Quasi free K cations confined in hollandite-type tunnels for catalytic solid (catalyst)-solid (reactant) oxidation reactions

Identification of catalytically active species and reaction pathway in catalytic solid (catalyst)-solid (reactant) reactions is a nontrivial task as exemplified in diesel soot oxidation (combustion), the technology for control of diesel particulate emissions. A physical contact between catalytically active species and solid soot is usually deemed necessary. Herein, thermally-stable hollandite-type alpha-MnO2 (KxMn8O16) nanorod catalysts have been synthesized with one-dimensional tunnel structures partially filled with relatively mobile K cations. These tunnel-confined quasi free K cations are revealed to be responsible for the catalytic soot oxidation activity, proving that physical contact between soot and K cations is unnecessary for solid-solid reaction. A novel catalyst, KyTi8O16 has been successfully designed to boost the catalytic activity in TiO2 toward soot oxidation by engineering a K-contained hollandite-type isostructure.