Inorganic Catalytic Nanofibers for the Production of Hydrogen Via Alkaline Hydrolysis of Biomass
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Here we propose to develop a farm-scale biorefining system that can convert cellulosic biomass into useable hydrogen gas. In particular, we focus on the development of cost-effective procedures for biomass pretreatment and catalysts for alkaline hydrothermal treatment, which is less studied as compared to conventional gasification and pyrolysis but with great potential. While we have made progress in chemical routes to directly incorporate catalysts into cellulose, one-dimensional materials also have been investigated to support catalysts thereby maintaining the nanoparticles' high surface area to volume ratio while inhibiting their aggregation tendency. Electrospinning in particular has garnered significant interest due to the cost effective nature and diversity of materials/morphologies available. In this study monoaxial and coaxial inorganic silica nanofibers with in-situ formed iron or nickel catalytic nanoparticles have been fabricated through sol-gel chemistry with a metallic precursor and subsequent thermal treatment with coaxial nanofibers deliberately tuning the catalyst location to the surface of the nanofiber. Further, a purely water based approach has been used by homogeneously binding high concentrations metallic and ceramic precursors to a polymer carrier. Electrospinning and subsequent thermal treatment generates nanoscale fiber diameters of morphologies consisting of pure metal nanofibers or discrete metal domains in a ceramic substrate through monoaxial electrospinning, or purely metallic shells surrounding a purely ceramic core or discrete metal domains tuned toward the surface of the nanofiber through coaxial electrospinning. The morphology, oxidation state and crystal location are studied using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The resulting nanofibers were applied as a catalytic system for the alkaline hydrolysis of biomass to selectively produce hydrogen with minimal carbon monoxide or dioxide byproducts. Our results indicate that by tuning the catalyst type, catatlyst morphology, substrate composition, reaction temperature and heating rate, nearly 100% conversion can be achieved at low temperatures and low pressures with a mole fraction of hydrogen greater than 97%. With these preliminary results, this system is especially exciting because it lends itself easily to the potential on site, cost effective generation of useable fuel gas from a biomass feed stock.