The potential of combined operando UV-Vis/Raman/XAFS has been explored by studying the active site and deactivation mechanism of silica-and alumina-supported molybdenum oxide catalysts under propane dehydrogenation conditions.Ideally scientists would like to take real-time spectra inside a catalytic reactor when a catalytic process is operating, giving them detailed insight into the working principles of the catalytic material. 1 On this basis, it would then be possible to improve upon existing catalyst formulations or design completely new ones, which are more active and/or selective. Such rational catalyst design is still a dream since the experimental tools available to study the active catalyst do not yet provide sufficient insight. In this respect, it is advantageous to look on catalytic systems from different perspectives by making use of multiple characterisation techniques. In recent years, many attempts have been made to combine multiple spectroscopic techniques into one experimental set-up. The following combinations of two spectroscopic techniques have been recently reported for studying heterogeneous catalysts in action: EPR/UV-Vis, NMR/UV-Vis, XAFS/IR, UV-Vis/Raman and IR/UV-Vis. [2][3][4][5][6][7] Here, we describe a newly developed and powerful operando set-up to measure combined energy-dispersive (ED)-XAFS, UVVis and Raman to study a working catalytic solid. To our best knowledge, this is the first device which couples three spectroscopic techniques in one reactor, focuses on the same spot of a metal oxide catalyst under true reaction conditions and is capable of delivering sub second time resolution. A scheme of the set-up is given in Fig. 1. Further details are given in the ESI.{The operando device developed is widely applicable in the field of heterogeneous catalysis and its potential has been explored for the dehydrogenation of propane (5% in He) over supported Mo catalysts which have shown potential for alkane activation. 8,9 We have studied 13 wt% Mo/Al 2 O 3 and Mo/SiO 2 catalysts during successive propane dehydrogenation cycles at 550 uC. The three techniques are sensitive to changes in the oxidation/coordination states of Mo allowing us to obtain complementary information on the catalysts behaviour during dehydrogenation and regeneration. The set-up allows us to discriminate between the dynamics of both catalysts under reaction conditions and to identify the possible active site and deactivation pathways. Also the complementary aspects of this setup are demonstrated by showing how the catalyst undergoes changes which cannot be followed using one of the techniques alone and how it is possible to obtain quantitative Raman information without the use of an internal standard. Fig. 2 shows data collected using the three techniques during the first propane dehydrogenation cycle (PC1) for Mo/SiO 2 . The initial features observed in the spectra included a distinct 1s-4d pre-edge feature at 20002 eV in the ED-XANES, a strong LMCT band at ca. 350 nm in the UV-Vis and Raman bands at 992 (nMoLO), 82...

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Abstract:The stabilization of a mononuclear copper(II) complex with one MIm2Pr ligand [MIm2Pr ) 3,3-bis(1-methylimidazol-2-yl)propionate] in the supercages of zeolite Y was attempted, and the resulting materials were tested for their activity in oxidation catalysis. The preparation procedure yielded initially two species (labeled 1 and 2) within the pore system of the zeolite material, which differ in molecular structure and chemical composition as determined by UV/vis, ESR, IR, and XAFS spectroscopy. In species 1, the copper was found to be five-coordinated, with one MIm 2Pr ligand in a facial-type NNO coordination toward copper, the other two coordination sites being occupied by oxygen atoms from either the zeolite framework and/or a water molecule. The total charge of this complex is 1+. In species 2, the copper is surrounded by two MIm2Pr ligands, both in a facial-type coordination mode, identical to the homogeneous Cu(MIm2Pr)2 complex. This neutral species 2 is easily washed out of the zeolite, whereas the mononuclear species 1 remains inside the zeolite material upon washing. The spectroscopic characteristics and activity for 3,5-di-tert-butylcatechol and benzyl alcohol oxidation of species 1 compared closely with that of the zeoliteimmobilized Cu(histidine) complexes but differed from that of the homogeneous Cu(MIm2Pr)2 complex. It was therefore found that encapsulation in zeolite offers a route to stabilize a 5-fold-coordinated copper complex with novel catalytic properties. This 1:1 Cu(MIm2Pr) complex is not formed in solution.

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