Oxygen Isotope ( 18 O 2 ) Evidence on the Role of Oxygen in the Plasma-Driven Catalysis of VOC Oxidation
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Oxygen Isotope (18O2) Evidence on the Role of Oxygen in the Plasma-Driven Catalysis of VOC Oxidation Hyun-Ha Kim • Atsushi Ogata • Milko Schiorlin Ester Marotta • Christina Paradisi
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Received: 8 August 2010 / Accepted: 29 October 2010 / Published online: 16 November 2010 Ó Springer Science+Business Media, LLC 2010
Abstract This paper reports isotopic evidence on nonthermal plasma-induced fixation of gas-phase oxygen on the surface of several catalysts such as TiO2, Ag/TiO2, Ag/ c-Al2O3 and Ag/MS-13X at atmospheric-pressure. On-line mass spectrometric analysis and stoichiometric comparison of reactants and products revealed that the fixed surface oxygen can be activated by nonthermal plasma. The fixed 18 O by nonthermal plasma survived for a certain period of time (about 30 min), and involved in the formation of isotope-exchanged oxygen (18O16O) and isotope containing COx (CO and CO2). Keywords Plasma-driven catalysis Heterogeneous catalyst Isotope oxygen VOC oxidation
1 Introduction Atmospheric-pressure nonthermal plasma (NTP) offers unique chemical environment for the removal of dilute air pollutants. Electrical energy is converted into chemically reactive species in the plasma. On the other hand, extensive studies during the last two decades pointed out several limitations of the plasma alone processes for the extended practical use in industry. These include large energy consumption, low selectivity, and formation of unwanted byproducts. Combination of nonthermal plasma with H.-H. Kim (&) A. Ogata National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba 305-8569, Japan e-mail: [email protected] M. Schiorlin E. Marotta C. Paradisi Department of Chemical Science, Padova University, Padova, Italy
heterogeneous catalyst is currently considered as a possible way to overcome these problems. Two types of combination, single-stage and two-stage, are currently being studied to improve the process performance. Single-stage process is more complex compared to two-stage process, and little knowledge is presently available on the interaction between plasma and catalyst. Nevertheless, this complementary combination has been experimentally proved to provide better selectivity for plasma and lower working temperature for catalyst [1–3]. For example, it has been reported that the combination of dielectric barrier discharge plasma and manganese catalyst enhances TCE decomposition and CO2 selectivity [4, 5]. The loading of active metals not only enhance CO2 selectivity for various VOCs [6–8], but also extend plasma area over the surface of catalyst [9]. The important role of oxygen was confirmed by varying O2 content in gas mixtures. The larger the oxygen content, the higher the decomposition efficiency of VOC and the CO2 selectivity [10, 11]. Fundamental research works are under progress for a better understanding of the interaction between plasma and catalyst. Roland et al. experimentally studied the stabilization of plasma-formed oxidants on the surface of LaCoO3 [12]. When CO/N2 mix
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