High-pressure XPS of crotyl alcohol selective oxidation over metallic and oxidized Pd(111)

Here, we report on the first application of high-pressure XPS (HP-XPS) to the surface catalyzed selective oxidation of a hydrocarbon over palladium, wherein the reactivity of metal and oxide surfaces in directing the oxidative dehydrogenation of crotyl alcohol (CrOH) to crotonaldehyde (CrHCO) is evaluated. Crotonaldehyde formation is disfavored over Pd(111) under all reaction conditions, with only crotyl alcohol decomposition observed. In contrast, 2D Pd5O4 and 3D PdO overlayers are able to selectively oxidize crotyl alcohol (1 mTorr) to crotonaldehyde in the presence of co-fed oxygen (140 mTorr) at temperatures as low as 40 °C. However, 2D Pd5O4 ultrathin films are unstable toward reduction by the alcohol at ambient temperature, whereas the 3D PdO oxide is able to sustain catalytic crotonaldehyde production even up to 150 °C. Co-fed oxygen is essential to stabilize palladium surface oxides toward in situ reduction by crotyl alcohol, with stability increasing with oxide film dimensionality.

Redox-controlled crotyl alcohol selective oxidation:in situ oxidation and reduction dynamics of catalytic Pd nanoparticles via synchronous XANES/MS

In-situ, synchronous MS/XANES reveals the Pd catalyzed selective aerobic oxidation of crotyl alcohol is regulated by the balance between the oxidation state and reducibility. Dynamic XANES measurements provide a new, rapid method to determine redox kinetics of nanoparticles and identify important parameters to optimize catalyst design. © 2012 American Chemical Society.

Synthesis and characterisation of electrospun gold on ceria catalysts

Cerium oxide in catalysis can be used both as support and as a catalyst itself. Ceria catalyses many oxidations reactions, its excellent catalytic properties are due to its store oxygen storage capacity (OSC) and the reticular defects present on its surface. Different morphologies expose different reticular planes, and different reticular planes can expose different amounts of defects. The preparation method of cerium oxide can influence the surface area, morphology, and the number of defects in the sample. This work is focused on different preparation methods for gold nanoparticles supported on 1D nanostructures of cerium oxide prepared via electrospinning, their XRD, DRUV-Vis and Raman characterizations, and their catalytic performance on the oxidation reaction of HMF to FDCA.

Topochemical distribution of lignin and hydroxycinnamic acids in sugar-cane cell walls and its correlation with the enzymatic hydrolysis of polysaccharides

Background: Lignin and hemicelluloses are the major components limiting enzyme infiltration into cell walls. Determination of the topochemical distribution of lignin and aromatics in sugar cane might provide important data on the recalcitrance of specific cells. We used cellular ultraviolet (UV) microspectrophotometry (UMSP) to topochemically detect lignin and hydroxycinnamic acids in individual fiber, vessel and parenchyma cell walls of untreated and chlorite-treated sugar cane. Internodes, presenting typical vascular bundles and sucrose-storing parenchyma cells, were divided into rind and pith fractions. Results: Vascular bundles were more abundant in the rind, whereas parenchyma cells predominated in the pith region. UV measurements of untreated fiber cell walls gave absorbance spectra typical of grass lignin, with a band at 278 nm and a pronounced shoulder at 315 nm, assigned to the presence of hydroxycinnamic acids linked to lignin and/or to arabino-methylglucurono-xylans. The cell walls of vessels had the highest level of lignification, followed by those of fibers and parenchyma. Pith parenchyma cell walls were characterized by very low absorbance values at 278 nm; however, a distinct peak at 315 nm indicated that pith parenchyma cells are not extensively lignified, but contain significant amounts of hydroxycinnamic acids. Cellular UV image profiles scanned with an absorbance intensity maximum of 278 nm identified the pattern of lignin distribution in the individual cell walls, with the highest concentration occurring in the middle lamella and cell corners. Chlorite treatment caused a rapid removal of hydroxycinnamic acids from parenchyma cell walls, whereas the thicker fiber cell walls were delignified only after a long treatment duration (4 hours). Untreated pith samples were promptly hydrolyzed by cellulases, reaching 63% of cellulose conversion after 72 hours of hydrolysis, whereas untreated rind samples achieved only 20% hydrolyzation. Conclusion: The low recalcitrance of pith cells correlated with the low UV-absorbance values seen in parenchyma cells. Chlorite treatment of pith cells did not enhance cellulose conversion. By contrast, application of the same treatment to rind cells led to significant removal of hydroxycinnamic acids and lignin, resulting in marked enhancement of cellulose conversion by cellulases.

