I will present an overview of the theoretical methods and concepts (together with selected applications) we developed to achieve a predictive modeling, and thus a rational design, of the functional properties of metal-based nano-materials. In our research, emphasis is on catalytic and optical response, and on the development of hierarchical techniques starting from quantum-mechanical approaches and reaching up to meso-scale systems under realistic conditions and environment. I will first discuss a Reactive Glocal Optimization (RGO) approach as a computational protocol able to explore the reactive phase space of these systems in the presence of reactant molecules [1]. I will then show how the application of RGO systematic sampling under realistic conditions naturally leads to the concept of ligand/cluster/support catalytic complex, i.e., an in-situ-formed aggregate which acts as the catalytically active species [2], and how this is demonstrated in subnanometer - or ultra-nano - alloyed Ag-Pt metal clusters achieving record CO oxidation activity [3]. Second, I will illustrate how harsh reactive ligands can lead to phase transformations to nano-porous systems via de-alloying, such as it happens in Ni-Pt nanostructures under electrochemical ORR (oxygen reduction reaction - the rate-determining step in low-temperature hydrogen fuel cells for sustainable and energy-efficient electrical power) [4], and how the relationships between the resulting nano-porous surface coordination and reaction mechanisms can explain the enhanced ORR performance of these systems, and finally lead to the design and experimental realization of systems exhibiting record ORR activity, with a 50-fold enhancement with respect to catalysts used in commercial devices, i.e., de-alloyed pure platinum ultrafine nano-wires, in excellent agreement with theoretical predictions [5]. Finally, I will present results of an extensive multi-scale investigation of the ammonia synthesis Haber-Bosch (HB) process (conversion of hydrogen, H2, and nitrogen, N2, into NH3) over iron-based catalysts, chosen for its societal importance (100+ millions of tons of ammonia annually produced, consuming 2% of the world's energy supply) and as a prototypical case of heterogeneous nano-catalysis under realistic environment. In our computational protocol, we focus on Fe bcc(111) surface - the most active environmentally compatible single-metal catalyst surface - and, starting from Quantum-Mechanics values of free-energies and barriers, we build up a kinetic Monte Carlo (kMC) model, which allows us to predict steady-state catalytic reaction rates averaged over a time scale > tens of seconds, and thus to validate our predictions against experimental kinetic data from literature [6]. We will then use the detailed knowledge derived for this system to consider modifications of the catalyst such as doping, devising a hierarchical high-throughput screening (HHTS) approach to catalyst design to single out the most promising dopant elements and configurations [6]. References 1) F. R. Negreiros, et al., Nanoscale 4, 1208 (2012); ACS Cat. 2, 1860 (2012). 2) F. R. Negreiros, et al., Comptes Rendue Chim. 17, 625-633 (2014); Phys. Chem. Chem. Phys. 16, 26570-7 (2014); Inorg. Chim. Acta 431, 150-155 (2015).3) A. El Abed and V. Taly, Optical Materials 36, 64 (2014). 3) F. R. Negreiros, et al., Angew. Chem. Int. Ed. 57, 1209-1213 (2018); A. Fortunelli, S. Vajda, H. Yasumatzu, Patent US-2017087538 (30/03/2017) 4) A. Fortunelli et al. Chem. Sci. 6, 3915-3925 (2015); 5) M. Li at el. Science 354, 1414-1419 (2016). 6) J. Qian et al. J. Am. Chem. Soc. 140, 6288-6297 (2018); submitted (2018).
Hierarchical First-Principles-Based Modeling of Metal Nanostructured Catalysts
Alessandro Fortunelli
2019
Abstract
I will present an overview of the theoretical methods and concepts (together with selected applications) we developed to achieve a predictive modeling, and thus a rational design, of the functional properties of metal-based nano-materials. In our research, emphasis is on catalytic and optical response, and on the development of hierarchical techniques starting from quantum-mechanical approaches and reaching up to meso-scale systems under realistic conditions and environment. I will first discuss a Reactive Glocal Optimization (RGO) approach as a computational protocol able to explore the reactive phase space of these systems in the presence of reactant molecules [1]. I will then show how the application of RGO systematic sampling under realistic conditions naturally leads to the concept of ligand/cluster/support catalytic complex, i.e., an in-situ-formed aggregate which acts as the catalytically active species [2], and how this is demonstrated in subnanometer - or ultra-nano - alloyed Ag-Pt metal clusters achieving record CO oxidation activity [3]. Second, I will illustrate how harsh reactive ligands can lead to phase transformations to nano-porous systems via de-alloying, such as it happens in Ni-Pt nanostructures under electrochemical ORR (oxygen reduction reaction - the rate-determining step in low-temperature hydrogen fuel cells for sustainable and energy-efficient electrical power) [4], and how the relationships between the resulting nano-porous surface coordination and reaction mechanisms can explain the enhanced ORR performance of these systems, and finally lead to the design and experimental realization of systems exhibiting record ORR activity, with a 50-fold enhancement with respect to catalysts used in commercial devices, i.e., de-alloyed pure platinum ultrafine nano-wires, in excellent agreement with theoretical predictions [5]. Finally, I will present results of an extensive multi-scale investigation of the ammonia synthesis Haber-Bosch (HB) process (conversion of hydrogen, H2, and nitrogen, N2, into NH3) over iron-based catalysts, chosen for its societal importance (100+ millions of tons of ammonia annually produced, consuming 2% of the world's energy supply) and as a prototypical case of heterogeneous nano-catalysis under realistic environment. In our computational protocol, we focus on Fe bcc(111) surface - the most active environmentally compatible single-metal catalyst surface - and, starting from Quantum-Mechanics values of free-energies and barriers, we build up a kinetic Monte Carlo (kMC) model, which allows us to predict steady-state catalytic reaction rates averaged over a time scale > tens of seconds, and thus to validate our predictions against experimental kinetic data from literature [6]. We will then use the detailed knowledge derived for this system to consider modifications of the catalyst such as doping, devising a hierarchical high-throughput screening (HHTS) approach to catalyst design to single out the most promising dopant elements and configurations [6]. References 1) F. R. Negreiros, et al., Nanoscale 4, 1208 (2012); ACS Cat. 2, 1860 (2012). 2) F. R. Negreiros, et al., Comptes Rendue Chim. 17, 625-633 (2014); Phys. Chem. Chem. Phys. 16, 26570-7 (2014); Inorg. Chim. Acta 431, 150-155 (2015).3) A. El Abed and V. Taly, Optical Materials 36, 64 (2014). 3) F. R. Negreiros, et al., Angew. Chem. Int. Ed. 57, 1209-1213 (2018); A. Fortunelli, S. Vajda, H. Yasumatzu, Patent US-2017087538 (30/03/2017) 4) A. Fortunelli et al. Chem. Sci. 6, 3915-3925 (2015); 5) M. Li at el. Science 354, 1414-1419 (2016). 6) J. Qian et al. J. Am. Chem. Soc. 140, 6288-6297 (2018); submitted (2018).I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
