Sunday, March 28, 2010

Bio-Inspired Iron-Nickel Sulfide Nano-Catalysts for CO2 Conversion Under Development at University College London

University College London scientists led by Professor Nora De Leeuw will work with Johnson Matthey to mimic biological systems and produce a catalytic reactor that can convert CO2 into useful chemicals for applications such as fuel cells in laptops and mobile phones. Other investigators in the $1.69 million project (£1.138 million) include Professor CRA Catlow, Dr. J Darr, Professor ES Fraga, Dr. G Hogarth and Dr. KB Holt

The reactor will use novel nano-catalysts based on compounds formed in warm springs on the ocean floor that are considered to have triggered the emergence of life. The team’s design will take inspiration from biological systems that can carry out complex processes to convert CO2 into biological material, and exploit a wide range of computational and experimental chemistry techniques.

Professor De Leeuw says: “If we were able to emulate nature and convert CO2 into useful products without having to use large amounts of energy, the benefits would be enormous. One of the major gases responsible for climate change would become an important raw material for the chemical and pharmaceutical industries.”

Despite the high thermodynamic stability of CO2, biological systems are capable of both activating the molecule and converting it into a range of organic molecules, all of which under moderate conditions. It is clear that, if we were able to emulate Nature and successfully convert CO2 into useful chemical intermediates without the need for extreme reaction conditions, the benefits would be enormous: One of the major gases responsible for climate change would become an important feedstock for the chemical and pharmaceutical industries!

Iron-nickel sulfide membranes formed in the warm, alkaline springs on the Archaean ocean floor are increasingly considered to be the early catalysts for a series of chemical reactions leading to the emergence of life. The anaerobic production of acetate, formaldehyde, amino acids and the nucleic acid bases - the organic precursor molecules of life - are thought to have been catalyzed by small cubane (Fe,Ni)S clusters (for example Fe5NiS8), which are structurally similar to the surfaces of present day sulfide minerals such as greigite (Fe3S4) and mackinawite (FeS).

Contemporary confirmation of the importance of sulfide clusters as catalysts is provided by a number of proteins essential to modern anaerobic life forms, such as ferredoxins, hydrogenases, carbon monoxide dehydrogenase (CODH) or acetyl-coenzyme A synthetase (ACS), all of which retain cubane (Fe,Ni)S clusters with a greigite-like local structure, either as electron transfer sites or as active sites to metabolize volatiles such as H2, CO and CO2.

In view of the importance of (Fe,Ni)S minerals as catalysts for pre-biotic CO2 conversion, we propose employing a robust combination of state-of-the-art computation and experiment in a grand challenge to design, synthesise, test, characterise, evaluate and produce for scale-up novel iron-nickel sulfide nano-catalysts for the activation and chemical modification of CO2. The design of the (Ni,Fe)S nano-particles is inspired by the active sites in modern biological systems, which are tailored to the complex redox processes in the conversion of CO2 to biomass.

The scientific outcome of the Project will be the design and development of a new class of sulphide catalysts, tailored specifically to the reduction and conversion of CO2 into chemical feedstock molecules, followed by the fabrication of an automated pilot device. Specific deliverables include:

i. Atomic-level understanding of the effect of size, surface structure and composition on stabilities, the redox properties and catalytic activities of (Fe,Ni)S nano-catalysts;

ii. Development of novel synthesis methods of Fe-M-S nano-clusters and -particles with tailored catalytic properties (M = Ni and other promising transition metal dopants);

iii. Rapid production and electro-catalytic screening of lead nano-catalysts for the activation/conversion of CO2;

iv. Development and application of a new integrated design-synthesis-screening approach to produce effective nano-catalysts for desired reactions;

v. Construction of a prototype device capable of catalyzing low-temperature reactions of CO2 into products at typical low-voltages, that can be obtained from solar energy;

vi. Identification of optimum process for scale-up in Stage 2, from the Economic, Environmental and Societal Impact evaluation

The target at the end-point of Stage 1 is the fabrication of a photo-electrochemical reactor capable of harvesting solar energy to (i) recover CO2 from carbon capture process streams, (ii) combine it with hydrogen, and (iii) catalyze the reaction into product. In Stage 2 of the project, the prototype will be developed into a scaled-up commercially viable device, using optimum catalyst(s) in terms of (i) reactivity/selectivity towards the desired reaction; (ii) economic impact; and (iii) environmental, ethical and societal considerations.

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