Ni–Pt/H-Y Zeolite Catalysts for Hydroisomerization of n-Hexane and n-Heptane

Abstract

Ni–Pt/H-Y zeolite catalysts with different Ni contents were prepared and applied to the hydroisomerization of n-hexane and n-heptane in the temperature range 225-375 °C. ESCA studies show the complete reduction of Ni species up to 0.3 wt% Ni addition over 0.1 wt% Pt/H-Y and further addition leads to the occurrence of unreduced nickel species as NiAl₂O₄. A TEM study shows the formation of bimetallic (Ni–Pt) particles of nanoscale size and the average particle size is found to increase with increasing Ni loading. Acidity measurements by NH₃-TPD and pyridine-adsorbed FTIR spectroscopy show the increasing occupation of acid sites by the added nickel when increasing the nickel loading. The catalytic activity of Ni–Pt/H-Y zeolite and Pt/H-Y catalysts was compared and it was found that addition of Ni up to 0.3 wt% increases the n-hexane and n-heptane conversion, multibranched isomer selectivity and sustainability of the catalysts due to better metal-acid synergism, complete reduction of Ni species and the formation of catalytically active Ni–Pt bimetallic particles. Further Ni addition leads to a decrease in conversion and multibranched isomer selectivity and an increase in the cracked products, which may be due to the presence of unreduced Ni species and pore blockage by larger-sized bimetallic particles formed.