In situ infrared (FTIR) study of the mechanism of the borohydride oxidation reaction

Early reports stated that Au was a catalyst of choice for the BOR because it would yield a near complete faradaic efficiency. However, it has recently been suggested that gold could yield to some extent the heterogeneous hydrolysis of BH(4)(-),therefore lowering the electron count per BH(4)(-), especially at low potential. Actually, the blur will exist regarding the BOR mechanism on Au as long as no physical proof regarding the reaction intermediates is not put forward. In that frame, in situ physical techniques like FTIR exhibit some interest to study the BOR. Consequently, in situ infrared reflectance spectroscopy measurements (SPAIRS technique) have been performed in 1 M NaOH/1 M NaBH(4) on a gold electrode with the aim to detect the intermediate species. We monitored several bands in B-H ((nu) over bar similar to 1180,1080 and 972 cm(-1)) and B-O bond regions ((nu) over bar =1325 and similar to 1425cm(-1)), which appear sequentially as a function of the electrode polarization. These absorption bands are assigned to BH(3), BH(2) and BO(2)(-) species. At the light of the experimental results, possible initial elementary steps of the BOR on gold electrode have been proposed and discussed according to the relevant literature data.

Sulfonated Schiff base copper(ii) complexes as efficient and selective catalysts in alcohol oxidation: syntheses and crystal structures

The reaction between 2-aminobenzenesulfonic acid and 2-hydroxy-3-methoxybenzaldehyde produces the acyclic Schiff base 2-[(2-hydroxy-3-methoxyphenyl) methylideneamino] benzenesulfonic acid (H2L center dot 3H(2)O) (1). In situ reactions of this compound with Cu(II) salts and, eventually, in the presence of pyridine (py) or 2,2'-bipyridine (2,2'-bipy) lead to the formation of the mononuclear complexes [CuL(H2O)(2)] (2) and [CuL(2,2'-bipy)]center dot DMF center dot H2O (3) and the diphenoxo-bridged dicopper compounds [CuL(py)](2) (4) and [CuL(EtOH)](2)center dot 2H(2)O (5). In 2-5 the L-2-ligand acts as a tridentate chelating species by means of one of the O-sulfonate atoms, the O-phenoxo and the N-atoms. The remaining coordination sites are then occupied by H2O (in 2), 2,2'-bipyridine (in 3), pyridine (in 4) or EtOH (in 5). Hydrogen bond interactions resulted in R-2(2) (14) and in R-4(4)(12) graph sets leading to dimeric species (in 2 and 3, respectively), 1D chain associations (in 2 and 5) or a 2D network (1). Complexes 2-5 are applied as selective catalysts for the homogeneous peroxidative (with tert-butylhydroperoxide, TBHP) oxidation of primary and secondary alcohols, under solvent-and additive-free conditions and under low power microwave (MW) irradiation. A quantitative yield of acetophenone was obtained by oxidation of 1-phenylethanol with compound 4 [TOFs up to 7.6 x 10(3) h(-1)] after 20 min of MW irradiation, whereas the oxidation of benzyl alcohol to benzaldehyde is less effective (TOF 992 h(-1)). The selectivity of 4 to oxidize the alcohol relative to the ene function is demonstrated when using cinnamyl alcohol as substrate.

Kinetics of selective oxidation of lactose to lactobionic acid over Pd-active carbon catalyst

