Diffusion measurements of hydrocarbons in H-MCM-41 extrudates with pulsed-field gradient nuclear magnetic resonance spectroscopy.

Mesoporous materials are promising catalysts for production of biofuels. Herein, H-MCM-41 catalysts with different concentrations of the silica Bindzil binder (10-50 wt%) were prepared and characterized using pulsed-field gradient (PFG) NMR in the powder form and as extrudates. Effective diffusion coefficients (De) are measured in all cases. Diffusivities of n-hexadecane were found smaller for extrudates as compared to the powder catalysts. The estimates of diffusive tortuosity were also determined. PFG NMR data showed one major component that reveals diffusion in interconnected meso- and micropores and one other minor component (1-2%) that may correspond to more isolated pores or may represent complex effects of restricted diffusion. Therefore, several approaches including initial slope analysis of spin-echo attenuation curves, two-component fitting and Laplace inversion were used to discuss different aspects of diffusional transport in the studied H-MCM-41 materials. Correlations between De and the amount of Bindzil, the specific surface area, the micropore volume, the particle size, the total acid sites and the Lewis acid sites are discussed.

SO3H-Containing Functional Carbon Materials: Synthesis, Structure, and Acid Catalysis.

The "sulfonated carbons" are a new class of metal-free solid protonic acids characterized by their unique carbon structure and Brønsted acidity (-H0 = 8-11) on par to concentrated H2SO4. These carbon materials covalently functionalized with SO3H groups via C-PhSO3H or C-SO3H linkages can act as versatile water-tolerant solid acids. Due to their low production costs, unique surface chemistry, high chemical and thermal stability, as well as tailorable pore structures they are regarded as potential substitutes to liquid H2SO4. Catalysis, in particular, biomass and large molecule catalysis, is one of the important areas in which acidic carbons have demonstrated exceptional activity and selectivity, outperforming traditional solid acid catalysts (cation-exchange resins, sulfated oxides, and acidic zeolites). In this review we address developments in the different types SO3H- and PhSO3H-functionalized acidic carbon materials, their structure, active sites, and surface properties, applications in catalysis, as well as activation and deactivation characteristics covering important literature since 2004. In particular, we aim to provide a systematic discussion on the specific merits and demerits of such materials obtained from different carbon precursors and functionalization methods which directly influence the structure-stability-acidic properties and catalytic performance.

Zeta Potential of Beta Zeolites: Influence of Structure, Acidity, pH, Temperature and Concentration.

Measurements of the zeta potential of solid heterogeneous supports are important for preparation of metal supported catalysts and for shaping zeolites into extrudates. In the current work, different types of heterogeneous support materials such as SiO2, Al2O3, and a range of beta zeolites of different silica- to-alumina ratio were analysed. It was observed that parameters such as temperature, pH and acidity significantly affect the zeta potential. In several instances, depending on the materials' acidity and microstructure, maxima in zeta potential were observed. The solid materials were thoroughly characterized using XRD, SEM, EDX, TEM, nitrogen physisorption, Al-NMR and FTIR with pyridine before zeta potential measurements.

Kinetics of lactose and rhamnose oxidation over supported metal catalysts.

Several mono- and bimetallic Pd, Pt, Rh and Ru supported on alumina and active carbon catalysts were characterized by CO chemisorption, nitrogen adsorption, XPS and XRD and acidity titrations were performed for active carbon supported catalysts. These catalysts were tested in oxidation of two sugars, namely lactose and rhamnose, at 60 °C and at 70 °C under slightly alkaline conditions (pH 8) with molecular oxygen. The results revealed that there is an optimum metal particle size in a range of 3-10 nm giving the highest initial TOFs for both oxidations. Furthermore, the catalytic activities and conversions were related to other catalyst properties, such as the type and amount of promoters and the presence of different phases. In situ catalyst potential measurements revealed that there is an inverse correlation between the increase of catalyst potential as a function of sugar conversion and the catalyst activity after prolonged reaction times. This method is a valuable tool for in situ characterization of catalysts correlating well with their activities.

Catalytic Hydrogenation/Hydrogenolysis of 5-Hydroxymethylfurfural to 2,5-Dimethylfuran.

Recent developments in transformations of biobased 5-hydroxymethylfurfural to 2,5-dimethylfuran, a potential liquid fuel, are critically summarized. The highest yield of 2,5-dimethylfuran (more than 98 %) from 5-hydroxymethylfurfural are obtained over bimetallic Cu-Co supported on carbon at 180 °C under 5 bar hydrogen in 2-propanol and over Ni supported on mesoporous carbon at 200 °C under 30 bar hydrogen in water in a batch reactor. The desired catalyst should have relatively high metal dispersion and some acidity to facilitate both hydrogenation and hydrogenolysis. However, overhydrogenation and overhydrogenolysis forming 2,5-dimethyltetrahydrofuran and methylfuran, respectively, should be suppressed. Furthermore, a hydrophobic support is more selective than oxide-based support. After a careful adjustment of the residence time in a continuous reactor it is also possible to produce high yields of 2,5-dimethylfuran even over Pt/C. The main challenges limiting the industrial feasibility of these reactions are relatively low initial reactant concentration, catalyst deactivation by sintering, leaching and coking. In addition to selection of optimum reaction conditions and catalyst properties, kinetic modelling was also summarized.

