Tuning the Catalytic Activity of Doped Graphene by Computational Design

Climate change and environmental pollution are two of the biggest threats faced by humankind in this century. In the past few decades, an increasing concern about the severe impact on health and climate change from the presence of nitrogen oxides (NOx) in fuel exhaust has led legislators to a drastic decrease in the permitted amount of NOx emissions from automotive engines and power stations. In this context, while facing an unprecedented global increase in CO2 and NOx emissions, with emerging catastrophic effects, this grant proposal aims at designing new graphene-based 2D materials for green catalysis.

Industrial catalysis is a highly energy intensive process that requires access to diminishing mineral resources, such as precious and rare earth metals. Graphene, the new "Miracle 2D Material" discovered in 2004, could offer a solution, but pure graphene is not chemically active for heterogeneous catalysis. The vision behind this research proposal is to use computational tools and modelling to design catalytically active graphene-based materials in which the properties of the active sites are tuned according to the desired chemical activity toward CO2 and NOx. In particular, we will investigate the role of chemical doping by substitutional insertion of boron, nitrogen and phosphorus (B-, N- and P-doping), defects (single vacancies, SW vacancies and edges), defect densities and strain on industrially and environmentally critical processes: 1) the reduction of NOx (deNOx process); 2) the sequestration and conversion of CO2. The specific aims of this proposal can therefore be summarized as follows:

1) Reduction of NOx: the current technology employed in deNOx treatment of NOx-rich fuel gas exhausts often requires increasingly expensive precious metals such as Pt, Pd and Rh. In order to reduce the concentration of the active metal phase in the deNOx catalysts the metal phase is often prepared as nanoparticles dispersed on an inert support or bound into coordination complexes with inorganic oxides. The catalyst preparation presents several technological challenges because the metal nanoparticles employed as active sites on inorganic supports, zeolites and metalorganic frameworks and are difficult to synthetize and grow in the desired size, shape and concentration. Alternative catalysts, in particular those based on activated 2D carbon materials, offer a viable alternative to costly traditional catalysts because they intrinsically offer much higher surface area, are extremely robust and flexible and can be prepared from common organic chemicals such as hydrocarbons, pyridine or ammonia (for N-doped graphene), phosphine or pyridine (for P-doped graphene).

2) Sequestration and conversion of CO2: To address the current trend in CO2 emission and global warming requires novel technology to both limit the amount of CO2 produced and to capture the CO2 contained in the gas exhausts from energy processes. In the past few years, graphene has generated considerable interest for its capacity to increase the efficiency of solar-fuel generation in photocatalytic materials. Graphene based technology has been shown to promote the reduction of CO2 to hydrocarbons and water. In these novel technologies, graphene has several roles: from suppressing the charge recombination and increasing the migrations of photogenerated electrons and holes, to the direct catalytic dissociation of CO2 and production of CO2-xH2x species (CH4, CH2O) and CH3OH. In this research, we will investigate the mechanism of CO2 sequestration and conversion on doped and defective graphene with the aim of designing the most promising functional modification of graphene that would be catalytically active while simultaneously maintaining a higher carrier mobility.

Global warming is one of the most critical crisis that our planet has ever faced. This incredibly complex problem requires novel and sustainable technological solutions and a strategic approach to scientific research. The UK has been leading the international effort in rising to the challenge of climate change and investing in green technologies and renewable energy sources. Fighting global warming with new, sustainable materials, industrial processes and reducing the emission of Green House gas, continues to be a national priority, as evidenced by the recent Clean Growth Strategy paper. The computational research project we propose, centred on the development of made-for-measure 2D materials for environmental catalysis, aims at reducing the cost and increasing the efficiency of materials for carbon capture and for the deNOx treatment of gas exhaust.
Graphene, the new "Miracle 2D Material" discovered in Manchester in 2004, has outstanding physical and thermal properties that can be exploited for creating novel carbon-based catalysts, but without a full theoretical analysis followed by a computer-based rational material design, graphene-based technological applications in this area might never succeed or arrive too late to the market. It is in this context that our project, in the area of computational surface science, offers a multidisciplinary approach to the design of graphene-based materials that goes beyond the traditional boundaries of material science, nanotechnology and catalysis. The work we propose aims at tuning the chemical activity of graphene towards CO2 and NOx by specific chemical doping and by introducing reactive sites in the form of point and line defects of the hexagonal graphene lattice. For this study, we will employ state-of-the art computational methods based on Density Functional Theory (DFT) and Ab Initio Molecular Dynamics (AIMD), which offer both high accuracy and flexibility. By accessing High Performance Computing (HPC) facilities, we will be able to simulate and characterize systems comprising thousands of atoms.
My group has a good track record of successful implementation of first-principle computational methods for catalysis and, for this project, we will collaborate with industrial and academic partners with a huge expertise and knowhow in 2D materials, catalysis and graphene. In particular, among our industrial partners there are global leaders in their respective market sectors: Johnson Matthey, producer of materials for environmental catalysis (i.e., hydrogen production, carbon capture and carbon sequestration), and Versarien, producer of graphene and other 2D carbon materials. Our academic partners are: Dr David Watson (surrey), who has an extensive experience in experimental catalysis and surface chemistry, Prof Ravi Silva (ATI, Surrey), who leads a very successful research group in the area of technological applications of graphene and 2D materials, and Dr Andrew Pollard (NPL), an authority in the field of metrology of 2D materials.
By combining theoretical modelling with experimental validation, material testing and applied catalysis, we will be able to accelerate the development of new catalytic carbon materials and exploit commercially our results for maximising the societal impact of this research. The PI on this project is also actively involved in a scientific and policy advising role within the Royal Society and he will make sure that communication and interaction with the policy makers, national academies and global strategic partners will continue during the course of the grant. Finally, a wide set of training opportunities will be available to the researchers on this grant thanks to the resources provided by the host institution as well as by the very generous in-kind training and mentoring contributions offered by our academic and industrial partners.