Platinum poisoning

In selecting reference electrodes for practical use, one should apply two criteria that of reducing the diffusion potentials and that of a lack of interference of RE components with the system being studied. Thus, mercury-containing REs (calomel or mercury-mercuric oxide) are inappropriate for measurements in conjunction with platinum electrodes, since the mercury ions readily poison platinum surfaces. Calomel REs are also inappropriate for systems sensitive to chloride ions. 

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 )... 

Catalyst poisoning. The more or less permanent deactivation of a catalyst by chemical reaction with a contaminant. Sulfur will poison platinum catalysts vanadium will poison zeolyte catalysts. 

Such electronic transfer induced by sulfur adsorption was also pointed out by using cinnamic acid as a probe molecule (48). The UV-visible reflexion spectra of adsorbed cinnamic acid on nonpoisoned and partly poisoned platinum catalysts shows that adsorption on pure platinum induces a shift of the peaks toward the higher wavelengths and an appearance of fine structure. Sulfurization of platinum induces a further enhancement of higher wavelength peaks. Binding energy of cinnamic acid is thus increased by sulfur adsorption on Pt catalysts. 

Whereas the hot systems can consume CO, the cool systems suffer CO-poisoned platinum catalysts, and must have a shift reactor to consume the CO. Platinum poisoning is an irreversibility. The alkaline fuel cell (AFC), although without platinum, is especially incompatible with CO because of its KOH electrolyte. It needs a pure hydrogen fuel, and air with CO removed. The latter two purifications carry their own irreversibilities. 

The composition of a reforming catalyst is dictated by the composition of the feedstock and the desired reformate. The catalysts used are principally molybdena-alumina, chromia-alumina, or platinum on a silica-alumina or alumina base. The nonplatinum catalysts are widely used in regenerative process for feeds containing, for example, sulfur, which poisons platinum catalysts, although pretreatment processes (e.g., hydrodesulfurization) may permit platinum catalysts to be employed. 

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Continuing the line of catalytic oxidation on platinum. Peregrine Philips (1831, British Patent No. 6096) patented the oxidation of SO2 to SO3 on platinum, but he must have died before the first contact process plant for the production of sulfuric acid went on stream. And finally, along this line of work, Schweigger in the same year discovered that hydrogen sulfide poisoned platinum. 

The presence of NO2 did not poison platinum electrocatalyst as no surface species were detected in cychc voltammograms however, fuel cell performance was degraded by 50% compared to pure air performance and it was completely recovered after 24 h imder constant flow of neat air (Mohtadi et al, 2004). 

In our original work, an E. coli host containing three plasmids was used to catalyze the conversion of glucose into cw,cw-muconic acid under shake flask conditions.Our most recent construct uses a single plasmid and catalyzes the conversion of glucose into c/5,cw-muconic acid under controlled, fed-batch fermenter conditions similar to those employed for microbe-catalyzed synthesis of shikimic acid and quinic acid from glucose. After removal of the biocatalyst, the clarified fermentation broth is treated with activated carbon to remove unidentified molecules in the broth that poison platinum catalysts. The d5,ci5-muconic acid can then be hydrogenated over a platinum-on-carbon catalyst to afford adipic acid in nearly quantitative yield. 

Straight-run naphthas, used as feedstock for catalytic reforming and steam reforming processes. They must contain less than 1 ppm of sulfur and nitrogen to avoid poisoning platinum or nickel catalysts. 

An intermediate reaction pathway in the carbon-containing fuel oxidation will include carbon monoxide, which poisons platinum catalysts at the low temperatures of PEFCs. Thus, a catalyst such as Pt-Ru that has a CO tolerance will generally be more effective than pure platinum. 

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