原位衰减全反射红外（ATR-IR）研究NO₂⁻、NH₂OH和NH₄⁺在Pd/Al₂O₃和Pt/Al₂O₃上的吸附

In situ attenuated total reflection infrared (ATR-IR) study of the adsorption of NO2-, NH2OH, and NH4+ on Pd/Al2O3 and Pt/Al2O3.

作者信息

Ebbesen Sune D, Mojet Barbara L, Lefferts Leon

机构信息

Catalytic Processes and Materials, Faculty of Science and Technology, Institute of Mechanics Processes and Control Twente (IMPACT) and MESA+ Institute for Nanotechnology, University of Twente, P.O. Box 217, 7500 AE, Enschede, The Netherlands.

出版信息

Langmuir. 2008 Feb 5;24(3):869-79. doi: 10.1021/la7027725. Epub 2008 Jan 11.

DOI:10.1021/la7027725

PMID:18186656

Abstract

In relation to the heterogeneous hydrogenation of nitrite, adsorption of NO2-, NH4+, and NH2OH from the aqueous phase was examined on Pt/Al2O3, Pd/Al2O3, and Al2O3. None of the investigated inorganic nitrogen compounds adsorb on alumina at conditions presented in this study. NO2-(aq) and NH4+(aq) on the other hand show similar adsorption characteristics on both Pd/Al2O3 and Pt/Al2O3. The vibrational spectrum of the NO2- ion changed substantially upon adsorption, clearly indicating that NO2- chemisorbs onto the supported metal catalysts. On the contrary, adsorption of NH4+ does not lead to significant change in the vibrational spectrum of the ion, indicating that the NH4+ ion does not chemisorb on the noble metal but is stabilized via an electrostatic interaction. When comparing the adsorption of hydroxylamine (NH2OH(aq)) on Pd/Al2O3 and Pt/Al2O3, significant differences were observed. On Pd/Al2O3, hydroxylamine is converted into a stable NH2(ads) fragment, whereas on Pt/Al2O3 hydroxylamine is converted into NO, possibly via HNO(ads) as an intermediate.

摘要

关于亚硝酸盐的多相氢化反应，研究了在Pt/Al2O3、Pd/Al2O3和Al2O3上从水相中吸附NO2-、NH4+和NH2OH的情况。在本研究提出的条件下，所研究的无机氮化合物均不吸附在氧化铝上。另一方面，NO2-(aq)和NH4+(aq)在Pd/Al2O3和Pt/Al2O3上表现出相似的吸附特性。NO2-离子的振动光谱在吸附后发生了显著变化，清楚地表明NO2-化学吸附在负载型金属催化剂上。相反，NH4+的吸附不会导致离子振动光谱的显著变化，这表明NH4+离子不会化学吸附在贵金属上，而是通过静电相互作用稳定下来。当比较羟胺(NH2OH(aq))在Pd/Al2O3和Pt/Al2O3上的吸附情况时，观察到了显著差异。在Pd/Al2O3上，羟胺转化为稳定的NH2(ads)片段，而在Pt/Al2O3上，羟胺可能通过HNO(ads)作为中间体转化为NO。