En route to CO2-containing renewable materials: catalytic synthesis of polycarbonates and non-isocyanate polyhydroxyurethanes derived from cyclic carbonates

Combining CO2-chemistry with biomass conversion allows renewable polymeric materials including polycarbonates and polyhydroxyurethanes (PHUs) to be generated. The demand for robust materials with modular properties that can be prepared on an industrial scale is important and, to date, the most important polymeric materials are derived from petrochemicals. These materials inevitably result in CO2 emissions, and therefore making robust materials from renewable sources will contribute to a more sustainable society. An attractive way to address this challenge is to combine biomass transformations with CO2-fixation and material science. An identified target that combines all three aspects involves the preparation of PHUs (or non-isocyanate polyurethanes, NIPUs) via the polymerization of fully renewable cyclic carbonates derived from biomass and CO2 with a diamine compound that can also been derived from biomass sources. In this review, we critically analyze the progress in catalyst development for the efficient transformation of epoxides and CO2 to cyclic carbonates and polycarbonates. We also discuss the synthesis of PHUs from cyclic carbonates and diamines (not restricted to fully renewable compounds), including challenges in regiocontrol and biodegradability, as well as the role catalysts play in the synthesis of these polymers.

Nanostructured Electrocatalysts for Water Splitting Reactions

Lucas-Alexandre Stern

At the dawn of the 21st century, mankind is facing an important energy challenge. Future energy demand can only be met by large scale exploitation of renewable energy resources. Solar energy is abundant, with a sufficient capacity for the growing energy demand. However, it is necessary to implement renewable energy storage means. Hydrogen is considered as the energy carrier of the future. An energy economy based on hydrogen is viable only if hydrogen is produced from sustainable means. Water electrolysis is the most promising technique to produce hydrogen directly from water. Yet, the efficiency is limited and electrocatalysts are required to drive both the hydrogen evolution reaction and oxygen evolution reaction. Scarce and expensive materials are currently used to drive these reactions. It is, thus, imperative that efficient Earth-abundant catalysts are developed. Nanostructuring enhances the performance of inexpensive materials for water splitting and several catalysts were studied for this goal. Chapter 2 describes the application of nanostructuring technique to the archetypical catalysts that are nickel oxides for oxygen evolution. The prepared nanoparticles show superior activity towards oxygen evolution than that of their bulk counterpart. The ultrafine size of nanoparticles synthesized allowed the exposure of a higher number of active sites. The activity for oxygen evolution was, thus, significantly enhanced. We also detailed that short conditioning of the electrode improved the performance of the evaluated materials. In chapter 3 we carefully studied nanoparticles and nanowires of nickel phosphide. The catalysts is known to be really active for hydrogen evolution. Our group suspected that this material was, also, a potential oxygen evolution catalyst. We proved, for the first time, that nickel phosphide is a remarkable oxygen evolution catalyst. Under alkaline conditions, used for oxygen evolution, we observed an in-situ formation of a core-shell heterostructure, a typical nanostructure architecture. The surface oxidation of this material allowed high oxygen evolution capabilities. We concluded that careful oxidation of nanostructured materials, as observed for nickel phosphide, is essential for the preparation of future outstanding oxygen evolution catalysts. Chapter 4 details the fabrication of direct solar-to-fuel electrode using cobalt phosphide as hydrogen evolving catalyst. Instead of using the electrical energy provided by solar energy, solar irradiation on the developed assembly allows direct hydrogen production. The careful design of the light-sensitive electrode (photocathode) is detailed. Simple incorporation of cobalt phosphide by means of photodeposition alleviates the cost of the electrode fabrication. The assembled electrode is active for hydrogen evolution under visible light irradiation. In the chapter 5 we sought to fabricate a 3-dimensional hydrogen evolving catalyst. This nanostructure is based on polymer brushes on a flat conducting substrate. Once the brushes are grown on the substrate, a molybdenum sulfide catalyst is then incorporated by simple soaking technique. We were able to tune the loading of the catalyst and the corresponding activity by changing the polymer properties. The height of the polymer was modified as well as its packing density. The resulting activity proved superior to similar approaches and to previous reports on carefully engineered molybdenum sulfide catalysts.

EPFL2017

Catalyst design for C-O bond hydrogenolysis of renewable materials.

Antoine Philippe Van Muyden

Anthropogenic carbon dioxide emissions leading to climate change require to use of renewable carbon sources such as CO2 and biomass which differ from fossil resources by having a higher number of oxygen atoms. Therefore, catalytic C-O bond cleavage will play a pivotal role in their conversion into carbon neutral fuels, materials and chemicals. This thesis will focus on the most challenging substrate for selective C-O bond hydrogenolysis, diaryl ether present in lignin (i.e. one of the components of biomass), summarise the state of research and improve the comprehension in the characteristics a catalyst requires to selectively cleave these bonds without altering other functionalities. We showed that the modification in the electronic state and the resulting polarity between two different metals present in a bimetallic nanoparticle favour the selectivity towards hydrogenolysis of a polar C-O bonds over aromatic ring hydrogenation. In addition, we demon-strate that single metal sites cannot hydrogenate an aromatic ring and hence are selective. Final-ly, we applied our knowledge in C-O bond cleavage in CO2 conversion using propylene carbonate as a relay molecule to produce propylene glycol and methane.

