No abstract

UDC 541.128.13:546.172.5 T. M. Boichuk and S. N. OrlikConditions were found for facilitation of the conversion of nitrous oxide in the presence of Fe-containing zeolite catalysts by oxidants (NO, SO 2 , and O 2 ). The results were interpreted in the framework of a mechanism involving decomposition of N 2 O. The effect of NO x on the reduction of nitrous oxide by C 3 -C 4 alkanes was established.The contribution of nitrous oxide to the greenhouse effect in the atmosphere is estimated to be 6% [1]. A significant amount of N 2 O waste (29%) is due to the chemical industry, in particular, the production of adipic and nitric acids. A promising catalytic process to eliminate N 2 O involves the direct decomposition and reduction of nitrous oxide in the presence of iron-and cobalt-containing catalysts. The use of reducing agents to reduce the temperature for high conversions of both NO and N 2 O is based on the relatively low temperatures of industrial gaseous wastes (250-500°C). Analysis of the literature shows that reducing the inhibition by oxidants (NO, SO 2 , O 2 , and H 2 O) is a critical factor in the design of N 2 O decomposition catalysts in tail gases.In previous work [5, 6], we showed that 90-96% conversion of N 2 O is achieved at 500-550°C in the presence of iron-containing zeolite catalysts differing in structural type (faujasite, mordenite, and pentasil). The addition of C 3 -C 4 alkanes as reducing agents lowers the temperature of nitrous oxide by 70-150°C, including cases in an oxidizing atmosphere (selective catalytic reduction conditions).In the present work, we studied the effect of NO and SO 2 on the conversion of nitrous oxide on iron-containing mordenite (M) and ZSM-5 catalysts, which were the most active of the catalysts studied in our previous work [6].The catalytic activity of the samples was defined as the conversion of N 2 O to nitrogen and determined in a flow system (the flow rate was 100 mL/min) in a gradientless quartz reactor at atmospheric pressure and 250-550°C. The following reaction mixtures were used (vol.%) 1% N 2 O and 0.15-2.0% NO or 0.5% N 2 O, 0.2% (2 : 1) C 3 H 8 -C 4 H 10 and 0.25% NO (5% O 2 ) with 3000 h -1 volumetric gas flow rate; 0.2% N 2 O, 0.1% NO, 0.1% C 3 H 8 -C 4 H 10 , 2.5% O 2 with V = 9000 h -1 . In studying the effect of sulfur dioxide on nitrous oxide decomposition, the reaction mixture contained 0.15% SO 2 . The catalyst sample (1-3 mm fraction) was heated in a helium flow at 550°C for 1 h prior to testing. The reagents and reaction products were analyzed chromatographically using columns packed with CaA molecular sieves (N 2 , NO, CO, O 2 ) and Polysorb-1 (N 2 O and CO 2 ). In an oxidizing atmosphere (selective reduction conditions), NO was analyzed using a 344 KhL-04 gas analyzer with a chemiluminescence detector. 2500040-5760/06/4204-0250

Hierarchical alumosilicate BEA zeolites with aggregated nanoparticle morphology and MOR zeolites with nanolayer morphology possess high concentrations of Brønsted and Lewis acid sites localized on the rather well-developed mesopore surface. The hydrogen forms of the starting BEA and MOR zeolites as well as their analogs modified by indium oxide display catalytic activity in the combined reduction of N 2 O and NO by propylene.Alumosilicate zeolites are commonly used as acid-base catalysts in many industrial reactions [1][2][3][4]. The catalytic activity of these zeolites depends on a combination of several factors such as structural type, nature and concentration of introduced heteroelements, distribution of the catalytically-active sites, site strength, and site stability [5]. A number of methods have been developed in the past two decades for the preparation of zeolites with a well-developed external surface and, thus, high accessibility of the active sites. A promising approach is the formation of stable zeolite nanolayers with the thickness of one or several unit cells using organic surfactants of a given structure (Gemini type SDA) as templates [6,7]. Such molecules may form micelles acting as structure-directing agents (templates) for the formation of not only zeolites with nanolayer morphology (2D nanoparticles) but also 0D nanoparticles or nanorods (1D nanoparticles). Mesophase materials containing crystalline nanoparticles of various structural types (MFI, MTW, BEA, MRE) were obtained using a similar approach [8,9]. Such zeolite materials, which are often named hierarchical, differ in their adsorption characteristics from ordinary 3D zeolites and, in particular, have a well-developed external surface and greater accessibility of the active sites, which leads to high catalytic activity in acid-base and redox reactions [10].There is considerable present work underway on the development of new operationally-stable catalytic systems for the removal of nitrogen oxides by their reduction to molecular nitrogen in an oxygen-enriched medium (selective catalytic reduction or SCR) as an efficient method for the elimination of NO x emissions [11][12][13]. The search is underway to find catalysts and elucidate the conditions for the combined reduction of N 2 O and NO by light hydrocarbons. Moisture-resistant indium-containing catalysts have been proposed for the reduction of nitrogen oxides (NO x ) in a highly-moist oxidizing atmosphere [14,15].The acidity of the surface of both zeolite and oxide catalysts, in particular, zirconium oxide catalysts, is important for obtaining SCR activity [12,16]. The effect of the acid properties of the surface of zeolite and aluminum oxide catalysts containing indium oxide and cobalt oxide on the activity in deNO x reactions has been studied by various workers [13,17,18]. 900040-5760/16/5202-0090