화학공학소재연구정보센터
Applied Catalysis A: General, Vol.526, 95-104, 2016
Formation of weak and strong Bronsted acid sites during alkaline treatment on MOR zeolite
Aluminum rich mordenite zeolite (Si/Al = 10) was hierarchized by using mild (0.2 M NaOH and 70 degrees C) and severe (0.4 M NaOH and 85 degrees C) alkaline treatments. The textural characterization was made by nitrogen adsorption. Acidic properties, i.e. nature (N), concentration (C), strength (S), accessibility (A) and location (L), were drawn from adsorption of two probes molecules followed by infrared spectroscopy: pyridine for N, C, L and S properties while CO for N and S properties. The catalytic model reaction of m-xylene transformation was also used to determine C, S and L properties. The severe alkaline treatment promoted (i) silicon extraction of zeolite framework, without considerable loss of crystallinity, (ii) creation of intracrystal mesopore and widening of micropore diameter due to formation of interconnection between main canals, and (iii) accessibility of Bronsted acid sites (BAS) located in side pockets. The silicon removal is inevitably followed by formation of extraframework aluminum species (EFAL) that leads to formations of Lewis acid sites, weak extraframework BAS and very strong BAS due to interaction between EFAL with the bridged hydroxyl, evidenced by a correlation between turnover frequency in m-xylene transformation and concentration of LAS. (C) 2016 Published by Elsevier B.V.