Chalcogen catalysts

Alonso-Vante N, Zeltaiay P, Choi JH, Wieckowski A, Cao D (2009) Chalcogen catalysts for polymer electrolyte fuel cell. US Patent 7,588,857... 

Since Furukawa s work, new chalcogen catalysts with great structural variation were synthesised (Scheme 7.52) [180-202]. The best results were reported by Metzner [181-184,194], Aggarwal [195] and Huang [196]. 

Perspectives for fabrication of improved oxygen electrodes at a low cost have been offered by non-noble, transition metal catalysts, although their intrinsic catalytic activity and stability are lower in comparison with those of Pt and Pt-alloys. The vast majority of these materials comprise (1) macrocyclic metal transition complexes of the N4-type having Fe or Co as the central metal ion, i.e., porphyrins, phthalocyanines, and tetraazaannulenes [6-8] (2) transition metal carbides, nitrides, and oxides (e.g., FeCjc, TaOjcNy, MnOx) and (3) transition metal chalcogenide cluster compounds based on Chevrel phases, and Ru-based cluster/amorphous systems that contain chalcogen elements, mostly selenium. 

With respect to non-noble and non-Ru catalysts, transition metal chalcogenides with spinel and pyrite structures have been investigated and shown that these can also be active to oxygen reduction processes. The motivation in the present case is that chalcogen addition might enhance the stability and activity toward the ORR... 

Campbell S. 2006. Ballard Power System. Development of transition metal/chalcogen based cathode catalysts for PEM fuel cells. DOE Hydrogen Program Review, May 16-19, Washington, DC. Available at http //www.hydrogen.energy.gov/annual review06 fuelcells.html (click on catalysts section). 

Diphosphine mono-chalcogenides are able to bind to metal centres from either one of or both the phosphorus(III) and chalcogen donor centres. This has led to their study as hemi-labile ligands in catalyst systems, whereby one of the donor centres binds strongly to the metal centre and the other one is weakly bound and hence can be readily dissociated or reattached to reveal or protect the active site at a metal centre.28... 

Most of the catalysts employed in PEM and direct methanol fuel cells, DMFCs, are based on Pt, as discussed above. However, when used as cathode catalysts in DMFCs, Pt containing catalysts can become poisoned by methanol that crosses over from the anode. Thus, considerable effort has been invested in the search for both methanol resistant membranes and cathode catalysts that are tolerant to methanol. Two classes of catalysts have been shown to exhibit oxygen reduction catalysis and methanol resistance, ruthenium chalcogen based catalysts " " and metal macrocycle complexes, such as porphyrins or phthalocyanines. ... 

Catalyst precursors of Group 4, 4-8 Chalcogen atoms coordinating E-E bonds, 59-61... 

As the atomic number of M increases, the possibility of reducing R3MH rises sharply as well. For example, the reduction of organohalides by trialkylsilanes (M = Si) requires the use of catalysts (AICI3, Ni, Pt and others), but the heavier R3MH (M = Ge, Sn, Pb) react in the absence of catalysts. The reactivity of the M—H bond in R3MH towards elemental chalcogens increases as the atomic number of M increases. 

It should be kept in mind that it is often difficult to ascertain what the active catalyst is. There are, in fact, very few proven catalytic mechanisms where the structure of the actual catalyst is known with certainty. There are, to the author s knowledge, few, and possibly no, proven useful homogeneous catalytic processes that involve metal dimers in the catalytic cycle. In an excellent review on cluster catalysis, Muetterties lists the following processes as metal-cluster-catalyzed reactions (see Table 2). This review also lists the important classes of metalloenzyme clusters however, these compounds do not normally involve metal-metal bonds per se but are usually bridged by chalcogens, such as sulfur or oxygen donors. 

Ge amidinate complexes are susceptible to oxidation of elemental chalcogens. Many of these complexes are excellent catalysts for the cycUzation of aryl isocyanates. ... 

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