NO and NO2 Adsorption on Al2O3 and Ga Modified Al2O3 Surfaces: A Density Functional Theory Study

摘要

Al2O3 and its supported metal catalysts are widely used in deNO_x catalysis, but the true nature of the catalytic sites and the structure-activity relationships are still unclear. By a set of systematic and comparative calculations, this study investigates the adsorption of NO and NO2, and nitrate formation via the oxidation of NO on Al2O3 and Ga modified Al2O3 surfaces using density functional theory. It is found that NO_x gases (NO and NO2) preferentially adsorb on (110) planes, and are oriented in different configurations. While NO bonds with the (110) surfaces through an N-down orientation, the most stable mode of adsorption of NO2 on the (110) surfaces is a bidentate configuration, causing much higher net charge transfer from the surface and noticeable elongation of the N-O bond. Both the NO and NO2 adsorption and activation are promoted on the Ga modified Al2O3 (110) surface. Moreover, the activation energy barrier for nitrate formation via NO oxidation, a process crucial for the selective catalytic reduction of NO_x, is about 35% less on the Ga modified Al2O3 (110) surface compared to the pristine Al2O3 (110) surface. This is one of the reasons for the high activity of Ga2O3-Al2O3 catalyst for the selective catalytic reduction of NO_x.