Chapter Four · failure evidence
What Catalytic Degradation & Redox Cleavage got wrong, from 33 dissertations
The records describe various challenges encountered in catalytic degradation and redox cleavage processes across environmental, synthetic, and polymer applications. Many attempts failed due to catalyst deactivation, recalcitrant chemical bonds, unwanted side reactions, and suboptimal reactor or material configurations. These records come from PhD theses at 21 institutions, 2021 to 2026. Each links to its thesis. They were extracted by language models reading the full text, so treat each as a lead to read, not a verdict.
Catalysts and molecular photooxidants suffer from deactivation and self degradation during redox operation
Catalytic systems often fail because active materials, molecular photooxidants, and immobilization linkages degrade or detach under oxidative and photoelectrochemical conditions. High excitation intensity, reactive oxidants, or harsh operating environments accelerate catalyst deactivation and prevent sustainable long term performance.
Tried and failed
increasing excitation intensity to improve quantum yield applied to heterogeneous photocatalytic charge accumulation. Outcome: worse than baseline. Reason: optical saturation and catalyst photodegradation at high fluence
Spectroelectrochemical studies of multi-redox catalysts for water splitting · Imperial
Tried and failed
homogeneous metal-complex photocatalyst degradation applied to pharmaceutical pollutant removal in water. Outcome: unstable. Reason: rapid catalyst deactivation and lack of recyclability during photocatalytic reaction
Considered and rejected
Considered and rejected: Discarded persulfate flash-quencher systems with tethered nanoparticle-photooxidants due to persulfate-mediated oxidative degradation of the organic photooxidant.
Tried and failed
tethering molecular photooxidants to metal oxide catalysts applied to photoelectrochemical water oxidation. Outcome: unstable. Reason: dye molecules detached under operating conditions and underwent oxidative degradation rather than driving catalysis
Lost to a baseline
Mixed-metal and Fe-based catalysts (NiFe2O4, NiCoO2, Ni0.5Co0.5Fe2O4) had much higher overpotentials and degradation rates than baseline IrO2 (and Co3O4) in pure-water MEAs despite being superior in 3-electrode alkaline liquid cells
Advancing Anion-Exchange-Membrane Water Electrolyzer Devices: Catalyst Layer Interactions, Degradation Pathways, and Operational Development · Scholars' Bank
Lost to a baseline
CuAg catalyst prepared by electrodeposition (CuAgdep/Cu) exhibited faster activity degradation (-0.146 vs -0.044 degradation rate slope) and physical detachment compared to galvanically prepared CuAgglv/Cu.
Profitable and sustainable use of biomass in developing technologies · Iowa State
Tried and failed
covalent catalyst immobilisation via amide linkages applied to electrochemical biomass oxidation. Outcome: unstable. Reason: amide linkages underwent hydrolytic cleavage under anodic oxidation potentials
Catalysis of electrochemical biomass valorisation · Imperial
Targeted chemical and redox bond cleavages trigger unintended side reactions and decomposition
Attempts to cleave specific double bonds, rings, or aryl linkages frequently result in substrate decomposition or undesired carbocation fragmentations. Competing processes such as secondary self-metathesis, radical cyclization, and resinification prevent selective formation of the desired cleavage products.
Tried and failed
oxidative cleavage of exocyclic double bonds applied to strained bicyclic olefins. Outcome: unstable. Reason: leads to undesired carbocation fragmentation pathways instead of the cleaved product
Aminative Functionalizations of 1,3-Dienes and Total Synthesis of Crokonoid A · EPFL
Tried and failed
olefin cross-metathesis with symmetrical internal alkenes applied to long-chain polyunsaturated lipid cleavage. Reason: competing secondary self-metathesis occurred despite large excess of cleavage reagent
Monitoring changes to alkenone biosynthesis in commercial Tisochrysis lutea Microalgae · Woods Hole
Tried and failed
electrochemical or halogen-mediated oxidative ring expansion applied to cyclopropanols and cyclopentanols. Outcome: did not generalise. Reason: afforded destructive ring cleavage or complex decomposition instead of expansion
The discovery and application of metal-free cyclobutanol ring expansion reactions · Imperial
Tried and failed
Oxazolidine ring cleavage applied to spirocyclic oxazolidine-cyclopropane derivatives. Outcome: unstable. Reason: cleavage attempts led solely to unreacted starting material or substrate decomposition
Stereoselective palladium-catalyzed carboetherification of cyclopropenes via a tethering strategy · EPFL
Considered and rejected
Considered and rejected: Rejected standard strong acid cleavage (HCl, HBr, HI, TFA, H2SO4) of alkoxymethoxyphenyl ethers due to resinification and tar formation.
