Reduced transition metal colloids: a novel family of reusable catalysts

Metal-mediated reductive hydrodehalogenation of organic halides.

The preparation and catalytic applications of dispersed metal catalysts supported on organic functional polymers are presented. The advantages of these catalysts, such as the easy tailoring with respect to the nature of the used support, the “nanoscale” size control of metal crystallites by the polymer framework, the high accessibility and consequent catalytic activity in a proper liquid or liquid–vapor reaction systems are stressed. Various proposed catalytic processes making use of these materials are presented and evaluated, including multifunctional catalysis, e.g. redox-acid. Interesting peculiar aspects such as the enhancement of the hydrogenation rate by nitrogen containing moieties anchored to the polymer backbone are emphasised. When suitable, a comparison with catalysts based on inorganic supports is given.

Catalysis by metal nanoparticles supported on functional organic polymers

Gold nanoparticle catalysts for selective hydrogenations

Catalysis has been an important field for polyurethane chemistry and many improvements have been accomplished in recent years. Some of the greatest challenges however still remain. There is not yet a satisfactory catalytic way for the direct oxidation of propene to propene oxide in spite of ruthless activities by all major players over decades. New methods of catalysts screening and improved tools for catalyst characterization may help to solve this problem in the near future. Catalyst development in the area of polyether synthesis has recently opened new routes to completely new products. New raw materials may become attractive and new polyether polyol structures will be accessible with new catalysts. The range of new polymers will open up new opportunities. In the field of isocyanates the optimization of all manufacturing steps (nitration, hydrogenation, phosgenation) is an ongoing process since commercial production started an incremental improvements are accomplished and implemented constantly. Major improvements for existing processes, including all their catalytic reaction steps, are not to be expected in the near future. Significant improvements seem only possible by alternative ways of isocyanate manufacturing. In this area, catalytic reactions and the modern tools of catalysts research will play a key-role. However, as for all new developments, they will have only a chance on realization on a commercial scale, if they are economically competitive to well established processes.

Trends in industrial catalysis in the polyurethane industry

Polymer-achored monometallic palladium catalyst PVP-PdCl2 (PVP = poly(N-vinyl-2-pyrrolidone)) exhibits very high activity for the hydrogenation of p-chloronitrobenzene (CNB) to aniline (AN) in the presence of base at 65°C and atmospheric pressure. In this case, the substrate is rapidly hydrodechlorinated to nitrobenzene (NB) which is then reduced to AN. Using the polymer-anchored bimetallic palladium-ruthenium catalyst, PVP-PdCl2-RuCl3, and in the presence of 1.0 mol% of sodium acetate, a strong synergic effect gives rise to a remarkable increase of the selectivity for p-chloroaniline (CAN) and the maximum selectivity of CAN is up to 94%. For the hydrogenation of the non-halo-substituted nitroaromatics to the corresponding aromatic amines, the monometallic PVP-PdCl2 catalyst only shows mild or poor activity, but the colloidal polymer-anchored bimetallic palladium-platinum catalyst, PVP-Pd-1 4Pt , exhibits very high activity and selectivity.

Hydrogenation of nitroaromatics by polymer-anchored bimetallic palladium-ruthenium and palladium-platinum catalysts under mild conditions

A synergic effect of the polymer-anchored bimetallic palladium-ruthenium catalysts can lead to a remarkable increase in the selectivity for p-chloroaniline in the selective hydrogenation of p-chloronitrobenzene under atmospheric pressure and in the presence of a small amount of base.

A remarkable synergic effect of polymer-anchored bimetallic palladium–ruthenium catalysts in the selective hydrogenation of p-chloronitrobenzene

Highly active polymer-anchored bimetallic palladium-based catalysts (PVP-PdCl 2 -MY, PVP = poly(N-vinyl-2-pyrrolidone, MY = the second transition metal component) exhibit very high catalytic activity and selectivity for the carbonylation of allyl halides (CH 2 =CH−CH 2 X, X = Cl or Br) in toluene/dilute alcoholic-aqueous solution at 40°C and atmospheric pressure in the presence of NaOH. These catalysts were prepared by the addition of a second transition metal compound to the alcoholic or aqueous solution of the polymer-anchored monometallic palladium catalyst PVP-PdCl 2 , i.e. FeCl 3 -6H 2 O, Co(OAc) 2 4H 2 O, NiCl 2 ·6H 2 O, RuCl 3 ·3H 2 O, or RhCl 3 ·H 2 O was added to PVP-PdCl 2 /EtOH, and [RUCl 2 (TPPTS) 2 ] 2 , RhH(CO)(TPPTS) 3 , H 2 IrCl 6 , IrH(CO)(TPPTS) 3 or IrCl(CO)(TPPTS) 2 was added to PVP-PdCl 2 /H 2 O (TPPTS = ( m -NaSO 3 C 6 H 4 ) 3 P). For allyl chloride, a remarkable synergic effect of the polymer-anchored bimetallic catalysts led to an obvious increase in the carbonylation rate and/or selectivity for the desired product, β, γ-butenoic acid. For allyl bromide, only a weak synergic effect was observed by the addition of RhCl 3 ·3H 2 O or IrCl(CO)(TPPTS) 2 to the monometallic catalyst.

Bin Yang

Papers

Hydrogenation of nitroaromatics by polymer-anchored bimetallic palladium-ruthenium and palladium-platinum catalysts under mild conditions

A remarkable synergic effect of polymer-anchored bimetallic palladium–ruthenium catalysts in the selective hydrogenation of p-chloronitrobenzene

Highly active polymer-anchored bimetallic palladium-based catalysts for the carbonylation of allyl halides under atmospheric pressure