Speaker
Description
The adsorption of CO$_2$ on hematite α-Fe$_2$O$_3$(012) was investigated in ultra-high vacuum (UHV) using temperature-programmed desorption (TPD) and infrared reflection absorption spectroscopy (IRAS). CO$_2$ adsorption on this surface exhibits unusual behavior in TPD for coverages up to one molecule per unit cell (corresponding to 0.5 molecules per Fe$^{2+}$ cation). Two desorption features centered around 150 K, and 220 K increase concurrently with increasing coverage. IRAS measurements reveal that this behavior arises from the thermal activation of weakly bound, physisorbed CO$_2$ at temperatures above 100 K. Infrared bands in the carbonate region appear, indicating that activated CO$_2$ interacts with surface oxygen to form surface carbonate (CO$_3^{2-}$) species. This activation pathway directly competes with molecular desorption. By supplying CO$_2$ at temperatures just below the carbonate desorption temperature, enhanced surface carbonate coverages can be achieved. These findings contribute to our understanding of CO$_2$ activation on Fe$_2$O$_3$(012) and will be a prerequisite for surface reaction studies.