Considered and rejected
Considered and rejected: Rejected using degradation/oxidation reactions for hydrocarbon structure determination because degradation frequently induces intermolecular terpene rearrangements
A Study of the Addition Reactions of the Lower Boiling Fraction of East Texas Cedar · TXST Digital Repository
Tried and failed
one-electron reductive cleavage of radical cations applied to biaryl radical cations. Reason: promoted intramolecular cyclization to furan derivatives instead of cleaving to monomers
Heterogeneous photocatalytic degradation is constrained by light scattering and active site accessibility
Increasing catalyst loading or immobilizing powders into thin films impairs degradation rates through optical self-screening, light scattering, and mass transfer limitations. Furthermore, complex heterogeneous formulations often perform worse than homogeneous oxidation or uncatalyzed photolysis baselines.
Tried and failed
increasing heterogeneous photocatalyst loading applied to photocatalytic pollutant degradation in water. Outcome: worse than baseline. Reason: excess suspended catalyst particles cause light scattering and self-screening, reducing photon absorption efficiency
Tried and failed
thin film deposition of porous powders applied to photocatalytic pollutant degradation. Outcome: worse than baseline. Reason: immobilization into film reduced active surface area and mass transfer compared to dispersed powder
Tried and failed
photocatalytic degradation without metal coordination sites applied to organic pollutant degradation in water. Outcome: worse than baseline. Reason: removal of catalytic copper coordination centers severely suppressed photocatalytic degradation activity
Lost to a baseline
Pristine TiO2 outperformed the optimal B/N-graphene/Cu/TiO2 hydrogen evolution photocatalyst in aqueous 2-chlorophenol degradation.
Development of porous material dual-functional reactors for the facile synthesis of sustainable chemicals · Leibniz Universität Hannover Repository
Lost to a baseline
Photocatalytic degradation of Dotarem using TiO2 (k = 1.45 x 10^-5 L g^-1 s^-1) had a lower second-order rate constant than uncatalyzed UVC photolysis (k = 2.10 x 10^-5 L g^-1 s^-1).
Preparación de materiales para el tratamiento de gadoterato de meglumina · Repositorio Institucional BUAP
Lost to a baseline
Homogeneous catalytic oxidation of DES using FeCl3·6H2O/H2O2 at pH 2.6 achieved 100% degradation in 2 hours, whereas the heterogeneous catalyst required 160 minutes.
Novel Heterogeneous Catalyst in the Oxidation of Sulphur Compounds · De Montfort Open Research Archive (DORA)
Cleavage extent in polymer networks and biomass is difficult to control
Chemical degradation of polymer networks and biopolymers often results in incomplete dissolution because cleavage remains confined to specific crosslinks without sufficient backbone breakdown. Conversely, excessive residence times or overly aggressive cleavage catalysts cause uncontrolled over-cracking, severe carbohydrate degradation, and unwanted methane production.
Tried and failed
aminolysis-based chemical degradation of crosslinked polymer networks applied to trithiocarbonate-crosslinked photopolymer resins. Reason: cleavage of trithiocarbonates in the network caused swelling and decoloration but insufficient backbone degradation for dissolution
Control of Network Topology in Photopolymer Networks for Additive Manufacturing · MIT
Lost to a baseline
Ru/C achieved higher mass-specific C-C bond cleavage rates (cleaving more total bonds) than mSiO2/Pt/MCM-48, but suffered from high methane generation (producing ~0.070 g methane from 0.63 g LDPE).
Unlocking the potential of waste polyolefins: Exploring architecture-mediated chemical upcycling strategies for polyolefin conversion to value-added products · Iowa State University Digital Repository
Considered and rejected
Considered and rejected: Rejected acid-catalyzed polysaccharide esterification due to random backbone degradation via glycosidic cleavage and interchain ester crosslinking.
Mixed Polysaccharide Esters for Amorphous Solid Dispersion Oral Drug Delivery Vehicles · Virginia Tech
Considered and rejected
Considered and rejected: Rejected batch solvolysis at 250 °C because prolonged residence times caused severe carbohydrate degradation (glucan/xylan retention dropped to 63.5% and 43.3%) and reactor wall charring.
Selective conversion of lignin derivatives to drop-in petrochemical intermediates through molybdenum oxide-based catalysts · Iowa State University Digital Repository
Fluorinated compounds exhibit thermodynamic and kinetic recalcitrance against oxidative degradation
Perfluorooctanoic acid and related fluorinated degradation intermediates resist breakdown due to positive free energy barriers and high activation energies for radical oxidation and hydrolysis. In addition, low-voltage electrochemical systems fail to supply sufficient potential to generate the surface holes and radicals necessary to overcome this recalcitrance.
