Search

The production of renewable chemicals using lignocellulosic biomass has gained significant attention in green chemistry. Among biomass-derived chemicals, secondary amines have emerged as promising intermediates for synthetic applications. Here, we report a systematic study on the reductive amination of phenolics with cyclohexylamine using Pd/C and Rh/C as catalysts. The catalytic tests were performed in batch reactors under different reaction conditions (various: amine concentration (0.1–0.4 mol/L), hydrogen pressure (0–2.5 bar), temperature (80–160 °C), and substituted phenols (phenol, o-cresol, p-cresol, and methoxyphenol)) and using tert-amyl alcohol as a solvent. The experimental observations were consistent with a multi-step mechanism, where hydrogenation of phenol to cyclohexanone is followed by condensation of the ketone with cyclohexylamine to form an imine, which is finally hydrogenated to produce secondary amines. In addition, there was evidence of parallel self-condensation of the cyclohexylamine. The study also supported a limited dehydrogenation capacity of Rh/C, unlike Pd/C, which increases this capacity at higher temperatures generating a higher yield of cyclohexylaniline (up to 15%). The study of the alkylated phenols demonstrated that the nature and propensity of hydrogenation of the phenolic controls their amination. Kinetic analysis revealed reaction orders between 0.4 and 0.7 for H2, indicating its dissociative adsorption. Meanwhile, phenol’s order (between 1–1.8) suggests a single participation of this compound in the hydrogenation step. The order of 0.4 for cyclohexylamine suggests its participation as a surface-abundant species. The apparent activation energies derived from a power law approximation were of 37 kJ/mol and 10 kJ/mol on Pd/C and Rh/C, respectively.

Funding Information: The authors would like to thank FONDECYT Grant 1190063, ACE Grant 210012, 2260311 AD/EQ and FONDEQUIP EQM Grant170077 for their financial support. Publisher Copyright: © 2022 The Royal Society of Chemistry. The heterogeneously catalyzed reductive amination of phenolics from lignin is considered an attractive sustainable route for the synthesis of primary or high-order aromatic and aliphatic amines. Here, the reductive amination of phenol with cyclohexylamine was studied, and insights into the role of the catalyst support, metal nanoparticle sizes, and acidic properties were provided. Bulk and surface characterization, IR experiments, and kinetic measurements were performed, and their results were correlated with the catalytic performance and the content of Lewis acid sites (Pd/Al2O3 > Pd/C > Pd/SiO2). The Lewis acid sites in the support and those formed by H2 spillover assisted phenol hydrogenation and C=N bond activation, enhancing the formation of secondary amines (selectivity >90%). The Pd coordination in the particles strongly affected the catalytic activity, indicating that phenol amination is a structure-sensitive reaction. The turnover frequency vs. dispersion profiles combined with the site distributionsin the Pd particles (edge, corner, and terraces) indicate that low-coordination sites favor phenol amination, which was confirmed via diffuse reflectance infrared spectroscopy with Fourier transform and high-resolution transmission electron microscopy. This study could contribute to the upcycling of fresh and recycled lignin fractions to produce aromatic and aliphatic amines.

Iron-catalyzed tar decomposition is studied by inspecting changes in catalytic activity and its correlation to the metal oxidation numbers. A carbon-aerogel-supported iron (Fe/CAG) catalyst was used herein to decompose toluene (model tar) at between 500 °C and 700 °C. The catalytic decomposition was studied in a conventional reaction system, and the catalyst was characterized prior to and after the reaction to understand the effect of the structural changes in the catalytic activity. The results demonstrated that the iron oxidation state and coke deposition strongly depend on the reaction temperature. The X-ray diffraction patterns confirmed that at T

Tar removal from gasification gases is a determinant step to guarantee the operational feasibility of gasification-to-chemicals/energy systems. However, this is a very complex process requiring catalytic materials to proceed under reasonably low temperatures and to convert the tars into fuel gases (i.e., CHx). The use of Fe-based catalysts for application has been reported before, however, there are still unsolved questions related to its stability and interaction with some species of gasification gases. Therefore, we evaluated carbon-supported Fe for the decomposition of tar using simulated gasification gases, and toluene, naphthalene, and benzene as models for tar. The effects of temperature (565 < T < 665 °C) and co-feeding CO on the catalytic activity and stability were inspected at laboratory and bench scales. The activity of catalysts for decomposing tars was in the following order: benzene > toluene e > naphthalene. Moreover, there was evidence validating a reversible elemental step toluene⇔benzene over the Fe surface. The characterization of the spent catalysts evidenced the oxidation of the active phase and the carbon deposition on the surface. The formation of FexOy caused a marked loss of activity. Conversely, the carbides were stable and still active for tar decomposition.

The hydrogenation of CO2 to methanol is a viable alternative for mitigating greenhouse gas net emissions as well as a route for hydrogen storage and transportation. In this work, we studied the nature of the active sites generated by the promotion of Pd with Ga and the surface species and their reactivity under reaction conditions, in the hydrogenation of CO2 to methanol. SiO2-supported Pd and Pd–Ga catalysts with different Pd/Ga molar ratios were synthesized. Results show that in a narrow interval of Pd/Ga molar ratio (0.5 to 1), the methanol formation rates increased by up to two orders of magnitude compared to that on non-promoted Pd. Interestingly, the CO formation rates were barely changed, which resulted in a high selectivity (60% at 800 kPa and 280 °C). Characterization by quasi in situ XPS, XRD, CO adsorption DRIFTS and TEM-EDS demonstrates that the primary cause for the increase in activity towards methanol synthesis is the formation of intermetallic compounds such as Pd2Ga, rather than a cooperative mechanism between Pd and Ga2O3. The variation of the Pd/Ga ratio defines the surface concentration of Ga2O3, where the deposition of excess Ga in its oxidized form on the mono or bimetallic (Pd or Pd–Ga) phases of the catalysts inhibits their catalytic performance. Additionally, operando DRIFTS characterization showed the formation of bidentate formate species (b-HCOO) on the metallic Pd or Pd–Ga sites acting as intermediates in the hydrogenation of CO2 to methanol. Unlike that of methanol, the CO formation rate is mainly dependent on the amount of surface metallic sites, irrespective of their nature (Pd or Pd–Ga). Results show that the presence of PdGa intermetallic compounds is necessary to improve the methanol formation rate of Pd–Ga/SiO2 catalysts.

