Mesoporous ZSM-5 zeolite catalysts prepared by desilication with organic hydroxides and comparison with NaOH leaching.

ABSTRACT The use of organic hydroxides directly produced the protonic form of the mesoporous zeolite upon calcination, simplifying the final ion exchange with NH4NO3 characteristic of the NaOH treatment The optimal hierarchical ZSM-5 zeolite (treated in 1 M TPAOH at 338 K and 8 h) had a mesopore surface area of 160 m 2 g -1 and the intrinsic zeolite properties were largely preserved.

Introduction The microporous nature of these solid acids imposes diffusion limitations in reactions involving bulky hydrocarbons. Mass-transfer constraints limit the catalytic activity and occasionally also the selectivity and lifetime Hierarchical zeolites have emerged as an important class of materials leading to improved catalytic performance compared to their microporous parents ， This is typically assigned to the shortened micropore diffusion path length as a result of a secondary mesopore network of inter- or intracrystalline nature

The use of strong organic bases as the desilicating agent, such as quaternary ammonium hydroxides, can simplify the final ionexchange step intrinsic of the inorganic hydroxides. The organic cation can be decomposed by calcination, rendering the zeolite in its protonic form.

Experimental 5cm 3 of 1 M TPAOH 338K 30min-8h quenched by icewater zeolite powder (166 mg) 500rpm filtered washed until pH neutral calcined dried at 373 K for 12 h 823 K 5 h 5 K min -1

Results and discussion PH=14 PH=13.2

无需离子交换

0.9nm 0.19nm

Conclusions 1 、 This makes the demetallation process highly controllable 2 、 directly produced the protonic form of the mesoporous zeolite upon calcination. 3 、 higher Si/Al ratios in the mesoporous zeolites are attained But tetraalkylammonium hydroxides as desilication agent is the high cost compared to NaOH

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