Development of Catalytic Nanomaterials for Three Industrial Processes

Doctoral thesis, 2007

Nanotechnology is a relatively new research topic that attracts increasing interest from scientists and engineers all over the world, due to its novel applications. The use of nanomaterials has extended to a broad range of applications, for example chemical synthesis, catalytic combustion and microporous media synthesis, contributing to achievement of improved or promising results. Microemulsion (ME) is considered a powerful tool for synthesis of nanomaterials, due to its unique properties. This thesis concentrates on the use of the ME as a catalyst synthesis route for obtaining metal nanoparticles for three challenging concepts: 1) Hydrogen production by a membrane reactor, 2) selective catalytic oxidation (SCO) of ammonia in gasified biomass and 3) synthesis of Fischer-Tropsch (FT) fuel for low emissions in diesel engines. The environmental importance of these three applications under investigation is great, since all applications minimise the emissions of harmful exhaust gases (CO2, CO, NOx, SOx, unburned hydrocarbons) and soot which contribute to various environmental (greenhouse effect, ozone layer depletion, acid rain) and health problems. At the same time, the depletion of fossil fuels makes the use of renewable energy sources, such as gasified biomass, very attractive. Particularly, for the scope of the fist concept presented in this thesis, palladium nanoparticles were synthesised from ME and characterised in order to be deposited on zeolite composite membranes to improve the H2 / CO2 separation (hydrogen production) ability. The membranes were first impregnated with Pd nanoparticles and then tested in a metal reactor for the permeance and selectivity towards H2 and CO2. Regarding the second concept, a series of Ni catalysts supported on mixed-metal oxides (Ce, La and Zr) and alumina were prepared by both conventional methods and ME, characterised and tested for their activity towards SCO of ammonia in gasified biomass. Finally, for the scope of the third concept, iron-based catalysts promoted with K and Cu were synthesised (by both conventional methods and ME), characterised and tested for their activity towards FT fuel synthesis utilising H2-poor syngas (H2+CO) from gasified biomass. The results obtained from this work and presented analytically in this thesis are considered successful and at the same time very promising, since further research on the ME method may even lead to improvement of the current achievements. The impregnation of the zeolite composite membranes with Pd nanoparticles considerably improved the membrane performance towards H2 production and CO2 capture. Moreover, almost complete NH3 conversions with ultra-low NOx emissions were obtained by the SCO of ammonia in gasified biomass. Finally, both high FT activity and selectivity towards heavier hydrocarbons (C5+) were achieved by testing the iron-based catalysts. Concluding, the ME-prepared catalysts showed improved performance for the last two processes, compared to the same catalysts prepared by conventional methods.