Platinum-based catalyst

Earlier processes (e.g. hydroforming) used MoO,i —AI2O3 catalysis but platinum-based catalysts are now extensively used, enabling longer on-stream times before catalyst replacement. 

Thermal cure system. The thermal cure system is based on a hydrosilylation addition reaction between vinyl-functionalized and silicon-hydrido functionalized polysiloxanes [32,33,35], Unsaturated organic groups react with a Si-H functionality in the presence of a platinum-based catalyst (Scheme 10). 

EfiBdent hydrogen supply iiom decalin was only accomplished by the si terheated liquid-film-type catalysis under reactive distillation conditions at modaate heating tempaatures of 210-240°C. Caibcm-supported nano-size platinum-based catalysts in the si ietheated liquid-film states accelerated product desorption fixjm file catalyst surface due to its temperature gradient under boiling conditions, so that both hi reaction rates and conversions were obtained simultaneously. 

AXB) shows time courees of amounts of evolved hydrogen and decalin conversions with caibon-supported platinum-based catalysts unda" supeiheated liquid-film conditions. Enhancement of dehydrogenation activities for decalin was realized by using fiiese composite catalysts. The Pt-W / C composite catalyst exhibited the hipest reaction rate at the initial stage, whereas the Pt-Re / C composite catalyst showed the second highest reaction rate in addition to low in sensitivity to retardation due to naphthaloie adsorbed on catalytic active sites [1-5], as indicated in Fig. 2(A) ). 

Recently, a palladium-catalyzed reaction has been reported which provides exclusive cA-addition and good selectivity for the terminal silane similar to platinum-based catalysts. The catalyst system, Pd2(dba>3+ 4PCy3, is unreactive to internal alkynes and succeeds with a range of aryl and akyl terminal alkynes.45... 

Another key part of a PEM membrane is the thin layer of platinum-based catalyst coating that is used. It makes up about 40% of the fuel cell cost. The catalyst prepares hydrogen from the fuel and oxygen from the... 

Searching for a better catalyst than platinum to oxidize methanol to COad ° y be a new direction of the catalyst search. If such a catalyst is combined with a good catalyst for COad oxidation to C02> the overall catalytic activity may exceed that of platinum based catalysts. Platinum has catalytic activities for both reactions to some extent. For each reaction, however, platinum is not necessarily the best. Palladium may be a good catalyst to oxidize methanol to COad because it is known as a good catalysts for dehydrogenation of hydrocarbons. 

Podbielniak analysis See POD analysis. pad bel ne.ak a.nal a sos poison CHEM A substance that exerts inhibitive effects on catalysts, even when present only In small amounts for example, traces of sulfur or lead will poison platinum-based catalysts. poiz an )... 

Fuel supply is usually from liquid hydrogen or pressurized gaseous hydrogen. For other fuels, a fuel processor is needed, which includes a reformer, water gas shift reactors and purification reactors, in order to decrease the amount of CO to an acceptable level (below a few tens of ppm), which would otherwise poison the platinum-based catalysts. This equipment is still heavy and bulky and limits the dynamic response of the fuel cell stack, particularly for the electric vehicle in some urban driving cycles. 

Platinum-based catalysts are widely used in low-temperature fuel cells, so that up to 40% of the elementary fuel cell cost may come from platinum, making fuel cells expensive. The most electroreactive fuel is, of course, hydrogen, as in an acidic medium. Nickel-based compounds were used as catalysts in order to replace platinum for the electrochemical oxidation of hydrogen [66, 67]. Raney Ni catalysts appeared among the most active non-noble metals for the anode reaction in gas diffusion electrodes. However, the catalytic activity and stability of Raney Ni alone as a base metal for this reaction are limited. Indeed, Kiros and Schwartz [67] carried out durability tests with Ni and Pt-Pd gas diffusion electrodes in 6 M KOH medium and showed increased stability for the Pt-Pd-based catalysts compared with Raney Ni at a constant load of 100 mA cm and at temperatures close to 60 °C. Moreover, higher activity and stability could be achieved by doping Ni-Al alloys with a few percent of transition metals, such as Ti, Cr, Fe and Mo [68-70]. 

In an acidic medium, a PEMFC fed with ethanol allows power densities up to 60 mW cm to be reached at high temperatures (80-120 °C), but this needs platinum-based catalysts, which may prevent wider applications for portable electronic devices. On the other hand, in an alkaline medium, the activity of non-noble catalysts for ethanol or ethylene glycol oxidation and oxygen reduction is sufficient to reach power densities of the order of 20 mW cm at room temperature. This opens up the hope of developing SAMFCs that are particularly efficient for large-scale portable applications. 

