Over the last two centuries mankind habits and activities were influenced by a technical revolution which dramatically increased the energy needs, that were fulfilled mainly by coal, oil, and natural gas, due to their high energy density and availability. CO2 is consequently accumulating in the atmosphere, and this phenomenon is among the main causes of climate change. CO2 activation by means of green hydrogen through Reverse Water Gas Shift (RWGS) reaction (CO2+H2⇄CO+H2O) can be a valuable route to carbon neutrality. This reaction generates CO, a key intermediate to produce methanol and liquid hydrocarbons. Noble metals dispersed nanoparticles (NPs) on a support material are usually adopted as heterogeneous catalysts for RWGS. These catalysts dynamically change structure when exposed to different conditions during the reaction, varying their activity and selectivity. This thesis is framed within SPOON project, which aims at developing an experimental methodology that combines surface plasmon resonance (SPR) and catalysis, for the in-operando characterization of NPs shape and size. SPR can be monitored under reaction conditions integrating a UV-Vis spectrometer with a reactor for kinetic analyses. In this way, investigating morphological changes during reaction will allow to shed light on the structure-activity dynamics, and to optimize catalyst performances. This work will firstly deal with the MATLAB implementation of Mie model, that can be used to describe SPR phenomenon. Then, the synthesis of gold NPs supported on alumina, chosen for their high catalytic activity during RWGS combined with an intense SPR, will be discussed. Samples were investigated through HRTEM, FESEM and ex situ UV-Vis spectroscopy, allowing to correlate the SPR to the NPs morphology. Furthermore, we designed and optimized an operando UV-Vis setup, to monitor RWGS reaction kinetic while collecting spectroscopic data. For this study we mainly used a powder reactor. Some initial investigations were also performed with an annular reactor, which will be furtherly studied in future works together with the possibility to extend the proposed methodology to Rh and Pt catalysts.
La rivoluzione tecnica degli ultimi due secoli ha influenzato le abitudini e le attività dell'uomo e ha aumentato notevolmente il fabbisogno energetico, soddisfatto principalmente da carbone, petrolio e gas, per via dell’elevata disponibilità e densità energetica. Questo ha portato a un progressivo accumulo di CO2 in atmosfera, diventando una delle cause principali del cambiamento climatico. In questo contesto, la conversione della CO2 tramite la Reverse Water Gas Shift (RWGS) con l’impiego di idrogeno verde (CO2+H2⇄CO+H2O) rappresenta una possibile via per la carbon neutrality. Il CO prodotto è, infatti, una molecola chiave per la sintesi di metanolo e idrocarburi liquidi. Le nanoparticelle (NPs) di metalli nobili depositate su un supporto sono degli efficaci catalizzatori eterogenei per la RWGS ed esse cambiano struttura in funzione delle condizioni di reazione, variando la loro attività e selettività. Questa tesi rientra nel progetto SPOON, che mira a combinare la risonanza plasmonica di superficie (RPS) e la catalisi per lo studio in operando della forma e delle dimensioni delle NPs. L’RPS può essere monitorata in condizioni di reazione integrando uno spettrofotometro UV-Vis con un reattore per analisi cinetiche. Lo studio dei cambiamenti morfologici in reazione permette infatti di studiare la dinamica tra struttura e attività del catalizzatore, per ottimizzarne le prestazioni. In questo lavoro l'implementazione MATLAB del modello di Mie è stata utilizzata per descrivere l’RPS. È discussa inoltre la sintesi di NPs d’oro su allumina, che presentano una significativa attività catalitica per la RWGS e un’intensa RPS. I campioni sono stati studiati con HRTEM, FESEM e tramite spettroscopia UV-Vis ex situ, ottenendo così una correlazione tra l'RPS e la morfologia delle NPs. Inoltre, è stato progettato e ottimizzato un setup UV-Vis operando, che ha permesso di misurare in simultanea la cinetica di reazione della RWGS e i dati spettroscopici. Per questo studio è stato principalmente utilizzato un reattore in polvere. Infine, è stata condotta un’indagine preliminare per ampliare l’uso del setup anche ad un reattore anulare e a nuovi catalizzatori a base di Rh e Pt.
Monitoring catalytic nanoparticle dynamics by UV-Vis operando spectroscopy : an application to CO2 activation via reverse water gas shift on Au
COLOMBO, RICCARDO;ALLEVA, FEDERICO
2020/2021
Abstract
Over the last two centuries mankind habits and activities were influenced by a technical revolution which dramatically increased the energy needs, that were fulfilled mainly by coal, oil, and natural gas, due to their high energy density and availability. CO2 is consequently accumulating in the atmosphere, and this phenomenon is among the main causes of climate change. CO2 activation by means of green hydrogen through Reverse Water Gas Shift (RWGS) reaction (CO2+H2⇄CO+H2O) can be a valuable route to carbon neutrality. This reaction generates CO, a key intermediate to produce methanol and liquid hydrocarbons. Noble metals dispersed nanoparticles (NPs) on a support material are usually adopted as heterogeneous catalysts for RWGS. These catalysts dynamically change structure when exposed to different conditions during the reaction, varying their activity and selectivity. This thesis is framed within SPOON project, which aims at developing an experimental methodology that combines surface plasmon resonance (SPR) and catalysis, for the in-operando characterization of NPs shape and size. SPR can be monitored under reaction conditions integrating a UV-Vis spectrometer with a reactor for kinetic analyses. In this way, investigating morphological changes during reaction will allow to shed light on the structure-activity dynamics, and to optimize catalyst performances. This work will firstly deal with the MATLAB implementation of Mie model, that can be used to describe SPR phenomenon. Then, the synthesis of gold NPs supported on alumina, chosen for their high catalytic activity during RWGS combined with an intense SPR, will be discussed. Samples were investigated through HRTEM, FESEM and ex situ UV-Vis spectroscopy, allowing to correlate the SPR to the NPs morphology. Furthermore, we designed and optimized an operando UV-Vis setup, to monitor RWGS reaction kinetic while collecting spectroscopic data. For this study we mainly used a powder reactor. Some initial investigations were also performed with an annular reactor, which will be furtherly studied in future works together with the possibility to extend the proposed methodology to Rh and Pt catalysts.| File | Dimensione | Formato | |
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https://hdl.handle.net/10589/186640