ffi ELSEVI ER Available online at www.sciencedirect.com ^T scrENcE (d)o,"=.t. Applied Catalysis A: General 310 (2006) 127-137 www.elsevier. corn/locate/aDcata Effect of metal oxide additives on the activity and stability of CulZnOlZrO, catalvsts in the svnthesis of methanol frtm CO" ani H" J. Sł oczyńSH u'* , R. Grabowski u, P. olszewski u, A' Kozł owska u, J. Stochu, M. Lachowskab, J. Skrzypekb " Institute of Catalysis And Surface Chemistry, Polish Academy of Sciences, Niezapomirnjek Street, 30-239 Kraków, Poland " Institute Of Chemical Engineering, Polish Academy of Sciences, 5 Battycka Street, 44-100 Gliwice, Poland Received 12 January 2006; received in,:"ffi"a"?T,lt t# il 2006; accepted 2f May 2006 Abstract The CulZnOIZrO2 catalyst has been modified by adding small amounts of B, Ga, In, Gd, Y Mn and Mg oxides. Two series of catalysts were obtained: series A: by the co-precipitation of basic carbonates and seńes B: by complexing with citric acid. The oxide additives were found to influence the catalytic activity in the reaction of methanol synthesis from CO2, dispersion of Cu, surface composition of the catalyst, and the stability of catalysts during their operation. In both series of catalysts, the Ga2O3 additive was especially useful. The mechanism of copper sintering and the performance of the oxide additives are discussed. O 2006 Elsevier B.V. All rights reserved. Keywords: CO2 hydrogenation; Methanol synthesis; Effect of oxide additions; Sintering of Cu APPLI ED CATALYSI S A; GENEML 1. Introduction Methanol is a key material for Cl chemistry [1] and tilt today is produced on a large scale by synthesis with the use of heterogenous catalysts [2]. Recently, the synthesis ofmethanol from carbon dioxide and hydrogen has been intensely studied in connection with the attempts to reduce the emission of CO2 to atmosphere [3-5]. The cost of methanol produced by the hydrogenation of CO2 is higher than the cost of methanol obtained from the CO + CO2 mixture. However, the utilization of CO2 which is a waste gas in many chemical processes (CO2 is removed from the synthesis gas in ammonia synthesis or is coming from biogases), allows a decreased spending in the synthesis of methanol. On the other hand, CO2 may be regenerated in the hydrogenation-steam conversion cycle and the produced hydrogen may be used in fuel cells [G8]. It has been well documented that the CulZnOlZrOTcatalyst is active in the methanol synthesis from CO2 and H2 [9-21] and in the * Conesponding author. Tel.: + 48 12 639 5160; fax: + 48 12 425 19f3. E.mail address: ncgrabow@cyf-kr.edu.pl (J. Sł oczyński). 0926.8ó0x/$ _ see front matter o 200ó Elsevier B.v All ńghts reserved' doi: I 0.1 0 1 6/j.apcata.2006.05.035 steam reforming of methanol t22-251. In order to increase its activity and stability, this basic catalyst was often modified by different oxide additives. Besides ZrO2, other irreducible oxides like A12O3, TiO2, Ga2O3 have been investigated [26]. The effect of several additives such as boron, chromium, vanadium, tungsten and manganese, taken from the patents, has been discussed in a review article [27]. Several detailed papers were further devoted to the influence of small amounts of such additives as VO, [20,281,MnO.117,29,30] and MgO [30]. In 1990s, Saito et al. [3 1] reported the promoting action of Ga2O3 oxide on the activity of Cu/ ZnO catalysts in the methanol synthesis from CO2. On the basis of these results, a very active and stable multicomponent CulZnOlZrO2lAl2O3l Ga2O3 catalyst was elaborated and tested out with success in a pilot installation [32]. Lately, Toyir et al. described similar active and selective.Cu/ZnOlGa2O3 catalysts for the synthesis of methanol from CO2 [33]. The aim of this work has been a systematic study of the influence of oxide additives on the structure and activity of the CulZnOlZrO2 catalyst in the synthesis of methanol from CO2. Evolution of the size of crystallites, especially the Cu crystallites, as well as of the surface composition during the