Expertise
Catalysts Characterisation
Poisoning
XPS and SIMS are sensitive tools for studying catalyst poisoning providing there is little associated fouling. In some cases analytical STEM is able to identify the growth of new structures. Poison fronts may be determined from cross-sections.
By sub sampling from different areas of a bed and corresponding analyses, a profile of the extent of catalyst poisoning can be envisaged. Heavy metals such as mercury, lead and arsenic possibly originating in feedstocks, passed through the catalyst bed cause poisoning and failure. Mercury 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 a few ppb to around 50 ppm of mercury.
The same instrument can be used for the direct examination of mercury in feedstocks.
Lead, arsenic and many other elements including phosphorus can be determined by ICP techniques after bringing the catalyst into solution. Detection limits for ICP-OES are ppb level in solution, whereas for ICP-MS are ppt level in solution for many elements.
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.
Chlorine deposition can be determined by oxidative microcoulometry. whereas water soluble anions can often be leached from catalysts and determined by ion chromatography.
Nitrogen contamination can be determined either by a CHN analyser, or for low levels a combustion analyser with chemiluminescence detection.
Catalyst poisoning in some processes routinely progresses to the point of forming a discrete crystalline phase. This is most often seen with sulphur and metal sulphides can be measured by XRD. Appropriate high surface area materials, e.g. oxides, may be used as guard beds to protect a catalyst. In both cases, monitoring the relative content of active / unconverted phase and of the sulphide gives an indication of performance and life-expectancy.
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