The use of hydrothermal media presents an opportunity to harness the complex and varied chemistry of water for catalytic transformations; with water acting not only as a solvent but also as a reactant and catalyst. Hydrothermal media, or high temperature water (HTW), describes water between 180 °C and 374 °C and at a sufficient pressure to ensure that it remains as a liquid. When compared with ambient water, HTW has a lower dielectric constant, fewer and weaker hydrogen bonds and a higher isothermal compressibility. The use of H2O as a hydrogen-donating solvent offers an exciting possibility to conduct reactions in the absence of gas-phase H2, while the use of binary water/alcohol solvents offers further opportunities to tailor the reaction media. Here we demonstrate the use of HTW in both the direct conversion of CO2; and in the production of renewable carbon catalysts. The conversion of CO2 in HTW has been carried out at 300 °C and an initial CO2 pressure before heating of 25 bar in the presence of iron catalysts. The reaction products vary with conditions, however in all cases methanol is produced alongside more complex species including 2-octanonone and phenol (Figure 1). The conversion of biomass including bread waste to hydrochars in water/alcohol mixtures has also been studied. These hydrochars have applications as sorbents, catalysts and supports. Using binary mixtures of alcohols and water has a direct impact on the physical characteristics of the char produced; Figure 2 shows a representative SEM micrograph. Carbon-supported iron catalysts have also been produced through conducting the synthesis in the presence of iron sulfate. These catalysts have applications including in the conversion of CO2 described above. This work demonstrates the use of OH groups as H-donors in place of H2 and to the ability to use the innate structuring of water and water/alcohol mixtures to control the products of catalytic and catalyst synthesis.

Hydrothermal water a solvent, reactant, and catalyst for sustainable catalytic engineering

2019 Fall National Meeting

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