Catalytic oxidation of ethyl acetate over a cesium modified cryptomelane catalyst V.P. Santos, M.F.R. Pereira, J.J.M. O ´ rfa ˜o, J.L. Figueiredo * Laborato ´rio de Cata ´lise e Materiais (LCM), Laborato ´rio Associado LSRE/LCM, Departamento de Engenharia Quı´mica, Faculdade de Engenharia, Universidade do Porto, Rua Dr. Roberto Frias, 4200-465 Porto, Portugal 1. Introduction Increasing concern about environmental and health effects resulting from emission of volatile organic compounds (VOC) has led to more stringent regulation standards, which require efficient and economic methods for VOC abatement [1]. Among the various methods that can be applied to efficiently control VOC emissions, catalytic oxidation seems to be the most efficient and cost-effective technology [2–4]. Catalyst formulation plays a key role towards the performance of the process. Manganese oxides (b-MnO 2 , g-MnO 2 , Mn 2 O 3 , Mn 3 O 4 ) have been extensively studied as catalytic materials in the oxidation of many pollutants such as ethanol, acetone, propane and propene, ethyl acetate and CO [5–9]. Although the nature of the active sites for catalytic oxidation is not well established, several authors attribute their high catalytic activity to the mixed valence of framework manganese, and to the high mobility of oxygen species, implying the participation of the lattice oxygen in the reaction [10,11]. Among the various manganese oxides studied, micro- porous manganese oxides with hollandite structure (cryptome- lane, OMS-2) have received appreciable attention for over 50 years, due to their exceptional catalytic properties and their shape- selective character [11–13]. Cryptomelane is a type of manganese oxide composed of 2  2 edge shared MnO 6 octahedral chains, which are corner connected to form one-dimensional tunnels (0.46 nm  0.46 nm). Manganese in the octahedra is mainly present as Mn(IV) and Mn(III), and cations such as K + and small amounts of water partially occupy the tunnel to provide charge balance and stabilize the tunnel structure [14,15]. In order to further improve the electronic and catalytic properties, other metal cations have been introduced inside the tunnels or into the framework, by subsequent ion-exchange [16–20] or by substitu- tion during synthesis [21–23]. The introduction of alkali metal into the tunnel can significantly modify the physical and chemical properties of cryptomelane, specially the surface acid–base properties [16]. Liu et al. [20] synthesized for the first time manganese oxides with Li + , Na + , Rb + as tunnel cations and found that the nature of the cation greatly influences the catalytic properties of OMS-2 towards total oxidation of cyclohexanol. Moreover, octahedral molecular sieves with Co 2+ , Ag + and Cu 2+ as tunnel cations showed high catalytic activities for CO oxidation at low temperatures [24,25]. The effect of cesium cations on the catalytic activity of cryptomelane for the oxidation of ethyl acetate was the subject of this study. It was expected that the presence of cesium into the tunnel structure of crytpomelane would change the surface acid– base properties and improve catalytic performance. A positive effect of alkali doping has been observed by several researchers in various systems [19,26,27] and has been related to the basic and acid surface properties of the catalyst and with the possible creation of new reaction pathways. Applied Catalysis B: Environmental 88 (2009) 550–556 ARTICLE INFO Article history: Received 29 July 2008 Received in revised form 7 October 2008 Accepted 12 October 2008 Available online 1 November 2008 Keywords: Ethyl acetate Oxidation Cryptomelane Cesium Basicity ABSTRACT Cryptomelane-type manganese oxide was synthesized by redox reaction under acid and reflux conditions. Cesium was incorporated into the tunnel structure by the ion-exchange technique. The catalytic oxidation of ethyl acetate in low concentration (1600 ppmv) was used to test the performance of the catalysts prepared. The presence of small amounts of cesium was found to improve the catalytic performance of cryptomelane. This behaviour was correlated with the basic properties of the catalyst. Temperature programmed experiments, and tests without oxygen in the feed, suggest that lattice oxygen atoms can react with ethyl acetate at low temperatures and are involved in the mechanism of ethyl acetate oxidation. ß 2008 Elsevier B.V. All rights reserved. * Corresponding author. Tel.: +351 22 508 1663; fax: +351 22 508 1449. E-mail addresses: santos.vera@fe.up.pt (V.P. Santos), fpereira@fe.up.pt (M.F.R. Pereira), jjmo@fe.up.pt (J.J.M. O ´ rfa ˜o), jlfig@fe.up.pt (J.L. Figueiredo). Contents lists available at ScienceDirect Applied Catalysis B: Environmental journal homepage: www.elsevier.com/locate/apcatb 0926-3373/$ – see front matter ß 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2008.10.006