Acrolein Formation Research Articles

Development of Two Stable Isotope Dilution Assays for the Quantitation of Acrolein in Heat-Processed Fats

Two stable isotope dilution assays were developed for the quantitation of acrolein in fats and oils using [(13)C(3)]-acrolein as the internal standard. First, a direct GC-MS headspace method, followed by an indirect GC-MS method using derivatization with pentafluorophenyl hydrazine, was established. Analysis of six different types of oils varying in their pattern of fatty acids showed significant differences in the amounts of acrolein formed after heating at various temperatures and for various times. For example, after 24 h at 140 °C, coconut oil contained 6.7 mg/kg, whereas linseed oil was highest with 242.3 mg/kg. A comparison of the results showed that the extent of acrolein formation seemed to be correlated with the amount of linolenic acid in the oils. Although the acrolein concentrations were lowered in all six oils after frying of potato crisps, linseed and rapeseed oil still contained the highest amounts of acrolein after frying. By applying both methods on different thermally treated fats and oils, nearly identical quantitative data were obtained.

Pyrolysis behavior of pectin under the conditions that simulate cigarette smoking

In this paper, the formation mechanism of pyrolysis gases released during the pyrolysis of pectin under the conditions that simulate cigarette smouldering was investigated by thermogravimetric analysis coupled to Fourier transform infrared spectrometer (TG–FTIR). Moreover, the combustion behavior of pyrolysis gases was studied by micro-scale combustion calorimetry (MCC). TG–FTIR results illustrated that the composition of the gaseous products was mainly composed of CO 2, H 2O, CO, methanol, methane and carbonyl compounds. MCC results demonstrated that the combustion of pectin was mainly determined by the prolysis gases formed in the temperature range of 200–300 °C. Flash pyrolysis experiment in combination with high performance liquid chromatography (FPy–HPLC) was used to study the pyrolytic formation of eight carbonyl compounds (i.e. formaldehyde, acetaldehyde, acetone, acrolein, propionaldehyde, crotonaldehyde, methyl ethyl ketone and butyraldehyde) during the pyrolysis of pectin under the pyrolysis conditions of cigarette puffing. Results demonstrated that pyrolysis temperature influenced the formation of acetaldehyde, acrolein, propionaldehyde and butyraldehyde greatly, while nitrogen flow affected the generation of formaldehyde, acetone, crotonaldehyde and methyl ethyl ketone deeply.

Tungsten-Vanadium mixed oxides for the oxidehydration of glycerol into acrylic acid

In this paper we report on the one-pot transformation of glycerol into acrylic acid, catalyzed by W/V mixed oxides, with hexagonal tungsten bronze (HTB) structure. The reaction requires two different catalyst functions, i.e., an acid one, which is given by W oxide, and an oxidizing one, given by the V ions incorporated within the WO3 lattice. W–O bronze is very active and moderately selective in acrolein formation, but yields only traces of acrylic acid. The incorporation of increasing amounts of V inside the hexagonal tungsten bronze structure, with the development of a monophasic compound, allows the consecutive oxidation of acrolein into acrylic acid. An optimal atomic ratio between W and V equal to V/(W + V) = 0.12–0.21 made it possible to obtain an acrylic acid yield of 25% (with selectivity to residual acrolein of 11%). However, during reaction under the oxygen-containing feed, the V4+ incorporated into the hexagonal bronze structure underwent a slow oxidation into V5+, which caused a progressive decline of selectivity to acrylic acid and a concomitant increase of COx formation; the hexagonal structure however was stable during lifetime experiments. On the other hand, in the absence of oxygen a very rapid deactivation of the catalyst occurred, with a decrease in selectivity to acrolein and increase in heavy by-products.

