The Preparation And The Reaction Of CO Oxidation Over The Supported Pt/Fe₂O₃ Catalyst

It has very good prospects for development and significance to eliminate CO at room temperature and humidity conditions by using precious metal catalyst in many aspects of military and civilian, and it can be important in catalysis applications, so at room temperature and humidity conditions to achieve elimination of CO oxidation has become an important research direction. Recent research has found that supported gold catalysts at low temperatures showed a high CO oxidation activity and resistance to water, but there are some deficiencies that when used in high temperature pretreatment and stored at room temperature even in the course of the reaction, gold particles are very prone to grow up together, it can be known that size effect made the catalytic activity decrease quickly. So based on this case, researchers began to study supported platinum-based catalysts. Now it has proved that platinum-based catalysts existed which had a good low-temperature CO oxidation catalytic performance, strong water resistance.In this paper, we continue to explore good catalyst for CO oxidation at low temperature. In previous work, it has found that Pt/Fe₂O₃ catalyst prepared by colloid deposition method at room temperature had good CO activity, and its water resistance and stability were better. The main result of this thesis work is to understand the structure and nature of the catalyst, active sites and reaction mechanism by means of various characterization of the catalyst. Because the catalyst particle size of platinum species have a great impact in the catalytic activity directly, so the process of gel preparation was studied, and some of the factors affecting platinum particle size on colloid prepared process was investigated. Different particle size of platinum colloid supported the catalyst were studied, too. In addition, it has confirmed that the pretreatment process, the different calcination temperature will have a significant impact on activity of the catalyst, so this effect of calcination temperature was further study in this paper. The study results were as follows:1,Affect factors of colloidal particle size prepared by colloid deposition method This study focuses on the possible affect factors of colloidal particle size prepared by colloid deposition method. It investigated the effect of precursor liquid water content, gel concentration, reduction time, reduction temperature, reducing agent, alkali type, alkali on the preparation of the platinum particle size, but also repeatability of this method. The results show that increasing water content and precursor solution concentration of chloroplatinic acid, the platinum particle size increases. Through the modulation of these factors, we can obtain colloidal particles of platinum which are up to 3.7nm, the smallest is less than 1nm. Colloids prepared by this method are in uniform size, and it is proved repeatable, the error can be controlled within±0.3nm range.2,Effect of different Pt size on catalytic performanceA series of catalysts were prepared by different particle size, and catalytic performance was investigated by these supported catalysts. The results showed that when Pt particle size is in the range of 1.9±0.2nm, 1% Pt/Fe₂O₃ catalyst shows the highest activity. When the particle size becomes smaller or larger, the catalytic activity gets worse, and the platinum particle size was increased, the catalytic performance degradation is more prominent.3,Research of the process of formation of platinum colloidThe process of formation of platinum colloid was investigated by the UV. After chloroplatinic acid, sodium hydroxide and ethylene glycol mixed and stirred, the Cl-originally in octahedral form of combination with Pt⁴⁺ was replaced by water molecules, Pt⁴⁺-Cl was destroyed and replaced by Pt⁴⁺-O or Pt⁴⁺-OH. At the same time the zero-valence state of platinum particles appeared gradually. This process become quickly with the oil bath temperature rising, the original oxidation state of platinum rapidly become into Pt particles, the solution color changed and the colloid appeared. Major changes in this process are: Pt⁴⁺-Cl→Pt⁴⁺-O or Pt⁴⁺-OH→Pt particles.4,Effect of different calcination temperature on catalyst performanceEffect of different calcination temperature on catalyst performance was investigated by the characterization of Pt/Fe₂O₃ catalyst calcined by different temperature. It has proved that after calcination at 200℃, any original organic matter in the catalyst was removed, and active center was exposed gradually, platinum species in the catalyst began to be oxidized to the form of Pt²⁺, Fe (OH) 3 generated thermal decomposition dehydration to get Fe₂O₃, while there is a certain strength of MSI between carriers and the metal, the synergy of these factors are favorable for CO oxidation, so this case shows the best catalytic activity. Throughout the process, the platinum species occurred Pt0→Pt²⁺→Pt⁴⁺ changes, catalysts were Fe (OH) 3→??Fe₂O₃.