EPFL2020

Development of a Photo-Fenton Catalyst Supported on Modified Polymer Films

Félicien Mazille

The work presented in this thesis is a part of the European project INNOWATECH. The global objective of this project was to provide effective technological solutions for the treatment of industrial wastewater, to propose new concepts in wastewater treatment with potential benefits for the protection of the environment. In particular photo-assisted Fenton oxidation was investigated. It is a promising technology to decontaminate industrial wastewater as it makes use of the natural energy that provides the sun, abundant chemicals (iron ions and hydrogen peroxide) and does not produce toxic waste. Apart from short detour about homogenous photo-Fenton reaction (chapter 2) where the influence of pollutant physico-chemical properties on reactivity is studied, this thesis focuses on photo-Fenton treatment using a new solid catalysis. The immobilization of iron oxide on a suitable support is a strategy proposed to overcome the practical limitation related to homogeneous photo-Fenton treatment (i.e. the limited operational pH range and the problems caused by the separation of catalyst from the effluent). The preparation and the surface characterization of new photo-Fenton catalysts based on iron oxide supported on modified polymer films is described in chapters 3 and 4. The photocatalytic activities of prepared materials were evaluated mainly toward organic pollutant degradation both at laboratory (chapter 3-5) and at pilot (chapter 6) scales. In detail, chapter 2 focuses on the effect of contaminant physico-chemical properties on the reactivity via photo-assisted Fenton catalysis. Several para-substituted phenols were used in order to cover a wide range of electronics effects. Many physico-chemical descriptors were correlated with the initial Fenton and photo-Fenton degradation rates (r0). Electronic descriptors such as calculated zero point energy (Ezero) and energy of the highest occupied orbital were found to be the most adequate to predict Fenton and photo-assisted Fenton reactivity. The preparation of iron oxide-coated polymer films is described in chapter 3. Polyvinyl fluoride (PVF) film surface was functionalized by different methods, either by Vacuum-UV radiation, radio-frequency plasma, photo-Fenton oxidation or TiO2 photocatalysis. These pre-treatments were performed to increase iron oxide adhesion to polymer surface. Afterward the functionalized polymers films were immersed in an aqueous solution for the deposition of iron oxide layer by hydrolysis of FeCl3. The catalytic activities of resulting materials were compared during hydroquinone degradation in presence of H2O2 and under simulated solar light illumination. The most efficient and stable catalyst obtained was prepared by means of TiO2 photocatalytic functionalization of polymers followed by iron oxide coating (leading to so called Pf-TiO2-Fe oxide), therefore this preparation procedure was selected in chapters 4-6. Chapter 4 focuses on the study of the mechanisms involved during the preparation and use of Pf-TiO2-Fe oxide. In particular, the modifications induced by TiO2 photocatalysis on polymer surface such as oxygen group formation and deposition of TiO2 particles were characterized by x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and UV-visible spectrophotometry. The photocatalytic activity of Pf-TiO2-Fe oxide in presence of H2O2 and under simulated solar light radiation was evaluated toward HQ degradation. The occurrence of important synergistic effects between TiO2 and iron oxide was discussed. Finally, the effect of preparation parameters on photocatalytic activity of Pf-TiO2-Fe oxide/H2O2/light system was determined allowing the optimization of preparation procedure. Hence highly efficient photocatalysts for hydroquinone degradation and E. Coli inactivation were obtained. The degradation of hydroquinone and nalidixic acid (NA) mediated the system Pf-TiO2-Fe oxide/H2O2/light was examined (chapter 5). The contribution of homogeneous photo-Fenton oxidation in the degradation process was determined and the mechanisms involved in iron leaching are discussed. Besides, the effect of operational parameters on degradation rates was assessed. The rates are independent on initial pH and NaCl presence but were enhanced by increasing temperature. Long-term stability of Pf-TiO2-Fe oxide was evaluated by repetitive nalidixic acid degradation runs. The adaptation of Pf-TiO2-Fe oxide to pilot scale in a compound parabolic collector (CPC) solar photoreactor is described in chapter 6: solar photocatalytic degradation of phenol, nalidixic acid, mixture of pesticides, and another of emerging contaminants, in water was investigated. The influences of operational pH and pollutant structure on the degradation rates were evaluated. It was found that compounds with chelating moieties (or carboxylic acids) were the most quickly removed by Pf-TiO2-Fe oxide/H2O2/light and allowed the photo-Fenton catalyst to be efficient at higher pH values.