Multi-scale, Multi-modal Imaging of Nanoporous Catalysts.

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Project Aims: To identify the impacts of various manufacturing parameters on the pellet structure. To establish the relationship between pellet manufacturing route and pellet effectiveness. To study in more detail at finer resolution the presence of structural features that particularly impacting large-scale molecular exchange between regions of the pellet. To develop a novel pore-network model for those regions of the pellet that prove to be controlling the mass-transport rates.Project Summary:Increasing catalyst pellet effectiveness factors is one of the key ways to deliver improved performance of products that catalyse diffusion-limited reactions. This requires a detailed understanding of the factors in pellet pore structure that limit mass transport, and the parameters in the manufacturing process that produce these particular pore structure features. This research project aims to investigate the relationship between catalyst pellet manufacturing process and the pellet transport properties, as mediated by the pellet structural characteristics that a specific set of forming conditions produce. It will consider how changing particular parameters of the manufacturing process leads to specific changes in the pellets structure, and determine the impact of those features on the rate of mass transport.Methanol synthesis catalyst pellets (Copper/Zinc oxide/Alumina) manufactured via pelleting, using either roll compacted or spray dried feed, have been studied using a number of different characterisation techniques. Integrated mercury porosimetry and gas adsorption rate of uptake experiments have been used to study the changes in the rate of mass transport before and after mercury entrapment. This method demonstrates the impact that the lost pores, filled with mercury, have on the rate of uptake and thus their importance to overall mass transport. Different pores may arise from different aspects of the fabrication process. Hence, these findings can be used in the design and optimisation of the pellet manufacturing process. Computerised X-ray tomography (CXT) and differential scanning calorimetry (DSC) have also been employed to establish the spatial distribution of mercury entrapped in the blocked void-space of the pellets. Preliminary results from the experiments carried out on the sample so far show that the pellets have a very similar pore size distributions and intrusion volume profiles. However, the spatial distribution of entrapped mercury following different intrusion pressures indicates pellet feed character greatly impacts general pore network accessibility. In the future, additional characterisation techniques such as the transient diffusional ingress of hyperpolarized Xenon gas (Xe-129) using magnetic resonance imaging (MRI), nuclear magnetic resonance (NMR) cryoporometry and scanning electron microscopy (SEM) will all be used to study the samples.