Synergizing metal and acid sites via intracrystalline confinement of NiO clusters near 12-membered ring junction region for hydrogen transfer deoxygenation

The catalytic upgrading of bio-oil via hydrogen transfer deoxygenation necessitates catalysts capable of simultaneously activating C H bonds and oxygen-containing functionalities. Herein, we report a confined Ni@Y zeolite catalyst synthesized through a hydrothermal encapsulation approach, wherein NiO clusters are predominantly confined within the FAU micropore network and preferentially stabilized near the 12-membered ring junction regions connecting supercages and sodalite cages. Structural characterization confirms that this spatial confinement enhances metal dispersion, generates additional Lewis acid sites, and strengthens synergistic effect of metal and acid sites. Spectroscopic analyses combined with density functional theory calculations suggest that the intracrystalline NiO fraction stabilized in the 12-membered ring junction environment facilitate the activation of C H bonds and oxygen-containing functionalities. Owing to the synergistic interplay between well-dispersed metal sites and proximal acid centers, the Ni@Y zeolite exhibits superior catalytic activity in the hydrogen-transfer deoxygenation of salicylaldehyde with tetralin, achieving the highest deoxygenation efficiency (63.4%), highest water yield (3.6%), and lowest coke yield (6.1%), outperforming conventional HY and impregnated Ni/Y-IM zeolites. These findings provide mechanistic insights into the molecular-scale role of confined metal-acid synergy and offer theoretical guidance for the rational design of zeolite-based catalysts for bio-oil valorization.