Activity and selectivity of bifunctional platinum catalysts in hydrocarbon reactions

Abstract

Conversions of a number of C 6C 8-alkanes, naphthenes, and aromatics on bifunctional platinum/carrier catalysts, on Pt-black, and on the acidic carriers of the bifunctional catalysts are investigated in the temperature range 300–500 °C and at hydrogen partial pressures of 0–45 bars in a continuously operated fixed-bed reactor and in microcatalytic pulse reactors. Three activity and selectivity levels of the platinum in bifunctional Pt/acidic carrier catalysts may be broadly recognized: (1) temperatures below 350 °C where mainly platinum-catalyzed reactions contribute to the measured product distributions, (2) a temperature region around 400 °C where platinum drastically changes its activity and selectivity in hydrogenolysis and isomerization reactions due to removable carbonaceous deposits and (3) a region above about 400 °C where due to irreversible carbiding platinum only displays (de)hydrogenation activity. The product distributions from conversions of the model compounds on irreversibly carbided Pt/carrier catalysts are mainly governed by acid-catalyzed interconversions through nonclassical carbonium ion intermediates.