Fig. 6. DFT calculations on Pd/ZnO catalysts. (a) Energy diagrams for the semi-hydrogenation of C2H2 into C2H4 and the further hydrogenation into byproduct C2H6 on the surfaces of 50-Pd/ZnO, 150-Pd/ZnO, and 300-Pd/ZnO catalysts. The horizontal axis shows the reaction intermediates and transition states (TSs), and the vertical axis shows the relative energy of each state. (b and c) Isosurfaces (level 0.005) of charge density differences on Pd/ZnO catalysts with (b) C2H2 and (c) C2H4. (d) Dissociation of H2 and (e) migration of active *H on the surfaces of different Pd/ZnO catalysts.
