Platinum clusters reaction with

Trevor D J, Whetten R L, Cox D M and Kaldor A 1985 Gas-phase platinum cluster reactions with benzene and several hexanes evidence of extensive dehydrogenation and size-dependent chemisorption J. Am. Chem. Soc. 107 518... 

Several explanations have been advanced for the unique performance of Pt/LTL zeolite catalysts. There is a consensus that dehydrocyclization is catalyzed by the platinum clusters alone, with the support providing no catalytic sites [23,38,40]. The support must be nonacidic to prevent acid-catalyzed isomerization and hydrocracking as side reactions [41-43] The aromatic selectivity increases with the basicity of the LTL zeolite support. The interaction of the platinum clusters with the basic support has been suggested to result in an increase in the... 

In further work of the group of Ervin, the activity of palladium cluster anions in the CO oxidation catalysis was examined and it was found that Pd also efficiently catalyzes the CO combustion reaction. The palladium clusters, however, are reported to exhibit more fragmentation than the platinum clusters, consistent with the weaker meal-metal bond strength in palladium relative to platinum [22]. 

The reaction of these platinum or palladium clusters with transition metal compounds has also been studied and many cluster derivatives have been prepared for this method, which included reactions with gold,3 02-3306 silver, 302,33 3,3307-3310 copper 3302,3303,3309-3311 Qr mercury com ... 

This overview is organized into several major sections. The first is a description of the cluster source, reactor, and the general mechanisms used to describe the reaction kinetics that will be studied. The next two sections describe the relatively simple reactions of hydrogen, nitrogen, methane, carbon monoxide, and oxygen reactions with a variety of metal clusters, followed by the more complicated dehydrogenation reactions of hydrocarbons with platinum clusters. The last section develops a model to rationalize the observed chemical behavior and describes several predictions that can be made from the model. 

Platinum clusters, n = 2-11 react with di oxygen at a rate that is within an order of magnitude of gas kinetic. There is no distinct size selective behavior. Products of these gas phase reactions observed with 7.87 eV ionization laser, are PtpO where for m=l,... 

Electrospray ionization will often produce ions that are fully coordinated, stable, and nonreactive in the gas phase. These ions may be probed by removal of ligands to form coordinatively unsaturated ions that are generally reactive. The chemical activity of metal cluster ions differs markedly and often shows size specific enhanced reactivity or lack of reactivity. Silver cluster ions Ag are fairly inert similar to Ag+. Platinum cluster ions PL are quite reactive similar to Pt+. Often, large cluster ions only appear to react with one donor molecule such as benzene this may be due to low concentrations of reactants or short reaction times. Similar clusters may react with a larger number of smaller molecules, and so until more information is available, rules for the coordination behavior of metal clusters are as yet not available. 

By the example of 34 different alkynes, it was convincingly demonstrated that the product of the treatment of [PtCLJ with CO at 40-110 °C is a very powerful alkyne hydration catalyst some of the reactions are shown on Scheme 9.7 [25], The best medium for this transformation is THF containing 5 % H2O. The reaction can also be performed in a water-organic solvent two-phase system (e.g. with 1,2-dichloroethane), however in this case addition of a tetralkylammonium salt, such as Aliquat 336, is required to facilitate mass transfer between the phases. After the reaction with CO, the major part of platinum is present as H2[ Pt3(CO)6 n], but the catalytic effect was assigned to a putative mononuclear Pt-hydride, [PtHCl(CO)2], presumably formed from the cluster and some HCl (supplied by the reduction of [PtCU]). The hydration of terminal acetylenes follows Markovnikov s mle leading exclusively to aldehyde-free ketones. 

Beyer and coworkers later extended these reactions to platinum clusters Ptn and have demonstrated that similar reaction sequences for the oxidation of carbon monoxide can occur with larger clusters [70]. In addition, they were able to demonstrate poisoning effects as a function of surface coverage and cluster size. A related sequence for Pt anions was proposed by Shi and Ervin who employed molecular oxygen rather than N2O as the oxidant [71]. Further, the group of Bohme has screened the mononuclear cations of almost the entire transition metal block for this particular kind of oxidation catalysis [72,73]. Another catalytic system has been proposed by Waters et al. in which a dimolybdate anion cluster brings about the oxidation of methanol to formaldehyde with nitromethane, however, a rather unusual terminal oxidant was employed [74]. 

The Pt2Ru4(CO)i8 cluster reacts with H2 to form Pt3Ru6(CO)2i(/i3-H)-(jt-H)3 in which the platinum and ruthenium atoms are arranged in triangular layers of the pure elements.10 This complex can be converted to Pt3Ru6(CO)20(/i3-C2Ph2X/i-H)2 by reaction with diphenylacetylene.10 The latter complex was found to be an active catalyst for the hydrogenation... 

Dehydrocyclization of n-hexane to form benzene has been a subject of considerable academic and industrial interest since Bernard first reported that platinum clusters supported inside the channels of zeolite L catalyze the reaction with exceptional activity and selectivity (7). The nonacidic nature of the Pt-zeolite L catalyst and correlation of reaction rate with Pt content are consistent with the accepted view that the catalyst is monofunctional, depending solely on Pt metal for catalytic activity (7). However, comparison of aromatization reactivity over nonacidic Pt-zeolites to conventional non-zeolitic catalysts revealed that additional factors contribute to the unusual performance of Pt-zeolites (2). 

Scheme 7.5 Preparation of bis(l,5-cyclooctadiene)platinum(0) (19) and its reactions with ethene to tris(ethene)platinum(0) (20) and with tert-butylisocyanide to the trinuclear platinum cluster 21 (R = fBu)...

Gmelin Handbook of Inorganic Chemistry, System No. 68, Platinum. Main Volume, (a) Part A in Sections 1-6, 1938-1951 (Platinum Metals, Occurrence, History, Preparation, Alloys) (b) Part B The Element in Sections 1-4,1939-1942, Physical and Electrochemical properties of Platinum (Chemical reactions of Pt in Section 4) (c) Part C The Compounds of Platinum. Section 1. Compounds with Noble Gases, H, O, N, Halogens, S, Se, Te, B, C,Si, P, As, Sb, Bi, 1939 (d) Section 2. Compounds with the alkali metals and ammonium, mainly the alkali metal platinum double salts, 1940 . (e) Section 3 Other Compounds, 1940 (f) Part D Complexes with Neutral ligands, 1957. Supplement Volume (g) Part A. Section 1. Technology of Platinum Metals. 1986 (h) Section 2. Isotopes, Atoms, Molecules and Clusters. 1989. 

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