Insight in cyclohexene hydroconversion process using catalysts containing 0.35% Pt on amorphous and zeolite supports

Abstract

Commercial non crystalline silica and γ-alumina were used as supports, whereas Na-Y, Na-ZSM-5 and Na-MOR-zeolites were exchanged with NH4NO3 to obtain the corresponding NH4-zeolites and calcined producing the H-zeolites which were then impregnated with H2PtCl6 to obtain 0.35% Pt on each support. These catalysts were characterized via TPD, TPR, XRD and Pt dispersion using H2 chemisorption and tested for cyclohexene hydroconversion in atmospheric flow-type reactor. TPR of the calcined samples showed that PtOx species supported on SiO2were the most easily reducible among all catalysts, i.e., at 80°C, since SiO2 acquires the weakest Pt–support-interaction. Hence, Pt particles dispersion on SiO2 was the lowest (28.2%) and this catalyst was the least active for cyclohexene hydroconversion. However, the Pt/γ-alumina catalyst exhibited the highest hydrogenation and dehydrogenation activities due, principally, to acquiring the highest Pt dispersion (86.5%). In general, the zeolite loaded catalysts possessed higher Pt–support interaction compared to very weakly acidic amorphous catalysts. The most acidic zeolite supported catalysts (Pt/H-MOR and Pt/H-ZSM-5) possessed the highest hydroisomerization and hydrocracking activities by virtue of their higher acid site strength. Although, Pt/H-ZSM-5 acquires lower acid sites number and strength than Pt/H-MOR, it is found more active for these reactions. We assume that the more active Brönsted acid sites in H-ZSM-5 have overcompensated the higher acidity of Pt/H-MOR. The Pt/HY catalyst, although acquires the largest acid site density and widest channels, it is the least active zeolite for CHE isomerization and hydrocracking most probably due to its weaker acid sites strength.