Vol 57, No 6 (2016)

Although oxygenated fuel additives are effective in reducing soot emissions, the extent to which molecular structure of the oxygenate plays a role in soot reduction has remained unclear and controversial. To gain a deeper insight in this field, a detailed chemical kinetic modeling approach was used to examine the phenomenon of suppression of sooting by the addition of oxygenated hydrocarbon species to the fuel. For this task, the PREMIX code in conjunction with Chemkin II and models resulting from the merging of validated kinetic schemes describing the oxidation of the components of the n-butanol-benzene mixtures were used to investigate the effect of n-butanol addition on the formation−depletion of acetylene recognized as soot precursor in flames under fuel-rich conditions. The first part of this study treats the dependence of the soot precursor amounts on n-butanol percentage in the fuel mixture, whereas the second part defines the key reaction mechanisms responsible for the observed reduction in C₂H₂ and consequently in polycyclic aromatic hydrocarbons and soot amounts induced by the oxygenate additive. The principal objective of the current study was to obtain fundamental understanding of the mechanisms through which the oxygenate compound affects the soot precursor amounts. The modeling results indicated that there was a dramatic decrease in the acetylene peak height with the addition of the oxygenated addtitive. This finding was found to be due to the increase in the C₂H₂ consumption rates induced by n-butanol addition. Finally, the modeling results provided evidence that n-butanol played a role in changing acetylene formation mechanism by enhancing the role of C₃H₄P, C₃H₄ and aC₃H₅ and by eliminating the role of C₆H₄, C₅H₅, C₅H₆, H₂CCCCH, C₄H₂, C₅H₄O, C₂H, CHCHCHO, H₂C₄O and C₄H₄.

The kinetics of diethyl sulfide (Et₂S) oxidation by aqueous sodium peroxoborate (Na₂[В₂(О₂)₂(ОН)₄]) solutions in a wide acidity range (from [HClO₄] = 1 mol/L to рН 12) has been studied using a kinetic distribution method. The kinetic data together with the results of ¹¹B NMR spectroscopy demonstrate that the monoperoxoborate B(O₂H)₃^-(OH) and diperoxoborate B(O₂H)₂(OH)₂^- anions are the active species in Et₂S oxidation by sodium peroxoborate at рН 8–12. It is assumed that, at a high acidity of the medium ([HClO₄] = 0.05–1.0 mol/L), peroxoboric acid (ОН)₂ВООН or its protonated form (OH)₂BOOH₂⁺ are direct reactants along with Н₂О₂ and HOOH₂⁺.

Based on experimental and theoretical data obtained in the mechanism study of the 5-amino-6-methyluracil-inhibited radical chain oxidation of 1,4-dioxane, a scheme for the process is proposed. A kinetic analysis of the scheme has been performed to obtain an equation describing the regularities of oxygen consumption that agree with the experimental data and provide evidence in favor of the chain consumption of the inhibitor under certain conditions. The composition of resulting products confirms the proposed mechanism.

Isotherms of copper cation sorption by H-ZSM-5 zeolite from aqueous and aqueous ammonia solutions of copper acetate, chloride, nitrate, and sulfate are considered in terms of Langmuir’s monomolecular adsorption model. Using UV-Vis diffuse reflectance spectroscopy, IR spectroscopy, and temperatureprogrammed reduction with hydrogen and carbon monoxide, it has been demonstrated that the electronic state of the copper ions is determined by the ion exchange and heat treatment conditions. The state of the copper ions has an effect on the redox properties and reactivity of the Cu-ZSM-5 catalysts in the selective catalytic reduction (SCR) of NO with propane and in N₂O decomposition. The amount of Cu²⁺ that is sorbed by zeolite H-ZSM-5 from aqueous solution and is stabilized as isolated Cu²⁺ cations in cationexchange sites of the zeolite depends largely on the copper salt anion. The quantity of Cu(II) cations sorbed from aqueous solutions of copper salts of strong acids is smaller than the quantity of the same cations sorbed from the copper acetate solution. When copper chloride or sulfate is used, the zeolite is modified by the chloride or sulfate anion. Because of the presence of these anions, the redox properties and nitrogen oxides removal (DeNO_x) efficiency of the Cu-ZSM-5 catalysts prepared using the copper salts of strong acids are worse than the same characteristics of the sample prepared using the copper acetate solution. The addition of ammonia to the aqueous solutions of copper salts diminishes the copper salt anion effect on the amount of Cu(II) sorbed from these solutions and hampers the nonspecific sorption of anions on the zeolite surface. As a consequence, the redox and DeNO_x properties of Cu-ZSM-5 depend considerably on the NH₄OH/Cu²⁺ ratio in the solution used in ion exchange. The aqueous ammonia solutions of the copper salts with NH₄OH/Cu²⁺ = 6–10 stabilize, in the Cu-ZSM-5 structure, Cu²⁺ ions bonded with extraframework oxygen, which are more active in DeNO_x than isolated Cu²⁺ ions (which form at NH4OH/Cu2+ = 30) or nanosized CuO particles (which form at NH₄OH/Cu²⁺ = 3).

The direct conversion of ethanol into the linear primary alcohols C_nH_2n+1OH (n = 4, 6, and 8) in the presence of the original mono- and bimetallic catalysts Au/Al₂O₃, Ni/Al₂O₃, and Au–Ni/Al₂O₃ was studied. It was established that the rate and selectivity of the reaction performed under the conditions of a supercritical state of ethanol sharply increased in the presence of Au–Ni/Al₂O₃. The yield of target products on the bimetallic catalyst was higher by a factor of 2–3 than that reached on the monometallic analogs. Differences in the catalytic behaviors of the Au, Ni, and Au–Ni systems were discussed with consideration for their structure peculiarities and reaction mechanisms.

The reaction of carbon dioxide with propylene oxide in the presence of the (salen)CoCl or (TPP)CoCl (salen = bis(3,5-di-tert-butyl-salicylidene)-1,2-diaminocyclohexane, TPP = 5,10,15,20-tetraphenylporphyrin) catalyst and the PPNCl (bis(triphenylphosphine)iminium chloride) cocatalyst has been carried out at 20–60°С and a СО₂ pressure of 0.6 MPa to investigate the effect of the ligand nature on the reaction rate and selectivity. The change in the reaction rate and selectivity in relation to the temperature and cocatalyst/catalyst ratio has been studied. The activation energy of the copolymerization of СО₂ with propylene oxide catalyzed by the (salen)CoCl complex have been obtained.

Metal gold particles were supported onto the surface of aluminum oxide by physical vapor deposition. The effects of thermal treatments at 30−800°C both in a vacuum and in an atmosphere of O₂ (5 mbar), CO (5 mbar), or a mixture of CO + O₂ (5 mbar of each) on the samples of Au/Al₂O₃ were studied by X-ray photoelectron spectroscopy. An increase in the Au4f line intensity in the course of gold deposition was accompanied by a shift of this line toward smaller binding energy. Upon the supporting of a maximum quantity of gold, the binding energy E_b(Au4f_7/2) became smaller than the value characteristic of the bulk metal. It was hypothesized that this can be explained by the formation of negatively charged Au^δ− particles due to electron density transfer from the support to the particles of gold. In the course of the heating of Au/Al₂O₃ in a vacuum or in a reaction atmosphere, the agglomeration of small gold particles occurred; this fact manifested itself in a decrease in the atomic ratio [Au]/[Al]. In all of the atmospheres, the Au particles supported on Al₂O₃ exhibited high thermal stability; considerable changes in the ratio [Au]/[Al] were observed only at temperatures higher than 600°C.

The platinum–palladium/Nafion metal–polymer nanocomposites were synthesized by the chemical reduction of ions in the aqueous organic solutions of inverted microemulsions. The functional characteristics of the nanocomposites were studied by cyclic voltammetry, atomic force microscopy, and scanning electron microscopy. The nanocatalysts obtained exhibited high activity in the reactions of oxygen reduction and hydrogen oxidation. The influence of synthesis conditions on the catalytic activity of the metal–polymer nanocomposites was studied.

The formation of Pd–Ag nanoparticles deposited from the heterobimetallic acetate complex PdAg₂(OAc)₄(HOAc)₄ on α-Al₂O₃, γ-Al₂O₃, and MgAl₂O₄ has been investigated by high-resolution trans-mission electron microscopy, temperature-programmed reduction, and IR spectroscopy of adsorbed CO. The reduction of PdAg₂(OAc)₄(HOAc)₄ supported on γ-Al₂O₃ and MgAl₂O₄ takes place in two steps (at 15–245 and 290–550°C) and yields Pd–Ag particles whose average size is 6–7 nm. The reduction of the Pd–Ag catalyst supported on α-Al₂O₃ occurs in a much narrower temperature range (15–200°C) and yields larger nanoparticles (~10–20 nm). The formation of Pd–Ag alloy nanoparticles in all of the samples is demonstrated by IR spectroscopy of adsorbed CO, which indicates a marked weakening of the absorption band of the bridged form of adsorbed carbon monoxide and a >30-cm^–1 bathochromic shift of the linear adsorbed CO band. IR spectroscopic data for PdAg₂/α-Al₂O₃ suggest that Pd in this sample occurs as isolated atoms on the surface of bimetallic nanoparticles, as is indicated by the almost complete absence of bridged adsorbed CO bands and by a significant weakening of the Pd–CO bond relative to the same bond in the bimetallic samples based on γ-Al₂O₃ and MgAl₂O₄ and in the monometallic reference sample Pd/γ-Al₂O₃.