Palladium oxidative redispersion

It is usually difficult to discuss unambiguously on the role of the formation of sulphate, which may explain the deactivation. Their formation can equally occur on the support and on the noble metals. The poisoning effect of S02 has been reported by Qi el al. on Pd/Ti02/Al203 [112], However, in the presence of water, the stabilisation of hydroxyl groups could inhibit the adsorption of S02 [113], Burch also suggested a possible redispersion of palladium oxide promoted by the formation of hydroxyl species [114], Such tentative interpretations could correctly explain the tendencies that we observed irrespective to the nature of the supports, which indicate an improvement in the conversion of NO into N2 at high temperature. Nevertheless, the accentuation of those tendencies particularly on prereduced perovskite-based catalysts could be in connection with structural modifications associated with the reconstruction of the rhombohedral structure of... 

The oxidative redispersion of 2-3 nm palladium particles was achieved with NO acting as oxidant and complexing agent at room temperature [142] (see Sect. 3.1.2), and rhodium particles in Y zeolite were disrupted and redispersed into Rh (CO)2 species by CO adsorption at room temperature [143] (see Sect. 3.1.3). 

Based on the above results, we have proposed a classical Chalk-Harrod-like mechanism for the Pd nanocluster catalyzed reaction (Scheme 3.10). " The first step involves the reduction of Pd(OAc)2 to zero-valent palladium nanoparticles followed by stabilization with a polysiloxane network. These particles followed the conventional pathway of oxidative-addition and reductive-elimination cycles to generate sUyl esters. After the transformation was over, these palladium colloids precipitated out of the solution as a black solid supported on a polysiloxane network. The presence of the soluble polysiloxane matrix, which was not fully condensed in the form of silica, allows particle redispersion— thus allowing particles to be reused as catalyst... 

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