Poisoning conclusions

Ammonia seems to be too strong a base if specific adsorption is required. A characterization of the chemical nature and a determination of the number of catalytically active sites by means of poisoning experiments with ammonia will, therefore, not readily be possible. Ammonia can thus not be recommended as a simply acting specific poison. Conclusive results may, however, be obtained by stepwise poisoning, adding successive small quantities of ammonia, provided that the modes of interaction with the catalyst of this ammonia are controlled by spectroscopic techniques under the reaction conditions. 

In line with the conclusions derived in the model study10), the effect of solvent on initiator reactivity can also be explained on the basis of halogen polarizability in MeX. A detailed discussion of these trends is given in Section VIII. Mel is a poison in isobutylene polymerization. The poisoning activity of Mel will be discussed in Section VII. 

An increase in urinary coproporphyrin has long been recognized in workers and children with lead poisoning and used as an indicator of excessive exposure to lead (EPA 1986a). EPA (1986a) identified a LOAEL for elevated coproporphyrin at a PbB level of 40 pg/dL for adults and 35 pg/dL for children, but did not present the basis for this conclusion. 

Silvestri, Naro, and Smith 142) have shown that cyclization reactions are strongly poisoned by adsorbed sulfur, although the activity for olefin formation was not much affected. This agrees with the conclusions of Shephard and Rooney 136). 

As mentioned above, to apply to insects a conclusion drawn directly from tests on mammals may sometimes be misleading.3 For instance, American cockroaches have a remarkably high tolerance for acetylcholine,4 but, on the other hand, a substance showing some of the pharmacological properties of acetylcholine does accumulate in flies and cockroaches poisoned with D.D.T. Similarly, Hopf, working with locusts, was unable to demonstrate any increase in toxicity of eserine or T.E.P.P. resulting from the subsequent injection of acetylcholine. From this, Lord and Potter infer that acetylcholine may not be directly involved in the insecticidal action of organo-phosphorus compounds, either because the enzymes which hydrolyse acetylcholine are not inhibited to any considerable extent in vivo or because the functions performed by acetylcholine in mammals are performed by another substance in insects. 

Sinee water was shown to be a poison for Cu-ZSM-5, it is espeeially important to examine the effeet of water vapor on the activity of Cu-Al-MCM-41 in NO-SCR. A full study is currently undertaken in our laboratory. Figm-e 35 shows the dynamie effeet of introdueing 10% H2O in the feed, on eatalytic activity at 400 °C. The deerease in NO eonversion was sensible but still not very high and by sequential suppression of the water in the gas feed the effect was found to be reversible. The low and reversible deactivation by water vapor during NO-SCR is also signifieant for potential commereial application of these new eatalysts. The surface chemistry of the support, its hydrophilieity, will require investigations before any definitive conclusion can be made. 

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