(583ai) Catalytic Deoxygenation Mechanisms: Using Electronic Structure Calculations to Understand Decarboxylation Over Transition-Metal Catalysts

The catalytic conversion of biomass to hydrocarbons represents a potential source of renewable hydrocarbon fuels. These fuels can be produced from abundant, inexpensive raw feedstocks, and because they are chemically identical to conventional petroleum fuels they require no substantial new infrastructure. Raw biomass and pyrolysis-derived oils are poor fuels because of a higher oxygen content, and therefore a lower energy density, than comparable hydrocarbons. Therefore, a more complete understanding of biomass deoxygenation reactions is of value in optimizing those reactions. We have conducted a density functional theory (DFT) analysis of the catalytic decarboxylation and decarbonylation reactions, which are the primary mechanisms of catalytic oxygen removal, in order to determine the catalytic deoxygenation reaction mechanisms for the carboxylic acid function group. This includes identifying possible end products and the network of reaction steps that could eventually yield those products. Comparisons of the different intermediate energies and energy barriers allow us to predict the mechanisms that predominate under different reaction conditions. Knowledge of the reaction mechanism in turn allows future research to focus on specific aspects of the catalytic biomass deoxygenation, such as: optimizing reactors to selectively favor saturated products (produced via decarboxylation) over unsaturated products (produced via decarbonylation); the effect of feed carbon chain length on the reaction; how the reaction is negatively influenced by catalyst poisoning; and the role of hydrogen in the deoxygenation reaction.