The influence of silver on the properties of cryptomelane type manganese oxides in N 2 O decomposition reaction Wojciech Gac a, * , Grzegorz Giecko a , Sylwia Pasieczna-Patkowska a , Tadeusz Borowiecki a , Leszek Ke ˛pin ´ski b a Maria Curie-Sklodowska University, Faculty of Chemistry, Department of Chemical Technology, 3 Maria Curie-Sklodowska Square, 20-031 Lublin, Poland b Institute of Low Temperature and Structure Research, PAS, Okolna 2, 55-422 Wroclaw, Poland Received 25 July 2007; received in revised form 24 October 2007; accepted 8 November 2007 Available online 10 January 2008 Abstract The cryptomelane type oxides were prepared by the redox precipitation technique using Mn(CH 3 COO) 2 and KMnO 4 precursors. Nitrogen sorption, XRD, TEM and TPD of oxygen studies showed changes of the surface, structural and redox properties of the samples upon silver introduction. Samples were investigated in the N 2 O decomposition reaction. Direct introduction of silver to the synthesis mixture caused partial distortion of regular channel-like structure of the oxides, leading to the decrease of Mn–O bonds strength. As results samples showed slightly better catalytic activity at low temperatures, but were less stable at high temperatures. An introduction of silver by the impregnation method caused the decrease of the surface area of the samples, increase of surface oxygen mobility, leading to the small changes of activity. # 2007 Elsevier B.V. All rights reserved. Keywords: Manganese oxide; Silver; HREM; TPD; N 2 O decomposition 1. Introduction Nitrous oxide, N 2 O is recently perceived as a relatively strong greenhouse gas with long atmospheric lifetime and large global warming potential [1,2].N 2 O participates in the depletion of stratospheric ozone. It is estimated, that about 60–70% of the total emission comes from anthropogenic contribution. The main source of N 2 O emission is agriculture. The intensification of microbial nitrification, dentrification, and chemical processes, which occur in the soils, result from the agricultural activities, including an application of nitrogen synthetic fertilizers [3]. Strong impact on the N 2 O emission shows wastewater sector. The major sources of N 2 O emission are also the industrial processes, mainly nitric and adipic acids production, energy industry, manufacturing industries and transport. Therefore the reduction of emissions in the energy and chemical industry by the development of the production technologies, or the application of the catalytic abatement systems is an important target. The molecule of N 2 O is thermodynamically unstable, and at high temperatures above 700 8C decomposes to nitrogen and oxygen. Nitrous oxide can be removed by chemical reaction with CO, H 2 , C or NO. Direct catalytic decomposition of N 2 O to N 2 and O 2 has been observed over large number of different types of catalysts, including noble metals, transition metal oxides, mixed oxides, spinels, perovskites, hydrotalcites, and zeolites [1,4]. The enhancement of the decomposition has been mainly attributed to the weakening the N–O bond. The first step of this process has been generally described as the adsorption of N 2 O over active site, and then decomposition to N 2 and surface oxygen. Oxygen (O 2 ) is desorbed after surface reaction of two oxygen species or surface oxygen with N 2 O molecule. The nature of the active sites has been widely discussed in the literature. High catalytic activity of iron- or cobalt-exchanged ZSM-5 catalysts has been attributed to the presence of isolated metal cations, which easily change their oxidation state during reaction cycle. The active sites in the supported or bulk oxide systems have been often related to the presence of coordinatively unsaturated surface transition metal ions. Manganese oxides show large diversity of the structures and composition. The oxidation state of manganese in the oxides www.elsevier.com/locate/cattod Available online at www.sciencedirect.com Catalysis Today 137 (2008) 397–402 * Corresponding author. Tel.: +48 81 5375526; fax: +48 81 5375565. E-mail address: wojtek@hermes.umcs.lublin.pl (W. Gac). 0920-5861/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.cattod.2007.11.008