Alumina-Supported Pt-Rh Catalysts: I. Microstructural Characterization

• Published in: Journal of catalysis 1995-07, Vol.154 (2), p.261-275
• Main Authors: Lakis, R.E., Lyman, C.E., Stenger, H.G.
• Format: Article
• Language: English
• Subjects: Catalysis; Catalysts: preparations and properties; Chemistry; Exact sciences and technology; General and physical chemistry; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.1995.1168

Analytical electron microscopy was performed on several Pt-Ph bimetallic catalysts. All catalysts prepared for this investigation contained alloy particles, but their composition distributions varied with preparation procedure. A catalyst with approximately 1 wt% total metal content and a relative metal composition of 60 wt% Pt and 40 wt% Rh, reduced at 300°C for 12 h, displayed a bimodal particle composition distribution with particle compositions centered at approximately 10 wt% Pt and 90 wt% Pt. Few particles possessed the expected average composition of 60 wt% Pt. The same catalyst when reduced at 700°C for 72 h displayed a broad particle composition distribution centered at about 60 wt% Pt. Together, these composition distributions and those observed for several other catalysts are consistent with the presence of a low-temperature miscibility gap in the Pt-Rh equilibrium phase diagram. Catalysts were also prepared that were observed to contain only Pt-rich or only Rh-rich particles. High-resolution electron microscopy identified two discrete particle morphologies, particles >7 mn in diameter were faceted and often internally faulted or twinned, while particles