Direct synthesis of zeolite coatings on cordierite supports by in situ hydrothermal method

A simple and green in situ hydrothermal method, free of organic templates or zeolite seeds, was examined and introduced by depositing several typical microporous aluminosilicate zeolites (Linde A, Linde Y, mordenite and ZSM-5) on cordierite supports. Such preparative factors as crystallization time, crystallization temperature and basic strength were systematically investigated to discuss their effect on the growth of zeolites on cordierite supports. The as-prepared zeolite/cordierite samples were characterized by various techniques and a supposed in situ growth mechanism of zeolites on supports was given. The aluminium atoms on cordierite supports were activated by OH− and these activated atoms subsequently built a zeolite framework together with the silicon atoms and aluminium atoms of the synthesis gel. Based on this, the in situ deposition of zeolites can be easily extended to other aluminium-containing supports. With respect to pure zeolite powders, the in situ coated zeolites on supports exhibited much better stability and accessibility, which were thought essential for industrial applications. Copper ion-exchanged ZSM-5/cordierite was studied as catalyst for the direct decomposition of NO and selective catalytic reduction of NO by propane in excess oxygen. Cu-ZSM-5/cordierite was found to exhibit an obviously enhanced turnover frequency compared to Cu-ZSM-5 powders, which made it a potential deNOx catalyst for future applications.