High-performance, low Pd-loading microfibrous-structured Al-fiber@ns-AlOOH@Pd catalyst for CO coupling to dimethyl oxalate

Thin-sheet microfibrous-structured Al-fiber@ns-AlOOH@Pd catalysts with low Pd-loading engineered from micro- to macro-scale are developed for the gas-phase CO coupling to dimethyl oxalate, providing unique combination of high activity/selectivity and good stability with high permeability and high thermal conductivity. The support of Al-fiber@ns-AlOOH is initially prepared via endogenous growth of boehmite nanosheets (ns-AlOOH) on 3D network of 60-μm Al-fiber. The palladium is then placed onto the surface of the ns-AlOOH rooted on the Al-fiber via incipient wetness impregnation method with a toluene solution of palladium acetate. As an example, the catalyst with a low Pd-loading of 0.25 wt% delivers ∼66% CO conversion and ∼94% DMO selectivity for a feed of CH₃ONO/CO/N₂ (10/14/76, vol%) with a gas hourly space velocity of 3000 L kg^-1 h^-1, and particularly, is stable for at least 200 h without deactivation. Our Al-fiber@ns-AlOOH@Pd catalyst demonstrates two times higher intrinsic activity (expressed by turnover frequency) compared to a traditional Pd/α-Al₂O₃. The existence of Pd-hydroxyl synergistic interaction is paramount to the enhanced catalytic performance for the CO coupling reaction, by nature, as the result of hydroxyl-promoted adsorption of bridged CO on the Pd surface.