Journal of Catalysis 248 (2007) 249–257 www.elsevier.com/locate/jcat Evaluation of deactivation mechanisms of Pd-catalyzed hydrog of 4-isobutylacetophenone Nakul Thakar ∗ , Tilman J. Schildhauer, Wim Buijs, Freek Kapteijn, Jacob A. Moulij Catalysis Engineering, DelftChemTech, Delft University of Technology, Julianalaan 136, 2628 BL, Delft, The Netherlands Received 4 December 2006; revised 12 March 2007; accepted 13 March 2007 Available online 27 April 2007 Abstract Pd catalysts were investigated for the hydrogenation of 4-isobutylacetophenone (4-IBAP) and for Pd/SiO 2 an improved (compared with the non-patented literature) yield of nearly 80% of the desired product 1-(4-isobutylphenyl)ethanol (4-IBPE) was obtained. Ho deactivation was observed. The spent catalyst was characterized using a wide variety of thermal (TGA,TPO-MS),microscopic (TEM), and spectroscopic (DRIFT, LEIS) characterization techniques. Pd leaching did not occur. Oligomerization of 4-IBAP by conden to the acidity imparted by the presence of isolated silanol groups on SiO 2 is proposed as one of the causes of catalyst deactivation. Pd cr growth and strong chemisorption of the H 2 O liberated by 4-IBPE hydrogenolysis also contributed to the loss of catalytic activity. Th are supported by the high stability of Pd black in catalyzing the reaction.  2007 Elsevier Inc. All rights reserved. Keywords: Pd catalysts; Aryl ketone hydrogenation; Catalyst deactivation; LEIS 1. Introduction The liquid-phase hydrogenation of 4-isobutylacetophenone (4-IBAP)(Scheme 1) using supported noble metal catalysts is a step in the new catalytic route developed by Hoechst– Celanese [1] for the synthesis of ibuprofen, a nonsteroidal anti-inflammatory drug. The secondary alcohol derivative, 1-(4-isobutylphenyl)ethanol (4-IBPE) is the product of inter- estin this case. The 4-IBPE is further carbonylated to yield ibuprofen. Most of the earlier work on 4-IBAP hydrogenation is patented, and only a few publications deal with the reac- tion mechanism and selectivity issues. The existing literature on the hydrogenation of 4-IBAP is presented in Table 1 [2]. The Hoechst–Celanese patent [1] focuses on the carbonylation step for the synthesis of ibuprofen, and the hydrogenation step is only mentioned in one example; for this step, a large quan- tity of Pd/C catalyst is used (4-IBAP: 5% Pd/C in a weight ratio of 7:1). The knowledge provided by the patents is very limited and general in nature. The hydrogenation of 4-IBAP * Corresponding author. Fax: +31 (0) 15 2785006. E-mail address: n.thakar@tudelft.nl (N. Thakar). using Ru/Al 2 O 3 and Ni/HY has been investigated in detail [ 3],and the kinetics for these catalysts have been determi In general, it is observed that the use of high hydrogen p pressures and a co-catalyst system are desirable for obta high selectivity to the desired 4-IBPE. The use of a suppo Pd catalyst is preferred, because Pd is well known to sel hydrogenate the carbonyl functional group of an aromati tone atrelatively mild conditions to the hydroxyl group [4]. Consequently, Pd was tested over various supports, including SiO 2 , C, and CaCO 3 , with the aim of maximizing the yield of the desired product 4-IBPE. Deactivation of noble metal catalysts is quite common in the bulk chemicals industry and has been well documented [5,6].Loss of catalytic activity due to coke formation is we known forfluidized catalytic cracking (FCC), oxidative de- hydrogenation, and reforming processes [7]. Albers et al. [8] reviewed the poisoning and deactivation of supported palla- dium catalysts and concluded that the nature of the carbona- ceous deposits and the strength of their interactions with face sites of palladium catalysts are crucial with respect to a detrimental impacton activity. Only a few reports exist on catalyst deactivation in the much more complex fine chem cal industry [9]. Although no mention has been made of cat 0021-9517/$ – see front matter  2007 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2007.03.019