from first principles PP-I-1

PP-III-5The Catalytic Oxidation of Hydrazine with Nitric Acid in the Presence ofRu and Bimetallic Pt-Ru CatalystsAnaniev A.V., Tumentsev M.S.A.N. Frumkin Institute of Physical Chemistry and Electrochemistry of RAS, Moscow, RussiaTumentsev@ipc.rssi.ruThe stoichiometry, kinetics and the mechanism of heterogeneous catalytic hydrazinedecomposition reaction in nitric acid solutions over 5% Ru/SiO 2 catalysts were studied. Thereaction was shown to proceed via formation of gaseous nitrogen, hydrazoic acid anddinitrogen monoxide. Also it was found that the catalyst surface in solutions of HNO 3 isoxidized.Hydrazine decomposition results from two processes: the catalytic dissociation of hydrazinenitrate on the oxidized catalyst surface accompanying by ruthenium dioxide recovery to ametallic state and the oxidation of hydrazine with HNO 2 catalytically generated in the reactionof metallic Ru sites oxidation with nitric acid. The established mechanism of the catalytichydrazine decomposition reaction in nitric acid solutions over Ru/SiO 2 catalysts involves thecatalytic redox cycle on ruthenium surface atoms implying both the oxidation and thereduction steps to obey chemisorption’s regularities. For this reason it is sensible to considerthe overall reaction to be governed by principles of chemisorption.Bimetallic Ru-Pt catalysts with particles of different size, morphology and Ru/Pt ratio loadedon granulated silica gel were synthesized and examined in the reaction of hydrazinedecomposition in HNO 3 solutions. A strong synergistic effect between two metals wasobserved for bimetallic catalysts in the reaction comparing to monometallic counterparts.While studying influence of the Pt/Ru ratio in the catalysts (from pure Ru to pure Pt at thesame total mass loading of metals – 5%) on the reaction rate constants a volcanic curve wasobtained having a maximum near 66% (at.) of Pt. The rate constants of the most activeprepared bimetallic catalyst (60% Pt, 40% Ru, at. %) exceed these of monometallic Pt catalystin 4,5 times. This is an apparent illustration of synergistic effect between two metals takinginto account the fact that pure Ru catalyst is at least in 3 times less active than Pt one in thereaction of hydrazine decomposition in nitric acid solutions! The explanation of reportedsynergistic effect phenomenon is expected to be proposed after further investigations.156