N₂ speeds up hydrogenation on Ru surface

Gaseous nitrogen is a bit of a chemical wallflower. While high temperatures and pressures such as those used in the Haber-Bosch process can convince the compound to react, gaseous N₂ rarely acts as an active catalytic species. Now a group of international researchers has found that adding N₂ gas to a ruthenium-based catalyst speeds up the hydrodeoxygenation of p-cresol into toluene by over 400%; it’s a reaction that could have applications in converting bio-oils into useful chemicals (Nat. Catal. 2019, DOI: 10.1038/s41929-019-0368-6). Led by Jun Li from Tsinghua University and Edman Tsang and Dermot O’Hare from the University of Oxford, the researchers stumbled across this chemistry when trying to pressurize their reactor with an inert gas, O’Hare says. They added gaseous N₂ to a solid-state titanium oxide–supported Ru catalyst, with hydrogen gas and p-cresol, and found that the Ru surface activates the N₂ to form either N₂H or N₂H₂. These acidic hydrogens help boot the –OH groups off the p-cresol, shifting the rate-determining step from –OH hydrogenation to N₂ hydrogenation. The group found that the reaction worked well over multiple supports, including Al₂O₃, ZrO₂, and active carbon. This work shows chemists that N₂ “cannot be simply viewed as an inert bystander,” Li says.