Active species identification in Zn and Mn-based materials for application in alcohol oxidation reactions

Abstract

Surface and bulk properties and catalytic performance during benzaldehyde synthesis of inexpensive Zn modified-MnCO3 catalysts (xZnMn), prepared by impregnation method and covering a wide range of Zn loadings (1.0 wt% Zn < x < 22.6 wt% Zn) were deeply investigated for the first time. XRD, TPN2 (temperature-programmed decompositions in N2) and XPS characterization showed that different crystalline phases containing Mn and/or Zn species are present in xZnMn. In these phases Mn oxidation state changes from 2+ toward higher values (3+ and 4+) as Zn content increases entailing the transformation of MnCO3 to ZnMn2O4 spinel and MnOx oxides. During benzyl alcohol oxidation at mild reaction conditions using oxygen, the highest benzaldehyde yield (∼70 %) was obtained on 15.4ZnMn sample after 6 h of reaction. The superior catalytic performance of the 15.4ZnMn catalyst was attributed to a synergistic interaction of both metals.