The influence of oxygenated fuels on emissions of aldehydes and ketones from a two-stroke spark ignition engine

A spark-ignited two-stroke chainsaw engine was used to study the influence of pure oxygenated fuels on exhaust emissions of carbonyls (aldehydes and ketones) and regulated emissions, i.e. hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NO_x). Three fuels—methanol, methyl tert-butylether (MTBE), and ethyl tert-butylether (ETBE)—were used in the tests, each at three air/fuel ratios (λ) and the generated emissions were compared to those observed in previous tests with ethanol, aliphatic gasoline, and regular gasoline. Use of all four oxygenated fuels (ETBE, ethanol, methanol and MTBE) resulted in substantially higher total carbonyl emissions (11, 11, 8.9 and 7.8 g/kWh, respectively) than use of both aliphatic and regular gasoline (2.1 and 2.6 g/kWh, respectively). Further, up to 44-fold higher levels of specific carbonyls were generated from the oxygenated fuels than from regular gasoline: significant amounts of formaldehyde were produced from all of the oxygenated fuels, but they were especially high from methanol and MTBE; acetaldehyde was formed in high amounts from ethanol and ETBE; while acetone and methacrolein were formed from both MTBE and ETBE. In addition, increases in λ increased exhaust emissions of formaldehyde, acetaldehyde, acetone, and methacrolein in cases where these were the main carbonyls formed. Increasing λ also variously increased, reduced or had no significant effect on emissions of other measured carbonyls. Lower amounts of CO and NO_x emissions were formed from all oxygenates (especially methanol) than from regular gasoline.     

Solvent-free synthesis of C9 and C10 branched alkanes with furfural and 3-pentanone from lignocellulose

Jet fuel range branched alkanes were first synthesized under solvent-free conditions by the aldol condensation of furfural and 3-pentanone from lignocellulose followed by the one-step hydrodeoxygenation (HDO). Among the investigated solid base catalysts, CaO and KF/Al₂O₃ demonstrated the highest activity for the aldol condensation reaction of furfural and 3-pentanone. The aldol condensation product of furfural and 3-pentanone (liquid at room temperature) was directly hydrodeoxygenated to 4-methyl-nonane and 4-methyl-octane. These alkanes have low freezing points (174.1 K and 159.8 K) and can be blended into jet fuel without hydroisomerization. Among the investigated HDO catalysts, the Ni-Cu/SiO₂ exhibited the best performance.     

Reaction between methanol and acetic acid catalyzed by SiO2‐supported V‐P‐O catalyst in oxygen atmosphere

SiO₂‐supported V‐P‐O catalysts prepared by the incipient‐wetness impregnation method beginning with ammonium metavanadate and phosphoric acid were used in the catalytic reaction between methanol and acetic acid in an oxygen atmosphere. The SiO₂‐supported V‐P‐O catalysts were composed of VOPO₄ and (VO)₂P₂O₇ phases. Both the acidic and alkaline sites were co‐present in the catalysts. The vanadium species catalyzed the oxidation of methanol to formaldehyde. The V‐P‐O(20–30 wt%)/SiO₂ catalysts with a P/V mole ratio of 2:1 exhibited higher catalytic activity for the formation of acrylic acid and methyl acrylate with a total selectivity of ～28 % at 380 °C. The acid sites of the catalysts also catalyzed the formation of methyl acetate with a selectivity of ～65 %. Methanol can be an alternative to formaldehyde for the synthesis of both acrylic acid and methyl acrylate through the aldol condensation reaction.     

Polynitroalcohols obtained through nitro aldol reaction between nitro oligomers and C1‐C2‐aldehydes

Polynitroalcohols (PNA) were obtained by A_N‐reaction of nitro oligomers from ground waste rubbers (NO‐GWR) with C₁‐C₂‐aldehydes in presence of organic bases triethanolamine, triethylamine and cyclopropylamine. The A_N‐reaction was studied at temperatures from 30 to 50°C, time 4 h, and NO‐GWR : aldehyde = 1 : 0.5/2.0 mass ratios in the solution. PNA were characterized by elemental analyses, such as ¹H NMR spectra, IR spectroscopy—baseline method with internal standard and thermal analyses. The quantitative functional composition of PNA (%NO₂, %C?O, and %OH groups) was proved to be similar to the composition of PNA obtained from model butadiene–styrene nitro oligomer (BSNO). It was concluded that NO‐GWR could replace NO based on elastomers in nitro aldol reaction with formaldehyde and acetaldehyde. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3241–3250, 2006     