Determination of acrolein in french fries by solid-phase microextraction gas chromatography and mass spectrometry

The frying of foods in the home can be a cause of indoor pollution due to the formation of acrolein. The emission of acrolein formed during frying in soybean, corn, canola, sunflower and palm oils was studied. A GC/MS method has been developed to determine acrolein in French fries using SPME as the sampling technique after derivatization with 2,4-dinitrophenylhydrazine (DNPH). Optimum SPME conditions included desorption at 250 °C for 2 min after an adsorption time of 10 min at room temperature. The method presented good resolution, repeatability, detection and quantification limits, and linearity of response. French fries were prepared in five different oils with four frying steps. The results showed that changes in acrolein concentration occurred after frying potatoes in different types of oil and at different frying cycles. Potatoes fried in soybean oil contained the lowest concentration of acrolein. Shoestring potatoes contained a lower concentration of acrolein than potato chips and French fries, respectively, because of the higher surface/volume ratio.

Size-dependent selectivity and activity of silver nanoclusters in the partial oxidation of propylene to propylene oxide and acrolein: A joint experimental and theoretical study

Model silver nanocatalysts between 9 and 23 nm in size were prepared by size-selected cluster deposition from a free cluster beam on amorphous alumina films and their size-dependent catalytic performance studied in the partial oxidation of propylene under realistic reaction conditions. Smaller clusters preferentially produced acrolein, while the 23 nm particles were considerably more selective towards the formation of propylene oxide, at reaction rates far exceeding those previously reported for larger silver particles. The activity of clusters dropped significantly with increasing particle size. First-principle calculations, of the activation energies for oxygen adsorption and its dissociation, at variable surface coverage yielded surface energies which resulted in particle shapes resembling the experimentally observed shapes of partially oxidized silver clusters. The calculated activation barriers for propylene oxide and acrolein formation on various facets and on the edges of the nanoparticles provided detailed information about the energetics of the competing reaction pathways. The size- and corresponding morphology dependent theoretical activity and selectivity are in good accord with experimental observations.

Role of dispersion of vanadia on SBA-15 in the oxidative dehydrogenation of propane

A series of vanadia catalysts supported on the mesoporous silica SBA-15 are synthesized using an automated laboratory reactor. The catalysts contain from 0.6 up to 13.6V atoms/nm 2 and are structurally characterized by various techniques (BET, XRD, SEM, TEM, Raman, IR, UV/Vis). Samples containing up to 3.1V/nm 2 are structurally rather similar. They all contain a mixture of tetrahedral (VO x ) n species, both monomeric and oligomeric. The ratio of monomeric and oligomeric species depends on the vanadia loading. At the highest loading of 13.6V/nm 2, in addition to tetrahedral (VO x ) n , also substantial amounts of three-dimensional, bulk-like V 2O 5 are present in the catalyst. The structural similarity of the low-loaded catalysts is reflected in their alike catalytical activity during the oxidative dehydrogenation (ODH) of propane between 380 and 480 °C. Propene, CO, and CO 2 are formed as reaction products, while neither the formation of ethene nor acrolein or acrylic acid is observed in other than trace amounts. The activation energy for ODH of propane is ∼140 kJ/mol. The catalyst with the highest loading yields varying activation energies for different reaction conditions, which is probably related to rearrangements between bulk-like and dispersed, two-dimensional (VO x ) n . Rather than the monomer to oligomer ratio, the ratio of two-dimensional to three-dimensional vanadia seems to be crucial for the catalytic properties of silica supported vanadia in the ODH of propane.

