Aromatic Oxygen Research Articles

Controlling Catalytic Selectivity via Adsorbate Orientation on the Surface: From Furfural Deoxygenation to Reactions of Epoxides.

Specificity to desired reaction products is the key challenge in designing solid catalysts for reactions involving addition or removal of oxygen to/from organic reactants. This challenge is especially acute for reactions involving multifunctional compounds such as biomass-derived aromatic molecules (e.g., furfural) and functional epoxides (e.g., 1-epoxy-3-butene). Recent surface-level studies have shown that there is a relationship between adsorbate surface orientation and reaction selectivity in the hydrogenation pathways of aromatic oxygenates and the ring-opening or ring-closing pathways of epoxides. Control of the orientation of reaction intermediates on catalytic surfaces by modifying the surface or near-surface environment has been shown to be a promising method of affecting catalytic selectivity for reactions of multifunctional molecules. In this Perspective, we review recent model studies aimed at understanding the surface chemistry for these reactions and studies that utilize this insight to rationally design supported catalysts.

C-O cleavage of aromatic oxygenates over ruthenium catalysts. A computational study of reactions at step sites.

We studied the C-O cleavage of phenolate and catecholate at step sites of a Ru catalyst using periodic DFT methods at the GGA level. Both C-O scission steps are associated with activation barriers of about 75 kJ mol(-1), hence are significantly more facile than the analogous reactions on Ru terraces. With these computational results, we offer an interpretation of recent experiments on the hydrodeoxygenation of guaiacol (2-methoxyphenol) over Ru/C. We hypothesize that the experimentally observed dependency of the product selectivity on the H2 pressure is related to the availability of step sites on a Ru catalyst.

Biomass gasification: Influence of torrefaction on syngas production and tar formation

The paper contains results of comparative gasification of standard wood biomass pellets, torrefied pellets and sawdust in a robust industrial fixed-bed gasifier. Parameters such as process stability, operating difficulties, gas parameters and tar content in syngas were analysed. The operating conditions were optimised to maximise production of liquid hydrocarbons, which can be both a problematic by-product and a valuable component. In order to collect the data concerning quantity and composition of the tars, the experimental set-up was equipped with a syngas cooler.The test runs conducted with sawdust and ordinary pellets did not cause any operational problems. The most complicated part of the experiment was maintaining process stability during gasification of torrefied pellets. The stabilisation effect of grinding of torrefied pellets and blending these pellets with wet sawdust were tested. It was concluded that effective and stable gasification of torrefied pellets in the tested type of fixed-bed gasifier is possible, but this type of fuel is much more suitable for co-gasification.The cleaned syngas from standard pellets had a relatively stable composition and calorific values in the range of 4.8–5.6MJ/Nm3. Cold gas efficiencies of the process were in the range of 0.72–0.77MJ/Nm3. Using torrefied pellets as a feedstock led to a higher calorific value of syngas, but the cold gas efficiency remained similar (0.75). For sawdust both the calorific value of syngas (LHV=3.0MJ/Nm3) and cold gas efficiency (0.57) were significantly lower than for pellets. The collected condensates contained a water fraction with dissolved organic compounds and thick viscous organic substances tar. It was observed that tar production from torrefied pellets is slower, characterised by lower yield, and technically more difficult in comparison to untreated biomass. The effectiveness of liquid hydrocarbon collection (tar to fuel ratio) varied between 0.0138 [kgtar/kgfuel] for torrefied pellets and 0.0213 [kg/kg] for sawdust. The main component of water fractions were organic acids. The content of organic acids in these fractions was as follows: 79.5% from South African pellets, 67% from Polish pellets, 64% from Polish sawdust and 59% from torrefied pellets respectively. The main organic species in tar from torrefied biomass remained acids, whereas in other cases tars were composed of alkylophenols, linear and cyclic aliphatic oxygenates and polyfunctional aromatic oxygenates.

