Pyridine assisted desilication of mordenite

Abstract

Pyridine assisted alkaline desilication has been elaborated as new post-synthetic modification strategy of mordenite. The addition of pyridine during the desilication treatment revealed to impact materials properties through a dual action on textural and chemical properties; substantially different in comparison to the classical alkaline treatment or CTAB assisted desilication. As far as texture is concerned the use of pyridine permits to greatly modify the desilication scheme, hence yielding aggregates of smaller zeolite particles with substantially higher amount of external silanols. The presence of pyridine in the as-synthesized mordenites allows to in situ generate extra-framework aluminium (EFAL) species during final calcination step. Both of these features, smaller particle size and the presence of EFAL species improve catalytic properties considerably. Whilst the achievement of smaller particles reduces diffusion path length, the presence of EFAL species allow for exalting acidity and hence catalytic activity in n-hexane cracking and propene transformation.

Recent Progress in Synthesis and Application of Nanosized and Hierarchical Mordenite—A Short Review

“…Modifications with The mordenite structures obtained by this method possess high thermal and acid stability in combination with zeolite acidity and porosity through which bulky molecules can pass. A similar approach to recrystallization by replacement of the surfactant with pyridine was proposed by H. Issa et al [72]. The authors concluded that pyridine interacts with external hydroxides which selectively directs the desilication towards small zeolite particles.…”

State of the Art and Perspectives of Hierarchical Zeolites: Practical Overview of Synthesis Methods and Use in Catalysis

“…A pure alkaline treatment was performed by several groups. [262][263][264][265][266][267][268] Pastvova et al treated a parent mordenite in a 0.2 m NaOH solution. [262] This concentration, however, was varied in another study from Huang et al who concluded that extracting Si from the framework by an alkaline treatment could generate intracrystalline mesopores with diameters of 3-30 nm.…”

“…For instance, in the pyridine-assisted desilication from Issa et al, a material yield of ≈76% was obtained. [266] Another strategy is an alkaline treatment that is followed by an acid wash. This is done by several research groups.…”

“…A pure alkaline treatment was performed by several groups. [ 262–268 ] Pastvova et al. treated a parent mordenite in a 0.2 m NaOH solution.…”

“…For instance, in the pyridine‐assisted desilication from Issa et al., a material yield of ≈76% was obtained. [ 266 ]…”