Bulgarian Chemical Communications, Volume 49, Special Issue L (pp. 24-29) 2017 24 Gas phase ozone decomposition over co-precipitated Ni-based catalysts T. T. Batakliev*, V. F. Georgiev, P. A. Karakashkova, M. V. Gabrovska, D. A. Nikolova, M. P. Anachkov, S. K. Rakovsky Institute of Catalysis, Bulgarian Academy of Sciences, Acad. G. Bonchev St., Bldg. 11, 1113 Sofia, Bulgaria Submitted November 10, 2016; Revised April 6, 2017 The effect of nickel content in the catalyst was investigated in this work in regard to the catalytic activity, stability and mechanical strength of the mixed metal oxides generated by thermal treatment of co-precipitated Ni-Cu-Al samples as catalyst precursors in the reaction of ozone decomposition. The impact of the silver present as a promoter on the catalytic activity was also examined. The catalytic activity of the metal oxide catalysts was estimated by monitoring of the inlet and outlet ozone concentrations and calculating the conversion degree of ozone into molecular oxygen. It was established that at room temperature all the catalysts demonstrate stable and almost constant conversion degree in the course of time on stream. It was found out that all tested catalyst samples have activity in ozone decomposition but the maximal conversion degree (more than 90%) was observed with the catalyst sample impregnated with 3% Ag2O. The properties of the catalysts were characterized by using various physical methods such as PXRD, TEM and SEM. Keywords: Ni-Cu-Al metal oxide catalysts, Ag promoter, Co–precipitation, Ozone decomposition INTRODUCTION Ozone is widely used in the industrial and environmental processes more specifically in semiconductor manufacturing, deodorization, disinfection and water treatment [1]. Ozone in the atmosphere protects the Earth’s surface against UV radiation, but on the ground level it is accepted to be one of the criteria for air contamination [2]. An effective method for purification of toxic gases containing ozone is the heterogeneous catalytic decomposition [3]. The most effective catalysts for this process are those containing platinum and platinum group metals, however, these metals are very expensive and this fact is limiting their application on a large-scale. Hence, efforts are made to replace precious metals by low cost non- noble transition metals and metal oxides of Mn, Co, Ni, Cr, Ag, Cu, Ce, Fe, V and Mo supported on high specific surface area carriers such as γ-Al2O3, SiO2, TiO2, ZrO2 and charcoal [4]. It has been reported that the transition metals oxides exhibit high catalytic activity in the decomposition of ozone [5]. Among them, the catalysts based on manganese oxide demonstrate the highest activity in the ozone decomposition reaction [3]. The behaviour of silver-containing catalysts in the above mentioned reaction is the subject of several insightful publications. Silver- and nickel- based catalysts deposited on γ-Al2O3 by the impregnation method have been evaluated for the removal of toluene in different plasma catalytic systems. It was reported that NiO/Al2O3 catalyst displayed a higher enhancement of CO2 selectivity and ozone decomposition efficiency [6]. Ru-Mn-promoted Ni-based catalysts and commercial Ni-based catalysts have been compared in the reaction of catalytic steam reforming of toluene in the temperatures range 6731073 K. Generally, it was found out the conversion of toluene and the H2 content in the product gas increased with the temperature increase [7]. The performance of cassava rhizome gasification has been carried out at high temperatures ranging from 873 up to 1073 K in the presence of Ni/Al2O3 and it was reported that the higher temperature improved the conversion of this material into fuel gas [8]. Efficient degradation of 2,4- dichlorophenoxyacetic acid in aqueous solutions has been achieved on NiO/SiO2 catalysts in the presence of ozone [9]. In this work NiO nanoparticles have been deposited on the silica surface by impregnation and liquid phase photodeposition in the presence of acetone or benzophenone. The most promising method of preparation appeared to be the sensitized photodeposition allowing a higher reduction degree of the precursor Bis(2,4-pentanedionato)nickel(II) after short irradiation time interval. The authors claim that according to the results on catalytic ozonation of 2,4-dichlorophenoxyacetic acid, the initial specific activity of the photodeposited catalyst was almost 7 times higher compared with that of the impregnated catalyst sample. The influence of NiO addition on the activity of cement containing catalyst has been studied in the reaction of ozone decomposition [10]. It was found *) To whom all correspondence should be sent: E-mail: todor@ic.bas.bg © 2017 Bulgarian Academy of Sciences, Union of Chemists in Bulgaria