Fig. 3: Oxides and metal.
From: Operando probing of the surface chemistry during the Haber–Bosch process
Owing to trace contaminations in the gases, the surfaces can form oxides. a, Two cases in which a thick oxide forms at low temperatures and 500 mbar in a 1:3 N2:H2 gas mixture, but the oxide thins and disappears as the temperature increases. The grey rectangle shows the region in which iron oxide peaks are present. b, The ratio of oxide to metal as a function of pressure and temperature for the Fe catalysts. The Fe(110) is grey, whereas the Fe(210) is blue. The solid line shows the lower-pressure data at 200 mbar, whereas the dashed line is the higher-pressure data at 500 mbar; at no point was the Ru catalyst oxidized. c, Example spectra of the metal peaks during NH3 formation at 623 K, showing a singular metallic peak for all catalysts. a.u., arbitrary units.
