Microreactors for environmental catalysis—Selective catalytic reduction of NO X with hydrocarbons over a Ag/alumina catalyst Jose ´ R. Herna ´ndez Carucci * , Kalle Arve, Kari Era ¨nen, Dmitry Yu. Murzin, Tapio Salmi Laboratory of Industrial Chemistry, Process Chemistry Centre, A ˚ bo Akademi University, Biskopsgatan 8, FIN-20500 A ˚ bo/Turku, Finland Available online 26 December 2007 Abstract Microstructured-etched plates previously coated with Al 2 O 3 , were further impregnated with Ag. The plates were characterized by means of laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) and scanning electron microscopy (SEM). The silver loading on the alumina-coated plates was determined to be between 0.8 and 1.6% and the distribution along the microchannels was proved to be almost uniform. The microplates were tested in a microreaction chamber for selective catalytic reduction of NO using different hydrocarbons (HC-SCR). A clear relationship between the number of carbon atoms in the hydrocarbon chain and the NO reduction was found. The results are compared to those obtained in minireactors under similar reaction conditions. The outcome indicates that microreactors are a useful, fast and effective way for studying selective catalytic reduction of NO with hydrocarbons. # 2007 Elsevier B.V. All rights reserved. Keywords: Microreactor; NO X reduction; Ag/Al 2 O 3 ; HC-SCR; Impregnation 1. Introduction Global climate warming has become an issue of tremendous importance nowadays. CO 2 is the main component that produces the greenhouse effect leading to the increase of the temperature in our planet. Referring to the Kyoto protocol, it is necessary to diminish carbon dioxide emissions from vehicles. Hence, new technologies have appeared during the last years, i.e., lean burn engines, which operate under a large excess of oxygen. These engines are able to reduce the fuel consumption, consequently the CO 2 formation. The main problem arises with the NO X emissions. Due to the excess of oxygen present in the exhaust and to the hydrothermal conditions needed (high content of H 2 O, i.e., up to 12 vol.%), the NO X cannot be removed by conventional three-way catalysts. In this sense, the selective catalytic reduction using hydrocarbons (HC-SCR) is an attractive and effective way for depleting the NO X emissions [1,2]. On the other hand, in the last two decades powerful processes have been developed for the fabrication of three- dimensional microdevices from a wide variety of materials based on electronic technologies. The advantages of micro- reactors have been previously demonstrated and have been found to be vast [3,4]. One of the main features of these devices is their high surface-to-volume ratio, which tends to be from 100 to 500 times higher compared to conventional laboratory vessels [5]. Moreover, the heat transfer in these devices has been determined to be very good. The high transfer ratio is very convenient in cases where highly exothermic or endothermic reactions occur. In the cases where a catalyst is present, an efficient heat transfer allows to exploit the full potential of the catalyst, avoiding hot spots as it was demonstrated in [6]. Higher reaction temperatures are permitted, leading to reduced reaction volumes and amounts of catalyst. This results in a reduction of the operation costs of the reactor, and in having smaller and lighter reaction devices. Delsman et al. [7] presented a comparison study between conventional fixed-bed and microreactor technology for a portable hydrogen produc- tion case. However, a more detailed economic analysis escapes from the scope of our predominantly exploratory paper. In addition, because of the sizes of the microchannels, the amount of reagents employed for the catalytic testing tends to be much lower compared to the total quantity needed in conventional reactors, resulting in a significant improvement in safety while dealing with dangerous chemicals: using micro- reactors greatly reduces the hazardous potential associated with www.elsevier.com/locate/cattod Available online at www.sciencedirect.com Catalysis Today 133–135 (2008) 448–454 * Corresponding author. E-mail address: johernan@abo.fi (J.R.H. Carucci). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.11.015