Preparation, properties, and ESCA characterization of oxygen sensitive Manganese surface compounds and dispersions on silicagel

Abstract

Oxygen sensitive MnO, MnO/SiO2 dispersions, and manganese(II) surface compounds on silica gel with “one” and “two legged” surface attachments were systematically prepared and their surface states ascertained by considering variations in the Mn 2p3/2 binding energy levels. A differentiation by ESCA between very finely divided MnO/SiO2 surface dispersions and the cited “true” surface compounds was possible. Aqueous impregnations with Mn(NO3)2 above 1.2–1.5 wt.% Mn concentration range were found to give predominantly green MnO/SiO2 dispersions and not real surface compounds as was originally suggested in a previous paper [11]. The  unit chemically attached to manganese has an electron withdrawing effect (comparable in magnitude to the Cl functional group) which is an almost linearly additive function in a surface compound. The support behaves therefore as a “quasi electron sink”. The results with Mn confirm as well as complement and extend published ESCA findings for other transition metal surface compound systems. Oxygen sensitivity was observed to decrease and olefin polymerization ability to increase with removal of electron density from the central manganese atom. The possible mode of action of some manganese based oxygen absorbers is discussed.