Ethanol oxidation on a high temperature PBI-based DEFC using Pt/C, PtRu/C and Pt3Sn/C as catalysts

A high temperature ethanol-fed polymer electrolyte membrane fuel cell has been implemented by using H₃PO₄-doped m-polybenzimidazole as polymeric electrolyte. Commercial Pt/C, PtRu/C and Pt₃Sn/C catalysts are used in the anode. The performance was assessed in terms of polarization curves at different temperatures, feeding the cell with a high concentration ethanol solution (water/ethanol mass ratio of 2). The product distribution was measured with the support of a gas chromatograph. The use of bimetallic catalysts increased the current density. PtRu/C showed the best performance up to 175 °C, but it is outperformed by Pt₃Sn/C at 200 °C. In terms of oxidation products, higher temperatures and current densities favour the oxidation of ethanol. However, Pt₃Sn/C promoted the generation of more oxidized products compared to PtRu/C (in which most of the ethanol is oxidized to acetaldehyde), especially at high temperature. This accounts for the large current density. In terms of complete oxidation of ethanol to CO₂, Pt/C was by far the most efficient catalyst for C–C scission, achieving percentages of 56 % of CO₂, although operating above 175 °C dramatically boosted an undesirable methanation process that slashed the efficiency. The combination of fuel cell results and product distribution helped to suggest the different oxidation routes on the surface of the different catalysts.     

Aqueous-Phase Processing of Bio-oil Model Compounds Over Pt–Re Supported on Carbon

The aqueous-phase processing (APP) of biomass-derived bio-oil model compounds such as ethanol, acetaldehyde, formic acid and acetic acid over Pt?CRe/C was examined. For the APP of ethanol at 250?°C, the product distribution was determined and quantified. H₂, CO₂, CH₄, C₂H₆, acetaldehyde, ethyl ether, ethyl acetate, acetic acid were found to be primary products and C₃H₈, methanol, butanol and acetal were found to be minor products. By also exploring the product distributions of acetaldehyde, acetic acid and formic acid under APP conditions with the Pt?CRe/C, the reaction network associated with the APP conversion of ethanol was determined. Using this reaction network, flux analysis was performed on the ethanol reaction system to determine the reaction pathway and relative rates (v₁?Cv₈) for each step. From this analysis, it was found that the dehydrogenation of the ethanol was the most active reaction in the reaction system.     

Ethanol electrooxidation on novel carbon supported Pt/SnOx/C catalysts with varied Pt:Sn ratio

Novel carbon supported Pt/SnO_x/C catalysts with Pt:Sn atomic ratios of 5:5, 6:4, 7:3 and 8:2 were prepared by a modified polyol method and characterized with respect to their structural properties (X-ray diffraction (XRD) and transmission electron microscopy (TEM)), chemical composition (XPS), their electrochemical properties (base voltammetry, CO_ad stripping) and their electrocatalytic activity and selectivity for ethanol oxidation (ethanol oxidation reaction (EOR)). The data show that the Pt/SnO_x/C catalysts are composed of Pt and tin oxide nanoparticles with an average Pt particle diameter of about 2 nm. The steady-state activity of the Pt/SnO_x/C catalysts towards the EOR decreases with tin content at room temperature, but increases at 80 °C. On all Pt/SnO_x/C catalysts, acetic acid and acetaldehyde represent dominant products, CO₂ formation contributes 1-3% for both potentiostatic and potentiodynamic reaction conditions. With increasing potential, the acetaldehyde yield decreases and the acetic acid yield increases. The apparent activation energies of the EOR increase with tin content (19-29 kJ mol⁻¹), but are lower than on Pt/C (32 kJ mol⁻¹). The somewhat better performance of the Pt/SnO_x/C catalysts compared to alloyed PtSn_x/C catalysts is attributed to the presence of both sufficiently large Pt ensembles for ethanol dehydrogenation and C-C bond splitting and of tin oxide for OH generation. Fuel cell measurements performed for comparison largely confirm the results obtained in model studies.     

