Tuning Catalyst Surfaces to Control Aldol Reactions in Biomass Conversion

Oil is the most important source of energy worldwide, accounting for some 35% of primary energy consumption and the majority of the chemical feedstocks; tackling the current world energy crisis is recognised as a top priority for both developed and developing nations, with sustainable sources of chemicals and fuels urgently sought in response to both diminishing world oil reserves and increasing environmental concerns over global climate change. Sustainable 'carbon-neutral' energy sources derived from biomass can play a major role in achieving this goal, with projections suggesting annual greenhouse gas emissions could be reduced by up to 12.4 Gtons. Transportation fuels can be generated from bio-oils which are readily obtained from sustainable biomass resources such as waste agricultural crops, forestry products, high yielding inedible plants such as Switchgrass, however, bio-oils cannot be used directly as transportation fuels and require catalytic upgrading before use. Likewise the US Department of Energy identified 12 'Platform Chemicals' that can be produced directly from sugars via chemical or biochemical transformation of lignocellulosic biomass and provide the basic feedstocks for sustainable chemicals manufacture. These molecules are highly oxygenated and contain a range of desirable functional groups such as acid, alcohol, carboxyl groups often required in synthetic materials. Thus in contrast to current chemicals synthesis starting from oil where oxygen insertion is required to generate functional materials, biomass derived building blocks necessitate new technology to selectively isomerise and/or 'deoxygenate' these highly functional molecules to reach the target molecule.

Catalysis has a rich history of facilitating energy efficient selective molecular transformations and contributes to 90% of chemical manufacturing processes and to more than 20% of all industrial products. In a post-petroleum era catalysis will be central to overcoming the engineering and scientific barriers to economically feasible routes to bio-fuels and chemicals. This proposal will address the major technological challenge of selectively converting sugars to platform chemicals or fuels and bio-oil to fuels; both of which involve common reactions, namely a combination of condensation and deoxygenation reactions to produce alkanes. Current commercial catalysts are not designed for such applications and have inherently poor lifetimes and selectivity. The specific goal of our research will be to improve catalyst selectivity and efficiency via a combination of materials design (at Cardiff) to create controlled pore architectures containing interconnected macro- and mesopores specifically aimed to reduce diffusion limitation of bulky and viscous feedstocks common to biomass. The design of materials will be guided by in-situ spectroscopic analysis of working catalysts (at Oklahoma) which will allow us to identify key features that lead to improved performance and thus allow the nature of the active site to be tailored accordingly. These samples will be tested in both laboratories under liquid (Cardiff) and vapor phase (Norman) conditions. We will use the acquired knowledge to design improved solid catalysts for aldol condensations, which are crucial for the conversion of biomass to chemicals and fuels. The proposed research thus addresses national and global needs for sustainability.

This project seeks to provide new mechanistic insight into surface mechanism of aldol condensation and associated production of biofuels. By evaluating catalytic materials and obtaining fundamental understanding via a combination of in-situ and detailed kinetic information we hope to tailor the catalyst surfaces to improve lifetime and selectivity thus generating new knowledge of catalytic systems and designing materials optimised for the transformation of biomass to fuels and chemicals. The resulting structure activity correlations and fundamental adsorption properties identified from the insitu studies will be of interest to materials and catalytic and surface chemists looking to develop new catalytic materials, while the kinetic work will interest chemical engineers involved in process design.

At a fundamental level this research will be of interest to both materials and catalytic scientists who will gain access to new classes of tailored materials for liquid phase acid and base catalysis. Such materials could be employed more widely in Organic Synthesis for condensation reactions (as well as other classes of reaction (e.g. esterification, alkylation, isomerisation). The development of selective heterogeneous catalysts will also be of wider interest to the synthetic community looking to apply green chemistry principles and replace conventional homogeneous reagents with cleaner technologies

The proposed activities will also advance discovery and promote scientific education within the US by involving senior and junior faculty, postdoctoral researchers, and graduate, undergraduate and high school students. The students will be exposed to the fundamental questions associated with the conversion of biomass to fuels, including the challenges posed by the high oxygen content of biomass, the thermodynamically feasible ways to reduce the oxygen content, and the challenge in developing catalysts that promote such reactions selectively, economically and with minimal environmental impact. Additionally, the students will be: 1) familiarized with the concepts of homogeneous and heterogeneous catalysis, and their application for chemicals processing; 2) will learn how the disciplines of Chemical Engineering and Chemistry are combined to work towards implementation of a novel process; 3) provide cutting-edge cross-disciplinary scientific and technical training and an international exchange experience for the involved researchers, including knowledge transfer in respective areas of spectroscopy and materials synthesis.

Society will benefit through the results and in the training of researchers who will become part of the workforce in sustainable technologies. The research will provide the scientific foundation for (i) future catalytic processes that would reduce the U.S. (and global) dependence on foreign fossil feedstock as well as CO2 emissions and for (ii) replacement of currently used caustic catalysts by environmentally sound, solid materials. The proposed research thus addresses national and global needs for sustainability.