Effect of boron substitution in chabazite framework : IR studies on the acidity properties and reactivity towards methanol

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 H 2 O allows the T d -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 CH 3 OH 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.