Concerns about the depletion of fossil fuel reserves and the pollution caused by continuously increasing energy demands make hydrogen an attractive alternative energy source. Hydrogen is currently derived from nonrenewable natural gas and petroleum, but could in principle be generated from renewable resources such as biomass or water. However, efficient hydrogen production from water remains difficult and technologies for generating hydrogen from biomass, such as enzymatic decomposition of sugars, steam-reforming of bio-oils and gasification, suffer from low hydrogen production rates and/or complex processing requirements. Here we demonstrate that hydrogen can be produced from sugars and alcohols at temperatures near 500 K in a single-reactor aqueous-phase reforming process using a platinum-based catalyst. We are able to convert glucose -- which makes up the major energy reserves in plants and animals -- to hydrogen and gaseous alkanes, with hydrogen constituting 50% of the products. We find that the selectivity for hydrogen production increases when we use molecules that are more reduced than sugars, with ethylene glycol and methanol being almost completely converted into hydrogen and carbon dioxide. These findings suggest that catalytic aqueous-phase reforming might prove useful for the generation of hydrogen-rich fuel gas from carbohydrates extracted from renewable biomass and biomass waste streams.

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Reaction kinetics measurements of the water-gas shift reaction were carried out at 373 K on Pt/Al2O3 in vapor phase to investigate the effects of CO, H2, and H2O partial pressures. Results of in situ ATR-IR studies conducted in vapor phase under similar conditions suggest that the Pt surface coverage by adsorbed CO is high (approximately 90% of the saturation coverage), leading to a negligible effect of the CO pressures on the rate of reaction. The negative reaction order with respect to the H2 pressure is caused by the increased coverage of adsorbed H atoms, and the fractional positive order with respect to the water pressure is consistent with non-equilibrated H2O dissociation on Pt. Results of in situ ATR-IR studies carried out at 373 K show that the presence of liquid water leads to a slight decrease in the Pt surface coverage by adsorbed CO (approximately 80% of the saturation coverage) when the CO partial pressure is the same as in the vapor-phase studies. The rate of the WGS reaction in the presence of liquid water is comparable to the rate under complete vaporization conditions when other factors (such as CO partial pressure) are held constant. Reaction kinetics measurements of methanol reforming were carried out at 423 K over a total pressure range of 1.36-5.84 bar. In situ ATR-IR studies were conducted at 423 K to determine the Pt surface coverage by adsorbed CO in completely vaporized methanol feeds and in aqueous methanol solutions. The decomposition of methanol is found to be slower during the reforming of methanol in liquid phase than in vapor phase, which leads to a lower rate of hydrogen production in liquid phase (0.08 min(-1) at 4.88 bar) than in vapor phase (0.23 min(-1) at 4.46 bar). The lower reaction order with respect to methanol concentration observed for vapor-phase versus liquid-phase methanol reforming (0.2 versus 0.8, respectively) is due to the higher extent of CO poisoning on Pt for reforming in vapor phase than in liquid phase, based on the higher coverage by adsorbed CO observed in completely vaporized methanol feeds (55-60% of the saturation coverage) than in aqueous methanol feed solutions (29-40% of the saturation coverage).

Hydrogen can be produced from aqueous solutions containing 10 wt% glucose with high selectivities through the combined use of a hydrogenation reactor for conversion of glucose to sorbitol, followed by a reforming reactor for conversion of sorbitol to H(2) and CO(2) and then a gas-liquid separator for the removal of high-pressure H(2)-rich reformate gas, ready for use in a fuel cell.

The production of fuel-cell-grade hydrogen, containing very low levels of CO, is critical for the global transition to a hydrogen society. In spite of ongoing efforts to make fuel cells more CO-tolerant, [1] the use of hydrogen fuel-cells in portable applications (e.g., automobiles, battery replacement devices) is particularly challenging, as the production of hydrogen by steam-reforming of hydrocarbons [2] requires a complex combination of multiple processes [3][4][5][6][7] to achieve the required low CO levels (e.g., 100-500 ppm).[1] An important step toward a simple process for the production of hydrogen containing low levels of CO is made possible by the discovery [8] that hydrogen can be produced by catalytic reforming of biomass-derived oxygenated hydrocarbons in liquid water at temperatures near 500 K. This process has the advantage that the reforming of oxygenated hydrocarbons and the water-gas shift (WGS) reaction are both thermodynamically favorable at the same low temperatures, thus making it possible to conduct both reactions in one reactor. These low levels of CO, combined with the fact that our low-temperature process uses biomass-derived renewable feedstocks, makes aqueous-phase reforming of oxygenates an attractive process for applications in portable devices.Herein, we show results from studies of the aqueousphase reforming of ethylene glycol (EG) to produce H 2 , with specific emphasis on the levels of CO produced as a function of the process conditions. We show the importance of the reaction operating conditions for achieving low levels of CO in the effluent gas from our single-reactor reforming process, and we elucidate the factors that control the ultimate levels of CO that can be attained.Aqueous-phase reforming of oxygenates to produce H 2 takes place on metal catalysts [9] through CÀC cleavage to make CO and H 2 , [Eq. (1)].(Undesired alkanes are formed through C À O cleavage.) Adsorbed CO undergoes WGS [Eq. (2)], which increases theamount of H 2 produced and removes CO from the catalyst surface.[10]The lowest partial pressure of CO that can be achieved depends on the thermodynamics of the WGS reaction and the operating conditions, [Eq. (3)].K WGS is the equilibrium constant for the vapor-phase WGS and P j are partial pressures. Since H 2 , CO 2 , and small amounts of alkanes (primarily CH 4 ) are produced by aqueous-phase reforming, [8] gas bubbles are formed within the liquid-phase flow reactor. The pressure in these bubbles can be approximated to be equal to the system pressure, [Eq. (4)].The partial pressures of the reaction products and water vapor are dictated by the feed concentrations, system pressure and temperature, as outlined below. For dilute product concentrations and system pressures above the saturation pressure of water, the bubbles contain water vapor at a pressure equal to its saturation pressure at the reactor temperature, and the remaining pressure is the sum of the partial pressures of the product gases. The extent of vaporization, y, is defined as the percent of wate...