Non-parametric determination of reactivity distribution for nitrided Mo/Al2O3Mo/Al2O3 catalysts during dibenzothiophene HDS

The non-parametric determination of the activity distribution of the catalytic sites on a nitrided 12.5% Mo/Al2O3Mo/Al2O3 catalyst during the hydrodesulfurization (HDS) of dibenzothiophene was studied. The equation for dibenzothiophene HDS was described as a Fredholm integral equation of the first kind, r(t)=∫h(t,k)·f(k)dk, where r(t)r(t) is the rate of the HDS reaction, h(t,k)h(t,k) is a kernel of exp(-kt)exp(-kt) and f(k)f(k) is the distribution of reactivity of the adsorbed species on the surface sites, i.e., the distribution of activity of the catalytic sites. The 12.5% Mo/Al2O3Mo/Al2O3 nitrided at 973 K contained one active site with an average k1k1 value of 0.55 at a population of 60.6%, while the others contained fewer active sites below the k1k1 value of 0.13 at 39.4%. These two distinct patterns supported the fact that two active sites with different rate constants imposed the C–S hydrogenolysis and hydrogenation of dibenzothiophene on the nitrided 12.5% Mo/Al2O3Mo/Al2O3 catalysts. The active sites with an average k1k1 value of 0.55 were 36–49 times larger than those that exhibited smaller k2k2 values. The activity and distribution of the catalytic sites of the nitrided 12.5% Mo/Al2O3Mo/Al2O3 catalysts during the dibenzothiophene HDS are discussed.