(95f) Fluidized Bed Plasmas Reactor for Catalyst Preparation. Application for SCR NOx by Hydrocarbons in Mobile Sources

Nowadays, almost all major chemicals are produced by catalytic processes. Among them, heterogeneous catalysis plays a very active role, because of environmental concerns. The use of plasmas for catalysis is now well developed1. Plasma treatment in a low pressure systems has been already used to replace the thermal calcinations of catalysts. Fluidized bed reactors offer the possibility to lead to homogenous treatment and have the additional advantage of excellent heat transfer rates between the gas and the particles2, so that it can modify the catalytic properties of the prepared materials3. The aim of our work is to prepare plasma-prepared catalysts dedicated to NOx abatement in mobile sources. In such applications, silver based catalysts could be used4 since ethanol was chosen as reducing agent for NOx removal in lean burn conditions. After typical catalysts preparation, cold fluidized bed plasma reactors were used to activate alumina supported silver catalysts in order to obtain a sustainable synthesis process. For the sake of comparison, a classical calcination in air at 500°C was performed. Concerning the plasma process, we have studied the influence of the plasma exposure time as well as the nature of the gas treatment (Ar and Ar/O2 plasmas). First, the alumina was sieved between 200 and 350 µm in order to obtain a homogeneous fluidization, and to avoid the loss of powders in the pumping system. The 2.5 wt% Ag/alumina was prepared by an excess impregnation method with AgNO3 as precursors in reduced pressure. Then, the catalyst was dried at 120°C overnight, prior to the two different processes, i.e. (i) calcination in air at 500°C for 2 h (10°C.min-1) or (ii) plasma treatment in the fluidized bed reactor. The fluidized bed reactor (FBR) consisted in a cylindrical Pyrex glass tube. The impregnated powders were fluidized by an Ar gas or a mixture of Ar/O2 gas passing through a porous glass plate. Two external electrodes were connected to the radio frequency generator in order to create the plasma in the fluidized bed region. The excited species formed in the plasma were characterized by in-situ diagnostic such as optical emission spectrometry (OES). Different samples were treated in Ar for different plasma treatment times (10 to 60 min) and one sample was prepared in O2/Ar mixture during 30 min. In order to understand the effect of the plasma treatment on silver based catalysts, a bench of surface characterizations such as TEM, UV-VIS, TPO were performed. In order to select the more efficient plasma treatment, SCR NOx by ethanol was performed, with a GHSV= 190,000h-1, under 500ppm NO, 10%O2 and 2500ppm C2H5OH in argon. Alumina supported silver based catalysts prepared under plasma conditions followed the same trends than the one obtained with the classical calcination (Fig 1.). A volcano type curve was always obtained due to the competition between ethanol oxidation and NOx reduction. The maximum of NOx conversion was found at 410°C on calcined catalyst whereas this maximum was shifted to lower temperatures depending on the plasma treatment. The higher activity was found for catalyst treated in argon during 30 min (RF-2). These catalysts were characterized by different surface analyses in order to understand the difference in terms of catalytic activity and in order to indentify the silver species. The first results in TPO showed that nitrates species were still present on the surface of catalysts after plasma treatment (RF-2), whereas these species completely disappeared when the catalysts were calcined. Furthermore, UV-VIS measurements revealed the presence of the same ionic silver species (Ag+, Agn+) on both plasma (RF-2) and calcined samples, whereas the metallic silver species were only observed on calcined catalysts. These preliminary tests could explain the difference observed in deNOx mostly at low temperatures. Conclusions Other characterizations are in progress in order to confirm these results. Moreover, we plan to replace the R.F generator by a microwave source, which presents the advantage to create plasma with higher density of energy. We would wish to try to test another catalyst in order to validate these first on another catalyst systems in the field of the stationary sources for example the palladium based catalysts were chosen since the main reducing agent is methane5. References 1.A. Brockhaus, D. Korzec, F. Werner, Y. Yuan, J. 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