Platinum activation

Pt/H-MCM-22 catalysts for methane combustion have been prepared by ion-exchange of a highly crystalline H-MCM-22 zeolite using [Pt(NH3)4](N03)2. The activation procedure of the catalyst precursor has been optimized and all steps monitored by HRTEM, SEM and FTIR of CO adsorbed. The preliminary decomposition/calcination of the ion exchanged sample is very crucial in that influence the final properties of platinum active species. 

From the comparison of calculated oxygen and OH adsorption energies to M(lll) versus activity of the metals toward O2 reduction, a peak shaped curve is obtained, Pt being situated almost on top of the volcano plot [63] palladium and platinum activities should be quite close. The relation between the amount of adsorbed oxygen and the number of unpaired d electrons of the metal had been mentioned earlier [48]. 

The advantage over most other kinds of reduction is that usually the product can be obtained simply by filtration from the catalyst, then distillation. The common catalysts are nickel, palladium, copper chromite, or platinum activated with ferrous iron. Hydrogenation of aldehyde and ketone carbonyl groups is much slower than of carbon-carbon double bonds so more strenuous conditions are required. This is not surprising, because hydrogenation of carbonyl groups is calculated to be less exothermic than that of carbon-carbon double bonds ... 

Pt-based electrocatalysts are usually employed in proton exchange membrane fuel cells (PEMFC) and direct methanol fuel cells (DMSC). In direct-methanol fuel cells (DMFCs), aqueous methanol is electro-oxidized to produce COj and electrical current. To achieve enhanced DMFC performance, it is important to develop electrocatalysts with higher activity for methanol oxidation. Pt-based catalysts are currently favored for methanol electro-oxidation. In particular, Pt-Ru catalysts, which gave the best results, seem to be very promising catalysts for this application. Indeed, since Pt activates the C-H bounds of methanol (producing a Pt-CO and other surface species which induces platinum poisoning), an oxophilic metal, such as Ru, associated to platinum activates water to accelerate oxidation of surface-adsorbed CO to... 

In studies of dual-functional catalysis the mixed catalyst technique has many advantages, two of which are mentioned. (1) It allows separate and independent preparation of each component for example, a platinum preparation can be made in any manner desired in order to obtain a certain platinum activity without regard to what such procedures might do to the acidic properties of the oxide base, this interdependence always being a matter of concern in conventional direct impregnation techniques. (2) A component s relative activity contribution can be flexibly varied in a perfectly known and controllable manner by simply varying its bulk amount in admixture with the other. 

The pulse technique provides very brief contacts of the catalyst with hydrocarbon charge and allows measurements to be made at the very high fresh platinum activities. 

On the Pt-Ce catalyst, after this oxidation reaction, its activity is decreased for the hydrocarbon reaction. We may think that the oxidation state of cerium is reinforced and the oxide blocks platinum active sites. 

Nevertheless, despite the strong hydrogenation platinum activity, the butene fraction remained higher over the Pt/Ga-silicate. 

The introduction of platinum active phase does not affect the structural data of both supports and the thermal stability remains the same. A slight difference in platinum content is observed this difference can be related to the difference in porous volume ( "Al203Si 0.48 cm g" AlaOsSi 0.40 cm. g" ) or to the larger 6-AI2O3 content of the oil-drop sample. This phase can increase the... 

A test procedure involving an isomerization reaction of an olefin would obviously be most desirable for testing the activity of the acid function of a dual-function catalyst. Such a test appeared out of question because of the certain interference with this reaction by the platinum activity of the samples under study. Cumene (isopropyl benzene) is known to undergo reaction (dealkylation) on acidic catalysts. We have found the reactivity of cumene to be a useful measure of the activity for other acid-catalyzed reactions (4) of at least certain classes of compositions. Furthermore, we have foimd it to be useful on dual-function class catalysts, i.e., to yield a relative measure of their acidic activity despite the simultaneous presence of platinum. 

Fig. 5. Constancy of total gas production rate and variation in gas composition with increasing platinum activity in cumene test.

