Synthesis and Characterization of Chromium-Added Pt/Beta Zeolite and its Catalytic Performance for n-Heptane Isomerization

Catalysis of Pt/beta zeolite catalyst modified via the addition of various elements (Ca, Cr, Mn, Fe, Co, Ni or Cu) for n-heptane skeletal isomerization was investigated at 513 K in a conventional flow reactor with a fixed catalyst bed. It was found that, among the catalysts tested, PtCr/beta was the most promising, since its use resulted in relatively high yields of multi-branched alkanes in conjunction with a very low selectivity for cracking products. Ion exchange was found to be an effective method for the addition of chromium to zeolite, compared to the evaporation to dryness process. Platinum particle sizes were observed using STEM. While particles ~10–30 nm in size were evident on the surface of Pt/beta, they were rarely observed on the PtCr/beta catalyst. It was concluded that platinum homogeneously dispersed within beta zeolite micropores resulted in the observed decreased cracking activity during n-heptane isomerization and that the addition of chromium had been effective in increasing degree of platinum dispersion.