Laktoosi eli maitosokeri on tärkein ainesosa useimpien nisäkkäiden tuottamassa maidossa. Sitä erotetaan herasta, juustosta ja maidosta. Laktoosia käytetään elintarvike- ja lääketeollisuuden raaka-aineena monissaeri tuotteissa. Lääketeollisuudessa laktoosia käytetään esimerkiksi tablettien täyteaineena. Hapettamalla laktoosia voidaan valmistaa laktobionihappoa, 2-keto-laktobionihappoa ja laktuloosia. Laktobionihappoa käytetään biohajoavien pintojen ja kosmetiikkatuotteiden valmistuksessa, sekä sisäelinten säilöntäliuoksissa, joissa laktobionihappo estää happiradikaalien aiheuttamien kudosvaurioiden syntymistä. Tässä työssä laktoosia hapetettiin laktobionihapoksi sekoittimella varustetussa laboratoriomittakaavaisessa panosreaktorissa käyttäenkatalyyttinä palladiumia aktiivihiilellä. Muutamissa kokeissa katalyytin promoottorina käytettiin vismuttia, joka hidastaa katalyytin deaktivoitumista. Työn tarkoituksena oli saada lisää tietoa laktoosin hapettamisen kinetiikasta. Laktoosin hapettumisessa laktobionihapoksi havaittiin selektiivisyyteen vaikuttavan muunmuassa reaktiolämpötila, paine, pH ja käytetyn katalyytin määrä. Katalyyttiä kierrättämällä eri kokeiden välillä saatiin paremmat konversiot, selektiivisyydet ja saannot. Parhaat koetulokset saatiin hapetettaessa synteettisellä ilmalla 60 oC lämpötilassa ja 1 bar paineessa. Tehdyissä kokeissa pH:n säätö tehtiin manuaalisesti, joten pH ei pysynyt koko ajan haluttuna. Laktoosin konversio oli parhaimmillaan 95 %. Laktobionihapon suhteellinen selektiivisyys oli 100% ja suhteellinen saanto 100 %. Kinetiikan matemaattinen mallinnus tehtiin Modest-ohjelmalla käyttäen kokeista saatuja mittaustuloksia.Ohjelman avulla estimoitiin parametreja ja saatiin matemaattinen malli reaktorille. Tässä työssä tehtiin kineettinen mallinnus myös ravistelureaktorissa tehdyille laktoosin hapetuskokeille, missä pH pysyi koko ajan haluttuna 'in-situ' titrauksen avulla. Työn yhteydessä selvitettiin myös mahdollisuutta käyttää monoliittikatalyyttejä laktoosin hapetusreaktiossa.

Recovery of biomass-derived valuable compounds using chromatographic and membrane separations

Utilization of biomass-based raw materials for the production of chemicals and materials is gaining an increasing interest. Due to the complex nature of biomass, a major challenge in its refining is the development of efficient fractionation and purification processes. Preparative chromatography and membrane filtration are selective, energy-efficient separation techniques which offer a great potential for biorefinery applications. Both of these techniques have been widely studied. On the other hand, only few process concepts that combine the two methods have been presented in the literature. The aim of this thesis was to find the possible synergetic effects provided by combining chromatographic and membrane separations, with a particular interest in biorefinery separation processes. Such knowledge could be used in the development of new, more efficient separation processes for isolating valuable compounds from complex feed solutions that are typical for the biorefinery environment. Separation techniques can be combined in various ways, from simple sequential coupling arrangements to fully-integrated hybrid processes. In this work, different types of combined separation processes as well as conventional chromatographic separation processes were studied for separating small molecules such as sugars and acids from biomass hydrolysates and spent pulping liquors. The combination of chromatographic and membrane separation was found capable of recovering high-purity products from complex solutions. For example, hydroxy acids of black liquor were successfully recovered using a novel multistep process based on ultrafiltration and size-exclusion chromatography. Unlike any other separation process earlier suggested for this challenging separation task, the new process concept does not require acidification pretreatment, and thus it could be more readily integrated into a pulp-mill biorefinery. In addition to the combined separation processes, steady-state recycling chromatography, which has earlier been studied for small-scale separations of high-value compounds only, was found a promising process alternative for biorefinery applications. In comparison to conventional batch chromatography, recycling chromatography provided higher product purity, increased the production rate and reduced the chemical consumption in the separation of monosaccharides from biomass hydrolysates. In addition, a significant further improvement in the process performance was obtained when a membrane filtration unit was integrated with recycling chromatography. In the light of the results of this work, separation processes based on combining membrane and chromatographic separations could be effectively applied for different biorefinery applications. The main challenge remains in the development of inexpensive separation materials which are resistant towards harsh process conditions and fouling.

