Effect of nickel incorporation on the acidity and stability of HZSM-5 zeolite in the MTO process

A study has been carried on the effect of Ni incorporation on the acidity (acid strength distribution and total acidity), on the hydrothermal stability of a HZSM-5 zeolite and on the kinetic performance of this catalyst in the MTO process at high temperature (up to 500 °C, in order to increase selectivity to olefins) and when there is a high water content in the feed (in order to minimise deactivation by coke). The incorporation of Ni in the HZSM-5 zeolite implies a decrease in the total acidity and in the acid strength of the zeolite and, consequently, the activity of the catalyst decreases. Nevertheless, the catalysts with Ni are hydrothermally more stable than the parent zeolite catalyst. A Ni content around 1 wt% is the optimum, as it allows for uninterrupted operation in reaction–regeneration cycles, with water contents higher than 50 wt% in the medium, without irreversible deactivation, whereas a higher Ni content produces an unnecessary loss of initial activity.