Korányi Tamás I, Mihály Judith, Pfeifer Eva, Németh Csaba, Yuzhakova Tatiana, Mink János
Department of Molecular Spectroscopy, Institute of Structural Chemistry, Chemical Research Center of the Hungarian Academy of Sciences, P. O. Box 17, H-1525 Budapest, Hungary.
J Phys Chem A. 2006 Feb 9;110(5):1817-23. doi: 10.1021/jp055745b.
The infrared emission spectra of CO adsorbed on alumina-supported 1, 3, and 5 wt % Rh, Ir, and Pt metal-containing catalysts were studied at 423 and 473 K. While CO is adsorbed in dicarbonyl (dimer), linearly (on-top) bonded and bridged carbonyl forms on rhodium and platinum, the dimer form is dominant on iridium. The relative intensity of Rh-CO and Ir-CO linear bands decrease with increasing temperature compared to the intensity of the dicarbonyl bands; the corresponding bands on Pt behave the opposite way. Two dicarbonyl and two linear Pt-CO bands were identified in the infrared spectra of Pt/Al(2)O(3) catalysts. The surface structure (kinked or planar Pt atoms), the dispersity of the metal, the temperature, and the quantity of adsorbed CO on the surfaces all have an effect on the fine structure of the Pt-CO stretching bands. The metal-carbon and CO stretching force constants were calculated for surface dicarbonyl, linearly bonded CO, and bridged carbonyl species. The metal-carbon stretching wavenumbers and force constants were predicted and compared between surface species and metal carbonyl complexes. The iridium-carbon bonds were found always stronger than the Rh-C and Pt-C ones in all surface species. The observed stretching wavenumbers and force constants seem to support the idea that CO and metal-carbon bonds are always stronger in metal carbonyl complexes than in adsorbed surface species. The distribution and mode of CO adsorption on surface metal sites can be effectively studied by means of infrared emission spectroscopy.
研究了在423 K和473 K下，吸附在氧化铝负载的含1 wt%、3 wt%和5 wt%铑、铱和铂金属催化剂上的CO的红外发射光谱。虽然CO以二羰基（二聚体）、线性（顶位）键合和桥式羰基形式吸附在铑和铂上，但二聚体形式在铱上占主导。与二羰基带的强度相比，Rh-CO和Ir-CO线性带的相对强度随温度升高而降低；铂上的相应带表现出相反的趋势。在Pt/Al₂O₃催化剂的红外光谱中鉴定出两个二羰基和两个线性Pt-CO带。表面结构（扭结或平面铂原子）、金属的分散度、温度以及表面上吸附的CO量都会影响Pt-CO伸缩带的精细结构。计算了表面二羰基、线性键合CO和桥式羰基物种的金属-碳和CO伸缩力常数。预测并比较了表面物种与金属羰基配合物之间的金属-碳伸缩波数和力常数。发现在所有表面物种中，铱-碳键总是比Rh-C和Pt-C键更强。观察到的伸缩波数和力常数似乎支持这样一种观点，即CO和金属-碳键在金属羰基配合物中总是比在吸附的表面物种中更强。通过红外发射光谱可以有效地研究CO在表面金属位点上的吸附分布和模式。
