Pretreatment chemistry in the preparation of silica-supported Pt, Ru, and PtRu catalysts: An in situ UV diffuse reflectance study

• Published in: Journal of catalysis Vol. 133; no. 1; pp. 202 - 219
• Main Authors: Zou, Weiqing, Gonzalez, Richard D.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 1992; Elsevier
• Subjects: 400201 - Chemical & Physicochemical Properties; ABSORPTION SPECTROSCOPY; AGGLOMERATION; ALLOYS; BIMETALS; Catalysis; CATALYST SUPPORTS; CATALYSTS; Catalysts: preparations and properties; CHALCOGENIDES; CHEMICAL PREPARATION; CHEMICAL REACTIONS; CHEMISORPTION; Chemistry; DIFFUSION; DISTRIBUTION; ELECTROMAGNETIC RADIATION; ELECTRON MICROSCOPY; ELEMENTS; Exact sciences and technology; General and physical chemistry; HYDROGEN; INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; METALS; MICROSCOPY; NONMETALS; OPTICAL PROPERTIES; OXIDES; OXYGEN COMPOUNDS; PHYSICAL PROPERTIES; PLATINUM; PLATINUM ALLOYS; PLATINUM METAL ALLOYS; PLATINUM METALS; PRECURSOR; RADIATIONS; REDUCTION; REFLECTIVITY; REFRACTORY METAL COMPOUNDS; RUTHENIUM; RUTHENIUM ALLOYS; RUTHENIUM COMPOUNDS; RUTHENIUM OXIDES; SEPARATION PROCESSES; SILICON COMPOUNDS; SILICON OXIDES; SORPTION; SPECTROSCOPY; SURFACE PROPERTIES; SYNTHESIS; TEMPERATURE DEPENDENCE; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; TRANSITION ELEMENT COMPOUNDS; TRANSITION ELEMENTS; TRANSMISSION ELECTRON MICROSCOPY; ULTRAVIOLET RADIATION; X-RAY SPECTROSCOPY; Mixed catalyst; Ruthenium; Platinum; Preparation; Transition metal; Platinoid Complexes; Ammino complex; Transition metal Complexes; Pretreatment; Experimental study; Platinoid; Supported catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(92)90198-Q

Silica-supported metal catalysts were prepared from strongly absorbing Pt(NH3)4(NO3)2 and Ru(NH 3) 6Cl 3 precursors at a pH of 9. When supported [Pt(NH 3) 4] 2+ was directly reduced in H 2 at 400°C, a Pt dispersion of 40% was obtained. Pretreatment in flowing oxygen resulted in a Pt dispersion of 70%. The in situ diffuse UV reflectance data suggest that pretreatment in H 2 results in the formation of a mobile [Pt(NH 3) 2(H) 2] 0 Species. Surface diffusion during reduction results in the agglomeration of Pt particles to form a supported catalyst with a relatively low dispersion. When the decompositon of the Pt precursor is carried out in flowing O 2, a Pt 2+ precursor with low surface mobility is formed. This results in the formation of a much more highly dispersed Pt catalyst. Studies carried out using Ru(NH 3) 6Cl 3 as the metal precursor resulted in very low dispersions when the pretreatment was carried out in O 2. The Ru dispersion was a direct function of the oxidative pretreatment temperature. It was concluded that the mobile surface species consisted of Ru oxides, most likely RuO 4. Reduction in H 2 resulted in the formation of highly dispersed Ru. In addition to diffuse reflectance spectroscopy, surface characterization techniques included TEM, EDXS, and chemisorption.