Modification of Cordierite Honeycomb Ceramics Matrix for DeNOx Catalyst
- PDF / 206,989 Bytes
- 6 Pages / 432 x 648 pts Page_size
- 93 Downloads / 161 Views
Modification of Cordierite Honeycomb Ceramics Matrix for DeNOx Catalyst Qingcai Liu, Yuanyuan He, Jian Yang, Wenchang Xi, JuanWen, Huimin Zheng College of Materials Science and Engineering, Chongqing University, Chongqing, 400030, China ABSTRACT To obtain highly dispersed and highly active catalysts by impregnating of active species onto the monolith directly, cordierite honeycomb ceramics were modified by nitric acid solution of 68wt%. Effects of acid treatment temperature and time on the performance of cordierite were investigated. Specific surface area, pore size distribution, morphology and structure of cordierite were characterized by N2-physical adsorption, SEM, XRD, respectively. Concentrations of ions in the acid solution were measured by AAS. It is shown that the corrosion content of cordierite increases and more micropores are generated with increasing time of acid treatment, leading to an upward trend of specific surface area. The coefficient of thermal expansion and compression strength decrease obviously at a higher temperature, which is mainly attributed to the removal of Al and Mg ions from the silicate structure and delayed formation of free amorphous silica on the surface of the cordierite. The optimal modification process of cordierite matrix acid erosion is at 110℃ for 6 h. INTRODUCTION Cordierite(2MgO•2Al2O3•5SiO2) is a crystalline magnesium alumosilicate with hexagonal framework. It is the most widespread commercial material for high-temperature catalyst applications, especially the substrate for automobile exhaust catalyst, because the cordierite has some special characteristics such as high mechanical stability and low coefficient of thermal expansion (CTE). Cordierite is in the form of a honeycomb monolith because of the requirements of low pressure drop and high geometrical surface area. However, cordierite monoliths are not suitable for using as catalyst supports due to quite small specific surface area. It is not possible to obtain highly dispersed and highly active catalysts by impregnating of active species onto the monolith directly[1,2]. It has been reported that alumina, perovskites, silica, zirconia, titania, and zeolites are effective to perform the washcoating, and lead to high BET surface areas by depositing a layer of these highly porous materials[3-5]. In addition to the washcoating process, organic or inorganic acid treatment on the surface of cordierite monoliths has been studied and proves to be an available approach to increase surface areas[5-9]. Furthermore, the relevant studies focus on the select of acid and the processing conditions[6,8-10]. Whereas the influence of acid leaching on the CTE and mechanical strength of cordierite honeycomb ceramics were rarely reported from previous studies[2,10]. In the current work, therefore, the CTE and mechanical strength of cordierite were discussed to optimize the time and temperature for nitric acid (68% of concentration) treatment. Specific surface area, pore size distribution, morphology and structure of acid-corrosion cordierit
Data Loading...
