KINETIC-STUDY OF THE THERMAL COLLAPSE OF MAZZITE SAMPLES OF DIFFERENT MORPHOLOGIES

The kinetics of thermal decomposition of zeolite omega in air has been followed between 850 and 920-degrees-C for prismatic single crystals (sample A) and between 660 and 800-degrees-C for spheroidal particles (sample B). The order in function of time is one for sample A at 875 and 900-degrees-C and the activation energy 92 kcal/mole. X-ray diffraction and infrared spectra show that the collapse of the structure occurs with dealumination of the lattice, which affects selectively S4R sites. In the case of sample B, the kinetics appear to be limited by diffusion (activation energy 6.8 kcal/mole) at low temperature, but not at high temperature (activation energy 60 kcal/mole). The lattice collapse of sample B occurs with much less dealumination. The different stabilities of the two samples can be attributed to different partitioning of aluminum between the two T sites: Dealumination of S6R sites more populated in sample B leads to lattice collapse.