Platinum degradation

Catalytic dewaxiag (32) is a hydrocrackiag process operated at elevated temperatures (280—400°C) and pressures, 2,070—10,350 kPa (300—1500 psi). However, the conditions for a specific dewaxiag operatioa depead oa the aature of the feedstock and the product pour poiat required. The catalyst employed for the process is a mordenite-type catalyst that has the correct pore stmcture to be selective for normal paraffin cracking. Platinum on the catalyst serves to hydrogenate the reactive iatermediates so that further paraffin degradation is limited to the initial thermal reactions. 

Catalyst Deactivation. Catalyst deactivation (45) by halogen degradation is a very difficult problem particularly for platinum (PGM) catalysts, which make up about 75% of the catalysts used for VOC destmction (10). The problem may weU He with the catalyst carrier or washcoat. Alumina, for example, a common washcoat, can react with a chlorinated hydrocarbon in a gas stream to form aluminum chloride which can then interact with the metal. Fluid-bed reactors have been used to offset catalyst deactivation but these are large and cosdy (45). 

Promoters, usually present in smaU amount, which enhance activity or retard degradation for instance, rhenium slows coking of platinum reforming, and KCl retards vaporization of CuCU in oxy-chlorination for vinyl chloride. 

The benzylic position of an alkylbcnzene can be brominated by reaction with jV-bromosuccinimide, and the entire side chain can be degraded to a carboxyl group by oxidation with aqueous KMnCfy Although aromatic rings are less reactive than isolated alkene double bonds, they can be reduced to cyclohexanes by hydrogenation over a platinum or rhodium catalyst. In addition, aryl alkyl ketones are reduced to alkylbenzenes by hydrogenation over a platinum catalyst. 

Electro-catalysts which have various metal contents have been applied to the polymer electrolyte membrane fuel cell(PEMFC). For the PEMFCs, Pt based noble metals have been widely used. In case the pure hydrogen is supplied as anode fuel, the platinum only electrocatalysts show the best activity in PEMFC. But the severe activity degradation can occur even by ppm level CO containing fuels, i.e. hydrocarbon reformates[l-3]. To enhance the resistivity to the CO poison of electro-catalysts, various kinds of alloy catalysts have been suggested. Among them, Pt-Ru alloy catalyst has been considered one of the best catalyst in the aspect of CO tolerance[l-3]. 

An interesting study examined the anodic oxidation of EDTA at alkaline pH on a smooth platinum electrode (Pakalapati et al. 1996). Degradation was initiated by removal of the acetate side chains as formaldehyde, followed by deamination of the ethylenediamine that formed glyoxal and oxalate. Oxalate and formaldehyde are oxidized to CO2, and adsoption was an integral part of the oxidation. 

Mamian M, Torres W, Larmat EE (2009) Electrochemical degradation of atrazine in aqueous solution at a platinum electrode. Portugaliae Electrochim Act 27(3) 371-379... 

As the data in Table XIV indicate, over platinum demethylation of a ring is slow compared to C—C bond rupture within a ring. On the other hand, it is well established [e.g., Kochloefl and Bazant (161) that if one uses a supported nickel catalyst which is known to favor stepwise alkane degradation, reaction with an alkylcycloalkane is largely confined to the alkyl group (s) which are degraded in a stepwise fashion and are finally removed entirely from the ring. 

Iridium-platinum alloys, 79 602 Iripallidal degradation products, 24 577 Irish moss, common and scientific names, 3 188t... 

In fuel cell development, the high cost of precious metals has led to ways to lower the platinum content. Methods include raising the activity of the catalyst, so less is needed and finding more stable catalyst structures that do not degrade over time while avoiding reactions that can... 

Photolytic. Water containing 2,000 ng/pL of dibromochloromethane and colloidal platinum catalyst was irradiated with UV light. After 20 h, dibromochloromethane degraded to 80 ng/pL bromochloromethane, 22 ng/pL methyl chloride, and 1,050 ng/pL methane. A duplicate experiment was performed but 1 g zinc was added. After about 1 h, total degradation was achieved. Presumed transformation products include methane, bromide, and chloride ions (Wang and Tan, 1988). 

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