Phase change of catalysts derived from a LDH-deoxycholate intercalated compound and its impacts on NO reduction from stationary source emissions Thakul Wongkerd, Apanee Luengnaruemitchai, Sirirat Jitkarnka * The Petroleum and Petrochemical College, Chulalongkorn University, Chula 12, Patumwan, Bangkok 10330, Thailand Received 5 January 2007; received in revised form 21 August 2007; accepted 11 September 2007 Available online 16 September 2007 Abstract Deoxycholate and keggin-type polyoxometalate (PW 12 O 40 and SiW 12 O 40 ) pillared-hydrotalcite-type clay catalysts were prepared, and the effects of calcination temperature were studied on selective catalytic reduction of NO by NH 3 over excess oxygen in the reaction temperature range 150–450 8C. The results showed that over 99% N 2 /N 2 O selectivity was achieved at all testing temperatures for all pillared-clay catalysts. The activity of all pillared-clay catalysts increased significantly with temperature beyond 300 8C. It was found that all pillared clays had different thermal transition behaviors at various stages of calcinations temperature, which affected the SCR activity. The dehydroxylated intermediates and amorphous mixed oxide forms, whose Brønsted acid sites were still preserved after calcinations, appeared to yield high NO conversion with high N 2 /N 2 O selectivity. Generally, the PW 12 -clay-derived catalysts seem to have the highest activity. Five percent Fe loading by impregnation method significantly increased activity of pillared-clay catalysts while high N 2 /N 2 O selectivity was maintained. Fe-loaded catalysts also showed obviously higher N 2 /N 2 O selectivity than the commercial catalyst; 4.4% V 2 O 5 –8.2% WO 3 /TiO 2 . # 2007 Elsevier B.V. All rights reserved. Keywords: SCR; Keggins; Polyoxometalates; Pillared clay; Hydrotalcite 1. Introduction In the commercial SCR unit for stationary sources, vanadia-based catalysts (V 2 O 5 /TiO 2 catalyst) mixed with WO 3 and/or MoO 3 as promoters are used as effective catalysts. However, their toxicity due to vanadium content and high selectively toward toxic N 2 O are currently the disadvantages. Several catalysts were studied in order to overcome these disadvantages. One of the most outstanding works was accomplished by Yang’s group [1–8] in which cationic clays such as bentonite intercalated with titania (TiO 2 –PILC) and doped with metal oxides with or without ion-exchanged elements were extensively studied as catalysts for this application. They successfully discovered that Fe– TiO 2 –PILC, a vanadium-free catalyst gave the best activity and selectivity among those tested and over the commercial catalysts [2,5]. Moreover, their comprehensive study showed that pre-sulfation of the Fe–TiO 2 –PILC catalyst significantly enhanced NO conversion and suppressed NH 3 oxidation in accordance with the discovery that the activity was improved by the presence of SO 2 in the feed due to the increase in surface acidity [9]. Inspired by Yang’s work, for this application, clays are an interesting alternative support or catalyst to us, especially hydrotalcite-type clays, which are anionic Mg–Al-based clays reported to have high capacity of SO x sorption [10,11], possibly due to basicity of the clay sheets. The SO x capturing ability was presumably expected to increase the acidic part of catalyst, and then enhance the activity. They also have attractive features such as high porosity, high thermal stability and exchangeable cations [7]. Hydrotalcite-type clay is a class of layered double hydroxide (LDH) anionic clays possessing various adjustable lateral anion spacings suitable for the negatively charged such as polyoxometalate (POM) pillars, which present a wider range of thermal stability than polynuclear transition metal halides, and hydroxyl metal cations [12–15]. Kwon et al. synthesized V 10 O 28 6 -pillared hydrotalcite (d = 11.9 A ˚ ) by direct exchange of decavanate anion (V 10 O 28 6 ) with Cl  interlayer anion [16]. * Corresponding author. Tel.: +66 2 218 4148. E-mail address: sirirat.j@chula.ac.th (S. Jitkarnka). 0926-3373/$ – see front matter # 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2007.09.008