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Our research focuses on the hydrothermal conversion of carbon dioxide into formate with the aid of zerovalent iron. Conventionally, a one-step approach is applied wherein both (I) the production of hydrogen gas, through the oxidation of zerovalent iron in an aqueous medium and (II) the conversion of carbon dioxide with this hydrogen gas into formate/formic acid, are performed under the same reaction conditions at a temperature of approximately 300 °C. Until now, the yields of formate/formic acid mentioned in the literature are, in the absence of a catalytic substance, low (13.5%). Recently, we developed a hydrothermal hydrogen gas production method based on the oxidation of zerovalent iron and performed under mild conditions (temperature of 160 °C). This synthesis method produces hydrogen gas with a high purity (>99 mol%) and a significant yield (approximately 80 mol%). These experimental results suggested that the optimal hydrothermal reaction conditions for the production of hydrogen gas and the conversion of carbon dioxide, are strongly different in case of applying zerovalent iron as the reducing agent. Therefore, this paper studies the potential of a two-step approach to enhance the carbon conversion yields. The first step is the production of hydrogen gas via the developed method at 160 °C. The second step is the conversion of carbon dioxide at higher temperatures (250-350 °C). This study reveals that the solubility of hydrogen gas into the aqueous solution is a key parameter in order to achieve a high amount of carbon conversion. Therefore, a high temperature, the degree of filling and the initial hydrogen gas amount are necessary to successfully perform the carbon dioxide conversion step with high carbon conversion yields. Applying these insights have led to the experimental observation that via a two-step approach the conversion of potassium hydrogen carbonate into potassium formate can be successfully performed with higher carbon conversion yields, up to 77.9 wt%, and a selectivity of at least 81% when applying a reaction temperature of 280 °C for 24 hours, a degree of filling with water of 50 vol% and an initial amount of hydrogen gas of 100 mmol.

RESUMEN

A new method to graft titania with organic groups has been developed. In contrast to common condensation based grafting methods, this method uses organometallic chemistry to bond organic groups directly at the surface. Thereby the introduction of hetero elements at the bonding interface is avoided.

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The porous structure of nanostructured silicas MCM-41 and SBA-15 has been characterized using N2 adsorption at 77 K, before and after n-nonane preadsorption, together with immersion calorimetry into liquids of different molecular dimensions. Selective blocking of the microporosity with n-nonane proves experimentally that MCM-41 is exclusively mesoporous while SBA-15 exhibits both micro- and mesopores. Additionally, N2 adsorption experiments on the preadsorbed samples show that the microporosity on SBA-15 is located in intrawall positions, the micropore volume accounting for only approximately 7-8 % of the total pore volume. Calorimetric measurements into n-hexane (0.43 nm), 2-methylpentane (0.49 nm), and 2,2-dimethylbutane (0.56 nm) estimate the size of these micropores to be < or = 0.56 nm.

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In the field of heterogeneous catalysis, in situ spectroscopy is one of the topics with growing interest. The characterization of a catalyst under working conditions is essential to identify the catalytic active site and to study the relation between the surface structure of a catalyst and its catalytic performance. For the first time, the design of an in situ spectroscopic cell for FT-Raman is presented and its performance is demonstrated by monitoring the thermal conversion of as synthesized mesoporous titanium and by characterizing the molecular surface structure of the vanadium oxides grafted on MCM-48 after exposure to a probe molecule. The results in both cases indicate that the in situ FT-Raman cell is a promising technique for characterizing the molecular surface structure of catalyst materials.

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A post-synthesis deposition of vanadium silicalite-1 zeolite nanoparticles in the pores of SBA-15 results in a highly ordered hexagonal templated silica material with V-silicalite zeolitic plugs, giving rise to an increased crystallinity of the amorphous mesoporous walls.

RESUMEN

A new and generally applicable synthesis procedure is developed in order to synthesise micelle-templated mesoporous titania built up of nanosized anatase walls with thermal stability up to 600 degrees C.