Effect of pH on the Nitrite Hydrogenation Mechanism over Pd/Al2O3 and Pt/Al2O3: Details Obtained with ATR-IR Spectroscopy
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- 作者：Sune D. Ebbesen ; Barbara L. Mojet ; Leon Lefferts
- 刊名：Journal of Physical Chemistry C
- 出版年：2011
- 出版时间：February 3, 2011
- 年：2011
- 卷：115
- 期：4
- 页码：1186-1194
- 全文大小：530K
- 年卷期：v.115,no.4(February 3, 2011)
- ISSN：1932-7455
文摘
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 NOlass="stack">stepslass="stack">1620鈥塩m鈭? and 鈥淗NO鈥?sub class="stack">(ads)lass="stack">1540鈥塩m鈭?, 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 (NOlass="stack">(ads)lass="stack">1720鈥塩m鈭?) and NH4+ (NHlass="stack">2(ads)lass="stack">1510鈥塩m鈭?).