Mechanism of the Reaction NO + H2 on the Pt(100)-hex Surface under Conditions of the Spatially Nonuniform Distribution of Reacting Species
نویسندگان
چکیده
The interaction of hydrogen with NO ads /1 × 1 islands produced by NO adsorption on the reconstructed surface Pt(100)-hex was studied by high-resolution electron energy loss spectroscopy (HREELS) and the temperature-programmed reaction (TPR) method. The islands are areas of the unreconstructed surface Pt(100)1 × 1 saturated with NO ads molecules. The hexagonal phase around these islands adsorbs much more hydrogen near room temperature than does the clean Pt(100)-hex surface. It is assumed that hydrogen is adsorbed on the hexagonal surface areas that are adjacent to, and are modified by, the NO ads /1 × 1 islands. The reaction of adsorbed hydrogen atoms with NO ads takes place upon heating and has the character of so-called surface explosion. The TPR peaks of the products of this reaction—nitrogen and water—occur at T des ~ 365–370 K, their full width at half-maximum being ~5–10 K. In the case of the NO ads /1 × 1 islands preactivated by heating in vacuo above the NO desorption onset temperature (375–425 K), after the admission of hydrogen at 300 K, the reaction proceeds in an autocatalytic regime and the product formation rate increases monotonically at its initial stage. In the case of activation at 375 K, during the initial, slow stage of the reaction (induction period), hydrogen reacts with nitric oxide molecules bound to structure defects (NO def ). After activation at 425 K, the induction period is characterized by the formation and consumption of imido species (NH ads ). It is assumed that NH ads formation involves N ads atoms that have resulted from NO ads dissociation on defects upon thermal activation. The induction period is followed by a rapid stage of the reaction, during which hydrogen reacts with NO 1 × 1 molecules adsorbed on 1 × 1 areas, irrespective of the activation temperature. After the completion of the reaction, the areas of the unreconstructed phase 1 × 1 are saturated with adsorbed hydrogen. The formation of H ads is accompanied by the formation of a small amount of amino species (NH 2ads ). DOI: 10.1134/S0023158407060158 MECHANISMS OF CATALYTIC REACTIONS
منابع مشابه
CATALYTIC REFORMING OF n-HEPTANE ON PLATINUM-TUNGSTEN SUPPORTED ON GAMMA-ALUMINA
The mono-metallic and bi-metallic catalysts have been prepared by impregnating with solutions containing a compound of H2PtCl6,WO3 and 1ml HCl (0.1 mol). It should be noted that the catalysts’ activity and selectivity have been determined under these conditions : 450-5000C ,and 15-25atm by H2. For converting n-heptane , the molar ratio H2/C7H16 is 5 , and LHSV is 1.5ml/h. It has been proved tha...
متن کاملبررسی سینتیک و سازوکار سنتز NH3 بر سطح کاتالیستهای مدل Fe(100) و K/Fe(100)
In this investigation kinetics and mechanism of NH3 synthesis over Fe(100) and K/Fe(100) model catalysts have been studied. In this context, adsorption kinetics of both N2/Fe (100) and H2/Fe (100)systems is initially investigated. By using statistical mechanic approach, we have determined the adsorption coefficient for N2 and H2 molecules as well as transition probability of different states ...
متن کاملCATALYTIC REFORMING OF n-HEPTANE ON PLATINUMNIOBIUM SUPPORTED ON GAMMA-ALUMINA
The series of mono-metallic and bi-metallic catalysts have been prepared by impregnatingwith solutions containing compound of H2PtC15,NbC15 and lml HC1 (0.1 mol). The activityand selectivity of the catalysts have been determined under conditions at 450-500°C, 15-30atm. Molar ratio H2/C7H16=5 and VVH=1.5/h for converting n-heptane. Under theseexperimental conditions it has been established that ...
متن کاملKinetic Mechanism Reduction Using Genetic Algorithms, Case Study on H2/O2 Reaction
For large and complex reacting systems, computational efficiency becomes a critical issue in process simulation, optimization and model-based control. Mechanism simplification is often a necessity to improve computational speed. We present a novel approach to simplification of reaction networks that formulates the model reduction problem as an optimization problem and solves it using geneti...
متن کاملInvestigation of Activity and Selectivity of n-Heptane by Reforming Pt-Ta Catalyst Supported on y-Alumina
The catalyst Pt-Ta supported on 7-alumina was prepared by impregnation with solution containing compoundsof II21K1.0. and Ta205 The Pt concentration was kept constant at 0.2 vet% while the concentration of thetantalum was 0,4 wt%. The activity and selectivity of catalyst were determined under conditions at 450-500 °Cand 15-30 atm.. with molar ratio H2/C[H,e5 and WH=1.5mL/h for converted n-hepta...
متن کامل