Proton exchange membrane fuel cell (PEMFC) has been reported as clean and efficient energy technology from conversion of H₂. However, one of the main challenges remains the storage and transport of hydrogen. The promising alternative is to produce H₂ on site by a reformer using a H₂-dense liquid as a fuel, a technology known as fuel processing. Methanol is an attractive source of H₂ compared to other fuels as it presents several advantages, i.e. it is obtained sulphur-free, has a high H to C ratio and therefore produces a H₂-rich reformate, can be reformed at low temperatures (200 - 300°C) and is a liquid at ambient conditions so that it can be easily handled. Typically, Cu-based catalysts are used for steam reforming of methanol due to their high activity (i.e. H₂ production) and high selectivity towards CO₂. As CO poisons anodic catalyst of PEMFC, high selectivity towards CO₂ is crucial so as to eliminate or at least minimize CO removal load downstream a fuel processor. However, Cubased catalysts are thermally unstable and suffer deactivation due to sintering at high temperatures (> 250°C). Moreover, Cu-based catalysts are pyrophoric and therefore difficult to handle. Recent studies show that PdZn catalysts are very promising as they exhibit comparable activity and selectivity to Cu-based ones. Furthermore, PdZn catalysts are thermally stable in the typically methanol steam reforming temperature range (200 - 300°C). Most literature attributes high CO₂ selectivity of PdZn catalysts to formation of PdZn alloy. It is generally agreed that PdZn alloy is formed when PdZn catalysts are reduced in H₂ at high temperatures (> 250°C). In this work, a Pd/ZnO catalyst aimed at 2.5 wt% Pd was successfully prepared via incipient wetness impregnation and the duplicate preparation of the catalyst was successful. Both impregnation catalysts were confirmed by ICP-OES to contain similar weight Pd loadings i.e. 2.8 and 2.7 wt%, respectively. The actual Pd loading (ICP-OES) was slightly higher than the target loading (2.5 wt%) due to Pd content of Pd salt underestimated during catalyst preparation. Furthermore, crystallite size distribution, i.e. PdO crystallites on ZnO support, was similar (i.e. 6.7 ± 2.4 nm and 6.3 ± 1.9 nm) for both impregnation catalysts.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/24325 |
| Date | January 2015 |
| Creators | Xalabile, Philasande |
| Contributors | Fletcher, Jack, Luchters, Niels, Malatji, Peter |
| Publisher | University of Cape Town, Faculty of Engineering and the Built Environment, Centre for Catalysis Research |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc (Eng) |
| Format | application/pdf |
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