Characterization of the Pd-O Bond Strength

3 Characterization of the Pd-O Bond Strength - It is generally agreed that at least two types of PdO species may exist under methane oxidation conditions  

The presence of two distinct states of Pd has also been demonstrated by TPR studies which usually show two or more H2 consumption peaks. The consumption peak observed below room temperature has been ascribed to the reduction of bulk PdO clusters, while consumptions at higher temperatures have generally been related to metal-support interactions. The negative peak typically observed near 60 °C is due to H2 release from the decomposition of P Pd-hydride. TPR has been used to correlate the amount of H2 consumption with methane oxidation activity. It has been observed that the fresh catalyst that exhibited low activity had a H2/Pd ratio of 0.3. As the catalyst activated and reached its maximum rate the H2/Pd ratio increased to 1.6, and finally after 7 h on stream the partially deactivated catalyst exhibited a H2/Pd ratio of 1.25. 

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