Johnson Matthey Technology Review - Volume 68, Issue 4, 2024

Heterogeneous Cu/ZnO-based catalysts are widely used for CO2 hydrogenation to methanol, but limitations remain for industrial applications. These include achieving high methanol selectivity and conversion and mitigating deactivation by water poisoning. Part I of this review explores the role of active sites on Cu/ZnO-based catalysts in CO2 conversion. The synergistic interaction between copper and zinc oxide is emphasised, particularly regarding interfacial effects on carbon monoxide activation and formate formation. The discussion covers theoretical and experimental perspectives on active site characteristics, including defects, vacancies, steps and strain. Additionally, the review explores the connection between Cu/ZnO-based catalysts properties and methanol synthesis activity.

Part II of this review continues to explore the connection between Cu/ZnO-based catalysts properties and methanol synthesis activity. This work continues from Part I (1).

Part II of this review examines how preparation methods influence catalyst performance and the impact of doping with elements like ceria, alumina and zirconia on CO2 conversion selectivity. We conclude that zinc oxide enhances copper dispersion and promotes a synergistic effect at the interface, leading to improved catalytic performance. This work presents the continuation of and conclusions from Parts I (1) and II (2).

In this article, we will examine ultrafast spectroscopy techniques and applications, covering time-resolved infrared (TR-IR) spectroscopy, time resolved visible (TA) spectroscopy, two-dimensional infrared (2D-IR) spectroscopy, Kerr-gated Raman spectroscopy, time-resolved Raman and surface sum-frequency generation (SSFG) spectroscopy. In addition to introducing each technique, we will cover some basics, such as what kinds of lasers are used and discuss how these techniques are applied to study a diversity of chemical problems such as photocatalysis, photochemistry, electrocatalysis, battery electrode characterisation, zeolite characterisation and protein structural dynamics.

Compared to other energy-generating technologies and energy conversion devices, intermediate-temperature solid oxide fuel cells (IT-SOFCs) have gained significant attention from energy experts due to its high energy density, moderate operating temperature (600–800°C), low emissions and reliability. Enhancing the performance of IT-SOFCs requires suitable and excellent cathode materials. Thus, a perovskite-type Nd0.5Ba0.5Zr0.8Fe0.2O3+δ (NBZFO) material was synthesised via traditional solid-state reaction technique and analysed as a potential cathode material for IT-SOFCs. Analysis of X-ray diffraction data (XRD) revealed a single-phase perovskite material that crystallises in cubic space group (pm-3m). The thermal and electrochemical properties were analysed with the aid of thermogravimetric analysis (TGA) and electrochemical impedance spectroscopy (EIS). NBZFO has an electrical conductivity in air of 80 S cm⁻¹ at 400°C and a polarisation resistance (Rp) of 0.106 Ω cm² at 800°C. TGA reveals a slight loss in weight of about 0.58%, thereby suggesting a highly stable cathode material for IT-SOFC. Electrochemical investigation shows that NBZFO has good electronic and ionic conductivity and excellent oxygen stichometry. Further studies are required to understand the effects of varying B-site composition of the cathode material.

Ammonia is a globally transported chemical used for a variety of applications, most notably, the production of fertiliser. Over the past decade, attention has been afforded to the use of ammonia as an energy carrier, coupling global supply of renewable energy to demand regions. Ammonia’s advantages as an energy carrier include its ease of liquefaction and established international transportation routes; overcoming its low reactivity, excessive production of nitrogen oxides and its toxicity remain as challenges. For energy applications, fuel delivery is a critical aspect of effective combustion in boilers, burners and engines. Due to its adaptable phase change characteristics, ammonia fuel may be injected as a liquid or vapour, each with respective advantages or disadvantages. The focus of this review concerns the characterisation of liquid ammonia fuel injection for combustion, including recent research findings from experimental and simulation studies. Liquid ammonia injection can result in the highly dynamic so-called ‘flashing’ or ‘flash boiling’ phenomena. Research findings have been drawn from other related applications such as accidental hazardous releases. Bespoke optical experimental rigs together with diagnostic techniques and two-phase computational fluid dynamics (CFD) simulations have enabled studies of the flashing jets under various initial or final conditions, with recent work also examining ammonia spray combustion. The review concludes with an insight into future trends and requirements for liquid ammonia combustion. Reciprocating engines for marine propulsion are cited as potential early adopters of ammonia energy.

Over the past few years, there has been a notable surge in research interest surrounding high entropy alloys (HEAs) owing to their exceptional properties. Unlike conventional alloys, HEAs consist of five or more principal elements, which offer endless possibilities for developing new alloy systems. HEAs exhibit a high concentration of mixing elements, resulting in high disorderliness of the atomic structure within the material, known as high entropy. This unique nature provides HEAs with desirable properties, including excellent mechanical and physical properties at elevated temperatures, making them ideal for high-temperature applications like cryogenic engines and gas turbines. Moreover, HEAs have shown remarkable corrosion resistance, positioning them as viable options for applications in demanding environments such as marine settings, oil and gas pipelines and chemical processing plants. This comprehensive review paper analyses recent studies on various HEAs. Part I introduces HEAs and describes their synthesis, microstructure, hardness and strength properties.

