On the Behaviour of Nitrate Esters in Acid Solution. II. Hydrolysis and oxidation of nitroglycol and nitroglycerin

The behaviour of ethylene glycol dinitrate (nitroglycol) and nitroglycerin in moderately concentrated aqueous sulphuric acid, as models of “spent acids”, has been studied. The nitrate esters initial reaction is the simple hydrolysis to yield the alcohols which are eventually oxidized by nitric acid. This reaction, however, is unmeasurably slow in the absence of nitrous acid.     

The Mechanism Studies of Ethanol Oxidation on PdO Catalysts by TPSR Techniques

The paper studies the direct oxidation of ethanol and CO on PdO/Ce_0.75Zr_0.25O₂ and Ce_0.75Zr_0.25O₂ catalysts. Characterization of catalysts is carried out by temperature-programmed desorption (TPD), temperature-programmed surface reaction (TPSR) techniques to correlate with catalytic properties and the effect of supports on PdO. The simple Ce_0.75Zr_0.25O₂ is in less active for ethanol and CO oxidation. After loaded with PdO, the catalytic activity enhances effectively. Combined the ethanol and CO oxidation activity with CO-TPD and ethanol-TPSR profiles, we can find the more intensive of CO₂ desorption peaks, the higher it is for the oxidation of CO and ethanol. Conversion versus yield plot shows the acetaldehyde is the primary product, the secondary products are acetic acid, ethyl acetate and ethylene, and the final product is CO₂. A simplified reaction scheme (not surface mechanism) is suggested that ethanol is first oxidized to form intermediate of acetaldehyde, then acetic acid, ethyl acetate and ethylene formed going with the formation of acetaldehyde, acetic acid, ethyl acetate; finally these byproducts are further oxidized to produce CO₂. PdO/Ce_0.75Zr_0.25O₂ catalyst has much higher catalytic activity not only for the oxidation of ethanol but also for CO oxidation. Thus the CO poison effect on PdO/Ce_0.75Zr_0.25O₂ catalysts can be decreased and they have the feasibility for application in direct alcohol fuel cell (DAFC) with high efficiency.     

Oxidation of Acetaldehyde and Propionaldehyde on a VOx/TiO2 Catalyst in the Presence of Water Vapor

The partial oxidation of acetaldehyde and propionaldehyde on a TiO₂ supported VO_x catalyst in the presence of water vapor was investigated at temperatures from 120 to 280 °C. Depending on the kind of aldehyde and reaction temperature, the selective oxidation to the appropriate carboxylic acid and an oxidative splitting to lower carboxylic acids took place. Acetaldehyde was oxidized to acetic acid with selectivities up to 82 % at ～ 200 °C whereas propionic acid was formed only with selectivities of about 20 % at ～ 140 °C in the oxidation of propionaldehyde. The oxidative cleavage of propionaldehyde led to the formation of more acetic acid than formic acid, which was in agreement with the higher formation of CO_x compared to that in the acetaldehyde oxidation. The presence of water and the increasing concentration of oxygen in the feed was found to enhance the selectivity towards the formation of C₁ to C₃ carboxylic acids by inhibiting the total oxidation of aldehydes and carboxylic acids.     

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.     

Mechanism of formation of C2-oxygenated compounds from CO + H2 reaction over SiO2-supported Rh catalysts

The mechanism of acetaldehyde and ethanol formation from the CO + H₂ reaction below atmospheric pressure has been investigated by combining infrared spectroscopic measurement and ¹³CO and C¹⁸O isotopic tracer studies with reaction kinetics. The rates of acetaldehyde and ethanol formation are markedly dependent on the nature of metal precursors employed. The addition of sodium cations depresses the total catalytic activity, while the selectivity for ethanol is increased by the addition of manganese cations. From the behavior of surface species under reaction conditions, it is concluded that acetaldehyde is formed through the following two steps: (i) CO insertion into C₁ species which are reaction intermediates for not only hydrocarbons but also for the methyl group in acetaldehyde, and (ii) subsequent formation of acetate ions whose one oxygen atom is supplied from the support, finally producing acetaldehyde. Differences in ¹⁸O distribution in acetaldehyde and ethanol during the C¹⁸O + H₂ reaction indicate that ethanol is not produced via direct hydrogenation of acetaldehyde.     

