Chemical Engineering Journal 158 (2010) 468–473 Contents lists available at ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej Fuels combustion effects on a passive mode silver/alumina HC-SCR catalyst activity in reducing NO x K. Theinnoi a,1 , A. Tsolakis a,∗ , S. Sitshebo a , R.F. Cracknell b , R.H. Clark b a School of Mechanical Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK b Shell Global Solutions, Cheshire Innovation Park, Chester CH1 3SH, UK article info Article history: Received 17 September 2009 Received in revised form 11 January 2010 Accepted 12 January 2010 Keywords: Fuels Combustion HC-SCR Ag/Al2O3 catalyst Hydrogen abstract The activity of a Ag/Al 2 O 3 catalyst in reducing NO x emissions in a passive mode hydrocarbon selective catalytic reduction (HC-SCR) was investigated using exhaust gas from the diesel engine operation on diesel, biodiesel (RME) and low temperature Fischer–Tropsch synthetic diesel (SD). The HC 1 :NO x ratio in the engine exhaust from the combustion of these fuels followed the order: diesel > SD > biodiesel and this order was mirrored in the catalyst activity in reducing NO x in presence of hydrogen (1000 ppm). Com- pared to diesel fuel, biodiesel combustion produces a higher amount of NO x with reduced concentrations of HCs, while both HC and NO x emissions were reduced in the engine exhaust from the combustion of SD fuel. Although, a higher NO x reduction in the SCR process was seen in the case of diesel fuelling, due to higher HC 1 :NO x ratio in the engine exhaust compared to biodiesel (RME) and SD, at low exhaust temper- atures (190 ◦ C) there was a gradual loss of the catalyst, NO x reduction activity. The incorporation of EGR within the engine operation, increased significantly HC 1 :NO x ratios in the exhaust, mainly by lowering the NO x concentration. Under these conditions, which can assumed to represent typical HC 1 :NO x ratios of a modern automotive diesel engine, higher NO x conversion was seen with SD, followed by diesel and biodiesel. For all the cases examined here the SD fuelling provides the lowest tailpipe NO x emissions. Hydrogen addition, i.e. at 500, 1000, 1500 and 3000 ppm in the passive mode Ag/Al 2 O 3 SCR catalyst needs to be optimized for the different HC 1 :NO x ratios and hydrocarbon species in the exhaust from the combustion of the three fuels. © 2010 Elsevier B.V. All rights reserved. 1. Introduction To date, several methods have been proposed as a way to reduce NO x and PM emissions in diesel engines, and catalytic aftertreat- ment systems such as NO x traps, Selective Catalyst Reduction (SCR) using urea, Diesel Oxidation Catalysts (DOCs) and Diesel Particulate Filters (DPF) have proved to be the most effective [e.g. 1]. The selec- tive catalytic reduction of NO x emissions in diesel engine exhaust gas with hydrocarbons (HC-SCR) has attracted considerable inter- est [e.g. 2]. Silver on alumina (Ag/Al 2 O 3 ) catalysts are seen as the main candidates for this technology, and have been investigated in a laboratory and engine environment with model hydrocarbons and diesel fuel [e.g. 3–9]. However, there is only limited informa- tion on the activity of these catalysts under passive mode operation (no external hydrocarbon addition) and how the different species ∗ Corresponding author. Tel.: +44 0121 414 4170; fax: +44 0121 414 7484. E-mail addresses: ktn@kmutnb.ac.th (K. Theinnoi), a.tsolakis@bham.ac.uk (A. Tsolakis). 1 Present address: College of Industrial Technology, King Mongkut’s University of Technology North Bangkok, 1518 Pibulsongkram Road, Bangkok 10800, Thailand. in a diesel engine exhaust (i.e. C-containing) from the combustion of the different fuels can influence their activity performance in reducing NO x emissions. The combustion of different diesel-type fuels (i.e. diesel, syn- thetic diesel (SD), biodiesel) produces exhaust with a range of HC:NO x ratios and hydrocarbon species that are mainly dependant on the physical and chemical properties of the fuels used for combustion. In Ag/Al 2 O 3 HC-SCR, hydrocarbon concentration and composition are very influential in the effectiveness of the catalyst in removing NO x emissions under lean conditions [4–6]. At low exhaust temperatures, increased carbon and nitrate species can deposit on the catalyst and reduce significantly the NO x removal efficiency [5,10–12]. Recently, we have reported that in order to avoid catalyst deactivation at low temperatures a balance between accumulation rate and oxidation rate of these species on the catalyst surface is required. This can possibly be achieved by controlling the concentration of hydrocarbon emissions reaching the SCR catalyst, i.e. engine out and quantity of the hydrocarbons injected (active control) [5,7]. In addition, hydrogen in small con- centrations (less than 1500 rpm) apart from improving the catalyst activity in reducing NO x emission, can also keep the catalyst clean by enhancing NO to NO 2 oxidation over the catalyst that helps 1385-8947/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.cej.2010.01.021