Catalytic cracking of n-octane over alkali-treated MFI zeolites

The catalytic cracking of n-octane over alkali-treated MFI zeolites was studied to investigate the catalytic roles of acidity and pore structure in the catalytic cracking of naphtha. The alkali treatment on the MFI zeolite induced the dissolution of silica and alumina, resulting in the loss of strong acid sites and the formation of mesopores. The low acidity and short residence time induced the reduction of cracking activity, lowering the conversion and enhancing the selectivity for primary cracking products. The alkali treatment, therefore, shows the cracking path of n-octane in zeolite pores. The acidity was the predominant factor in determining the conversion level and product composition, so a high conversion and a high yield of alkene were obtained over the MFI zeolite with a large amount of strong acid sites. Mesopores formed during the alkali treatment suppressed the production of longer alkanes such as hexane and heptane by reducing further oligomerization. The alkali treatment was not effective in enhancing overall alkene selectivity, but the selectivity for propene was high over alkali-treated zeolites, due to the rapid elution of primary cracking products.