Supported Silver Nanoparticles as Catalysts for Liquid-Phase Betulin Oxidation.

Herein, it has been shown that betulin can be transformed into its biologically active oxo-derivatives (betulone, betulinic and betulonic aldehydes) by liquid-phase oxidation over supported silver catalysts under mild conditions. In order to identify the main factors determining the catalytic behavior of nanosilver catalysts in betulin oxidation, silver was deposited on various alumina supports (γ-alumina and boehmite) using deposition-precipitation with NaOH and incipient wetness impregnation methods, followed by treatment in H2 or O2. Silver catalysts and the corresponding supports were characterized by X-ray diffraction, nitrogen physisorption, inductively coupled plasma optical emission spectroscopy, photoelectron spectroscopy and transmission electron microscopy. It was found that the support nature, preparation and treatment methods predetermine not only the average Ag nanoparticles size and their distribution, but also the selectivity of betulin oxidation, and thereby, the catalytic behavior of Ag catalysts. In fact, the support nature had the most considerable effect. Betulin conversion, depending on the support, increased in the following order: Ag/boehmite < Ag/boehmite (calcined) < Ag/γ-alumina. However, in the same order, the share of side reactions catalyzed by strong Lewis acid centers of the support also increased. Poisoning of the latter by NaOH during catalysts preparation can reduce side reactions. Additionally, it was revealed that the betulin oxidation catalyzed by nanosilver catalysts is a structure-sensitive reaction.

Heterogeneous Catalytic Synthesis of Methyl Lactate and Lactic Acid from Sugars and Their Derivatives.

Recent developments in sugar transformations to methyl lactate and lactic acid are critically summarized. The highest yield of methyl lactate from glucose obtained over Sn(salen)/octylmethyl imidazolium bromide catalyst was 68 % at 160 °C whereas the highest yield of lactic acid of 58 % was achieved over hierarchical Lewis acidic Sn-Beta catalysts at 200 °C under inert atmosphere. In addition to the desired products also humins are formed in water whereas in methanol alkyl glucosides- and -fructosides as well as acetals were generated, especially in the presence of Brønsted-acidic sites. The main challenges limiting the industrial feasibility of these reactions are incomplete liquid phase mass balance closure, complicated product analysis and a lack of kinetic data. In addition to reporting optimized reaction conditions and catalyst properties also catalyst reuse and regeneration as well as kinetic modelling and continuous operation are summarized.

Hydrodeoxygenation of Isoeugenol over Alumina-Supported Ir, Pt, and Re Catalysts.

Hydrodeoxygenation (HDO) of isoeugenol (IE) was investigated using bimetallic iridium-rhenium and platinum-rhenium catalysts supported on alumina in the temperature and pressure ranges of 200-250 °C and 17-40 bar in nonpolar dodecane as a solvent. The main parameters were catalyst type, hydrogen pressure, and initial concentration. Nearly quantitative yield of the desired product, propylcyclohexane (PCH), at complete conversion in 240 min was obtained with Ir-Re/Al2O3 prepared by the deposition-precipitation method using 0.1 mol/L IE initial concentration. High iridium dispersion together with a modification effect of rhenium provided in situ formation of the IrRe active component with reproducible catalytic activity for selective HDO of IE to PCH. The reaction rate was shown to increase with the increasing initial IE concentration promoting also HDO and giving a higher liquid phase mass balance. Increasing hydrogen pressure benefits the PCH yield.

Pharmaceuticals and Surfactants from Alga-Derived Feedstock: Amidation of Fatty Acids and Their Derivatives with Amino Alcohols.

Amidation of renewable feedstocks, such as fatty acids, esters, and Chlorella alga based biodiesel, was demonstrated with zeolites and mesoporous materials as catalysts and ethanolamine, alaninol, and leucinol. The last two can be derived from amino acids present in alga. The main products were fatty alkanol amides and the corresponding ester amines, as confirmed by NMR and IR spectroscopy. Thermal amidation of technical-grade oleic acid and stearic acid at 180 °C with ethanolamine were non-negligible; both gave 61% conversion. In the amidation of stearic acid with ethanolamine, the conversion over H-Beta-150 was 80% after 3 h, whereas only 63% conversion was achieved for oleic acid; this shows that a microporous catalyst is not suitable for this acid and exhibits a wrinkled conformation. The highest selectivity to stearoyl ethanolamide of 92% was achieved with mildly acidic H-MCM-41 at 70% conversion in 3 h at 180 °C. Highly acidic catalysts favored the formation of the ester amine, whereas the amide was obtained with a catalyst that exhibited an optimum acidity. The conversion levels achieved with different fatty acids in the range C12-C18 were similar; this shows that the fatty acid length does not affect the amidation rate. The amidation of methyl palmitate and biodiesel gave low conversions over an acidic catalyst, which suggested that the reaction mechanism in the amidation of esters was different.

