Nanostructured MnOx catalysts in the liquid phase selective oxidation of benzyl alcohol, with oxygen: Part I. Effects of Ce and Fe addition on structure and reactivity

The effects of Ce (Ce-at/Mn-at, 0-1) and Fe addition ((Ce-at +Fe-at)/Mn-at, 0.3) on the texture, structure and redox properties of MnOx systems have been investigated. Irrespective of their loading, the Ce and Fe promoters lead to nanostructured composite systems with a much larger surface area than the oxide component alone. Both Ce and Fe ions improve catalyst reducibility because of structural effects enhancing the surface availability of high oxidation number Mnn+ (n >= 4) sites. At variance with the inactivity of the CeO2 and Fe2O3 promoters, the bare and promoted MnOx catalysts drive the liquid phase oxidation of benzyl alcohol with oxygen in the range of 323-353 K with total aldehyde selectivity. The dependence of activity level on MnOx loading and unchanging activation energy barrier (52 +/- 5 kJ/mol) substantiate the lack of electronic effects attributable to both Ce and Fe promoters. Although a marked activity loss recorded after the 1st reaction cycle, calcination at T >= 473 K fully restores the catalyst functionality. (C) 2014 Elsevier B.V. All rights reserved.