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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A clean stream of alkanes from renewable biomass resources is obtained through aqueous‐phase reforming in a single reactor. Alkanes are produced from biomass‐derived sorbitol through a bifunctional pathway (see scheme) that involves the dehydration of sorbitol on acid sites (SiO2/Al2O3) and hydrogenation of intermediates on a metal catalyst under a H2 atmosphere. Hydrogen is produced from sorbitol and water on the metal catalyst in the same reactor.

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Quantum chemical calculations employing density functional theory were performed to investigate the interactions of C 2 H x (ads) species on Pt 10 clusters and on Pt(111) and Pt(211) slabs. We calculate the binding energies of experimentally observed surface species, such as di-σ-bonded ethylene, ethylidyne species, and di-σ/π vinylidene species. In addition, we calculate the binding energies of the other species, such as ethyl, ethylidene, and vinyl species, that are postulated to be reactive intermediates in surface reactions. Furthermore, we calculate the activation energies for C-C bond dissociation of various C 2 H x (ads) species. We show that the bonding energies are dependent on the geometry of the surface, leading to the observed structure sensitivity of ethane hydrogenolysis. We show that the underlying parameter for understanding the stronger binding of various species on the step edge of Pt(211) compared to Pt (111) is the position of the metal d-band center. With estimates from these DFT calculations of the potential energy surface involved in the formation and reactivity of various C 2 H x (ads) species on Pt, we show that the primary reaction pathways for ethane hydrogenolysis on platinum involve highly hydrogenated species, such as C 2 H 5 (ads).

Kinetic analysis employing a mechanism that captures the essential surface chemistry of the reaction allows quantitative interpretation of diverse experimental data. This approach is used with a Horiuti-Polanyi mechanism, modified by hydrogen activation steps, to describe the surface chemistry for ethylene hydrogenation over platinum catalysts. In this investigation, kinetic analysis provides a quantitative means of comparing, contrasting, and consolidating results from steady-state kinetic studies, deuterium tracing measurements, vibrational spectroscopy, and temperature programmed desorption. A noncompetitive pathway is dominant at low temperatures, involving sites for hydrogen adsorption that are not blocked by carbonaceous species. At higher temperatures and lower ethylene pressures, more surface sites become available for hydrogen adsorption, and the reaction shifts to a pathway involving competitive hydrogen and ethylene adsorption.