cost, selective and stable catalysts to meet the stringent environmental regulations.

This dissertation discusses about the different sources of NOx, its adverse effect on the ecosystem and legislation standards. The main portion of the review discusses the progress and development of various catalysts for NOx removal from exhaust by NO decomposition, NO reduction by NH3/LPG/H2-LPG etc. Some conclusions are made on the various catalytic approaches to NOx abatement.

A total of 11 base metal catalysts (Mn/TiO2, Mn/SiO2, Mn/Al2O3, VWTi, Cu/Al2O3, NiCo2O4) were prepared by various methods like co-precipitation method, reactive grinding method, wet-impregnation and nano-casting method. The catalysts were doped by various promoters (Co, Ce and Rh). The catalysts were characterized by various techniques such as X-ray diffraction (XRD), Low temperature N2 adsorption (BET), Scanning electron microscopy (SEM), and Energy dispersive X-ray (EDX), X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR). The influence of promoters and reductants (NH3, LPG, H2-LPG) were investigated for NO reduction over the SCR catalysts. The catalysts activities were evaluated in tubular flow reactor under the following experimental conditions: catalyst = 200mg, NO = 500ppm, O2=8%, NH3= 1.0%, in Ar, GHSV= 30,000 h1. The inlet and outlet gases of the reactor were analyzed by NOx chemiluminescence CLD 62 and online GC. The catalyst activity was dependent on the reductants, catalysts and promoters used. The orders of NO reduction activity of the catalyst were as follows: Cat-I > Cat-E> Cat-A> Cat-F> Cat-D> Cat-G> Cat-J > Cat-B> Cat-K> Cat-C> Cat-H. The performance order of the reductants is as follows: H2-LPG> LPG> NH3. 99 % NO reduction is achieved over the Cat-I at 202 0C with H2 assisted LPG-SCR. A total of 175 references were cited in the dissertation.