(158c) Synthesis and Characterization of Carbon-Based Iron Catalysts Prepared by Ultrasonic Spray Pyrolysis

Carbon materials have been used in heterogeneous catalysis, both as direct catalysts and catalyst supports, for many years [1,2]. As a catalyst support, carbon provides desirable characteristics including chemical inertness, stability (in the absence of oxygen), mechanical resistance, and high surface area and desired porosity. Traditionally, carbon catalysts are prepared through a multistage process: (1) selection, preparation, and modification of a carbon support with desired physico-chemical properties; (2) loading of catalyst precursor with different methods including incipient-wetness, excess-solution, and ion-exchange impregnation or physical/chemical vapor deposition; and (3) conversion of the catalyst precursor to active catalyst species by physical (e.g., heating) and/or chemical (e.g., reduction) treatments. In this work, we considered a new approach for preparation of carbon catalysts through a continuous and possibly more efficient process. A novel, one-step synthesis method was used to simultaneously pyrolyze a carbon precursor, develop porosity, and disperse nano-sized metal catalyst particles onto the porous carbon support. An Ultrasonic Spray Pyrolysis (USP) system that has been previously used to prepare porous carbon powders was utilized [3]. An aqueous solution of sucrose, NaCl, and FeCl3 of selected stoichiometry was ultrasonically nebulized to produce a fine mist that was carried to a furnace with nitrogen flow. After solvent evaporation, sucrose and ferric chloride decomposed to form a carbon/NaCl/iron composite. A fine powder exiting the furnace was collected in water bubblers, where the NaCl crystals were dissolved, leaving behind a porous carbon structure supporting highly dispersed nano-sized iron particles. An experimental matrix was designed to investigate the impacts of pyrolysis temperature, aerosol flow rate, iron concentration, and iron-to-sucrose ratio on the carbon support's porosity and the iron catalyst's dispersion. Experiments were also conducted to determine the individual roles of NaCl, FeCl3, and solution pH on the product's yield and properties. Prepared catalysts were characterized for: surface area and pore size distribution (N2 adsorption); surface and bulk elemental composition (SEM-EDX, XPS, and ICP-MS); and carbon texture, support diameter, and catalyst particle size (SEM and TEM). Additional characterizations to identify carbon surface functionalities by spectroscopic methods and iron dispersion by CO chemisorption are planned. Tests to assess the catalytic activity of these materials for gas- and liquid-phase environmental applications, such as oxidation of NO in flue gas streams or destruction of water pollutants (e.g., trichloroethylene), are also planned. Characterization results show that carbon microspheres (0.5 ìm