The importance of methanol to light olefins (MTO) process in today's economy, using H-SAPO-34 as a catalyst, has stimulated the investigation of new zeolitic material with the same CHA topology but characterized by a different acidic strength. In this work, we report a detailed IR investigation on the symmetry, accessibility, acidic strength, and reactivity of B sites in a CHA framework. As the prepared material exhibits [B(OSi)(4)] units in a T-d-like geometry, upon template burning, the break of a B-O-Si bond results in [B(OSi)(3)] units in a D-3h-like geometry, testified by the appearance of the IR fingerprint at 1390 cm(-1). Interaction with a strong base as H2O allows the Td-like geometry to be reversibly restored. Weak bases, such as H-2 and CO, are unable to displace B species from the D-3h-like geometry but testify the weak Bronsted acidity of internal OH species. Interaction with CH3OH gives rise to a much more complex spectroscopy, reflecting a rich reactivity of methanol with both [B(OSi)(3)] units and adjacent SiOH species. This reactivity, discovered in the present IR investigation, justifies on a molecular level the unsuitability of the B-CHA system for the MTO process.
Effect of boron substitution in chabazite framework: IR studies on the acidity properties and reactivity towards methanol
REGLI, LAURA;BORDIGA, Silvia;LAMBERTI, Carlo;ZECCHINA, Adriano
2007-01-01
Abstract
The importance of methanol to light olefins (MTO) process in today's economy, using H-SAPO-34 as a catalyst, has stimulated the investigation of new zeolitic material with the same CHA topology but characterized by a different acidic strength. In this work, we report a detailed IR investigation on the symmetry, accessibility, acidic strength, and reactivity of B sites in a CHA framework. As the prepared material exhibits [B(OSi)(4)] units in a T-d-like geometry, upon template burning, the break of a B-O-Si bond results in [B(OSi)(3)] units in a D-3h-like geometry, testified by the appearance of the IR fingerprint at 1390 cm(-1). Interaction with a strong base as H2O allows the Td-like geometry to be reversibly restored. Weak bases, such as H-2 and CO, are unable to displace B species from the D-3h-like geometry but testify the weak Bronsted acidity of internal OH species. Interaction with CH3OH gives rise to a much more complex spectroscopy, reflecting a rich reactivity of methanol with both [B(OSi)(3)] units and adjacent SiOH species. This reactivity, discovered in the present IR investigation, justifies on a molecular level the unsuitability of the B-CHA system for the MTO process.
I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
