Operando Single Particle Catalysis - Combining a Nanoreactor and Plasmonic Nanospectroscopy

Heterogeneous catalysis is an important cornerstone of modern society with strong ties to the development of sustainable sources of energy and products. Catalysts are typically realized as supported metal nanoparticles that offer active sites that can accelerate chemical reactions by providing energetically more favorable reaction paths. Despite their broad use, the scrutiny of catalysts under realistic application conditions, such as high pressure and temperature, is a major experimental challenge. This difficulty is further amplified by the complexity present in real catalysts, often consisting of large ensembles of nanoparticles that all are unique. Furthermore, reactors used in catalysis studies often give rise to ill-defined reaction conditions in terms of catalyst distribution, reactant concentration and temperature. To mitigate these challenges, techniques are being developed to enable studies of catalytic nanoparticles under relevant operation conditions, so-called operando techniques. In this context, down-sized chemical reactors can be utilized to achieve precise control of both the catalyst, and the operating conditions. In this thesis, I have performed in situ studies of chemical reactions in/on nanoparticles by utilizing plasmonic nanospectroscopy based on the localized surface plasmon resonance (LSPR) phenomenon. The resonance condition for LSPR depends on both nanoparticle properties (size, shape, material) and the surrounding medium, which makes it possible to determine the physical and chemical state of individual nanoparticles optically. The LSPR response was used to study the oxidation of Cu nanoparticles, revealing the complex nature of nanoparticle oxidation kinetics, as well as particle specific oxidation mechanisms. Furthermore, a nanoreactor platform was developed and used in combination with plasmonic nanospectroscopy to perform operando characterization of individual Cu and Pt catalyst nanoparticles during CO oxidation. The obtained results illustrate how the oxidation of Cu results in catalyst deactivation and how reactant gradients formed inside the catalyst bed strongly affects the state of the catalyst, and thus its activity. Moreover, the nanoreactor enabled operando characterization of catalyst beds comprising 1000 well defined nanoparticles that could be individually addressed

Greening an Integrated Marketing Communication\u27s Course: An Assessment of Sustainability Literacy

This article showcases efforts of incorporating Sustainability Issues in an Integrated Marketing Communications (IMC) class during three semesters during the academic years of 2013/2014 and 2014/2015. The course was re-designed using Fink’s (2013) course recommendations of designing significant learning goals. In addition to the way the course was delivered (both face-to-face and online), the instructor worked with a Higher Ed publisher to customize a textbook to include sustainability issues related to the course content (i.e., reflecting IMC topics). The course re-design included sustainability assignments such as Virtual Field Trips (visiting corporate websites and other organizations to study their CSR statements and sustainability efforts). Sustainability related articles were pre-requisites for all assignments. In addition, the students had to watch several movies, including “So Right So Smart,” “Story of Stuff,” and other voluntary (not controlled for) movies dealing with social justice, natural capital or the dark side of “business as usual” provided through the university’s sustainability film series

Combining Nanoplasmonics and Nanofluidics for Single Particle Catalysis

Nanoparticles are, due to their large exposed surface area, widely used in the field of heterogeneous catalysis where they accelerate and steer chemical reactions. Although catalysis has been known about for centuries, the scrutiny of catalysts under realistic application conditions is still a major challenge. This difficulty originates from the fact that real catalyst materials are very complex, often consisting of large ensembles of nanoparticles that all are unique. Furthermore, the typically used macroscopic reactors in catalysis studies gives rise to locally, at the level of the active site, ill-defined reactant concentrations and diffusion limitations.To overcome these limitations, on one hand, techniques are being developed that are sensitive enough to probe individual catalytic particles and that at the same time can operate under realistic reaction conditions. On the other hand, strategies to more carefully control the amount and structure of catalyst material, as well as to precisely control mass transport to and from the active catalyst, are being investigated by scaling down the size of the used chemical reactor. To further push the limit of downsizing, in this thesis, I present a miniaturized reactor platform based on nanofluidic channels that have been carefully decorated with catalytic nanoparticles, and that is integrated with plasmonic nanospectroscopy readout. This optical technique relies on the nanoscale phenomenon known as the Localized Surface Plasmon Resonance (LSPR) and enables the study of individual metal nanoparticles in operando by means of dark-field scattering spectroscopy.As the first step in this development, we constructed a nanofluidic device with integrated plasmonic nanoparticles to detect minute changes in the liquid flowing through the channels, as well as molecules binding to the nanoparticles. As the second step, we developed the nanofluidic system with an integrated heater and to facilitate gas flow through the nanochannels with the possibility to connect to a mass spectrometer for on-line product analysis. This system was then successfully used to correlate activity with surface and bulk oxidation state changes taking place on individual catalytic Cu and Pt nanoparticles during CO oxidation, measured by means of plasmonic nanospectroscopy. To this end, in a separate study, I also employed the plasmonic approach to study the oxidation process of Cu nanoparticles both experimentally and by electrodynamics simulations

