Preparation, Characterization And Properties Study Of Cerium Supported Au Nanoparticles

Catalysis using homogeneous and heterogeneous gold nanoparticles is a topic of much current interest. When the gold nanoparticles were supported on the metallic oxide to form the heterogengous gold catalysts, they can be used for a series of reactions, in which they performed excellent catalytic activity. The primary role of the support is to avoid coalescence and agglomeration of the gold nanoparticles. In addition, supports can go further than simple carriers and can play a direct or indirect role in gold catalyzed reactions. Among the various investigated metallic oxide supports, CeO2nanoparticles have performed as either good catalysts or supports for CO oxidation under low temperature. because of their high oxygen storage capacity (OSC), and the rich oxygen vacancies along with the low redox potential between Ce3+and Ce4+. CeO2nanoparticles have demonstrated a unique advantage to be adopted into many areas such as CO oxidation, Water-Gas shift reaction, and reducing the hydrocarbons and NOx and methanol cracking reaction. On the other hand however, as the supports, CeO2also has some drawbacks, such as the poor strength of the material and the relatively small surface area, which is the primary reason to limit its practical application. To overcome these problems, fabricating CeO2nanospheres, nanorods, particularly the nanotubes which have the hollow structure or regular nanopolyhedra can effectively improve the surface area of CeO2, therefore to increase its supporting capacity. Recently, great efforts have been made on the preparation of the CeO2supported Au nanoparticles as well as the catalytic mechanism. CeO2can avoid coalescence and agglomeration of the gold nanoparticles effectively, and to improve the catalytic capacity and stability of the catalyst greatly by activation of the surface oxygen of CeO2and the synergistic effect with the Au nanoparticles. In this work, we have studied the synthesis, structure and formation mechanism of two series of Au@CeO2nanoparticles. The catalytic performance and the catalytic mechanism have also been studied with CO oxidation reaction. 1、In situ growth of Au@CeO2core-shell nanoparticles and CeO2nanotubes from Ce(OH)CO3nanorodsWe synthesized the Au@CeO2core-shell nanoparticles supported on CeO2nanotubes through an in situ redox reaction between HAuCl4and Ce(OH)CO3, and systematically studied a series of impact factors that have influence on the size of gold particle and the morphology of CeO2nanotubes, such as reaction time, temperature, the kinds of deoxidizer and precursor and the concentration of HAuCl4·6H2O. Small gold nanoparticles located on regular CeO2nanotubes were obtained using Ce(OH)C03as precursor, and the HAuCl4·6H2O as deoxidizer to react for2hs under90℃. The reaction and the formation mechanism of the Au and CeO2nanoparticles were studied in detail. Subsequently, the CO oxidation reaction were carried out to examine the catalytic performance of the as obtained Au@CeO2nanocomposites, which demonstrate high catalytic activities and especially high stability during the recycling catalytic tests.2、Investigating catalytic performances of Au/CeO2nanocomposite with and without ascorbic acid along with the impact of different morphology of CeO2.We obtained CeO2nanoparticles, nanocubes and nanorods via hydrothermal method. After reduced by ascorbic acid, those three kinds of CcO2with different morphology were loaded by Au nanoparticles by a deposition-precipitation method (DP). In our study, the ingredients and the structure were tested via XRD, TEM and raman spectrum. It was also demonstrated that the Au/CeO2composite without ascorbic acid reducing has higher catalytic activities for CO oxidation. Obviously, those three reduced CeO2according to the catalytic capacity for CO oxidation performed as follow:CeO2nanoparticles> CeO2nanorods> CeO2nanocubes. While the other three without reducing by ascorbic acid performed that CeO2nanorods> CeO2nanoparticles> CeO2nanocubes. The principle was also explained why those different morphology have different performances in our experiment.