Effect of pH on the Nitrite Hydrogenation Mechanism over Pd/Al2O3 and Pt/Al2O3: Details Obtained with ATR-IR Spectroscopy

Sune Dalgaard Ebbesen, Barbara L. Mojet, Leon Lefferts

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    Abstract

    It is well-known that activity and selectivity to N2 during nitrite hydrogenation over noble metal catalysts in water depend on the pH of the solution, but mechanistic understanding is lacking. Attenuated total reflection infrared (ATR-IR) spectroscopy is an ideal tool to perform detailed studies on catalytic surfaces in water. In this paper, the influence of pH was studied on adsorption and subsequent hydrogenation of nitrite in water between pH 5 and 9 over Pd/Al2O3 and Pt/Al2O3, using ATR-IR spectroscopy. On both catalysts, pH clearly influenced the surface coverage and reaction rates of intermediates. For Pt/Al2O3, lowering the pH induced the increasing surface coverage of key reaction intermediates like NOsteps1620cm−1 and “HNO”(ads)1540cm−1, as well as increased hydrogenation rates, explaining the higher TOF at lower pH as reported in the literature. For Pd/Al2O3, the effect of pH on selectivity is controlled by the rate constants of the formation and hydrogenation of the most stable reaction intermediates to N2 (NO(ads)1720cm−1) and NH4+ (NH2(ads)1510cm−1).
    Original languageEnglish
    JournalJournal of Physical Chemistry Part C: Nanomaterials and Interfaces
    Volume115
    Issue number4
    Pages (from-to)1186-1194
    ISSN1932-7447
    DOIs
    Publication statusPublished - 2011

    Keywords

    • Solid Oxide Fuel Cells

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