Nanostructured Ceria-Based Materials: Effect of the Hydrothermal Synthesis Conditions on the Structural Properties and Catalytic Activity

Abstract

Abstract:In this work, several nanostructured ceria catalysts were prepared by means of a hydrothermal procedure, in which the synthesis conditions (i.e., temperature and pH values) were varied. CeO 2 samples of different shapes and structural properties were obtained, namely cubes, rods, cube and nanorod mixtures, and other polyhedra. The prepared materials were tested using four probe catalytic reactions: CO oxidation, NO oxidation, NO x -free soot oxidation, and NO x -assisted soot oxidation. The physicochemical properties of the prepared catalysts were studied by means of complementary techniques (i.e., XRD, N 2 -physisorption at −196 • C, CO-TPR (temperature-programmed reduction), field emission scanning electron microscopy (FESEM), micro-Raman spectroscopy). The abundance of defects of the catalysts, measured through in-situ Raman spectroscopy at the typical temperatures of each catalytic process, was correlated to the CO and NO oxidation activity of the prepared catalysts, while the soot oxidation reaction (performed in loose conditions), which was hindered by a poor soot-catalyst contact, was found to be less sensitive to the observed structural defects.

Recent Advances on the Rational Design of Non-Precious Metal Oxide Catalysts Exemplified by CuOx/CeO2 Binary System: Implications of Size, Shape and Electronic Effects on Intrinsic Reactivity and Metal-Support Interactions

“…Based on a thorough in situ and ex situ characterization study, a perfect relationship between the CO oxidation performance and the following parameters was disclosed: (i) Relative population of Cu + /Ce 3+ redox pairs, (ii) abundance of loosely bound oxygen species, expressed in terms of surface-to-bulk oxygen reducibility, (iii) relative concentration of oxygen vacancies, evidenced by the ID/IF2g Raman ratio (Figure 7c) [115]. Similar conclusions in relation to the key role of ceria morphology in the CO oxidation activity have been reported by several groups [117,134,154,158,210,212,[229][230][231], most of these revealing the superiority of nanorods.…”

“…There are several synthetic approaches for the preparation of ceria nanoparticles, including precipitation [119][120][121], thermal decomposition [121,122], template or surfactant-assisted method [123][124][125][126], microwave-assisted synthesis [127][128][129], the alcohothermal [124,130] or hydrothermal [121,124,[131][132][133][134][135] method, microemulsion [133,136,137], solution combustion [138,139], sol-gel [140][141][142], sonochemical [143,144], etc. However, not all methods lead to particles of well-ordered size and shape with uniform dispersion on the catalyst surface [145].…”

“…However, not all methods lead to particles of well-ordered size and shape with uniform dispersion on the catalyst surface [145]. Among the different methods, the hydrothermal one has attracted considerable attention, due to the simplicity of the precursor compounds used, the short reaction time, the homogeneity in morphology, as well as the acquisition of various nanostructures, such as rods, polyhedra, cubes, wires [107,117,121,124,131,134,135,[146][147][148][149][150][151][152][153][154][155][156][157][158][159]. Ceria nanocrystals have three low-index lattice facets of different activity and stability, namely, {100}, {110}, {111} [48,106], as shown in Figure 6.…”

Nanostructured Equimolar Ceria-Praseodymia for Total Oxidations in Low-O2 Conditions

“…In fact, cerium's ability to easily change its oxidation state from Ce 4+ to Ce 3+ is associated with a high Oxygen Storage Capacity (OSC), i.e., the possibility of releasing oxygen species, which can be exploited to oxidize different pollutants (e.g., CO or soot). Moreover, ceria nanoparticles with tailored shape can be obtained by tuning the synthesis conditions [12]. The morphology plays a key role in defining ceria activity, because it affects not only the specific surface area and exposed crystal planes, but also the type and quantity of solid-solid contact points in the case of the soot oxidation [12][13][14][15].…”

Comparative Study Between Aluminum Monolith and Foam as Carriers for The Intensification of The CO Water Gas Shift Process

“…However, LTS catalysts are only active in a reduced range of temperatures and present serious problems of pyroforicity [30]. On the other hand, noble metal-based formulations seems to be the best alternative [31]; good results have been obtained with the use of platinum supported on reducible oxides such as ceria [32,33]. Furthermore, the use of highly active catalytic formulations at intermediate temperatures allows for hypothesizing their use in a single stage process [34].…”