High Surface-Area Catalytic Oxides
High surface-area powders are a critical component in many catalytic systems. The thermal stability of these ceramic powders is essential to the performance of catalytic systems. We have been studying the synthesis of oxide nanoparticles such as ZrO2, CeO2, Al2O3, SiO2, and MnOx with the aim of maintaining high surface area at elevated temperatures. It was shown that impurities within the powders are a key factor in determining the thermal stability of oxide powders. Furthermore, synthesis conditions such as heat treatment temperature and time, as well as precursor concentration were shown to be controlling parameters in achieving high surface area. We discovered that the colloidal coating approach of precipitation an oxide in the presence of the support oxide can enhance the surface area of the mixed oxides due to morphological change. Our study provides a basic understanding to the important industrial processes in obtaining thermally stable, high surface-area ceramic particles.
Conversion of Coal Wastes into Microporous and Mesoporous Materials
Annually, in the state of Pennsylvania alone, 8.4 million tons of fly ash, a coal combustion waste, is generated. Due to the increasingly tighter environmental regulations, the disposal of such a large amount of fly ash poses a challenge. In the past few years, we have chemically converted fly ash into zeolites which have a wide range of applications such as molecular sieves, catalysts, adsorbents, etc. Zeolites are crystalline forms of aluminosilicates and the fly ash is composed of mainly silica and alumina. Therefore, it is expected that fly ash can be converted to zeolites. This study represents a new approach in dealing with waste materials. It not only eliminates the disposal problem of coal wastes and more importantly turns the waste material into a useful one. We have found a fusion method that can convert a variety of ashes into zeolites with high yields. The zeolites converted from fly ash were shown to have good ion-exchange property with heavy metals such as Cs and Co. Our results show that the converted fly ash has a great potential in immobilizing nuclear wastes and toxic ions in waste streams.
As an extension of our work on zeolites, the formation of mesoporous molecular sieves that were recently discovered by researchers at Mobil was investigated. The mesoporous molecular sieves are composites of organic (surfactant) and inorganic (for example, silicate) species. After calcination (heat treatment), the organic part is burned out and the remaining porous materials contain periodic pores of sizes in the order of 20-100 angstroms. The mesoporous materials have a wide range of possible applications such as catalysts, molecular sieves, and adsorbents. We have succeeded in converting fly ashes into mesoporous aluminosilicates. Furthermore, we synthesized mesoporous nickel silicates using the same approach. The mesoporous nickel silicates show great promise as energy storage electrodes in electrochemical cells. Currently our expertise in this area has been applied to the separation of CO2/N2 gases. In the DOE funded program, we worked on synthesizing a microporous membrane material that can effectively separate CO2 from N2 due to preferential adsorption of CO2.