Design of cooperative acid-base catalysts for aldol condensations

As fossil resources are depleting due to an increasing world population and the associated energy and chemicals demand, it is of strategic importance to search for renewable alternatives. Lignocellulosic biomass is a promising renewable resource which can be converted into liquid hydrocarbon fuels via routes which includes aldol condensations. At present, at the industrial scale, aldol condensations are typically catalyzed by homogeneous base catalysts. However, in a pursuit of more sustainable chemical processes, heterogeneous catalysts are desired. In this work, the possibility to efficiently increase the aldol condensation rate using heterogeneous cooperative acid-base catalysts has been investigated. These materials are studied experimentally as well as by (kinetic) modeling. The mechanism by which aldol condensations are carried out on this type of materials is further elucidated. Also insights in the catalyst properties which determine the reaction, such as the spatial positioning of the acid function with respect to the base function, the type of acid and base and the hydrophilic or hydrophobic character of the support, have been obtained. In addition, the properties of the reactants and the reaction environment are investigated via the presence of an electron withdrawing group on the aromatic ring of the reagents and the amount of water in the reaction mixture. The research eventually led to a proposal for an optimal acid-base catalyst for aldol condensations

Assignment of capacitance spectroscopy signals of CIGS solar cells to effects of non-ohmic contacts

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Tuning component enrichment in amino acid functionalized (organo)silicas

A straightforward procedure to synthesize cysteine functionalized materials with tailored support properties has been developed. It allows tuning the hydrophobicity of the material via the incorporation of aliphatics, aromatics or silica in the framework structure. The aldol condensation of 4-nitrobenzaldehyde and acetone, as a probe reaction for the catalytic activity of the produced materials, exhibited a remarkable interplay between the reactant, solvent, traces of water and support hydrophobicity. A selective enrichment in the catalyst pores of specific bulk phase molecules is believed to be the key to achieve the targeted catalyst performance

Nanotechnology in catalysis: the force awakens

Nanotechnology - defined as Key Enabling Technology in Europe - plays an important role in our society, e.g., in medicine, in sports, in water treatment applications, in energy devices and is now also emerging in the field of catalysis. It strongly encompasses research and development to synthesize, control, and manipulate catalytic systems of enhanced or even novel properties. These properties can be attributed to the size of the nanomaterial which is ranged in one or more external dimensions from approximately 1 to 100 nm

Monometallic cerium layered double hydroxide supported Pd-Ni nanoparticles as high performance catalysts for lignin hydrogenolysis

Monometallic cerium layered double hydroxides (Ce-LDH) supports were successfully synthesized by a homogeneous alkalization route driven by hexamethylenetetramine (HMT). The formation of the Ce-LDH was confirmed and its structural and compositional properties studied by XRD, SEM, XPS, iodometric analyses and TGA. HT-XRD, N-2-sorption and XRF analyses revealed that by increasing the calcination temperature from 200 to 800 degrees C, the Ce-LDH material transforms to ceria (CeO2) in four distinct phases, i.e., the loss of intramolecular water, dehydroxylation, removal of nitrate groups and removal of sulfate groups. When loaded with 2.5 wt% palladium (Pd) and 2.5 wt% nickel (Ni) and calcined at 500 degrees C, the PdNi-Ce-LDH-derived catalysts strongly outperform the PdNi-CeO2 benchmark catalyst in terms of conversion as well as selectivity for the hydrogenolysis of benzyl phenyl ether (BPE), a model compound for the alpha-O-4 ether linkage in lignin. The PdNi-Ce-LDH catalysts showed full selectivity towards phenol and toluene while the PdNi-CeO2 catalysts showed additional oxidation of toluene to benzoic acid. The highest BPE conversion was observed with the PdNi-Ce-LDH catalyst calcined at 600 degrees C, which could be related to an optimum in morphological and compositional characteristics of the support

Recent advances on the utilization of layered double hydroxides (LDHs) and related heterogeneous catalysts in a lignocellulosic-feedstock biorefinery scheme

Layered double hydroxides (LDHs) and derived materials have been widely used as heterogeneous catalysts for different types of reactions either in gas or in liquid phase. Among these processes, the valorization/upgrading of lignocellulosic biomass and derived molecules have attracted enormous attention because it constitutes a pivotal axis in the transition from an economic model based on fossil resources to one based on renewable biomass resources with preference for biomass waste streams. Proof of this is the increasing amount of literature reports regarding the rational design and implementation of LDHs and related materials in catalytic processes such as: depolymerization, hydrogenation, selective oxidations, and C-C coupling reactions, among others, where biomass-derived compounds are used. The major aim of this contribution is to situate the most recent advances on the implementation of these types of catalysts into a lignocellulosic-feedstock biorefinery scheme, highlighting the versatility of LDHs and derived materials as multifunctional, tunable, cheap and easy to produce heterogeneous catalysts