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WIREs Energy Environ.
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Production of renewable hydrogen by reformation of biofuels

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Environmental concerns and sustainability issues dictate the production of energy carriers from renewable resources. Hydrogen is thought to be the most appropriate energy carrier in this respect, especially in combination with fuel cell technologies and distributed power generation schemes. Although renewable hydrogen can be produced from excess renewable electricity, this approach imposes difficulties related to storage, handling, and transportation. The use of biomass has been proposed for production of renewable hydrogen. The most effective way is to utilize biofuels as intermediates in the hydrogen and power production sequence. Appropriate biofuels are bioethanol, biogas, bio‐oil, and glycerol. These molecules can be catalytically reformed, most efficiently with steam, at elevated temperatures, to yield hydrogen and carbon dioxide. For this purpose, appropriate catalysts have been developed, which exhibit high activity, selectivity toward hydrogen production and long‐term stability. Stability of operation is very critical as deposition of coke on the catalyst surface is thermodynamically feasible and kinetically favorable in many cases and operating envelopes. Although noble metals are active and rather resistant to coke deposition, they are rare and expensive. Nickel and other transition metals have been investigated and significant research efforts have been extended to improve catalytic characteristics by appropriate choice of support material, metal dispersion, and additives in the metal or the carrier phases. Furthermore, elucidation of mechanistic aspects of the reformation reactions, other reactions which occur in sequence or in parallel as well as carbon deposition routes, is also utilized toward the development of appropriate catalytic materials and processes. This article is categorized under: Bioenergy > Science and Materials Fuel Cells and Hydrogen > Science and Materials
(a) Conversions of ethanol and (b) selectivities toward hydrogen obtained as functions of reaction temperature over 20% Ni/(La2O3/Al2O3), 0.5% Rh/Al2O3, 3% Ru/TiO2, and 20% Co/Al2O3 catalysts and in the absence of catalyst (homogeneous reactions). Experimental conditions: mass of catalyst: 0.1 g; particle diameter, 0.25 < dp < 0.50 mm; total flow: 350 cm3/min; feed composition: 25% EtOH, 75% H2O; P = 1 atm. (Reproduced with permission from Ref . Copyright 2002, Elsevier.)
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Hydrogen productions paths from biomass derived energy carriers.
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(a) H2 selectivity and (b) glycerol conversion at selected temperatures over Al2O3‐supported catalysts. Reaction conditions: Water/glycerol ratio = 6:1, FFR: 0.5 mL/min (GHSV = 51,000 h−1), data collected after 1 h of operation. (Reproduced from Ref . Copyright 2004, Elsevier.)
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Comparison among thermodynamic data (lines) and experimental results (symbols) of molar ratios of H2 (♦), CO2 (▪), CH4 (●) and CO (▲), and the conversion of glycerine (▼) on 13 wt% Ni–6 wt% La2O3/Al2O3 catalyst at steady state, 0.4 MPa, different temperatures, and 1:9 glycerol/water ratio. (Reproduced from Ref . Copyright 2012, Elsevier.)
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Schematic representation of the bifunctional mechanism proposed by Takanabe for the steam reforming of acetic acid over a Pt/ZrO2 catalyst. (Reproduced from Ref . Copyright 2004, Elsevier.)
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Methane conversion for transition metal catalysts supported on either silica or alumina [reacting mixture: CH4:CO2:He (10:10:80); total flow rate: 100 mL/min]: (a) at 723 K, TOS 45 min; (b) at 1023 K TOS 5 min. (Reproduced from Ref . Copyright 1996, Elsevier.)
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Reaction steps for the dry reforming of methane. (a) Adsorption and dissociation of CH4 and CO2 on the metal and the metal–support interface, respectively. (b) CO and H2 desorption are fast steps. (c) Surface hydroxyls are formed from hydrogen and oxygen spillover. (d) Surface oxygen species or hydroxyls oxidize the hydrogen depleted surface methyl‐like species (*CHx), forming *CHxO species and finally CO and H2. (Reproduced from Ref . Copyright 2012, Springer.)
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(a) Effect of the nature of the support on the catalytic performance and (b) selectivity toward CO over Pt (0.5 wt%) supported on the indicated commercial oxide carriers. Experimental conditions: same as in Figure . (Reproduced in part from Ref . Copyright 2012, Elsevier.)
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Ethanol conversion (XEtOH) as a function of reaction temperature over 0.5% Pt/Al2O3, 1% Pd/Al2O3, 2% Rh/Al2O3, and 5% Ru/Al2O3 catalysts. Experimental conditions: mass of catalyst: 0.65 g; particle diameter: 0.18 < dp < 0.25 mm; TOTAL Flow: 120 cm3/min; GHSV = 9350 h−1; feed composition: 12.5% EtOH, 37.5% H2O (balance He); P = 1 atm. (Reproduced with permission from Ref . Copyright 2008, Springer.)
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