Reaction Kinetics, Mechanisms and Catalysis

The effect of sulfur on diesel emission control is reviewed in this paper. Diesel exhaust differs from that of petrol engine exhaust in two major characteristics. Firstly, diesel exhaust contains a far higher amount of particulate matter, and secondly, the exhaust is far leaner, that is, far more oxidizing than a typical exhaust from petrol engines. Under these conditions, the conventional three-way catalysts are not effective in reducing NOx . Emission from diesel engines is a complex phenomenon. The composition, the properties and the amount of these emissions depend on strictly technical parameters such as engine design and engine operation characteristics and on fuel and lube oil composition. Diesel fuel contains a small amount of sulfur which has an adverse effect even on the raw particulate emissions. The investigations on the effect of sulfur on hydrocarbons, CO and NOx abatement in diesel exhaust gas is reviewed together with the newest technologies to avoid catalyst deactivation by unwanted SO2 reactions.

Model bimetallic Ni–Fe catalysts were prepared by coprecipitation from aqueous solutions of nitrates and by mechanical alloying of metal powders. Pure nickel samples subjected to the similar procedures were used as references. The obtained samples were characterized by scanning electron microscopy and X-ray diffraction analysis. Catalytic chemical vapor deposition of 1,2-dichloroethane over the catalysts was studied in a quartz flow reactor equipped with a McBain balance. It was shown that in the case of coprecipitation followed by reduction, Ni–Fe solid solution is formed within the studied range of Fe loading (1–10 wt%). Activation times of 6 min and longer are required to obtain this solid solution by the mechanical alloying method. Despite the known catalytic activity of nickel and iron in hydrocarbon decomposition in accordance with carbide cycle mechanism, iron doping was found to worsen the behavior of nickel in the studied reaction where chlorinated alkane plays a role of substrate to be decomposed. The formation of thermodynamically more stable iron chloride in relation to nickel chloride leads to deactivation of the catalyst and deceleration of the overall process.

A series of MnOx-CeO2/ZSM-5 catalysts with different Ce loadings were prepared through the impregnation method and characterized by BET, XRD, SEM, H2-TPR, and XPS. The performances of selective catalytic reduction (SCR) of NO/NO2 with NH3 and NO oxidation over MnOx-CeO2/ZSM-5 catalysts were investigated. The result showed that the MnOx dispersions, redox abilities and proportions of Mn4+ of catalysts were enhanced by the doping of CeO2. However, the excessive Ce loadings led to the accumulation of active components on the catalyst surface. The sample with Ce/Mn molar ratio of 0.39 exhibited the best SCR performance, the NOx conversion achieved 95.4% at 150 °C, and maintained higher than 95% in a wide operating temperature range (150–350 °C). MnOx-CeO2/ZSM-5 also exhibited considerable catalytic performance of NO oxidation, the maximum conversion of NO achieved 56.5% at 350 °C.

IR spectra of pyridine adsorbed on zirconium phosphate and zeolite HNaY were studied at temperatures of 400–500 K. Protonation heats of pyridine determined on the OH groups of zirconium phosphate and zeolite HNaY having theυOH at 3640 cm−1, are 65±6.0 and 172±16 kJ/mol, respectively.

The existence of organic pollutants in water discharges has made wastewater treatment extremely difficult. This is mainly due to the release of various hazardous substances into waterways, which cause significant damage to humans and the aquatic ecosystem. This paper discusses the biosynthesis process of pure ZnO and Ag co-doped ZnO (1%Ag_ZnO and 2%Ag_ZnO). Highly pure nanoparticles (NPs) were obtained by simple and ecological route, through employment of Zn-nitrate as host and Ag-nitrate as dopant and phytochemicals of Zizyphus lotus fruit as reduction agent. The Ag_ZnO NPs were prepared in a one pot synthetic mode (1 and 2% Ag). The obtained samples were characterized by XRD analysis and FTIR spectroscopy which revealed the hexagonal Wurtzite structure of crystals with an average crystallite diameter varying from 16 to 29 nm. The elimination capability of NPs was investigated through the photo-degradation of tartrazine (TR) under solar light irradiation. The operating parameters namely the catalyst dose, initial TR concentration (Co) have been optimized for the TR degradation as function of time. The dye TR was more effectively removed by doped ZnO NPs under solar irradiation. The best performance was obtained with 2%Ag/ZnO, due mainly to the radicals O2·− and ·OH. Results indicated also that the TR removal rate increases with the increase in catalyst load and the decreased in the initial TR concentration.

Alkaline transesterifications (methanolysis, ethanolysis) of vegetable oils (soybean, sunflower) were conducted under conditions selected by an experimental design, producing biodiesels (fatty methyl esters 97.5 wt%; fatty ethyl esters 96.7 wt%) with high quality characteristics identified by reduced sodium content (0.11 mg kg−1), low levels of glycerol concentration (0.01 wt%), acidity (0.31 mg NaOH g−1) and viscosity (4.81 mm2 s−1). Evidence indicated that in a first stage, the triglyceride slowly dispersed in the alcohol phase, and then promoted the rapid production of esters: the biodiesel yield increased from 52.0 to 97.5% in methanolysis and from 44. 0 to 96.7% in ethanolysis. A mathematical model was formulated, including biphasic effects between the liquid phases, with respect to partition equilibrium, mass transfer and chemical reaction. The kinetics of the biphasic transesterification processes were characterized quantitatively through the order of magnitude of the mass transfer coefficient of the triglycerides (K TG  = 5.82 × 10−4 s−1, at 303 K − 5.86 × 10−2 s−1, at 353 K), and of the specific reaction rate (k = 3.48 × 10−3 s−1, at 303 K − 5.78 × 10−3 s−1 at 353 K). Resistances related to these effects indicated that they compete during the evolution of the processes.

New active and selective catalysts were prepared by adding different quantities of Te to CdMoO4. These were already selective at low Te levels, but the one with a Cd/Te/Mo ratio of 1/1/1 was specific for butadiene. The catalytic behavior of the Cd−Te−Mo−O system has been correlated mainly with the CdTeMoO6 phase in the region rich in Te and with the CdMoO4 phase with Te as dopant in the region poor in Te.

The influence of temperature in the 20–100°C range on processes of bimolecular interaction in the aerosil-phenanthrene-trinitrobenzene system has been studied. Temperature-stimulated CTC accumulation on the surface is found. Activation energies of complex formation are estimated. Quenching of phenanthrene fluorescence by acceptor has a mixed static and dynamic character.

The FT-IR characterization showed that anhydrous zinc acetate hardly interacted with dimethyl carbonate, but it could coordinate with 1,5-naphthalene diamino to form a new complex. As a result, a new mechanism on 1,5-naphthalene diamino activation was proposed for the methoxycarbonylation of 1,5-naphthalene diamino with dimethyl carbonate over anhydrous zinc acetate.