546115 Real-Time Coking and Regeneration of a Working ZSM-5 Zeolite Monitored Via Operando Space-Resolved X-Ray Diffraction

Tuesday, June 4, 2019: 4:24 PM
Texas Ballroom EF (Grand Hyatt San Antonio)
Georgios N. Kalantzopoulos1, Daniel Rojo Gama2, Dimitrios K. Pappas2, Karl Petter Lillerud1, Unni Olsbye1, David S. Wragg2 and Stian Svelle1, (1)Department of Chemistry, University of Oslo, OSLO, Norway, (2)Department of Chemistry, Centre for Materials Science and Nanotechnology, University of Oslo, OSLO, Norway

H-ZSM-5 is known to be the archetype zeolite for the conversion of methanol to gasoline (MTG) due to its three dimensional structure consisting of straight and sinusoidal channels that enhance the diffusion of products, improving the resistance towards deactivation. One of the main hurdles that a zeolite framework inherently exhibits when used as a catalyst in the MTG reaction is the loss of catalytic performance over time due to coking. The loss of activity on H-ZSM-5 during the MTG reaction is reported to follow the “burning cigar” model proposed by Haw1,2,3. Using real structural parameters obtained from the XRD we can track the development of coke at different points in the reactor and link this to a kinetic model to correlate catalyst deactivation with structural changes occurring in the material4.

Consecutive exposure of the catalyst to suitable oxidative conditions leads to the burning of the coke, making the acid sites accessible for a new MTG cycle. To the best of our knowledge, very little is reported regarding the evolution of the H-ZSM-5 structure during its regeneration. In this work we have used operando space-resolved X-Ray diffraction to study the local structural transformations of the H-ZSM-5 catalyst during deactivation and removal of coke under variable temperature oxidative conditions, resulting in catalyst regeneration. Finally, high-energy 3D X-ray micro-tomography has been employed to monitor the evolution of the carbon gradient and of local structural transformations in shaped catalyst objects.

Figure 1. Evolution of the (a-b) parameter of the H-ZSM-5 unit cell over time on stream (TOS) and along the catalyst bed (a). Cross-section of partially deactivated zeolite catalyst extrudate (b). Evolution of individual coke occupancies within the ZSM-5 framework during regeneration at increasing TOS (c).

References

[1] Catal. Today. 2010, 154, 183-194.

[2] Rojo-Gama, D.; Etemadi, S.; Kirby, E. et al, Faraday Discuss. 2017, 197, 421-446.

[3] Haw, J. F.; Marcus, D. M. Top Catal 2005, 34, 41-48.

[4] Rojo-Gama, D.; Mentel, L.; Kalantzopoulos, G.N. et al. J Phys Chem Letters, 2018, 9, 1324-1328.


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