Heterogeneity on Metal Surfaces

Hydrogen adsorption rates on copper catalysts at 1 atmosphere. 

The data illustrated in the two diagrams are evidence that the same phenomenon of desorption and readsorption is found with copper catalysts, either supported or essentially pure metal, as is found with the oxides. 

With doubly-promoted iron synthetic ammonia catalysts the same type of observations are repeated. Data on desorption and readsorption are shown in Fig. 7, while in Fig. 8 are the values obtained on raising and lowering the temperature. It will be noted that the latter curves do not show the double maxima at —78 and 110 C. earlier found by Brunauer and Emmett (10) and examined by them in detail as types A and B adsorption. 

Isobaric hydrogen adsorption on iron CF 413-9 at 1 atmosphere. O Raising temperature A Lowering temperature 

The present curve does not show the maximum found by the previous authors at — 78°C. Private communication from Dr. Paul Emmett indicates that the possible explanation for this is that the reduction procedure here employed may have failed to reduce the iron in those areas where the low temperature chemisorption of hydrogen occurs. According to Emmett these areas are only uncovered by reduction at around 500 C. in a rapid stream of hydrogen freed from oxygen and well dried before passing into the reduction zone. The data in Fig. 7 do, however, show that from room temperature upwards there is alwa s evidence of desorption on raising the temperature followed by readsorption, and the 

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