Hydroconversion of n-paraffins in light naphtha using Pt/Al2O3 catalysts promoted with noble metals and/or chlorine

Abstract

The effect of combining 0.35 wt.% Pt with 0.35 wt.% of either Ir, Rh, Re or U on γ-Al2O3 support was investigated for the hydroconversion of n-pentane and n-hexane in a pulsed micro-reactor system at a temperature range of 300–500°C, except for Rh/Al2O3 (150–500°C). The dispersion of the metals in the catalysts under study was determined by H2 chemisorption. The effect of chlorine addition between 1.0 and 6.0 wt.% was investigated and a content of 3.0 wt.% Cl being of optimum promotion. Highest activities for hydroisomerization, hydrocracking and hydrogenolysis were exhibited by Pt, Ir and Rh/Al2O3 catalysts, respectively, whether the catalysts were Cl-free or containing 3% Cl. However, Re and U catalysts were inactive. Maximum hydroisomerization selectivities using chlorinated bimetallic catalysts could be arranged in the following order: PtU/Al2O3>PtRe/Al2O3>PtIr/Al2O3>PtRh/Al2O3. However, PtRh/Al2O3, before and after chlorination, was the most active catalyst for hydrogenolysis. The apparent reaction rate constants as well as the apparent activation energies (Ea) for the hydroconversion of n-pentane and n-hexane were calculated and the compensation effect relationship between Ea and logarithm of the pre-exponential factor was estimated. n-hexane reaction on PtRh/Al2O3 catalysts deviates from this relationship for mechanistic variation