Electrooxidation of ethanol at polycrystalline and platinum stepped single crystals: A study by differential electrochemical mass spectrometry

The electrooxidation of adsorbed and bulk solution of 10⁻² M ethanol and D₆-ethanol at polycrystalline platinum, smooth, roughened and Ru modified Pt(3 3 2), Pt(3 3 1) and Pt(1 1 1) electrodes was studied by on-line differential electrochemical mass spectroscopy (DEMS) using a dual thin layer flow through cell.On polycrystalline Pt, the main (or even single) product is acetaldehyde; due to the flow through conditions the amount of acetaldehyde further oxidized to acetic acid is negligible. At stepped single crystals with (1 1 1) terraces (Pt(s)[n(1 1 1) × (1 1 1)], acetic acid is produced at a lower potential than acetaldehyde. This demonstrates that in addition to the reaction path involving C-C bond splitting leading to CO₂ (via adsorbed CO and CH_x) and the reaction path leading to acetaldehyde there is a third, direct reaction path leading to the formation of acetic acid.Step decoration by Ru does not lead to an increased reactivity. This is different from the strong cocatalytic effect of Ru at step sites on the oxidation of CO. Furthermore, Ru does not influence the relative amount of acetaldehyde formed.     

Sustainable production of acetaldehyde from lactic acid over the carbon catalysts

The synthesis of acetaldehyde from lactic acid over the carbon material catalysts was investigated. The carbon materials were characterized by scanning electron microscopy for morphologic features, by X-ray diffraction for crystal phases, by Fourier transform infrared spectroscopy for functional group structures, by N₂ sorption for specific surface area and by ammonia temperature-programed desorption for acidity, respectively. Among the tested carbon catalysts, mesoporous carbon displayed the most excellent catalytic performance. By acidity analysis, the medium acidity is a crucial factor for catalytic performance: more medium acidity favored the formation of acetaldehyde from lactic acid. To verify, we compared the catalytic performance of fresh activated carbon with that of the activated carbon treated by nitric acid. Similarly, the modified activated carbon also displayed better activity due to a drastic increase of medium acidity amount. However, in contrast to fresh carbon nanotube, the treated sample displayed worse activity due to decrease of medium acidity amount. The effect of reaction temperature and time on stream on the catalytic performance was also investigated. Under the optimal reaction conditions, 100% lactic acid conversion and 91.6% acetaldehyde selectivity were achieved over the mesoporous carbon catalyst.     

Aspects of the surface and bulk nitration of cellulose in nitric acid,nitric acid/water,and nitric acid/dichloromethane mixes

Electron spectroscopy for chemical analysis (ESCA) has been employed to follow the surface nitration of cellulose papers in nitric acid–water and nitric acid–dichloromethane mixes with the aim of: elucidating the identity of the nitrating species in these mixes and from comparison of surface and bulk degree of substitution (DOS) further understanding on the role that morphology plays in the nitration of cellulose in these mixes. In nitric acid, nitric acid–water and nitric acid–dichloromethane mixes, surface nitration was observed to be slow (cf. to that reported in mixed acids) and the concentration of nitronium ion was observed to be low (cf. to mixed acids). On the basis of these observations and from the results of kinetic experiments, reported herein, it is proposed that the nitronium ion, NO₂⁺, is the important nitrating species of cellulose in these nitric acid mixes. Nitration in all but the most concentrated nitric acid–dichloromethane mixes produced equal surface and bulk DOS; however, nitration in pure nitric acid produced different surface and bulk DOS. The latter result implies that the heterogeneous nature of the nitration reaction can influence the DOS achieved.     

Electrochemical oxidation of organic compounds in fluorosulfuric acid—III. Voltammetric investigation of aromatic carboxylic acids and acylium ions

The anodic behavior of a series of substituted benzoic acids $\text{1a}$–$\text{1w}$ and of the corresponding benzoylium ions $\text{5}$ is investigated by cyclic voltammetry in fluorosulfuric acid at ?76°C. The acids are oxidized to cation radicals, the stability of which decreases with decreasing number of alkyl substituents. As a subsequent reaction the functionalization of one of the methyl groups to the fluorosulfonyloxymethyl group is found. After dissolving at room temperature of the acids with one o-alkyl group are between 80 and 100% and the acids with two o-alkyl groups are completely transformed into benzoylium ions $\text{5}$, which are between 450 and 560 mV more positively oxidized than the acid. The main reaction of the dication radical formed is the addition of SO₃F^? to the carbonylium C-atom. As the number of alkyl substituents decreases this reaction competes with the functionalization of a methyl group. The difference between the voltammetric data in HSO₃F and acetonitrile is discussed in terms of a protonation of the benzoic acids and their oxidation products.     

