How can a catalyst be poisoned

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By sampling from different areas of a bed and corresponding analyses, a profile of the extent of catalyst poisoning can be determined. Catalyst poisoning is caused by heavy metals such as mercury, lead and arsenic, possibly originating in feedstocks, having passed through the catalyst bed, causing expensive catalyst poisoning and failure.

In some cases analytical STEM is able to identify the growth of new structures. Catalyst poison fronts may be determined from cross-sections. Mercury catalyst poisoning can be determined directly on the catalyst without the need for digestion, by the use of a combustion-atomic absorption analyser. The working range is from ppb to 50 ppm of mercury.

The same instruments can be used for the direct examination of mercury in feedstocks. Lead, arsenic and many other suspect elements including phosphorus can be determined by ICP techniques after bringing the catalyst into solution.

The sulphur content of new and used catalysts can be examined after combustion in a stream of oxygen, using infra red detection of the combustion products. At the same time carbon determination is performed on the same instrument. Major to minor levels of sulphur and carbon are determined. Should there be a need to measure trace levels of sulphur then microcoulometric detection on a different instrument can be applied. Chernyshev , Valentine P.

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By accident, they came across dibenzocyclooctatetraene, a homogenous catalyst poison, to work as a ligand. After screening, they finally found that phenyl attachement to the catalyst poison was a very efficient ligand. The dibenzocyclooctatetraene tightly binds to the Ru center by its nature. One of the keys for this high catalytic activity probably arises from the steric effect of the phenyl group.

In the presence catalysis giving skipped dienes, the formed skipped diene molecules are prone to stay on the catalyst as a stable intermediate but the phenyl group sweeps the product molecule away from the catalyst. As the result, the catalyst can take actions for further catalysis.

They are nuisances in catalyses because they tightly bound to the active site in catalysts. However, the strongly bind nature to the catalyst is an advantage as a ligand in homogeneous catalysts.