Confining Co-Based Nanocatalysts by Ultrathin Nanotubes for Efficient Transfer Hydrogenation of Biomass Derivatives.

Catalytic transfer hydrogenation (CTH) based on non-noble-metal catalysts has emerged as an environmentally friendly way for the utilization of biomass resources. However, the development of efficient and stable non-noble-metal catalysts is crucially challenging due to their inherent inactivity. Herein, a metal-organic framework (MOF)-transformed CoAl nanotube catalyst (CoAl NT) with unique confinement effect was developed via a "MOF transformation and reduction" strategy, which exhibited excellent catalytic activity for the CTH reaction of levulinic acid (LA) to γ-valerolactone (GVL) with isopropanol (2-PrOH) as the H donor. Comprehensive characterizations and experimental investigations uncovered that the confined effect of the ultrathin amorphous AlO nanotubes could modulate the electronic structure and enhance the Lewis acidity of Co nanoparticles (NPs), thus contributing to the adsorption and activation of LA and 2-PrOH. The synergy between the electropositive Co NPs and Lewis acid-base sites of the CoAl NT catalyst facilitated the transfer of α-H in 2-PrOH to the C atom of carbonyl in LA during the CTH process via a Meerwein-Ponndorf-Verley mechanism. Moreover, the confined Co NPs embedded on am-AlO nanotubes endowed the CoAl NT catalyst with superior stability and the catalytic activity was nearly unchanged for at least ten cycles, far surpassing that of the Co/am-AlO catalyst prepared by the traditional impregnation method.