Carbon catalyst poisoning

Some natural gases have also been found to contain mercury, which is a reformer catalyst poison when present in sufftciendy large amounts. Activated carbon beds impregnated with sulfur have been found to be effective in removing this metal. 

Eor shifting coal-derived gas, conventional iron—chromium catalysts can be used. Because coal gas has a significantly higher concentration of carbon monoxide than is found in gas streams in conventional refineries, the catalyst must be able to withstand high thermal loads. However, potential catalyst poisons such as phenol and other hydrocarbons are not a concern in entrained-bed gasifiers. 

Contrary to the expectation that a sulfur-containing substituent will be a catalyst poison, a phenylthio group serves as an effective selectivity control element in TMM cycloadditions. A single regioisomer (30) was obtained from the carbonate precursor (31) in good yield. The thermodynamically more stable sulfide (32) is readily accessible from (30) via a 1,3-sulfide shift catalyzed by PhSSPh. A wide array of synthetically useful intermediates could be prepared from the sulfides (30) and (32) with simple transformations (Scheme 2.10) [20]. 

Catalyst Poisons. Hausberger, Atwood, and Knight (33) reported that nickel catalysts are extremely sensitive to sulfides and chlorides. If all materials which adversely affect the performance of a catalyst were classified as poisons, then carbon laydown and, under extreme conditions, water vapor would be included as nickel methanation catalyst poisons. 

The effect of synthesis gas composition on conversion, catalyst life, carbon black formation, etc. was determined in numerous tests. Characteristic variables in the synthesis gas composition are the H2/CO ratio, residual C02 content, and content of trace components in the form of higher hydrocarbons and catalyst poisons. 

The results from Figures 6 and 7 support the observation that acetic acid combustion is accelerated by the presence of Au and KOAc. The evolution of carbon dioxide is enhanced by both Au and KOAc, while the evolution of carbon monoxide is enhanced by the presence of KOAc and suppressed by the presence of Au. This shows that acetic acid combustion is more complete with a Pd-Au loy versus Pd alone which is important since carbon monoxide can act as a tempor catalyst poison in the process. These results agree with Nakamura and Yasui s (1980) on acetic acid oxidation which showed an increase in acetic acid combustion when KOAc is added to a Pd catalyst. 

This reaction serves for removal of carbon monoxide from gas mixtures and is usually carried out over supported metal catalysts. In reforming techniques, carbon monoxide, poisonous for the catalyst in fuel cells, is removed in such a way. It is also applied in automobiles for reducing the exhaust gas carbon monoxide to an environmentally acceptable level. 

On the surface of metal electrodes, one also hnds almost always some kind or other of adsorbed oxygen or phase oxide layer produced by interaction with the surrounding air (air-oxidized electrodes). The adsorption of foreign matter on an electrode surface as a rule leads to a lower catalytic activity. In some cases this effect may be very pronounced. For instance, the adsorption of mercury ions, arsenic compounds, or carbon monoxide on platinum electrodes leads to a strong decrease (and sometimes total suppression) of their catalytic activity toward many reactions. These substances then are spoken of as catalyst poisons. The reasons for retardation of a reaction by such poisons most often reside in an adsorptive displacement of the reaction components from the electrode surface by adsorption of the foreign species. 

Most low-valence metal complexes are generally deactivated by air and sometimes also by water. Carbon monoxide, hydrogen cyanide, and PH3 frequently act as poisons for these catalysts. Poisoning by strongly co-ordinating molecules occurs by formation of catalytically inert complexes. An example is the poisoning of Wilkinson s catalyst for alkene hydrogenation ... 

It is well known that palladium on carbon catalysts are poisoned by hydrogen cyanide and thiol products or hydrogen sulfide (6). Therefore, it was of interest to investigate the reduction of perfluoroalkyl thiocyanates as a function of tin concentration, keeping the concentration of palladium and reaction conditions constant. Figure 15.1 delineates the % conversion vs. Sn/Pd ratio, under the same reaction conditions of 175°C, 700 psig H2 for 2 hours with 5% Pd on carbon catalysts in ethyl acetate solvent at a 1000 1 substrate catalyst molar ratio. The increase in... 

Extensive catalyst poisoning results from the deposition of carbon in or on the catalyst surface. In technological parlance, this is usually referred to as the formation of coke. At temperatures in excess of those normally used for catalysis, hydrocarbon decomposition at metal surfaces is known... 

The ideal performance of a fuel cell depends on the electrochemical reactions that occur with different fuels and oxygen as summarized in Table 2-1. Low-temperature fuel cells (PEFC, AFC, and PAFC) require noble metal electrocatalysts to achieve practical reaction rates at the anode and cathode, and H2 is the only acceptable fuel. With high-temperature fuel cells (MCFC, ITSOFC, and SOFC), the requirements for catalysis are relaxed, and the number of potential fuels expands. Carbon monoxide "poisons" a noble metal anode catalyst such as platinum (Pt) in low-temperature... 

The second, which passes through a dimetallacyclopentane type intermediate [87], requires the presence of adjacent platinum atom assemblies. The mechanism should consequently be strongly inhibited by platinum site isolahon, due to tin addition or to catalyst poisoning by carbon. 

The purification step in the route 1 approach removes all of the H2S and COS in the raw product gas from the gasifier in addition to the carbon dioxide. Sulfur acts as a catalyst poison to Fischer-Tropsch, methanation and methanol catalyst systems, so pure sulfur-free gases must be used in these synthesis reactions. 

---