Investigation of additively manufactured substrates in heterogeneous catalysis
Creators: name: Hurt, Christopher
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 340601
subject: Catalysis and mechanisms of reactions
classificationCode: 400408
subject: Reaction engineering (excl. nuclear reactions)

description: Selective Laser Melting (SLM) is an additive manufacturing technology for alloys capable of producing complex, miniature geometries and as such the pursuit of functionalising catalysts effectively onto these SLM-printed materials, like catalysts for dimethyl ether (DME) synthesis processes, presents an opportunity to open the research space into miniature catalytic reaction vessels, termed by some as ‘reactionware’ [1]. However, there is precious little evidence in the literature of a thorough attempt to catalytically functionalise SLM substrates and demonstrate activity in chemical reactions. This is a little-explored field due to the difficulty of properly immobilising the catalyst materials on the metallic alloys that SLM is capable of printing. It follows that the major aim of this project was to develop, produce and test miniature, functionalised reactor components made by SLM, both in liquid and gaseous phase catalytic reactions. Methods to coat catalysts on SLM substrates were explored for several catalytic applications:<br><br>Dry reforming of methane (DRM), a step towards DME synthesis<br>4-Nitrophenol reduction, a reaction applicable to water purification.<br>Glycerol acetalisation, this synthesis provides a bio-diesel fuel additive.<br>Flat, planar substrates printed by SLM with Ti6Al4V and 17-4 PH were coated with the relevant catalysts to explore the chemical activity of these systems in batch or continuous setups of these reactions.<br><br>Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS) were used to assess the structure, composition, and topography of the catalytic coatings applied to the various substrates used in this research project. Online and offline gas chromatography (GC) as well as uv-vis spectroscopy were used to determine conversion and/or selectivity of the reactions undertaken by the various catalytic systems. For some reactions, more complex structures were SLM-printed and functionalised with the relevant catalyst and exposed to continuous flow of the reactants.<br><br>In the process of testing SLM substrates for catalytic activity, it was found that some catalysts were active but would not remain immobilised during the reaction and some remained immobilised but failed to demonstrate suitably high activity. Au nanoparticles anchored effectively on Ti6Al4V substrates but demonstrated low or inconsistent conversion in 4-nitrophenol (4-NP) reduction. Conversely FeCl3 coats &amp; Pd nanoparticles on Ti6Al4V substrates gave higher conversions (53% &amp; ~100%) for these reactions but were immediately stripped off the substrates during the glycerol acetalisation &amp; 4-NP reduction reactions.<br><br>The best catalyst for DRM was metallic supported by magnesium alumina on 17-4 PH steel with a 5 wt.% Ni loading, a small conversion of both CH4 and CO2 at ~1.5% and ~4% was achieved respectively. The most active catalyst for Glycerol Acetalisation was a FeCl3 catalyst on a Ti6Al4V titanium alloy; this gave a glycerol conversion of 53.55%. For 4-Nitrophenol Reduction, the best catalyst was dip-coated Pd on Ti6Al4V titanium alloy which reduced 4-Nitrophenol to 4-Aminophenol at near 100% conversion in 20 minutes or less for the calcined and untreated conditions alike.<br><br>This early work demonstrates that catalytic functionalisation of SLM substrates is viable and worth further investigation.