Catalysts poisoning susceptibility

It has been suggested that a pilot plant operation to determine the feasibility of developing this process be carried out in a tubular flow reactor with a volume of 0.15 m3. It is suggested that the reactor operate at 450 °C and 1 atm with a feed flow rate of 41.7 moles of pure tetra-chloroethane per kilosecond. Will the catalyst be susceptible to poisoning under these operating conditions ... 

Example 22 removal of allyl group attached to a phosphorus centre with Pd, Pt and Rh complexes is a well established procedure [51] but is inconvenient for synthesis of therapeutic compounds on a large scale. During the deprotection step the palladium catalyst is susceptible to poisoning especially with P-S compounds resulting in loss of catalytic efficiency. Furthermore traces of organometallic compounds remain in the product after deprotection. In the paper of Manoharan et al. other methods of deprotection of allyl... 

Another limitation on the use of catalytic oxidation is the susceptibility of the catalysts to various deactivators or poisons, although according to the vendor the phase out of the use of volatile lead alkyls as antiknock agents in U.S. gasoline, catalyst poisoning is today rarely encountered. 

Voltz and Weller (14S) found that both the oxidized and reduced catalysts were susceptible to poisoning by small amounts of water vapor and,... 

This term refers to the sensitivity of a catalyst to poisoning under specified conditions. Two other terms are typically used to describe poisoning susceptibility. Poisoning resistance is the degree to which a catalyst resists deactivation, i.e., a catalyst which deactivates slowly is more resistant to poisoning than one that deactivates rapidly. Poisoning tolerance is defined typically as either the ultimate amount of poison a catalyst can adsorb and... 

Homogeneous catalysts often have the advantages of better catalyst reproduci bility and better selectivity. They are also less susceptible to catalyst poisoning (heterogeneous catalysts are usually poisoned by small amounts of sulfur, often found in rubber stoppers, or by sulfur-containing compounds, such as thiols and sulfides). On the other hand, heterogeneous catalysts are usually easier to separate from the reaction mixture. 

Apparently there is not a clear relationship between the catalyst nature and the coke poisoning susceptibility but the tendency to retain and withstand higher metal poisoning of some catalysts over others is clear. Catalysts with pore size near to 120 A present the maximum metals retention for this type of feeds, but a better definition of the texture needs more information and is the reason of further research at ICP. 

Selective hydrogenation catalysts are susceptible to contact with a wide variety of contaminants (S, Hg, As, Si, Na, Fe, etc.) during their lifetime. Their influence on catalytic performance depends on the type of reaction, the operating conditions, the active phase and the contaminant itself [1-3]. The effects range from a simple reversible inhibition to an irreversible poisoning and consequently the necessity to change the catalyst. 

Steam-reforming catalysts are susceptible to sulfur poisoning. At reforming conditions, all sulfur compounds are converted to hydrogen sulfide, which is chemisorbed on the metallic surface... 

We further developed a temperature-stable eopper/mixed oxide catalyst by fabricating it in a structured form that has the same activity as the powder. This catalyst can be activated in air and does not lose activity after exposure to air at temperatures up to 300°C. The ANL copper/mixed oxide catalyst has the potential to reduce the volume of the WGS reactor by 20% compared with the commercial catalysts. The copper catalyst showed susceptibility to poisoning by H2S in the reformate feed. We have also developed cobalt and ruthenium catalysts with higher activity than commercial iron-chrome (325-400°C) by using a promoter to suppress methane formation. 

As with all catalysts, palladium and its alloys are susceptible to poisoning [69]. Catalysts must be designed with resistance to poisoning, and proper precautions must be taken to minimize exposure of the membranes to catalyst poisons [69]. Typical poisons for palladium include H2S and other compounds of sulfur such as carbon disulfide (CS2), carbonyl sulfide (COS), aromatic thiophenes and mercap-tans (thiols, R-SH). Palladium is poisoned by the Group VA elements, P, As, Sb and Bi, the halides (Cl, Br, I), and Si, Pb and Hg. Alkenes and unsaturated organic compounds can poison palladium as can elemental carbon deposited from decomposition of carbonaceous materials. Carbon monoxide in high concentrations and at low temperatures can form a monolayer which blocks adsorption and dissociation of molecular hydrogen. Carbon monoxide can also decompose to produce car-... 

Steels are less susceptible to hydrogen cracking above room temperature, with iron becoming a better catalyst for the reaction Had + H + e" H2. Hence, more hydrogen escapes as molecular H2 and less adsorbed H is available to enter the metal, contrary to the effects of catalyst poisons, which retard the above reaction. 

The potassium silicate materials are less versatile in terms of formulation flexibility than the sodium silicate materials. However, they are less susceptible to crystallization in high concentrations of sulfuric acid so long as metal ion contamination is minimal. Potassium silicate materials are available with halogen free hardening systems, thereby removing the remote possibility for catalyst poisoning in certain chemical processes. 

Carbon-phosphorus bonds may also be formed. Chemists at Merck developed a synthesis of either enantiomer of the valuable ligand BINAP 133 from the more easily resolved BINOL 2.612, using a triflate-phosphine coupling reaction (Scheme 2.183). They reasoned that nickel catalysis would be more effective as this metal is harder than palladium and, therefore, less susceptible to catalyst poisoning by the product. BINAP 133 could be obtained with no loss of chirality. They also reported a resolution procedure for BINOL 2.612.224... 

PEMFCs are very clean systems and act as filters for impurities introduced from ambient air, fuel used, and even degradation products from the cell materials. Both the membrane and the catalyst are susceptible to cmitamination and poisoning. Electrode degradation of PEMFCs can occur as a result of various impurities found in the fuel feed, air stream, as well as corrosimi by-products from fuel cell components such as the bipolar plate, catalysts, or membrane. 

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