Catalytic upgrade of ethanol to n-butanol by Guerbet chemistry

Moving towards a more sustainable society requires the discovery and development of alternative catalytic routes to replace the current dependence of fossil fuels and petrochemical industry. In this respect, the valorisation of biomass into commodity compounds, such as alcohols, represents a great oportunity. The most prominent bioalcohol to date is ethanol; however, several drawbacks prevent this compound from its full implementation as biofuel. This thesis provides a detailed investigation of a catalytic route to upgrade renewable ethanol to a more efficient biofuel as is n-butanol, through the so-called Guerbet reaction. This work begins in Chapter 3, with a first approach to the Guerbet reaction using Ru-based homogeneous catalyst is presented, the elucidation of the mechanistic aspects of the Guerbet chemistry and the problems related to the use of homogeneous catalysts in basic conditions. Taking the knowledge gained from the study of this system, a different approach is adopted, tackling the different steps of the Guerbet upgrade of ethanol through model reactions, in order to find the most appropiated catalyst for every step to finally combine them in one optimised process. With this aim, in Chapter 4, the first step of the Guerbet reaction, the acceptorless dehydrogenation of alcohols, is investigated using a Pd based catalyst, where various kinetic, steric, electronic, and thermodynamic elements of this transformation are evaluated in great detail. Following this, Chapter 5 is focused on the next steps of the Guerbet reaction, the Aldol condensation and the Meerwein–Ponndorf–Verley reduction, using Lewis acidic heterogeneous catalysts, paying special attention to the selectivity and durability of the catalysts selected. Subsequently, the combination of the selected catalysts in previous chapters is discussed in Chapter 6, showing how the choice of metal, support, operational conditions and relative amount of each catalyst determines the product distribution and catalytic activity obtained. In closing, Chapter 7 evaluates the consequences of the findings of this research, and the pertaining challenges from this work