Artículos SCI

The reaction mechanism of the reverse water gas shift (RWGS) reaction was investigated using two commercial gold-based catalysts supported on Al2O3 and TiO2. The surface species formed during the reaction and reaction mechanisms were elucidated by transient and steady-state operando DRIFTS studies. It was revealed that RWGS reaction over Au/Al2O3 proceeds through the formation of formate intermediates that are reduced to CO. In the case of the Au/TiO2 catalyst, the reaction goes through a redox mechanism with the suggested formation of hydroxycarbonyl intermediates, which further decompose to CO and water. The Ti-3+ species, the surface hydroxyls, and oxygen vacancies jointly participate. The absence of carbonyl species adsorbed on gold particles during the reaction for both catalysts indicates that the reaction pathway involving dissociative adsorption of CO2 on Au particles can be discarded. To complete the study, operando ultraviolet visible spectroscopy was successfully applied to confirm the presence of Ti3+ and to understand the role of the oxygen vacancies of TiO2 support in activating CO2 and thus the subsequent RWGS reaction.

The rapid mechanochemical synthesis of nanocrystalline CuFeS2 particles prepared by high-energy milling for 60 min in a planetary mill from copper, iron and sulphur elements is reported. The CuFeS2 nanoparticles crystallize in tetragonal structure with mean crystallite size of about 38 ± 1 nm determined by XRD analysis. HRTEM study also revealed the presence of nanocrystals with the size of 5–30 nm with the tendency to form agglomerates. The Raman spectrum confirms the chalcopyrite structure. Low temperature magnetic data for CuFeS2 support the coexistence of antiferromagnetic and paramagnetic spin structure. Moreover, the hysteresis loops taken at temperatures from 5 K to 300 K revealed a presence of very small amount of ferromagnetic phase, which seems to be associated with the non-consumed elemental Fe in as-prepared nanoparticles. The optical band gap of CuFeS2nanoparticles has been detected to be 1.05 eV, larger than band gap of the bulk material. The wider gap possibly resulted from the nano-size effect. Photoresponses of CuFeS2nanoparticles were confirmed by I-V measurements under dark and light illumination. It was demonstrated that mechanochemical synthesis can be successfully employed in the one step preparation of nanocrystalline CuFeS2 with good structural, magnetic, optical and electrooptical properties.