Equilibrating metal-oxide cluster ensembles for oxidation reactions using oxygen in water

被引:163
作者
Weinstock, IA
Barbuzzi, EMG
Wemple, MW
Cowan, JJ
Reiner, RS
Sonnen, DM
Heintz, RA
Bond, JS
Hill, CL
机构
[1] US Forest Serv, Chem & Pulping Res Work Unit, USDA, Forest Prod Lab, Madison, WI 53705 USA
[2] Emory Univ, Dept Chem, Atlanta, GA 30322 USA
[3] Univ Wisconsin, Dept Chem Engn, Madison, WI 53706 USA
关键词
D O I
10.1038/35102545
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
Although many enzymes can readily and selectively use oxygen in water-the most familiar and attractive of all oxidants and solvents, respectively-the design of synthetic catalysts for selective water-based oxidation processes utilizing molecular oxygen(1-4) remains a daunting task(5,6). Particularly problematic is the fact that oxidation of substrates by O-2 involves radical chemistry, which is intrinsically non-selective and difficult to control. In addition, metallo-organic catalysts are inherently susceptible to degradation(5) by oxygen-based radicals, while their transition-metal-ion active sites often react with water to give insoluble, and thus inactive, oxides or hydroxides(7). Furthermore, pH control is often required to avoid acid or base degradation of organic substrates or products. Unlike metallo-organic catalysts, polyoxometalate anions are oxidatively stable and are reversible oxidants(8,9) for use with O-2 (refs 8-10). Here we show how thermodynamically controlled self-assembly of an equilibrated ensemble of polyoxometalates, with the heteropolytungstate anion(11,12) [AIV(V)W(11)O(40)](6-) as its main component, imparts both stability in water and internal pH-management. Designed to operate at near-neutral pH, this system facilitates a two-step O-2-based process for the selective delignification of wood (lignocellulose) fibres. By directly monitoring the central Al atom, we show that equilibration reactions typical of polyoxometalate anions(13,14) keep the pH of the system near 7 during both process steps.
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页码:191 / 195
页数:5
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