Robert David Armstrong

Quantitative correlative ¹H – ¹³C NMR has long been discussed as a potential method for quantifying the components of complex reaction mixtures. Here we show that quantitative HMBC NMR can be applied to understand the complexity of the catalytic oxidation of glucose to glucaric acid, which is a promising bio- derived precursor to adipic acid, under aqueous aerobic conditions. It is shown through 2D NMR analysis that the product streams of this increasingly studied reaction contain lactone and dilactone derivatives of acid products, including glucaric acid, which are not observable/ quantifiable using traditional chromatographic techniques. At 98 % glucose conversion, total C₆ lactone yield reaches 44 %. Furthermore, a study of catalyst stability shows all Pt catalysts to undergo product- mediated chemical leaching. Through catalyst development studies, it is shown that sequestration of leached Pt can be achieved through use of carbon supports.

The one-step vacuum carbonization synthesis of a platinum nano-catalyst embedded in a microporous heterocarbon (Pt@cPIM) is demonstrated. A nitrogen-rich polymer of an intrinsic microporosity (PIM) precursor is impregnated with PtCl₆²⁻ to give (after vacuum carbonization at 700 °C) a nitrogen-containing heterocarbon with embedded Pt nanoparticles of typically 1–4 nm diameter (with some particles up to 20 nm diameter). The Brunauer-Emmett-Teller (BET) surface area of this hybrid material is 518 m² g⁻¹ (with a cumulative pore volume of 1.1 cm³ g⁻¹) consistent with the surface area of the corresponding platinum-free heterocarbon. In electrochemical experiments, the heterocarbon-embedded nano-platinum is observed as reactive towards hydrogen oxidation, but essentially non-reactive towards bigger molecules during methanol oxidation or during oxygen reduction. Therefore, oxygen reduction under electrochemical conditions is suggested to occur mainly via a 2-electron pathway on the outer carbon shell to give H₂O₂. Kinetic selectivity is confirmed in exploratory catalysis experiments in the presence of H₂ gas (which is oxidized on Pt) and O₂ gas (which is reduced on the heterocarbon surface) to result in the direct formation of H₂O₂.

Eschewing the common trend towards use of catalysts comprising of Cu, it is reported that PdZn alloys are active for CO₂ hydrogenation to oxygenates. It is shown that enhanced CO₂ conversion is achievable through the introduction of Brønsted acid sites, which promote dehydration of methanol to dimethyl ether. We report that deposition of PdZn alloy nanoparticles onto the solid acid ZSM-5, via chemical vapour impregnation affords catalysts for the direct hydrogenation of CO₂ to DME. This catalyst shows dual functionality; catalysing both CO₂ hydrogenation to methanol and its dehydration to dimethyl in a single catalyst bed, at temperatures of > 270 ^oC. A physically mixed bed comprising 5% Pd 15% Zn/ TiO₂ and H-ZSM-5 shows a comparably high performance, affording a dimethyl ether synthesis rate of 546 mmol kgcat^-1 h^-1 at a reaction temperature of 270 ^oC.

Catalytic methane oxidation using N₂O was investigated at 300 °C over Fe‐ZSM‐5. This reaction rapidly produces coke (retained organic species), and causes catalyst fouling. The introduction of water into the feed‐stream resulted in a significant decrease in the coke selectivity and an increase in the selectivity to the desired product, methanol, from ca. 1 % up to 16 %. A detailed investigation was carried out to determine the fundamental effect of water on the reaction pathway and catalyst stability. The delplot technique was utilised to identify primary and secondary reaction products. This kinetic study suggests that observed gas phase products (CO, CO₂, CH₃OH, C₂H₄ and C₂H₆) form as primary products whilst coke is a secondary product. Dimethyl ether was not detected, however we consider that the formation of C₂ products are likely to be due to an initial condensation of methanol within the pores of the zeolite and hence considered pseudo‐primary products. According to a second order delplot analysis, coke is considered a secondary product and its formation correlates with CH₃OH formation. Control experiments in the absence of methane revealed that the rate of N₂O decomposition is similar to that of the full reaction mixture, indicating that the loss of active alpha‐oxygen sites is the likely cause of the decrease in activity observed and water does not inhibit this process.

Catalytic upgrading of CO₂ to value-added chemicals is an important challenge within the chemical sciences. Of particular interest are catalysts which are both active and selective for the hydrogenation of CO₂ to methanol. PdZn alloy nanoparticles supported on TiO₂ via a solvent-free chemical vapour impregnation method are shown to be effective for this reaction. This synthesis technique is shown to minimise surface contaminants, which are detrimental to catalyst activity. The effect of reductive heat treatments on both structural properties of PdZn/TiO₂ catalysts and rates of catalytic CO₂ hydrogenation are investigated. PdZn nanoparticles formed upon reduction showed high stability towards particle sintering at high reduction temperature with average diameter of 3–6 nm to give 1710 mmol kg⁻¹ h of methanol. Reductive treatment at high temperature results in the formation of ZnTiO₃ as well as PdZn, and gives the highest methanol yield.

Partial oxidative upgrading of C₁–C₃alkanes over Cu/ZSM‐5 catalysts prepared by chemical vapour impregnation (CVI) has been studied. The undoped ZSM‐5 support is itself able to catalyse selective oxidations, for example, methane to methanol, using mild reaction conditions and the green oxidant H₂O₂. Addition of Cu suppresses secondary oxidation reactions, affording methanol selectivities of up to 97 %. Characterisation studies attribute this ability to population of specific Cu sites below the level of total exchange (Cu/Al<0.5). These species also show activity for radical‐based methane oxidation, with productivities exceeding those of the parent zeolite supports. When tested for ethane and propane oxidation reactions, comparable trends are observed.

Glucaric acid has potential applications in food, pharmaceutical and polymer industries yet no methodology exists within the public domain for isolation of this key bio‐derived platform molecule as a pure, crystalline solid. Here we demonstrate the difficulties, which arise in doing so and report development of a process for derivation of free‐glucaric acid from its Ca²⁺/K⁺ glucarate salts, which are both commercially available. Employing Amberlyst‐15 (H⁺) exchange resin and azeotrope drying, powdered glucaric acid is prepared at > 99.96 % purity in 98.7 % dry yield.