Molecular mobility in fixed-bed reactors investigated by multiscale NMR techniques.

Area of Science:

• Chemical Engineering
• Materials Science
• Analytical Chemistry

Background:

• Fixed-bed reactors with catalytically active particles are crucial in industrial processes.
• Coke formation during reactions blocks active sites and shrinks pore space, hindering transport.
• Understanding pore structure and fluid dynamics is vital for catalyst performance.

Purpose of the Study:

• To demonstrate the feasibility of various Nuclear Magnetic Resonance (NMR) techniques for investigating catalyst pore structures.
• To analyze the intra- and interparticle pore space in fixed-bed reactors across different length scales.
• To assess the impact of coke residue on fluid molecule mobility and transport within catalysts.

Main Methods:

• Nuclear Magnetic Resonance (NMR) spectroscopy (including 129Xe spectroscopy).
• NMR cryoporometry, relaxation dispersion measurements, and diffusivity investigations.
• Velocity-encoded imaging for fluid density and velocity distribution mapping.

Main Results:

• NMR techniques successfully probed intra- and interparticle pore spaces from nanometers to centimeters.
• 129Xe spectroscopy, cryoporometry, and relaxation dispersion revealed coke residue effects on fluid mobility.
• Velocity-encoded imaging provided insights into fluid dynamics in the larger interparticle voids.

Conclusions:

• NMR is a versatile tool for characterizing complex pore structures in fixed-bed catalytic reactors.
• The study highlights NMR's capability to monitor catalyst deactivation due to coking.
• Combined NMR methods offer comprehensive analysis of pore space and fluid transport in industrial catalysts.