Express method for total content assessment of aromatic hydrocarbons and oxygen in finished gasolines by refractometry and densimetry

This paper presents routine refracto-densimetric indicators which may be used to identify unbalanced automobile gasoline and falsifications (surrogates). These criteria are supposed to reduce considerably the amount of testing via standard chromatographic and spectroscopic methods. Refracto-densimetric method for controlling the limiting weight content of oxygen is based on substantial difference between specific refractions of oxygenates and hydrocarbon gasoline components. Application of the refractive intercept which is additive in the volume fractions of components and constant for different homologous series of hydrocarbons allowed to establish its maximum value, the excess of which identifies a gasoline with a high content of aromatic hydrocarbons. In addition, the excess of refractive intercept of certain limit value can also indicate the possible presence of conjugated diolefins in gasoline and bicyclic arenes.

Hydrodeoxygenation of Guaiacol over Ru(0001): A DFT Study

The hydrodeoxygenation (HDO) of aromatic oxygenates over ruthenium was studied computationally on the model system guaiacol (2-methoxyphenol) on Ru(0001) using a DFT method. In addition to the adsorption geometries of the aromatic intermediates, the study focused on the energetics of elementary reaction steps that occur during the HDO of guaiacol. Bond scissions at the aliphatic side group were calculated to have barriers of at most 69 kJ mol–1. In contrast, barriers for the cleavage of the aromatic bonds Caryl–O were determined at more than 100 kJ mol–1. On the basis of calculated energetics, a reaction pathway for the HDO of guaiacol is proposed in which first the methyl group of the methoxy moiety is removed to yield catecholate. Subsequently, the oxo groups are replaced by H, yielding first phenolate and, finally, benzene. For the removal of the first oxygen center of catecholate, a substantially lower barrier (106 kJ mol–1) than for the Caryl–O cleavage of phenolate (189 kJ mol–1) was calculated. This is rationalized by the strained structure of adsorbed catecholate. The high barrier for the second Caryl–O scission step is line with recent experiments that yield phenol as the main product of guaiacol HDO over Ru/C.

Promotion of Activity and Selectivity by Alkanethiol Monolayers for Pd-Catalyzed Benzyl Alcohol Hydrodeoxygenation

In reactions of aromatic oxygenates, one promising strategy for improving selectivity toward desirable products is to control the ensembles of available surface sites and thus the adsorbed conformations of reactive intermediates. For this study, alkanethiolate self-assembled monolayers with variable surface densities were employed to restrict the conformation of adsorbed benzyl alcohol on Pd for enhancing hydrodeoxygenation selectivity to toluene and reducing decarbonylation selectivity to benzene. Toluene selectivity was dramatically improved on a 1-octadecanethiol-coated catalyst at the cost of a large decrease in reaction rate. On the other hand, deposition of a sparser 1-adamantanethiol (AT) coating improved selectivity to a smaller extent, but resulted in a higher reaction rate than that of the uncoated catalyst. Auger electron spectroscopy and temperature-programmed desorption (TPD) were used to further characterize this chemistry on a Pd(111) surface in ultrahigh vacuum. The TPD results match the s...

Benzyl Alcohol Oxidation on Pd(111): Aromatic Binding Effects on Alcohol Reactivity

To investigate how surface oxygen participates in the reaction of important aromatic oxygenates, the surface chemistry of benzyl alcohol (PhCH2OH) and benzaldehyde (PhCHO) has been studied on oxygen-precovered Pd(111) (O/Pd(111)) using temperature-programmed desorption (TPD) and high-resolution electron energy loss spectroscopy (HREELS). On both Pd(111) and O/Pd(111), TPD using isotopically labeled benzyl alcohol and low-temperature HREEL spectra show that the oxidation of benzyl alcohol proceeds through a benzyl alkoxide (PhCH2O-) intermediate to adsorbed benzaldehyde so that the sequence of bond scission is O-H followed by C(α)-H. In the presence of surface O, some benzaldehyde desorbs from the surface below 300 K, consistent with the presence of a weakly adsorbed η(1) aldehyde state that is bound to the surface through its oxygen lone pair. Benzaldehyde also reacts with surface oxygen to produce benzoate (PhCOO-). Shifts in the OCO stretching frequency suggest that the benzoate orientation changes as the surface becomes less crowded, consistent with a strong interaction between the phenyl group and the surface. Adsorbed benzaldehyde and benzoate undergo decomposition to CO and CO2, respectively, as well as benzene. Deoxygenation of benzyl alcohol to toluene occurs at high coverages of benzyl alcohol when the relative surface O coverage is low. Experiments conducted on (18)O/Pd(111) reveal exchange occurring between surface O and the benzaldehyde and benzoate intermediates. This exchange has not been reported for other alcohols, suggesting that aromatic binding effects strongly influence alcohol oxidation on Pd.