The Oxidative Fermentation of Ethanol in Gluconacetobacter diazotrophicus Is a Two-Step Pathway Catalyzed by a Single Enzyme: Alcohol-Aldehyde Dehydrogenase (ADHa)

Gluconacetobacter diazotrophicus is a N₂-fixing bacterium endophyte from sugar cane. The oxidation of ethanol to acetic acid of this organism takes place in the periplasmic space, and this reaction is catalyzed by two membrane-bound enzymes complexes: the alcohol dehydrogenase (ADH) and the aldehyde dehydrogenase (ALDH). We present strong evidence showing that the well-known membrane-bound Alcohol dehydrogenase (ADHa) of Ga. diazotrophicus is indeed a double function enzyme, which is able to use primary alcohols (C2–C6) and its respective aldehydes as alternate substrates. Moreover, the enzyme utilizes ethanol as a substrate in a reaction mechanism where this is subjected to a two-step oxidation process to produce acetic acid without releasing the acetaldehyde intermediary to the media. Moreover, we propose a mechanism that, under physiological conditions, might permit a massive conversion of ethanol to acetic acid, as usually occurs in the acetic acid bacteria, but without the transient accumulation of the highly toxic acetaldehyde.     

Partial oxidation of ethanol over Pd/CeO2 and Pd/Y2O3 catalysts

The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H₂, CO₂ and acetaldehyde formation was favored on Pd/CeO₂, whereas CO production was facilitated over Pd/Y₂O₃ catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y₂O₃ catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH₄ and CO at high temperatures. On Pd/CeO₂ catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H₂, CH₄ and CO. The CO formed is further oxidized to CO₂, which seems to be promoted on Pd/CeO₂ catalyst.     

Application of Ti/RuO2-Ta2O5 electrodes in the electrooxidation of ethanol and derivants: Reactivity versus electrocatalytic efficiency

The influence of the preparation method on the performance of RuO₂-Ta₂O₅ electrodes was evaluated toward the ethanol oxidation reaction (EOR). Freshly prepared RuO₂-Ta₂O₅ thin films containing between 30 and 80 at.% Ru were prepared by two different methods: the modified Pechini-Adams method (DPP) and standard thermal decomposition (STD). Electrochemical investigation of the electrode containing RuO₂-Ta₂O₅ thin films was conducted as a function of electrode composition in a 0.5-mol dm⁻³ H₂SO₄ solution, in the presence and absence of ethanol and its derivants (acetaldehyde and acetic acid).At a low ethanol concentration (5 mmol dm⁻³), ethanol oxidation leads to high yields of acetic acid and CO₂. On the other hand, an increase in ethanol concentration (15-1000 mmol dm⁻³) favors acetaldehyde formation, so acetic acid and CO₂ production is hindered, in this case.Electrodes prepared by DPP provide higher current efficiency than STD electrodes for all the investigated ethanol concentrations. This may be explained by the increase in electrode area obtained with the DPP preparation method compared with STD.     

Conversion of graphite into mellitic acid

A fast one step oxidation method for converting poorly crystalline graphite, identified by its X-ray diffraction angle of from 26.5 to 26.7°, into mellitic acid has been developed. The oxidant used is a mixture consisting of nitric, sulphuric, and perchloric acids in a ratio of 1:6:1. Oxidation goes to completion within 7 hr at atmospheric pressure and the reaction time can be further reduced to 1.25–2.5 hr by the presence of a catalyst such as V₂O₅, MoO₃, PbO₂, Al₂O₃, Ag₂O or Na₂O₂. The reaction product was found to contain only mellitic acid with an over-all yield of about 30%.     

Coal demineralization using sodium hydroxide and acid solutions

A coal product which exceeds the purity requirements for ash, iron and silicon in Hall Cell anode carbon was prepared by a unique leaching sequence involving caustic treatment, followed by treatments with sulphuric and nitric acids. The two acid leaching steps for the three-step process can also be combined with no adverse effect on the coal quality for anode purposes. In the process, the majority of the pyrite reacts with NaOH, forming Fe₂O₃ and Na₂S. Na₂S is dissolved in the leaching liquor and Fe₂O₃ is trapped in the coal matrix. The incorporation of sodium with organic sulphur increases the ash content and decreases the heating value of caustic leached coal on a dry basis. The silicon and aluminium contents are lowered by reactions with NaOH. While most of the reaction products are soluble sodium silicates and aluminates, the remaining silica and alumina form noselite. Dilute sulphuric acid dissolves nearly all of the sodium salts. The remaining iron compounds are dissolved by nitric acid.     

