Acetaldehyde yield and reaction products in the catalytic destruction of gaseous ethanol S.G. Poulopoulos, H.P. Grigoropoulou, and C.J. Philippopoulos * Department of Chemical Engineering, Chemical Process Engineering Laboratory, National Technical University of Athens, Heroon Politechneiou 9, Zographou Campus, GR-157 80 Athens, Greece Received 12 June 2001; accepted 30 October 2001 The catalytic destruction of ethanol 0.5% v/v) over a typical three-way catalyst Pt/Rh/Ce) and two base catalysts 1% CuO and 10% CuO on -Al 2 O 3 ) was studied in a continuous ¯ow reactor, under atmospheric pressure. The eect of the temperature 100±500 8C) and of the oxygen concentration 0±10% v/v) on the operation of the tested catalysts and on the product pro®les is presented. The formation of acetaldehyde during the catalytic destruction of ethanol, the main concern of ethanol addition to fuels, was extremely dependent on the oxygen concentration. It is noteworthy that more acetaldehyde was produced during the oxidation of ethanol in oxygen de®cit conditions than during its decomposition in the absence of oxygen. Copper addition on -Al 2 O 3 enhanced acetaldehyde formation, while less acetaldehyde amounts were produced over the noble metal catalyst. KEY WORDS: three-way catalysts; copper catalysts 1. Introduction Oxygenated compounds have been used as gasoline additives to compensate the knock behavior of lead since 1970. The concern about urban air quality has led to the idea of using these compounds in increased amounts in unleaded gasoline in order to reduce combustion-related pollution from vehicles by providing oxygen during the combustion process. Among the several possible oxygenated additives, methyl-tert-butyl ether MTBE) and ethanol are the most frequently used ones. The use of oxygenated fuels generally decreases the total hydro- carbon HC), carbon monoxide CO) and nitrogen oxide NO x ) emissions under moderate temperatures. They seem to produce, however, increased amounts of air pollutants such as aldehydes and peroxyacetyl nitrates, which are known toxics but not yet regulated [1,2]. The eect of MTBE addition to gasoline on the exhaust and evaporative emissions from cars has been extensively studied [3±6]. However, its use is accom- panied by many problems owing to its potential for carcinogenicity and its high solubility in water. MTBE has been detected in vast portions of ground and surface water reservoirs, and leaking underground storage tank systems as well as faulty pipeline systems and accidental spills are thought to be the sources. Therefore, extensive consideration has been given to other oxygenated com- pounds, especially to ethanol since its use seems to be bene®cial in terms of water contamination and there are no signi®cant adverse impacts to public health or the environment from switching to ethanol [7]. Ethanol can be used either as supplemental blending stock or as a substitute for gasoline [8] and diesel [9]. Fewer studies are devoted to the exhaust emissions from internal combustion engines operating on ethanol-contain- ingfuels.Themostimportantdisadvantageofethanoladdi- tion to gasoline is the production of acetaldehyde [10,11]. Someresearchhasbeenconductedonthecatalyticcom- bustion of ethanol. Catalysts containing noble metals Pt, Pd, Rh, Ag) as well as base metal oxides CuO, Cr 2 O 3 , Fe 2 O 3 , NiO, V 2 O 3 , Co 3 O 4 , Mn 2 O 3 ) were tested for the oxidation of ethanol and acetaldehyde [12±23]. Excess oxygen conditions were used and acetaldehyde, CO, ethylene, diethylether and methane were detected in the reaction products. Pt from the ®rst group and CuO from the second one were found to be the most active in ethanol oxidation. The in¯uence of oxygen concentration on reaction product distribution and especially on acetalde- hyde production through the partial oxidation of ethanolÐthe main drawback of ethanol addition to gasolineÐis signi®cant and should be further examined. In the present study, the oxidation of ethanol on a commercial three-way catalyst and on two base-metal CuO) laboratory catalysts is presented. Acetaldehyde and the other reaction products are detected under various oxygen concentrations, and temperature ranges are studied where these concentrations are the highest. 2. Materials and methods 2.1. Materials Pt-Rh-Ce Pt: 3.27  10 ÿ3 gg ÿ1 cat , Rh: 0.64  10 ÿ3 gg ÿ1 cat , Ce: 51.78  10 ÿ3 gg ÿ1 cat ), a standard commercial three-way Catalysis Letters Vol. 78, Nos. 1±4, March 2002 # 2002) 291 1011-372X/02/0300-0291/0 # 2002 Plenum Publishing Corporation * To whom correspondence should be addressed. E-mail: kphilip@chemeng.ntua.gr