from first principles PP-I-1

PP-III-59Catalytic CO Oxidation over Pt and Pd supported over WO 3Lisnyak V.V. 1 , Ischenko E.V. 1 , Byeda A.A. 1 , Mischanchuk A.V. 2 , Safonova V.V. 1 ,Yatsymyrskyi A.V. 1 , Boldyreva O.Yu. 11 Kyiv National Taras Shevhenko University, Kyiv, Ukraine2 Institute of Surface Chemistry, Kyiv, Ukrainelisnyak@chem.univ.kiev.uaA series of Pt/WO 3 and Pd/WO 3 catalysts was prepared by incipient wetness impregnationmethod and reduced by H 2 -Ar at different temperatures being in the range 80–500 °C. Thecatalytic properties of H 2 -reduced WO 3 with Pt and Pd metals for the oxidation of CO werestudied in the gas mixtures with O 2 excess. It was shown that the catalysts reduced at 400 °Ccharacterized by highest activity in the CO oxidation. XRD and TPR studies showed that thereduction process of Pt/WO 3 and Pd/WO 3 varied with the temperature, gas flow velocity andthe composition of reduction mixture. The reduction of Pt/WO 3 and Pd/WO 3 involved theformation of H x WO 3 which presence in the reacting gas mixtures can yield the active speciesfor CO oxidation. It is shown by TPD-MS that the estimated energy of CO desorption (E des )changes symbate with the catalytic activity and the lowest E des values are found for the mostactive catalysts reduced at 400 °C. The CO conversion temperature dependence characterizesby abrupt transition from low active (LA) to high active (HA) states of the catalysts and by acounterclockwise temperature hysteresis. The CO oxidation over the catalysts is the first orderwith respect to CO and the zeroth order with respect to oxygen (HA). The reaction was foundto be zeroth in CO and first-order in oxygen (LA). The clockwise by C(CO) and counterclockwiseby C(O 2 )) hysteresis phenomena were observed for r − f(C(CO) and r − f(C(O 2 ),respectively, at the intermediate range of temperatures. The dependences of r − f(C(O 2 )) andr − f(C(CO)) observed at kinetic studies over the catalysts can be well explained by possiblechanging of CO oxidation reaction mechanism from heterogeneous Langmuir-Hinshelwood(LA) to the direct-impact Eley-Rideal and/or heterogeneous-homogeneous mechanisms (HA).213