Journal of Photochemistry and Photobiology A: Chemistry 134 (2000) 209–217 Photocatalytic decomposition of NO by TiO 2 particles Tak Hyoung Lim a , Sang Mun Jeong a , Sang Done Kim a,∗ , Janos Gyenis b a Department of Chemical Engineering and Energy and Environment Research Center, Korea Advanced Institute of Science and Technology, TaeJon, 305-701, South Korea b Research Institute of Chemical and Process Engineering, Pannon University of Agricultural Sciences, H-820 Veszprem, Egyetem u.2, Hungary Received 10 September 1999; received in revised form 26 February 2000; accepted 8 March 2000 Abstract The effects of initial NO concentration, gas-residence time, reaction temperature and ultraviolet (UV) light intensity on the photocatalytic decomposition of NO have been determined in an annular flow-type and a modified two-dimensional fluidized-bed photoreactors. The decomposition of NO by photocatalysis increases with decreasing initial NO concentration and increasing gas-residence time. The reaction rate increases with increasing UV light intensity. The light transmission increases exponentially with the bed voidage at superficial gas velocity above 1.3 times the minimum fluidizing velocity (U mf ) in the two-dimensional fluidized-bed photoreactor. In the two-dimensional fluidized-bed photoreactor, NO decomposition reaches >70% at the gas velocity of 2.5 U mf . A two-dimensional fluidized-bed photoreactor is an effective tool for high NO decomposition with efficient utilization of photon energy. © 2000 Elsevier Science S.A. All rights reserved. Keywords: TiO 2 photocatalyst; NO decomposition; Two-dimensional fluidized bed 1. Introduction Nitrogen oxides (NO x ) are the major air pollutants that have to be removed before emitting flue gas into the atmosphere. Various processes, such as the selective cat- alytic reduction (SCR) and selective non-catalytic reduction (SNCR), are under operation to remove NO from flue gas [1–3]. However, these processes require high operating temperatures and costs. Recently, a great deal of research work has been carried out on the heterogeneous photo- catalytic reactions due to lower energy consumption and operating cost for treatment of polluted water and air [4–8]. This photocatalytic process has the advantage of complete breakdown of organic pollutants to yield CO 2 ,H 2 O and the mineral acid [9]. Recently, studies on photocatalytic decomposition of NO have been reported [10,11]. It has been found that Cu + /zeolite catalysts exhibit photocatalytic reactivities for the decomposition of NO x into N 2 and O 2 at 275 K [10]. In addition, a mixture of TiO 2 and activated carbon is found to be an appropriate photocatalyst for the removal of low-concentration (sub-ppm) NO x from air [11]. When a photocatalytic reaction takes place in a gas–solid reactor, it is necessary to achieve both exposures of the cat- ∗ Corresponding author. Tel.: +82-42-869-3913; fax: +82-42-869-3910. E-mail address: kimsd@cais.kaistac.kr (S.D. Kim) alysts to light irradiation and a good contact between reac- tants and catalyst. A two-dimensional fluidized-bed photore- actor not only brings more contact of catalysts and gas, but also enhances UV light penetration compared with a packed bed reactor in which light cannot penetrate easily into the interior of the catalyst bed [12]. Therefore, it is important to design a fluidized-bed photoreactor having higher light throughputs and lower pressure drops. In the present study, the effects of gas-residence time, initial NO concentration, reaction temperature and UV light source on the photocatalytic decomposition of NO has been determined in an annular flow-type reactor. In addition, a modified two-dimensional fluidized-bed photoreactor was designed to improve the contact of gas, photocatalyst and UV light. The efficiency of NO decomposition in the fluidized-bed reactor has been compared with that in the annular flow-type photoreactor. 2. Experimental 2.1. Materials The catalyst powder used was Degussa P-25 titanium dioxide which is mostly anatase with the primary par- ticle diameter of 30 nm and the specific surface area 1010-6030/00/$ – see front matter © 2000 Elsevier Science S.A. All rights reserved. PII:S1010-6030(00)00265-3