Porous polyimides from polycyclic aromatic linkers: Selective CO2 capture and hydrogen storage

Porous polyimides are important class of macromolecules owing to their excellent redox behaviour, efficient capture of CO2 and H2 gases, interesting photocatalytic properties and superior thermal and chemical stabilities. Here we describe in detail, the synthesis and gas storage properties of a series of porous polyimides (Tr-NPI, Tr-PPI, Tr-CPI, Td-PPI and Td-CPI) with various network topologies derived from polycyclic aromatic hydrocarbon linkers. These polyimides are synthesized in a single step by the condensation of corresponding polycyclic aromatic dianhydrides (NDA, PDA and CDA) with structure directing amine (TAPA and TAPM) monomers, having trigonal and tetrahedral geometry. The structure of all the polymers was fully characterized by various techniques. The present work also introduces for the first time porous polyimides containing rigid polycyclic aromatic compounds such as coronene. All the polyimides presented here exhibit high thermal stability and show selectivity towards CO2 uptake at room temperature (293 K), due to the presence of aromatic clouds and CO2 phillic oxygen and nitrogen functionalities on their pore surface. Moreover these polymers also showed significant uptake of H2 gas (77 K). The present work has significant implications on the design of robust porous organic solids from small molecules for efficient capture of CO2 and H2 gases.

Cation⋯π interaction and microhydration effects in complexes formed by pyrrolidinium cation and aromatic species in amino acid side chains

A computational study has been carried out in complexes formed by pyrrolidinium cation and aromatic units present in amino acid side chains. The interaction is stronger with indole (-21.9 kcal mol(-1) at the CCSD(T) complete basis set level) than with phenol (-17.4 kcal mol(-1)) or benzene (-16.1 kcal mol(-1)). Most stable structures show a N-H···π contact between pyrrolidinium cation and the phenyl ring of the three aromatic species, except in phenol complexes where the most stable minimum shows a N-HO hydrogen bond. In phenol and indole complexes, secondary contacts are established between the C-H groups of the carbon skeleton of pyrrolidinium and the aromatic rings or hydroxyl oxygen, being the main reason for the enhanced stability with respect to benzene, where these contacts are not possible. The interaction is mainly controlled by electrostatics, but contributions from induction and dispersion are also significant, especially the latter in indole complexes. These three attractive contributions increase their intensity when going from benzene to phenol and indole. Microhydration effects have been estimated by including up to three water molecules in the complexes. In monohydrated pyrrolidiniumbenzene complex the most stable structure shows the water molecule coordinated to the cation without interacting with the ring. In phenol and indole, otherwise, the water molecule interacts with both the cation and the aromatic species, forming a cyclic hydrogen bond pattern π(phenyl)···H-N-H···O-H···X (X = π, O). This pattern is also present among the most stable structures found for complexes with two and three water molecules, though a variety of almost isoenergetic minima showing different hydrogen bond patterns have been found. Water molecules remove the stability differences between phenol and indole complexes, which already with two water molecules show similar stabilities, though around 5 kcal mol(-1) larger than benzene ones.

Applicability of Static Supercritical Carbon Dioxide Extraction in Biogeochemical Characterization of Oil Shales

This study aimed at the assessment of applicability of static supercritical carbon dioxide extraction method (SFE) in biogeochemical characterization of oil shales as an alternative to the standard Soxhlet extration. A comparative investigation on yields and compositions of the solvent soluble bitumoids and their constituents extracted from Estonian Kukersite and Dictyonema oil shales by using Soxhlet extraction method (SEM) and static CO2 supercritical fluid extraction in an autoclave at varied subpyrolysis temperatures was carried out. Resulting from TLC- and GC-MS-analyses, aliphatic and aromatic hydrocarbons and neutral oxygen compounds were separated and identified. For the first time, in the composition of the Kukersite bitumoid, homologous series of n-alkanones-3 to n-alkanones-7 were detected. The extracts obtained were similar in both group and individual composition, and geochemical parametres calculated on the basis of aliphatic hydrocarbons including that made static SFE applicable to geochemical investigation of oil shales.

