DOI: 10.1002/chem.201201006 Discovering the Active Sites for C3 Separation in MIL-100(Fe) by Using Operando IR Spectroscopy Stefan Wuttke, [a, b] Philippe Bazin, [a] Alexandre Vimont, [a] Christian Serre, [b] You-Kyong Seo, [c] Young Kyu Hwang, [c] Jong-San Chang, [c] GØrard FØrey, [b] and Marco Daturi* [a] Introduction Operando spectroscopy is a methodology that allows the in- vestigation of a material during its working conditions. The Latin term operando derives from the field of heterogene- ous catalysis, in which the spectroscopic characterisation of a catalytic material takes place during the reaction with the simultaneous measurement of catalytic activity/selectivity. [1, 2] In contrast, in situ spectroscopy deals with the analysis of the material under controlled environments. The goal is a qualitative and quantitative characterisation of the surface species correlated with the catalytic performances of the material. Although the studied surface induces changes in comparison to the catalytic active one, an in situ study is always necessary before carrying out the operando experi- ments. [3] This is due to a better understanding of the surface species as well as the determination of their absorption coef- ficients under in situ conditions. Both techniques are com- plementary and necessary for the full understanding of the catalyst. [4, 5] The simultaneous characterisation of the surface of the material as well as the functionality of a device under operation is also important in other fields (sensors, nanoma- terials, energy, health etc.) of material science. Herein, we report for the first time, the infrared spectroscopic charac- terisation of a metal–organic framework (MOF) under flow- ing conditions for separation by using the operando method- ology during the separation process. MOFs are a new class of materials synthesised in a build- ing-block fashion from metal-ion vertices. They are intercon- nected by organic linker molecules in a self-assembly proc- ess for the purpose of creating highly tailorable crystalline materials with pores of nanometre dimensions. [6] The infinite variations of the nature of the organic linkers added to the possibility of using di-, tri- (including rare earth) or tetrava- lent cations, lead to near-limitless possibilities for networks. One remarkable feature of MOFs is the virtual absence of dead volume, which principally gives them the highest po- rosities and record-holding surface areas. [7–9] In addition, the possibility of tuning the pore size, the presence of accessible coordinatively unsaturated metal sites (CUSs), functionalisa- tions of the organic linkers (by using functionalised ligands during the synthesis [10] or post-synthetic modification (PSM) of the linker [11] ) and the easy, inexpensive synthesis of MOFs make this new class of materials suitable for different applications for example, catalysis, [12–16] selective gas adsorp- tion and separation, [17–19] gas storage [17, 20, 21] or drug deliv- [a] Dr. S. Wuttke, Dr. P. Bazin, Dr. A. Vimont, Prof. M. Daturi Laboratoire Catalyse et Spectrochimie ENSICAEN, UniversitØ de Caen, CNRS, 6 Boulevard MarØchal Juin, 14050 Caen (France) Fax: (+ 33) 31452822 E-mail: marco.daturi@ensicaen.fr [b] Dr. S. Wuttke, Dr. C. Serre, Prof. G. FØrey Institut Lavoisier (UMR CNRS 8180) UniversitØ de Versailles Saint-Quentin-en-Yvelines 45, Avenue des Etats-Unis, 78035 Versailles (France) [c] Dr. Y.-K. Seo, Dr. Y.K. Hwang, Dr. J.-S. Chang Biorefinery Research Group Catalysis Center for Molecular Engineering Korea Research Institute of Chemical Technology (KRICT) Jang-dong 100, Yuseong, Daejeon 305-600 (South Korea) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.201201006. Abstract: A reducible MIL-100(Fe) metal–organic framework (MOF) was investigated for the separation of a propane/propene mixture. An operan- do methodology was applied (for the first time in the case of a MOF) in order to shed light on the separation mechanism. Breakthrough curves were obtained as in traditional separation column experiments, but monitoring the material surface online, thus pro- viding evidences on the adsorption sites. The qualitative and quantitative analyses of Fe II and, to some extent, Fe III sites were possible, upon different activation protocols. Moreover, it was possible to identify the nature and the role of the active sites in the separation process by selective poisoning of one family of sites: it was clearly evidenced that the unsaturated Fe II sites are mainly responsible for the separation effect of the propane/propene mixture, thanks to their affinity for the unsatu- rated bonds, such as the C =C entities in propene. The activity of the highly concentrated Fe III sites was also high- lighted. Keywords: active sites · hydrocar- bon separation · IR spectroscopy · metal–organic frameworks · IR spectroscopy · reaction mechanisms Chem. Eur. J. 2012, 00,0–0  2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim These are not the final page numbers! ÞÞ &1& FULL PAPER