Water evolved during catalyst reduction

One of the most important variables in the TPD of CO from a supported Pt catalyst is the sample pretreatment. Calcination at 500°C for one hour followed by reduction is the conventional method to obtain the maximum exposed Pt and this follows closely to refinery practice for start-up and regeneration of commercial catalysts. The final step in our case was a 600°C He sweep for 30 minutes to ensure a fully dehydrated catalyst up to this temperature so that no water evolved during the subsequent TPD. We had previously observed that a high temperature He sweep could reduce the Pt catalyst without a prior H reduction presumably by the decomposition of the Pt oxide. 

The composition of the catalyst can affect its performance in many ways. For example, changes in the formulation to lower the amoimt of hydrogen sitl-fide evolved during reduction led to a significant physical weakening of the catalyst, which became much more prone to damage caused by the condensation of water or contamination by potash. Any water that condensed ditring plant start-up could also wash out any soluble chromium and lead to loss of stability. Most problems led to an increase in pressure drop or maldistribution of gas. Cat... 

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