Primary coloured electrochromism of aromatic oxygen and sulfur diesters

Eleven aromatic diesters and thioic S,S′-diesters were synthesized and investigated using electrochemical (cyclic voltammetry and controlled potential electrolysis) and UV-vis spectroscopic techniques over a range of temperatures. Nine of the compounds exhibited vibrant colour changes from a colourless state in their neutral forms to brightly coloured upon one-electron electrochemical reduction in acetonitrile. The compounds were found to display either red, green or blue colours in their one-electron reduced states. The electrochromic properties of 3 of the compounds that displayed the most vibrant colour changes were examined in solution using a gold micro-mesh electrode laminated inside a polymer film.

Evaluation of the Ion Selectivity of Cyclotriveratrylene Derivatives for Inorganic Ions

Abstract Four C3-functionalized cyclotriveratrylene (CTV) derivatives 1–4 were synthesized, and the ion selectivity of CTV derivatives for inorganic ions was evaluated. Upon potentiometric measurements, CTV derivatives bearing three quinolinylmethyl or pyridinylmethyl groups (1 or 2) were found to exhibit high selectivity for the Ag+ ion. However, CTV derivatives bearing three benzyl or cyclohexylmethyl groups (3 or 4) exhibited rather high selectivity for the Li+ ion. The aromatic nitrogen and methoxy oxygen atoms in the CTV derivatives were observed to play important roles as effective coordination donor sites for the Ag+ or the Li+ ions.

Caking and coking properties of the thermal dissolution soluble fraction of a fat coal

In the coal blending for coke-making, fat coal has a very important role for the caking and coking properties of the coal blends. In this study, a fat coal was thermally dissolved, and the caking and coking properties of the thermal dissolution soluble factions (TDSFs) from different solvents and temperatures were characterized. It was found that the caking properties of TDSFs were better than that of fat raw coal. The TDSFs obtained from non-polar solvents have a higher caking property than those obtained from polar solvents at the same thermal dissolution (TD) temperature. During TD process, polar solvents can thermally dissolve more polyaromatic compounds into TDSF, thus increasing the softening temperature and decreasing the caking property of the TDSF. For the same TD solvent, the TDSFs obtained from higher temperatures have a lower caking property compared to those obtained from lower temperatures because of more aromatic components and oxygen functional groups entering them. Crucible coking determinations were carried out to evaluate the coking property of the TDSFs. The result suggests that when 5% of TDSF and 5% of non-caking sub-bituminous coal were used instead of the same amount of fat coal and gas coal, respectively in the coal blends, the quality of the coke obtained could get to the level of the coke obtained from the standard coal blends (i.e. without TDSF and sub-bituminous coal). Therefore, the use of TDSF in coal blending for coke-making is one of the effective methods for opening the coking coal resources.

Performance of lignin derived aromatic oxygenates in a heavy-duty diesel engine

The possibility to reduce dependence on fossil fuel resources has led to an increasing interest in the use of bio-fuels. This study builds on earlier work on (aromatic) cyclic oxygenates [1,2], but a far wider window of engine operation has been investigated in this paper. Two parametric variations of engine operation were performed and discussed: (1) non-EGR operation by means of varying the load via injection duration/quantity without EGR and (2) EGR operation by gradually increasing the level of EGR. The aromatic oxygenates in question are anisole, benzyl alcohol and 2-phenyl ethanol. The purpose of this work is to evaluate the feasibility of these lignin-derived bio-fuels in a compression ignition (CI) engine with a wide operation range and to assess the impact of the position of the functional oxygen group relative to the aromatic ring. For a better understanding of the combustion process, Heat Release Rates (HRR) have been compared and emissions of soot, NOx and unburnt products (HC, CO) have also been evaluated. The results demonstrate that both the soot-NOx trade-off and engine efficiency are improved for all oxygenates with respect to diesel. Moreover, the results indicate that EGR plays a very important role in further improving aforementioned tradeoff. With EGR, the improvement in the soot-NOx trade-off correlated to some extent with the position of the functional oxygen group to the ring, with better overall emission behavior observed as the oxygen group was farther removed (i.e. separated by carbon atoms) from the ring in the order anisole→benzyl alcohol→2-phenyl ethanol. However, with respect to indicated efficiency, benzyl alcohol blend performed best in both non-EGR and EGR operation.

