We show the potential of coupling numerical and experimental approaches in the fundamental understanding of catalytic reactors, and in particular fluidized beds. The applicability of the method was demonstrated in a lab-scale fluidized bed reactor for the platinum-based catalytic oxidation of hydrogen. An experimental campaign has been carried out for synthesizing the catalyst powders by means of atomic layer deposition in a fluidized bed reactor and characterizing them. Catalytic testing has been also run to collect data both in fixed and fluidized bed configurations. Then, after the validation of the in-house first-principles multiscale Computational Fluid Dynamic - Discrete Element Method (CFD-DEM) model, the fundamental understanding which can be achieved by means of detailed numerical approaches is reported. Thus, the developed framework, coupled with experimental information, results in an optimal design and scale-up procedure for reactor configurations promising for the energy transition.

The feasibility of gas phase deposition using a Ti alkoxide precursor for precise surface modification of catalysts was demonstrated by modifying a mesoporous alumina support with a Ti oxide overcoat. Titanium tetra-isopropoxide yields a Ti oxide layer that covers homogeneously the alumina surface. Uniformity of the deposited TiO₂ was verified by SEM-EDX, on both intra-particle and inter-particle levels. Only a few atomic layer deposition (ALD) cycles were required in order to obtain Ti contents with a relevance for industrial application. The pore size distribution of the overcoated catalyst support was barely affected by the coating process. Synthesized CoMo catalysts based on the Ti-alumina carrier showed up to 40% higher activity compared to a catalyst supported on pristine alumina, in hydroprocessing under industrial testing conditions. The TiO₂ coating appeared to be stable, showing no agglomeration characteristics after reaction as corroborated by TEM-EDX. ALD provides a scalable route with low waste generation for the production of precisely structured TiO₂-Al₂O₃ hydroprocessing catalyst supports.

Nanoencapsulated phase change materials (nePCMs) are nowadays under research for thermal energy storage purposes. NePCMs are composed of a phase change core surrounded by a shell that confines the core when molten. One of the main concerns of nePCMs when subjected to thermal processes is the mechanical failure of the passivation shell initially present in commercial metallic nanoparticles. In order to overcome this issue, multi-coated nePCMs, based on the synthesis of an additional coating by atomic layer deposition, appear to be as a candidate solution. With the objective of studying the influence of the composition and thickness of the additional nePCM shells on their probability of failure, a numerical tool combining a thermomechanical finite element model with phase change and Monte Carlo algorithms is developed. This tool also allows including the uncertainty of material and geometrical properties into the numerical analysis to account for their influence in the mechanical performance of nePCMs. In the present work, the mechanical reliability of SiO₂ and Al₂O₃ coatings on Sn@SnO_x nanoparticles is assessed by considering both deterministic and probabilistic failure criteria and Al₂O₃ coatings appear to have a better mechanical performance than their SiO₂ counterparts.

Atomic layer deposition in a fluidized bed is utilised for the coating of polyamide powders with thin films of silicon dioxide. By varying the number of exposure cycles the amount of deposited material can be precisely controlled, allowing for tailoring wetting, flowing, and melting behaviour of the powder. The favourable process operation characteristics enable a facile envisioning of scalable production in volumes complying with the demands of 3D printing applications.

Nanoencapsulated phase-change materials (nePCMs) are investigated for enhancing thermal energy storage. However, the shell of these nanocapsules may fail due to stress developed during thermal processes, leading to melting enthalpy loss. To overcome this problem, SiO₂ and Al₂O₃ coatings on Sn nanoparticles are synthesized by atomic layer deposition (ALD). To study the influence of shell thickness and composition on the probability of failure (POF) of nePCM shells in single- and multicoated nePCMs, a probabilistic numerical tool combining Monte Carlo techniques and a thermomechanical finite-element model with phase change are used. The uncertainties of the material and geometrical properties of nePCMs are included in the analysis. Both deterministic and probabilistic failure criteria are taken into account to consider the effect of dispersion on tensile strength. The results indicate that multicoated nePCMs enhance thermomechanical performance in relation to their single-coated counterparts. Both the numerical simulations and experiments confirm that the POF of nePCM shells and melting enthalpy loss in multicoated nePCMs lower with shell thickness. The results after 50 ALD cycles indicate that Al₂O₃ coatings exhibit better performance because a POF of 1.66% is obtained with 1.1% enthalpy loss, while the POF for SiO₂ is 72.38% with 3.5% enthalpy loss.

