Nanosized CHA zeolites with high thermal and hydrothermal stability derived from the hydrothermal conversion of FAU zeolite

Abstract

Nanosized CHA zeolites approximately 100 nm in size with high thermal and hydrothermal stability were synthesized by hydrothermal conversion of FAU zeolites in the presence of N,N,N-trimethyl-1-adamantammonium hydroxide (TMAdaOH) as a structure-directing agent. The crystal size of CHA zeolites depended strongly on the silica/alumina source (FAU zeolite or amorphous aluminosilicate hydrogel) and the Si/Al ratio of starting material. An increase in the hydrothermal synthesis temperature enhanced the thermal stability of nanosized CHA zeolites without increasing the crystal size, and the structural framework of the nanosized CHA zeolites was maintained even after thermal treatment at 1000 °C for 1 h. The potential of nanosized CHA zeolites as solid acid catalysts and as catalyst supports was evaluated by the ethanol conversion reaction and the selective catalytic reduction (SCR) of NOx with NH3, respectively. A protonated nanosized CHA zeolite catalyst effectively produced propylene from ethanol by suppressing catalytic deactivation arising from carbonaceous deposition. A Cu-loaded nanosized CHA zeolite catalyst exhibited good performance for the NH3-SCR of NOx even after hydrothermal treatment at 900 °C for 4 h. The results indicate that hydrothermal zeolite conversion is very effective in producing nanosized CHA zeolites with high thermal and hydrothermal stabilities.