The hydrogenation of CO2 to methanol is a viable alternative for reducing greenhouse gases net emissions as well as a route for hydrogen storage and transportation. In this context, the synthesis of active and selective catalysts is a relevant objective. In this work, we study the promotion of Pd with Ga and Zn in the hydrogenation of CO2 to methanol at 800 kPa and 220–280 °C. Mono and intermetallic catalysts (Pd/SiO2, Pd Ga/SiO2 and Pd Zn/SiO2) were synthesized by incipient wetness impregnation with the aid of triethanolamine as an organic additive, obtaining similar average metal particle sizes (between 9 and 12 nm). Kinetic analysis reveals that the addition of Ga and Zn increases the turnover frequency for methanol formation by an order of magnitude without significant changes in the reaction rate of the reverse water-gas shift (r-WGS) which is a parallel undesired reaction. The selectivity to methanol (at 220 °C) thus increases from 3% for Pd/SiO2 to 12% for Pd Ga/SiO2 and 30% for Pd Zn/SiO2. XPS studies, Infrared analysis of CO adsorption, and XRD analyses show the presence of intermetallic phases Pd2Ga and PdZn on the surface. The results suggest that Ga and Zn promote Pd, increasing its activity towards the synthesis of methanol, by creating more active sites for this reaction. These sites are likely formed by intermetallic compounds such as Pd2Ga and PdZn.

The present study reports on the technical, economic and environmental analysis of small-scale gasification-ICE systems integrated into sawmills in Chile. Two scenarios were considered, (i) a 100 kWe system for self-consumption in a sawmill and (ii) a 1000 kWe system for using residues from different sawmills. The gasification system was technically assessed by a comprehensive mathematical model implemented on Aspen One 10.0, while economics were studied by the Levelized cost of electricity (LCOE) and environmental impacts were quantified by a Life cycle assessment of forestry, sawmills and power plant processes. Results demonstrate that heat recovery is critical for the process economy, which exhibits an LCOE between 0.15 and 0.32 USD/kWh, and a return on investment of 6.4 years. Nevertheless, the gasification system is far for being an economically-feasible alternative for Chile, where electricity price is 0.08–0.10 USD/kWh. In contrast to economic assessment, the implementation of the gasification-ICE power plant would be a promising alternative for decarbonization of the Chilean energy matrix, showing a reduction of 93% of carbon emissions versus actual practices (viz. co-firing process). From the environmental point of view, biomass harvesting and transport are the critical stages during the whole life cycle of energy production, regardless of the scenario.

Metal catalysts based on Ni, Co, and Pd supported on SiO2 were evaluated in the catalytic pyrolysis of waste tires using pyrolysis experiments coupled to gas chromatography/mass spectrometry (Py–GC/MS) and thermogravimetric analysis coupled with Fourier Transform Infrared spectrometer (TGA–FTIR) techniques. The effect of temperature and the nature of metals on the product distribution and reaction pathways was determined. Catalytic pyrolysis promoted aromatization and cracking reactions at particularly low temperatures ca. 350 °C, leading mainly to the formation of alkenes (isoprene), aromatic terpenes (p-cymene), aliphatic terpenes (d,l-limonene), and other aromatic compounds such as benzene, toluene, and xylenes (BTX). The Pd/SiO2 catalyst was the most selective toward aromatic compounds (around 40 %), owing to its well-known hydrogenation/dehydrogenation capacity, while CC bond cleavage reactions, leading to alkenes, were more favored on the Ni/SiO2 and Co/SiO2 catalysts. In all cases, high selectivity to limonene and isoprene was observed at low temperature. Above 400 °C, no significant differences in product distribution were observed between catalyzed and uncatalyzed pyrolysis. Herein, selectivity toward high-value hydrocarbons (i.e., d , l -limonene, isoprene, BTX, and p-cymene) during the catalytic pyrolysis of waste tires was tuned by the nature of the supported transition metals (i.e., Ni, Co, Pd) and the reaction temperature (e.g., Centro de Investigación y Desarrollo en Ciencias Aplicadas

The CO hydrogenation reaction was studied under methanation conditions (H2/CO >3, 250–300 °C) on Co/SiO2 catalysts with different mean Co nanoparticle size (dp = 4 nm, 13 nm and 33 nm). The catalysts were prepared by incipient wetness impregnation; the cobalt loading and reduction conditions were suitably selected in order to produce catalysts with different dp. Operando FTIR and kinetic measurements provided consistent data for the heat of CO adsorption at low and full coverage. The results confirm the structural sensitivity of the CO hydrogenation reaction on supported cobalt catalysts and demonstrate the energetic heterogeneity of the cobalt surface. A model derived from the Temkin formalism accurately fits the kinetic data and renders the heterogeneity of the cobalt surface by capturing the change in the heat of CO adsorption with the CO coverage. This change is normalized by the heat of CO adsorption at high coverage (ΔQCO/Q1) in order to quantify and compare the heterogeneity of cobalt surfaces. The CO hydrogenation turnover rates are lower on the catalyst with smaller nanoparticles. This surface shows higher heterogeneity and lower apparent activation energy, which is attributed to a larger amount of the more active B5-B sites in this catalyst.

The size of copper nanoparticles affects the intrinsic rate of methanol and CO formation in the hydrogenation of CO2 at 230–270 °C and total pressure 8 bar. Cu/SiO2 catalysts with different mean Cu particle sizes were prepared by water-in-oil microemulsions and suitably pretreated to obtain samples with mean particle size between 4 and 36 nm. The intrinsic rates of methanol and CO formation are 3-fold higher for large particles (>10 nm) than for smaller ones (ca. 4 nm). The reaction path was studied by means of kinetic experiments, H/D isotopic substitution, and in situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS). Results demonstrate that the hydrogenation of formic acid is the rate-determining step (rds) for methanol synthesis, whereas for CO formation the reaction proceeds with the assistance of H atoms and the dissociation of the carboxyl intermediate is the rds. This reaction scheme implies that the ratio of CO to methanol formation rates is inversely proportional to H2 partial pressure, which is also consistent with results for similar catalysts reported in earlier studies. The similar kinetic parameters and H/D kinetic isotope effect observed for catalysts with significantly different Cu mean particle sizes suggests that active surface sites have similar topology regardless of Cu particle size. Step-edge sites whose relative abundance increases with particle size in a way similar to activity are suggested as the active sites for methanol and CO formation reactions.

