Support-catalyst interactions

Pristine CNTs are chemically inert and metal nanoparticles cannot be attached [111]. Hence, research is focused on the functionalization of CNTs in order to incorporate oxygen groups on their surface that will increase their hydrophilicity and improve the catalyst support interaction (see Chapter 3) [111]. These experimental methods include impregnation [113,114], ultrasound [115], acid treatment (such as H2S04) [116— 119], polyol processing [120,121], ion-exchange [122,123] and electrochemical deposition [120,124,125]. Acid-functionalized CNTs provide better dispersion and distribution of the catalysts nanoparticles [117-120],... 

Catalysts for coal liquefaction require specific properties. Catalysts of higher hydrogenation activity, supported on nonpolar supports, such as tita-nia, carbon, and Ca-modified alumina, are reasonable for the second stage of upgrading, because crude coal liquids contain heavy polar and/or basic polyaromatics, which tend to adsorb strongly on the catalyst surface, leading to coke formation and catalyst deactivation. High dispersion of the catalytic species on the support is very essential in this instance. The catalyst/support interactions need to be better understood. It has been reported that such interactions lead to chemical activation of the substrate 127). This is discussed in more detail in Section XIII. 

Roozeboom et al106 in an investigation of both unsupported V2 Os and a number of supported catalysts observed that at low temperatures dehydration of methanol to dimethyl ether is a side-reaction on some catalysts and at higher temperatures consecutive oxidation of dimethyl ether and/or formaldehyde to CO. Selectivity to formaldehyde increased with decreasing reducibility of the catalyst, which itself was a function of the catalyst-support interaction. 

One of the most controversial issues in AFCs is the formation of carbonates. It is generally accepted that the C02, both originally in the air and formed by corrosion reaction of the carbon catalyst support, interacts with the electrolyte according to the following equation ... 

M. Sheintuch, J. Schmidt, Y. Lecthman, and G. Yahav, Modelling catalyst-support interactions in carbon monoxide oxidation catalysed by Pd/Sn02, Appl. Catal. 49, 55-65 (1989). 

Considering the importance of these metal-metal and metal-catalyst support interactions, a Cyclic Deactivation procedure will be preferred in order to simulate the actual metal distribution and interactions on the catalyst surface and to mimic the correct metal age distribution (2, 23, 27, 34]. 

The 3d transition metals are widely employed as catalyst and catalyst support materials in industry [3]. To gain insight into how these support materials and the catalyst support interaction influence catalytic activity, GIB-MS experiments were undertaken in our laboratory to determine the structural characteristics of cobalt oxide and nickel oxide clusters as well as their reactivity with CO. CID experiments were conducted employing Xe gas to elucidate the structural building blocks of the larger clusters. These studies provided insight into how additional (i-electrons impact the dissociation pathways and bonding motifs of 3d transition metal oxide clusters. Reactivity studies with CO were carried out, which revealed that oxide clusters composed of different 3d metals have specific stoichiometries which are most active for CO oxidation. 

Various solid state reactions are involved in the process. In addition to those governing sintering, catalyst-support interactions may alter the nature and catalytic activity of the solid and may stabilise or destabilise the solid towards sintering. Thus, for example, the formation of nickel aluminate, NiAlgO, is well established in steam reforming catalysts [21,22], and this compound is catalytically inactive. However, its presence may affect the thermal stability of the solid [23], as is the case in cobalt-molybdenum and nickel-molybdenum based catalysts supported on alumina and used for hydro-treating [24]. 

In order to know the effect of the catalyst-support interaction on the surface basicity and base strength distribution, the chemisorption of CO2 at 100 C and TPD of CO2 from 50 to 900°C for the unsupported La-CaO cmd supported La-CaO ( with or without precoating the support by MgO or La203) catalysts have been measured. The data on the surface basicity of the catalysts is included in Table 3. 

Ghoudary, V. R., Mulla, S. A. R., and Uphade, B. S. 1997. Oxidative coupling of methane over supported LajOj and La-promoted MgO catalysts influence of catalyst-support interactions. Ind. Eng. Chem. Res. 36 2096-2100. 

Richard et al. studied a model Pt/Al203 catalyst by transmission electron microscopy and Auger electron microscopy. Oxygen treatments under industrial catalyst regeneration conditions transform a monomodal distribution of platinum particles (mean diameter 1.8 nm) into a bimodal distribution consisting of a phase of particles 10 to 40 nm in diameter and a phase of very small clusters (diameter <1 nm). This observation of stable small clusters is direct evidence for platinum catalyst support interaction. An exchange of water between particles that operate on a molecular scale and might include platinum oxide is postulated. 

The model of electrochemical promotion regards the phenomenon as catalysis in presence of an electrically controlled double layer formed by spillover-backspillover mechanism at the gas-exposed catalyst surface. This shows strong analogy with catalyst-support interactions... 

Scott and co-workers recently reported applying IR, and Si solid-state CP/MAS NMR to investigate catalyst/ co-catalyst/support interactions in silica-supported olefin polymerization catalysts based on Cp TiMe3. Finally, we mention the research of Lindner et al. on supported organometallic complexes. 

Mattevi C, Wirth CT, Hofmann S, Blume R, Cantoro M, Ducati C, et al. In-situ X-ray photoelectron spectroscopy study of catalyst—support interactions and growth of carbon nanotube forests. J Phys Chem C 2008 112 12207-13. 

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