NMR imaging of mass transport processes and catalytic reactions

Abstract

c Boreskov Institute of Catalysis, 5 Acad. Lavrentiev Pr., Novosibirsk 630090, Russia NMR imaging and spectroscopy techniques are applied to study flow and filtration of liquids, gases and granular solids in various geometries and to the in situ studies of the interplay of mass transport and catalytic reactions in porous media. In particular, quantitative spatially resolved maps of flow velocities of liquids and gases in the channels of monoliths have been obtained. A comparative study of the filtration of water and propane through model porous media has revealed that the dispersion coefficients for water are dominated by the holdup effects even in a bed of nonporous glass beads. Similar experiments performed with the gravity driven flow of liquid-containing fine solid particles through a porous bed have yielded the distributions of particle velocities for various flow rates. The NMR imaging technique was employed to visualize the propagation of autocatalytic waves for the Belousov-Zhabotinsky reaction carried out in a model porous medium. It was demonstrated that the wave propagation velocity decreases as the wave crosses the boundary between the bulk liquid and the flooded bead pack. The images detected during the catalytic hydrogenation of a-methylstyrene on a single catalyst pellet at elevated temperatures have revealed that the reaction and the accompanying phase transition alter the distribution of the liquid phase within the pellet.

Advection of Chemical Reaction Fronts in a Porous Medium

“…To remedy the situation, it is tempting to recall that in the case of transport in a porous medium, one often employs the reaction-dispersionadvection equation, which is equivalent to eq 3, but with D eff ) D 0 + D, with D being the flow-induced dispersion coefficient. This gives It was demonstrated experimentally for the BZ reaction 7,10,11 that, in the case of supportive flow, the graph of V f versus U has a slope larger than unity. Apparently, this is in a qualitative agreement with eq 6, since D(U) is known to increase with U.…”

“…It was demonstrated experimentally for the BZ reaction ,, that, in the case of supportive flow, the graph of V f versus U has a slope larger than unity. Apparently, this is in a qualitative agreement with eq 6, since D ( U ) is known to increase with U .…”

Spatially resolved NMR spectroscopy of heterogeneous gas phase hydrogenation of 1,3-butadiene with parahydrogen

“…[1][2][3][4] Advances in the understanding of heterogeneous catalysts with spatial visualization of reagents and reaction products inside a working reactor can be made using magnetic resonance imaging (MRI). [5][6][7][8][9][10][11][12][13] However, harnessing the full power of MRI to study heterogeneous catalysts at work has a number of challenges. In particular, in the case of gas-solid reactions the spin density of gaseous media is ca.…”

Robust In Situ Magnetic Resonance Imaging of Heterogeneous Catalytic Hydrogenation with and without Hyperpolarization

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Magnetic resonance imaging (MRI) is a powerful technique to characterize reactors during operating catalytic processes. Magnetic resonance imaging (MRI) is a tool applicable to operando studies that provide information for example about the distribution of liquids in the catalyst pellet during hydrogenation of α-methylstyrene [2] or heptene, [3] the coke profiles within a catalyst pellet, [4] the flow of water [5] or propane [6] through a packed bed, the structure of a porous medium and the water flow during the deposition of fines, [7] or the velocities of particles in a fluidized bed. While hyperpolarization techniques such as parahydrogen induced polarization (PHIP) can substantially increase the NMR signal intensity, this general strategy to enable MR imaging of working heterogeneous catalysts to date remains underexplored.

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“…are at the cornerstone of chemical and petrochemical industry [1] and, to make these processes more sustainable, control over reaction selectivity, conversion rates, mass and heat transport inside the working reactor (that is under operando conditions) is required. Magnetic resonance imaging (MRI) is a tool applicable to operando studies that provide information for example about the distribution of liquids in the catalyst pellet during hydrogenation of α-methylstyrene [2] or heptene, [3] the coke profiles within a catalyst pellet, [4] the flow of water [5] or propane [6] through a packed bed, the structure of a porous medium and the water flow during the deposition of fines, [7] or the velocities of particles in a fluidized bed. [8][9][10] MRI of reactors utilizing gases are not as developed as studies of liquids because the spin density in the gas phase is ca.…”