Hydrogenation catalysts development

The use of silver fluoroborate as a catalyst or reagent often depends on the precipitation of a silver haUde. Thus the silver ion abstracts a CU from a rhodium chloride complex, ((CgH )2As)2(CO)RhCl, yielding the cationic rhodium fluoroborate [30935-54-7] hydrogenation catalyst (99). The complexing tendency of olefins for AgBF has led to the development of chemisorption methods for ethylene separation (100,101). Copper(I) fluoroborate [14708-11-3] also forms complexes with olefins hydrocarbon separations are effected by similar means (102). 

The strategy of the catalyst development was to use a rhodium complex similar to those of the Wilkinson hydrogenation but containing bulky chiral ligands in an attempt to direct the stereochemistry of the catalytic reaction to favor the desired L isomer of the product (17). Active and stereoselective catalysts have been found and used in commercial practice, although there is now a more economical route to L-dopa than through hydrogenation of the prochiral precursor. 

The SRC-II process, shown in Figure 2, was developed in order to minimise the production of soHds from the SRC-I coal processing scheme. The principal variation of the SRC-II process relative to SRC-I was incorporation of a recycle loop for the heavy ends of the primary Hquefaction process. It was quickly realized that minerals which were concentrated in this recycle stream served as heterogeneous hydrogenation catalysts which aided in the distillate production reactions. In particular, pyrrhotites, non stoichiometric iron sulfides, produced by reduction of iron pyrite were identified as being... 

Electroless reactions must be autocatalytic. Some metals are autocatalytic, such as iron, in electroless nickel. The initial deposition site on other surfaces serves as a catalyst, usually palladium on noncatalytic metals or a palladium—tin mixture on dielectrics, which is a good hydrogenation catalyst (20,21). The catalyst is quickly covered by a monolayer of electroless metal film which as a fresh, continuously renewed clean metal surface continues to function as a dehydrogenation catalyst. Silver is a borderline material, being so weakly catalytic that only very thin films form unless the surface is repeatedly cataly2ed newly developed baths are truly autocatalytic (22). In contrast, electroless copper is relatively easy to maintain in an active state commercial film thicknesses vary from <0.25 to 35 p.m or more. 

In the preceding section, it has been shown that considerable attention has been devoted to palladium as a heterogeneous catalyst. The present section describes the homogeneous palladium catalysts developed for hydrogenation of NBR. The main drive behind the development of various catalyst systems is to find suitable substituents of the Rh catalyst. Palladium complexes are much cheaper as compared with Rh and exhibit comparable activity and selectivity to Rh and Ru complexes. 

All tests reported here were performed with a special methanation catalyst developed by BASF, Ludwigshafen, for the process. The catalyst had a relatively high nickel content on a carrier. It was charged to reactors D2 and D3 in unreduced form and had to be activated by reduction with hydrogen. 

Dr. Woodward I tried to indicate in my paper that in ammonia-hydrogen plant operation, in comparison with several other catalysts in such plants, the methanation catalyst situation is really well under control. Speaking for our company, and I would guess others, it s not a particularly active research area because we have higher priorities in catalyst development. As regards methanation catalysts for SNG, I did not discuss that today and perhaps I should let some other fellows answer first. Sulfur tolerance is one area for future development. 

The Rh-NHC complexes, with or without phosphine co-ligands, have been stndied as hydrogenation catalysts of alkenes with molecular hydrogen, with the aim to develop more active, selective (and/or enantioselective) and thermally stable catalysts. 

The fundamental concepts of enantioselective hydrogenation were introduced in Section 2.5.1 of Part A, and examples of reactions of acrylic acids and the important case of a-acetamido acrylate esters were discussed. The chirality of enantioselective hydrogenation catalysts is usually derived from phosphine ligands. A number of chiral phosphines have been explored in the development of enantioselective hydrogenation catalysts,21 and it has been found that some of the most successful catalysts are derived from chiral 1, l -binaphthyldiphosphines, such as BINAP.22... 

With tethering technology, immobilized Rh(DiPFc) catalyst, a veiy selective hydrogenation catalyst was developed by Engelhard (26) and Chirotech (27). Rh(DiPFc)(COD)BF4 is one of most interesting homogeneous catalysts due to its chemo-selectivity and sulfur tolerant behavior. The anchored complex y-... 

More recently homogeneous hydrogenation catalysts, such as RhCl(Ph3P)3, have been developed which are soluble in the reaction medium. These are believed to transfer H to an alkene via a metal hydride intermediate they, too, lead to a considerable degree of SYN stereoselectivity in hydrogen addition. 

The alloy hydride has been investigated as a useful hydrogenation catalyst for a wide variety of substrates under mild conditions. It is however pyrophoric in air, and an experimental procedure has been developed to avoid this hazard. A related hydride, LaNi4.5Alo.5H5 has similar properties. 

It is believe that the HDS sites (rim sites and edge sites) are different than the olefin hydrogenation sites (rim sites) opening an opportunity for the development of selective HDS catalysts [45 171. Another concept to exploit in catalyst development is the competitive adsorption, by which the sulfur compounds inhibit olefins hydrogenation [48]. 

Many cationic Rh- or Ir-based hydrogenation catalysts were subsequently developed. Members of the Rh series were prepared according to Equation (3).22-25... 

Among the most active catalysts for the asymmetric transfer hydrogenation of prochiral ketones and imines to chiral alcohols and amines are arene-ruthenium(II) amino-alcohol (or primary/ secondary 1,2-diamine)-based systems, with an inorganic base as co-catalyst, developed by Noyori139-141 and further explored by others (Scheme 27).142-145... 

Other advances over the past few years have been the development of (a) homogeneous hydrogenation catalysts for substrates normally not readily reduced, e.g., aromatics, isonitriles, and nitro compounds, and (b) a number of catalyst systems with unusual selectivity properties, e.g., with the capability of reducing a,/3-unsaturated aldehydes to the corresponding a,/3-unsaturated alcohols (see Sections II,B,2 and VII). 

CATACARB [Catalyzed removal of carbon dioxide] A process for removing carbon dioxide and hydrogen sulfide from gas streams by absorption in hot potassium carbonate solution containing a proprietary catalyst. Developed and licensed by Eickmeyer and Associates, KS, based on work at the U.S. Bureau of Mines in the 1950s. More than a hundred plants were operating in 1997. See also Benfield, Carsol, Hi-pure, Giammarco-Vetrocoke. 

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