Active Sites and Structure-Activity Relationships of Copper-Based Catalysts for Carbon Dioxide Hydrogenation to Methanol
Active Sites and Structure-Activity Relationships of Copper-Based Catalysts for Carbon Dioxide Hydrogenation to Methanol
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DOI：
10.1021/cs300008g
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发表时间：
2012-08-01
期刊：
影响因子：
12.9
通讯作者：
Matranga, Christopher
中科院分区：
文献类型：
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作者：
Natesakhawat, Sittichai;Lekse, Jonathan W.;Matranga, Christopher
采用程序升温还原（TPR）、X射线衍射（XRD）、透射电子显微镜（TEM）、X射线光电子能谱（XPS）和N2 O分解等方法，研究了一系列共沉淀铜基催化剂在CO2和H2反应中的活性位和结构-活性关系.实验表明，还原态催化剂和废催化剂表面均存在金属Cu，没有发现单价Cu+存在。这一发现提供了关于甲醇合成催化剂中Cu的活性氧化态的保证，因为观察到6种组合物具有不同的金属氧化物添加剂、Cu粒度和不同程度的ZnO结晶度。较小的Cu颗粒表现出较大的周转频率（TOF）甲醇形成，确认该反应的结构敏感性。没有观察到TOF和Cu微晶中的晶格应变之间的相关性，这表明该结构参数不是活性的原因。此外，观察到的速率的变化可能归因于不同铜晶面的相对分布，因为含有小铜颗粒和无定形或分散良好的ZnO的催化剂上存在更开放和低折射率的表面。在一般情况下，这些系统的活性结果从大的铜表面积，高铜分散，和铜和金属氧化物载体组分之间的协同作用，说明这些是关键参数的发展基本机理洞察到铜基甲醇合成催化剂的性能。
Active sites and structure-activity relationships for methanol synthesis from a stoichiometric mixture of CO2 and H-2 were investigated for a series of coprecipitated Cu-based catalysts with temperature-programmed reduction (TPR), X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and N2O decomposition. Experiments in a reaction chamber attached to an XPS instrument show that metallic Cu exists on the surface of both reduced and spent catalysts and there is no evidence of monovalent Cu+ species. This finding provides reassurance regarding the active oxidation state of Cu in methanol synthesis catalysts because it is observed with 6 compositions possessing different metal oxide additives, Cu particle sizes, and varying degrees of ZnO crystallinity. Smaller Cu particles demonstrate larger turnover frequencies (TOF) for methanol formation, confirming the structure sensitivity of this reaction. No correlation between TOF and lattice strain in Cu crystallites is observed suggesting this structural parameter is not responsible for the activity. Moreover, changes in the observed rates may be ascribed to relative distribution of different Cu facets as more open and low-index surfaces are present on the catalysts containing small Cu particles and amorphous or well-dispersed ZnO. In general, the activity of these systems results from large Cu surface area, high Cu dispersion, and synergistic interactions between Cu and metal oxide support components, illustrating that these are key parameters for developing fundamental mechanistic insight into the performance of Cu-based methanol synthesis catalysts.