Operando MAS NMR Reaction Studies at High Temperatures and Pressures

Operand MAS NMR studies provide unique insights into the details of chemical reactions; comprehensive information about temperature- and time-dependent changes in chemical species is accompanied by similarly rich information about changes in phase and chemical environment. Here we describe a new MAS NMR rotor (the WHiMS rotor) capable of achieving internal pressures up to 400 bar at 20 degrees C or 225 bar at 250 degrees C, a range that includes many reactions of interest. The MAS NMR spectroscopy enabled by these rotors is ideal for studying the behavior of mixed-phase systems, such as reactions involving solid catalysts and volatile liquids, with the potential to add gases at high pressure. The versatile operation of the new rotors is demonstrated by collecting operando H-1 and C-13 spectra during the hydrogenolysis of benzyl phenyl ether, catalyzed by Ni/gamma-Al2O3 at ca. 250 degrees C, both with and without H-2 (g) supplied to the rotor. The 2-propanol solvent, which exists in the supercritical phase under these reaction conditions, serves as an internal source of H-2. The NMR spectra provide detailed kinetic profiles for the formation of the primary products toluene and phenol as well as secondary hydrogenation and etherification products.