Operando MAS NMR Reaction Studies at High Temperatures and Pressures

Abstract

Operando 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 °C or 225 bar at 250 °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 1 H and 13 C spectra during the hydrogenolysis of benzyl phenyl ether, catalyzed by Ni/γ-Al 2 O 3 at ca. 250 °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.

Enhanced Selective Production of Arenes and Regenerating Rate in Aryl Ether Hydrogenolysis over Mesoporous Nickel in Plug-Flow Reactors

“…The absorption peaks at 948 and 1013 cm −1 may help in attributing them to absorbed cyclohexanol surface species on the Ni-based catalysts. Finally, formation of surface cyclohexanol has been considered a consequence of phenol surface reactions on metal nanoparticles [37]. These results confirm the desorption results of poisoning species on the Ni-based catalysts shown in Figure 3.…”

Unraveling the Dynamic Network in the Reactions of an Alkyl Aryl Ether Catalyzed by Ni/γ-Al2O3 in 2-Propanol

“…Recently, we demonstrated the use of sealed MAS NMR rotors in reactions conducted in near-supercritical 2-PrOH (225 °C, P = 200 bar). [32][33] At room temperature, the 13 C MAS-NMR spectrum of 2-PrOH consists of two singlets at  25.3 (methyl) and 63.6 (methine) ppm, Figure 1. As the temperature of the sealed NMR rotor approaches 150 °C, the methyl and methine resonances shift to lower and higher frequencies, respectively, while two new resonances emerge at  23.2 and 63.1 ppm.…”

“…[38][39] No hydrogenation of either BPE or toluene was observed, although some hydrogenation of toluene was seen previously at a higher temperature and pressure (225 °C, 120 bar H 2 ). 32 However, phenol is more reactive, 13 and it was partially hydrogenated to cyclohexanol (ca. 3 % conversion in 10 h at 150 °C, Figure S3).…”

Correlating Structure and Properties of Super‐Concentrated Electrolyte Solutions: 17O NMR and Electrochemical Characterization

“…We tried to perform these MAS experiments, but the rotation was slow and uneven. In order to spin such viscous materials, specific MAS systems are needed . The NMR signals have been referred to LiCl aq (0 ppm).…”

“…In order to spin such viscous materials, specific MAS systems are needed. [35,36] The NMR signals have been referred to LiCl aq (0 ppm). Single pulse experiments have been acquired with 516 scans, pulse length of 3.5 μs and delay time of 5 s. Spin-lattice relaxation times (T 1 ) were obtained at room temperature for both 17 O and 7 Li by using the standard Inversion Recovery (180°-τ-90°) sequence.…”