Search

A series of trimetallic Pt–Sn–Ce catalysts supported on chloride Al₂O₃ was prepared by a sequential impregnation method and applied for n-heptane reforming and characterized by several techniques, including N₂ physiosorption, transmission electron microscopy, X-ray diffraction, hydrogen temperature-programmed reduction, CO chemisorption, ammonia temperature-programmed desorption, pyridine desorption Fourier-transform infrared spectroscopy, and in situ diffuse reflectance infrared Fourier transform spectroscopy. We have demonstrated that the introduction of Ce can promote isomerization reactions by suppressing undesirable hydrogenolysis reactions, whereas it does not significantly influence the dehydrocyclization reactions. The characterization results show that CeOₓ can enhance the reducibility of Pt species via enhancing the Pt dispersion. In addition, Ce increases the proportion of medium-strength acid sites, which does not only promote isomerization activity, but also suppresses the undesirable reactions such as hydrogenolysis and cracking.

Catalytic reforming of n-heptane over a series of Pt-based catalysts modified by Sn and Ce has been conducted in a fixed-bed reactor. Introducing Sn and Ce resulted in changes in the electronic environment of the Pt particles and acidity properties of the γ-Al2O3 support, causing changes in product distribution. Results from in-situ Diffusion Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), X-ray Photoelectron Spectroscopy (XPS) and density functional theory (DFT) evidenced that the metal promoters altered the metal-support interaction, endowing the generation of negatively charged Pt particles which favored the adsorption of n-heptene, a commonly accepted intermediate for n-heptane aromatization. A mechanistic study on the interaction of n-heptene and the Pt clusters with different chemical states based on n-heptene- Temperature Programmed Desorption (TPD) and Density-function theory (DFT) calculations suggested that negatively charged Pt clusters (Ptδ−) were thermodynamically favorable for the adsorption of n-heptene and its further cyclization step.