A strategy to develop improved catalysts is to create systems that merge the advantages of heterogeneous and molecular catalysis. One such system involves supported liquid-phase catalysts, which feature a molecularly defined, catalytically active liquid film/droplet layer adsorbed on a porous solid support. In the past decade, this concept has also been extended to supported ionic liquid-phase catalysts. Here we develop this idea further and describe supported catalytically active liquid metal solutions (SCALMS). We report a liquid mixture of gallium and palladium deposited on porous glass that forms an active catalyst for alkane dehydrogenation that is resistant to coke formation and is thus highly stable. X-ray diffraction and X-ray photoelectron spectroscopy, supported by theoretical calculations, confirm the liquid state of the catalytic phase under the reaction conditions. Unlike traditional heterogeneous catalysts, the supported liquid metal reported here is highly dynamic and catalysis does not proceed at the surface of the metal nanoparticles, but presumably at homogeneously distributed metal atoms at the surface of a liquid metallic phase.

Gallium-rich Pd–Ga phases as supported liquid metal catalysts

For many years, it has been customary to classify catalysts as “homogeneous” or “heterogeneous.” The former commonly operate through the formation of “intermediate compounds,” and the latter, by adsorption of the reactants on the catalyst surface. The line between the two is a fine one, for the distinction between adsorption and compound formation is not at all clear, and seems to be becoming less and less clear as we learn more about adsorption. In recent years, several writers [l-7] have stressed the point that there is a good deal of overlap between homogeneous and heterogeneous catalysis. Experimental evidence supporting this point of view is accumulating, and while we are not prepared to say that there is no distinction, we can say with certainty that many homogeneous catalysts can be converted into heterogeneous ones, retaining the advantages of great activity and selectivity inherent in homogeneity and, at the same time, assuming the ready recovery which is the great advantage of heterogen...

“heterogenizing” homogeneous catalysts

From supported homogeneous catalysts to heterogeneous molecular catalysts

Publisher Summary For many years, most of the intentionally used catalysts were heterogeneous and in which reaction was promoted by the adsorption of some or all of the reactants on the catalyst surface. Catalysis occurs through the formation of intermediate compounds. The major disadvantage of homogeneous catalysts is the problem of separating the very expensive catalyst from the products at the end of the reaction. Distillation is inevitably an endothermic process and is, therefore, expensive. Homogeneous catalysts have the advantage over heterogeneous catalysts of being totally reproducible, because they have a definite stoichiometry and structure. The thermal stability of heterogeneous catalysts––such as pure metals and metal oxides––is often much higher than that of homogeneous catalysts. The use of fluid-bed catalysts represents an attempt to homogenize heterogeneous catalysts. Polystyrene resins with a range of substituents other than tertiary phosphines have been used as supports. The reaction of a metal complex with a support accompanied by the reduction of the metal to a lower oxidation state has been used to prepare supported rhodium and platinum catalysts. Hydroformylation literally involves the addition of a hydrogen atom to one end of an olefinic double bond and a formyl group to the other. Both the rhodium and the cobalt complexes catalyze olefin isomerization, as well as olefin hydroformylation. The formation of alcohols as an end product is promoted by using more vigorous conditions for both the cobalt and rhodium catalysts.

Supported Transition Metal Complexes as Catalysts

The reactions of SnCl2 with the complexes cis-PtCl2P2, P=trialkyl and triaryl phosphines and phosphites, in CDCl3 and CD2Cl2 have been studied using 31P and 195Pt NMR. methods. For equimolar amounts of Sn and Pt, products of the type PtCl(SnCl3)P2 are formed with the complex geometry depending on the nature of P. For PPEt3 and P(OPh)3, further addition of SnCl2 produces trans-Pt(SnCl3)2 complexes. The syntheses of trans-PtCl(SnCl3) (PEt3)2 and trans-Pt(SnCl3)2 (OPh3)2 are described.

G.C. Bond

Papers

The use of supported solutions of rhodium trichloride for homogeneous catalysis

Homogeneous catalysis by noble metal salts: II. Isomerization of 1-pentene by a platinum(ll)-tin(ll) complex

Homogeneous catalysis by noble metal salts: I. The homogeneous isomerization of olefins by palladium compounds