An Verberckmoes

Ordered mesoporous phenolic resins: Highly versatile and ultra stable support materials

Ordered mesoporous phenolic resins and carbons - an advanced class of ultra-stable mesoporous materials - offer potential applications in the field of catalysis, electrodes and adsorbents. This review gives an extensive overview of the main principles and the recent progress made in the synthesis of these innovative materials using the soft-template method. Furthermore, the versatility towards functionalization and the incorporation of hetero-atoms in the organic framework of the mesoporous resins and carbons are considered. Finally, the broad range of potential applications is discussed and future perspectives in the field of mesoporous polymers and carbons are given.

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.

In situ UV–Vis diffuse reflectance spectroscopy — on line activity measurements of supported chromium oxide catalysts: relating isobutane dehydrogenation activity with Cr-speciation via experimental design

The dehydrogenation of isobutane over supported chromium oxide catalysts was studied by a combination of in situ UV-Vis diffuse reflectance spectroscopy and on line GC analysis. A well-defined set of experiments, based on an experimental design, was carried out to develop mathematical models, which quantitatively relate Cr-speciation and dehydrogenation activity with reaction temperature and time, support composition, gas composition and Cr loading. It will . 2qr 3q be shown that: 1 the dehydrogenation activity is proportional with the amount of in situ measured surface Cr , and . 3q maximum for a 7.5 wt.% CrrAl O catalyst operating at 5008C in 2% isobutane in N ; and 2 Cr -sites are more active in

Framework and extra-framework Co2+ in CoAPO-5 by diffuse reflectance spectroscopy

Five different samples are studied to characterize spectroscopically cobalt in and out of the lattice: two CoAPO-5 samples of different quality, CoAPO-5 gel, Co2+-impregnated AlPO4-5 and Co2+-impregnated alumina. Characterizations with diffuse reflectance spectroscopy (DRS) of the as-synthesized, calcined, and reduced samples lead to the following conclusions: (1) Only frame work Co2+ is susceptible to reversible redox behavior, whereas extra-framework Co2+ remains in the divalent state both in oxidizing and in reducing conditions; and (2) details in the DRS spectra can provide some criteria to distinguish between framework and extra-framework Co2+, Tetrahedral Co2+ in the lattice in as-synthesized CoAPO-5 is characterized by ν2 = 6,700 cm−1 and ν3 = 17,300 cm−1, and after reduction the framework Co is pseudo-tetrahedral with ν2 = 5,500 cm−1 and ν3 = 15,150 cm−1. Extra-framework tetrahedral Co2+ is characterized by ν2 = 5,500 cm−1 and ν3 = 16,850 cm−1, and octahedral Co2+ is characterized by ν1 = 8,100 cm−1 and ν3 = 19,550 cm−1.

The effect of water on the structure of supported vanadium oxide structures: an FT-RAMAN, in situ DRIFT and in situ UV-VIS diffuse reflectance study

A promising way to create supported metal oxide catalysts consists of the irreversible adsorption and subsequent thermolysis of metal acetylacetonate complexes. Spectroscopic techniques are often used in the evaluation and assessment of the final catalytic surface structure. In this paper, the use of FT-RAMAN, in situ UV-VIS diffuse reflectance DRS and in situ diffuse reflectance infrared spectroscopy is discussed in the evaluation of silica supported VOx structures. It is argued that water drastically influences the surface structure of these catalysts. Its effects are noticeable in the stages of pretreatment of the support, the actual synthesis and in the post-synthesis storage of the catalyst

Clay intercalated Cu(II) amino acid complexes : Synthesis, spectroscopy and catalysis

Abstract Complexes of Cu(lysine)2+2 and Cu(histidine)2+2 have been intercalated between the layers of saponite clays by a simple cation exchange procedure from aqueous solutions of preformed Cu(amino acid)2-complexes. Successful immobilization was obtained with an amino acid:Cu2+ ratio of 5, and a pH of 10 and 7.3 for lysine and histidine, respectively. The synthesized materials were investigated as powders and as thin films by electron spin resonance (ESR), diffuse reflectance spectroscopy (DRS) and X-ray diffraction (XRD). The light blue clays are characterized by an axially symmetric ESR spectrum with A∥= 192 G, g∥= 2.23 and g⊥ = 2.07, and a d-d absorption band around 600 nm, due to the intercalated planar Cu2+-complexes. Ammonia interacts reversibly with these intercalated complexes, suggesting the presence of a free coordination site. The novel synthesized materials are active in various oxidation reactions with t-butyl hydroperoxide as oxidant.

Improvement of the hydrothermal stability of SAPO-34

Hydrothermal stability of SAPO-34 is greatly improved by the treatment of the acidic form of the SAPO-34 with NH3.

Alkane oxidation by dinuclear iron complexes in hexagonal mesoporous solids

Biomimetic oxygen activation on binuclear iron active sites occluded within the voids of mesoporous oxides such as HMS (hexagonal mesoporous silica) is an interesting new field of research. As guests, binuclear iron(III) complexes were chosen. Heptapodate N,N,N′,N′-tetrakis(2-R methyl)-2-hydroxy-1,3-diaminopropane ligands in which R is either a pyridyl or a benzimidazole group allow metal coordination as in methane mono-oxygenase active sites. The physicochemical characterization with SEM, TGA and sorption analysis shows the interactions of the complexes with the support. IR, Raman and diffuse reflectance-UV-Vis-NIR spectroscopy is used to monitor interaction of oxygen (16O2 and 18O2) or peroxides with the supported active sites. The cyclohexane, cyclohexylhydroperoxide and isobutane oxidation is described and the mono- and binuclear mechanisms that are occurring in nucleophilic and electrophilic activation pathways 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.

Tuning the Pore Geometry of Ordered Mesoporous Carbons for Enhanced Adsorption of Bisphenol-A

Mesoporous carbons were synthesized via both soft and hard template methods and compared to a commercial powder activated carbon (PAC) for the adsorption ability of bisphenol-A (BPA) from an aqueous solution. The commercial PAC had a BET-surface of 1027 m2/g with fine pores of 3 nm and less. The hard templated carbon (CMK-3) material had an even higher BET-surface of 1420 m2/g with an average pore size of 4 nm. The soft templated carbon (SMC) reached a BET-surface of 476 m2/g and a pore size of 7 nm. The maximum observed adsorption capacity (qmax) of CMK-3 was the highest with 474 mg/g, compared to 290 mg/g for PAC and 154 mg/g for SMC. The difference in adsorption capacities was attributed to the specific surface area and hydrophobicity of the adsorbent. The microporous PAC showed the slowest adsorption, while the ordered mesopores of SMC and CMK-3 enhanced the BPA diffusion into the adsorbent. This difference in adsorption kinetics is caused by the increase in pore diameter. However, CMK-3 with an open geometry consisting of interlinked nanorods allows for even faster intraparticle diffusion.