Wet oxidation of biomass for chemical production

Tämän kandidaatintyön tarkoituksena oli tutkia märkähapetusprosessia jätevesien käsittely-menetelmänä ja mahdollisena menetelmänä kemikaalien tuottamiseksi jätevesistä. Erityishuomio on kiinnitetty paperiteollisuudessa syntyviin jätevesiin. Teoriaosassa käsitellään vesikiertoja paperitehtaassa, paperitehtaalla syntyvän jäteveden ominaisuuksia sekä itse märkähapetusprosessia. Märkähapetusprosessissa perehdytään tavalliseen happea käyttävään märkähapetukseen sekä vetyperoksidia käyttävään menetelmään sekä näissä prosesseissa syntyviin väli- ja lopputuotteisiin. Märkähapetus (WO) on terminen hapetusmenetelmä, jolla voidaan käsitellä jätevesiä, jotka ovat liian konsentroituja biologisiin käsittelyihin tai jotka ovat huonosti biohajoavia. Märkähapetuksen tarkoituksena on parantaa molekulaarisen hapen ja orgaanisen aineen välistä kontaktia, jolloin orgaaninen aines pilkkoutuu muodostaen pääasiassa karboksyylihappoja, aldehydejä, hiilidioksidia ja vettä. Märkähapetuksessa hapettavana kaasuna voidaan käyttää joko puhdasta happea tai ilmaa. Vetyperoksidia käyttävässä märkähapetuksessa (WPO) hapettava kaasu on korvattu nestemäisellä vetyperoksidilla. Kokeellisessa osassa tutkittiin orgaanisen aineksen hapetusta käyttäen Fentonin reagenssia, jolloin katalyyttina reaktiossa toimii rautaionit (Fe2+ ja Fe3+) ja hapettimena vetyperoksidi. Hapetettavana jätevetenä käytettiin paperitehtaan hiomolta saatua kiertovettä, TMP-vettä. Hapetuskokeita tehtiin eri vetyperoksidin annoksilla ja katalyytin määrillä eri lämpötiloissa. Hapetuksen jälkeen näytteistä mitattiin kemiallinen hapenkulutus (COD), orgaanisen hiilen kokonaismäärä (TOC) sekä pH. Lisäksi näytteistä määritettiin nestekromatografilla (HPLC) tyypillisten välituotteiden, kuten oksaalihapon, muurahaishapon ja etikkahapon, määrät. Tehdyissä kokeissa COD-arvoja saatiin pienennettyä 50-88 % siten, että suodatetuissa näytteissä muutos oli suurempi kuin suodattamattomissa näytteissä. Lisäksi TOC-arvot laskivat 28-58 %. Tehdyissä kokeissa saatiin myös tuotettua välituotteina karboksyylihappoja, joista etikkahappoa ja oksaalihappoa tuotettiin suurimmat määrät. Myös muurahaishappoa ja meripihkahappoa saatiin tuotettua.

Topochemistry of physical and chemical pretreatments of biomass as investigated by FE-SEM, XPS and ToF-SIMS

