Synthesis Of Nanostructured Metal Films And Mathematical Simulation Of Propane Dehydrogenation In Membrane Reactors

Well-defined periodic nanostructured metal materials are promising candidates with potential applications in catalysis, batteries, fuel cells and sensors. Lyotropic liquid crystalline templating strategy is a versatile approache for the synthesis of this new kind of materials. In this thesis, ordered nanostructured metal / bimettalic films were deposited chemically or electrochemically on different substrates by using lyotropic liquid crystalline templates exhibited by the nonionic surfactant Brij56. The performance of the as-resulted membrane reactors composed of nanostructured Pt films on Al2O3 or on dense Pd membranes was compared with that of conventional fixed-bed and Pd membrane reactors for the catalytic dehydrogenation of propane. The major research works might be summarized as follows:Lamellar and hexagonal liquid crystalline phases were formed by mixing Brij56 and aqueous precursor solutions containing one or two metal salts. The effects of the precursor nature and the composition of the templating mixture on the nanostructure and stability of the liquid crystalline phase were investigated by means of POM and low-angle XRD.Reactions between hydrazine hydrate and metal salts dissolved in aqueous domains of the liquid crystalline templates resulted in the nanostructured metal Pd and Pt films chemically deposited on porousα-Al2O3 substrates. These films possessed well-defined lamellar or hexagonal nanostructure and strongly adhered to the substrates.Co-reduction of two-metal species in the presence of liquid crystalline phase by hydrazine hydrate produced lamellar nanostructured PdAg and hexagonal nanostructured PdPt bimetallic films chemically deposited onα-Al2O3 substrates. Composition and distribution of two metals in the as-resulted bimetallic films were analyzed.Dense Pd membrane was electrolessly plated onα-Al2O3 substrates and the effect of plating procedure on the quality of the Pd coating was studied. Electrochemical deposition of nanostructured Pt films on the surface of post-treated dense Pd membrane produced Pt-Pd two-layer films. The composition was analyzed and the nanostructure of Pt films was characterized with low-angle XRD and TEM. Effects of deposition potentials and precursor concentration in aqueous domains of liquid crystalline templates on the nanostructure and lattice parameter were investigated. Cyclic voltammetry experiments gave the active specific surface areas of Pt films of 13.8 m2 g-1.Relations between the template media and the templated inorganic structures were discussed with focus on the reasons leading to size mismatch between them. In fact, this founding might be a simple and convenient way controlling over nanostructure.Simulation of the propane dehydrogenation process in the mesoporous Pt membrane reactors and Pt-Pd two-layer membrane reactors was employed. The performance of the two types of membrane reactors had been compared with that of fixed-bed reactors and conventional Pd membrane reactors using this simulation. Comparative studies were carried out to analyze the performances of reactors containing different membranes in terms of sweep gas, pressure, temperature, space time and reactors inner tube radius. The results show that the Pt-Pd two-layer membrane reactors are superior to the conventional ones in that they retain higher propane conversion even in minuscule reactor chamber as well as prevent from packing granular catalysts.