Metal/Acid Bifunctional Catalysis and Intimacy Criterion for Ethylcyclohexane Hydroconversion: When Proximity Does Not Matter

Abstract

The apparent kinetics in metal/acid bifunctional catalysis is generally strongly affected by the metal to acid sites ratio, and their proximity. Although, these two key parameters are not systematically investigated in scientific literature. Such study is provided here for bifunctional catalysts using platinum as metallic function and EU-1 zeolite as acidic function.Two series of bifunctional catalysts with different metal to acid sites ratios and different metal to acid sites distances were prepared and tested in ethylcyclohexane hydroconversion. Increasing the metal to acid site ratio, the catalytic activity and isomerization selectivity increased until a plateau was reached, an observation which is in agreement with the classical bifunctional mechanism. At the same time, the intimacy criterion of Weisz was evaluated: strikingly, for a given metal to acid sites ratio, activities and selectivities are not affected by their distance (up to a micrometer scale). A dual function kinetic model was successfully applied in order to quantify

Bifunctional Intimacy and its Interplay with Metal‐Acid Balance in Shaped Hydroisomerization Catalysts

“…To further evaluate the influence of the metal to acid sites ratio, the dual‐function kinetic model, previously proposed by us and validated over different catalytic systems and hydroconversion reactions, was employed. This model was developed based on a detailed mechanism for both metal‐ and acid‐catalyzed reactions.…”

Deactivation and regeneration of Pt‐modified zeolite Beta–Bindzil extrudates in n‐hexane hydroisomerization

“…Metal–acid bifunctional catalysts are widely used in many industrially significant chemical processes, e.g. hydrocracking of heavy oils, dewaxing, reforming, selective ring opening and hydroisomerization 1–9 . Hydroisomerization of C 5 –C 6 n ‐alkanes involving three steps, namely dehydrogenation of alkanes, skeletal isomerization of olefins and hydrogenation of the latter, is one of the cheapest ways to improve fuel quality (increase in octane number) 3,4,9–11 .…”

“…Pt, Pd, Mo, W, Co, Ni), while isomerization or hydrocracking steps proceed on the acid sites (e.g. amorphous silica–alumina oxides, zeolites and mesoporous aluminosilicates) 1–3,5,9,12 …”

“…Many studies of metal–acid bifunctional catalysts have been performed with powder catalysts under the kinetic regime 1,11,16,18–28 . However, in an industry where shaped catalytic bodies containing binders are used, the mass transport limitation regime is almost unavoidable.…”

“…Several studies on C 7 –C 16 n ‐alkane hydroisomerization used crushed shaped Pt catalysts (0.1–0.8 mm) with Pt deposition on either the shaped supports 1,2,40,41 or on a zeolite 1,2,21,42 . However, detailed studies of the uncrushed shaped bifunctional catalysts are still lacking in the open literature 2,3 .…”