Comparison of emissions and performance between saturated cyclic oxygenates and aromatics in a heavy-duty diesel engine

Emissions and fuel economy are evaluated for two types of biofuels, namely 2-phenyl ethanol and cyclohexaneethanol. Both are derived from lignin, a form of lignocellulosic biomass. The former and latter oxygenates have an aromatic and aliphatic (i.e. saturated) ring structure, respectively. Two parametric engine sweeps were performed. First, non-EGR operation by means of varying the load via injection duration/quantity. Second, EGR operation by gradually increasing the level of EGR. The goal of this work is to evaluate the overall performance of these lignin-derived biofuels in a compression ignition (CI) engine over a wide range of operation conditions. More specifically, the research is focused on the effect of oxygenate aromaticity. The rationale behind this is that, starting from lignin, itself an aromatic molecule, it would require an expensive hydrogenation step to ultimately produce saturated ringed oxygenates like cyclohexaneethanol from the more lignin-like 2-phenyl ethanol. If there are no adverse effects of using the latter over the former, it makes no sense to consider further hydrogenation upgrading. The engine experiments have been conducted on a modified DAF heavy-duty diesel engine. The results demonstrate that further processing of aromatic oxygenates by means of hydro-treating to saturated rings is not only expensive, but also disadvantageous for the NOx-soot trade-off.

Nucleophile‐Directed Selective Transformation of cis‐1‐Tosyl‐2‐tosyloxymethyl‐3‐(trifluoromethyl)aziridine into Aziridines, Azetidines, and Benzo‐Fused Dithianes, Oxathianes, Dioxanes, and (Thio)morpholines

A five-step procedure for the synthesis of cis-1-tosyl-2-tosyloxymethyl-3-(trifluoromethyl)aziridine was developed, starting from 1-ethoxy-2,2,2-trifluoroethanol, involving imination, aziridination, ester reduction, hydrogenation, and N-,O-ditosylation steps. Further synthetic elaborations revealed a remarkable difference in the reactivity of cis-1-tosyl-2-tosyloxymethyl-3-(trifluoromethyl)aziridine with respect to aromatic sulfur and oxygen nucleophiles, thus enabling the selective deployment of this versatile substrate as a building block for the synthesis of functionalized aziridines, azetidines, and benzo-fused dithianes, oxathianes, dioxanes, and (thio)morpholines.

Stability of Pt/γ-Al2O3 Catalysts in Lignin and Lignin Model Compound Solutions under Liquid Phase Reforming Reaction Conditions

The stability of a 1 wt % Pt/γ-Al2O3 catalyst was tested in an ethanol/water mixture at 225 °C and autogenic pressure, conditions at which it is possible to dissolve and depolymerize various kinds of lignin, and structural changes to the catalysts were studied by means of X-ray diffraction (XRD), 27Al MAS NMR, N2 physisorption, transmission electron microscopy (TEM), H2 chemisorption, elemental analysis, thermogravimetric analysis-mass spectrometry (TGA-MS), and IR. In the absence of reactants the alumina support is found to transform into boehmite within 4 h, leading to a reduction in support surface area, sintering of the supported Pt nanoparticles, and a reduction of active metal surface area. Addition of aromatic oxygenates to mimic the compounds typically obtained by lignin depolymerization leads to a slower transformation of the support oxide. These compounds, however, were not able to slow down the decrease in dispersion of the Pt nanoparticles. Vanillin and guaiacol stabilize the aluminum oxide more than phenol, anisole, and benzaldehyde because of the larger number of oxygen functionalities that can interact with the alumina. Interestingly, catalyst samples treated in the presence of lignin showed almost no formation of boehmite, no reduction in support or active metal surface area, and no Pt nanoparticle sintering. Furthermore, in the absence of lignin-derived aromatic oxygenates, ethanol forms a coke-like layer on the catalyst, while oxygenates prevent this by adsorption on the support by coordination via the oxygen functionalities.

