Zeolite structures based on the chabazite topology, such as H-SAPO-34, possess unique shape-selectivity properties for converting methanol into light olefins. In addition to the topology, zeolite acidity is inherently linked to catalyst activity and selectivity. The acidic properties of high silica Chabazite (H-SSZ-13) have attracted much attention the last decade and conclusions drawn so far have essentially been founded on quantum chemical methods. An experimental based benchmark of the acidity of H-SSZ-13 has hitherto not been available. In this work, transmission FTIR spectroscopy provides a description of the different acidic sites of H-SAPO-34 by using water and methanol as probe molecules and compare the results with those obtained with the zolitic homologue: H-SSZ-13. The results demonstrate that both materials are strongly acidic, essentially having two distinct sets of Bronsted sites that show a different accessibility. However all sites interact with bases forming strong H-bonded adducts; moreover, in presence of high water and or methanol loadings, clear evidences of protonation have been found only in case of II-SSZ-13.
Acidity properties of CHA-zeolites (SAPO-34 and SSZ-13): an FTIR spectroscopic study
REGLI, LAURA;BORDIGA, Silvia;ZECCHINA, Adriano;
2005-01-01
Abstract
Zeolite structures based on the chabazite topology, such as H-SAPO-34, possess unique shape-selectivity properties for converting methanol into light olefins. In addition to the topology, zeolite acidity is inherently linked to catalyst activity and selectivity. The acidic properties of high silica Chabazite (H-SSZ-13) have attracted much attention the last decade and conclusions drawn so far have essentially been founded on quantum chemical methods. An experimental based benchmark of the acidity of H-SSZ-13 has hitherto not been available. In this work, transmission FTIR spectroscopy provides a description of the different acidic sites of H-SAPO-34 by using water and methanol as probe molecules and compare the results with those obtained with the zolitic homologue: H-SSZ-13. The results demonstrate that both materials are strongly acidic, essentially having two distinct sets of Bronsted sites that show a different accessibility. However all sites interact with bases forming strong H-bonded adducts; moreover, in presence of high water and or methanol loadings, clear evidences of protonation have been found only in case of II-SSZ-13.
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