Restructured surface

The surface structure in Fig. 12e, obtained after annealing at 710 K in 1x10-6 mbar 02, shows the presence of (1x2) strands on otherwise flat, (1x1) terminated surfaces. This is in agreement with Onishi and Iwasawa s results described above [99]. From atomically-resolved images of strands connected to rosettes as well as UHV annealing experiments of restructured surfaces it has been shown that these strands also have the Ti203 structure depicted in Fig. 11 [98]. 

Surface Science of Ammonia Synthesis Structure Sensitivity of Ammonia Synthesis Kinetics of Dissociative Nitrogen Adsorption Effects of Aluminum Oxide in Restructuring Iron Single-Crystal Surfaces for Ammonia Synthesis Characterization of the Restructured Surfaces Effect of Potassium on the Dissociative Chemisorption of Nitrogen on Iron Single-Crystal Surfaces in UHV... 

Characterization of the Restructured Surfaces The observation that the AlfOv/Fe(l 10) and Al,Oy/Fe(100) become as active as the Fe(l 11) surface for ammonia synthesis suggests that new crystal orientations are being created upon restructuring the Al,Ov/Fe(l 10) and Al,0v/Fe(100) surfaces in water vapor. A sug-... 

The clean Fe(llO), Fe(lOO), and Fe(lll) surfaces restructured with 20ton of water vapor produce the same TPD spectra as the Al O restructured surfaces. Deactivation of the (100) and (110) clean restructured iron surfaces is rapid under the conditions of ammonia synthesis, and the P2 peaks become equivalent in intensity to those on the respective clean surfaces within one hour of ammonia synthesis. 

To realize fully the promotional effects of potassium and aluminum oxide, the promoters must be added at different times during the preparation of the active catalyst. " In Fig. 4.27, the partial pressure of ammonia in the reaction loop versus the time of reaction for clean Fe(lOO), restructured Alj,O /Fe(100), and restructured 0.25 MLK/25% Al O /Fe(100) where the potassium was added after the restructuring procedure is plotted (see the figure for conditions). The restructured Al ,Oy/Fe(100) surface with 0.25% Al O is about one order of magnitude more active than the clean Fe(lOO) surface when the surface areas of the samples are taken into account. The addition of 0.25 MLK to a restructured Al O /Fe(100) surface increases the activity of the restructured surface twofold at an ammonia partial pressure of 20torr. Thus the restructured 0.25 MLK/25% Alj Oy/Fe(100) surface is now 20 times more active than the clean Fe(lOO) surface. The only way to achieve this level of enhancement is to restructure the surface in the presence of aluminum oxide alone, and then to add the potassium. 

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