Effect of sulfur on n-octane aromatization over Sn- and Ge-promoted Pt/KL catalysts

Abstract

In previous studies, it was found that PtSn/KL catalysts prepared by vapor-phase co-impregnation exhibit remarkably high stability and selectivity to C8-aromatics for n-octane aromatization. One of the serious drawbacks of Pt/KL-based catalysts is their high sensitivity to even traces of sulfur. The addition of Ge was found to improve sulfur tolerance of P1/A1₂O₃ catalyst. In this work, the sulfur tolerance of Sn- and Ge-promoted Pt/KL catalysts, including the effects of varying Ge content, have been investigated. The catalysts prepared by vapor-phase co-impregnation were characterized by TPR, TPO, hydrogen chemisorptions, TEM, DRIFTS, and XPS. Reaction measurements were carried out at 500 °C and atmospheric pressure. It was found that, in the absence of sulfur, Pt-Sn/KL and Pt-Ge/KL could improve the catalytic activity and the selectivity to C8-aromatics compared with unpromoted Pt/KL catalyst. In the case of bimetallic Pt-Ge catalyst, the appropriate amount of Ge loading with 0.6 wt% Pt loading selected to prepare the catalyst was 0.6 wt%. In the presence of 25 ppm sulfur, the unpromoted Pt/KL catalyst for n-octane aromatization was not extremely high sensitivity to sulfur as much as for n-hexane aromatization. The sensitivity to sulfur was also found in the aromatization of n-octane on Pt-Ge/KL catalyst. By contrast, on the Pt-Sn/KL catalyst, the n-octane aromatization activity was not diminished by the presence of sulfur, but actually increased. TEM images displayed higher distributed metal clusters on Pt-Sn/KL and Pt-Ge/KL compared to the unpromoted Pt/KL catalyst.