Adsorption And Adhesion Energies Of Metal Films And Nanoparticles Studied By Adsorption Calorimetry

Author : Wei Zhang
Publisher :
ISBN 13 :
Total Pages : 195 pages
Book Rating : 4.:/5 (119 download)

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Download or read book Metal and Gas Adsorption on High-surface-area Catalyst Support Materials written by Wei Zhang and published by . This book was released on 2020 with total page 195 pages. Available in PDF, EPUB and Kindle. Book excerpt: Along with the increase in the world population and global economy, the world primary energy consumption is also growing year by year, which in turn has brought about energy shortage and global warming. Developing renewable energy and increasing its total fraction in the world energy portfolio is one of the strategies to tackle the energy and environmental hurdles. The forward progression can be seen in that 14.8% of the increase in primary energy in 2017 was provided by renewable energy (including biofuels), which grew rapidly driven by robust growth in both wind and solar power. However, the total fraction of world energy portfolio from all renewables is expected to amount to just 8% according to the report published by National Research Council in 2008 and fossil fuels will be a major part of the world primary energy portfolio for the next few decades to come. Therefore, accelerating the pace of improvement in energy productivity (i.e., the amount of energy needed to produce a unit of output), especially the utilization of fossil fuels, becomes an urgent task. In order to complete this task, this dissertation brings two strategies into attention, (1) developing highly active, selective, and thermodynamically stable heterogeneous catalysts for the chemicals and energy industries and (2) developing and applying porous adsorbent materials for the capture of CO2 and other toxic gases and for the storage and utilization of cleaner, high-energy-density, and lower-carbon fuels such as hydrogen and methane. Heterogeneous catalysis has been at the center of the chemicals and energy industries since more than 90% of chemical manufacturing processes utilize catalysts. Late transition metal nanoparticles supported on high area oxide surfaces are the key ingredients of many catalysts and electrocatalysts with numerous applications in the energy, chemical, and environmental industries. The catalytic activity and selectivity of these catalysts often varies dramatically with the size and shape of the metal nanoparticles, and with the support materials. In many cases, the supported metal nanoparticles are rendered inactive due to particle sintering (i.e., coarsening into fewer, larger particles), which also depends strongly on the particle size and support materials. These properties have been proven to be closely correlated with the strength of bonding of the metal atom and nanoparticles to the support surface. To clarify structure–activity relationships in such catalysts and their sintering kinetics, our group has been measuring the strength of the interaction between metal nanoparticles and the support surfaces using metal vapor adsorption calorimetry. Chapter 2 describes the standard procedure and experimental setup for metal vapor adsorption calorimetry and equilibrium adsorption isotherm (EAI). The metal vapor adsorption calorimeter described in Section 2.1 has been applied to drop-cast films of metal–organic frameworks (MOFs) NU-1000 described in Chapter 3. The Brunauer–Emmett–Teller (BET) system described in Section 2.2 has been used to measure equilibrium adsorption isotherms for many small gases on NU-100 in Chapter 6. A Zr-based metal–organic framework (MOF) NU-1000 as a heterogeneous catalyst support onto which transition metal nanoparticles can be deposited is introduced in Chapter 3. The nature and energy of the reactions between Ca vapor and the internal surfaces of the NU-1000 have been studied by adsorption microcalorimetry, low energy He+ ion scattering spectroscopy (LEIS), X-ray photoelectron spectroscopy (XPS), and Kohn−Sham density functional theory (DFT). Chapter 4 introduces a novel calorimeter design to study metal vapor adsorption calorimetry on surfaces of nanomaterials that are deposited from liquid solutions, as is typical when preparing industrial catalyst materials. It uses a LiTaO3 crystal for heat detection, which has a Curie point of 893 K, thus theoretically allowing samples to be heated up to ~890 K to clean before use. Its capability has been demonstrated by measuring the bond energies of Ag vapor onto the clean surfaces of high-surface-area TiO2 powdered support materials. Mixed or binary metal oxides (i.e., oxides with two metal elements) are often used as supports in catalysis with considerable improvement on various aspects of catalyst performance. Chapter 5 proves that we can measure adsorption energies, using the new metal vapor adsorption calorimeter introduced in Chapter 4, on any atomically smooth well-ordered mixed-oxide surface and demonstrates that thin Langmuir-Blodgett (LB) films of layered perovskite nanosheets provide a powerful new approach to study surface chemistry on single-crystal mixed-oxide surfaces. A shift away from coal and oil into cleaner, high-energy-density, and lower-carbon fuels such as hydrogen and methane, is considered as another strategy to increase energy efficiency and alleviate greenhouse effect. While hydrogen and methane have so many ubiquitous merits, the biggest challenge for large-scale transportation and utilization is to develop a safe, lightweight, and economical gas storage technique. The Zr-based MOF NU-1000 is a particularly interesting adsorbent material for gas storage and separation because it is water- and temperature-stable, has a high BET surface area and large pore volumes that allow NU-1000 to efficiently trap various gas molecules inside its framework. Its application as a storage media for gas molecules depends on the adsorption capacity and selectivity for the adsorbates of interest. As such, Chapter 6 reports the combined experimental and theoretical study of small gases adsorption on NU-1000, which make NU-1000 perhaps the best understood MOF in terms of gas adsorption properties and serve as a prototype system for studying the surface chemistry of MOFs in general, thus guiding most applications on MOFs. To sum up, this dissertation provides deeper and systematic understandings of metal and gas adsorption on high-surface-area catalyst support materials, in the fields of heterogeneous catalysis and gas storage and separation relevant to energy and environmental industries. Here, I want to emphasize the importance of the new metal adsorption calorimeter introduced in Chapter 4. To clarify the structure–activity relationships in supported metal nanoparticle catalysts and their sintering kinetics, researchers have adopted a model catalysts approach whereby structurally well-defined samples are prepared by vapor deposition of the metal onto single-crystal oxide surfaces, which encounters the well-known “materials gap” with respect to real industrial catalysts. To bridge this materials gap, this calorimeter allows one to measure the strength of metal atom bonding and the adhesion energy of metal nanoparticles to clean surfaces of technologically relevant catalyst support materials. This opens up new opportunities for discovering better support materials and for basic scientific study of structure / function relationships with respect to metal / support bond energies.