Tuning the Catalytic Activity of Doped Graphene by Computational Design

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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.