Plasmonic Metasurface for Spatially Resolved Optical Sensing in Three Dimensions

The highly localized sensitivity of metallic nanoparticles sustaining localized surface plasmon resonance (LSPR) enables detection of minute events occurring close to the particle surface and forms the basis for nanoplasmonic sensing. To date, nanoplasmonic sensors typically consist of two-dimensional (2D) nanoparticle arrays and can therefore only probe processes that occur within the array plane, leaving unaddressed the potential of sensing in three dimensions (3D). Here, we present a plasmonic metasurface comprising arrays of stacked Ag nanodisks separated by a thick SiO2 dielectric layer, which, through rational design, exhibit two distinct and spectrally separated LSPR sensing peaks and corresponding spatially separated sensing locations in the axial direction. This arrangement thus enables real-time plasmonic sensing in 3D. As a proof-of-principle, we successfully determine in a single experiment the layer-specific glass transition temperatures of a bilayer polymer thin film of poly(methyl methacrylate), PM/VIA, and poly(methyl methacrylate)/poly(methacrylic acid), P(MMA-MAA). Our work thus demonstrates a strategy for nanoplasmonic sensor design and utilization to simultaneously probe local chemical or physical processes at spatially different locations. In a wider perspective, it stimulates further development of sensors that employ multiple detection elements to generate distinct and spectrally individually addressable LSPR modes

Entrepreneurship Marketing in North Carolina’s Wine Industry

Entrepreneurial marketing seeks to create, communicate and deliver value to customers and manage customer relationships in ways that benefit the organization. This paper explores whether increased entrepreneurial marketing practices at North Carolina wineries can lead to enhanced winery performance. A web survey was delivered to N.C. wineries by email. The results suggest that winery customer intensity and innovation was positively related to winery satisfaction of winery performance. Also, innovation and value creation were found to be positively related to percentage sales change at wineries

Resolving single Cu nanoparticle oxidation and Kirkendall void formation with in situ plasmonic nanospectroscopy and electrodynamic simulations

Copper nanostructures are ubiquitous in microelectronics and heterogeneous catalysis and their oxidation is a topic of high current interest and broad relevance. It relates to important questions, such as catalyst active phase, activity and selectivity, as well as fatal failure of microelectronic devices. Despite the obvious importance of understanding the mechanism of Cu nanostructure oxidation, numerous open questions remain, including under what conditions homogeneous oxide layer growth occurs and when the nanoscale Kirkendall void forms. Experimentally, this is not trivial to investigate because when a large number of nanoparticles are simultaneously probed, ensemble averaging makes rigorous conclusions difficult. On the other hand, when (in situ) electron-microscopy approaches with single nanoparticle resolution are applied, concerns about beam effects that may both reduce the oxide or prevent oxidation via the deposition and cross-linking of carbonaceous species cannot be neglected. In response we present how single particle plasmonic nanospectroscopy can be used for the in situ real time characterization of multiple individual Cu nanoparticles during oxidation. Our analysis of their optical response combined with post mortem electron microscopy imaging and detailed Finite-Difference Time-Domain electrodynamics simulations enables in situ identification of the oxidation mechanism both in the initial oxide shell growth phase and during Kirkendall void formation, as well as the transition between them. In a wider perspective, this work presents the foundation for the application of single particle plasmonic nanospectroscopy in investigations of the impact of parameters like particle size, shape and grain structure with respect to defects and grain boundaries on the oxidation of metal nanoparticles

Shedding light on CO oxidation surface chemistry on single Pt catalyst nanoparticles inside a nanofluidic model pore

Investigating a catalyst under relevant application conditions is experimentally challenging and parameters like reaction conditions in terms of temperature, pressure, and reactant mixing ratios, as well as catalyst design, may significantly impact the obtained experimental results. For Pt catalysts widely used for the oxidation of carbon monoxide, there is keen debate on the oxidation state of the surface at high temperatures and at/above atmospheric pressure, as well as on the most active surface state under these conditions. Here, we employ a nanoreactor in combination with single-particle plasmonic nanospectroscopy to investigate individual Pt catalyst nanoparticles localized inside a nanofluidic model pore during carbon monoxide oxidation at 2 bar in the 450-550 K temperature range. As a main finding, we demonstrate that our single-particle measurements effectively resolve a kinetic phase transition during the reaction and that each individual particle has a unique response. Based on spatially resolved measurements, we furthermore observe how reactant concentration gradients formed due to conversion inside the model pore give rise to position-dependent kinetic phase transitions of the individual particles. Finally, employing extensive electrodynamics simulations, we unravel the surface chemistry of the individual Pt nanoparticles as a function of reactant composition and find strongly temperature-dependent Pt-oxide formation and oxygen spillover to the SiO2 support as the main processes. These results therefore support the existence of a Pt surface oxide in the regime of high catalyst activity and demonstrate the possibility to use plasmonic nanospectroscopy in combination with nanofluidics as a tool for in situ studies of individual catalyst particles

Operando detection of single nanoparticle activity dynamics inside a model pore catalyst material

Nanoconfinement in porous catalysts may induce reactant concentration gradients inside the pores due to local conversion. This leads to inefficient active material use since parts of the catalyst may be trapped in an inactive state. Experimentally, these effects remain unstudied due to material complexity and required high spatial resolution. Here, we have nanofabricated quasi-two-dimensional mimics of porous catalysts, which combine the traits of nanofluidics with single particle plasmonics and online mass spectrometry readout. Enabled by single particle resolution at operando conditions during CO oxidation over a Cu model catalyst, we directly visualize reactant concentration gradient formation due to conversion on single Cu nanoparticles inside the “model pore” and how it dynamically controls oxidation state-and, thus, activity-of particles downstream. Our results provide a general framework for single particle catalysis in the gas phase and highlight the importance of single particle approaches for the understanding of complex catalyst materials