TY - JOUR
T1 - Acidic properties of nanolayered ZSM-5 zeolites
AU - Wu, L.
AU - Magusin, P.C.M.M.
AU - Degirmenci, V.
AU - Li, M.
AU - Almutairi, S.M.T.
AU - Zhu, X.
AU - Mezari, B.
AU - Hensen, E.J.M.
PY - 2014/5/1
Y1 - 2014/5/1
N2 - The acidic properties of nanolayered ZSM-5 zeolites synthesized with the aid of multiquaternary ammonium surfactants were investigated in detail. A substantial fraction of Al is present in highly dispersed form at extraframework positions indicative of the defective nature of the calcined nanolayered zeolites. Acidity characterization reveals that the Brønsted acid sites are similar in strength to those in bulk HZSM-5. Nanolayered zeolites contain a higher amount of Brønsted acid sites (BAS) at their external (mesopore) surface. Unilamellar zeolites have a higher concentration of external BA and silanol sites than multilamellar ones. The number of BAS in the nanolayered zeolites is considerably lower than the tetrahedral Al content, the difference increasing with nanolayer thickness. Except for one particular sample (nanolayered ZSM-5 synthesized from COH template), the total turnover of methanol normalized per BAS trends inversely with the concentration of BAS. There is no correlation with the concentration of external BAS. Catalyst deactivation due to coke mainly depends on the BAS concentration. A unilamellar ZSM-5 zeolite prepared using COH displayed substantially improved performance in terms of a much lower rate of coke deactivation in line with earlier data Choi et al. [10]. Since the acidic and textural properties of this zeolite did not differ significantly from the others, it remains to be determined why this zeolite performs so much better.
AB - The acidic properties of nanolayered ZSM-5 zeolites synthesized with the aid of multiquaternary ammonium surfactants were investigated in detail. A substantial fraction of Al is present in highly dispersed form at extraframework positions indicative of the defective nature of the calcined nanolayered zeolites. Acidity characterization reveals that the Brønsted acid sites are similar in strength to those in bulk HZSM-5. Nanolayered zeolites contain a higher amount of Brønsted acid sites (BAS) at their external (mesopore) surface. Unilamellar zeolites have a higher concentration of external BA and silanol sites than multilamellar ones. The number of BAS in the nanolayered zeolites is considerably lower than the tetrahedral Al content, the difference increasing with nanolayer thickness. Except for one particular sample (nanolayered ZSM-5 synthesized from COH template), the total turnover of methanol normalized per BAS trends inversely with the concentration of BAS. There is no correlation with the concentration of external BAS. Catalyst deactivation due to coke mainly depends on the BAS concentration. A unilamellar ZSM-5 zeolite prepared using COH displayed substantially improved performance in terms of a much lower rate of coke deactivation in line with earlier data Choi et al. [10]. Since the acidic and textural properties of this zeolite did not differ significantly from the others, it remains to be determined why this zeolite performs so much better.
UR - http://www.scopus.com/inward/record.url?eid=2-s2.0-84896316971&partnerID=8YFLogxK
U2 - 10.1016/j.micromeso.2013.08.042
DO - 10.1016/j.micromeso.2013.08.042
M3 - Article
AN - SCOPUS:84896316971
SN - 1387-1811
VL - 189
SP - 144
EP - 157
JO - Microporous and Mesoporous Materials
JF - Microporous and Mesoporous Materials
ER -