Catalysts and support materials

Hutchings and coworkers (78-83) pioneered the use of supercritical antisolvent precipitation to prepare a number of catalyst and support materials including vanadium phosphates. Vanadium phosphate precursor solutions were prepared from VOCI3 and H3PO4 refluxed in isopropanol. In the supercritical antisolvent precipitation method, a solution of the material to be precipitated and supercritical CO2 are pumped through a coaxial nozzle at temperatures and pressures above the critical point of... 

Transition metal catalysts, specifically those composed of iron nanoparticles, are widely employed in industrial chemical production and pollution abatement applications [67], Iron also plays a cracial role in many important biological processes. Iron oxides are economical alternatives to more costly catalysts and show activity for the oxidation of methane [68], conversion of carbon monoxide to carbon dioxide [58], and the transformation of various hydrocarbons [69,70]. In addition, iron oxides have good catalytic lifetimes and are resistant to high concentrations of moisture and CO which often poison other catalysts [71]. Li et al. have observed that nanosized iron oxides are highly active for CO oxidation at low tanperatures [58]. Iron is unique and more active than other catalyst and support materials because it is easily reduced and provides a large number of potential active sites because of its highly disordered and defect rich structure [72, 73]. Previous gas-phase smdies of cationic iron clusters have included determination of the thermochemistry and bond energies of iron cluster oxides and iron carbonyl complexes by Armentrout and co-workers [74, 75], and a classification of the dissociation patterns of small iron oxide cluster cations by Schwarz et al. [76]. 

In the catalysis community, it is generally accepted that there are two types of support materials for heterogeneous oxidation catalysts [84]. One variety is the reducible supports such as iron, titanium, and nickel oxide. These materials have the capacity to adsorb and store large quantities of molecules. The adsorbed molecules diffuse across the surface of the support to the catalyst particle where they are activated to a superoxide or atomically bound state. The catalytic reaction then takes place between the reactant molecules and the activated on the catalyst particle. Irreducible supports, in contrast, have a very low ability to adsorb O. Therefore, can only become available for reaction through direct adsorption onto the catalyst particle. For this reason, catalysts deposited on irreducible supports generally exhibit turnover frequencies that are much lower than those deposited on reducible supports [84]. More recent efforts in our laboratory are focused on characterizing catalyst support materials that are commonly used in industry. These studies are aimed at deciphering how specific catalyst and support material combinations result in superior catalytic activity and selectivity. 

Vapor-phase epoxidation of propylene using H2 and O2 was carried out over gold catalysts supported on mesoporous ordered (MCM-41) and disordered titanosilicates prepared hydrothermally or by modified sol-gel method. Gold nanoparticles were homogeneously dispersed on the titanosilicate supports by deposition-precipitation (DP) method. The catalysts and support materials were characterized by XRD, UV-Vis, surface area measurements (N2 adsorption) and TEM. NaOH was found to be the best precipitant to prepare Au catalysts with optimum propylene oxide yields and H2 efficiency. The extent of catalysts washing during preparation was found to affect the activity of the catalyst. The activity and hydrogen efficiency was found to depend on the type of mesoporous support used. 

Table S-44 Specific surface areas of catalysts and support materials...

A chemically stable ORR electrocatalyst should not be oxidized or corroded by O2 or proton. However, some catalyst components such as the alloy metals such as Fe, Co, Ni, Mn, Cu, etc., in Pt alloy catalysts could be chemically oxidized by either proton or O2 to leach out. Some metal oxide supports and non-noble metal catalysts could also dissolve in acidic environment. Therefore, developing ORR catalysts and support materials with chemical stability is necessary. 

At the current stage of technology, carbon-supported Pt and Pt-based alloy catalysts are the most active and stable catalysts for an ORR, which have been used for fuel cell cathodes. The major research effort for Pt and Pt-based alloy cattdysts is to optimize (1) the size and dispersion of nanoparticles, (2) interaction between Pt catalyst and supporting materials, and (3) Pt-alloying strategy. 

Table4.5.1 Specific surface areas of catalysts and support materials (Hagen, 1999) and typical prices (oral communication from Sud Chemie, 2010 forthe Pt wire, the price of pure Pt from Sept. 2012 is given).

The typical surface area of catalysts and support materials is in the range 10-1000 (Table 4.5.1). If the term surface area is used in the context of solid... 

There are two principal strategies for the selection of an appropriate linker for a given set of catalyst and support material. One is to choose a long linker to avoid interference of the catalyst with the support material the other is to use a short linker in order to generate additional interactions with the solid support material. 

Based on the results presented in this section, the design criteria for UTCLs can be refined (i) the thickness should be 200 nm (or less), (ii) charging properties of catalyst and support materials should be such that cpP > 0.7 Vshe, (iii) the pore radius is not a significant parameter, as long as it remains within a range of 2 nm < l p < 20 nm, and (iv) too small a radius may affect the intrinsic transport properties of the pore (not accounted for in the present model), whereas too large a radius could infringe on requirements in terms of thickness and ECSA. 

S. ZUs, P. Bleith, F. Ettingshausen,]. Suffner, A. Wolz, M. Michel, C. Roth, Alternative support materials and the role of the support morphology for the electrode structure, ICCE 19 in Shanghai (2011) session organized by P. Bele on Novel Catalysts and Support Materials for Fuel Cells. 

In a carbon-supported metal electrocatalyst, the electronic interaction between metal and carbon support has a significant effect on its electrochemical performance [4], For carbon-supported Pt electrocatalyst, carbon could accelerate the electron transfer at the electrode-electrolyte interface, leading to an accelerated electrode process. Typically, the electrons are transferred from platinum clusters to the oxygen species on the surfece of a carbon support material and the chemical bond formation or the charge transfer process occurs at the contacting phase, which is considered to be beneficial to the enhancement of the catalytic properties in terms of activity and stability of the electrocatalysts. Experimentally, the investigation into the electron interaction between metal catalyst and support materials could be realized by various physical, spectroscopic, and electrochemical approaches. The electron donation behavior of Pt to carbon support materials has been demonstrated by the electron spin resonance (ESR) X-ray photoelectron spectroscopy (XPS) studies, with the conclusion that the electron interaction between Pt and carbon support depends on their Fermi level of electrons. It is considered that the electronic structure change of Pt on carbon support induced by the electron interaction has positive effect toward the enhancement of the catalytic properties and the improvement of the stability of the electrocatalyst system. However, the exact quantitative relationship between electronic interaction of carbon-supported catalyst and its electrocatalytic performance is still not yet fully established [4]. 

This chapter reviews the current state of the art in membranes for direct methanol fuel cells (DMFCs), with a particular focus on research developments (as opposed to commercial products, of which there are few). The focus is exclusively on membranes however, given the tight integration that is necessary between membranes and the adjacent fuel/oxidant distribution layers, catalysts, and support materials, there is some mention of these materials as they must necessarily be compatible with the selected membrane. Given the difficulty in finding reliable cost data for most of the membrane materials, a review of the cost-effectiveness of the membranes is not attempted, although for similar cation exchange membranes at least a cursory attempt at cost-effectiveness can be derived from the cost of the membrane precursors and solvents used in the synthesis [1]. 

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