Surface chemistry is of great importance in plant biomass engineering and applications. The surface chemical composition of biomass which includes lignin, carbohydrates and extractives influences its interactions with chemical agents, such as pulp processing/papermaking chemicals, or enzymes for different purposes. In this thesis, the changes in the surface chemical composition of lignocellulosic biomass after physical modification for the improvement of resulting paper properties and chemical treatment for the enhancement of enzymatic hydrolysis were investigated. Low consistency (LC) refining was used as physical treatment of bleached softwood and hardwood pulp samples, and the surface chemistry of refined samples was investigated. The refined pulp was analysed as whole pulp while the fines-free fibre samples were characterized separately. The fines produced in LCrefining contributed to an enlarged surface specific area as well as the change of surface coverage by lignin and extractives, as investigated by X-ray photoelectron spectroscopy (XPS). The surface coverage by lignin of the whole pulp decreased after refining while the surface coverage by extractives increased both for pine and eucalyptus. In the case of pine, the removal of fines resulted in reduction of the surface coverage by extractives, while the surface coverage by lignin increased on fibre sample (without fines). In the case of eucalyptus, the surface coverage by lignin of fibre samples decreased after the removal of fines. In addition, the surface distribution of carbohydrates, lignin and extractives of pine and eucalyptus samples was determined by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS). LC-refining increased the amounts of pentose, hexose and extractives on the surface of pine samples. ToF-SIMS also gave clear evidence about xylan deposition and reduction of surface lignin distribution on the fibre of eucalyptus. However, the changes in the surface chemical composition during the physical treatment has led to an increase in the adsorption of fluorescent whitening agents (FWAs) on fibres due to a combination of electro-static forces, specific surface area of fibres and hydrophobic interactions. Various physicochemical pretreatments were conducted on wood and non-wood biomass for enhancing enzymatic hydrolysis of polysaccharides, and the surface chemistry of the pretreated and enzymatically hydrolysed samples was investigated by field emission scanning electron microscopy (FE-SEM), XPS and ToF-SIMS. A hydrotrope was used as a relatively novel pretreatment technology both in the case of wood and non-wood biomass. For comparison, ionic liquid and hydrothermal pretreatments were applied on softwood and hardwood as well. Thus, XPS analysis showed that the surface lignin was more efficiently removed by hydrotropic pretreatment compared to ionic liquid or hydrothermal pretreatments. SEM analysis also found that already at room temperature the ionic liquid pretreatments were more effective in swelling the fibres compared with hydrotropic pretreatment at elevated temperatures. The enzymatic hydrolysis yield of hardwood was enhanced due to the decrease in surface coverage of lignin, which was induced by hydrotropic treatment. However, hydrotropic pretreatment was not appropriate for softwood because of the predominance of guaiacyl lignin structure in this material. In addition, the reduction of surface lignin and xylan during pretreatment and subsequent increase in cellulose hydrolysis by enzyme could be observed from ToF-SIMS results. The characterisation of the non-wood biomass (e.g. sugarcane bagasse and common reed) treated by hydrotropic method, alkaline and alkaline hydrogen peroxide pretreatments were carried out by XPS and ToF-SIMS. According to the results, the action for the removal of the surface lignin of non-wood biomass by hydrotropic pretreatment was more significant compared to alkaline and alkaline hydrogen peroxide pretreatments, although a higher total amount of lignin could be removed by alkaline and alkaline hydrogen peroxide pretreatment. Furthermore, xylan could be remarkably more efficiently removed by hydrotropic method. Therefore, the glucan yield achieved from hydrotropic treated sample was higher than that from samples treated with alkaline or alkaline hydrogen peroxide. Through the use of ToF-SIMS, the distribution and localization of lignin and carbohydrates on the surface of ignocelluloses during pretreatment and enzymatic hydrolysis could be detected, and xylan degradation during enzymatic hydrolysis could also be assessed. Thus, based on the results from XPS and ToF-SIMS, the mechanism of the hydrotropic pretreatment in improving the accessibility of enzymes to fibre and further ameliorating of the enzymatic saccharification could be better elucidated.

Polymer-supported nitroxyl catalysts for selective oxidation of alcohols

Novel non-toxic poly(ethylene glycol)-supported 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) moieties are demonstrated to give an excellent interfacial catalysis for the selective oxidation of alcohols to the corresponding carbonyl species in biphasic media and investigation for the recovery of these new macromolecular catalysts via precipitation with diethyl ether after catalysis has also been briefly studied.

Poly(ethylene glycol)-supported nitroxyls: branched catalysts for the selective oxidation of alcohols

Nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) are highly selective oxidation catalysts for the conversion of primary alcohols into the corresponding aldehydes. In this study, direct tethering of TEMPO units onto linear poly(ethylene glycol) (PEG) has afforded macromolecular catalysts that exhibit solubility in both aqueous and organic solvents. Recovery of the dissolved polymer-supported catalyst has been carried out by precipitation with a suitable solvent such as diethyl ether. The high catalyst activities and selectivities associated traditionally with nitroxyl-mediated oxidations of alcohols are retained by the series of "linker-less" linear PEG-TEMPO catalysts in which the TEMPO moiety is coupled directly to the PEG support. Although the selectivity remains unaltered, upon recycling of the linker-less polymer-supported catalysts, extended reaction times are required to maintain high yields of the desired carbonyl compounds. Alternatively, attachment of two nitroxyl radicals onto each functionalized PEG chain terminus via a 5-hydroxyisophthalic acid linker affords branched polymer-supported catalysts. In stark contrast to the linker-less catalysts, these branched nitroxyls exhibit catalytic activities up to five times greater than 4-methoxy-TEMPO alone under similar conditions. In addition, minimal decrease in catalytic activity is observed upon recycling of these branched macromolecular catalysts via solvent-induced precipitation. The high catalytic activities and preservation of activity upon recycling of these branched systems is attributed to enhanced regeneration of the nitroxyl species as a result of intramolecular syn-proportionation.

