Experimental and Model FTIR Distinction of Internal and External Brønsted Acidic Sites on CHA and SAPO-34 Zeolites

Proton exchanged Chabazite and SAPO-34 show substantial shifts in their Brønsted acidic peak positions when measured by diffuse reflectance or transmission FTIR.  Experimental and DFT based evidence is presented that this shift is due to vibration differences of surface and bulk Brønsted hydroxyls with potential implications on their catalytic performances.