The development of advanced heat transfer fluids (HTF) with enhanced heat transfer properties has been identified as a key target to increase the efficiency of industrial processes. In this work, heat transfer performance improvements of a novel nanofluid, consisting of metallic nanoparticles dispersed in a commercial thermal oil, were investigated. Nanofluids combining tin nanoparticles (1 mass %) with Therminol 66 (TH66) were synthesised using the two step-method and experimentally analysed. The effectiveness of biosurfactant addition and nanoparticle polyethylene terephthalate (PET) nanocoating for high temperature nanofluid stabilisation were independently investigated. The PET nanoscale coatings were grown by molecular layer deposition, which has been used for the first time in this field. The thermal conductivity, dynamic viscosity and specific heat capacity of the stable, oil-based nanofluids were characterised at high temperatures, and the results were compared and in good agreement with models found in the relevant literature. Finally, the heat transfer performance of the nanofluids with respect to their base fluids was evaluated, employing empirical values for the thermophysical properties of the involved materials. In this way, increments of the heat transfer coefficients up to 9.3% at 140 °C, relevant to industrial applications were obtained.

Renewable energy has become of great interest over the past years in order to mitigate Global Warming. One of the actions gaining attention is the enhancement of the thermal energy storage capacity of Concentrated Solar Power plants. The addition of nanoencapsulated phase change materials (core-shell nanoparticles) to the already used materials has been proposed for that purpose, due to the possibility of increasing thermal storage through the contribution of both core latent heat and sensible heat. In this work, Atomic Layer Deposition has been used to synthesise SiO₂ and Al₂O₃ nanoscale coatings on tin nanoparticles. The multi-encapsulated phase change materials have been characterised in terms of chemical composition, crystalline structure, particle size, thermal stability and thermal storage capacity. Sn@Al₂O₃ nanoparticles present the best thermal behaviour as they show the lowest reduction in the phase change enthalpy over 100 cycles due to the oxidation barrier of the coating. Moreover, the specific heat of both nanoparticles and solar salt-based nanofluids is increased, making the nanoencapsulated phase change material suitable for thermal energy storage applications.

Atomic layer deposition (ALD) is an excellent technique to make nanostructured particles: particles of which the surface is either covered by an ultrathin film or by nanoclusters, with applications in e.g. energy and health. This compact review discusses recent developments in the field of applying ALD to particles and powders. ALD—also known under the alternative names molecular layering and atomic layer epitaxy—was already applied to particulate materials decades ago in the former USSR and in Finland. Later on, significant research efforts were devoted to its development in the United States; currently, it is studied worldwide. The most widely used reactor type is the fluidized bed. Since a batch of particles has a very large surface area—especially in the case of very small or porous particles—it is crucial to be efficient with precursor utilization; we discuss efforts in this direction. Moreover, the effects of gas flow rate and temperature are briefly discussed, while the influence of pressure on ALD on particles is also elaborated. A clear impression of the potential of scaling up ALD on particulate materials is presented, both regarding a novel continuous reactor concept—the pneumatic transport reactor—and the economic aspects of processing large amounts of material. We conclude that ALD is suited to produce nanostructured particles with very high precision and in large quantities.

Although the gas-phase production of nanostructured solids has already been carried out in industry for decades, only in recent years has research interest in this topic begun to increase. Nevertheless, despite the remarkable scientific progress made recently, many long-established processes are still used in industry. Scientific advancements can potentially lead to the improvement of existing industrial processes, but also to the development of completely new routes. This paper aims to review state-of-the-art synthesis and processing technologies, as well as the recent developments in academic research. Flame reactors that produce inorganic nanoparticles on industrial- and lab-scales are described, alongside a detailed overview of the different systems used for the production of carbon nanotubes and graphene. We discuss the problems of agglomeration and mixing of nanoparticles, which are strongly related to synthesis and processing. Finally, we focus on two promising processing techniques, namely nanoparticle fluidization and atomic layer deposition.