Heterogeneous catalysis using noble and non-noble metals nanoparticles supported on metal-oxide catalysts

Aleyadah, Layla 2024. Heterogeneous catalysis using noble and non-noble metals nanoparticles supported on metal-oxide catalysts. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The main objective of this work is to use investigate non-noble metals with the aim of reducing the cost of noble metals catalysts while preserving effective performance across a range of applications. AuPd bimetallic catalysts were compared with NiPd bimetallic catalysts with the aim to assess the reactivity of the non-noble metals with the noble metals counterparts in liquid-phase reactions. 1 wt% AuPd activity was first studied on various supports, including TiO2, Nb2O5, and activated carbon (AC) using the liquid phase hydrogenation of nitrobenzene to aniline as a test reaction. Between all the supports, TiO2 showed the maximum activity, converting 100% of nitrobenzene and with 100% aniline selectivity in one hour It was determined that the high dispersion of metal nanoparticles on TiO2 support was the cause in addition to the availability of active sites present on the TiO2 surface. Subsequently, the activity of AuPd and NiPd supported on TiO2 with different ratios was examined. In particular, the effects of varying the catalyst ratios (0.10Au 0.90Pd, 0.25Au 0.75Pd, 0.50Au 0.50Pd, and 0.75Au 0.25Pd) and (0.10Ni 0.90Pd, 0.25Ni 0.75Pd, 0.50Ni 0.50Pd, and 0.75Ni 0.25Pd) were tested. Furthermore, the individual metal activity of Pd, Au, and Ni was studied. In Chapter Four, the activity of catalysts in the liquid phase hydrogenation of nitrobenzene to aniline was examined. It was discovered that the 75Au 25Pd catalyst performed best and that the AuPd activity varied as the ratio changed. The concentration of Au was then increased to 90Au 10Pd and 95Au 5Pd in order to investigate the effect of Au concentration. It was found that this caused the activity of the catalysts to decrease. In addition, the activity in the NiPd catalysts increased as the Pd content increased. Studies were carried out to examine the impact of various factors, such as the amount of catalyst used and the catalysts' activity over time. The synergistic effect of Ni and Pd, the availability of active sites, and the enhancement of catalyst dispersion were all factors in the excellent results that NiPd catalysts produced, achieving 100% conversion of nitrobenzene and selectivity of aniline for III 25Ni 75Pd and 94% conversion of nitrobenzene and selectivity of aniline for 75Ni 25Pd in one hour using a 100 mg of the catalyst. In Chapter Five, the activity of the same catalysts was investigated in the direct synthesis of hydrogen peroxide. The catalyst 10Ni 90Pd was more active than monometallic Pd, producing 82 mol H2O2 Kgcat-1h -1 and 0.163 wt % H2O2. That is only a 10.6 % less than its AuPd equivalent which generated 0.269 wt % of H2O2 for 75% Au 25% Pd. The reusability test was conducted for the best results obtained in both AuPd and NiPd catalysts in both applications in order to evaluate the stability of metals. Following the final run, the metals exhibited leaching and the NiPd catalyst demonstrated a promising outcome. The catalysts were characterised using XPS, XRD, TEM, HAADF-STEM, EELS, FFT, and UV-vis DRS. The size of the particles and the changes in the nature of the active sites made by the NiPd alloy over the monometallic are key factors in determining the activity. The result is a promising finding that highlights the importance of using non-noble metals as catalysts alternative to the current noble metal-based catalysts.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry
Date of First Compliant Deposit:	26 March 2025
Last Modified:	26 Mar 2025 16:26
URI:	https://orca.cardiff.ac.uk/id/eprint/177166

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