Föttinger Karin, Emhofer Waltraud, Lennon David, Rupprechter Günther
Institute of Materials Chemistry, Technische Universität Wien, Getreidemarkt 9/BC/01, 1060 Vienna, Austria.
School of Chemistry, University of Glasgow, Joseph Black Building, University Avenue, Glasgow, G12 8QQ Scotland, UK.
Top Catal. 2017;60(19):1722-1734. doi: 10.1007/s11244-017-0852-7. Epub 2017 Aug 18.
γ-Alumina is widely used as an oxide support in catalysis, and palladium nanoparticles supported by alumina represent one of the most frequently used dispersed metals. The surface sites of the catalysts are often probed via FTIR spectroscopy upon CO adsorption, which may result in the formation of surface carbonate species. We have examined this process in detail utilizing FTIR to monitor carbonate formation on γ-alumina and zirconia upon exposure to isotopically labelled and unlabelled CO and CO. The same was carried out for well-defined Pd nanoparticles supported on AlO or ZrO. A water gas shift reaction of CO with surface hydroxyls was detected, which requires surface defect sites and adjacent OH groups. Furthermore, we have studied the effect of Cl synthesis residues, leading to strongly reduced carbonate formation and changes in the OH region (isolated OH groups were partly replaced or were even absent). To corroborate this finding, samples were deliberately poisoned with Cl to an extent comparable to that of synthesis residues, as confirmed by Auger electron spectroscopy. For catalysts prepared from Cl-containing precursors a new CO band at 2164 cm was observed in the carbonyl region, which was ascribed to Pd interacting with Cl. Finally, the FTIR measurements were complemented by quantification of the amount of carbonates formed via chemisorption, which provides a tool to determine the concentration of reactive defect sites on the alumina surface.
γ-氧化铝在催化领域被广泛用作氧化物载体，由氧化铝负载的钯纳米颗粒是最常用的分散金属之一。催化剂的表面位点通常通过傅里叶变换红外光谱（FTIR）在一氧化碳吸附时进行探测，这可能导致表面碳酸盐物种的形成。我们利用FTIR详细研究了这一过程，以监测γ-氧化铝和氧化锆在暴露于同位素标记和未标记的一氧化碳和二氧化碳时碳酸盐的形成情况。对于负载在氧化铝或氧化锆上的明确的钯纳米颗粒也进行了同样的研究。检测到一氧化碳与表面羟基的水煤气变换反应，这需要表面缺陷位点和相邻的羟基。此外，我们研究了氯合成残留物的影响，导致碳酸盐形成大幅减少以及羟基区域的变化（孤立的羟基部分被取代甚至不存在）。为了证实这一发现，通过俄歇电子能谱证实，将样品故意用氯中毒至与合成残留物相当的程度。对于由含氯前体制备的催化剂，在羰基区域观察到一个新的2164 cm处的一氧化碳谱带，这归因于钯与氯的相互作用。最后，通过化学吸附对形成的碳酸盐量进行定量，对FTIR测量进行补充，这提供了一种确定氧化铝表面活性缺陷位点浓度的工具。
