Abstract
Previous reports usually co-doping various additional transition metals to improve the NH3-SCR performance of V/TiO2 catalyst. However, seldom work understood the so-called enhancement from an atom scale. This work first selected nine elements (Me) mainly from a same VIB family or a same fourth period, and compared them in transition states of MeV/TiO2 during NH3-SCR. The dehydrogenation step of adsorbed NH3 resulted to be the key step and W substitution got the lowest dehydrogenation energy of 1.29 eV. After estimating the key atoms, the total width of Me-O-V hybridization followed the order of 1.7 eV (WV/TiO2) > 1.3 eV (V/TiO2) > 1.1 eV (CoV/TiO2) > 0.9 eV (LaV/TiO2). The deeper hybridization was attributed to a shorter Me-O-V bond. Both V and W were in a high-spin state while Co and La were in a low-spin state. Moreover, W atom had four semi full d orbitals, bigger than that (three) of V, which were more conducive to electron transfer, and resulting in the biggest overlapping of atomic orbitals. The above prediction was consistent with the afterward experimental result, in which MeV/TiO2 showed a NH3-SCR conversion order of 81 % (WV/TiO2) > 59 % (V/TiO2) > 41 % (CoV/TiO2) > 2 % (LaV/TiO2) at 300 °C. The main result of this work is in favor of designing an effective catalyst from the atom scale.
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