Jianlin Deng

Elucidation of the high CO2 reduction selectivity of isolated Rh supported on TiO2: a DFT study

Methanation and reverse water-gas shift reaction are two important reactions that could happen simultaneously during the process of CO2 reduction. Exploiting new catalysts with high selectivity towards one single process is highly desirable. It has been shown that isolated-Rh/TiO2 can selectively generate CO rather than CH4. A molecular level understanding would provide more insight into catalyst design for CO2 reduction. In the present contribution, the density functional theory method was employed to study the CO2 reduction reaction by H2 based on a Rh1/TiO2 (101) model. The co-adsorbed CO2 and H2 on the Rh atom can react with each other to form CO. The inhibition of further H2 adsorption on the CO pre-adsorbed Rh atom stops the following sequential hydrogenation of CO. This can explain the experimentally observed high selectivity of Rh1/TiO2 to CO. Different co-adsorption properties can be understood by the frontier orbital charge density symmetry matching principle. The same method has been extended to other metal systems (Ru, Pd and Pt) to identify candidate catalysts with high selectivity for CO2 reduction. Similar adsorption properties of isolated Pd with Rh may induce high selectivity towards CO. These results are expected to provide a prediction to find new selective catalysts for CO2 reduction.

Selective catalytic reduction of NO with NH3 over Mo–Fe/beta catalysts: the effect of Mo loading amounts

A series of Mox–Fe/beta catalysts with constant Fe and variable Mo content were synthesized and investigated for selective catalytic reduction (SCR) of NOx with NH3. It was found that the Mo0.2–Fe/beta catalyst exhibited excellent activity, N2 selectivity and preferable resistance to H2O and SO2. The Mox–Fe/beta catalysts were characterized by various analytical techniques. TEM and SEM images showed that the addition of Mo could enhance the dispersion of iron oxides. The results of NH3-TPD and Py-IR indicated that the introduction of Mo resulted in a change of Bronsted acidity, which was associated with high-temperature SCR activity. XPS and XANES results showed that the introduction of Mo resulted in a change of Fe2+ content, which determined the low-temperature activity. DFT calculations showed the strong effects of Mo on the crystal structure, charge distribution and oxygen vacancy formation energy of iron oxides, which further explained the role of Mo in the catalyst behaviors during the SCR process.

Facet-dependent photocatalytic decomposition of N2O on the anatase TiO2: a DFT study

The photocatalytic N2O dissociation on anatase TiO2 is an attractive reaction and the mechanism of the photocalytic process, the role of excited electrons, and the favorable facet for higher activity need a more detailed study at the molecular level. Using DFT + U calculations, we investigate the dissociation process of N2O into N2 with and without photoexcited electrons on anatase TiO2 (001) and (101) facets to unravel such puzzles. The optical absorption properties of TiO2 (001) and (101) facets are compared in combination with electronic analysis. The localization of excited electrons on the two surfaces with the existence of oxygen vacancies is explored. When there is no photo-excitation, on a perfect TiO2 surface, N2O decomposition is difficult due to the inhibitive high reaction energy. In contrast, the reaction energy decreases dramatically in the presence of photoexcited or excess electrons on the TiO2 surface. The reaction energy is related to the electronic state of dissociated O. The more negative charges make O more stable, and accordingly lead to higher exothermic reaction energy. Based on this point, the influence of surface morphology and excited states can be understood. This is the first theoretical study of the photocatalytic process of N2O elimination, which will guide further experimental study and improve its activity.

Unraveling the structure–sensitivity of the photocatalytic decomposition of N2O on CeO2: a DFT+U study

The photocatalytic activity of N2O dissociation on CeO2 strongly depends on the exposed surface termination, with the (110) surface being much more reactive than the (111) surface. However, the physical nature requires a more detailed molecular level study. Using the DFT+U method, in the present study, we intend to explore the influence of surface termination from the following three aspects: the optical absorption, transfer kinetics of electron polaron, and the photo-chemical reaction process based on comparative studies of CeO2 (111) and (110) model surfaces. Due to the large band gap value, both CeO2 surfaces show negligible optical absorption difference. For both surfaces, the electron polaron is preferably localized on the surface rather than in the bulk. The Ce3+ ion close to the oxygen vacancy repels the excited electron due to Coulomb interactions. The migration barrier of the electron polaron from the bulk to the surface on the (110) surface is slightly lower than that on the (111) surface, suggesting a higher transfer rate of the electron polaron. The dissociation process of N2O into N2 with and without the photoexcited electron on CeO2 (110) and (111) surfaces is explored. On the stoichiometric CeO2 surface, N2O decomposition is difficult due to the inhibitive high reaction energy. In contrast, the reaction energy dramatically decreases in the presence of photoexcited or excess electrons on the CeO2 surface. The reaction energy is related to the electronic state of dissociated O. More negative charges make O more stable and accordingly lead to higher exothermic reaction energy.