Conjugation of linoleic acid over a hydrogen pre-activated heterogeneous catalyst.

Development of a new heterogeneous catalytic pathway for isomerization of linoleic acid to conjugated linoleic acids at mild reaction conditions over Ni/H-MCM-41 in a soluted system.

Switchable ionic liquids as delignification solvents for lignocellulosic materials.

The transformation of lignocellulosic materials into potentially valuable resources is compromised by their complicated structure. Consequently, new economical and feasible conversion/fractionation techniques that render value-added products are intensely investigated. Herein an unorthodox and feasible fractionation method of birch chips (B. pendula) using a switchable ionic liquid (SIL) derived from an alkanol amine (monoethanol amine, MEA) and an organic super base (1,8-diazabicyclo-[5.4.0]-undec-7-ene, DBU) with two different trigger acid gases (CO2 and SO2 ) is studied. After SIL treatment, the dissolved fractions were selectively separated by a step-wise method using an antisolvent to induce precipitation. The SIL was recycled after concentration and evaporation of anti-solvent. The composition of undissolved wood after MEA-SO2 -SIL treatment resulted in 80 wt % cellulose, 10 wt % hemicelluloses, and 3 wt % lignin, whereas MEA-CO2 -SIL treatment resulted in 66 wt % cellulose, 12 wt % hemicelluloses and 11 wt % lignin. Thus, the MEA-SO2 -SIL proved more efficient than the MEA-CO2 -SIL, and a better solvent for lignin removal. All fractions were analyzed by gas chromatography (GC), Fourier transform infrared spectroscopy (FT-IR), (13) C nuclear magnetic resonance spectroscopy (NMR) and Gel permeation chromatography (GPC).

Selective Preparation of trans-Carveol over Ceria Supported Mesoporous Materials MCM-41 and SBA-15.

Ce-modified mesoporous silica materials MCM-41 and SBA-15, namely 32 wt % Ce-Si-MCM-41, 16 wt % Ce-H-MCM-41 and 20 wt % Ce-Si-SBA-15, were prepared, characterized and studied in the selective preparation of trans-carveol by α-pinene oxide isomerization. The characterizations of these catalysts were performed using scanning electron microscopy, X-ray photoelectron spectroscopy, nitrogen adsorption and FTIR pyridine adsorption. Selective preparation of trans-carveol was carried out in the liquid phase in a batch reactor. The activity and the selectivity of catalyst were observed to be influenced by their acidity, basicity and morphology of the mesoporous materials. The formation of trans-carveol is moreover strongly influenced by the basicity of the used solvent and in order to achieve high yields of this desired alcohol it is necessary to use polar basic solvent.

Imidazolium-based poly(ionic liquid)s as new alternatives for CO2 capture.

Solid imidazolium-based poly(ionic liquid)s with variable molecular weights that contain the poly[2-(1-butylimidazolium-3-yl)ethyl methacrylate] (BIEMA) cation and different counter anions were evaluated in terms of CO2 capture and compared with classical ionic liquids with similar counter anions. In addition to poly(ionic liquid)s with often-applied ions such as BF4 (-) , PF6 (-) , NTf2 (-) , trifluoromethanesulfonate (OTf(-) ) and Br(-) , for the first time [BIEMA][acetate] was synthesised, which revealed a remarkably high CO2 sorption performance that exceeded the poly(ionic liquid)s studied previously on average by a factor of four (12.46 mg gPIL (-1) ). This study provides an understanding of the factors that affect CO2 sorption and a comparison of the CO2 capture efficiency with the frequently used sorbents. Moreover, all the studied sorbents were reusable if regenerated under carefully selected conditions and can be considered as suitable candidates for CO2 sorption.

Transforming triglycerides and fatty acids into biofuels.

Fuels derived from biobased materials are attracting attention for their potential in securing the energy supply and protecting the environment. In this Minireview, we evaluate the use of biobased sources, particularly fatty acids and triglycerides from seed oils and animal fats, as fuels. The physical and chemical properties of these fatty acids and triglycerides are discussed, including the link to their sources and current availability to meet fuel demands. The current technologies, also known as the first-generation ones, for converting triglycerides into fuels are covered, including conventional methods such as transesterification, pyrolysis, cracking, and emulsions. Recent, second-generation technological developments that lead to more commercially viable biofuels based on diesel-like hydrocarbons are also discussed.