Kinetics, catalyst deactivation and modeling in the hydrogenation of β-sitosterol to β-sitostanol over microporous and mesoporous carbon supported Pd catalysts

Kinetics of the hydrogenation of β-sitosterol to β-sitostanol is of industrial interest, since the desired product is used for suppressing cholesterol absorption in human body. The main drawback when using microporous Pd/C catalyst in this reaction is catalyst deactivation. In the current work the performance of microporous and mesoporous Pd catalysts in the hydrogenation of β-sitosterol was compared. The catalytic hydrogenations were performed in a shaking batch reactor in 1-propanol as a solvent. With larger amounts of catalyst less catalyst deactivation occurred due to the fact that the catalyst support acted also as an adsorbent. The mesoporous 4 wt.% Pd/C (Sibunit) catalyst showed higher sitosterol conversions and less catalyst deactivation compared to a microporous 5 wt.% Pd/C catalyst. The kinetics of the hydrogenation of β-sitosterol to β-sitostanol was studied over 4 wt.% Pd/C (Sibunit) catalyst at different temperatures between 60 °C and 80 °C and by reusing the catalyst. The origin for catalyst deactivation was poisoning by phosphorus and sulphur, as well as coking. In situ catalyst potential measurements showed that there is a correlation between catalyst deactivation and decreasing catalyst potential with increasing sitosterol conversion. A mechanistic kinetic model including a deactivation factor was successfully applied to this reaction and the kinetic parameters were determined.