A comprehensive study of carbon aerogel-supported nickel (Ni/CAG) in the catalytic fast pyrolysis (CFP) of torrefied Eucalyptus globulus was performed in a micropyrolysis unit (Py-GCMS). Effects of pyrolysis temperatures (450–600 °C), catalyst-to-biomass ratio (1:1 pi 2 adsorption-desorption at 77 K, X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Regardless the use of catalysts, the pyrolysis vapors produced from torrefied biomass were depleted in carboxylic acids (selectivity 2 -depleted atmosphere, presumably by a synergistic effect between water gas shift and reforming reactions with transalkylation and decarbonylation of phenolics and furanics. It was demonstrated that metal cluster sizes influenced the reaction routes by favoring hydrogenation on metal facets and deoxygenation on step/corners sites.

Nickel and iron supported on thermostable cellulose-derived carbon aerogels (CAG), were used for the catalytic fast pyrolysis (CFP) of crude and torrefied Eucalyptus globulus . Pyrolysis vapors produced from torrefied biomass under non-catalytic conditions were reduced by 70% in carboxylic acids with respect to vapors originating from crude biomass, but also were richer in ketones and aromatics. In the case of CFP of both crude and torrefied E.globulus on CAG-supported iron and nickel (Fe/CAG and Ni/CAG), the metallic clusters were activated for ketonization, while Ni 0 provided additional hydrogenation sites, increasing the production of monoaromatics (c.a.18% selectivity), leading to a high acids-to-ketone (ξ A-K = 1.3) and heavy-to-light (ξ H-L = 1.0) ratios. Accordingly, Ni/CAG and Fe/CAG were more effective than HZSM-5 –a traditional cracking catalysts– for upgrading CFP vapors to light compounds. The combination of zeolite acid sites with the oxophilic Ni 0 and Fe 0 allows the deoxygenation of vapors while the ratio of polyaromatics to light aromatics (ξ PAHs ) was reduced by nearly 50%.

The effects of using (NH4)2SO4 as a carbonization promoter for producing cellulose-derived carbon aerogels (CAG) was studied. The effects of pretreatment on the textural, morphological, and chemical properties of pristine cellulose nanofibers (CNF) were analyzed through N2 adsorption, scanning electron microscopy (SEM), X-ray diffraction (XRD), elemental analysis, inductively coupled plasma optical emission spectrometry (ICP-OES), and Fourier transform infrared spectroscopy (FT-IR). Furthermore, the thermal behaviors of raw CNF and those impregnated with (NH4)2SO4 were investigated by coupling thermogravimetric analysis with mass spectrometry (TGA-MS). The results suggested that the pretreatment did not cause any morphological/structural changes in the nanofibers. However, the presence of (NH4)2SO4 affected their pyrolysis by favoring intermolecular dehydration, thereby reducing the formation of levoglucosan and increasing the carbon yield during pyrolysis. Interestingly, above certain impregnation level, the concentration of sulfate-derived species in the gas phase increased. This phenomenon was attributed to an excess of salt within the fiber structure and on their surfaces. Consequently, the levoglucosan-to-carbon route was inhibited, and the mechanisms of intra- and inter-molecular dehydration, chain scission, and crosslinking reactions were affected, leading to a reduced char yield. The chemical effects of ammonia-based salts is elucidated supported on the interpretation of MS signals and kinetic modeling results.

The liquid phase amination of the cyclohexanone (CyO) with aniline (PhNH2) was studied on a Pd/C catalyst using NaCO2H as a H-donor. Catalytic tests were performed in batch reactors by varying reactant concentrations (0, 0.1, 0.2 and 0.4 mol/L), the temperature (80–160 °C) and H2-equivalents availability (0, 2 and 4 H2-equivalents with respect to CyO). The results indicate that, the use of NaCO2H barely affect the reactivity (measured as initial reaction rate) while it does influence the selectivity to secondary amines. This effect was ascribed to the limited effectivity of the H2 transfer, which was controlled by the water formed after the condensation of the CyO with the PhNH2, hydrogen solubility in toluene, and the mass transfer from the liquid to the catalyst surface. The experimental observations were consistent with a multi-step mechanism consisting in: a first step of condensation of the ketone and the amine to form an imine, followed by the disproportionation of the imine into secondary amines. The kinetic measurements at initial rate conditions were well interpreted by a Langmuir Hinshelwood (L-H) kinetic model, which suggest that the surface reaction to form the intermediary imine is the rate limiting step (R.L.S).

The promotion of Ga on SiO2 supported Cu in the hydrogenation of CO2 to methanol at 800 kPa and 200–280 °C was investigated. Cu/SiO2 and CuGa/SiO2 catalysts were prepared by a water-in-oil microemulsion technique resulting in Cu clusters of 4–6.5 nm. It was found that Ga addition increased the methanol formation rate by an order of magnitude without significantly changing that for reverse water gas shift (RWGS). This trend is also evidenced by the decrease in the apparent activation barrier for methanol formation from 78 (for Cu/SiO2) to 26–39 kJ mol−1 when Ga was added, but not for RWGS (107–132 kJ mol−1). Kinetic and in situ DRIFTS analyses revealed that formate intermediates are adsorbed on both Cu and Ga2O3 and that methoxy hydrogenation could be the rate determining step of methanol synthesis. In the case of RWGS, a zero order of CO formation with respect to H2 concentration was consistent with a redox mechanism and with the reaction occurring predominantly on Cu sites. The results suggest that Ga promotes Cu increasing methanol selectivity, likely by creating new active sites for methanol formation without modifying its oxidation state, which under reaction conditions remains mostly metallic.

Catalysts of rhodium supported on pure oxides and modified alumina with 50, 75 and 100% of ZrO2 were prepared by the impregnation method, to be tested in the reaction of dry reforming of methane in order to study the effect of the metal-support interaction on the reaction rate. The catalysts were characterized by N2 adsorption isotherms, CO chemisorption, TEM, temperature programmed reduction, XRD and XPS. The reaction rate for CH4 conversion was measured at 500–700 °C, in the absence of transport limitation. The average Rh cluster size in catalysts with modified supports resulted similar as compared with the catalyst Rh/0%ZrO2–Al2O3, so that the modification of the support had no effect on the dispersion of Rh, which is associated with the similarity in the BET surface area of the pure and modified alumina. The Rh-support interaction is determined by the degree of coverage of alumina with zirconia and by the nature of ZrO2 phase formed in the grafted supports. The higher coverage of alumina with zirconia leads to a lower Rh-support interaction. However, the interaction of Rh with the monoclinic phase seems to be weaker than with the tetragonal phase of zirconia, the latter more abundant as the loading of ZrO2 is increased in the grafted supports. Consequently, the Rh-support interaction increases with the content of ZrO2. Despite the different Rh-support interaction, the structural sensitivity of dry reforming of methane on Rh catalysts was still evidenced, i.e., the DRM reaction rate is mainly determined by the coordination degree of Rh atoms on the catalyst surface.

Rapidly growing research on biomass reactivity has not benefited enough from the very abundant knowledge acquired on coal-derived materials. Literature comparisons using similar methods are scant and inconclusive. To clarify differences (or similarities) between coal- and biomass-derived chars, we performed a systematic study using three different carbon-based solids at different stages of coalification. Two biomass materials and a low-rank coal were demineralized and heat-treated between 550 and 1450 °C. Even after heat treatment, biomass-derived chars remained less structurally ordered, more microporous, and more reactive towards oxygen than their coal-derived counterparts. Through computational chemistry, we compared the thermodynamic driving forces and kinetic barriers for biomass-like and coal-like representative graphene clusters. The oxidation pathway to CO was the same for both clusters, but different for CO2 formation. We predict that the energy barrier of CO desorption is higher for coal-derived chars, whereas that of CO2 desorption is higher for biomass-derived chars; this is consistent with the dominant formation of CO2 at the relatively low reaction temperatures used in our study. We demonstrate also that in a kinetically controlled reaction regime, in the absence of catalytically active minerals, the reactivity differences can be explained on the basis of differences in char surface chemistry.

The influence of lanthanum stoichiometry in Ag-doped (La 1-x Ag x Mn 0.9 Co 0.1 O 3 ) and A-site deficient (La 1-x Mn 0.9 Co 0.1 O 3-δ ) perovskites with x equal to 10, 20 and 30 at.% has been investigated in catalysts for soot combustion. The catalysts were prepared by the amorphous citrate method and characterized by XRD, nitrogen adsorption, XPS, O 2 -TPD and TPR. The formation of a rhombohedral excess-oxygen perovskite for Ag-doped and a cubic perovskite structure for an A-site deficient series is confirmed. The efficient catalytic performance of the larger Ag-doped perovskite structure is attributed to the rhombohedral crystalline structure, Ag 2 O segregated phases and the redox pair Mn 4+ /Mn 3+ . A poor catalytic activity for soot combustion was observed with A-site deficient perovskites, despite the increase in the redox pair Mn 4+ /Mn 3+ , which is attributed to the cubic crystalline structure.

Reduction of Fe-phases in a slag from the copper smelting process is studied for its use as a catalyst in methanation of carbon oxide (CO). This material contains 36.4 wt% Fe and the main Fe-phases in its fresh and reduced forms were identified and quantified. Chemical analysis and X-ray diffraction (XRD) for crystalline phase detection and determination of Fe dispersion were carried out. Reducibility of Fe-oxides was studied by thermal programmed reduction (TPR) under H2 at 650 and 800 °C using 0.5 and 2 h soak time. In the fresh slag, iron was found to be in the form of Fe3O4 (17.4 wt%) and fayalite, Fe2SiO4 (43.4 wt%). The composition was experimentally determined and verified by stoichiometric balances and thermogravimetric analysis (TGA). Upon reduction at 800 °C and 2 h soak time, 87 % of the Fe-phases were reduced, leaving an activated catalyst with a 35.2 % Fe0, which is the active phase for CO hydrogenation to methane. An expression was derived to determine the Fe0 concentration in the reduced slag based on the composition of the fresh slag and its reduction degree. The catalytic activity of the reduced slag during CO hydrogenation was evaluated in a fixed bed differential reactor. The selectivity to methane, at 300 °C, was 87 %, thus confirming its catalytic activity for the selected reaction.

Biomass gasification is a promising way to obtain &ldquo, green energy&rdquo, but the gas composition makes it unsuitable for use in traditional technologies (i.e., IC engine). Gas purification over nickel and/or iron catalysts is an attractive alternative. Cellulose-based carbon aerogels (CAGs) have shown suitable physical chemical properties for use as catalyst supports. In this work, nickel and iron catalysts are supported on CAG made from cellulose microfibers. Microfibers were impregnated with (NH4)2SO4 to increase the mass yield. Carbonization was evaluated at different heating rates, maximum temperatures, and dwell times to generate CAGs. Resulting chars were characterized by N2 adsorption, X-ray diffraction (XRD), and Raman spectroscopy. The CAG with better properties (specific surface, pore size, thermal resistance) was impregnated with the metal precursor salt via incipient wetness and treated with H2. Catalysts were characterized by transmission electron microscopy (TEM), XRD, N2 adsorption, and inductively coupled plasma optical emission spectrometry (ICP-OES). Ammonia adsorption was studied over CAG and catalysts to estimate the thermodynamic parameters. The impregnation with ((NH4)2SO4 improves thermal resistance of the char obtained from carbonization. The catalysts exhibit higher adsorption capacity than CAG (without metal), indicating chemical interaction between ammonia and metals. The metal-ammonia interaction is stronger on Fe than on Ni catalyst, which is consistent with reported theoretical calculations.

Torrefaction is a thermal pretreatment leading to the improvement of most of the fuel properties of biomass, namely energy density, HHV (higher heating value), grindability and hydrophobicity. The aim of this study is to identify the most feasible temperature to carry out torrefaction of Eucalyptus globulus and nitens , based on chemical evidences associated to the release of volatiles during thermal treatment of biomass. With that end: (i) Devolatilization kinetics, (ii) Effects of temperature and residence time and (iii) volatiles composition during torrefaction of both wood and bark were analyzed. In all cases DTG (derivative thermogravimetric curves) exhibited the typical shape of lignocellulosic materials, with three decomposition phases and two reaction zones. Values of activation energies for hemicellulose decomposition, were in agreement with those reported in the literature (121–170 kJ/mol). Carboxylic acids, water and phenolic compounds showed two peaks, which were associated to torrefaction (below 310 °C) and pyrolysis (310–410 °C) respectively. The most feasible temperatures for torrefaction were estimated as a function of these peaks, and it ranged between 295 °C and 310 °C for all samples. Main volatile species at the torrefaction peaks were distributed as Water > Acetic Acid > CO 2 > Others, while Levoglucosan formation was marginal, due to the catalytic effect of inorganics.

The use of wood as feedstock for the production of energy and chemicals is a strategy used by both developing and developed countries because it increases the sustainability of their energy infrastructure. Torrefaction of forest resources for co-firing and densification of biomass energy is among the most prominent alternatives. This study is focused on technical aspects of torrefaction technology by analyzing both energy and exergy changes through a comprehensive physico-chemical model (Aspen One v8.6 software) of a plant operating in mild (250 °C) and severe (280 °C) regimes. The main wood species in Chilean plantations, Eucalyptus globulus and Pinus radiata , were processed in a lab-scale apparatus to obtain the data for model calibration. We found that xylan composition in hemicelluloses has a considerable effect on global thermal efficiency, volatiles energy content, energy density, and exergy yield of torrefied product. The highest efficiency (96%) is obtained for Eucalyptus at 250 °C when moisture in the feedstock is ≤ 20%. Combustion of volatile products (torgas) for drying does not result in substantial technical benefits for the overall process; however, their post-combustion does lead to lower exergy losses.

Kinetic and isotopic data on Pt clusters and activation free energy barriers from density functional theory (DFT) on Pt(1 1 1) are used to assess the elementary steps involved in NO–H2 reactions. Pt clusters 1–10 nm in diameter gave similar turnover rates, indicating that these elementary steps are insensitive to surface-atom coordination. N–O cleavage occurs after sequential addition of two chemisorbed H-atoms (H * )t o NO * which are quasi-equilibrated with H2 and NO co-reactants. The first step is equilibrated and forms HNO * , while the second addition is irreversible and forms * HNOH * ; this latter step limits NO–H2 rates and forms OH * and NH * intermediates that undergo fast reactions to give H2O, N2O, NH3, and N2. These conclusions are consistent with (i) measured normal H/D kinetic isotope effects; (ii) rates proportional to H2 pressure, but reaching constant values at higher pressures; (iii) fast H2–D2 equilibration during catalysis; and (iv) DFT-derived activation barriers. These data and calculations, taken together, rule out N–O cleavage via NO * reactions with another NO * (forming O * and N2O) or with vicinal vacancies (forming N * and O * ), which have much higher barriers than H * -assisted routes. The cleavage of

γ-Al 2 O 3 support was modified with zirconia by the grafting method, using zirconium(IV) n-propoxide as precursor. Rh catalysts were prepared by wet impregnation of pure γ-Al 2 O 3 (Rh/A), Zr modified γ-Al 2 O 3 (Rh/100Z-A), and pure ZrO 2 (Rh/Z) supports. Rh/A presents a good activity in dry reforming of methane and exhibits a high amount of surface oxidized rhodium (92% of surface Rh atoms) after the reaction. Rh/Z is poorly active and 45% of Rh surface atoms remain reduced during the reaction. The catalytic activity significantly increased when using Rh/100Z-A. Tetragonal ZrO 2 crystallites are formed on the surface of modified alumina. It was obtained that, after Rh deposition, the grafted catalyst is composed by Rh/A and Rh/Z, as separated catalytic particles in good contact. To further understand the high activity of the grafted catalyst, mechanical mixtures of Rh/A and Rh/Z catalysts were synthesized. Compared with the single catalysts, an important synergistic effect in methane conversion and yields to CO and H 2 was observed when high amounts of Rh/A were mixed with Rh/Z catalyst, along with a promotion of rhodium oxidation in Rh/Z, which leads to a high surface fraction of RhO x (88%) in the mixture. The formation of mixed phases between the supports and the migration of Rh atoms from one phase to the other were discarded. It is suggested that a catalytic cooperation occurs due to the presence and mobility of oxygen species generated by the dissociation of CO 2 on Rh/A, which migrate to the Rh/Z catalyst promoting the oxidation of rhodium at its surface, and the catalytic activity. This cooperation mechanism is also expected to operate in the Rh/100Z-A catalyst, between the Rh/A and Rh/Z particles present in the surface. The importance of oxidized Rh for dry reforming of methane is evident from the high catalytic activity achieved when highly oxidized rhodium atoms are present together with the metallic Rh sites where methane activation occurs. © 2014 Elsevier B.V.

This work shows that loading Fe into the K/MgO catalyst for soot combustion can reduce K volatilization due to the formation of potassium-iron oxide compounds. K/MgO and K–Fe/MgO catalysts were prepared by the impregnation of potassium and iron precursors on MgO, and their activity for soot combustion was assessed by thermogravimetric analysis. Catalysts were characterized by atomic absorption spectroscopy, BET surface area, X-ray diffraction and X-ray photoelectron spectroscopy. Fe addition on K/MgO catalyst enhanced its catalytic activity, which is ascribed to a larger K retention into the catalysts either as potassium oxides or as K–Fe–O compounds. The non-stoichiometric potassium oxide (KXOY) is considered as the active phase of this kind of catalysts; it tends to migrate to the surface and to coat the Fe and K–Fe oxides compounds, increasing the surface concentration of active sites for soot combustion. Thus, molecular oxygen from the gas phase is activated over these potassium oxides to generate highly active oxygen species that finally oxidize the carbonaceous matter through an oxygen-transfer mechanism.

