Al 2 O 3 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 NO 2, and nitrate formation via the oxidation of NO on Al 2 O 3 and Ga modified Al 2 O 3 surfaces using density functional theory. It is found that NO x gases (NO and NO 2 ) 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 NO 2 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 NO 2 adsorption and activation are promoted on the Ga modified Al 2 O 3 (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 Al 2 O 3 (110) surface compared to the pristine Al 2 O 3 (110) surface. This is one of the reasons for the high activity of Ga 2 O 3 −Al 2 O 3 catalyst for the selective catalytic reduction of NO x .
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Liu et al. (2010) studied this question.