Since the 1990s, with the advent of nanocatalysts, the pervasiveness of catalysis for the creation of everyday products has become apparent.
Nanocatalysts, especially metallic nanoparticles (NPs), combine the high efficiency and selectivity of homogeneous catalysts with the ease of recovery and recycling of heterogeneous catalysts. The objective in NP catalyst design is to tailor materials to give higher activity, product selectivity, and longevity while lowering economic cost and environmental impact. At the nanoscale, properties of materials (catalytic, optical, magnetic, etc.) are often different from those of their bulk counterparts due to surface effects and quantum effects. Furthermore, recent significant advances in microscopy and spectroscopy techniques allow the structure of NPs to be resolved at the atomic level, and for their evolution to be monitored and even offer the possibility to perform in-situ studies of the chemistry and structures of NPs in a reactive environment.Although we now fully appreciate that NPs have unique capabilities, their chemistry is still poorly understood as we are not able to predict how the architecture (size, morphology, chemical composition and chemical ordering) of NPs depend on the preparation methodology used in their fabrication. This is an essential requirement for designing catalysts for current challenges in the chemicals and energy sectors.
To achieve control of NP properties through the design of synthetic methodology and environmental conditions in which they operate in actual catalysis application is the ultimate of the proposed research programme.The research objectives and methodology of the project are:(1) Explore the energy landscapes of Pd and Pt-based NPs and nanoalloys (alloying with cheaper metals such as Fe, Co, Ni, Cu), including their mechanical, chemical and thermal stability in the gas phase, and in different environments (substrates, solvent, ligands) using multiscale methodology. Accurate but computationally demanding first principles quantum mechanical (QM) calculations based on standard Density Functional Theory (DFT) (using VASP, NWChem and Gaussian) as well as reduced-scaling DFT (using the linear scaling ONETEP DFT code) for NPs with up to 1000 atoms will be used to validate and refine the parameters of molecular mechanics (MM) force-fields for more extensive simulations and for simulations with hybrid QM/MM models. The support will then be included in the simulations by considering a variety of surfaces (e.
g., graphene, titania, alumina) in contact with the NPs, aiming to simulate the liquid and gas phase techniques of catalyst synthesis using molecular dynamics (MD) simulations. Solvent molecules that participate in chemical reactions or strongly interact with the NP or the support will be treated explicitly at the DFT level. The effect of the bulk of the solvent will be incorporated using an implicit solvent model (polarisable medium) for QM/MM calculations of both unsupported and supported NPs. These studies aim to provide new insights into the nucleation-growth-coalescence-synthesis process in various realistic environments.(2) Use the sampling of NP energy landscapes and structures from all the simulation stages as the starting point for a new and original classification of the active surface arising from the definition of electronic and geometrical descriptors, as a function of the coverage.
Machine learning will be used to analyse the structural database (with a huge array of possible geometries and compositions) to classify NP structures.(3) Deduce the mechanisms of target green chemical reactions (oxidation of CO, reduction of CO2, H2 evolution etc.) at the atomic level and introduce lattice models, to link properties defined by the descriptors to catalytic performance via kinetic models that bridge the size, shape and material gap. Our aim here is to provide specific design rules for multi-metallic NPs, identifying the best NP architecture and the ideal environmental conditions.Being able to design NPs with specific chemical properties will result in huge improvements in efficiency (activity, selectivity, turnover frequency, catalyst lifetime) and cost savings relative to existing catalysts, by reducing the quantity of rare metals (a concern of the Birmingham Centre for Strategic Elements & Critical Materials).