Synthesis of Dimethyl Carbonate from Methanol and Carbon dioxide using Potassium Methoxide as Catalyst under Mild Conditions

Pd-supported on WO₃–ZrO₂ (W/Zr atomic ratio=0.2) calcined at 1073 K was found to be highly active and selective for gas-phase oxidation of ethylene to acetic acid in the presence of water at 423 K and 0.6 MPa. Contact time dependence demonstrated that acetic acid is formed via acetaldehyde formed by a Wacker-type reaction, not through ethanol by hydration of ethylene.     

Chlorination and bromination of some aromatic compounds by means of aqua regia and hydrobromic-nitric acid mixture

Chlorination and bromination of a series of aromatic compounds with mixtures of nitric acid and hydrochloric or hydrobromic acids yielded chloranil and bromanil respectively. The reaction was promoted by -OH, -NH₂ and -OCH₃ groups and inhibited by alkyl, -CHO, -COOH, -CN and -NO₂ groups.     

The nitric acid oxidation of 2-octanol. A model reaction for multiple heterogeneous liquid–liquid reactions

The oxidation of 2-octanol with nitric acid has been selected as a model reaction for a heterogeneous liquid–liquid reaction with an undesired side reaction. 2-Octanol is first oxidized to 2-octanone, which can be further oxidized to carboxylic acids. An extensive experimental program has been followed using heat flow calorimetry supported by chemical analysis. A series of oxidation experiments has been carried out to study the influence of different initial and operating conditions such as temperature, stirring speed and feed rate. In parallel a semi-empirical model has been developed to describe the conversion rates.     

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.     

In Vitro One-Pot 3-Hydroxypropanal Production from Cheap C1 and C2 Compounds

One- or two-carbon (C1 or C2) compounds have been considered attractive substrates because they are inexpensive and abundant. Methanol and ethanol are representative C1 and C2 compounds, which can be used as bio-renewable platform feedstocks for the biotechnological production of value-added natural chemicals. Methanol-derived formaldehyde and ethanol-derived acetaldehyde can be converted to 3-hydroxypropanal (3-HPA) via aldol condensation. 3-HPA is used in food preservation and as a precursor for 3-hydroxypropionic acid and 1,3-propanediol that are starting materials for manufacturing biocompatible plastic and polytrimethylene terephthalate. In this study, 3-HPA was biosynthesized from formaldehyde and acetaldehyde using deoxyribose-5-phosphate aldolase from Thermotoga maritima (DERA_Tma) and cloned and expressed in Escherichia coli for 3-HPA production. Under optimum conditions, DERA_Tma produced 7 mM 3-HPA from 25 mM substrate (formaldehyde and acetaldehyde) for 60 min with 520 mg/L/h productivity. To demonstrate the one-pot 3-HPA production from methanol and ethanol, we used methanol dehydrogenase from Lysinibacillus xylanilyticus (MDH_Lx) and DERA_Tma. One-pot 3-HPA production via aldol condensation of formaldehyde and acetaldehyde from methanol and ethanol, respectively, was investigated under optimized reaction conditions. This is the first report on 3-HPA production from inexpensive alcohol substrates (methanol and ethanol) by cascade reaction using DERA_Tma and MDH_Lx.     

Electrooxidation of ethanol on a Pt electrode in acid solutions: in situ ATR-SEIRAS study

The electrooxidation of ethanol was investigated on a Pt thin film electrode in a HClO₄ solution using surface enhanced infrared absorption spectroscopy (SEIRAS) with the attenuated total reflection (ATR) technique. The spectra indicate that during this reaction acetate and CO adsorbates are formed. The intensity of symmetric OCO stretching band of adsorbed acetate correlates well with voltammetry in the potential range between −0.1 and 0.85 V. The CO stretching band for adsorbed acetaldehyde and/or acetyl also was observed; these compounds are the reaction intermediates whose oxidation generates CO_ad and acetic acid. We also explored the oxidation behavior of adsorbed residues. The oxidation of acetaldehyde was studied for comparison.