The role of chlorine and additives on the density and strength of Lewis and Brønsted acidic sites of c-Al 2 O 3 support used in oxychlorination catalysis: A FTIR study N.B. Muddada a , U. Olsbye a , T. Fuglerud b , S. Vidotto c , A. Marsella c , S. Bordiga d , D. Gianolio d , G. Leofanti e , C. Lamberti d,⇑ a inGAP Centre of Research-based Innovation, Department of Chemistry, University of Oslo, Sem Saerlandsvei 26, N-0315 Oslo, Norway b Technology and Projects, INEOS ChlorVinyls, Heroya Industrial Park, N-3936, Porsgrunn, Norway c Vinyls R&D Team, INEOS Technologies, Via dell’Elettricità 39, I-30175, Venezia – Marghera, Italy d Department of Inorganic, Physical and Materials Chemistry and NIS Centre of Excellence, and INSTM Reference Center, Università di Torino, Via P. Giuria 7, 10125 Torino, Italy e Consultant, Via Firenze 43, 20010, Canegrate, Milano, Italy article info Article history: Available online 20 October 2011 Keywords: CuCl 2 /Al 2 O 3 IR spectroscopy Alumina Lewis acidity Brønsted acidity CsCl dopant MgCl 2 dopant LaCl 3 dopant Support modification Ethylene oxychlorination catalyst abstract In two recent contributions [PCCP 12 (2010) 5605; Dalton Trans. 39 (2010) 8437], we combined in situ and in operando XANES/EXAFS, CO chemisorption and catalytic tests to elucidate the role that dopants (LiCl, KCl, CsCl, MgCl 2 LaCl 3 ) have in the nature, relative fraction, reducibility, and dispersion of Cu-phases on CuCl 2 /c-Al 2 O 3 catalysts for C 2 H 4 oxychlorination reaction, a key step of PVC chemistry. In the present work, we extend these studies by investigating the effect that the dopants have on the nature, population, and strength of surface Lewis and Brønsted sites of the support, using IR spectroscopy of adsorbed CO at liquid nitrogen temperature. The doping eliminates all the surface Lewis acidity in CsCl- and KCl-doped catalysts and strongly suppresses it in the remaining cases. The increase of the strength of the Brønsted sites is remarkable in all cases but the CsCl-doped one. To understand both the effect of Cl - anions and dopant cations a set of dopant free, HCl-impregnated and of Cu-free dopant-impregnated supports have been investigated. Addition of chlorine decreases the density and the strength of Lewis sites, while it increases those of the Brønsted sites. Catalytic testing of each material revealed that formation of chlo- rinated by-products was directly correlated with the density of Lewis acid sites. Furthermore, an empir- ical correlation was found between the strength of the Brønsted acid sites of the support and the stretching frequency of CO adsorbed on the reduced fraction of the active copper chloride phase. The present study is aimed to complement the published literature on alumina, underlining the usefulness of the molecular approach made by IR spectroscopy low temperature adsorbed CO to investigate the sur- face of catalyst support. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction High surface area aluminas are widely used in catalysis as sup- port for the active phase; this explains why they have been sub- jected to so large an investigation [1–18]. Among all applications, in this paper, we focus on the use of c-Al 2 O 3 as a support for CuCl 2 in the oxychlorination of ethylene [19–23], a key step in the PVC chemistry. Nowadays, almost all the world production of PVC is obtained by the polymerization of vinyl chloride (VCM) [24], which is pro- duced by cracking 1,2-dichloroethane (EDC) following reaction: C 2 H 4 Cl 2 ! C 2 H 3 Cl þ HCl ð1Þ In its turn, EDC is produced by two parallel processes, direct chlori- nation (2) and oxychlorination (3) [24–26]: C 2 H 4 þ Cl 2 ! C 2 H 4 Cl 2 ð2Þ C 2 H 4 þ 2HCl þ 1=2O 2 ! C 2 H 4 Cl 2 þ H 2 O ð3Þ The latter reaction, recycling HCl produced by the cracking of 1,2-dichloroethane (1), is particularly important in industrial applications because it was specifically developed to reduce the Cl 2 consumption and the waste of HCl going outside the cycle, in agreement with the modern requirements of chemical industry [27–29]. The oxychlorination reaction (3) is performed at 490–530 K and 5–6 atm using both air and oxygen in fluid or fixed bed reactors. Commercial catalysts are produced by impregnation of c-alumina 0021-9517/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.jcat.2011.08.014 ⇑ Corresponding author at: Department of Inorganic, Physical and Materials Chemistry and NIS Centre of Excellence, Università di Torino, Via P. Giuria 7, 10125 Torino, Italy. Fax: +39 0116707855. E-mail address: carlo.lamberti@unito.it (C. Lamberti). Journal of Catalysis 284 (2011) 236–246 Contents lists available at SciVerse ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat