Mesoporous Ceria-Supported Gold Catalysts Self-Assembled from Monodispersed Ceria Nanoparticles and Nanocubes: A Study of the Crystal Plane Effect for the Low-Temperature Water Gas Shift Reaction

Physical and Chemical Synthesis of Au/CeO2 Nanoparticle Catalysts for Room Temperature CO Oxidation: A Comparative Study

In many heterogeneous catalytic reactions, such as low-temperature CO oxidation, the preparation conditions, and the role of the CeO2 support (oxygen vacancies and redox properties) in the dispersion and the chemical state of Au, are considered critical factors for obtaining gold nanoparticle catalysts with high catalytic performance. In this work, the physical and chemical preparation methods were compared, aiming at understanding how the preparation method influences the catalytic activity. The Au/CeO2 nanoparticle catalysts with 5% Au loading were prepared via the Physical Laser Vaporization Controlled Condensation method (LVCC), and the chemical Deposition-Precipitation method (DP) was used to investigate the effect of synthesis methods on the structure and the catalytic activity toward the CO oxidation. In this manuscript, we compare the activity of nanostructured Au/CeO2 catalysts. The structure and the redox properties of the catalysts were investigated by the XRD, SEM, TEM, TPR, and XPS. The catalytic activity for low-temperature CO oxidation was studied using a custom-built quartz tube flow reactor coupled with an infrared detector system at atmospheric pressure. The study reveals that the prepared CeO2-supported Au nanoparticles’ catalytic activity was highly dependent on the preparation methods. It showed that the sample prepared by the DP method exhibits higher catalytic efficiency toward CO oxidation when compared with the sample prepared by the LVCC method. The high catalytic activity could be attributed to the small particle size and shape, slightly higher Au concentration at the surface, surface-active Au species such as Au1+, along with the large interface between Au and CeO2. This study suggests that the stability, dispersion of Au nanoparticles on CeO2, and strong interaction between Au and CeO2 lead to strong oxidation ability even below room temperature. Considering the universal character of different physical and chemical methods for Au/CeO2 preparation, this study may also provide a base for supported Au-based catalysts for many oxidation reactions in energy and environmental applications.

Role of the Support in Gold-Containing Nanoparticles as Heterogeneous Catalysts

In this review, we discuss selected examples from recent literature on the role of the support on directing the nanostructures of Au-based monometallic and bimetallic nanoparticles. The role of support is then discussed in relation to the catalytic properties of Au-based monometallic and bimetallic nanoparticles using different gas phase and liquid phase reactions. The reactions discussed include CO oxidation, aerobic oxidation of monohydric and polyhydric alcohols, selective hydrogenation of alkynes, hydrogenation of nitroaromatics, CO₂ hydrogenation, C–C coupling, and methane oxidation. Only studies where the role of support has been explicitly studied in detail have been selected for discussion. However, the role of support is also examined using examples of reactions involving unsupported metal nanoparticles (i.e., colloidal nanoparticles). It is clear that the support functionality can play a crucial role in tuning the catalytic activity that is observed and that advanced theory and characterization add greatly to our understanding of these fascinating catalysts.

Comparison of the effects of the catalyst preparation method and CeO2 morphology on the catalytic activity of Pt/CeO2 catalysts for the water-gas shift reaction

The key factors (Pt⁰ dispersion & oxygen vacancies) should maintain high values to attain high catalytic activity and they are directly affected by the morphology and the preparation method of the catalyst.

Surfactant-Assisted Cooperative Self-Assembly of Nanoparticles into Active Nanostructures

Nanoparticles (NPs) of controlled size, shape, and composition are important building blocks for the next generation of devices. There are numerous recent examples of organizing uniformly sized NPs into ordered arrays or superstructures in processes such as solvent evaporation, heterogeneous solution assembly, Langmuir-Blodgett receptor-ligand interactions, and layer-by-layer assembly. This review summarizes recent progress in the development of surfactant-assisted cooperative self-assembly method using amphiphilic surfactants and NPs to synthesize new classes of highly ordered active nanostructures. Driven by cooperative interparticle interactions, surfactant-assisted NP nucleation and growth results in optically and electrically active nanomaterials with hierarchical structure and function. How the approach works with nanoscale materials of different dimensions into active nanostructures is discussed in details. Some applications of these self-assembled nanostructures in the areas of nanoelectronics, photocatalysis, and biomedicine are highlighted. Finally, we conclude with the current research progress and perspectives on the challenges and some future directions.

An eco-friendly route for template-free synthesis of high specific surface area mesoporous CeO2 powders and their adsorption for acid orange 7

An eco-friendly route was developed for the synthesis of mesoporous CeO₂ powders without any additional template. The original cerium precursors were separated from Ce³⁺ aqueous solution by (NH₄)₂CO₃ or Na₂CO₃via a chemical precipitation method, then H₂O₂ was introduced to induce the phase transformation from original cerium precursors to CeO₂ precursors with initial porous structures, finally the crystallinities of CeO₂ precursors were improved by a hydrothermal treatment, meanwhile the mesoporous structures of final CeO₂ powders were formed. The BET surface areas of mesoporous CeO₂ powders synthesized using (NH₄)₂CO₃ and Na₂CO₃ as precipitants were 106.1 and 76.9 m² g⁻¹, respectively. Moreover, a mesoporous CeO₂ sample with BET surface area of 100.0 m² g⁻¹ was also synthesized using commercial Ce₂(CO₃)₃·xH₂O as an existing cerium precursor under the same conditions as control, which could shorten experimental processes and reduce costs. The oxidation-induced phase transformation from original cerium precursors to CeO₂ precursors with initial porous structures was the precondition for further forming of mesoporous structures of final CeO₂ powders during the hydrothermal process. These mesoporous CeO₂ powders showed the rapid and effective adsorption for acid orange 7 dye from simulated wastewater without pH pre-adjustment at room temperature. Furthermore, the adsorption capacities of these mesoporous CeO₂ powders for removal of acid orange 7 dye were determined according to the Langmuir linear fits.

An eco-friendly route for template-free synthesis of mesoporous CeO₂ powders with high specific surface areas.