Adsorption of CO <sub>2</sub> on Amorphous and Crystalline Zirconia: A DFT and Experimental Study
Tatsuya Joutsuka, Shohei Tada
Abstract
Herein, we study the structural and electronic origins of molecular adsorption using experiments and density functional theory (DFT) calculations. We performed X-ray diffraction (XRD) and temperature-programmed desorption (TPD) of CO 2 on amorphous zirconia ( am -ZrO 2 ) and crystalline (tetragonal and monoclinic) zirconia. Using molecular dynamics simulations, the bulk structures of am -ZrO 2 and am -zirconium(IV) hydroxide ( am -Zr(OH) 4 ) were obtained and the reproducibility of the experimental structure was confirmed by comparing the radial distribution functions. In addition, the hydroxyl density on the hydrogenated ZrO 2 surfaces was found to be consistent with the experimental results. Both experiments and simulations indicate that the adsorption of CO 2 on an am -ZrO 2 surface is more heterogeneous and weaker than that on a crystalline zirconia surface. Because the charge environment and band structures of crystalline zirconia are approximately the same as those of am -ZrO 2, the weak adsorption on the am -ZrO 2 surface arises from the fewer and stronger Zr–O bonds on the surface. These findings provide molecular-level insight not only for the adsorption of CO 2 but also into the molecular adsorption on ZrO 2 -based catalysts.