In search of Netherlandish art: Cultural transmission and artistic exchanges in the Low Countries, an introduction

This article forms the introduction to this special issue of De Zeventiende Eeuw. It puts the case studies presented in this issue into a broader theoretical perspective, highlights connections and differences, and puts forward new research questions

Hard-Templated Carbon-Silica Nanocomposites: Application in Adsorption and Catalysis

Composite materials are highly anticipated in catalysis and adsorption applications as they offer new possibilities to resolve problems posed to classical materials such as zeolites. Their unique structure allows for the combination of the individual material strengths, a selective and multiple functionalisation, and the introduction of distinct surface polarities into one single material. In this work, the development of a new carbon-silica nanocomposite material (CSM) was envisioned. These CSMs present remarkable sorption properties and under the appropriate synthesis conditions shape selective effects are observed. The potential of such composite materials was further examined in catalysis and gas separation technology. CSMs are obtained by hard templating ordered mesoporous silica with furfuryl alcohol. After a subsequent polymerisation and pyrolysis, intraporous graphitic nanocrystals are obtained within the pores of the silica as external deposition could be prevented. Stacking of these nanoblocks generates microporosity as subtle control of the amount of carbon precursor allows tuning the porosity from meso, bi- down to fully microporous. By altering the template confinement and carbon loading, the size of the crystallites which, in combination with the thermal treatment conditions, determine the final shape selective behaviour, can readily be adapted. The separation of linear and branched alkanes is a common process for upgrading gasoline fractions. CSMs are able to match the separation factors of reference zeolites. Moreover, they retain a high adsorbent capacity which is highly relevant regarding the minimisation of the dimensioning of the separation equipment in order to reduce costs in industrial applications. Recently, the scientific community has focused on replacing harmful by bio-degradable chemicals. These compounds are preferably made out from green resources instead of fossil fuels. However, the chemical transformation of such substrates often comprises a complicated reaction scheme involving multiple reaction steps, thus requiring various catalytic functions in a well-controlled nano-environment, viz. polarity and spatial conformation. Alkyl lactates and lactic acid represent such green added-value chemicals as they are commonly used as solvent or moisturizer, and as food additive, anti-bacterial agent or monomer, respectively. In fact, they can readily be synthesized out from trioses or even common sugars. The selective conversion of trioses into alkyl lactates is known to occur with Lewis acid catalysts. Therefore Lewis acid groups were grafted onto a mesoporous silica. However, after the addition of carbon the final CSM catalyst demonstrated superior alkyl lactate yields. The increased activity is obtained by the addition of tuneable surface oxygen groups in the carbon phase, and indicates that the addition of these weak Brønsted acid sites accelerates the rate determining step thus improving the final TOFs of the Lewis acid sites. In addition, the absence of strong Brønsted acid sites prevented side reactions. The conversion straight from common hexoses however, requires an additional isomerisation and retro-aldol reaction in order to obtain the corresponding trioses. Consequently, the complexity of the reaction network increases as the additional intermediates are susceptible for side reactions in particular if Brønsted acid sites are present. Hence, a subtle tuning of the Lewis and Brønsted acidity was required to optimize alkyl lactate yields. The ability of tailoring the pore architecture further allows to control the accessibility to bulky substrates hence enables the high yield production of amphiphilic (long chain) alkyl lactates. Political issues and global awareness have pushed the demand for alternative energy sources and the reduction of CO2 emissions. Hydrogen presents a viable alternative as it has a high energy density and only produces water on burning. However, H2 production often involves CO and CO2 by-products. Moreover, the process is generally combined with a water gas shift reaction which emphasizes the need to separate CO2 from H2 mixtures. Reverse selective membranes represent a viable separation process as it is continuous, it avoids the selectivity-permeability trade-off, and it is highly cost-effective, especially if small H2 gas molecules can be retained at the high pressure side. Carbon properties are highly anticipated yet pure carbon membranes suffer from processing issues while dispersion of carbon particles proofs difficult. Using CSM as a membrane filler avoids these issues as the outer silica component allows an optimized dispersion of the fillers in the polymer matrix, while the interior carbon phase offers a superior CO2 affinity which enhances the CO2 selectivity and permeance. However, tuning of the CO2 affinity of the interaction sites is crucial. This was demonstrated by the introduction of nitrogen groups in the carbon phase which despite further increasing the selectivity hindered the penetration of the gas molecules due to an excessively strong interaction. Overall, the optimized CSM mixed matrix membranes present a significant improvement over current membrane solutions as they offer a high selectivity in combination with a superior membrane flux.nrpages: 265status: publishe