III International Conference

PP-I-10MECHANISMS OF MOLECULAR HYDROGEN ISOTOPE EXCHANGE ON THESUPPORTED METAL CATALYSTSBystrova O.S., Boeva O.A.D.I. Mendeleyev University of Chemical Technology of Russia, Moscow, RussiaE-mail: bystrov@mail333.com, olga_boeva@mail.ruThe activities of industrial nickel, ruthenium and palladium supported catalysts in themolecular hydrogen isotope exchange reaction were measured and the activation energies andpressure orders within 77-700 K range were determined. The dependencies of catalyticactivities of temperature and pressure were used to fit the parameters of model invoking thetransition state theory and two mechanisms of hydrogen dissociation on metals. A goodagreement between calculated and experimental data with realistic values of such parameterslike hydrogen-metal bond energy, mean vibrational temperature etc. was obtained.For various industrial reactions including molecular hydrogen its activation is thenecessary stage. The homomolecular hydrogen isotope exchange (for example H 2 + D 2 ↔2HD) also belongs to this class of reactions. The VIII group transition metals are the mostactive catalysts of this and similar processes. The supported metal catalysts are of the greatinterest from the point of view of their applications. However, they are quite complicatedsystems and their efficiencies are determined not only by the properties of metal or supportalone but also by their interaction, by size and shape of deposited particles and dynamics oftheir surface. Owing to its simplicity the molecular hydrogen exchange reaction mentionedabove may be considered as a convenient tool for clarifying mechanisms of hydrogenactivation on the metal particles because it is very sensitive to changes of reaction centers andforms of hydrogen adsorbed by metal surface.The objects of our investigations were the samples of the following industrial catalysts:0,5% Ru/Al 2 O 3 , 4% Ru/sibunit, 5% Pd/Al 2 O 3 , 0,5% Pd/sibunit, 15% Ni/Al 2 O 3 , 50% Ni/SiO 2 .The purposes of this study were observing the influence of metal size particles and nature ofmetal and support on the catalytic activity as well as analyzing the data to make a guess aboutthe common mechanism of hydrogen activation and isotope exchange. The dependencies ofcatalytic activity (K s ) on temperature (77-700 K) and pressure (15-400 Pa) and the activationenergy (E a ) and pressure order (n) values at different temperatures have been obtained. Theseresults are shown in the table below.25