Chemical characterisation and determination of sensory attributes of hydrolysates produced by enzymatic hydrolysis of whey proteins following a novel integrative process

The overall aim of this work was to characterize the major angiotensin converting enzyme (ACE) inhibitory peptides produced by enzymatic hydrolysis of whey proteins, through the application of a novel integrative process. This process consisted of the combination of adsorption and microfiltration within a stirred cell unit for the selective immobilization of β-lactoglobulin and casein derived peptides (CDP) from whey. The adsorbed proteins were hydrolyzed in-situ which resulted in the separation of peptide products from the substrate and fractionation of peptides. Two different hydrolysates were produced: (i) from CDP (IC50 =287μg/mL) and (ii) from β-lactoglobulin (IC50=128μg/mL). IC50 is the concentration of inhibitor needed to inhibit ACE by half. The well known antihypertensive peptide IPP and several novel peptides that have structural similarities with reported ACE inhibitory peptides were identified and characterized in both hydrolysates. Furthermore, the hydrolysates were assessed for bitterness. No significant difference was found between the control (milk with no hydrolysate) and hydrolysate samples at different concentrations (at, below and above the IC50).

Enzymatic hydrolysis of pretreated sugar cane bagasse using Penicillium funiculosum and Trichoderma harzianum cellulases

In this study, we investigated the enzymatic hydrolysis of pretreated sugarcane bagasse using eight different enzymatic blends obtained from concentrated crude enzyme extracts produced by Penicillium funiculosum and Trichoderma harzianum as well as from the extracts in combination with a commercial enzymatic cocktail. The influence of different levels of biomass delignification, degree of crystallinity of lignicellulose, composition of enzymatic activities and BSA on enzymatic hydrolysis yields (HYs) was evaluated. Our X-ray diffraction studies showed that crystallinity of lignocellulose is not a key determinant of its recalcitrance toward enzymatic hydrolysis. In fact, under the experimental conditions of our study, an increase in crystallinity of lignocellulosic samples resulted in increased glucose release by enzymatic hydrolysis. Furthermore, under the same conditions, the addition of BSA had no significant effect on enzymatic hydrolysis. The most efficient enzyme blends were obtained by mixing a commercial enzymatic cocktail with P. funiculosum or T. harzianum cellulase preparations (HYs above 97%) followed by the concentrated extract of P. funiculosum alone (HY= 88.5%). Increased hydrolytic efficiencies appeared to correlate with having an adequate level of both beta-glucosidase and xylanase activities in the blends. (C) 2011 Elsevier Ltd. All rights reserved.

In Situ Infrared (FTIR) Study of the Mechanism of the Borohydride Oxidation Reaction on Smooth Pt Electrode

Although Pt has been thoroughly studied regarding its activity for the borohydride oxidation reaction (BOR), the BOR mechanism at Pt remains unclear: Depending on the applied potential, spontaneous BH(4)(-) hydrolysis can compete with the direct BOR. The goal of the present work is to provide more insight into the behavior of smooth Pt electrodes toward the BOR, by coupling in situ infrared reflectance spectroscopy with electrochemistry. The measurements were performed on a Pt electrode in 1 M NaOH/1 M NaBH(4), so as to detect the reaction intermediate species generated as a function of the applied potential. Several bands were monitored in the B-H ((v) over bar approximate to 1180, 1080, and 972 cm(-1)) and B-O ((v) over bar = 1325 and similar to 1425 cm(-1)) bond regions upon increased electrode polarization. These absorption bands, which appear sequentially and were already detected for similar measurements on Au electrodes, are assigned to BH(3), BH(2), and BO(2)(-) species. In light of these experimental data and previous results obtained in our group for Pt- or Au-based electrodes, possible initial elementary steps of the BOR on platinum electrodes are proposed and discussed according to the relevant literature data.