Platinum monoxide is used to prepare platinum-based catalysts. 

To date, the only shock tube apparatus equipped to study surface reactions is the KIST facility at ATK GASL in New York. The tests done so far have studied methane oxidation, CFI4 + 2O2 CO2 + 2H2O on the surface of an SCT ferrous-based reactor impregnated with platinum based catalyst. To isolate the effects of the screen and the catalyst on the reaction, three types of tests were run catalyzed screen with combustible gases,... 

Reforming Both thermal and catalytic processes are utilized to convert naphtha fractions into high-octane aromatic compounds. Thermal reforming is utilized to convert heavy naphthas into gasoline-quality aromatics. Catalytic reforming is utilized to convert straight-run naphtha fractions into aromatics. Catalysts utilized include oxides of aluminum, chromium, cobalt, and molybdenum as well as platinum-based catalysts. 

The specificity with respect to the silane of the rhodium- and platinum-based catalysts are complementary since the order of activity of the rhodium catalysts is HSi(OEt)3 > HSiEt3 > HSiCls, whereas for... 

It uses a fixed bed of platinum-based catalyst promoted by a lithium salt which can tolerate sulfur contents up to 300 ppm in the benzene and whose LSHV in relation to liquid benzene is about 1.5 [63],... 

With regard to the electro-catalyst the main research issue is to identify a platinum-based catalyst, i.e. a binary, ternary or quaternary catalyst composed of platinum and one or more transition metals that will be more active (and thereby further reducing the applied potential), exhibit an improved lifespan, and have reduced platinum loadings to reduce the cost. The NWU, located in the North-West province of South Africa where the majority of the world s platinum is mined and produced, is currently setting itself up for the synthesis, characterisation and testing of platinum-based electro-catalysts specifically for normal water electrolysis as well as for S02 electrolysis. 

Whilst the ability of platinum-based catalysts to effect the dehydrogenation of alkanes to the corresponding alkenes is well established [1-4], carbon laydown and consequential deactivation of the catalyst during the dehydrogenation reactions is a well known phenomenon... 

An important possible future use for pure hydrogen is in proton-exchange-membrane fuel cells (PEMFCs) the basic source for the hydrogen could be either a hydrocarbon or an alcohol, either of which can be steam-reformed to produce water-gas.16,17 As explained above, the equilibrium concentration of carbon monoxide decreases as the temperature falls (Figure 10.1), but as little as 1% is detrimental to the operation of platinum-based catalysts in a fuel cell. Excess water, which is commonly used,18 serves to move the... 

Until recently rhodium catalysts gave lower enantioselectivity, but higher chemoselectivity and activity, than the platinum-based catalysts. However, in the past few years rhodium complexes of a few chiral diphosphites and phos-phinophosphito ligands have been reported. These complexes have excellent activities and high chemo-, regio-, and enantioselectivities. 

Kosak studied the hydrogenation of o-nitroanisole in details over palladium- and platinum-based catalysts at 95°C and 2.07 MPa H2.94 The hydrogenation of o-nitroanisole over palladium catalysts was always accompanied by the formation of o,o -hydrazoanisole, the amount of which varied significantly with different samples of starting o-nitroanisole. Impurities such as o-chloronitrobenzene and o,o -dichloroazoxybenzene present in o-nitroanisole were found to increase formation of the hydrazo compound with decrease in the yield of o-anisidine, while o-chloroanisole had no effect on the composition of the product. The hydrazo compounds were resistant to further hydrogenation under the conditions. Platinum-based catalysts were insensitive to the impurities and always gave o-anisidine of high purity. The results are summarized in eq. 9.46. 

The amount of catalyst in such cases is rather high 1000-5000 ppm and selectivity towards anti-Markovnikov addition is lower (80-90%), compared to hydrosilylation in the presence of platinum based catalyst. The synthesis of phenylethenyl substituted siloxanes is of commercial importance, driven by potential application in personal care products. Such materials should be in the form of fluids and thus in order to preserve this requirement two approaches have been exploited. One of them involved substitution of less than 100% phenylethenyl moieties, the other made use of 1-hexene as a co-reactant, leading to decreased crystallinity of the final materials. Depending on the structure of (methylhydrido)siloxanes and reaction conditions the resulting silicon fluids exhibited refraction indices ranging from 1.527 to 1.574 (Table 1). 

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