The Effect of the Position of Oxygen Group to the Aromatic Ring to Emission Performance in a Heavy-Duty Diesel Engine

In this paper the soot-NOx trade-off and fuel efficiency of various aromatic oxygenates is investigated in a modern DAF heavy-duty diesel engine. All oxygenates were blended to diesel fuel such that the blend oxygen concentration was 2.59 wt.-%. The oxygenates in question, anisole, benzyl alcohol and 2-phenyl ethanol, have similar heating values and cetane numbers, but differ in the position of the functional oxygen group relative to the aromatic ring. The motivation for this study is that in lignin, a widely available and low-cost biomass feedstock, similar aromatic structures are found with varying position of the oxygen group to the aromatic ring. From the results it becomes clear that both the soot-NOx trade-off and the volumetric fuel economy (i.e. ml/kWh) is improved for all oxygenates in all investigated work points. In general, the improvement in the soot-NOx trade-off correlated with the position of the functional oxygen group to the ring, with better overall emission behavior observed as the oxygen group was further from the ring. No distinct trend was observed with respect to fuel economy

AKRs expression in peripheral blood lymphocytes from smokers

Aldo-keto reductases (AKRs) metabolize a wide range of substrates, including polycyclic aromatic hydrocarbons (PAHs), generating metabolites (o-quinones) and reactive oxygen species (ROS), which are capable of initiating and promoting carcinogenesis. Exposure to PAHs, their metabolites, and ROS further increase AKRs isoform expression that may amplify oxidative damage. Human AKR enzymes are highly polymorphic, and allelic variants may contribute to different AKRs expression in individuals. Despite the importance of AKRs in PAHs metabolism, there are no studies that evaluate, in general human populations, the effect of PAHs on AKRs expression in peripheral blood lymphocytes (PBLs). The aim of this study was to determine the effect of tobacco smoke exposure, and AKR1A1*2 and AKR1C3*2 polymorphisms, on AKR1A1 and AKR1C1-AKR1C3 messenger RNA (mRNA) levels in PBLs from smokers. In the smoker group, there is a statistically significant positive association between AKR1A1, AKR1C1, and AKR1C3 mRNA induction and urine cotinine levels in individuals with a body mass index (BMI) less than 25. However, AKR1A1*2 and AKR1C3*2 alleles did not influence AKR1A1 and AKR1C1-AKR1C3 mRNA levels. These results suggest that AKRs induction by PAHs in smokers' PBLs is associated with BMI; therefore, the role of adipose tissue accumulation in PAHs' effects needs further investigation.

Chloride ions as an agent promoting the oxidation of synthetic dyestuff on BDD electrode

The effect of the presence of chloride ions on anodic oxidation of synthetic dye solution was investigated and compared to other anions (NO3-, HCO3- and SO42-). A boron-doped diamond electrode was used as an anode in bulk electrolysis. Dye degradation was monitored following the relative absorbance removal related to discolouration and aromatic derivates degradation and chemical oxygen demand (COD) removal. The study results showed that not only fast discolouration (k = 76.8) but also dye mineralisation is obtained with addition of chloride thanks to the electrogeneration of active chlorine (HClO/ClO-). The comparison effect using others support electrolytes such as nitrates and hydrogen carbonate revealed strong inhibition for NO3- concerning dye degradation. Average current efficiency and energy consumption (E) were also investigated. An addition of low chloride concentration (0.02 M) in Na2SO4 electrolyte significantly enhances the degradation rate of Cibacron Yellow. An optimised concentration of 0.05M NaCl leads to an increase by 42% of COD removal after 20 min of treatment and decreases the consumption of energy by 333 kWh (kg COD)-1. This result presents Cl- as a promoting agent of the mineralisation of the dye and is very interesting for a subsequent potential industrial application to dyeing waste water treatment for recycling.