Physical mixtures of Pd and ZnO for carbon dioxide hydrogenation to methanol

Fagan, Samantha 2026. Physical mixtures of Pd and ZnO for carbon dioxide hydrogenation to methanol. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

This thesis investigates the hydrogenation of CO2 to methanol using physical mixtures, specifically supported Pd on a variety of supports, mixed with bulk or supported ZnO. Initial testing involved a range of contact areas of mixing between Pd/TiO2 and ZnO. The change in hydrogen spillover distance from the Pd to the ZnO, resulted in different quantities of ZnO reduced. Zn then migrated through the gaseous phase, resulting in the formation of PdZn alloy on the TiO2 surface. This migration effect was explored through a range of reduction temperatures, with a correlation between the proportion of PdZn and the methanol selectivity observed for the catalysts. Changing of the support, to explore different spillover distances for Pd/Al2O3 and Pd/BN, resulted in similar trends. With further exploration into the phase of Al2O3 used, resulting in the presence of nanoparticle encapsulation and increased hydrogen spillover, changing the product selectivity. Consequently, highlighting how the support had an impact on the activity, even if indirectly. When Pd/C was investigated, it was discovered that methanol selectivity did not correlate with increasing PdZn formation. Pd/C + ZnO g showed the highest methanol productivity across all tested catalysts (4560 mmol h-1 molPd-1), but a lower proportion of PdZn (41.7%) than Pd/ZnO (62.8%) or Pd/TiO2 + ZnO g (47.1%). Subsequently, mixing ZnO/C with Pd/C resulted in the conclusion that supported ZnO contributed towards methanol activity. The oxygen vacancy sites within nanostructured ZnO were proposed as the essential component for the high methanol activity, activating CO2 which accepts hydrogen spillover from Pd. Meaning that the contribution from ZnO was not limited to the interface with Pd nanoparticles. Additionally, the inactivity of bulk ZnO within pPd/C + pZnO was proven. Enhancement in activity was only observed when Zn migration occurred resulting in the formation of PdZn and supported ZnO.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry Schools > Physical, Chemical & Environmental Sciences
Date of First Compliant Deposit:	4 September 2026
Last Modified:	04 Sep 2026 11:09
URI:	https://orca.cardiff.ac.uk/id/eprint/189390

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