Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides
Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides
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DOI：
10.1002/chin.199712253
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发表时间：
1997-03
期刊：
影响因子：
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通讯作者：
B. Weckhuysen;I. Wachs;R. Schoonheydt
中科院分区：
文献类型：
--
作者：
B. Weckhuysen;I. Wachs;R. Schoonheydt
在3d系列的过渡金属离子中，Cr由于其氧化态、配位数和分子结构的可变性而占据特殊的位置。1，2无机氧化物表面上这些Cr物种的阐明是一项复杂的任务，这对于理解Cr在环境、胶体和Cr基多相催化剂中的行为具有根本重要性。3-6铬的环境行为如图1所示。铬经常出现在矿物和地球化学沉积物中，7由于侵蚀和风化，铬成为表面物种或可释放到环境中。另一方面，Cr化合物用于工业如皮革鞣制、电镀和颜料生产，因此存在于固体废物和废水沃茨中。所有这些铬氧化物都具有高度溶解性，并且容易在固-水界面发生各种反应：氧化还原过程以及均相和非均相反应。土壤中的铬可能被土壤组分氧化或还原，这种氧化还原反应对铬的行为有着显著的影响。8、9水溶性和移动的Cr 6+有毒，而移动的Cr 3+的危害相对较低。锰氧化物是已知的天然存在的Cr 3+氧化剂，而Cr 6+被有机土壤成分（氨基、腐殖酸和富里酸）和Fe 2+还原成移动的较少的Cr 3+。铬基催化剂由负载在无机氧化物（如二氧化硅、氧化铝和分子筛）上的Cr氧化物组成。如图2所示，铬/二氧化硅（Cr/SiO2）是著名的菲利普斯催化剂，用于在相对较低的压力下进行乙烯聚合。10-13这种催化剂是生产高密度聚乙烯（HDPE）（最广泛使用的聚合物之一）的菲利普斯颗粒成型工艺的基础。其他重要的催化活性是氢化-脱氢、氧化、异构化、芳构化和DeNOx反应。14-28铬在如此广泛的反应中的活性的基础在于氧化态的可变性，配位环境的可变性，
Among the transition metal ions of the 3d series, Cr takes a particular position because of its variability in oxidation state, coordination numbers and molecular structure. 1, 2 The elucidation of these Cr species on inorganic oxidic surfaces is a complex task, which is of fundamental importance to understanding the behavior of Cr in the environment, colloids, and Cr-based heterogeneous catalysts. 3-6 The environmental behavior of Cr is illustrated in Figure 1. Chromium is frequently encountered in minerals and in geochemical deposits, 7 and due to erosion and weathering, chromium becomes a surface species or can be released into the environment. On the other hand, Cr compounds are used in industries such as leather tanning, electroplating, and pigment production and, therefore, are found in solid wastes and in waste waters. All these Cr oxides are highly soluble and susceptible to various reactions at the solid-water interface: redox processes and homogeneous and heterogeneous reactions. Chromium might be oxidized or reduced by soil constituents and such redox reactions have dramatic influences on the behavior of Cr. 8, 9 The water soluble and mobile Cr6+ is toxic, while the hazard of the less mobile Cr3+ is relatively low. Manganese oxides are the known naturally occurring oxidants of Cr3+, while Cr6+ is reduced to the less mobile Cr3+ by organic soil constituents (amino, humic, and fulvic acids) and Fe2+.Chromium-based catalysts are composed of Cr oxides supported on inorganic oxides, such as silica, alumina, and molecular sieves. Chromium on silica (Cr/SiO2), as illustrated in Figure 2, is the famous Phillips catalyst for the polymerization of ethylene at relatively low pressures. 10-13 This catalyst is the basis for the Phillips particle form process in the production of high-density polyethylene (HDPE), one of the most extensively used polymers. Other important catalytic activities are hydrogenation-dehydrogenation, oxidation, isomerization, aromatization, and DeNOx reactions. 14-28 The basis for the activity of Cr in such a wide spectrum of reactions lies in the variability of oxidation states, of coordination envi-