Effect of the Preparation Method on the Physicochemical Properties and the CO Oxidation Performance of Nanostructured CeO2/TiO2 Oxides

Abstract

Ceria-based mixed oxides have been widely studied in catalysis due to their unique surface and redox properties, with implications in numerous energy- and environmental-related applications. In this regard, the rational design of ceria-based composites by means of advanced synthetic routes has gained particular attention. In the present work, ceria–titania composites were synthesized by four different methods (precipitation, hydrothermal in one and two steps, Stöber) and their effect on the physicochemical characteristics and the CO oxidation performance was investigated. A thorough characterization study, including N2 adsorption-desorption, X-ray diffraction (XRD), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM/EDS), transmission electron microscopy (TEM) and H2 temperature-programmed reduction (H2-TPR) was performed. Ceria–titania samples prepared by the Stöber method, exhibited the optimum CO oxidation performance, followed by samples prepared by the hydrothermal method in one step, whereas the precipitation method led to almost inactive oxides. CeO2/TiO2 samples synthesized by the Stöber method display a rod-like morphology of ceria nanoparticles with a uniform distribution of TiO2, leading to enhanced reducibility and oxygen storage capacity (OSC). A linear relationship was disclosed among the catalytic performance of the samples prepared by different methods and the abundance of reducible oxygen species.

Synthesis and Characterization of B/NaF and Silicon Phthalocyanine-Modified TiO2 and an Evaluation of Their Photocatalytic Removal of Carbamazepine

“…The adsorption isotherms reported in Figure 3 can be classified as type IV [35,36], with the H3 hysteresis loop indicating the existence of mesopores [36], as supported by Figure S9 for both B/NaF-TiO 2 and B/NaF-TiO 2 -SiPc catalysts. The isotherm of pure TiO 2 showed a limited adsorption with respect to the others, indicating a smaller surface area and negligible porosity.…”

“…Such additional defects may be responsible for the existence of new weakly bound surface oxygen species not available in pure TiO 2 . TiO 2 , as studied thoroughly in the literature, revealed O1s signals at 529 and 531 eV attributed to Ti-O and -OH groups respectively[6,30,36].…”

“…From the TEM images of synthesized catalysts reported in the Figure 5, all samples show similar morphologies: the sizes of primary particles are in the range 20-50 nm (Table 1), though B/NaF-TiO2 reveals in some cases large spherical nanoparticles of sometimes more than 200 nm in diameter as well. The nanoparticles appear randomly more spherical in the case of B/NaF-TiO2, whereas B/NaF-TiO2SiPc shows nanopolyhedral shape [35,36]. However, pure TiO2 is clearly of a bulkier nature consisting of much larger and more agglomerated particles.…”

“…Concerning the co-doping effects, the use of boron does not affect the photocatalytic activity of pristine TiO 2 , thereby reducing the band gap, as it does not overlap the conduction band of TiO 2 [6,41], but it may instead affect the TiO 2 structure, leading to an increase in specific surface area. Such B-induced structural local disordering may increase also the defect population with a consequent positive effect on photocatalytic properties [36,41]. On the other hand, a fluorine atom can replace the oxygen atom of titanium dioxide, creating surface oxygen defects and vacancies that possibly trigger electron/hole recombination [3,6].…”

Immobilized TiO2/ZnO Sensitized Copper (II) Phthalocyanine Heterostructure for the Degradation of Ibuprofen under UV Irradiation

“…In many cases of heterogeneous environmental catalysts, modifications are needed in order to improve their activity, stability, selectivity, working window, or the overall performance. This is achieved via compositional changes i.e., impregnation with an active or synergistic metal/oxide phase, doping or modifications in composition [10][11][12] or even structural changes via synthesis methods introducing a specific nanostructure [12][13][14]. In both strategies, the aim is to improve materials physicochemical properties crucial for a better catalytic performance.…”