This is Part II of a comprehensive review analysing recent studies on various high entropy alloys (HEAs). Here, we present their magnetic and electrical properties, corrosion resistance, wear behaviour and different applications. Remaining challenges and perspectives are summarised. The anticipated findings of this two-part review are a milestone for future investigations on the production and analysis of HEAs. The discoveries hold great value for researchers, designers and manufacturers working in this field, as they offer valuable knowledge regarding the characteristics and possible uses of HEAs. Consequently, these findings lay the groundwork for further exploration in this promising field of materials science.

Performance of alumina-supported catalyst systems are significantly affected by how the tetrahedral (Al-O4) and octahedral (Al-O6) coordination are mixed and blended with each other. Characterisation of aluminium-oxygen coordination is thus important to understand how catalysts interact with alumina at the microscopic level. Here we report the application of two advanced electron microscopy techniques on aluminium-oxygen coordination. The first technique is electron energy loss spectroscopy (EELS) that can reveal detailed electronic structure profile of aluminium valence band to analyse how aluminium is coordinated by oxygen. The second technique is pair distribution function (PDF) based on electron diffraction (ED), employed to measure aluminium-oxygen bond lengths associated with the coordination geometry.

This article reviews recent work undertaken at the beamline B22 of the Diamond Light Source using infrared (IR) microspectroscopy to characterise zeolite catalysts and to study their reactivity in real time. The advantage of vibrational microspectroscopic analysis when linked to the brightness and spectral bandwidth of synchrotron IR light are illustrated. The high spatial resolution means that the uniformity of acid site concentrations within individual large crystals of zeolites and between different crystals can be readily checked and changes to acid site concentrations within crystals resulting from steam treatment mapped. When an in situ reaction cell is coupled with mass spectrometric analysis of evolved gases the rapid time response of the method has provided new insight into the initial stages of the conversion of methanol to hydrocarbons over ZSM-5 and SAPO-34 single crystals. Future prospects for applying the method to other types of zeolite catalysed reactions with improved reaction cell design are also discussed.

When platinum-containing diesel oxidation catalysts (DOC) are exposed to high temperatures under lean conditions, the platinum nanoparticles form volatile platinum dioxide on the catalyst surface. The exhaust flow carries the volatile platinum dioxide to the downstream aftertreatment catalyst, such as the selective catalytic reduction (SCR) catalyst, that is responsible for reducing the nitrogen oxides (NOx) emissions and can negatively impact its performance, by promoting the parasitic oxidation of ammonia. Here we investigate the factors such as exposure time, temperature and DOC design characteristics for their impact on the platinum dioxide migration, by characterising the amount of platinum deposited on the SCR catalyst at very low levels (<5 ppm), using inductively coupled plasma optical emission spectroscopy (ICP-OES) fire assay technique. Our results indicate that well-dispersed platinum, not associated with palladium, is most prone to platinum dioxide migration. We also compare several methods to suppress the platinum dioxide migration from the DOC, such as sintering of the platinum nanoparticles, stabilising the platinum nanoparticles via interaction with palladium or covering the platinum nanoparticles with a high surface area capture layer to trap the volatile platinum dioxide.

The mineralogical properties and distribution of information established in saprolite from Indonesia were investigated using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy energy dispersion spectroscopy (SEM–EDS) and differential thermal analysis (DTA) measurements. The findings suggest that laterite ore has a complex inner core. The percentages of nickel, iron, magnesium, aluminium and silicon in saprolite are 1.82 wt%, 30.47 wt%, 10–20 wt%, 4.86 wt% and 8.1 wt%. Saprolite has 53.1 wt% iron oxide/oxyhydroxide, 38.3 wt% lizardite and 8.7 wt% silicate. According to DTA, saprolite undergoes a phase shift from goethite to haematite at low temperatures (200–300°C). This is a suitable phase to optimise nickel diffusion in iron. Furthermore, the thermal upgrading approach was utilised for this saprolite.

Cellulose is a natural polymer contained in growing fibres, such as pineapple fibres. Cellulose can be modified into cellulose acetate, a modified polymer that can be used in the synthesis of a cellulose acetate/polyethylene glycol (CA/PEG) membrane. The phase inversion method was used in this study to produce CA/PEG membranes. Variations in polyethylene glycol (PEG) concentration with a ratio of 1:1 to cellulose acetate, where variations in PEG concentrations used are 2%, 5% and 8%. Acetone and dimethylformamide are used as organic solvents. Membrane morphological analysis using scanning electron microscopy (SEM) and functional group analysis using a Fourier transform infrared (FTIR) spectrometer were performed for membrane characterisation. The result of the synthesis of the CA/PEG membrane is in the form of a thin white layer. The characterisation results of the FTIR spectrometer showed the vibration of the carbonyl bond at wavenumber 1729 cm⁻¹ and the vibration of the hydroxyl bond torque at the wave number 648 cm⁻¹, where the vibration intensity decreased with each addition to the concentration. The results of SEM characterisation show that the increase in PEG concentration increases the percentage porosity of the membrane. The membranes with 2%, 5% and 8% PEG have porosity percentages of 51.54%, 68.70% and 73.50%, respectively. As the membrane with 2% PEG has the lowest percent porosity, it has more potential in removing or filtering solutes from a fluid.