Chapter 7 - Hydrogen from Bioethanol

Abstract

Bioethanol, ethanol produced from biomass by fermentation, is the most promising renewable source for hydrogen production. Ethanol is advantageous over other conventional substrates because it is readily available, easy to obtain from biomass and to transport, CO2 neutral and safe to handle. Ethanol is a well-established source of hydrogen by catalytic steam reforming, oxidative reforming or partial oxidation. An efficient catalyst for hydrogen production from ethanol has to dissociate the C–C bond, maintain a low CO concentration and be stable under catalytic operation. Noble metal-based catalysts perform well; they are stable and exhibit high activity. However, they are expensive and need high temperatures to be active. Nickel- and cobalt-based catalysts are inexpensive but under reaction conditions, they suffer from sintering and deactivation by carbon deposition. Supports with redox properties, based on CeO2, can oxidize carbon residues and prevent extensive carbon deposition due to its oxygen storage capacity and high oxygen mobility. The use of catalytic membrane reactors, with simultaneous generation and separation of hydrogen, appears as an attractive approach to simplify on-site/on-demand ethanol reformers and to reduce downstream separation costs. Looking for mobile applications, microreactor technologies have been applied to ethanol reforming processes as well. Recently, photocatalytic generation of hydrogen at room temperature from water–ethanol mixtures has been accomplished over noble metals supported over semiconductors.