The effect of lanthanum(III) and cerium(III) ions between layers of manganese oxide on water oxidation

Abstract

Manganese oxide structure with lanthanum(III) or cerium(III) ions between the layers was synthesized by a simple method. The ratio of Mn to Ce or La in samples was 0.00, 0.04, 0.08, 0.16, 0.32, 0.5, 0.82, or 1.62. The compounds were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction studies, and atomic absorption spectroscopy. The compounds show efficient catalytic activity of water oxidation in the presence of cerium(IV) ammonium nitrate with a turnover frequency of 1.6 mmol O2/mol Mn.s. In contrast to the water-oxidizing complex in Photosystem II, calcium(II) has no specific role to enhance the water-oxidizing activity of the layered manganese oxides and other cations can be replaced without any significant decrease in water-oxidizing activities of these layered Mn oxides. Based on this and previously reported results from oxygen evolution in the presence of H 2 (18) O, we discuss the mechanism and the important factors influencing the water-oxidizing activities of the manganese oxides.

Redox Processes Involving Oxygen: The Surprising Influence of Redox-Inactive Lewis Acids

“…Based on additional X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) studies, it was suggested that potassium might be involved in forming distinct KCo 3 O 4 cubanes, although other studies have debated such a role for potassium . The influence of redox-inactive metals on water oxidation has been studied more extensively in manganese oxides that are structurally similar to the birnessite family of minerals. − These manganese oxides form layers of edge-sharing MnO 6 octahedra, in which redox-inactive metals can intercalate . Studies on these synthetic mixed-manganese oxides revealed that, in the presence of redox-inactive metals, a marked increase in O 2 evolution was observed compared to plain manganese oxide. , The O 2 evolution activity followed the trend Ca 2+ > Sr 2+ ≫ Mg 2+ ∼ Na + , very similar to the activity profile of the OEC.…”

“… 267 The influence of redox-inactive metals on water oxidation has been studied more extensively in manganese oxides that are structurally similar to the birnessite family of minerals. 36 − 40 These manganese oxides form layers of edge-sharing MnO 6 octahedra, in which redox-inactive metals can intercalate. 37 Studies on these synthetic mixed-manganese oxides revealed that, in the presence of redox-inactive metals, a marked increase in O 2 evolution was observed compared to plain manganese oxide.…”

“…While a primarily structural role has been ascribed to Zn 2+ in Cu/Zn-SOD, ,− with SOD activity being largely retained upon Zn 2+ loss, the role of Ca 2+ in the OEC has not been conclusively elucidated. Consequently, synthetic models of the OEC have been targeted with the aim of unraveling fundamental reactivity relevant to biological water oxidation. − Interest in the effects of redox-inactive metals on redox processes involving oxygen has been further piqued by discoveries in the field of heterogeneous catalysis, where mixed-metal oxides containing both redox-active and -inactive components have gained significant attention as electrocatalysts in the oxygen evolution reaction (OER). − Moreover, employing multiple different metal centers in discrete complexes can likewise result in new physical properties and reactivity pathways beyond oxygen chemistry. − As a result, aspects of the effects of redox inactive metals on the redox reactivity of transition metals with oxygen have been addressed in several types of reactions, and this field has seen significant increase in research activity. − …”

“… 33 − 35 Interest in the effects of redox-inactive metals on redox processes involving oxygen has been further piqued by discoveries in the field of heterogeneous catalysis, where mixed-metal oxides containing both redox-active and -inactive components have gained significant attention as electrocatalysts in the oxygen evolution reaction (OER). 36 − 40 Moreover, employing multiple different metal centers in discrete complexes can likewise result in new physical properties and reactivity pathways beyond oxygen chemistry. 41 − 46 As a result, aspects of the effects of redox inactive metals on the redox reactivity of transition metals with oxygen have been addressed in several types of reactions, and this field has seen significant increase in research activity.…”