Sustainable Hydrogen from Bio-oil - Catalytic Steam Reforming of Acetic Acid as a Model Oxygenate

Introduction Hydrogen as a fuel has recently been an important issue due to developments in fuel cell technology. Hydrogen production from sustainable sources, e.g. biomass, is gaining attention for a CO2 neutral energy supply. Recent developments in flash pyrolysis technologies make it possible to convert lignocellulosic biomass efficiently to a bio-oil, which is easier for handling and transport. The bio-oil so generated contains a variety of aliphatic and aromatic oxygenates (aldehydes, ketones, acids, alcohols). Combination of catalytic steam reforming and water gas shift reaction is the most promising option to generate hydrogen since these reaction steps maximize hydrogen yield. During steam reforming of bio-oil, deactivation due to coke/oligomer deposition on the catalysts is a severe problem. It has been reported that deactivation is unavoidable even in the presence of excess steam (H2O/C > 5). Economically, lower steam/carbon (S/C) ratio (< 2) is preferable. In this study, Pt/ZrO2 has been investigated since earlier work 3 has shown excellent activity and stability for Pt/ZrO2 under conditions favorable for coke formation, for e.g., even in the absence of steam, during CO2 reforming of natural gas. Bio-oil is a mixture of oxygenates. In order to provide a knowledge base for the design of active and stable catalysts for steam reforming of bio-oil, studies have been initiated with model oxygenates. Acetic acid (HAc) has been chosen as a model compound in this study because it is a major component of bio-oil (up to 32 wt%). It is known that steam reforming and water gas shift reaction (CO + H2O CO2 + H2) occur simultaneously and the overall stoichiometry is represented (Equation 1), CH3COOH + 2H2O → 2CO2 + 4H2 ...(1) This study describes attempts to understand the reaction and deactivation mechanisms in order to establish guidelines for the design of efficient catalysts for steam reforming of bio-oil.