Johnson Matthey Technology Review - Volume 66, Issue 3, 2022

Most of the global production of ammonia requires fossil fuels and is associated with considerable greenhouse gas emissions. Replacing fossil fuel ammonia with green or zero-carbon ammonia is a major focus for academia, industry and governments. Ammonia is a key component in fertiliser but is also attracting increasing interest as a carbon-free fuel for the maritime sector and as a hydrogen vector. This review describes the use of green (electrolysed) hydrogen in conventional Haber-Bosch plants and predicts adoption of the technology by 2030. Further into the future, direct green ammonia synthesis by electrocatalytic and photocatalytic means may present a cost-effective alternative to the Haber-Bosch process. Electrocatalytic and photocatalytic routes to ammonia are reviewed, the catalytic systems are compared and their potential for meeting the likely demand and cost for ammonia considered.

Reliable storage and transportation of hydrogen at scale is a challenge which needs to be tackled to allow a robust and on-demand hydrogen supply when moving towards a global low carbon hydrogen economy with the aim of meeting net-zero climate goals. Numerous technologies and options are currently being explored for effective hydrogen storage and transportation to facilitate a smooth transition to the hydrogen economy. This paper provides an overview of different hydrogen storage and transportation technologies, focusing in more detail on liquid organic hydrogen carriers (LOHCs), its advantages and disadvantages and future considerations for the optimisation of the LOHC technology.

The deployment of hydrogen as an infrastructure fuel and an energy vector across a range of industries is expected to aid with meeting decarbonisation goals and achieving net zero emissions. For the transition towards a low carbon hydrogen economy, not only the production of hydrogen needs to be addressed, but also its transportation and storage. Liquid organic hydrogen carriers (LOHCs) are an attractive solution for the storage and transportation of hydrogen to allow a reliable and on-demand hydrogen supply, enabling industrial decarbonisation. This work describes the potential deployment and integration of LOHCs within different industries. These include: the transportation sector; steel and cement industries; the use of stored hydrogen to produce fuels and chemicals from flue gases and a system integration of fuel cells and LOHCs for energy storage.

Liquid organic hydrogen carriers (LOHCs) provide attractive opportunities for hydrogen storage and transportation. In this study, a detailed examination of the most prominent LOHCs is performed, with a focus on their properties and scope for successful process implementation, as well as catalytic materials used for the hydrogenation and dehydrogenation steps. Different properties of each potential LOHC offer significant flexibility within the technology, allowing bespoke hydrogen storage and transportation solutions to be provided. Among different LOHC systems, dibenzyltoluene/perhydro-dibenzyltoluene has been identified as one of the most promising candidates for future deployment in commercial LOHC-based hydrogen storage and transport settings, based on its physical and toxicological properties, process conditions requirements, availability and its moderate cost. Platinum group metal (pgm)-based catalysts have been proven to catalyse both the hydrogenation and dehydrogenation steps for various LOHC systems, though base metal catalysts might have a potential for the technology.

Transition metal carbides are attracting growing attention as robust and affordable alternative heterogeneous catalysts to platinum group metals (pgms), for a host of contemporary and established hydrogenation, dehydrogenation and isomerisation reactions. In particular, the metastable α-MoC1–x phase has been shown to exhibit interesting catalytic properties for low-temperature processes reliant on O–H and C–H bond activation. While demonstrating exciting catalytic properties, a significant challenge exists in the application of metastable carbides, namely the challenging procedure for their preparation. In this review we will briefly discuss the properties and catalytic applications of α-MoC1–x, followed by a more detailed discussion on available synthesis methods and important parameters that influence carbide properties. Techniques are contrasted, with properties of phase, surface area, morphology and Mo:C being considered. Further, we briefly relate these observations to experimental and theoretical studies of α-MoC1–x in catalytic applications. Synthetic strategies discussed are: the original temperature programmed ammonolysis followed by carburisation, alternative oxycarbide or hydrogen bronze precursor phases, heat treatment of molybdate-amide compounds and other low-temperature synthetic routes. The importance of carbon removal and catalyst passivation in relation to surface and bulk properties are also discussed. Novel techniques that bypass the apparent bottleneck of ammonolysis are reported, however a clear understanding of intermediate phases is required to be able to fully apply these techniques. Pragmatically, the scaled application of these techniques requires the pre-pyrolysis wet chemistry to be simple and scalable. Further, there is a clear opportunity to correlate observed morphologies or phases and catalytic properties with findings from computational theoretical studies. Detailed characterisation throughout the synthetic process is essential and will undoubtedly provide fundamental insights that can be used for the controllable and scalable synthesis of metastable α-MoC1–x.

