Mild hydrocracking of 1-methyl naphthalene (1-MN) over alumina modified zeolite

The catalytic activity and life of the NiMoS supported on alumina-USY zeolite (physical mixture of alumina and USY (NMAZ), USY zeolite coated with alumina (NMACZ-2)) were compared in the hydrocracking of 1-methyl naphthalene by a single run at the several reaction temperatures between 360 and 400 degrees C as well as repeated runs at 360 degrees C. The relative activity of NMAZ is slightly higher after 1 h at all reaction temperatures, but was lower after 2 h at reaction temperatures above 380 degrees C. The preference of NMACZ-2 became distinct and definite by further increasing the reaction time at all reaction temperatures. Too long reaction time, particularly at higher reaction temperature, decreased the yield of (alkyl)benzenes, indicating the significant progress of the successive reactions. Thus, the highest yield of alkyl(benzenes) of about 97% was obtained over NMACZ-2 after 4 h at 380-390 degrees C. This was much less than the yield of about 82% obtained over NMAZ after 4 h at 370 degrees C. Ten repeated runs at 360 degrees C for 6 h resulted in marked decrease of yield over NMAZ from 73% to 64%, while the decrease in yield over NMACZ-2 was only from about 80% to 78%. The decrease of catalytic activity appears to reflect the coke formation on the USY which occurs on the naked acidic site of the substrate, which are rather isolated from the NiMoS on alumina. In contrast, alumina-coated support keeps USY underneath the alumina, which carries NiMoS and acidic sites on the same surface. The acidity of surface alumina is moderated by the underneath USY. The adequate acidity of the neighboring NiMoS and high hydrogenation activity provide a good balance resulting in an excellent catalytic activity and life of NiMoS supported on alumina-coated USY zeolite. (c) 2012 The Korean Society of Industrial and Engineering Chemistry. Published by Elsevier B.V. All rights reserved.