Hydrogen spillover is the surface migration of activated hydrogen atoms from a metal catalyst particle, on which they are generated, onto the catalyst support. The phenomenon has been much studied ...and its occurrence on reducible supports such as titanium oxide is established, yet questions remain about whether hydrogen spillover can take place on nonreducible supports such as aluminium oxide. Here we use the enhanced precision of top-down nanofabrication to prepare controlled and precisely tunable model systems that allow us to quantify the efficiency and spatial extent of hydrogen spillover on both reducible and nonreducible supports. We place multiple pairs of iron oxide and platinum nanoparticles on titanium oxide and aluminium oxide supports, varying the distance between the pairs from zero to 45 nanometres with a precision of one nanometre. We then observe the extent of the reduction of the iron oxide particles by hydrogen atoms generated on the platinum using single-particle in situ X-ray absorption spectromicroscopy applied simultaneously to all particle pairs. The data, in conjunction with density functional theory calculations, reveal fast hydrogen spillover on titanium oxide that reduces remote iron oxide nanoparticles via coupled proton-electron transfer. In contrast, spillover on aluminium oxide is mediated by three-coordinated aluminium centres that also interact with water and that give rise to hydrogen mobility competing with hydrogen desorption; this results in hydrogen spillover about ten orders of magnitude slower than on titanium oxide and restricted to very short distances from the platinum particle. We anticipate that these observations will improve our understanding of hydrogen storage and catalytic reactions involving hydrogen, and that our approach to creating and probing model catalyst systems will provide opportunities for studying the origin of synergistic effects in supported catalysts that combine multiple functionalities.
Achromatic Talbot lithography (ATL) at extreme ultraviolet (EUV) wavelengths has been used to produce one or two-dimensional periodic patterns over large areas. In this work, an ATL transmission mask ...was used to perform EUV exposures at 13.5nm and 8.8nm illumination wavelengths at two different synchrotron facilities, to study the broadband nature of the method and the used mask as well as to investigate the influence of illumination parameters and experimental arrangements. The experiments were performed at the Swiss Light Source (SLS), PSI, Switzerland, and at the Shanghai Synchrotron Radiation Facility (SSRF), P. R. China. Achromatic Talbot lithography was proven to be a simple and robust interference lithography scheme for producing large area and high resolution patterns suitable for different wavelengths and for a variety of EUV sources and setups.
Display omitted
•High resolution patterning of 20nm dots at 100nm pitch using achromatic Talbot lithography at broadband EUV illumination.•Easy to fabricate ATL mask for efficient nano-lithography with various EUV beamlines of differing illumination parameters.•Exposures at the Swiss Light Source and the Shanghai Synchrotron Radiation Facility were performed and compared.
We present recent developments in top–down nanofabrication that have found application in catalysis research. To unravel the complexity of catalytic systems, the design and use of models with control ...of size, morphology, shape and inter-particle distances is a necessity. The study of well-defined and ordered nanoparticles on a support contributes to the understanding of complex phenomena that govern reactions in heterogeneous and electro-catalysis. We review the strengths and limitations of different nanolithography methods such as electron beam lithography (EBL), photolithography, extreme ultraviolet (EUV) lithography and colloidal lithography for the creation of such highly tunable catalytic model systems and their applications in catalysis. Innovative strategies have enabled particle sizes reaching dimensions below 10 nm. It is now possible to create pairs of particles with distance controlled with an extremely high precision in the order of one nanometer. We discuss our approach to study these model systems at the single-particle level using X-ray absorption spectroscopy and show new ways to fabricate arrays of single nanoparticles or nanoparticles in pairs over a large area using EBL and EUV-achromatic Talbot lithography. These advancements have provided new insights into the active sites in metal catalysts and enhanced the understanding of the role of inter-particle interactions and catalyst supports, such as in the phenomenon of hydrogen spillover. We present a perspective on future directions for employing top–down nanofabrication in heterogeneous and electrocatalysis. The rapid development in nanofabrication and characterization methods will continue to have an impact on understanding of complex catalytic processes.
