Generation of HO鈥?/sup> Radical from Hydrogen Peroxide Catalyzed by Aqua Complexes of the Group III Metals [M(H2O)n]3+ (M = Ga, In, Sc, Y, or La): A Theore
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- 作者：Alexander S. Novikov ; Maxim L. Kuznetsov ; Armando J. L. Pombeiro ; Nadezhda A. Bokach ; Georgiy B. Shul鈥檖in
- 刊名：ACS Catalysis
- 出版年：2013
- 出版时间：June 7, 2013
- 年：2013
- 卷：3
- 期：6
- 页码：1195-1208
- 全文大小：688K
- 年卷期：v.3,no.6(June 7, 2013)
- ISSN：2155-5435
文摘
The mechanism of the rate-limiting stage of alkanes oxidation with hydrogen peroxide, that is, formation of the hydroxyl radicals, catalyzed by aqua complexes, [M(Hb>2 b>O)b>n b>]3+ (<b>1b>), of the group III metals exhibiting a unique stable non-zero oxidation state (M = Ga, In, Sc, Y, or La) was theoretically studied in detail at the DFT level. The mechanism involves the substitution of a Hb>2 b>O ligand for Hb>2 b>Ob>2 b>, protolysis of the coordinated Hb>2 b>Ob>2 b>, substitution of another Hb>2 b>O ligand for Hb>2 b>Ob>2 b>, generation of the hydroxyl radical upon the homolytic O鈥揙 bond cleavage in the key complex [M(Hb>2 b>O)b>(n鈭?) b>(Hb>2 b>Ob>2 b>)(OOH)]2+, and closure of the catalytic cycle. The substitution steps proceed via the dissociative mechanism D (M = Ga and Y) or the associative mechanisms A [M = Sc, La, or In (second substitution)] or Ib>a b> [M = In (first substitution)]. The general catalytic activity of <b>1b> is determined by three main factors, that is, (i) lability of the complexes, (ii) acidity of the metal-bound ligands, and (iii) the Hb>2 b>Ob>2 b> activation toward the homolytic O鈥揙 bond cleavage. The Hb>2 b>Ob>2 b> activation, in turn, depends on the strength of the M鈥揙b>2 b>Hb>2 b> bond, delocalization of the spin density within a coligand (OOH鈥?/sup>), and ability of the coligand to be easily oxidized. The calculations predict that the catalytic activity of <b>1b> increases along the row of the metals Al 鈮?La < Y 鈮?In < Sc < Ga.<br>