In our previous study, retinyl palmitate was successfully encapsulated by melt dispersion using waxes as shell materials. Herein, the objective of the present research is to evaluate the shelf life and kinetic release of the developed microcapsules. The study was conducted by measuring actual loading capacity over a period of time using spectroscopic analysis. The transfer percentage of particles from nonwoven facial wipes to skin-like surfaces was also investigated by simulating the rubbing mechanism with a robotic transfer replicator. Although particles stored as powder form under room temperature showed only eight days of shelf-life, particles stored as a dispersion in a refrigerator maintained 60% of the theoretical loading capacity after one month. The kinetic release profile of the particles in ethanol with shaking at 100 rpm and 37±2°C showed an initial burst in the first half an hour, followed by a sustained release. It also showed that 98% of the retinyl palmitate content released within 4 h. Particles incorporated into wet nonwoven wipes gave approximately 22% transfer to skin-like fabric. Thus, the study shows potentials of delivering skincare properties by means of retinyl palmitate capsule loaded textile substrates.

There has been recent interest in the potential of nitrides, hydrides and carbides as novel heterogeneous catalysts for the production of ammonia in a sustainable manner on a local scale. It has been proposed that some of these materials can produce ammonia via Mars-van Krevelen based mechanistic pathways. Generally, for metal-based heterogeneous catalysts, dissociative nitrogen activation is believed to be the rate determining step in ammonia synthesis. However, associative pathways, which are more akin to enzymatic nitrogen activation, are being increasingly invoked in the literature. Such pathways may provide an opportunity for the development of novel catalysts that operate under milder reaction conditions. This brief overview provides a summary of some of the recent developments in relation to nitrides, carbides and hydrides as applied to ammonia synthesis.

Turkey is a home country for a good number of fermented beverages derived from milk, cereals, fruits and vegetables, and several studies have reported the probiotic potentiality of these beverages. Probiotics, otherwise known as beneficial microorganisms possess the ability to exert antimicrobial effects, which is one of the most important selection criteria for their use in commercial products. In the current study, the antimicrobial activities of potential probiotic bacteria isolated from five fermented traditional Turkish beverages (boza, kefir, ayran, shalgam juice and hardaliye) were evaluated. The bacterial isolates were morphologically characterised and genotypically identified by 16S rRNA gene sequence analysis. The antimicrobial effects of the isolates against selected human pathogens were assessed using spot-on-the-lawn and agar well diffusion assays. 18 of the 22 strains displayed varying degrees of antagonism against the tested pathogens. Amongst the isolates, the strongest antimicrobial effects were exhibited by strains from boza, kefir and shalgam which can be attributed to their greater microbiota diversity. Strain specificity in the activities of the obtained isolates and specificity with the different indicator pathogens tested was observed. The antimicrobial effects exhibited by boza, kefir and shalgam isolates offer a promising health benefit to consumers of these fermented probiotic products.

The performance of a particulate filter is determined by properties that span the macro, meso and atomic scales. Traditionally, the primary role of a gasoline particulate filter (GPF) is to reduce solid particles and liquid droplets. At the macro scale, transport of gas through a filter’s channels and interconnecting pores act as main transport arteries for catalytically active sites. At the meso scale, the micropore structure is important for ensuring that enough active sites are accessible for the gas to reach the catalyst nanoparticles. At the atomic scale, the structure of the catalyst material determines the performance and selectivity within the filter. Understanding all length scales requires a correlative approach but this is often quite difficult to achieve due to the number of software packages a scientist has to deal with. We demonstrate how current state-of-the-art approaches in the field can be combined into a streamlined pipeline to characterise particulate filters by digitally reconstructing the sample, analysing it at high throughput, and eventually use the result as an input for gas flow simulations and better product design.