Titanium metal-support interactions

Baker R.T.K., Kim K.S., Emerson A.B., Dumesic J.A. (1986) A Study of the Platinum-Titanium Dioxide System for the Hydrogenation of Graphite Ramifications of Strong Metal-Support Interactions, J. Phys. Chem. 90(5), 860-866. 

Tauster SJ, Fung SC, Garten RL. Strong metal-support interactions. Group 8 noble metals supported on titanium dioxide. J Am Chem Soc. 1978 100 170-5. 

Burch and Flambard (113) have recently studied the H2 chemisorption capacities and CO/H2 activities of Ni on titania catalysts. They attributed the enhancement of the catalytic activities for the CO/H2 reaction (after activation in H2 at 450°C) to an interfacial metal-support interaction (IFMSI). This interaction is between large particles of Ni and reduced titanium ions the Ti3+ is promoted by hydrogen spillover from Ni to the support, as pictured in Fig. 8. The IFMSI state differs from the SMSI state since hydrogen still chemisorbs in a normal way however, if the activation temperature is raised to 650°C, both the CO/H2 activity and the hydrogen chemisorption are suppressed. They define this condition as a total SMSI state. Between the temperature limits, they assumed a progressive transition from IFMSI to SMSI. Such an intermediate continuous sequence had been... 

Therefore, the promoting effect of titanium oxide species might be described as a synergistic effect on both CO and H2. In the next section we discuss the role of hydrogen in the metal-support interaction, which perhaps may be related to its role in the promotion of the CO-H2 reaction. 

Bonding modifiers are employed to weaken or strengthen the chemisorption bonds of reactants and products. Strong electron donors (such as potassium) or electron acceptors (such as chlorine) that are coadsorbed on the catalyst surface are often used for this purpose. Alloying may create new active sites (mixed metal sites) that can greatly modify activity and selectivity. New catalytically active sites can also be created at the interface between the metal and the high-surface-area oxide support. In this circumstance the catalyst exhibits the so-called strong metal-support interaction (SMSI). Titanium oxide frequently shows this effect when used as a support for catalysis by transition metals. Often the sites created at the oxide-metal interface are much more active than the sites on the transition metal. 

D.N. Belton, Y.M. Sun, and J.M. White. Thin-Film Models of Strong Metal-Support Interaction Catalysts. Platinum on Oxidized Titanium. J. Phys. Chem. 88 1690 (1984). 

J.A. Horsley. A Molecular Orbital Study of Strong Metal-Support Interaction between Platinum and Titanium Dioxide. J. Am. Chem. Soc. 101 2870 (1979). 

Even more pronounced changes in chemisorption properties are observed using the oxides of titanium, vanadium, tantalum, and niobium as supports. The Strong Metal Support Interaction (SMSI) " occurs when the catalyst is reduced at high temperatures (about 773 K) and is believed to be due to a combination of effects ... 

However, the Pt/Ti02 catalyst exhibits reduction at room temperature and at 112 °C, 372 °C, and above 500 °C, besides peak shift to lower temperatures due to the reduction of PtO. Partial reduction of Ti02 to Ti02 x occurs at higher temperatures which are attributed to the strong metal support interaction (SMSI). The presence of Pt atoms promoted the reduction of titanium which in turn facilitates the reduction of platinum at the surface. 

Horsley JA. A molecular orbital study of strong metal-support interaction between platinum and titanium dioxide. J Am Chem Soc. 1979 101(11) 2870. 

Warzelhan and Burger proposed to remove the cocatalyst before the introduction of C02 to avoid the possible influence of the cocatalyst on polymer radioactivity. However, two conditions have to be fulfilled to obtain correct data on Cp i) the life-time of an active metal-polymer bond has to be sufficiently long ii) the polymer must not contain Al—C bonds able to interact with a quenching agent. The possibility to use CO and CO2 for the quantitative determination of Cp was illustrated in the case of one-component catalysts (titanium dichloride supported organometallic catalysts when Cp values were independently determined by the use of other inhibitors including radioactive alcohol. 

The interactions between the anions and the Ti02 surface have also been investigated by other, more direct techniques than the potentiometric titrations. Thus, Sanchez and Augustynski have employed X-ray photoelectron spectroscopy to examine the adsorption of a series of anions onto titanium dioxide films of two kinds the relatively thick (10-15 nm) films, obtained by thermal decomposition of an alcoholic TiCl4 solution, and the natural, thin (15-20 A) films covering the surface of titanium metal. The Ti02 films of the first kind, supported onto Ti metal, have been extensively used as electrode materials in electrochemical and photoelectrochemical studies ... 

The nature of the agostic bonds was confirmed using the AIM formalism for several electron deficient titanium complexes [16]. More controversial were square planar d species, where a proton from one ligand may approach the metal in an axial direction, but again experiments and calculations did not support the assignment of these M - H interactions as agostic bonds [17, 4cj. 

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