ChemInform Abstract: Catalytic Reactions of n‐Dodecane on Aluminosilicates

Abstract

Abstract Catalytic reactions of n -dodecane at 400 °C have been studied on HY, LaY, amorphous silica-alumina, HZSM-5, and H-mordenite. The molar distributions of initial products are almost identical on HY and LaY, while the distributions are shifted toward lower molecular weight products on the other catalysts. This we associate with initiation of cracking at Bronsted sites, which have higher acidities on amorphous silica-alumina, H-mordenite, and HZSM-5 than those present on HY and LaY. With the exception of HZSM-5, initial ratios of branched/linear paraffins are similar on all catalysts and show a preference for the branched isomer in the range C 4 C 8 . On HZSM-5 the linear isomer is formed preferentially. This is attributed to restriction in the rearrangement of the carbonium ion in the narrower pores of the pentasil. The kinetic model previously applied to the cracking of linear paraffins on HY can also be applied to the cracking of n -dodecane on other aluminosilicate catalysts. The consequent kinetic parameters show that inhibition of the cracking reaction is greater on HY and LaY than on amorphous silica-alumina, H-mordenite, and HZSM-5. This is attributed to the stronger Lewis acidity of the carbenium ions formed by adsorption of product olefins at the stronger Bronsted sites on the later group of catalysts.