Direct synthesis of h2O2 and its application in water purification

Li, Rongjian 2025. Direct synthesis of h2O2 and its application in water purification. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The primary goal of the work within this thesis is to develop novel catalysts capable of generating hydrogen peroxide (H2O2) in situ, along with other reactive oxygen species (ROS), for the oxidative degradation of organic pollutants in water (e.g., phenolic, pesticides, pharmaceuticals). Current industrial H2O2 production, dominated by the auto-oxidation of anthraquinone, is only practical at very large scale. This process is complex, requires the periodic replacement of organic carriers, and yields a highly concentrated solution (~70 wt.% H2O2). Shipping these hazardous materials necessitates the addition of stabilizers (acid or halide), creating safety and environmental concerns. Meanwhile, routine applications like Fenton-based water treatment only require low concentrations (3 to 5 wt.%) and dilution from the pre-formed H2O2 is needed for the purpose of use, highlighting a clear need for a smaller and more efficient method that can supply H2O2 locally while avoiding the concerns and issues mentioned above. The work presented here demonstrates that a catalytic system capable of producing H2O2 in situ, together with its full suite of ROS, can provide a credible alternative pathway for in situ water treatment. The first part of this work primarily focused on the development of Fe-doped TiO2-supported AuPd catalysts for the direct synthesis of H2O2 from molecular H2 and O2 in a batch regime. Initial studies into the effect of Fe loading on the catalytic performance towards the direct H2O2 synthesis revealed that the trimetallic AuPdFe catalysts, containing a minimal Fe loading (at 0.02 wt.%) could effectively promote the H2O2 productivity up to 120 molH2O2 KgCat -1 h -1 at an operational pressure of 39 bar. This was nearly double than that of the bimetallic AuPd (70 molH2O2 KgCat -1 h -1 ) and Fe-rich trimetallic analogous (65 molH2O2 KgCat -1 h -1 ) under the identical reaction conditons. The enhancement observed in H2O2 yield was mainly attributed to the increased activity towards H2 activation rather than H2O2 selectivity. Further analysis through time on line and gas replacement experiments showed the excellent long-term operational potential of the optimal AuPdFe catalyst (0.3 wt.% H2O2 accumulated in time on line test and 0.76 wt.% H2O2 accumulated, respectively) compared to previously reported AuPd-based trimetallic series, in terms of the accumulated H2O2 concentration. Based on the initial investigation on the trimetallic AuPdFe catalysts for H2O2 synthesis, subsequent research into the catalytic degradation of phenol was conducted under reaction conditions more realistic for real-world operation (a water-only solvent, ambient temperatures). Initial studies revealed the effect of Fe loading on the oxidative degradation of phenol, with 2 ii wt.% Fe loading on the AuPd catalyst outperforms other trimetallic AuPdFe formulations, with the optimal catalyst exhibiting a phenol degradation in excess of 80%, with hydroquinone, catechol, and ring-opening molecules existed as the main phenolic intermediates, which is over 10 times better than that of the bimetallic AuPd formulation. Detailed intermediates analysis (hydroxylated and ring-opening byproducts) and radical quenching experiments revealed that the hydroxyl radical ( .OH) is the primary ROS in the oxidative degradation of phenol. Reactant control experiments were taken to exclude the contribution from H2 and O2, and also revealed the low efficiency in phenol degradation using bulk pre-formed H2O2, which only exhibited around 15% phenol conversion, compared to that offered by the in situ route. However, while the precious metal components were found to be stable, Fe leaching was considerable, as a result of the formation of many of the highly oxidised products of phenol degradation (hydroquinone, formic acid, oxalic acid, etc), highlighting the balance between activity and stability during the oxidative degradation of phenol. Finally, a series of AuPd catalysts was prepared via the wet incipient method and pelleted utilised for the in situ treatment of contaminated water in a continuous flow reactor. Preliminary tests suggested that all bimetallic formulations (up to 80% conversion of phenol) outperformed the monometallic Pd (58% conversion of phenol) and Au (2% conversion of phenol) catalysts under the identical reaction conditions. Reaction parameter investigation over the ideal bimetallic AuPd catalyst revealed the relationship between in situ phenol conversion rate and liquid/gas flow rate, system pressure, catalyst loading, as well as pollutant concentration. Relatively long contact times were found to be essential for effective phenol removal. Long-term stability tests demonstrated over 50 hours of continuous and stable operation in phenol conversion over the bimetallic AuPd catalysts, with no detectable metal leaching and minimal morphology changes of the AuPd alloys. Although the investigation on the effect of reactant gases on phenol conversion excluded the contribution from H2 and O2 solely, extensive studies conducted on the in situ degradation of other various organic pollutants revealed that while there may be a minimal contribution from the oxidative pathway, catalytic hydrogenation is the primary cause for the observed conversion of these pharmaceutical and pesticide organic groups.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Schools > Chemistry
Date of First Compliant Deposit:	21 January 2026
Last Modified:	21 Jan 2026 17:06
URI:	https://orca.cardiff.ac.uk/id/eprint/184090

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