PERGAMON Carbon 38 (2000) 2029–2039 Reaction of NO with carbonaceous materials: III. Influence of the structure of the materials 1 * ¨ Jun Yang , Enrico Sanchez-Cortezon, Norbert Pfander, Ute Wild, Gerhard Mestl , 1 ¨ Josef Find , Robert Schlogl Abteilung Anorganische Chemie des Fritz-Haber-Instituts der Max-Planck-Gesellschaft, Faradayweg 4-6, D-14195, Berlin, Germany Received 27 July 1999; accepted 25 February 2000 Abstract Four carbonaceous materials: carbon black, activated carbon, fullerene black and graphite, were employed in the NO–carbon reaction in order to study its structure sensitivity. The carbon structures were characterized by TEM and XRD analysis. The results obtained indicate that the internal structure of the samples employed greatly affects the reactivity of the samples towards NO. The reaction of NO with graphite shows a higher reaction rate per unit surface area than the reaction with the three amorphous carbons. The differences in reactivity between graphite and the amorphous carbons point to the presence of two kinds of active sites attributed to defective carbon sites and the carbon sites at the basal planes, respectively. The relative concentration of the different active sites depends on the structure of carbonaceous materials. The results obtained strongly suggest that the reaction between NO and carbon is a structure sensitive gas–solid reaction.  2000 Elsevier Science Ltd. All rights reserved. Keywords: A. Carbon black; Activated carbon; Fullerene; Graphite; D. Reactivity 1. Introduction of chars produced from different coals ranging from lignite to anthracite. It was found that the kinetics of the two The emission of nitrogen oxides from coal combustion reactions over char were dependent on the char structure. has attracted increasing attention because nitrogen oxides The impurities present in the chars, i.e. calcium, acceler- are responsible for acid rain and photochemical smog. The ated the reactions as catalysts. Chan et al. [4] found that emission of NO is reduced in fluidized-bed combustion the reaction of NO with graphite and de-ashed char (FBC) of coal. This is believed to be due to the in situ showed higher activation energies than that with a Mon- heterogeneous reaction between NO formed during the tana lignite char. This indicated the ease of the NO ´ ´ combustion of coal and the carbonaceous solid inter- reaction with ash-containing carbon. Garcıa-Garcıa et al. mediates of combustion. The study of the reaction of NO [5] studied the effect of coal rank and the content of with carbonaceous materials has, therefore, received great- minerals on the NO reduction over potassium-containing er attention lately. Some reviews concerning the kinetics of coal briquettes. It was found that the NO reduction activity the reaction between NO and carbonaceous materials were increased with decreasing rank of the coal precursor. The produced recently [1,2]. interaction of potassium with certain mineral impurities It has been found that the structure of carbonaceous present in raw coal greatly affected the activity. materials and the present impurities strongly affect their It is generally accepted that graphitic carbons have reactivity to NO oxidation. Rodriguez-Mirasol et al. [3] lower reactivity towards NO than activated carbons and investigated the reduction of NO and N O over a number chars that have not been extensively heat-treated. How- 2 ever, an unusually high specific reactivity of graphite has been observed [4]. The reaction of NO with graphite *Corresponding author. Tel.: 149-30-8543-4440; fax: 149- generally has a higher apparent activation energy than that 30-8413-4401. with activated carbons and chars. The effectiveness of E-mail address: mestl@fhi-berlin.mpg.de (G. Mestl) 1 carbonaceous materials in the reduction of NO normally Present address: Department of Chemical Engineering, Wor- cester Polytechnic Institute, Worcester, MA 01609-2208, USA. depends both on their surface properties and their inor- 0008-6223 / 00 / $ – see front matter  2000 Elsevier Science Ltd. All rights reserved. PII: S0008-6223(00)00062-2