Pentacoordinated Al3+‐Stabilized Active Pd Structures on Al2O3‐Coated Palladium Catalysts for Methane Combustion

Supported Pd catalysts are active in catalyzing the highly exothermic methane combustion reaction but tend to be deactivated owing to local hyperthermal environments. Herein we report an effective approach to stabilize Pd/SiO₂ catalysts with porous Al₂O₃ overlayers coated by atomic layer deposition (ALD). ²⁷Al magic angle spinning NMR analysis showed that Al₂O₃ overlayers on Pd particles coated by the ALD method are rich in pentacoordinated Al³⁺ sites capable of strongly interacting with adjacent surface PdO_x phases on supported Pd particles. Consequently, Al₂O₃‐decorated Pd/SiO₂ catalysts exhibit active and stable PdO_x and Pd–PdO_x structures to efficiently catalyze methane combustion between 200 and 850 °C. These results reveal the unique structural characteristics of Al₂O₃ overlayers on metal surfaces coated by the ALD method and provide a practical strategy to explore stable and efficient supported Pd catalysts for methane combustion.     

Neodymium(III) Complexes Capable of Multi‐Electron Redox Chemistry

A family of neodymium complexes featuring a redox‐active ligand in three different oxidation states has been synthesized, including the iminoquinone (L⁰) derivative, (^dippiq)₂NdI₃ ( 1‐iq ), the iminosemiquinone (L¹⁻) compound, (^dippisq)₂NdI(THF) ( 1‐isq ), and the amidophenolate (L²⁻) [K(THF)₂][(^dippap)₂Nd(THF)₂] ( 1‐ap ) and [K(18‐crown‐6)][(^dippap)₂Nd(THF)₂] ( 1‐ap crown ) species. Full spectroscopic and structural characterization of each derivative established the +3 neodymium oxidation state with redox chemistry occurring at the ligand rather than the neodymium center. Oxidation with elemental chalcogens showed the reversible nature of the ligand‐mediated reduction process, forming the iminosemiquinone metallocycles, [K(18‐crown‐6)][(^dippisq)₂Nd(S₅)] ( 2‐isq crown ) and [K(18‐crown‐6)(THF)][(^dippisq)₂Nd(Se₅)] ( 3‐isq crown ), which are characterized to contain a 6‐membered twist‐boat ring.