Catalytic gasification of glycerol in supercritical water

The conversion of glycerol in supercritical water (SCW) was studied at 510–550 °C and a pressure of 350 bars using both a bed of inert and non-porous ZrO 2 particles (hydrothermal experiments), and a bed of a 1% Ru/ZrO 2 catalyst. Experiments were conducted with a glycerol concentration of 5 wt% in a continuous isothermal fixed-bed reactor at a residence time between 2 and 10 s. Hydrothermolysis of glycerol formed water-soluble products such as acetaldehyde, acetic acid, hydroxyacetone and acrolein, and gases like H 2, CO and CO 2. The catalyst enhanced the formation of acetic acid, inhibited the formation of acrolein, and promoted gasification of the glycerol decomposition products. Hydrogen and carbon oxides were the main gases produced in the catalytic experiments, with minor amounts of methane and ethylene. Complete glycerol conversion was achieved at a residence time of 8.5 s at 510 °C, and at around 5 s at 550 °C with the 1 wt% Ru/ZrO 2 catalyst. The catalyst was not active enough to achieve complete gasification since high yields of primary products like acetic acid and acetaldehyde were still present. Carbon balances were between 80 and 60% in the catalytic experiments, decreasing continuously as the residence time was increased. This was attributed partially to the formation of methanol and acetaldehyde, which were not recovered and analyzed efficiently in our set-up, but also to the formation of carbon deposits. Carbon deposition was not observed on the catalyst particles but on the surface of the inert zirconia particles, especially at high residence time. This was related to the higher concentration of acetic acid and other acidic species in the catalytic experiments, which may polymerize to form tar-like carbon precursors. Because of carbon deposition, hydrogen yields were significantly lower than expected; for instance at 550 °C the hydrogen yield potential was only 50% of the stoichiometric value.

The influence of additives and their concentration on the selectivity of catalysts based on heteropoly compounds in the reaction of propane oxidation

The catalytic properties and X-ray phase structure of molybdophosphoric heteropoly acid modified with Sb, W, and Nb ions have been studied in the reaction of propane oxidation. The additive of Nb ions increases the total activity of catalyst and its selectivity to acrolein and acrylic acid and decreases the selectivity to propylene. The concentration of Nb ions in samples is varied from 0.025 to 1 mol %. The concentration of Nb ions at a level of 0.025–0.1 mol % has the most profound effect on the reaction selectivity and the yield of mild oxidation products. The reaction selectivity depends on both the concentration of added niobium and the reaction conditions. The growth in the reaction temperature increases the conversion and selectivity to acrolein and reduces the selectivity to acrylic acid and propylene. The use of reaction mixture with higher propane concentrations decreases sharply the selectivity to acrolein. The obtained data can be explained by the possibility of the rearrangement of Nb ions between the cationic and anionic sublattices of heteropoly acids and by the change in the ratio between the acrolein and acrylic acid formation rates. The development and application of heteropoly compounds modified with niobium permits to increase the yield of target products in the partial propane oxidation.

Roles of bulk γ(L)-Bi2MoO6 and surface β-Bi2Mo2O9 in the selective catalytic oxidation of C3H6

(1 0 1) plane of β-Bi 2 Mo 2 O 9 formed on γ(L)-Bi 2 MoO 6 seems to be active and selective sites for partial oxidation of C 3 H 6 . The acrolein formation from C 3 H 6 takes place at β-phase sites and the incorporation of oxygen from gaseous O 2 at the anion vacancies of γ(L)-phase. Bi ( ), Mo ( ), O ( ). γ(L)-Bi 2 MoO 6 (L: low temperature phase) catalysts, whose surface compositions have a Mo/Bi ratio above = 0.5, exhibited high selectivity in the partial oxidation of C 3 H 6 , while catalysts with Mo/Bi surface ratios near or below = 0.5 exhibited low selectivity. γ(L)-phase catalysts which have Mo/Bi surface ratios greater than = 0.5, were demonstrated to form β-Bi 2 Mo 2 O 9 on their surface. An interaction between the β- and γ(L)-phases was observed in these catalysts’ UV–vis spectra at 430 nm. The new β-phase material seems to grow along b -axis of γ(L)-phase, i.e., perpendicular to MoO 2 –Bi 2 O 2 layers. Structure visualizations revealed that the α-Bi 2 Mo 3 O 12 , β-, and γ(H)-phases, which are selective catalysts, contain twin Mo tetrahedral structures, and that their Mo and Bi ions lie on the same plane. The pure γ(L)-phase does not contain this structure. A model for the very rapid transfer of oxygen between the γ(L)- and β-phases is discussed in relation to the kinetics of C 3 H 6 oxidation.

Influence of environmental parameters on production of the acrolein precursor 3-hydroxypropionaldehyde by Lactobacillus reuteri DSMZ 20016 and its accumulation by wine lactobacilli

Lactic acid bacteria belonging to the genus Lactobacillus are known to convert glycerol into 3-hydroxypropionaldehyde (3-HPA) during anaerobic glycerol fermentation. Wine quality can be gravely compromised by the accumulation of 3-HPA, due to its spontaneous conversion to acrolein under wine making conditions. Acrolein is not only a dangerous substance for the living cell, but has been implicated in the development of unpleasant bitterness in beverages. This study evaluates the effect of individual environmental parameters on 3-HPA production by Lactobacillus reuteri DSMZ 20016, which only proved possible under conditions that allow accumulation well below the threshold concentration affecting cell viability. 3-HPA production was optimal at pH 6 and in the presence of 300 mM glycerol. Production increased with an increase in cell concentration up to an OD 600 of 50, whereas higher cell concentrations inhibited accumulation. Data presented in this study suggest that 3-HPA plays a role in regulating its own production through quorum sensing. Glycerol dehydratase possessing bacterial strains isolated from South African red wine, L. pentosus and L. brevis, tested positive for 3-HPA accumulation. 3-HPA is normally intracellularly reduced to 1,3-propanediol. This is the first study demonstrating the ability of wine lactobacilli to accumulate 3-HPA in the fermentation media. Recommendations are made on preventing the formation of acrolein and its precursor 3-HPA in wine.

Emissions of volatile aldehydes from heated cooking oils

Emissions of volatile organic compounds, including aldehydes, formed during heating of cooking oils: coconut, safflower, canola, and extra virgin olive oils were studied at different temperatures: 180, 210, 240, and 240 °C after 6 h. Fumes were collected in Tedlar ® bags and later analysed by GC–MS. The emissions of volatiles were constant with time and increased with the oil temperature. When the temperature of the oil was above its smoke point, the emission of volatiles drastically increased, implying that oils with low smoke point, such as coconut, are not useful for deep-frying operations. Canola was the oil generating the lowest amount of potentially toxic volatile chemicals. Acrolein formation was found even at low temperatures, indicating that home cooking has to be considered as an indoor pollution problem.

Combined temperature-programmed reaction and in situ x-ray scattering studies of size-selected silver clusters under realistic reaction conditions in the epoxidation of propene

The catalytic activity and dynamical shape changes in size-selected nanoclusters at work are studied under realistic reaction conditions by using a combination of simultaneous temperature-programmed reaction with in situ grazing-incidence small angle x-ray scattering. This approach allows drawing a direct correlation between nanocatalyst size, composition, shape, and its function under realistic reaction conditions for the first time. The approach is illustrated in a chemical industry highly relevant selective partial oxidation of propene on a monodisperse silver nanocatalyst. The shape of the catalyst undergoes rapid change already at room temperature upon the exposure to the reactants, followed by a complex evolution of shape with increasing temperature. Acrolein formation is observed around 50 degrees C while the formation of the propylene oxide exhibits a sharp onset at 80 degrees C and is leveling off at 150 degrees C. At lower temperatures acrolein is produced preferentially to propylene oxide; at temperatures above 100 degrees C propylene oxide is favored.

Trapping Effects of Green and Black Tea Extracts on Peroxidation-Derived Carbonyl Substances of Seal Blubber Oil

Green and black tea extracts were employed to stabilize seal blubber oil at 60 degrees C for 140 h. On the basis of the headspace SPME-GC-MS analysis, with the addition of green/black tea extracts, the contents of acetaldehyde, acrolein, malondialdehyde, and propanal, four major lipid peroxidation products, were reduced. The inhibition rates of acrolein formation by green tea and black tea extracts were 98.40 and 96.41% respectively, and were 99.17 and 98.16% for malondialdehyde, respectively, much higher than the inhibition of the formation of acetaldehyde and propanal. Because malondialdehyde and acrolein are reactive carbonyl species (RCS) and recent studies have suggested that phenolics can directly trap RCS, this study also investigated whether green tea polyphenols can trap acrolein or not. Acrolein was reduced by 90.30% in 3 h of incubation with (-)-epigallocatechin-3-gallate (EGCG). Subsequent LC-MS analysis revealed the formation of new adducts of equal molars of acrolein and EGCG. The reaction site for acrolein was elucidated to be the A ring of EGCG as evidenced by LC-MS/MS analysis and by testing of the acrolein-trapping capacities of the analogous individual A, B, and C rings of EGCG. Thus, EGCG's direct trapping of RCS may also contribute to the significant reduction of acrolein and other aldehydes in the peroxidation of seal blubber oil.

Reaction pathways for selective oxidation of propane to acrolein over Ce-Ag-Mo-P-O catalysts

Abstract The reaction pathways for selective oxidation of propane to acrolein on Ce 0.1 Ag 0.3 Mo 0.5 P 0.3 O x catalyst were investigated by three methods, (i) steady-state reaction test of the individual oxidation of propane and the probe molecule of possible reaction intermediates, (ii) temperature-programmed surface reaction (TPSR) study of propane oxidation in presence of gas phase O 2 or not, and (iii) in situ Raman spectroscopy investigation of propane oxidation and propylene oxidation on the catalyst. Based on the obtained results, three possible reaction pathways for selective oxidation of propane to acrolein on the catalysts are proposed. The major reaction pathway is that propylene (π-allyl species) is produced from the activation of the methylene C–H bond of propane and further oxidizes to acrolein through σ-allyl species. However, the presence of gas phase O 2 favors the formation of acrolein in propane oxidation on the catalyst.

Sustainable production of acrolein: Preparation and characterization of zirconia-supported 12-tungstophosphoric acid catalyst for gas-phase dehydration of glycerol

ZrO2-supported H3PW12O40 (HPW) catalysts were used to catalyze the dehydration of glycerol to produce acrolein at 315 °C under a high space velocity (GHSVGlycerol = 400 h−1). The catalysts were prepared by varying the loading of HPW on two ZrO(OH)2 supports of different preparations, followed by calcination in flowing nitrogen. The use of alcogel-derived ZrO(OH)2-AN for the support, compared with conventional hydrogel-derived ZrO(OH)2-CP, produced HPW/ZrO2 catalysts that showed higher surface areas and better catalytic performance for the selective formation of acrolein from glycerol dehydration. Independent of the preparation history of ZrO2, the Keggin-anion density (HPW nm−2) at the catalyst surface appeared as a key to the selectivity and mass-specific activity of HPW for acrolein production. Acrolein selectivity as high as 70 mol% was obtained over the catalysts having the intermediate densities (0.18–0.65 HPW nm−2), at which most of the Keggin HPW remained intact after calcination up to 650 °C. At higher densities, destruction of the Keggin HPW would occur during the calcination, which led to lower acrolein selectivity. High selectivity (71 mol%) and high yield (≥54%) for acrolein production were found sustainable over the best performing HPW/ZrO2-AN catalyst for reaction times up to 10 h.

“Catalysis for Renewables: From Feedstock to Energy Production”

Preface. List of Contributors. 1 Renewable Catalytic Technologies - a Perspective (Rutger A. van Santen). 1.1 Introduction. 1.2 Economic and Societal Background. 1.3 Technology Options. 1.4 Process Options for Biomass Conversion. 1.5 Conclusions. References. 2 Lignocellulose Conversion: An Introduction to Chemistry, Process and Economics (Jean-Paul Lange). 2.1 Overview. 2.2 Introduction. 2.3 Chemistry and Processes. 2.4 Economics. 2.5 Summary and Conclusions. References. 3 Process Options for the Catalytic Conversion of Renewables into Bioproducts (Pierre Gallezot). 3.1 Overview. 3.2 Introduction. 3.3 The Biore.nery Concept. 3.4 Strategies for Biomass Conversion into Bioproducts. 3.5 Concluding Remarks. References. 4 Industrial Development and Application of Biobased Oleochemicals (Karlheinz Hill). 4.1 Overview. 4.2 Raw Material Situation. 4.3 Ecological Compatibility. 4.4 Examples of Products. 4.5 Perspectives. References. 5 Fine Chemicals from Renewables (Herman van Bekkum and Leendert Maat). 5.1 Introduction. 5.2 Vanillin. 5.3 Monoterpenes. 5.4 Alkaloids. 5.5 Steroids. 5.6 Enantioselective Catalysis. 5.7 Artimisinine. 5.8 Tamiflu. 5.9 Final Remarks. References. 6 Options for Catalysis in the Thermochemical Conversion of Biomass into Fuels (Sascha R. A. Kersten, Wim P. M. van Swaaij, Leon Le.erts, and Kulathuiyer Seshan). 6.1 Introduction. 6.2 Biomass as Feedstock for Fuels. 6.3 Composition of Biomass. 6.4 Biore.nery. 6.5 Biomass Pretreatment. 6.6 Thermochemical Conversion of Lignocelluloses. 6.7 Biomass Gasi.cation. 6.8 Liquefaction of Biomass. 6.9 Upgrading Pyrolysis Oil to Fuels. 6.10 Hydrolysis. 6.11 Underlying Approach for Catalyst Design. 6.12 Summary. References. 7 Thermal Biomass Conversion (Simone Albertazzi, Francesco Basile, Giuseppe Fornasari, Ferruccio Trifiro, and Angelo Vaccari). 7.1 Introduction. 7.2 Biomass Resources and Biomass Pre-treatment. 7.3 Biomass Combustion. 7.4 Biomass Gasi.cation. 7.5 Pyrolysis. 7.6 Fuels via Thermal Biomass Conversion. 7.7 Conclusions. References. 8 Thermal Biomass Conversion and NOx Emissions in Grate Furnaces (Rob J.M. Bastiaans, Hans A.J.A. van Kuijk, Bogdan A. Albrecht, Jeroen A. van Oijen and L. Philip H. de Goey). 8.1 Introduction. 8.2 Tunable Diode Laser Measurements of Biomass Kinetics. 8.3 Propagation of Thermal Conversion Fronts. 8.4 Gas-phase CFD Modeling of Grate Furnaces. 8.5 Conclusions. References. 9 Bioethanol: Production and Pathways for Upgrading and Valorization (Stephane Pariente, Nathalie Tanchoux, Francois Fajula, Gabriele Centi, and Siglinda Perathoner). 9.1 Introduction. 9.2 Production, a Short Overview. 9.3 Uses as Biofuel. 9.4 Bioethanol Upgrading and Valorization. 9.5 Conclusions. References. 10 Conversion of Glycerol into Traffic Fuels (Tiia S. Viinikainen, Reetta S. Karinen, and A. Outi I. Krause). 10.1 Introduction. 10.2 Glycerol. 10.3 Etheri.cation of Glycerol with Isobutene. 10.4 Improvements to Biodiesel Process. 10.5 Reforming of Glycerol. 10.6 Future Aspects. References. 11 Catalytic Transformation of Glycerol (Bert Sels, Els D'Hondt, and Pierre Jacobs). 11.1 Introduction and Scope. 11.2 Catalytic Dehydration of Glycerol and Acrolein Formation. 11.3 Etheri.cation of Glycerol via Catalytic Dehydration. 11.4 Catalytic Oxidation of Glycerol. 11.5 Catalytic Hydrogenolysis of Glycerol. 11.6 Glycerol Reforming and Production. 11.7 Miscellaneous Oxidation Reactions. 11.8 Conclusions. References. 12 Catalytic Processes for the Selective Epoxidation of Fatty Acids: More Environmentally Benign Routes (Matteo Guidotti, Rinaldo Psaro, Maila Sgobba, and Nicoletta Ravasio). 12.1 Introduction. 12.2 Non-catalytic Epoxidation Systems. 12.3 Homogeneous Catalytic Systems. 12.4 Chemoenzymatic Epoxidation Systems. 12.5 Heterogeneous Catalytic Systems. 12.6 Epoxidation of FAMEs Over Titanium-based Catalysts: The Skills in Milan. 12.7 Conclusions. References. 13 Integration of Biocatalysis with Chemocatalysis: Cascade Catalysis and Multi-step Conversions in Concert (Tom Kieboom). 13.1 Overview. 13.2 Introduction. 13.3 Types of Cascades. 13.4 Technologies for Cascades. 13.5 Conclusions. References. 14 Production and Fuel Cells as the Bridging Technologies Towards a Sustainable Energy System (Frank A. de Bruijn, Bert Rietveld, and Ruud W. van den Brink). 14.1 Introduction. 14.2 Production from Natural Gas. 14.3 Novel Processes for Production with CO2 Capture. 14.4 Conclusions and Catalytic Challenges. References. 15 Pathways to and Green (Gert J. Kramer, Joep P. P. Huijsmans, and Dave M. Austgen). 15.1 Introduction. 15.2 Energy Resource Availability. 15.3 Modes of Production and Distribution. 15.4 The Cost of Fuel. 15.5 Clean Hydrogen and the Scope for CO2 Reduction. 15.6 Coal and Biomass. 15.7 Conclusions. References. 16 Solar Photocatalysis for Production and CO2 Conversion (Claudio Minero and Valter Maurino). 16.1 Introduction. 16.2 The Photocatalytic Process. 16.3 Photoelectrochemical Cells. 16.4 New Materials. 16.5 Conclusions. References. Conclusions, Perspectives and Roadmap (Gabriele Centi and Rutger A. van Santen). 1 Introduction. 2 Driver for a Biomass Economy. 3 Main Issues and Perspectives on Bioenergy and Biofuels in Relation to Catalysis. 3.1 Biofuels. 3.2 Biore.neries. 3.3 Use of By-products Deriving from Biomass Transformation. 3.4 Biomass as Feedstock for Chemical Production. 3.5 Use of Solar Energy. 4 Conclusions. References. Index.

The mechanism of propene oxidation to acrolein on iron antimony oxide

Density functional theory is used to investigate the microscopic mechanisms of oxidation of propene (CH 3 CH CH 2) to acrolein (CH 2 CH CHO) over iron antimony oxide (FeSbO 4). Two routes for acrolein formation are investigated. The first starts from a chemisorbed state, in which propene binds with the surface via the π orbitals; acrolein formation can be triggered first by the abstraction of an allylic H atom towards the active bridging O atom, followed by the abstraction of a second H atom toward either an O or an Sb atom and the subsequent desorption of the acrolein thereby formed. The second route starts from a direct dissociation of the propene molecule without the need to proceed through a chemisorbed precursor, which, however, is kinetically hindered. The first route is compared with the mechanisms proposed from experiment. We also discuss the mechanisms of propane oxidation to acrolein, in which propene oxidation is an important step.

Dehydration of glycerol in gas phase using heteropolyacid catalysts as active compounds

Different silica-, alumina-, and aluminosilicate-supported heteropolyacid catalysts were prepared using phosphomolybdic acid H 3PMo 12O 40⋅ xH 2O, phosphotungstic acid H 3PW 12O 40⋅ xH 2O, silicotungstic acid H 4SiW 12O 40⋅ xH 2O, and ammonium phosphomolybdate (NH 4) 3PMo 12O 40⋅ xH 2O as precursor compounds. The as-synthesised solids were characterised by nitrogen adsorption, XRD, TG/DTA, Raman spectroscopy, and TPD of ammonia. Silica-supported heteropolyacids are rather well crystallised, whereas alumina-supported samples are X-ray amorphous. Investigations using Raman spectroscopy of calcined samples and TG/DTA revealed that molybdenum-containing heteropolyacids tend to decompose partly close to 400 °C into molybdates and MoO 3 whereas tungsten-containing samples are stable. This makes in particular tungsten-based materials interesting acid catalysts for the dehydration of glycerol in the gas phase. In particular, the influence of selected support materials, catalyst loading, and temperature on acrolein formation was studied at standardised reaction conditions (10% by weight of glycerol in water, 225–300 °C, modified contact time 0.15 kg h mol −1). Surprisingly, alumina is found to be superior to silica as support material with regard to catalyst activity and selectivity. Nevertheless, tungsten based heteropolyacids showed outstanding performance and stability. Acrolein was always the predominant product with maximum selectivity of 75% at complete conversion over silicotungstic acid supported over alumina and aluminosilicate.

Selective oxidation of propylene over model supported V 2O 5 catalysts: Influence of surface vanadia coverage and oxide support

The selective oxidation of propylene to acrolein was investigated over well-defined supported vanadium oxide catalysts as a function of the oxide support (Al 2O 3, SiO 2, Nb 2O 5, TiO 2 and ZrO 2) and surface vanadia coverage in the sub-monolayer region (<8 V atoms/nm 2). The supported vanadia catalysts were synthesized by incipient wetness impregnation of vanadium isopropoxide/isopropanol solutions and subsequently dried and calcined at elevated temperatures to form the surface vanadia species. The molecular structures and oxidation states of the supported vanadia catalysts were examined with in situ UV–vis and Raman spectroscopy in different environments (oxidizing, reducing and during propylene oxidation reaction). The supported vanadia phase is found to be present as surface VO 4 species in the sub-monolayer region and becomes partially reduced during the propylene oxidation reaction environment. The propylene oxidation to acrolein TOF increases with surface vanadia coverage because two surface VO 4 sites are involved in the rate-determining-step for acrolein formation. At monolayer surface vanadia coverage, the acrolein TOF varies by a factor of ∼10 2 as a function of the specific oxide support: V 2O 5/ZrO 2 ∼ V 2O 5/TiO 2 > V 2O 5/Nb 2O 5 > V 2O 5/Al 2O 3 > V 2O 5/SiO 2. This reactivity trend inversely varies with the electronegativity of the oxide support cation, which controls the electron density on the bridging V O support bond and the availability of the bridging oxygen atom for redox reactions. This suggests that bridging V O support bond is the catalytic active site for the selective oxidation of propylene to acrolein.

Propene partial oxidation over Au–Ag Alloy and Ag catalysts using electrochemical oxygen

The partial oxidation of propene over Au–Ag alloy (14 mol%) and monometallic Ag supported over a dense Solid Electrolyte Membrane Reactor (SEMR) was studied and compared under electro-catalytic reaction conditions. Two partial oxidation products, namely acrolein and 1,5-hexadiene, in addition to carbon dioxide were detected. It was observed that the Au–Ag alloy was more selective towards acrolein formation, possibly promoted by oxygen adsorbed molecularly on exposed Ag surfaces whereas 1,5-hexadiene formation is promoted by oxygen species adsorbed atomically on silver surfaces. Taking into account that gold has no ability to dissociate molecular oxygen, and that acrolein and 1,5-hexadiene were not observed under open circuit conditions it is suggested that oxide ions are reduced at the triple phase boundary to form an active oxygen species which spills onto the catalyst surface to react with adsorbed propene. Differences in selectivity can only be explained by a difference in oxygen type and surface population of the catalysts based, for example, on a sufficiently large change in the work function of the catalysts.