Catalytic reduction of NO x in gasoline engine exhaust over copper- and nickel-exchanged X±zeolite catalysts Souvik Bhattacharyya a, * , Randip K. Das b a Department of Mechanical Engineering, Indian Institute of Technology, Kharagpur, 721302, India b Department of Engineering and Mining Machinery, Indian School of Mines, Dhanbad 826004, India Abstract Catalytic removal of NO x in engine exhaust gases can be accomplished by non-selective reduction, se- lectivereductionanddecomposition.Noblemetalsareextensivelyusedfornon-selectivereductionofNO x and up to 90% of engine NO x emissions can be reduced in a stoichiometric exhaust. This requirement of having the stoichiometric fuel±air ratio acts against eciency improvement of engines. Selective NO x re- ductioninthepresenceofdierentreductantssuchas,NH 3 ,ureaorhydrocarbons,requiresclosecontrolof the amount of reductant being injected which otherwise may be emitted as a pollutant. Catalytic decom- positionisthebestoptionforNO x removal.Nevertheless,catalystswhicharedurable,economicandactive for NO x reduction at normal engine exhaust temperature ranges are still being investigated. Three catalysts based on X±zeolite have been developed by exchanging the Na  ion with copper, nickel and copper±nickel metal ions and applied to the exhaust of a stationary gasoline engine to explore their potential for catalytic reduction of NO x under a wide range of engine and exhaust conditions. Some en- couragingresultshavebeenobtained.ThecatalystCu±XexhibitsmuchbetterNO x reduction performance at any temperature in comparison to Cu±Ni±X and Ni±X; while Cu±Ni±X catalyst exhibits slightly better performance than Ni±X catalyst. Maximum NO x conversion eciency achieved with Cu±X catalyst is 59.2%ataspacevelocitysv)of31000h 1 ;whileforCu±Ni±XandNi±Xcatalyststheequivalentnumbers are 60.4% and 56% respectively at a sv of 22000 h 1 . Unlike noble metals, the doped X±zeolite catalysts exhibit signi®cant NO x reduction capability for a wide range of air/fuel ratio and with a slower rate of decline as well with increase in air/fuel ratio. Ó 2001 Elsevier Science Ltd. All rights reserved. Keywords: NO x control; X±zeolite; Emission control; Catalytic reduction; Ion exchange Energy Conversion and Management 42 2001) 2019±2027 www.elsevier.com/locate/enconman * Corresponding author. Tel.: +91-3222-82904; fax: +91-3222-82278. E-mail address: souvik@mech.iitkgp.ernet.in S. Bhattacharyya). 0196-8904/01/$ - see front matter Ó 2001 Elsevier Science Ltd. All rights reserved. PII:S0196-890401)00059-0