EFFECT OF ALUMINA FLUORIDATION ON HYDROCONVERSION OF N-HEPTANE ON SULFIDED NIW AL2O3 CATALYSTS/

Hydroisomerization and hydrocracking of n-heptane on sulfided NiW cata lysts, supported on alumina modified with various amounts of fluoride, have been studied at 673, 698, and 723 K and at a total pressure of 3 MPa. It was found that alumina fluoridation increases the catalytic a ctivity for both hydroisomerization and hydrocracking and provides a h igher hydroisomerization selectivity, Differences in product selectivi ties for the hydroisomerization and hydrocracking of n-heptane indicat e that alumina fluoridation induces also changes in the various contri butions of the mechanisms involved in the transformation of n-heptane, A decrease in the ratio of 3-MC6 and 2-MC6 monobranched isomers predi cted by a branching mechanism via the protonated cyclopropane (PCP) in termediates and a decrease in the dimerization cracking mechanism in f avor of the classic bifunctional cracking mechanism were observed with increasing fluoride content, Theses changes are results of a better b alance of the (de)hydrogenation and acidity functions of the sulfided catalysts with increasing fluoride content since the incorporation of fluoride increases the (de)hydrogenation function and decreases the st rength of the acid sites. (C) 1997 Academic Press.