Optimization of Short-Range Order in Amorphous AlO_<i>x</i> Nanosheets for Enhanced Methane Oxidation.

Abstract

Heterogeneous catalysts often undergo dynamic evolution during catalysis, forming true active sites. Amorphous materials, due to their inherent structural flexibility, are particularly prone to evolution and self-adaptation under catalytic conditions. Herein, we demonstrate that the short-range order of an Al-O polyhedron in amorphous aluminum oxide nanosheets undergoes a transformation from a mixed AlO₆, AlO₅, and AlO₄ configuration to a randomly connected AlO₆ structure during both hydrothermal treatment and direct methane oxidation, confirmed by time-series ²⁷Al solid-state NMR spectroscopy. The resulting structural changes induce nanosheet wrinkling and a 5-fold increase in specific surface area, concomitant with a transition from weak to moderately strong basic sites, enabling the amorphous nanosheets to efficiently activate hydrogen peroxide and generate hydroxyl radicals. When coupled with supported Cu single atoms, the catalysis achieves an exceptional C₁ liquid oxygenate production rate of 5202 mmol g_Cu^-1 h^-1 with nearly 100% selectivity during methane oxidation.