Nanoparticles selective poisoning

Different model reactions were used in order to study the interaction between the modifier and the parent metal. It was observed that an inert additive introduced by a redox reaction generally poisons, more or less, the activity of the parent metal or strongly modifies the selectivity of the reaction, which indicates a deposition of the additive on the parent metal. For example, a decrease in activity for structure insensitive reactions, such as toluene hydrogenation [41] or cyclohexane dehydrogenation [43, 78] proves the existence of bimetallic nanoparticles. Likewise, in the case of the 2,2-dimethylpropane reaction, the modification of both the selectivity and the apparent activation energy, demonstrates an interaction between Pd and Au introduced by direct redox reaction. Conversely, no modification was observed on the catalysts prepared by incipient wetness co-impregnation [75]. 

In conclusion, we have demonstrated the first example of Pd nanoparticles as a selective and recyclable catalyst for the alcoholysis of polyhydrosiloxane. Fair numbers of alcohols with diverse structures (primary, secondary, sterically bulky, and functionalized alcohols) were selectively and efficiently grafted onto the poly-siloxane backbone without any side reactions and under moderate reaction conditions. Additionally, active participation of Pd nanoclusters during the catalytic transformations was established by in situ EM analysis and controlled poisoning experiments. Moreover, a new approach for the synthesis and stabilization of Pd nanoclusters as a stable isolable powder and their redispersion in common solvents was presented. 

Size of nanoparticle strength of polymer/particle interaction polymer grafting density polymer chain length binding constant pH influence redox state selectivity toxicity poisoning agents... 

Poisoning open sites on metal nanoparticles provides a method to observe how the activity and/or selectivity changes as function of the degree of opeimess of the site. The next few examples illustrate how different poisoning experiments can provide information about the identity of the catalytic active site. 

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