Lear Timothy, Marshall Robert, Lopez-Sanchez J Antonio, Jackson S David, Klapötke Thomas M, Bäumer Marcus, Rupprechter Günther, Freund Hans-Joachim, Lennon David
Department of Chemistry, Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, Scotland, United Kingdom.
J Chem Phys. 2005 Nov 1;123(17):174706. doi: 10.1063/1.2101487.
Five alumina-supported palladium catalysts have been prepared from a range of precursor compounds [palladium(II) nitrate, palladium(II) chloride, palladium(II) acetylacetonate, and tetraamminepalladium(II) tetraazidopalladate(II)] and at different metal loadings (1-7.3 wt %). Collectively, this series of catalysts provides a range of metal particle sizes (1.2-8.5 nm) that emphasize different morphological aspects of the palladium crystallites. The infrared spectra of chemisorbed CO applied under pulse-flow conditions reveal distinct groupings between metal crystallites dominated by low index planes and those that feature predominantly corner/edge atoms. Temperature-programmed infrared spectroscopy establishes that the linear CO band can be resolved into contributions from corner atoms and a combination of (111)(111) and (111)(100) particle edges. Propene hydrogenation has been used as a preliminary assessment of catalytic performance for the 1 wt % loaded catalysts, with the relative inactivity of the catalyst prepared from palladium(II) chloride attributed to a diminished hydrogen supply due to decoration of edge sites by chlorine originating from the preparative process. It is anticipated that refinements linking the vibrational spectrum of a probe molecule with surface structure and accessible adsorption sites for such a versatile catalytic substrate provide a platform against which structure/reactivity relationships can be usefully developed.
通过一系列前驱体化合物[硝酸钯(II)、氯化钯(II)、乙酰丙酮钯(II)和四氨合钯(II)四叠氮钯酸盐(II)]以及不同的金属负载量(1 - 7.3 wt%)制备了五种氧化铝负载的钯催化剂。总体而言，这一系列催化剂提供了一系列金属颗粒尺寸(1.2 - 8.5 nm)，突出了钯微晶不同的形态特征。在脉冲流动条件下施加的化学吸附CO的红外光谱揭示了以低指数平面为主的金属微晶与主要以角/边原子为特征的微晶之间的明显分组。程序升温红外光谱表明，线性CO带可分解为来自角原子以及(111)(111)和(111)(100)颗粒边缘组合的贡献。丙烯加氢已被用作对1 wt%负载催化剂催化性能的初步评估，由氯化钯(II)制备的催化剂相对不活泼归因于由于制备过程中氯对边缘位点的修饰导致氢供应减少。预计将探针分子的振动光谱与表面结构以及这种通用催化底物的可及吸附位点联系起来的改进方法将提供一个平台，据此可以有效地建立结构/反应性关系。
