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

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Mesoporous ZSM-5 zeolite catalysts prepared by
desilication with organichydroxides and
comparison with NaOH leaching
.
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ABSTRACT

• The use of organic hydroxides directly
  produced the protonic form of the mesoporous
  zeolite upon calcination, simplifying the ?nal
  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 m2g-1 and the
  intrinsic zeolite properties were largely
  preserved.

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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

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

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Experimental

• 5cm3of 1 M TPAOH 338K 30min-8h
  quenched by icewater
• zeolite powder (166 mg) 500rpm
  ?ltered
• washed until pH
  neutral calcined
• dried at 373 K for
  12 h 823 K 5 h
• 
  5 K min-1

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Results and discussion
PH14
PH13.2
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0.19nm
0.9nm
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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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