An extended theoretical investigation of the electronic and interface properties of titania and alumina with and without supported platinum nanoparticles is presented and compared to recent ...experimental data with the aim to understand the mechanism of hydrogen activation, adsorption, and spillover. Thirteen-atom platinum particles on titania adopt a distinct different structure than on alumina, which results in distinct hydrogen coverages. Upon hydrogen adsorption, titania is reduced with creation of Ti(III) electronic trap states, strongly interacting with the surface adsorbed protons. The combined Ti(III)/proton migration rate is slower than the one of single surface protons, and it is not influenced by the presence of coadsorbates, such as water molecules. Hydrogen is instead heterolytically split on defect sites on alumina with the formation of a surface proton and a hydride moiety, bound to the particularly reactive surface tricoordinated aluminum site. The electronic structure of alumina is only marginally altered, without formation of defect states. The mobility of the hydride moiety is limited, in particular in the presence of coadsorbed water molecules, that compete for the adsorption sites. Modeling of hydrogen spillover from a platinum cluster to the metal oxide demonstrates that the spillover rate depends on the hydrogen partial pressure and on the thickness of the oxide acceptor layer. Kinetic Monte Carlo results confirm that hydrogen spreading on titania leads to a homogeneous coverage, while on alumina hydrogen can only be found up to a few nm from the platinum cluster because of kinetic competition between diffusion and desorption.
Understanding the chemistry of nanoparticles is crucial in many applications. Their synthesis in a controlled manner and their characterization at the single particle level is essential to gain ...deeper insight into chemical mechanisms. In this work, single nanoparticle spectro-microscopy with top-down nanofabrication is demonstrated to study individual iron nanoparticles of nine different lateral dimensions from 80 nm down to 6 nm. The particles are probed simultaneously, under same conditions, during in-situ redox reaction using X-ray photoemission electron microscopy elucidating the size effect during the early stage of oxidation, yielding time-dependent evolution of iron oxides and the mechanism for the inter-conversion of oxides in nanoparticles. Fabrication of well-defined system followed by visualization and investigation of singled-out particles eliminates the ambiguities emerging from dispersed nanoparticles and reveals a significant increase in the initial rate of oxidation with decreasing size, but the reactivity per active site basis and the intrinsic chemical properties in the particles remain the same in the scale of interest. This advance of nanopatterning together with spatially-resolved single nanoparticle X-ray absorption spectroscopy will guide future discourse in understanding the impact of confinement of metal nanoparticles and pave way to solve fundamental questions in material science, chemical physics, magnetism, nanomedicine and nanocatalysis.
Well-defined model systems are needed for better understanding of the relationship between optical, electronic, magnetic, and catalytic properties of nanoparticles and their structure. Chemical ...synthesis of metal nanoparticles results in large size and shape dispersion and lack of lateral order. In contrast, conventional top-down lithography techniques provide control over the lateral order and dimensions. However, they are either limited in resolution or have low throughput and therefore do not enable the large patterning area needed to obtain good signal-to-noise ratio in common analytical and characterization techniques. Extreme ultraviolet (EUV) lithography has the throughput and simplicity advantages of photolithography as well as high resolution due to its wavelength. Using EUV achromatic Talbot lithography, we have obtained 15 nm particle arrays with a periodicity of about 100 nm over an area of several square centimeters with high-throughput enabling the use of nanotechnology for fabrication of model systems to study large ensembles of well-defined identical nanoparticles with a density of 10(10) particles cm(-2).
Well-defined model systems are needed for better understanding of the relationship between optical, electronic, magnetic, and catalytic properties of nanoparticles and their structure. Chemical ...synthesis of metal nanoparticles results in large size and shape dispersion and lack of lateral order. In contrast, conventional top-down lithography techniques provide control over the lateral order and dimensions. However, they are either limited in resolution or have low throughput and therefore do not enable the large patterning area needed to obtain good signal-to-noise ratio in common analytical and characterization techniques. Extreme ultraviolet (EUV) lithography has the throughput and simplicity advantages of photolithography as well as high resolution due to its wavelength. Using EUV achromatic Talbot lithography, we have obtained 15 nm particle arrays with a periodicity of about 100 nm over an area of several square centimeters with high-throughput enabling the use of nanotechnology for fabrication of model systems to study large ensembles of well-defined identical nanoparticles with a density of 10
10
particles cm
−2
.
Step-and-repeat EUV-ATL to obtain large-area nanoparticle arrays.
PDF
