Willinton Y. Hernández

Review of catalytic systems and thermodynamics for the Guerbet condensation reaction and challenges for biomass valorization

The Guerbet condensation reaction is an alcohol coupling reaction that has been known for more than a century. Because of the increasing availability of bio-based alcohol feedstock, this reaction is of growing importance and interest in terms of value chains of renewable chemical and biofuel production. Due to the specific branching pattern of the alcohol products, the Guerbet reaction has many interesting applications. In comparison to their linear isomers, branched-chain Guerbet alcohols have extremely low melting points and excellent fluidity. This review provides thermodynamic insights and unravels the various mechanistic steps involved. A comprehensive overview of the homogeneous, heterogeneous and combined homogeneous and heterogeneous catalytic systems described in published reports and patents is also given. Technological considerations, challenges and perspectives for the Guerbet chemistry are discussed.

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.

Ni-Cu Hydrotalcite-Derived Mixed Oxides as Highly Selective and Stable Catalysts for the Synthesis of β-Branched Bioalcohols by the Guerbet Reaction.

A series of Ni-Cu hydrotalcite-derived mixed oxides have been synthesized and evaluated as heterogeneous catalysts for the dimerization of linear aliphatic alcohols to afford β-branched Guerbet alcohols. The use of the hydrotalcite-structured catalyst precursor highly favors the catalyst stability. This Cu/Ni catalyst has an enhanced reducibility of Ni2+ species under reaction conditions, favoring the hydrogen transfer and hydrogenation capacity of the catalyst system. Catalytic results are reported for C8 , mixed C8 /C10 , and C18 alcohol feeds, with full conversions and Guerbet product purities of 72.5-96 %.

Structural and catalytic properties of Au/MgO-type catalysts prepared in aqueous or methanol phase: application in the CO oxidation reaction

AbstractAu/MgO and Au/Mg(OH)2-type catalysts for CO oxidation reaction were prepared by using two different synthesis methods in presence of either an aqueous or methanol phase. The influence of the porous and morphological properties of the starting magnesium oxide supports was analyzed and correlated with the catalytic performances of the final gold-supported catalysts. It was found that the deposition of gold in the presence of methanol as a solvent avoids the total rehydration of the MgO support and maintains the textural and morphological properties of the starting oxides. The support synthesized by a surfactant-assisted hydrothermal route, having a combined meso-macroporous structure (i.e., MgO-P) showed a positive influence on the CO oxidation reaction as it favored the dispersion of gold and the surface-to-gas phase interaction during the catalytic process.

Application toward Confocal Full-Field Microscopic X-ray Absorption Near Edge Structure Spectroscopy.

Using X-ray absorption near edge structure (XANES) spectroscopy, information on the local chemical structure and oxidation state of an element of interest can be acquired. Conventionally, this information can be obtained in a spatially resolved manner by scanning a sample through a focused X-ray beam. Recently, full-field methods have been developed to obtain direct 2D chemical state information by imaging a large sample area. These methods are usually in transmission mode, thus restricting the use to thin and transmitting samples. Here, a fluorescence method is displayed using an energy-dispersive pnCCD detector, the SLcam, characterized by measurement times far superior to what is generally applicable. Additionally, this method operates in confocal mode, thus providing direct 3D spatially resolved chemical state information from a selected subvolume of a sample, without the need of rotating a sample. The method is applied to two samples: a gold-supported magnesia catalyst (Au/MgO) and a natural diamond containing Fe-rich inclusions. Both samples provide XANES spectra that can be overlapped with reference XANES spectra, allowing this method to be used for fingerprinting and linear combination analysis of known XANES reference compounds.