Poison resistance

One feature of particular interest is the resistance that gold-based systems might display against sulphur poisoning. Only a little work has been carried out in this area to date, but gold on titania catalyses the Claus reaction and is 5-10 times more effective than titania itself, indicating that gold can be sulphur-tolerant  

In addition, the reduction of SO2 by CO using Au/Ti02 is also 5-10 times more active than with pure titania [206]. 

Marsh and co-workers [145] showed that gold on cobalt oxide particles, supported on a mechanical mixture of zirconia-stabilised ceria, zirconia and titania remains active in a gas stream containing 15 ppm SO2. Haruta and co-workers [207] found that although the low-temperature CO oxidation activity of Ti02-supported Au can be inhibited by exposure to SO2, the effect on the activity for the oxidation of H2 or propane is quite small. Venezia and co-workers [208] reported that bimetallic Pd-Au catalysts supported on silica/alumina are resistant to sulphur poisoning (up to 113 ppm S in the form of dibenzothiophene) in the simultaneous hydrogenation of toluene and naphthalene at 523 K. 

The reaction of photo-induced sulphur desorption from the surfaces of the metal oxide-supported (rutile and anatase Ti02, SrTiOs, ZnO, Fe203 and Sn02) Au nanoparticles in water at room temperature has also been studied [209]. It was found to be driven by an upward shift of the Fermi energy of the metal oxide-loaded Au nanoparticles with irradiation. It has also been demonstrated that this phenomenon is applicable to the low-temperature cleaning of sulphur-poisoned metal catalysts. 

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Catalysts having improved poison resistance have been developed. Catalysts are available that can destroy chlorine-, fluorine-, or bromine-containing organic compounds (5). 

G. R. Lester, andJ. C. Summers "Poison-Resistant Catalyst for Purification of Web Offset Press Exhaust," presented at Air Pollution Control... 

Cheekatamarla and Lane [62, 63] studied the effect of the presence of Ni or Pd in addition to Pt in the formulation of catalysts for the ATR of synthetic diesel. For both metals, a promotional effect with respect to catalytic activity and sulfur poisoning resistance was found when either alumina or ceria was used as the support. Surface analysis of these formulations suggests that the enhanced stability is due to strong metal-metal and metal-support interactions in the catalyst. 

We are currently involved in a three phase developmental program to extend the process to other hydrogen containing streams. The program involves screening candidate streams to identify poisonous species for the metal hydrides, developing poison resistant processes for each stream, and demonstrating the process(es) on a pilot scale to establish process economics. 

Validation of the Best Catalytic System 5.3.5.1 Poisoning Resistance... 

The most active formulation (ZSNbPt) was tested in a conventional reactor using as feedstream a mixture of light n-alkanes [n-pentane (20 wt%), n-hexane (60 wt.%) and n-heptane (20 wt%)] to simulate an industrial stream. Experiments were carried out in a conventional reaction system using a fixed-bed continuous -flow reactor. Reaction was carried out under the same conditions as the poisoning resistance experiments. The activity and selectivity of this catalyst (Fig. 5.13) have been compared with those obtained with sulfated zirconia impregnated with platinum (ZS). Fig. 5.13 represents the evolution of the conversion with reaction temperature. Clearly, the reactivity of the n-paraffm follows the order n-heptane > n-hexane > n-pentane for both catalysts, as expected when taking into account the adsorption heats of the different hydrocarbons [34]. 

One of the common limitations of catalytic-combustion-type analyzers is the poisoning of the filament by silicon, sulfur, chlorinated compounds, or lead compounds. A variety of filament protection means have been added to increase the poison resistance of the sensors. Life expectancies are usually defined in terms of exposure concentration hours. One high-concentration exposure of a poison has been known to knock out a sensor therefore, nonpoisoning techniques should be considered when poisoning is an issue. 

Pt-Ir With same sulfur coverage, Pt-Re catalysts are more deactivated than Pt or Pt-Ir. However, Ir presence increases sulfur poisoning resistance.93 ... 

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... 

Poison-resistant Catalyst for Automotive Emission Control... 

One paper [89] showed the potential of microporous catalytic membranes in poison resistant hydrogenation catalysis. 

S.H. Oh and J.C. Cavendish, Design aspects of poison-resistant automobile monolithic catalysts, lEC Prod. Res. Dev. 22 509 (1983). 

A reduction of the present levels of CO2 in the atmosphere has become a subject of increasing concern as regard the environmental pollution problem. Beside other choices currently under consideration its catalytic transformation at point sources, by hydrogenation into more valuable products (e.g. methanol), has been found particularly attractive. To this end, both commercial and novel (poison-resistant) types, among which supported catalysts based on Pd and other noble metals are gaining acceptance [1] and are now under scrutiny. 

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