Modification of HZSM-5 with trimethylphosphine

Abstract

Trimethylphosphine was found to adsorb selectively on SiOHAI and terminal SiOH groups in HZSM-5 zeolites. It desorbed on evacuation and heating without reaction. On calcination of the adsorption system at 573 K, the thermal stability of the adsorbed phosphine species increased significantly compared with the uncalcined sample. The phosphine compound was found to block all strong Bronsted acid sites up to reaction temperatures of 873 K. Above 873 K, it desorbed regenerating the original acidic properties of HZSM-5. The increase in stability was speculated to be due to the cleavage of one of the methyl groups of adsorbed trimethylphosphine.