There are few reports of alkene-deuterium reactions on bimetallic catalysts, but those few contain some points of interest. On very dilute solutions of nickel in copper (as foil), the only product of the reaction with ethene was ethene-di it is not clear whether the scarcity of deuterium atoms close to the presumably isolated nickels inhibits ethane formation, so that alkyl reversal is the only option, or whether (as with nickel film, see above) the exchange occurs by dissociative adsorption of the ethene. Problems also arise in the use of bimetallic powders containing copper plus either nickel, palladium or platinum. Activation energies for the exchange of propene were similar to those for the pure metals (33-43 kJ mol ) and rates were faster than for copper, but the distribution of deuterium atoms in the propene-di clearly resembled that shown by copper. It was suggested that the active centre comprised atoms of both kinds. On Cu/ZnO, the reaction of ethene with deuterium gave only ethane-d2. as hydrogens in the hydroxylated zinc oxide surface did not participate by reverse spillover. ... 

Our cubo-octahedral structures were of the core-shell t5rpe with inner core, formed by second component atoms - transition metals, while the shell in just one atomic layer was constructed by platinum - active catalyst of surface processes. Such structures in our own calculations [25] and others [26-27] are optimal in catalytic sense, because they cause effective way of surface reactions for oxygen reduction. On the other side such nanoclusters possess stability in aggressive acid environments, which lead to electrochemical corrosion of materials of catalysts. 

In the meantime, hundreds of other metal complexes have been shown to be active against various animal-tumor screens. These include predominantly analog structures of the parent drug, but also a scattering of complexes of metals other than platinum. Active pursuit of these areas may be highly rewarding. 

The phenol process based on the oxidation of cyclohexane has been operated for a short time by Monsanto in Australia and is of less importance. In this process, a mixture of cyclohexanone and cyclohexanol is dehydrogenated to phenol at 400 °C, using platinum/activated carbon or nickel/cobalt catalysts. The degree of conversion can reach 90 5%. The crude phenol is refined by distillation. A particular disadvantage of this process lies in the difficulty in refining the crude oxidation mixture from cyclohexane oxidation. 

Ruthenium catalyst impregnated onto an ion exchange resin may serve as a catalyst for the hydrolysis of sodium borohydride [99]. Other catalyst formulations reported in the literature are metal halides such as nickel and cobalt chloride, colloidal platinum, active carbon, raney nickel, fluorinated partides of magnesium-based material [100] and nickel boride [281]. Zhang et al. reported that nickel powder is an active catalyst under conditions of a batch reactor [282]. With some time delay, the reaction started from ambient conditions. 

Liang et al. reported a PtCla-catalyzed transformation of 3-(2-alkyl)phenyl-propynyl acetate 130 to prepare naphthalenyl acetate 131 (Scheme 50) [45]. The electrophihc Pt-allene complexes formed in situ worked as hydride acceptors. Mechanistically, the Pt(Il)-promoted [l,3]-OAc shift leads to the formation of platinum-activated allenyl ester 1, which undergoes a [l,5]-hydride shift to form 1,3,5-hexatriene II. A subsequent bir-electrocyclic ring closure affords intermediate... 

The platinum oxide catalyst converts the hexitols to the corresponding aldoses and ketoses which are carried through the above series of reactions by the oxygen. Mannitol is oxidized by Pt02 to D-mannose, isolated as methyl a-mannoside in a yield of 20%. Fructose is formed simultaneously. With a platinum-activated carbon catalyst, L-sorbose has been converted to 2-keto-L-gulonic acid, 2,3-0-isopropylidene-L-sorbose to2,3-0-isopropyl-... 

Hobbs BS, Tseung ACC. High performance, platinum activated tungsten oxide fuel cell electrodes. Nature 1969 222 556-8. 

A unique advantage of eleetrodes fabrieated by chemical techniques is improved proton conductivity due to sufficient contact between the Nafion membrane and the catalyst layer. The disadvantages are poor mass transportation through the catalyst layer and lower platinum activity, caused by large particle size. 

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