Promoting role of residual organic structure directing agent in skeletal butene isomerization over ferrierite

Abstract

This work examines how acid site concentration (FT-IR) and strength (NH₃-TPD) as well as pore mouth accessibility modulate the activity of the microporous zeolite ferrierite (H-FER) during the skeletal isomerization of 1-butene to iso-butene. Restricting the accessibility of catalyst pores and strong acid sites is achieved by selective oxidation of residual organic structure directing agent (OSDA) through precise control of calcination conditions. Because this reaction is mediated by catalytically active carbonaceous deposits, residual OSDA affects their formation. This work demonstrates that small amounts of residual OSDA (∼ 0.2 wt%) are beneficial to the reaction under industrially relevant reaction conditions in three ways. Selective poisoning of strong BAS with OSDA nearly halves the amount of dimerization and cracking byproducts and improves catalyst lifetime. Simultaneously, carbonaceous fragments of the OSDA act as coke precursors and help shorten the startup time. Hence, catalyst lifetime may be significantly improved through both optimal pre-treatment conditions and by designing catalysts with an increased number of accessible pore mouths.