Aldol condensation of acetaldehyde to form high molecular weight compounds on TiO2

Temperature-programmed desorption, hydrogenation, and oxidation are used to show that acetaldehyde undergoes continued aldol condensation beyond crotonaldehyde formation on Degussa P-25 titania to form hexan-2,4-diene-al and higher molecular weight compounds containing conjugated C=C bonds. Aromatic compounds also form, and at higher temperatures coke forms. Degussa P-25 TiO₂ has more sites that catalyze chain propagation reactions beyond formation of C₄ species than do pure anatase or rutile surfaces. These reactions may be responsible for deactivation observed during photocatalytic oxidation of acetaldehyde at elevated temperatures. This revised version was published online in August 2006 with corrections to the Cover Date.     

Selectivity and mechanism shifts in the reactions of acetaldehyde on oxidized and reduced TiO2(001) surfaces

Depending on the oxidation state of the TiO₂(001) surface, acetaldehyde can form C₄ products by either aldol condensation or reductive coupling routes. Aldol condensation generates crotonaldehyde and crotyl alcohol, and is favored on oxidized, stoichiometric surfaces. Reductive coupling produces butene, and occurs only on reduced surfaces. The switch-over in selectivity with increasing extents of surface oxidation provides important insights into the active site requirements for each of these reactions.     

Oxidative Reforming of Bio-Ethanol Over CuNiZnAl Mixed Oxide Catalysts for Hydrogen Production

Hydrogen (H₂) is expected to become an important fuel for the future to be used as an energy carrier in automobiles and electric power plants. A promising route for H₂ production involves catalytic reforming of a suitable primary fuel such as methanol or ethanol. Since ethanol is a renewable raw material and can be cheaply produced by the fermentation of biomass, the ethanol reforming for H₂ production is beneficial to the environment. In the present study, the steam reforming of ethanol in the presence of added O₂, which in the present study is referred to as oxidative steam reforming of ethanol (OSRE), was performed for the first time over a series of CuNiZnAl mixed oxide catalysts derived from layered double hydroxide (LDH) precursors. The effects of Cu/Ni ratio, temperature, O₂/ethanol ratio, contact time, CO co-feed and substitution of Cu/Ni by Co were investigated systematically in order to understand the influence of these parameters on the catalytic performance. An ethanol conversion close to 100% was noticed at 300 °C over all the catalysts. The Cu-rich catalysts favor the dehydrogenation of ethanol to acetaldehyde. The addition of Ni was found to favor the C–C bond rupture, producing CO, CO₂ and CH₄. Depending upon the reaction condition, a H₂ yield between 2.5 and 3.5 moles per mole of ethanol converted was obtained. A CoNi-based catalyst exhibited better catalytic performance with lower selectivity of undesirable byproducts, namely CH₃CHO, CH₄ and CO.     

The conversion of polysaccharides to hydrogen gas. Part II: The catalytic decomposition of formaldehyde in the aqueous phase

The aqueous phase decomposition of formaldehyde, to hydrogen gas, catalysed by platinum—copper chromite, has been carried out in the temperature range 20–60°C, at a solution pH of 12. The production of hydrogen was favoured by intermediate temperatures (40–50°C) and an activation energy of 22.2 kJ mol^?1 (5.3 kcal mol^?1) was recorded. The rate of reaction was first order with respect to OH^? ion concentration at low alkali concentrations and was first order with respect to HCHO concentration at all concentrations. At high alkali concentrations the reaction should become zero order with respect to OH^? ion concentration, but initial rates actually decrease under these conditions having passed through a maximum. The rate of reaction was directly proportional to catalyst weight at low catalyst loading, but the relationship became non-linear at high catalyst loadings. Conversions of formaldehyde to hydrogen gas were substantially less than theoretical. The decomposition reaction has to compete with a number of side reactions such as polymerization of formaldehyde at low temperatures (<40°C) and at higher temperatures with the Cannizzano reaction, aldol condensation, and possibly formaldehyde hydrogenation to methanol. In addition hydrogen loss may occur due to copper chromite reduction. A reaction mechanism is proposed involving a surface formate intermediate.     

