Alternative Metal Formulations

Although palladium occupies the dominant position in semi-hydrogenation catalysts, it is by no means the only metal suitable for formulation into a viable catalyst. Mention has already been made of the nickel boride alternatives, with or without copper promotion, for example. Other examples include the skeletal catalyst Raney nickel [69], alumina-supported nickel [70], and aluminum phosphate-supported nickel [71] (Eqs 21 and 22)  

1 Sobczak, T Boleslawska, M Pawlowska and W Palczewska, in Heterogeneous Catalysis and Fine Chemicals, M Guisnet et al (eds), Elsevier Science Publishers, 1988, pp 197-202. R A Raphael in, Acetylenic Compounds in Organic Synthesis, Butterworths Scientific Publications, 1955, p 26. 

A Sarkany, A H Weiss, T Szilagyi, P Sandor and L Guezi, Appl. Catal, 1984, 12, 373. 

Y Nitta, T Imanaka and S Teranishi, Bull Chem. Soc. Japan, 1981, 54, 3579. 

T H Cymbaluk, US Patent 4,659,687, assigned to Phillips Petroleum Company (1987). 

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Alternative catalyst formulations for methane ATR based on bimetallic catalysts have been studied, aiming at increasing the activity of nickel catalysts by the addition of low contents of noble metals. 

However, 1000 °C leads to a very rapid reaction if anode reform is attempted and in many cases the result is excessive thermal stress of the ceramic electrolyte, so that conventional reformers must be used. As a consequence there has come about a class of intermediate-temperature SOFCs based on alternative ceramic formulations, 500 °C operation having been achieved by a metal/ceramic fuel cell by the company Ceres (see Chapter 4) set up by Imperial College London. 

To date Sasol has used only iron-based catalysts. Not only is iron much cheaper than the alternative metals, but it also produces more olefins. For the fixed-bed reactors the silica-supported and alkali-promoted catalyst is prepared by precipitation techniques (ref. 2). A recent improvement in catalyst formulation has resulted in a more reactive catalyst as well as a lower cost per reactor charge. The catalyst used in the fluidized-bed reactors is prepared by fusing suitable iron oxides together with the... 

Among the possible four-membered ring systems, many 1,2 diphosphetenes (6.897a) and a few diphosphetes (6.897b,c) have been synthesised (6.898). Type (d) rings have only been obtained as metal coordination complexes. Alternative ylid formulations may be applicable to some of these compounds (6.899). Compounds of type (6.897c) are in some cases obtainable from phosphaalkynes (6.631)... 

An equation has been formulated to express the change in covalent radius (metallic radius) of an atom with change in bond number (or in coordination number, if the valence remains constant), the stabilizing (bond-shortening) effect of the resonance of shared-electron-pair bonds among alternative positions being also taken into consideration. This equation has been applied to the empirical interatomic-distance data for the elementary metals to obtain a nearly complete set of single-bond radii. These radii have been compared with the normal covalent... 

Slimicide and biocide toxic pollutants containing pentachlorophenol are used at mills in the pulp, paper, and paperboard industry. Initially, pentachlorophenol was used as a replacement for heavy metal salts, particularly mercuric types. Trichlorophenols are also used because of their availability as a byproduct from the manufacture of certain herbicides. Formulations containing organo-bromides and organo-sulfur compounds are also being used. Substitution of alternative slimicide and biocide formulations can lead to the virtual elimination of pentachlorophenol and trichlorophenol from these sources. 

One reason for the relatively large RMS deviations, compared to the active sites of MMO and RNR, is that the active-site residues are not coordinated to the selenium (see Figure 2-8). The lack of a structural anchor leads to a relatively unstable active-site geometry. An alternative formulation is that the presence of a metal center with strong ligand interactions is one reason the active-site model works comparatively well for many metal enzymes. 

This survey of theoretical methods for a qualitative description of homogeneous catalysis would not be complete without a mention to the Hartree-Fock-Slater, or Xot, method [36]. This approach, which can be formulated as a variation of the LDA DFT, was well known before the formal development of density functional theory, and was used as the more accurate alternative to extended Hiickel in the early days of computational transition metal chemistry. 

Thus, if the incorporation of some metal oxides indicated a notable improvement in the catalytic activity (permitting it to operate at lower reaction temperatures),the incorporation of metals, especially Pt and working in the presence of H2, has prolonged the hfe of the catalysts. However, new catalyst formulations have recently increased the resistance of these catalysts to such poisons as water or sulfur during the isomerization of n-C5 and n-C6 paraffins. Nevertheless, the use of other anions, by supporting WO3 or MoOf or heteropolyacids,which have higher thermal stability, can also be interesting alternative routes to develop new catalytic systems. 

Treatment of the chelate complexes with a large excess of bromine in hot benzene gives the same complexes PtBr4 (arsine), indicating the resistance of the metal carbon ff-bond to attack by bromine and also excluding ) their alternative formulation as dimeric platinum(II) complexes [PtBrg (arsine Br2)]2-... 

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