|M.Sc Student||Halperin Victor|
|Subject||Electrospinning of metal; Ceramic and Composite|
Nanofibers for Catalytic Applications
|Department||Department of Chemical Engineering||Supervisors||Professor Gideon Grader|
|Dr. Gennady Shter|
|Full Thesis text|
There is an ever-growing demand for highly active and selective heterogeneous catalysts. The numerous advantages of using such materials include decreasing the energy consumption and production costs, and increasing the process throughput. Much progress has been made in developing highly active and selective micro-porous catalysts on nanometric scale. One of the obstacles of using these materials is diffusion limitations inside the pores. Nano-fibrous materials with hierarchical structure offer advantages over traditionally shaped catalysts in overcoming this obstacle. In this work we propose to use the electrospinning process for fabrication of nanometer-sized fibrous materials due to its simplicity, low cost and future potential to scale-up the process if large fiber quantities are required.. This thesis presents an investigation of the interplay between precursor synthesis, electrospinning process and thermal treatment and the catalytic activity of fiber mats. The main question guiding this research was whether the catalysts activity and selectivity can be improved by their incorporation into the fibrous structures.
Uniform mats, containing fibers with 300-600 nm in diameter were prepared by electrospinning from a stable suspension of silver nanoparticles, silver nitrate, polyvinyl alcohol, water and ethanol. Thermal decomposition of the "green" mats was studied by thermogravimetric/differential thermal analyses (TGA/DTA) coupled with mass spectrometry (MS) in inert, strongly and mildly oxidizing atmospheres. Thermal treatment profiles were developed to obtain metallic silver as well as composite silver/carbon (~10 wt. % carbon) fiber mats. The effect of sintering conditions on the morphology and catalytic activity in partial methanol oxidation to formaldehyde were studied.
Precursors for ceramic and ceramic/polymer iron oxide based fiber mats were prepared via two conceptual routes: iron oxide nanoparticles suspension called the “suspension route”, and solutions of iron and aluminum acetylacetonates or nitrates called the “solution route”. Optimal treatment profiles were developed based on TGA/DTA/MS data to yield “white” ceramic mats. The as-prepared mats were tested at Ben-Gurion University of the Negev (the Blechner Center) as catalysts in process of carbon dioxide hydrogenation into hydrocarbons. In both cases the effectiveness of fibers based catalysts via electrospinning was demonstrated.
The superior behavior of the silver/carbon composite fibers over powdered analogs was demonstrated in partial methanol oxidation to formaldehyde. The CO2 conversion and C6 selectivity of fibrous K/Fe-Al-O spinel catalyst was similar to the performance of the initial powdered catalyst. The nanofiber catalyst structure is expected to increase the catalyst effectiveness factor, which ordinarily decreases with increasing catalyst size. This effect will be studied in future work.