Selective solvation of silver(I) bromate in methanol—acetonitrile and ethanol—acetonitrile mixtures at 30°C

The selective solvation of silver(I) bromate in the binary solvent mixtures of methanol + acetonitrile and ethanol + acetonitrile has been studied at 30°C by solubility and emf measurements. The solubility of the salt increases with the addition of acetonitrile up to a mole fraction (X_AN) of 0.6 and 0.7 in the case of methanol + acetonitrile and ethanol + acetonitrile respectively and then decreases with further addition of the same. The transfer free energy of the silver ion (molal scale) decreases continuously with the addition of acetonitrile in both the mixtures. The transfer free energies of bromate ion (molal scale) are found to be quite small up to X_AN ≈ 0.7 in both methanol + acetonitrile and ethanol + acetonitrile mixtures and then increase. The solvent transport number Δ, of acetonitrile is positive with a maximum at X_AN = 0.55 (Δ = 2.7) and at X_AN = 0.45 (Δ = 2.2) for methanol + acetonitrile and ethanol + acetonitrile systems respectively. These results have been interpreted as arising due to a heteroselective solvation of the salt with the silver ion being preferentially solvated by acetonitrile and the bromate ion by the amphiprotic component which is marked especially at higher compositions.     

Electrochemical effect of gold nanoparticles on Pt/α-Fe2O3/C for use in methanol oxidation in alkaline solution

A catalyst containing gold nanoparticles with Pt/α-Fe₂O₃/C was prepared by a co-precipitation method and its catalytic activity for the oxidation of methanol, formaldehyde, and formic acid in alkaline solutions was evaluated by an electrochemical method and high-performance liquid chromatography (HPLC). The addition of gold nanoparticles improved catalytic activity only for the oxidation of methanol and formaldehyde, and not for the oxidation of formic acid. HPLC analysis was performed for methanol oxidation to detect the oxidative products. In HPLC analysis, only formate anion could be detected in the electrolyte solution and the ratio of formate anion obtained to the total passed charge in Pt/nano-Au/α-Fe₂O₃/C was less than that in Pt/C, indicating that formic acid is not the final product of methanol oxidation. These results show that gold nanoparticles promoted methanol oxidation up to CO₂.     

Evidence for the Formation of an Enamine Species during Aldol and Michael‐type Addition Reactions Promiscuously Catalyzed by 4‐Oxalocrotonate Tautomerase

The enzyme 4‐oxalocrotonate tautomerase (4‐OT), which has a catalytic N‐terminal proline residue (Pro1), can promiscuously catalyze various carbon–carbon bond‐forming reactions, including aldol condensation of acetaldehyde with benzaldehyde to yield cinnamaldehyde, and Michael‐type addition of acetaldehyde to a wide variety of nitroalkenes to yield valuable γ‐nitroaldehydes. To gain insight into how 4‐OT catalyzes these unnatural reactions, we carried out exchange studies in D₂O, and X‐ray crystallography studies. The former established that H–D exchange within acetaldehyde is catalyzed by 4‐OT and that the Pro1 residue is crucial for this activity. The latter showed that Pro1 of 4‐OT had reacted with acetaldehyde to give an enamine species. These results provide evidence of the mechanism of the 4‐OT‐catalyzed aldol and Michael‐type addition reactions in which acetaldehyde is activated for nucleophilic addition by Pro1‐dependent formation of an enamine intermediate.     

Study of direct type ethanol fuel cells: Analysis of anode products and effect of acetaldehyde

The anode products are observed when ethanol fuel is circulated in the direct ethanol fuel cell system using Nafion^® as an electrolyte. The main products are CO₂ and acetaldehyde. I-V characteristics of a direct type fuel cell using ethanol and acetaldehyde as fuels are investigated. Anode and cathode overpotentials are also measured to analyze the characters of the polarization curves obtained for both fuels. The MEA consisted of PtRu anode catalyst. The voltage drops as the concentration of acetaldehyde solution increases. In the case of ethanol solution, the voltage increases as the concentration increases. The anode overpotential increases as the concentration of acetaldehyde increases although the increase of cathode overpotential is smaller than that of anode overpotential. The opposite result is observed for ethanol solutions, i.e., the anode overpotential increases as the concentration of ethanol decreases. This result shows that the voltage drop observed for acetaldehyde solution results from the anode overpotential. Rotating disc electrode (RDE) measurements and polarization curve measurements were also performed to confirm the relation between acetaldehyde concentration and overpotentials. It is supposed that the electrocatalytic oxidation mechanism of acetaldehyde on PtRu catalyst is different from that of ethanol.     

