In situ measurement of molecular diffusion during catalytic reaction by pulsed-field gradient NMR spectroscopy

Time-Resolved Study of Acetyl Radical in Zeolite NaY by Step-Scan FT-IR Spectroscopy

“…The nongeminate encounters of the radicals that would dominate the decay according to the computer simulations would follow a second-order reaction 2 described by eq 1 (ref ), where R is the concentration of acetyl radical, k the bimolecular reaction rate constant, D the diffusion coefficient of acetyl radical in zeolite NaY, and ρ the reaction radius. The diffusion coefficient of acetyl radical is assumed to be the same as the measured value of propylene, 4 × 10 -10 m 2 s -1 , which is of similar size and shape and has a similar degree of unsaturation . This assumption is further supported by the activation energy of 1.7 kcal mol -1 derived by the Arrhenius law from the temperature dependence of the acetyl radical decay rates in the case of the pinacolone experiment.…”

Microimaging of Transient Concentration Profiles of Reactant and Product Molecules during Catalytic Conversion in Nanoporous Materials

“…This is in particular true with respect to the evolution of the intrinsic profiles of the concentration of the reactant and product molecules, which remained inaccessible by direct observation. Though PFG NMR has been successfully employed for observing the diffusion and conversion of the various molecular species involved in catalytic reactions, [13] it fails to give any insight into the interplay of diffusion and reaction.…”

Exploring Mass Transfer in Mesoporous Zeolites by NMR Diffusometry

“…Only owing to this material it was possible to demonstrate [ 31 , 32 ] that early PFG NMR measurements of water in commercial FAU-type zeolites [ 33 ] did yield an effective (the “long-range”) rather than the true intracrystalline diffusivity. This novel type of measurement has become possible thanks to the unique zeolite material [ 34 ], synthesized by Professor Sergey Petrovich Zhdanov in Leningrad, in the Soviet Union, which was available in Leipzig, on the same side of the iron curtain at that time, and which has given rise to a number of papers dealing with intracrystalline diffusion in zeolites [ 35 , 36 ] as well as with diffusion under the special conditions of chemical reactions [ 37 ]. We dedicate this paper to the memory of Professor Zhdanov on the occasion of the 100th anniversary of his birthday on 18 April 2012, recognizing the most productive collaboration between his group and the group in Leipzig, in deep appreciation of his contribution to the development in the field and of the eventual break-down of the iron curtain.…”