The effect of Fe on Pt particle states in Pt/KL catalysts

• Two types of Fe-promoted Pt/KL catalysts were studied.
• Framework Fe and non-framework Fe were introduced by different methods.
• With the non-framework Fe, an electron-rich platinum species formed.
• With the framework Fe, an electron-deficient platinum species formed.
• Fe species affected the catalyst aromatization performance.

Two types of Fe-containing Pt/KL catalysts were prepared, characterized and examined using an n-hexane aromatization reaction. Pt/FeKL contained framework Fe, which was incorporated through hydrothermal synthesis, while Pt-Fe/KL contained non-framework Fe, which was introduced through impregnation. The differences between the framework and non-framework Fe were examined using XRD, FT-IR and Mössbauer spectroscopy. Pt dispersion and reducibility as well as the electronic states of the Fe and Pt particles were detected using H2-chemisorption, H2-TPR and XPS, respectively. With the non-framework Fe, an electron-rich platinum species (Ptδ−) formed after reduction. With the framework Fe, an electron-deficient platinum species (Ptδ+) was detected. The n-hexane aromatization results from adding 0.3 wt% non-framework Fe include conversion after 3.5 h on stream at 450 °C, H2/n-hexane = 3.0 (mole ratio) and 3 h−1 WHSV over the Pt-Fe/KL, which was maintained at 77%; these values are greater than the 41% Pt/KL and 25% Pt/FeKL. The Pt-Fe/KL benzene selectivity was 89%, which is also greater than the 83% Pt/KL and 53% Pt/FeKL. We discuss the effect of Fe on the Pt particle states and the relationship between the Pt states and catalyst activity.

With 0.3 wt% non-framework Fe added in the Pt/KL catalyst, electron-rich platinum specie (Ptδ−) was detected after reduction. With framework Fe incorporated in Pt/KL catalyst, electron-deficient platinum specie (Ptδ+) appeared. The order of aromatic activity and benzene selectivity for n-hexane aromatization, Pt-Fe/KL > Pt/KL > Pt/FeKL, was consistent with the catalysts’ Pt particle electron density.Figure optionsDownload high-quality image (130 K)Download as PowerPoint slide