Cracking of n-heptane on fluorinated γ-alumina catalysts in the presence of hydrogen: Catalytic activity and nature of acid active sites

Abstract

The cracking of n-heptane over fluorinated γ-alumina catalysts with different fluorine contents was studied using a tubular packed-bed reactor at 723 K and 2400 kPa. Maximum activity was obtained for the catalyst containing 2.5 wt.-% fluorine. Cracking and isomerization of n-heptane are the primary reactions. Hydrogen can be activated on the surface of fluorinated aluminas and the olefins formed during cracking are hydrogenated by hydride transfer from hydrogen. Two mechanisms for cracking, viz., β-scission and protolytic cracking, can explain the initial selectivities obtained, which means that both Lewis and Brønsted sites could be active in this process. The original Lewis sites present in γ-alumina have a very low cracking activity.