Influence Of Chemical Nature Research Articles

Catalysts for hydrogenation of CO2 into components of motor fuels

CO2 is a harmful greenhouse gas, a product of chemical emissions, the combustion of fossil fuels and car exhausts, and it is a widely available source of carbon. The review considers various ways of hydrogenation of carbon dioxide into components of motor fuels - methanol, dimethyl ether, ethanol, hydrocarbons - in the presence of heterogeneous catalysts. At each route of conversion of CO2 (into oxygenates or hydrocarbons) the first stage is the formation of CO by the reverse water gas shift (rWGS) reaction, which must be taken into account when catalysts of process are choosing. The influence of chemical nature, specific surface area, particle size and interaction between catalyst components, as well as the method of its production on the CO2 conversion processes is analyzed. It is noted that the main active components of CO2 conversion into methanol are copper atoms and ions which interact with the oxide components of the catalyst. There is a positive effect of other metals oxides additives with strong basic centers on the surface on the activity of the traditional copper-zinc-aluminum oxide catalyst for the synthesis of methanol from the synthesis gas. The most active catalysts for the synthesis of DME from CO2 and H2 are bifunctional. These catalysts contain both a methanol synthesis catalyst and a dehydrating component, such as mesoporous zeolites with acid centers of weak and medium strength, evenly distributed on the surface. The synthesis of gasoline hydrocarbons (≥ C5) is carried out through the formation of CO or CH3OH and DME as intermediates on multifunctional catalysts, which also contain zeolites. Hydrogenation of CO2 into ethanol can be considered as an alternative to the synthesis of ethanol through the hydration of ethylene. High activation energy of carbon dioxide, harsh synthesis conditions as well as high selectivity for hydrocarbons, in particular methane remains the main problems. Further increase of selectivity and efficiency of carbon dioxide hydrogenation processes involves the use of nanocatalysts taking into account the mechanism of CO2 conversion reactions, development of methods for removing excess water as a by-product from the reaction zone and increasing catalyst stability over time.

Influence of chemical nature, expansion ratio and cellular morphology on the fracture behaviour of flexible polyolefin-based foams assessed by the Essential Work of Fracture (EWF)

Several commercial polyolefin-based flexible foams produced by extrusion foaming were characterized in terms of their cellular morphology and fracture behaviour using the concept of the Essential Work of Fracture (EWF), focusing on the influence of foam's chemical nature, expansion ratio and cellular structure on the values of the fracture parameters. Correction procedures were proposed in order to take into account the complexity of foams in the obtained fracture parameters, particularly a correction procedure based on their expansion ratio, and a second one based on the fraction of polymer present in the foams determined from cellular structure characterization. Although doubts remain about the applicability of the EWF methodology to LDPE foams, the correction procedure based on the expansion ratio seemed to provide more accurate results than that based on polymer fraction, with EWF effectively distinguishing between polyolefin foams having different chemical nature. Comparatively, foams based on a P-E copolymer presented the highest values of the essential work of fracture in the MD direction, while significant differences were only observed in the TD direction for foams having a highly oriented cellular structure. All PP-based foams showed similar non-essential work of fracture values in both MD and TD directions.

Influence of chemical nature of aerosilogel surface on proton conductivity of the Nafion-containing composites

Aerosilogel modified with hydroxylaluminum (=Al-OH) groups has been synthesized via the molecular layering procedure, and aerosilogel modified with aminopropylsilyl groups [≡Si(CH2)3NH2] has been prepared via chemisorption of (3-aminopropyl)triethoxysilane. The modified aerosilogel have been further used to prepare composite Nafion-containing electrolytes Nafion. Electrical conductivity of the produced materials has been studied by impedance spectroscopy. Chemical modification of the gel surface strongly affects proton conductivity of Nafion-containing composites.

Some Peculiarities of Silica Modification under High Reagent Pressure. II. Influence of Chemical Nature of Modifying Reagent

The modes of interaction between organic substances and aerosilogel at high pressures and high temperatures were considered. The analysis was performed on the basis of data from IR spectroscopy and differential thermal analysis, and the porous structure characteristics of the modified aerosilogel. The following types of substances were used as modifiers of the silica surface: (a) substances which did not interact chemically with the silica surface; (b) substances capable of polymerization or polycondensation; and (c) substances capable of chemical reaction with the surface. From an analysis of data obtained for 26 adsorbents, it results that depending on the nature of the substance used for modification such substances can promote the process of silica mass transfer. During this process, the possibility occurs of the occlusion of the substances inside silica globules, changes in the parameters of the porous structure, physical or chemical bonding of the modifier molecules with the aerosilogel surface, destruction of the reaction products, etc. The mechanism of the reaction was discussed.

Influence of chemical nature and concentration of the catalyst on hydrocarbon pyrolysis

The dependence of pyrolysis rate of hydrocarbons on the concentrations of catalysts of various chemical nature has been studied. Substances active in pyrolysis can be divided into three groups: inhibiting the reaction and enhancing either its homogeneous or heterogeneous components.

Influence of Chemical Nature on Flow Behavior of Polymers. I. Shear Rate and Temperature Dependence

Abstract The flow behavior of low molecular weight liquid polybutadiene polymers was studied as a function of shear rate, temperature, and molecular structure. Measurements were made in the temperature range 15 to 50° C and shear rate range 1 to 15,000 sec−1 with a cone and plate and a capillary viscometer. Limiting low shear viscosity, flow activation energy, and critical shear rate marking onset of shear rate thinning were found to be strongly dependent upon the presence of functional groups such as hydroxyl, carboxyl, and nitrile. The modifying groups showed a greater effect than the molecular weight upon the properties measured.