III International Conference

PP-II-50HYDROGEN BINDING IN THE REDUCED COPPER CHROMITE CATALYST:INELASTIC NEUTRON SCATTERING STUDYKhassin A.A., Jobic H. 1 , Yurieva T.M., Parmon V.N.Boreskov Institute of Catalysis SB RAS, Novosibirsk, Russia1 Institut de Recherches sur la Catalyse, 2 av. A.Einstein, F 69626 Villeurbanne, FranceE-mail: aakhassin@catalysis.ruHomogeneous catalytic hydrogenation of C=O bond of ketones in the presence of metalcations in “protonic medium” is well known [1]. This reaction can be performed heterogeneouslytoo. Perfect copper chromite, CuCr 2 O 4 , acquires the catalytic activity in acetone hydrogenationafter being reduced in H 2 at 250-350 o C [2]. However, it remains rather inactive in the COconversion to methanol, unlike CuZnAl oxide catalyst which is active in both processes. Thereason of so striking difference in mechanisms of heterogeneous catalytic hydrogenation ofketones to alcohols and CO to methanol are still debated in literature.Neutron diffraction studies of the CuCr 2 O 4 evolution under reductive treatments made itpossible to formulate some specific features of the copper reduction in CuCr 2 O 4 [3].According to that study, the reduction of copper cations located in T d positions of the spinelstructure isn’t accompanied by escape of the water molecules. Instead, hydrogen is oxidizedgiving H + , which substitute Cu 2+ cations in crystallographic position e of the spinel structure(green tetrahedrons in Fig. 1). Moreover, a significant amount of hydrogen is absorbed in thecrystallographic position c (“forbidden” octahedrons, milk-white in Fig. 1). Thus, the reducedcopper chromite can be considered as Cu 0 particles over the surface of a solid solution ofcopper chromite and chromic acid, i.e. “solid protonic medium”. So, a certain analogy may bedrawn between heterogeneous catalytic reactions and homogeneous processes in liquid phase.Fig. 1. (left) The schematic representation of the reduced copper chromite structure according to theneutron diffraction data of [3]; (right) The spatial pattern of the absorbed hydrogen locations in e(green T d ) and c (milk-white O h ) structural positions of spinel structure.254