Polyoxometalates as bifunctional templates: engineering metal oxides with mesopores and reactive surfaces for catalysis

Abstract

Mesoporous metal oxides with optimized porosity and active surfaces usually exhibit unexpected performance in many applications. However, sacrificial templates and complicated processes are generally required to generate mesopores. Herein, we discover the bifunctional templating talent of polyoxometalates (POMs) for generating not only mesopores but also reactive surfaces in metal oxides, and a facile, recyclable, and general method is reported. By mechanochemical ion-sharing between metal salts and POMs, metal precursors undergo pyrolysis around large POM clusters, which can incorporate abundant mesopores into metal oxides (e.g., Co₃O₄, Fe₃O₄, NiO, La₂O₃, MnO₂, CeO₂, ZrO₂, and CuO) with ultrahigh specific surface areas (up to 210 m² g⁻¹) after simply being recycled by water washing. Unexpectedly, the oxidative feature of POMs naturally contributes to the formation of high valence metal cations on the material surface. As an example, the Co₃O₄ sample with both mesopores and enriched surface Co³⁺ species was more active than Co₃O₄ derived from a silica template (T₁₀₀ = 200 °C) and commercial Co₃O₄ (T₁₀₀ = 250 °C), in CO oxidation. The current strategy may provide a promising route for the commercialization of mesoporous metal oxides with preferred surface features.