Enhanced In situ Continuous-Flow MAS NMR for Reaction Kinetics in the Nanocages

A new approach of in situ continuous-flow laser-hyperpolarized Xe-129 MAS NMR together with C-13 MAS NMR is designed and applied successfully to study the adsorption and reaction kinetics in the nanospace. Methanol conversion in CHA nanocages has been investigated in detail for proof of principle demonstrating the prospect of in situ NMR of reaction kinetics. Our findings well elucidates that the reaction intermediate can be identified by C-13 MAS NMR spectroscopy, meanwhile the kinetic and dynamic processes of methanol adsorption and reaction in CHA nanocages can be monitored by one- and two-dimensional hyperpolarized Xe-129 MAS NMR spectroscopy under the continuous-flow condition close to the real heterogeneous catalysis. The kinetic curves and apparent activation energy of the nanocages involving the active site are obtained quantitatively. The advantages of hyperpolarized Xe-129 with much higher sensitivity and shorter acquisition time allow the kinetics to be probed in a confined geometry under real working conditions.