The Reactivity with Hydrogen and Nitrogen
In this chapter (reproduced from Chem. Rev. 2016), we present the reactivity of metal clusters with hydrogen and nitrogen. Hydrogen is known as a highly combustible diatomic gas, and the lightest element on the periodic table.
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The Reactivity with Hydrogen and Nitrogen
In this chapter,1 we present the reactivity of metal clusters with hydrogen and nitrogen [1–14]. Hydrogen is known as a highly combustible diatomic gas, and the lightest element on the periodic table. Hydrogen readily forms covalent compounds with many non-metallic elements and it is an important reducing agent of metallic ores. The H2 chemisorption and hydrogen evolution reactions upon metal clusters have been extensively studied in the past decades in view of the broad interest of hydrogen storage and green energy sources [15–35]. Nitrogen is the lightest pnictogen and it is the most abundant uncombined element having an electronegativity of 3.04. An N atom consists of five electrons in its outer shell allowing a triple bond in molecular nitrogen (N2 ). The strong N ≡ N triple bond results in difficulty of converting N2 into other compounds. Nitrogen is usually unreactive at standard temperature and pressure; however, metal lithium (or magnesium) does burn in an N2 atmosphere, giving rise to lithium nitride (or magnesium nitride).
5.1 The Reactivity with Hydrogen Metal-hydrogen cluster reactivity has been extensively studied with a focus on iron [19, 36], cobalt [15, 37–43], vanadium and niobium [44–48]. A typical example in Fig. 5.1 illustrates the reactivity of cationic Fen + and Vn + clusters with hydrogen (D2 was used in order to avoid mass degeneracy) [47, 48]. It was found that the presence of positive charge had a substantial influence on the reaction rate for the majority of iron and vanadium clusters [19, 49, 50], and the kinetics of D2 chemisorption on Fen + /Vn + clusters exhibited a non-monotonic dependence on n. It is interesting to mention that, studies of hydrogen chemisorption onto cationic Fen + (n = 4–22) found a generally enhanced (although size-selective) reactivity compared to that for neutral 1 This
chapter is reproduced from Chem. Rev. 2016.
© The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Singapore Pte Ltd. 2020 Z. Luo and S. N. Khanna, Metal Clusters and Their Reactivity, https://doi.org/10.1007/978-981-15-9704-6_5
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5 The Reactivity with Hydrogen and Nitrogen
Fig. 5.1 a Relative rate constants for reaction of cationic vanadium cluster Vn + toward D2 as a function of cluster size, as determined by bare cluster depletion. The Y-axis represents the reactivity equal to lnSx /[D2 ], where Sx is the fraction of bare clusters unreacted, i.e., the survival fraction, while [D2 ] is a factor directly proportional to the concentrations of D2 in the reactor. Typical uncertainties are estimated to be ±20%. Reproduced from Ref. [48]. Copyright 1989 American Chemical Society. b Reactivity of cationic Fen+ toward D2 under identical conditions. Typical uncertainties are ±10%. Reproduced with permission from Ref. [47]. Copyright 1988 American Institute of Physics
Fen . This behavior can be rationalized within a framework of the frontier orbital model of activated chemisorption of hydrogen by invoking an ac
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