Combination of hydroxides and metal catalysts enables the conversion of cellulose to high purity H2 and solid carbonates.

The alkaline thermal treatment of biomass has recently been proposed as a novel method for producing high purity H 2 with suppressed CO x formation under moderate reaction conditions (i.e., 523 K and ambient pressure). This technology has a great potential for sustainable bioenergy production because it can handle a wide range of feedstocks including biomass and biogenic wastes with high water content. Unfortunately, due to the complexity of the reactions involved, the alkaline thermal treatment of biomass is still poorly understood. In this study, using a model biomass system of glucose, a series of noncatalytic kinetic and mechanistic studies was performed to investigate the effects of reaction temperature and reactant ratios in terms of H 2 conversion, purity, and formation rates of H 2 as well as gaseous products such as CH 4 , CO, and CO 2 . The CO concentration is one of the important factors for the utilization of the product gas because CO is generally poisonous to catalytic systems such as those found in proton exchange membrane (PEM) fuel cells. Thus, high CO concentration would require additional gas cleanup processes. This study found that NaOH does play an important role in suppressing CO and CO 2 formation while facilitating H 2 production and promoting CH 4 formation. The noncatalytic alkaline thermal treatment of glucose resulted in a maximum H 2 conversion of about 27% at 523 K with a stoichiometric mixture of NaOH and glucose. While the H 2 conversion was limited in the absence of catalyst, the moderate reaction conditions, low CO x concentration, and solid−solid reaction scheme give advantages over conventional biomass conversion technologies. The solids analysis confirmed the presence of Na 2 CO 3 in the solid product, indicating the inherent carbon management potential of the alkaline thermal treatment process.

Monoaxial silica nanofibers containing iron species as well as coaxial nanofibers with a pure silica core and a silica shell containing high concentrations of iron nanocrystals were fabricated via electrospinning precursor solutions, followed by thermal treatment. Tetraethyl-orthosilicate (TEOS) and iron nitrate (Fe(NO(3))(3)) were used as the precursors for the silica and iron phases, respectively. Thermal treatments of as-spun precursor fibers were applied to generate nanocrystals of iron with various oxidation states (pure iron and hematite). Scanning electron microscopy (SEM), x-ray diffraction (XRD), and transmission electron microscopy (TEM) were used to probe the fiber morphology and crystal structures. The results indicated that the size, phase, and placement of iron nanocrystals can be tuned by varying the precursor concentration, thermal treatment conditions, and processing scheme. The resulting nanofiber/metal systems obtained via both monoaxial and coaxial electrospinning were applied as catalysts to the alkaline hydrolysis of glucose for the production of fuel gas. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), and bulk weight change in a furnace with residual gas analysis (RGA) were used to evaluate the performance of the catalysts for various ratios of both Fe to Si, and catalyst to glucose, and the oxidation state of the iron nanocrystals. The product gas is composed of mostly H(2) (>96 mol%) and CH(4) with very low concentrations of CO(2) and CO. Due to the clear separation of reaction temperature for H(2) and CH(4) production, pure hydrogen can be obtained at low reaction temperatures. Our coaxial approach demonstrates that placing the iron species selectively near the fiber surface can lead to two to three fold reduction in catalytic consumption compared to the monoaxial fibers with uniform distribution of catalysts.

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