SOCl2/EtOH: Catalytic system for synthesis of chalcones

In the presence of SOCl₂/EtOH as a catalyst, various substituted chalcones are synthesized by aldol condensation. The HCl is generated in situ by the reaction of SOCl₂ with absolute ethanol.     

Aromatization of ethanol on Mo2C/ZSM catalysts

The reaction of ethanol was investigated on Mo₂C, Mo₂C/SiO₂ and Mo₂C/ZSM-5 catalysts at temperature ranging 573–973 K under atmospheric pressure. Mo₂C and Mo₂C/SiO₂ catalyzed only the decomposition of ethanol to H₂, ethylene, acetaldehyde and different hydrocarbons. The main reaction pathway on pure ZSM-5 is the dehydration reaction yielding ethylene, small amounts of hydrocarbons and aromatics. Deposition of Mo₂C on zeolite greatly enhanced the yield of benzene and toluene by catalyzing the aromatization of ethylene formed in dehydration process of ethanol.     

Efficient carbon-carbon bond formation in ethanol homologation by CO/H2 with specific C1 oxygen retention over Cs/Cu/ZnO catalysts

The reactions of ethanol with CO/H₂ or CH₃OH to form 1-propanol proceed most efficiently over Cs/Cu/ZnO catalysts with selective oxygen retention from CO/H₂ or CH₃OH and removal of oxygen associated with the OH group of ethanol, in contrast to that predicted by the classic aldol condensation mechanism. Isotopic labeling experiments reveal a novel path¹²CH₃ ¹³CH₂OH+¹²CO/H₂¹³CH₃ ¹²CH₂ ¹²CH₂OH.     

Methanol Adsorption on V2O3(0001)

Well ordered V₂O₃(0001) layers may be grown on Au(111) surfaces. These films are terminated by a layer of vanadyl groups which may be removed by irradiation with electrons, leading to a surface terminated by vanadium atoms. We present a study of methanol adsorption on vanadyl terminated and vanadium terminated surfaces as well as on weakly reduced surfaces with a limited density of vanadyl oxygen vacancies produced by electron irradiation. Different experimental methods and density functional theory are employed. For vanadyl terminated V₂O₃(0001) only molecular methanol adsorption was found to occur whereas methanol reacts to form formaldehyde, methane, and water on vanadium terminated and on weakly reduced V₂O₃(0001). In both cases a methoxy intermediate was detected on the surface. For weakly reduced surfaces it could be shown that the density of methoxy groups formed after methanol adsorption at low temperature is twice as high as the density of electron induced vanadyl oxygen vacancies on the surface which we attribute to the formation of additional vacancies via the reaction of hydroxy groups to form water which desorbs below room temperature. Density functional theory confirms this picture and identifies a methanol mediated hydrogen transfer path as being responsible for the formation of surface hydroxy groups and water. At higher temperature the methoxy groups react to form methane, formaldehyde, and some more water. The methane formation reaction consumes hydrogen atoms split off from methoxy groups in the course of the formaldehyde production process as well as hydrogen atoms still being on the surface after being produced at low temperature in the course of the methanol ?? methoxy + H reaction.     

Methanol oxidation over model cobalt catalysts: Influence of the cobalt oxidation state on the reactivity

X-ray photoelectron and absorption spectroscopies (XPS and XAS) combined with on-line mass spectrometry were applied under working catalytic conditions to investigate methanol oxidation on cobalt. Two cobalt oxidation states (Co₃O₄ and CoO) were prepared and investigated as regards their influence on the catalytic activity and selectivity. In addition adsorbed species were monitored in the transition of the catalyst from a non-active state, to an active one. It is shown that the surface oxidation state of cobalt is readily adapted to the oxygen chemical potential in the CH₃OH/O₂ reaction mixture. In particular, even in oxygen-rich mixtures the Co₃O₄ surface is partially reduced, with the extent of surface reduction following the methanol concentration. The reaction selectivity depends on the cobalt oxidation state, with the more reduced samples favouring the partial oxidation of methanol to formaldehyde. In the absence of oxygen, methanol effectively reduces cobalt to the metallic state, also promoting H₂ and CO production. Direct evidence of methoxy and formate species adsorbed on the surface upon reaction was found by analysing the O 1s and C 1s photoelectron spectra. However, the surface coverage of those species was not proportional to the catalytic activity, indicating that they might also act as reaction inhibitors.