Hydrogen Free Selective Hydrogenation: Step Changing Innovation in Catalysis by Gold

This project sets out the ambitious goal of achieving atom efficiency and enhanced catalytic activity in "hydrogen free" hydrogenation in continuous flow operation. The work brings together two established research groups with expertise in heterogeneous catalyst preparation, characterisation and reaction engineering (Keane, Chemical Engineering, Heriot-Watt University) and catalytic surface science (Baddeley, Chemistry, St. Andrews University). The synergy that results from this collaboration allows innovation with respect to catalyst design and optimisation with the integration of fundamental and in situ surface science measurements into catalyst synthesis/characterisation and testing. Prior work has established ultra-selectivity in nitro- and carbonyl- group reduction over supported Au catalysts. However, reaction rates were appreciably lower than standard non-selective (Pt, Pd and Ni) metal catalysts due to the activation energy barrier for H2 dissociative adsorption on Au. Gold promoted hydrogenation is conducted in excess H2 that remains unreacted, resulting in fundamental process inefficiency and unsustainability. We propose an innovative coupling of catalytic dehydrogenation (as a source of reactive hydrogen) with hydrogenation. Preliminary data provide proof of concept for the coupling of 2-butanol dehydrogenation with furfural hydrogenation (to furfuryl alcohol) over physical mixtures of oxide supported Au and Cu. We have recorded (orders of magnitude) enhanced H2 utilisation in the coupled system and elevated selective hydrogenation rate relative to the single component Au catalyst. Furfural is a biomass derived heterocyclic aldehyde that can serve as a non-petroleum based renewable feedstock. The target furfuryl alcohol product is a high value chemical used to manufacture resins/rubbers/adhesives and as a chemical building block for drug synthesis. Our proposed coupling reaction is step changing and closes the sustainability gap in terms of unreacted hydrogen. As Au in effect 'borrows' hydrogen generated in situ via Cu promoted dehydrogenation, the coupled system circumvents the use of compressed H2, which has important safety implications for large scale chemical production.
We have set out to gain a fundamental understanding of coupled dehydrogenation/ hydrogenation through a programme of surface science measurements involving STM, RAIRS, XPS, TPD and DRIFTS analysis that will provide critical information on reactant/product surface interactions. The work will first focus on reaction coupling over supported Au and Cu physical mixtures, addressing sensitivity to metal particle size and electronic character, the role of the metal/support interface, hydrogen spillover, transport and reactivity. The molecular-level mechanistic understanding provided by the surface science methodologies coupled with a determination of the influence of the gas phase species on surface composition (MEIS) will inform synthesis of supported bimetallics (Au-Cu) with a programme of rational catalyst design directed at achieving the catalyst formulation that delivers the optimum hydrogen utilisation efficiency. Collaboration with Syngenta and Sasol Technology UK as industrial partners will ensure that the work delivers real commercial impact. The ultimate deliverable is a catalytic process than can deliver 100% selectivity at elevated rates in the sustainable hydrogen free hydrogenation of renewable furfuran platform reactants.
This proposal fits well with the EPSRC shaping capability agenda, notably the "catalysis" theme, underpinning "energy efficiency", "sustainability" and "frontier manufacturing" priorities. Moreover, the work tackles head on the "Dial-a-Molecule-100% Efficient Synthesis" Grand Challenge with a programme of work directed at the "catalytic paradigms for 100% efficient synthesis" theme.

Commercialisation of heterogeneous catalysts is critical throughout the chemical and pharmaceutical sectors. Advances in sustainable catalytic processes are paramount in the drive to cleaner production. We propose an innovative coupling of dehydrogenation with hydrogenation harnessing the ultra-selective action of supported Au catalysts in the atom efficient conversion of biomass-derived furfural to high value furfuryl alcohol without recourse to an external supply of pressurised hydrogen. We have demonstrated enhanced hydrogen utilisation in the coupled system with significantly higher hydrogenation rates than recorded for conventional operations. Our ultimate goal of identifying the optimum supported (Au-Cu) bimetallic catalyst formulation for "hydrogen free" hydrogenation of furan platform chemicals to high value products will represent a step change in hydrogenation operations, impacting on product inventories that run to millions of tonnes per year.
Economy
Our coupled system circumvents the use of compressed hydrogen, which has important safety, energy usage and cost implications for large scale chemical production. Delivery of atom efficient hydrogenation will have enormous impact across the UK chemical industry in a 10-50 year time-frame. This is recognised by our industrial partners (Syngenta and Sasol) with whom we will work to ensure commercial exploitation. Existing routes to fine chemicals involve high pressure batch processes that deliver low product yields and require multistage separations and waste treatment. The commercial sector face economic pressures including escalating disposal charges and increasing raw material/energy costs, which can be addressed by use of platform chemicals from bio-renewable resources, alternative hydrogen sources and improved process selectivity. This project will strengthen UK leadership in this field, providing significant employment and wealth creation.
Society and Environment
Cleaner, safer chemical production is essential to meet UK environmental and health/safety legislation, addressing crucial societal needs. We tackle sustainability in sourcing the organic reactants and supply of hydrogen. The US "National Academies", which bring together committees of experts across science and technology, has identified "Grand Challenges in Sustainability". These include "Green and Sustainable Chemistry and Engineering", directed at discovering new ways to carry out chemical transformations based on the ultimate premise that "it is better to prevent waste than to clean it up after it is formed": this underpins our proposal.
Scientist Training
Barriers exist in the commercial application of sustainable processing, which are largely a result of inadequate education, management and training of chemists/chemical engineers. A driver in this proposal is to provide research training that cuts across discipline boundaries. The PDRAs will draw on the Scottish Institute for Enterprise 'Business and Enterprise' training to meet the aims of RCUK to develop entrepreneurship and enterprise skills. Industry and/or academia will benefit via the provision of highly skilled individuals with unique technical and commercial skills that can contribute directly to the chemical sector as effective sustainability practitioners.
Cross-Disciplinary Beneficiaries
Real impact in achieving the ambitious goal of atom efficient chemical processing requires a strategic integration of cross-disciplinary research methodologies. This collaboration will enhance the activities of both investigators. The incorporation of catalyst testing in flow operation to inform surface measurements will redefine Baddeley's (Chem, USTAN) research while Keane (Chem Eng, HWU) will consider advanced surface analysis as a tool for catalyst design. This proposal exemplifies the required synergy between chemists and chemical engineers identified by the US National Academies as critical to achieving advances in sustainable processing.