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Steady-state isotopic transient kinetic analysis (SSITKA), transient isothermal, and temperature-programmed surface reaction in H 2 (H 2 -TPSR) techniques coupled with online mass spectroscopy (MS) and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) were used to study essential mechanistic and kinetic aspects of the selective catalytic reduction (SCR) of NO with the use of H 2 under strongly oxidizing conditions (H 2 -SCR) over a novel Pt/MgO CeO 2 catalyst. The main focus was to study and report for the first time the effects of reaction temperature on the chemical structure and surface concentration of the active NO x intermediate species thereby formed. The information obtained is essential to understanding the volcano-type profile of the catalyst activity versus reaction temperature observed here and also reported previously. In the present work, two active NO x intermediate species identified by SSITKA-DRIFTS were found in the nitrogen-reaction path toward N 2 and N 2 O formation, one species located in the vicinity of the Pt CeO 2 support interface region (nitrosyl [NO + ] coadsorbed with a nitrate [NO − 3 ] species on an adjacent Ce 4+ O 2− site pair) and the second located in the vicinity of the Pt MgO support interface region. The chemical structure of the second kind of active NO x species was found to depend on reaction temperature. In particular, the chemical structure was that of bidentate or monodentate nitrate (NO − 3 ) at T 200 ° C and that of chelating nitrite (NO − 2 ) at T > 200 ° C . The concentration of the active NO x intermediates that lead to N 2 formation was found to be practically independent of reaction temperature (120–300 °C) and significantly larger than 1 equivalent monolayer of surface Pt ( θ NO x = 2.4 – 2.6 ). The former result cannot be used to explain the volcano-type behavior of the catalytic activity versus the reaction temperature observed; alternative explanations are explored. The H-spillover process involved in the H 2 -SCR mechanism was found to be limited within a support region of about a 4–5 A radius around the Pt nanoparticles ( d Pt = 1.2 – 1.5 nm ).

We describe here the performance of a novel MgO-CeO2-supported Pt (0.1 wt%) catalyst towards the selective conversion of NO into N2 (SN2 > 80%) by using H2 (H2-SCR) under process conditions similar to those encountered in the NH3-SCR in the low-temperature range of 150-200 °C. At 200 °C, 100% conversion of NO and 85% N2-selectivity were obtained with a feed stream containing 1000 ppm NO, 5% O2, 5% H2O, 10% CO2, 0-0.5% CO, and using 1.5% H2 in the feed as reducing agent (GHSV = 40,000 h-1). Thus, a N2-yield of 85% similar to that obtained in most NH3-SCR applications could make H2-SCR as the most environmentally friendly NOx control catalytic technology with great potential to replace the existing NH3-SCR technology. The latter is currently used industrially mainly in power and nitric acid plants, gas turbines, furnaces, boilers, and waste incinerators for the elimination of NOx. However, this technology faces several problems such as catalyst deterioration, emissions of non-reacted toxic NH3 (ammonia slip), ash odor, air-heaters fouling, and a high running cost. © 2007 Elsevier B.V. All rights reserved. 75 3-4 147 156 Cited By :66

Ethylene decomposition over Ni supported on novel carbon nanotubes (CNT) and nanofibers under consecutive reaction/regeneration cycles to form CO-free hydrogen and carbon deposits have been investigated. The present work highlights the effects of support chemical composition, catalyst synthesis method and Ni metal loading on the catalytic activity and stability of nickel. A novel 0.5 wt.% Ni/CNT catalyst which presents the highest value of a constant hydrogen product yield (17.5 mol H2/mol Ni), following consecutive reaction (complete deactivation) → regeneration (20% O2/He, 400 °C) cycles, ever reported in the open literature has been developed. Transmission electron microscopy (TEM) and XRD studies revealed that the 0.5 wt.% Ni/CNT catalyst promotes the formation of two types of carbon nanofibers during ethylene decomposition at 400 °C, result that reduces significantly the rate of Ni encapsulation during reaction. The opposite is true in the case of 0.3 wt.% Ni/SiO2 catalyst. In the case of Ni/CNT, there is a narrow range of Ni loading for which maximum H2 product yield is obtained, while in the case of Ni/SiO2, a monotonic increase in the H2 product yield is obtained (Ni loading in the range 0.3-7.0 wt.%). © 2005 Elsevier B.V. All rights reserved. 102-103 78 84 Cited By :19