Cleavage of Lignin-Derived 4-O-5 Aryl Ethers over Nickel Nanoparticles Supported on Niobic Acid-Activated Carbon Composites

Cleavage of lignin-derived 4-O-5 aryl ethers has been conducted over nickel nanoparticles supported on niobic acid-activated carbon composite under mild conditions. The hydrated niobic acid has been successfully supported and well dispersed on activated carbon. Due to the coexisting Bronsted and Lewis acid sites on the hydrated niobic oxide, the Ni/xNbAC catalysts exhibited higher activities for cleavage of C–O ether bonds and dehydration than those of the Ni/AC catalyst. With increasing content of niobic acid, a larger amount of O-free alkane is obtained owing to niobic acid-promoted removal of oxygen from lignin-derived aryl ethers. The cleavage of C–O ether bonds and dehydration of cyclohexanol to cyclohexane are both favored at high temperature. The direct cleavage of the 4-O-5 aryl ether bond can also be achieved under low H2 pressure, forming phenol and benzene as intermediates, followed by hydrodeoxygenation of phenol to cyclohexane.