The effect of the preparation method and calcination temperature on the stability and activity of KNbO3 as catalysts for soot oxidation is reported. The solids were prepared by three different procedures: (i) by a citrate method using NbCl5 as niobium precursor; (ii) by a citrate method using NbF5 as niobium precursor; and (iii) by an autocombustion method using Nb2O5 as niobium precursor. The powders were calcined at 600 °C and 700 °C and characterized by N2 physisorption, oxygen desorption profiles, XRD and SEM. The catalytic activity is discussed in terms of both the Tm value, the temperature at which combustion of carbon black occurs at the maximum rate, and the apparent activation energy. It is found that KNbO3 calcined at 600 °C shows the higher catalytic activity. Also, a strong dependence on the preparation method is observed. The solids prepared by the citrate method show the higher catalytic activities, being the most active the one that use NbCl5 as niobium precursor. This highest catalytic activity is discussed in terms of nanosized perovskite structure and rough interfaces associated to the oxygen's vacancies. Moreover, lower apparent activation energies were obtained for the solids prepared by the citrate method. In addition, it is observed that no deactivation by metal loss after consecutive soot combustion cycles because of the stabilization of the alkaline metal inside the perovskite structure.

We studied the effect of the alkali metal type (Li, Na, and K) and the calcination temperature (500, 600 and 700 °C) in the activity for biodiesel production of catalysts prepared by impregnation method, with constant metal content of 10%w/w using ZrO2 as support. The results of the catalytic activity allowed to find an activity sequence regarding the alkali tested metals: Na > Li > K, with this sequence remaining constant independent of the calcination temperature. The high activity of the Na/ZrO2 system, and slightly lower activity of Li/ZrO2, can be explained by the fact that higher calcination temperatures promote the formation of alkali-based zirconate species, M2ZrO3 (M = Na or Li). The presence of these species is correlated with the higher activity of these catalysts, specifically with the Na and Li-based catalyst calcined at high temperatures (600-700 °C). These M2ZrO3 species show higher basicity respect to other alkali metal oxide species, as was demonstrated with CO2-TPD results. The higher activity corresponded to 10% Na supported on ZrO2 and calcined at 700 °C, which reached full conversion within just 30 minutes of reaction, which makes this system a promising heterogeneous replacement for the regular homogeneous systems.

Alumina supported catalytic systems K–Me (Me = Cu, Co and V) for the simultaneous removal of soot and NO x , were prepared by impregnation of a powder particle size alumina, using nitrate solutions of the corresponding metals. Physico-chemical characterization of the prepared catalysts was performed by means of XRD, SEM-EDX, ICP, N 2 -adsorption and TPR. The activity of the catalysts was assayed both, by thermogravimetric analysis and in a laboratory-scale fixed bed reactor. The effect of catalyst composition was examined. The catalysts showed high activity on the simultaneous removal of soot and nitrogen oxides at temperatures between 350 and 550 °C. Full selective conversion of NO x and total oxidation of the soot was attained; observing higher reaction rates in the case of the catalysts prepared using Cu as the active metal.

Catalytic filters for the simultaneous removal of soot and nitrogen oxides were prepared by means of coating cordierite monoliths with alumina-based suspensions containing Cu, Co or V and K as the catalytically active phase. Textural and chemical properties of the coated monoliths were determined by means of N2-physisorption, XRD, SEM-EDX and temperature programmed reduction. Activity of the catalytic filters in the simultaneous removal of soot and nitrogen oxides was tested in a fixed bed installation in absence and in presence of steam and CO2. Complete soot oxidation was measured for some of the assayed catalytic filters, with high selectivity to CO2 formation. NO reduction was preceded by a peak of NO2 formation, which corresponded to maximum soot oxidation rate, pointing to the formation of NO2 as a key step in the reaction mechanism for the simultaneous removal. Presence of steam and CO2 diminished catalytic activity and selectivity for soot oxidation.

Tar removal from gasification gases is a determinant step to guarantee the operational feasibility of gasification-to-chemicals/energy systems. This study aimed to develop novel carbon-supported catalysts for the elimination of tarry aromatics (toluene, naphthalene and benzene) from gasification gases. Effects of reaction temperature (700 < T < 900 °C) and catalyst nature (Fe0 and Ni0) on the activity were assessed by considering thermo-catalytic conversion and steam reforming, under a simulated gasification gas. The catalysts (Ni and Fe) and support (AC) were characterized by X-ray diffraction (XRD), N2 physisorption, thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and compositional analyses. Both catalysts and support, presented a mesoporous-like texture with a considerable high surface area (690 < SBET < 743 m2/g). Furthermore, dispersion of the metal nanoparticles (active phase) was uniform as confirmed by TEM images. Results from activity tests suggest that Ni/AC has higher effectivity for converting tars than Fe/AC, as confirmed by the low apparent activation energies (34 < Eapp < 98 kJ/mol) for naphthalene and benzene conversion between 700 and 900 °C. The conversion was 100% above 850 °C; nevertheless; below 750 °C, a sharp reduction in benzene conversion was observed, which was attributed to reversible carbon deposition.

