Lanthanum, cerium, and boron incorporated ZSM-12 zeolites for catalytic cracking of n-hexane

摘要

Zeolites have a vital role in the conversion of naphtha to more valuable products, especially when the price of crude oil is falling down. Medium-pore zeolites such as MTW zeolite, for instance, require further modification to produce more valuable products with higher selectivity and conversion. ZSM-12 (MTW) zeolite was synthesized and modified using an impregnation method by adding extra-framework elements, namely, cerium, boron, and lanthanum with different loadings to visualize the role of these extra-framework elements on the catalytic cracking. It was observed that impregnation has a negligible effect on the zeolitic phase of MTW zeolites as confirmed by XRD patterns. Weak and strong acid sites were affected by the presence of extra-framework elements. However, impregnation of ZSM-12 with extra-framework elements led to the decrease in Bronsted and increase in Lewis acid sites as observed from pyridine FTIR. The catalytic performance of impregnated ZSM-12 zeolite was applied in n-hexane cracking at 650 degrees C under atmospheric pressure. Despite the decrease in the catalytic conversion in the presence of the extra-framework, impregnation slightly enhanced the selectivity towards light olefins and depress the selectivity of the paraffin. The highest selectivity to olefins was observed over B-ZSM-12 zeolite with 2 wt.% of boron with an average selectivity of 69% and average conversion of 64% after 240 min.