Visualization of Structural Changes During Deactivation and Regeneration of FAU Zeolite for Catalytic Fast Pyrolysis of Lignin Using NMR and Electron Microscopy Techniques

Catalytic fast pyrolysis of pretreated lignin (with hydrogen chloride solution) over FAU (15) zeolite uniquely yielded a high fraction of phenols, phenol alkoxys, and aromatic hydrocarbons. However, the zeolite underwent rapid deactivation. This paper reports the visualization of the structural changes during deactivation and regeneration of the zeolite is reported. The deactivated and regenerated zeolites were characterized by means of N-2 physisorption, electron microscopy, X-ray diffraction, magic angle spinning (MAS), and multiple quantum (MQ) nuclear magnetic resonance (NMR) techniques. The results indicated that, during catalyst deactivation, there was excessive coke deposition in the zeolite pore structure resulted in both pore blockage and active site poisoning. The coke was removed by calcination of the spent catalyst in air at high temperature >550 degrees C which resulted in restoring the porosity and the activity to a large extent. However, the recovery of catalytic activity was incomplete attributing to irreversible structural changes in the catalyst during the deactivation and regeneration process. By fine-tuning the reaction conditions and the regeneration of the catalyst, the catalyst performance after reactivation was optimized. Catalyst regeneration after mild coke deposition (that is, after a few catalytic cycles) and mild oxidation conditions (low temperature and slow-heating ramp) are beneficial.