Tried and failed
microbially driven Fenton reaction applied to perfluorooctanoic acid degradation. Outcome: no signal. Reason: PFOA was recalcitrant to hydroxyl radical oxidation with 98% remaining after four cycles
Molecular mechanisms of microbial pathways for environmental contaminant remediation · Georgia Tech
Tried and failed
aqueous hydrolysis pathway applied to perfluorinated alcohol degradation intermediate. Reason: thermodynamically unfavorable with positive free energy change and high activation barrier
Development of electrochemical methods for the oxidation and reduction of halogenated organic compounds · Georgia Tech
Tried and failed
hydroxyl radical mediated degradation pathway applied to perfluorinated alcohol mineralization. Reason: Reaction was thermodynamically unfavorable with positive free energy change and high activation barrier.
Development of electrochemical methods for the oxidation and reduction of halogenated organic compounds · Georgia Tech
Tried and failed
low-voltage electrochemical oxidation with metal-oxide anodes applied to perfluorinated pollutant degradation. Outcome: no signal. Reason: applied cell voltage was insufficient to excite reactive surface holes and radicals for oxidation
The Development of Energy Efficient Wastewater Treatment: Electrochemical Oxidation and PFACs liquid-liquid Extraction · Georgia Tech
Left open by the authors
Problems the authors named and did not get to.
Left open
Develop complete chemical recycling protocols for PDHF using accelerated Fenton's reagent oxidative degradation into oligomers or small molecules. Blocker: Requires a wet chemistry laboratory and physical chemical reagents (Fenton's reagent, PDHF polymer samples).
Left open
Apply microbially driven Fenton reaction to partially fluorinated polyfluorinated compounds like fluorotelomer alcohols for degradation testing. Blocker: Requires wet lab microbial culture facilities, chemical reagents, and analytical instrumentation for PFAS degradation experiments
Molecular mechanisms of microbial pathways for environmental contaminant remediation · Georgia Tech
Left open
Incorporate ion implantation, diffusion, and cohesive degradation damage parameters into the thermo-mechanical finite element erosion model. Blocker: Lacks access to the custom coupled FE simulation codebase described in the thesis.
A plasma-wall interaction model for the erosion of materials under ion bombardment · Georgia Tech
Left open
Differentiate enzymatic from nonenzymatic degradation pathways by analyzing biomolecular fungal sequencing data for manganese peroxidase expression versus Fenton-reaction markers. Blocker: Requires collecting fungal biomolecular sequencing data from specific experimental redox-dynamic water samples.
Left open
Synthesize and test alternative stabilizers to atomically dispersed Pt for mitigating Fe-N-C catalyst degradation from Fenton reactions. Blocker: Requires a wet-chemistry synthesis and electrochemical testing laboratory.
Atomic iron in nitrogen-doped carbon electrocatalysts for proton exchange membrane fuel cells · Imperial
Left open
Extend ABAQUS FE models of EB-FRP strengthened RC beams to incorporate interface fracture mechanics and environmental degradation effects. Blocker: Lack of specific interface constitutive models, environmental exposure parameters, or experimental calibration data in the thesis description
Improvement on Design of RC Beams Strengthened in Shear with Externally Bonded FRP Composites · Texas Tech
Left open
Perform enzymatic degradation experiments on 6:2 FTCA, 6:2 FTS, and 7:3 FTCA in soil slurries or co-contaminant mixtures using citrate-phosphate buffer conditions. Blocker: Requires a wet chemistry/biology lab, physical PFAS compounds, soil slurries, and analytical instruments (LC-MS/MS).
Potential of a laccase-1-hydroxybenzotriazole system from Trametes versicolor to degrade per- and polyfluoroalkyl substances · Queens University Institutional Repository
Left open
Investigate the degradation mechanism of porous BN and the effect of P functionalisation during photocatalytic CO2 reduction. Blocker: Requires a wet chemistry lab, materials synthesis, and in-situ/operando photocatalysis characterization equipment
Left open
Evaluate alternative activated carbons and ion exchange resins to measure adsorption rates and selectivity for piperazine degradation and corrosion products. Blocker: Requires wet lab equipment and experimental facilities to test chemical adsorption with hazardous solvents
Mitigation methods for piperazine oxidation in post-combustion carbon capture · UT Austin
Left open
Investigate photoactivities of thin-film CeVO4/gamma-Al2O3 for organic pollutant degradation or ammonia reduction. Blocker: Requires experimental chemistry wet lab, photocatalytic testing equipment, and ALD synthesis apparatus
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