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This work compares the structure of industrially isolated lignin samples from kraft pulping and three alternative processes: butanol organosolv, supercritical water hydrolysis, and sulfur dioxide/ethanol/water fractionation. Kraft processes are known to produce highly condensed lignin, with reduced potential for catalytic depolymerization, whereas the alternative processes have been hypothesized to impact the lignin less. The structural properties most relevant to catalytic depolymerization are characterized by elemental analysis, quantitative 13 C and 2 D HQSC NMR spectroscopy, gel permeation chromatography, and thermogravimetric analysis. Quantification of the β-O-4 ether bond content shows partial depolymerization, with all samples having less than 12 bonds per 100 aromatic units. This results in theoretical monomer yields of less than 5 %, strongly suggesting the alternative fractionation processes generate highly condensed lignin structures that are no more suitable for catalytic depolymerization than kraft lignin. However, the different thermal degradation profiles suggest there are physicochemical differences that could be leveraged in other valorization strategies., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The nature of the surface species formed through the adsorption of CO 2 on amine-grafted mesoporous silica is investigated through in situ FTIR spectroscopy with the aid of 15 N dynamic nuclear polarization (DNP) and 13 C NMR spectroscopy. Primary, secondary, and tertiary amines are functionalized onto a mesoporous SBA-15 silica. Both isotopically labeled 13 CO 2 and natural-abundance CO 2 are used for accurate FTIR peak assignments, which are compared with assignments reported previously. The results support the formation of monomeric and dimeric carbamic acid species on secondary amines that are stabilized differently to the monocarbamic acid species on primary amines. Furthermore, the results from isotopically labelled 13 CO 2 experiments suggest the existence of two carbamate species on primary amines, whereas only one species is observed predominantly on secondary amines. The analysis of the IR peak intensities and frequencies indicate that the second carbamate species on primary amines is probably more asymmetric in nature and forms in a relatively smaller amount. Only the formation of bicarbonate ions at a low concentration is observed on tertiary amines; therefore, physisorbed water on the surface plays a role in the hydrolysis of CO 2 even if water is not added intentionally and dry gases are used. This suggests that a small amount of bicarbonate ions could be expected to form on primary and secondary amines, which are more hydrophilic than tertiary amines, and these low concentration species are difficult to observe on such samples., (© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The hydrodeoxygenation of guaiacol is investigated over bulk ceria and ceria-zirconia catalysts with different elemental compositions. The reactions are performed in a flow reactor at 1 atm and 275-400 °C. The primary products are phenol and catechol, whereas cresol and benzene are formed as secondary products. No products with hydrogenated rings are formed. The highest conversion of guaiacol is achieved over a catalyst containing 60 mol % CeO2 and 40 mol % ZrO2 . Pseudo-first-order activation energies of 97-114 kJ mol(-1) are observed over the mixed metal oxide catalysts. None of the catalysts show significant deactivation during 72 h on stream. The important physicochemical properties of the catalysts are characterized by X-ray diffraction (XRD), temperature-programmed reduction, titration of oxygen vacancies, and temperature-programmed desorption of ammonia. On the basis of these experimental results, the reasons for the observed reactivity trends are identified., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The chemical oxidation of activated carbon by H2 O2 and H2 SO4 is investigated, structural and chemical modifications are characterized, and the materials are used as catalysts for the hydrolysis of cellulose. Treatment with H2 O2 enlarges the pore size and imparts functional groups such as phenols, lactones, and carboxylic acids. H2 SO4 treatment targets the edges of carbon sheets primarily, and this effect is more pronounced with a higher temperature. Adsorption isotherms demonstrate that the adsorption of oligomers on functionalized carbon is dominated by van der Waals forces. The materials treated chemically are active for the hydrolysis of cellulose despite the relative weakness of most of their acid sites. It is proposed that a synergistic effect between defect sites and functional groups enhances the activity by inducing a conformational change in the glucan chains if they are adsorbed at defect sites. This activates the glycosidic bonds for hydrolysis by in-plane functional groups., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Solid oxide-supported amine sorbents for CO2 capture are amongst the most rapidly developing classes of sorbent materials for CO2 capture. Herein, basic γ supports are used as hosts for amine sites through the grafting of 3-aminopropyltrimethoxysilane to the alumina surface under a variety of conditions, yielding the expected surface-grafted alkylamine groups, as demonstrated by FTIR spectroscopy and (29)Si and (13)C cross-polarization magic-angle spinning (CPMAS NMR) spectroscopy. Grafting amine sites on the surface in the presence of water leads to a high density of amine sites on the surface whereas simultaneously creating a unique type of aluminum species on the surface, as demonstrated by both 1D and 2D (27)Al MAS NMR spectroscopy. The thus prepared sorbents result in higher CO2 adsorption capacities and amine efficiencies compared to sorbents prepared in the absence of water or similar amine loading sorbents prepared using silica supports. In situ FTIR spectra of the sorbents exposed to CO2 at various pressures show no distinct difference in the nature of the adsorbed CO2 species on alumina- versus silica-supported amines, whereas water adsorption isotherms show that the improved performance of the amine-grafted alumina support is not a consequence of retained water on the more hydrophobic aminoalumina materials. The findings demonstrate that amine-grafted, basic alumina materials can be tuned to be more efficient than the corresponding silica-supported materials at comparable amine loadings, further demonstrating that the properties of amine sites can be tuned by controlling or adjusting the support surface properties., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Herein, the hydrothermal stability of amorphous silica-alumina (ASA) is investigated under conditions relevant for the catalytic conversion of biomass, namely in liquid water at 200 °C. The hydrothermal stability of ASA is much higher than that of pure silica or alumina. Interestingly, the synthetic procedure used plays a major role in its resultant stability: ASA prepared by cogelation (CG) lost its microporous structure, owing to hydrolysis of the siloxane bonds, but the resulting mesoporous material still had a considerable surface area. ASA prepared by deposition precipitation (DP) contained a silicon-rich core and an aluminum-rich shell. In hot liquid water, the latter structure was transformed into a layer of amorphous boehmite, which protected the particle from further hydrolysis. The surface area showed relatively minor changes during the transformation. Independent of the synthetic method used, the ASAs retained a considerable concentration of acid sites. The concentration of acid sites qualitatively followed the changes in surface area, but the changes were less pronounced. The performance of different ASAs for the hydrolysis of cellobiose into glucose is compared., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The reactivity of monosaccharides, furfural, and 5-hydroxymethyl-2-furfural (HMF) in the presence of a Brønsted acid (added as H(2)SO(4)) in the ionic liquid 1-butyl-3-methylimidazolium chloride (BMImCl) is investigated at 120 °C. Fructose is converted much faster than mannose, glucose, and xylose and yields HMF with high selectivity, even in the absence of acid. Conversion of mannose, glucose, and xylose involves more complex reaction networks. Only small amounts of furfural and HMF are converted in the absence of other reactants but both compounds are consumed when monosaccharides and their degradation products are present. Acid-catalyzed degradation reactions also lead to the formation of solid residues (humins)., (Copyright © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)