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High-surface area γ-alumina is industrially used as a catalyst support. Catalytically active elements are doped onto the support, where they can bind to AlO4, AlO5 or AlO6 sites on the surface. Pretreating the surface with alkaline earth oxides can alter the availability of these surface sites, hence affecting the catalytic activity. The surface binding sites of strontium oxide (SrO) on γ-alumina were previously unknown. Direct 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) could not detect AlO5 sites at 9.4 T, so 1H–27Al cross-polarisation (CP) MAS NMR was used to preferentially select the surface environment signals. We directly observed the three surface environments on dehydrated γ-alumina as a function of SrO impregnation up to 4 wt% SrO. We found that Sr2+ preferentially binds to AlO5 and AlO6 surface sites. 1H MAS NMR revealed SrO impregnation causes a reduction in the terminal (−0.3 ppm) and bridging (2.2 ppm) hydroxyl environments, as well as the promotion of a new peak in between these sites, at 0.5 ppm. By using 1H–27Al CP/MAS NMR the relative proportions of surface sites on γ-alumina can be determined, allowing an optimal level of SrO doping that can saturate all the AlO5 sites. Importantly, this provides a method of subsequently depositing catalytically active elements on just the AlO4 or AlO6 sites, which can provide a different catalytic activity or stability compared to the AlO5 binding site.
Heterogeneous catalysis often involves the use of metal nanoparticles, often between 1–10 nm in size. These particles are usually finely dispersed onto high surface area supports and act as an active centre during a catalytic reaction. The performance of a supported catalyst can be directly related to the size and spatial distribution of the metal nanoparticles. Therefore, it is of...
This book represents the latest magnum opus in a line of multi-author books on process tomography, with the first dating from 20 years ago. Following in the tradition of Beck and Williams (1) this book presents a comprehensive overview of process relevant tomographic modalities, reconstruction techniques and industrial applications. The editor Professor Mi Wang has done an excellent job...
In Part I of this Final Analysis series (1), the identification and quantification of elements by X-ray (excited) photoelectron spectroscopy (XPS) was discussed. A statement was made that the core energy levels do not vary a great deal – but there is usually some variation for a given element in different chemical forms. This can be thought of as being caused by variations in the oxidation...
The water solubility of 22 platinum group metal (pgm) containing substances was evaluated to provide useful data for regulatory compliance and to aid assessment of their environmental impact. The flask method from OECD Guideline 105 (1) for the testing of chemicals (water solubility) was used to test each material. For substances that could not be isolated as pure solids, a simplified water solubility test was carried out. The results provide reliable data on solubility previously unavailable in the literature.
Small metallic nanoparticles used for polymer exchange membrane fuel cells (PEMFC) represent a characterisation challenge. Electron microscopy would seem the ideal technique to analyse their structure at high resolution. However, their minute size and sensitivity to irradiation damage makes this difficult. In this review, the latest techniques for overcoming these limitations in order to provide quantitative structural and compositional information are presented, focusing specifically on quantitative annular dark-field (ADF) scanning transmission electron microscopy (STEM) and quantitative energy dispersive X-ray (EDX) analysis. The implications for the study of bimetallic fuel cell catalyst materials are also discussed.
Neutron scattering is a severely underused technique for studies of catalysts. In this review we describe how and why neutrons are useful to catalysis. We illustrate the range of systems that have been studied by both elastic and inelastic neutron scattering. These range from structural studies of adsorbates in zeolites to determination of the structure of surface adsorbates, characterisation of nanoparticles, the measurement and mechanism of diffusion and spectroscopic characterisation of adsorbed species. We conclude with how to access neutron facilities and some future prospects for the application of these techniques to industrially useful materials.
An invitation-only event was held from 5th–6th September 2016 to launch the new state-of-the-art imaging facility, opened on 5th September 2016, which will see the University of Oxford, UK, Johnson Matthey Plc, UK, and Diamond Light Source, UK, in close collaboration on the study of nanoscale materials. The ePSIC is located at the Harwell Science and Innovation Campus in Oxfordshire, UK,...
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