Tuning the band gap of M-doped titanate nanotubes (M = Fe, Co, Ni, and Cu): an experimental and theoretical study.

Herein, we report a systematic experimental and theoretical study about a wide-ranged band gap tuning of protonated titanate nanotubes H2Ti3O7 (Ti-NT) by an easy ion-exchange method using a low concentration (1 wt%) of transition metal cations. To characterize and describe the effect of M doping (M = Cu2+, Ni2+, Co2+, and Fe3+) on the electronic, optical and structural properties, semiconductors were analyzed by a combination of experimental methods and density functional theory (DFT) calculations. The nanotube band gap can be modified from 1.5 to 3.3 eV, which opens the possibility to use them in several optoelectronic applications such as photocatalysts under solar light irradiation.

Dry reforming of methane over nickel supported on Nd-ceria: enhancement of the catalytic properties and coke resistance.

Nickel (5 wt%) supported on Nd-doped ceria was studied as catalysts in the DRM reaction at stoichiometric conditions in the range of 600-800 °C. Ce1-x Nd x O2-δ supports with different Nd contents (x = 0, 0.05, 0.1 and 0.2) were successfully synthesized. The role of oxygen vacancies by the incorporation of Nd3+ into the ceria lattice was investigated. These species were quantified by XRD and Raman spectroscopy, showing a linear dependence as a function of Nd content. Ni/Nd-ceria catalysts were prepared by wet impregnation. Although formation of oxygen vacancies, as well as microstructural features of the support (smaller crystallite sizes, higher surface area, and developed mesoporous structure) were improved as a function of the Nd content, no significant differences were observed in the catalytic properties of Ni/Nd-ceria in the DRM reaction. Despite this, compared to undoped ceria, all the Nd-doped CeO2 catalysts present an enhanced activity and stability, and the best catalytic performance was observed in the Ni/Ce0.95Nd0.05O2-δ sample. Quantification of carbon residues in spent catalysts showed, as expected, lower amounts in the Ni/Nd-ceria samples; nevertheless, among them, the catalyst with the higher amount of oxygen vacancies, is the one with the higher carbon residues. Incorporation of Nd in ceria changes the acid/base properties, diminishing the gasification capacity of the carbonaceous species. These results emphasize that the activity and stability in the Ni/Nd-ceria catalysts for the DRM reaction depend on two key factors, the redox and the acid/base properties of the CeO2 supports, offering insights about the necessary and adequate balance between these properties.