Supported Metal Catalysts: Preparation, Characterization, and Function: I. Preparation and Physical Characterization of Platinum Catalysts

The preparation, by impregnation (I), co-crystallization (C), and metal vapour deposition (M), of a range of silica-, alumina-, and molybdena-supported platinum catalysts is described. These materials (and the supports) have been thoroughly characterised in both pre- and postreduction states using a wide range of physical techniques including electronic spectroscopy, TGA, TPR, XPS, HRTEM. and EXAFS. UV-visible spectroscopic data for the impregnated materials is consistent with the presence of octahedral Pt(IV) environments in the prereduction state. Pt/silica (I) is essentially chloride-free after reduction, whereas Pt/alumina (I) retains a significant amount of chloride which is associated with the support rather than the metal. Pt/silica (M) is chloride-free and Pt/alumina (M) contains no more than the residual chloride initially associated with the alumina support. TGA and TPR data are largely as expected and, in the case of the molybdena-supported catalysts, are consistent with hydrogen bronze formation upon reduction. XPS data are consistent with the presence of Pt(0) in Pt/alumina (M) and the reduction of platinum to the metallic state in the case of Pt/silica (I). In contrast, with Pt/alumina (I), Pt/molybdena (I), and Pt/molybdena (C), the metal retains a significant δ+ character in the postreduction state. In the case of Pt/alumina (I), this behaviour is best interpreted in terms of a metal-support interaction, whereas that observed with the molybdena supports is consistent with hydrogen bronze formation. XPS, TGA, and TPR data show a high degree of internal consistency with respect to bronze stoichiometries. HRTEM and EXAFS data are self-consistent and, with the exception of Pt/molybdena (I), the platinum crystallites are extremely highly dispersed, with size distributions in the order Pt/alumina (M) ∼ Pt/silica (M) < Pt/molybdena (C) < Pt/alumina (I) < Pt/silica (I) ⪡ Pt /molybdena (I). Models for the platinum sites in Pt/alumina (I) and Pt/silica (I) have been developed.

[1]  G. Bond.  Source of the activation energy in heterogeneously catalysed reactions , 1993 .

[2]  G. Bond.  Catalytic properties of 0.3% Pt/Al2O3 (EUROPT-3) and of 0.3% Pt−0.3% Re/Al2O3 (EUROPT-4) , 1993 .

[3]  Geoffrey I. Webb,et al.  Supported Metal Catalysts: Preparation, Characterization, and Function: II. Carbon Monoxide and Dioxygen Adsorption on Platinum Catalysts , 1993 .

[4]  G. Webb,et al.  Supported Metal Catalysts: Preparation, Characterization, and Function: III. The Adsorption of Hydrocarbons on Platinum Catalysts , 1993 .

[5]  A. Auroux,et al.  Acidity and basicity of metal oxide surfaces. II, Determination by catalytic decomposition of isopropanol , 1991 .

[6]  G. Bond,et al.  Characterization of the standard platinum/silica catalyst EUROPT-1VI. Catalytic properties , 1988 .

[7]  D. Do,et al.  The role of deposited poisons and crystallite surface structure in the activity and selectivity of reforming catalysts , 1988 .

[8]  S. Jackson,et al.  Steady-state effects in the medium pressure hydrogenation of carbon monoxide over rhodium catalysts , 1986 .

[9]  P. Wells,et al.  Chemisorption and catalysis by metal clusters. Hydrogenation of ethene and hydrogenolysis of ethane catalysed by supported ruthenium clusters derived from Ru3(CO)12 and from H4Ru4(CO)12 , 1986 .

[10]  P. Wells,et al.  Chemisorption and catalysis by metal clusters. III: Hydrogenation of ethene, carbon monoxide, and carbon dioxide, and hydrogenolysis of ethane catalyzed by supported osmium clusters derived from Os3(CO)12 and from Os6(CO)18 , 1984 .

[11]  S. Kristyán,et al.  Mechanistic study of the catalytic hydrogenolysis of ethane , 1984 .

[12]  D. A. King,et al.  The Chemical Physics of Solid Surfaces and Heterogeneous Catalysis , 1981 .

[13]  K. Otto,et al.  Effects of the surface structure of Rhγ-Al2O3 on the hydrogenolysis of n-pentane, on the oxidation of n-butane, and on the reduction of nitric oxide , 1979 .

[14]  A. Frennet,et al.  Effect of multiple sites and competition in adsorption on the kinetics of reactions catalyzed by metals , 1978 .

[15]  G. Leclercq,et al.  Hydrogenolysis of saturated hydrocarbons: III. Selectivity in hydrogenolysis of various aliphatic hydrocarbons on platinum/alumina , 1977 .

[16]  G. Leclercq,et al.  Hydrogenolysis of saturated hydrocarbons: II. Comparative hydrogenolysis of some aliphatic light hydrocarbons on platinum-alumina , 1976 .

[17]  J. J. Burton.  STRUCTURE AND PROPERTIES OF MICROCRYSTALLINE CATALYSTS , 1974 .

[18]  P. Dickens,et al.  Thermochemistry of hydrogen tungsten bronze phases HxWO3 , 1973 .

[19]  J. Sinfelt.  Kinetics of ethane hydrogenolysis , 1972 .

[20]  R. V. Hardeveld,et al.  The statistics of surface atoms and surface sites on metal crystals , 1969 .

[21]  J. Sinfelt,et al.  The catalytic activity of rhodium in relation to its state of dispersion , 1967 .

[22]  J. Anderson,et al.  The mechanism of isomerization of aliphatic hydrocarbons at a platinum surface , 1967 .

[23]  J. L. Carter,et al.  Catalysis over Supported Metals. V. The Effect of Crystallite Size on the Catalytic Activity of Nickel , 1966 .

[24]  M. Boudart,et al.  ETHANE HYDROGENATION-CRACKING ON IRON CATALYSTS WITH AND WITHOUT ALKALI , 1954 .