The thermal degradation of metal complexes formed by chitosan with Cu(II), Ni(II), Co(II), and Hg(II), at different metal concentrations, was studied by thermogravi- metric analysis in a nitrogen atmosphere over the tempera- ture range 25-800 � C. The results indicate that thermal degradation of chitosan and chitosan-metal ion complexes could be of one or two-stage reaction. In the thermal degra- dation of chitosan with metal complexes, the temperature of initial weight loss and the temperature of maximum weight loss rate decrease. Fourier transform infrared spectroscopy was used to probe the interaction of chitosan with metal ions. The bands of ANAH, AC¼ ¼O, ACAOACA groups of chitosan are shifted or change their intensity in the presence of metal. These changes in the characteristic bands are taken as evidence of the influence of metal ions on the thermal stability of chitosan. Broido's method was employed to evaluate the activation energies as a function of the degree of degradation. The presence of metal ions provoked a decrease in the thermal stability of chitosan, which became more marked when the concentration of metal was increased. The dynamic study showed that the apparent activation energy values of the main stage of the thermal degradation of chitosan-metal complexes decrease as the strength of the polymer-metal interaction increases. V C 2009

Synthesis of nanocrystalline gadolinium doped ceria (Ce 0.9 Gd 0.1 O 1.95 ) was attempted by nitrate-fuel combustion technique involving different organic fuels namely urea, citric acid, glycine and poly ethylene glycol. As-combusted ceria precursors were calcined at 700 °C for 2 h for obtaining fully dense, nanocrystalline ceria powders. Cylindrical ceria discs were fabricated by uni-axial pressing and sintered intentionally at low temperature of 1200 °C for 2 h for assessing the sintering characteristics of the nano powders as well as the mechanical performance of the sintered ceria body. The study confirms that the nano powders could be sintered to 98% theoretical sintered density at 1200 °C with a grain size of 400 nm to 1 μm. The sintered samples exhibited the Vickers microhardness of 8.82 ± 0.2 GPa and the fracture toughness of 1.75 ± 0.3 MPa m 1/2 at a load 20 N for glycine and citric acid fuels derived ceria, respectively. A comparison between the fuels was made with respect to the sintering and mechanical properties of doped ceria. Citric acid and glycine fuels resulted in sintered ceria with high hardness where as the urea and polyethylene fuels derived nano ceria resulted in high fracture toughness.

Chile accounts for one of the most important forest areas in Latin America; nevertheless, both Chilean energy and chemical infrastructures heavily relies on imported fossil fuels. This study focuses on the analysis of several scenarios contributing to change this status quo by producing biomass-based Methanol and Synthetic Natural Gas (SNG). A comprehensive flowsheeting model, including such technologies, is developed and validated. The plants are assembled in a general superstructure to perform their energy integration and economic evaluation. For the studied scenarios, the energy efficiency of gasifier was 74%; Methanol and SNG yields were 0.59 kgMeOH/kgDry-biomass and 0.33 kgSNG/kgDry-biomass, respectively. The biomass-derived SNG has an average of 88% mol of methane and a Lower Heating Value of 41 MJ/kg. The unit energy cost ($/GJ) via SNG and Methanol were 18.41 $/GJ and 29.54 $/GJ for standalone operation, and both can be reduced by 12.7% and 9.5%, respectively, by using an integrated process scheme. Finally, near 25% of sensitivity on unit cost of products (energy based) was found when the feedstock price varied between 1 and 60 US$/tonne.

Carbon monoxide hydrogenation was studied over a γ-alumina-supported 1 wt% Rh catalyst by means of kinetic and in situ infrared measurements. The study was carried out at 200–300 °C, 0–22.5 kPa H2 and 1–7.5 kPa CO. The in situ FTIR scrutiny of the catalyst surface shows that adsorbed CO* species and vacancies dominate the Rh surface, while no effect of H2 and H2O pressures on surface coverage was observed under the conditions studied. The kinetic data are consistent with the mechanism in which the C–O bond dissociation is assisted by a double H-addition while H2 dissociative adsorption, CO molecular adsorption and the HCO* formation are quasi-equilibrated steps. A two-parameter Langmuir–Hinshelwood rate expression is deduced for CH4 formation, in agreement with the proposed sequence of elementary steps and kinetic data. The effect of temperature on parameters α and KCO leads to an apparent activation energy of 82.3 kJ mol−1, an average CO adsorption enthalpy of −14.1 kJ mol−1 and an entropy change of −17.9 J mol−1 K−1. In situ FTIR experiments show a full coverage of the Rh surface with adsorbed CO below 200 °C and this CO* coverage decreases as temperature increases in the range 200–300 °C; it is also observed that the heat of CO adsorption on the Rh surface decreases with CO* coverage.

Perovskite-type compounds (La1-xAgx)Mn 0.9Co0.1O3 (x = 0.0, 0.1, 0.2, 0.3), prepared by the amorphous citrate method, have been investigated as catalysts for soot combustion. The catalysts were characterized by nitrogen adsorption, XRD, SEM, TPR, O2-TPD, and XPS techniques. The silver addition to the perovskites produces a slight modification of the specific surface area and crystalline structure, while a new source of surface oxygen that comes from the interaction between O- and the low-coordinated metal site was detected. The results suggest that, during soot combustion, the activity of these materials is improved by an increase of the surface silver and superoxide ion content, responsible of the higher capacity for oxygen transfer from the catalyst to the carbons in the solids with higher Ag content., The authors thank CONICYT (Fondecyt 1130005) and Red Doctoral REDOC, MINEDUC Project UCO1202.

MNbO3 powders (M: Li, Na, K, Rb) are synthesized by a citrate method and calcined at 450, 550, 650, and 750 °C.

The lack of studies in the current literature about the assessment of alkaline niobates as catalysts for soot oxidation has motivated this research. In this study, the synthesis, characterization and assessment of alkaline metal niobates as catalysts for soot combustion are reported. The solids MNbO 3 (M = Li, Na, K, Rb) are synthesized by a citrate method, calcined at 450 °C, 550 °C, 650 °C, 750 °C, and characterized by AAS, N 2 adsorption, XRD, O 2 -TPD, FTIR and SEM. All the alkaline niobates show catalytic activity for soot combustion, and the activity depends basically on the nature of the alkaline metal and the calcination temperature. The highest catalytic activity, expressed as the temperature at which combustion of carbon black occurs at the maximum rate, is shown by KNbO 3 calcined at 650 °C. At this calcination temperature, the catalytic activity follows an order dependent on the atomic number, namely: KNbO 3 > NaNbO 3 > LiNbO 3 . The RbNbO 3 solid do not follow this trend presumably due to the perovskite structure was not reached. The highest catalytic activity shown by of KNbO 3 , despite the lower apparent activation energy of NaNbO 3 , stress the importance of the metal nature and suggests the hypothesis that K + ions are the active sites for soot combustion. It must be pointed out that alkaline niobate subjected to consecutive soot combustion cycles does not show deactivation by metal loss, due to the stabilization of the alkaline metal inside the perovskite structure.

