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Heterogeneous catalysis using supported metal nanoparticles for environmental applications

Alshammari, Khaled 2018. Heterogeneous catalysis using supported metal nanoparticles for environmental applications. PhD Thesis, Cardiff University.

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Abstract

In this study, monometallic and a series of bimetallic nanoparticles, composed of Au, Ag and Pd supported on different types of metal oxides (e.g. TiO2, CuO and NiO) have been synthesised via a sol-immobilization approach using PVA and NaBH4 as capping and reducing agents, respectively. The activity of these supported nanoparticles has been evaluated towards the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP), as a model reaction. The effect of using different reducing agents (such as NaBH4, formic acid and hydrous hydrazine) was also studied. The reaction parameters were also optimised under kinetic regime control. The catalysts showed promising activity towards the reduction of 4-NP to 4-AP with the highest activity and re-usability (up to 5 cycles) observed for the bimetallic AgPd supported alloyed nanoparticles particularly with an optimum molar ratio of Ag:Pd = 25:75. The successful synthesis of the targeted active components together with the structure-activity correlations have been probed by using different bulk and surface characterization techniques including; powder x-ray diffraction (XRD), MP-AES, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM), HAADF-STEM, and SBET surface area measurements. The results clearly demonstrated the successful preparation of mono- and bimetallic supported heterogenous systems via sol-immobilization route with high distribution and confinement of the supported nanoparticles onto the supports as evidenced by TEM and XRD analysis. Amongst all heterogenous systems, bimetallic Ag0.25Pd0.75/TiO2 and Au0.5Pd0.5/TiO2 catalysts showed the highest activity over other molar ratios. The results clearly proved that the observed activity of the supported nanoparticles is mainly depending on the degree of metal-metal interactions together with the strong metal-support interactions as well as the small particle sizes offered by the sol-immobilization method. This would help and facilitate the electron transfer from metal-to-metal at the metal/metal interfaces and hence the promote the synergistic effect between the two metals which eventually ended with an acceleration for the reaction.

Item Type: Thesis (PhD)
Date Type: Completion
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
Date of First Compliant Deposit: 16 May 2019
Last Modified: 30 Mar 2021 12:51
URI: http://orca.cardiff.ac.uk/id/eprint/122596

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