Characterization and Hydroisomerization Performance of Mg-Promoted, Pt/ZSM-23-Based Catalysts

The effect of Mg on the acidic and metal functions in Pt/ZSM-23 catalysts has been studied, using both pure zeolite (Z) and preshaped ZSM-23/Al2O3 composite (ZA) and varying the content and method of Mg loading. N-2 physisorption, CO chemisorption, H-2/O-2 titration, XRD, TEM, TPR, and FTIR were employed to characterize the phase composition, textural and acidic properties, platinum location and dispersion. The shaping procedure used left the acidity of the parent zeolite virtually intact, while Pt dispersion on the composite support was greatly increased. Despite the increased C-Pt/CH+ ratio, the Pt/ZA catalyst underperformed Pt/Z in the yield of branched isomers produced in n-decane hydroconversion. Irrespective of the support, its impregnation with Mg allowed tuning the surface acidity and improving the isomerization selectivity above the level characteristic of unpromoted Pt/Z. However, the addition of Mg through ion-exchange resulted in an opposite effect on the catalyst selectivity. Possible reasons of such a complex behavior are discussed.

Automated summary

This study investigates the effect of Mg on the acidic and metal functions in Pt/ZSM-23 catalysts. The results show that Mg loading can tune the surface acidity and selectivity of the catalyst, but the addition of Mg through ion-exchange has an opposite effect.