Halide imidazolium-based ionic liquids 1-butyl-3-methylimidazolium bromide [bmim][Br] and 1-propylamine-3-methylimidazolium bromide [pamim][Br] were synthesised and tested experimentally as absorbents for biogas upgrading . The former solvent is a conventional off-the-shelf room temperature ionic liquid (RTIL), which is soluble in water and expected to have a high CO 2 solubility. The second solvent is a new type of task-specific ionic liquid (TSIL) and has a straight amine-alkyl substitute incorporated to enhance CO 2 solubility. Experimental evidence suggests that the majority of known imidazolium-based ionic liquids are good CO 2 absorbents; adding these to a designed solvent that combines a long amino-alkyl lineal group is expected to improve the performance of CO 2 absorption over other alternatives under discussion. CO 2 absorption experiments were conducted in an absorbing column packed with randomly placed Raschig rings. A biogas model consisting of CO 2 (43% v/v) diluted in N 2 was used to test CO 2 uptake with aqueous solutions of the above-mentioned ILs at 5%, 10% and 15% (w/w) concentrations. The gaseous and liquid streams were operated under concurrent flow with a gas–liquid volumetric ratio of 1:2. Additionally, absorption tests were conducted with aqueous solutions of monoethanolamine (MEA) mixed with the ILs under investigation to elucidate potential activations of these amino solutions. In this experiment, the ILs used for biogas upgrading do not present a higher absorption than amino solutions, and there were no significant synergy results from mixing them with MEA, which could have enhanced the CO 2 uptake.

Reports suggest KNO3 as the active phase for the catalytic combustion of soot, through a redox mechanism with KNO2. Previously, the high activity of KNO3 for coal gasification (mechanism similar to that of soot combustion) was attributed to decomposition into active KxOy (y

La 1 − x Ca x FeO 3 ( x = 0.1, 0.2, 0.3 and 0.4) perovskites, prepared by the citrate method and characterized by AAS, XRD, TPR-H 2 and TPD-O 2 , were assayed, and its catalytic activity evaluated for soot combustion, using carbon black as a model compound for soot. The catalytic activity was determined by non-isothermal thermogravimetric analysis. A significant enhancement of the catalytic activity was found by increasing the degree of La 3+ substitution by Ca 2+ in the perovskites, which coincided with an increase of the α-oxygen concentration and thus, a probable enrichment of the CB surface with these oxygenated species, at the start of the combustion.

Se evaluo el efecto de envasado en atmosfera modificada (MAP) con bajo contenido de CO (0.1% y 0.4%) y presencia de CO2 sobre el color rojo y la vida util de carne de vacuno. Se determinaron caracteristicas microbiologicas, fisicoquimicas, organolepticas-sensoriales y de color del musculo y se compararon los resultados con el MAP de 70%O2+30%CO2. La vida util de las muestras con O2 fue de 30 dias mientras que para las muestras en MAP la vida util fue de 40 a 45 dias y no dependio de la concentracion de CO. La intensidad del color rojo para las muestras con CO aumento en forma sostenida en el tiempo, mientras que las envasadas con O2 presentaron un maximo al dia 16. Para 0.4 % de CO la intensidad del color rojo se mantuvo durante nueve semanas y la presencia de CO no afecto al crecimiento microbiano. La rancidez fue mayor en la carne con O2.

Beef chops (longissimus dorsi) were pre-treated with 5% carbon monoxide (CO) − 95% N2 for 24 h, vacuum packed in thermo-contractile bags and stored at 0 ± 2°C. Shelf life, as determined by the viable aerobic bacterial load, was 11 weeks. Vacuum-packed chops with heat-contractile film produced a smaller drip loss, had a more intense red colour and higher colour stability under storage than chops with non-heat-contractile film. Chops pre-treated with CO were redder during all the storage period than controls without CO. The pre-treatment did not affect pH, water-holding capacity, drip loss or rancidity of the meat stored in vacuum. Copyright © 2008 John Wiley & Sons, Ltd.

This paper explores the possible effect of the potassium precursor on the activity of K/MgO catalysts for soot combustion and, in particular, which of previously described potassium roles would be more affected. The catalytic activity of the prepared K-catalysts was evaluated through thermogravimetric assays using catalyst-carbon black mixtures. Selected catalyst samples were characterized by XPS, AAS, BET surface area, carbothermic reduction, DRIFTS and XRD. The effect of physical contact was also assessed. The experimental results show that the addition of potassium from different precursors (KOH, KNO3) affects the basic nature of the catalyst surface and its interaction with active species, and this is reflected in the catalytic activity. With KNO3 as the precursor, a more active catalyst was obtained, a result that is attributed to: (i) higher concentration and dispersion of potassium, (ii) greater mobility and reactivity of the activated oxygen species, and (iii) lower stability of surface carbonates and OH groups, facilitating the formation of active species and favoring the mobility of surface activated oxygen. (c) 2006 Elsevier B.V. All rights reserved.

Although coal blends are increasingly utilized at power plants, ash slagging propensity is a non-additive property of the pure coals and hence difficult to predict. Coal ash tendency to slag is related to its bulk chemistry and ash fusion temperatures, and the present study aims to compare the results obtained from thermodynamic simulation with characterization of samples obtained as outcomes of plant-based coal-blend combustion trials at three utilities located in the Centre and North of Chile. Pulverized coal and plant residues samples from five families of binary blends tested in an experimental program were characterized for chemistry, mineralogy and maceral composition. The slagging was evaluated by determination of fusion curves using the MTDATA software and NPLOX3 database for the main coal ash oxides. The ranking obtained was approximately the same as obtained from carbon in the fly ashes and from plant residues observations. The thermodynamic modeling was a valid option to predict the fusibility during the combustion of blends. (C) 2003 Elsevier Ltd. All rights reserved.