Ordered mesoporous alumina-supported metal oxides

The one-pot synthesis of alumina-supported metal oxides via self-assembly of a metal precursor and aluminum isopropoxide in the presence of triblock copolymer (as a structure directing agent) is described in detail for nickel oxide. The resulting mesoporous mixed metal oxides possess p6 mm hexagonal symmetry, well-developed mesoporosity, relatively high BET surface area, large pore widths, and crystalline pore walls. In comparison to pure alumina, nickel aluminum oxide samples exhibited larger mesopores and improved thermal stability. Also, long-range ordering of the aforementioned samples was observed for nickel molar percentages as high as 20%. The generality of the recipe used for the synthesis of mesoporous nickel aluminum oxide was demonstrated by preparation of other alumina-supported metal oxides such as MgO, CaO, TiO 2, and Cr 2O 3. This method represents an important step toward the facile and reproducible synthesis of ordered mesoporous alumina-supported materials for various applications where large and accessible pores with high loading of catalytically active metal oxides are needed.     

Facile oxygen reduction on a three-dimensionally ordered macroporous graphitic C3N4/carbon composite electrocatalyst

Honeycomb catalysis: a facile oxygen reduction reaction has been observed on a graphitic C(3)N(4)/carbon catalyst with three-dimensional interconnected macropores (see picture with SiO(2) template). This material not only shows catalytic activity that is comparable to that of commercial Pt/C, but also has much higher organic-fuel tolerance and long-term stability.     

Polymer-templated mesoporous carbons synthesized in the presence of nickel nanoparticles, nickel oxide nanoparticles, and nickel nitrate

Mesoporous carbon composites, containing nickel and nickel oxide nanoparticles, were obtained by soft-templating method. Samples were synthesized under acidic conditions using resorcinol and formaldehyde as carbon precursors, poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock co-polymer Lutrol F127 as a soft template and nickel and nickel oxide nanoparticles, and nickel nitrate as metal precursors. In addition, a one set of samples was obtained by impregnation of mesoporous carbons with a nickel nitrate solution followed by further annealing at 400 °C. Wide angle X-ray powder diffraction along with thermogravimetric analysis proved the presence of nickel nanoparticles in the final composites obtained using nickel and nickel oxide nanoparticles, and Ni(NO₃)₂ solution. Whereas, the impregnation of carbons with a nickel nitrate solution followed by annealing at 400 °C resulted in needle-like nickel oxide nanoparticles present inside the composites’ pores. Low-temperature (−196 °C) nitrogen physisorption, X-ray powder diffraction, and thermogravimetric analysis confirmed good adsorption and structural properties of the synthesized nickel-carbon composites, in particular, the samples possessed high surface areas (>600 m²/g), large total pore volumes (>0.50 cm³/g), and maxima of pore size distribution functions at circa 7 nm. It was found that the composites were partially graphitized during carbonization process at 850 °C. The samples are stable in an air environment below temperature of 500 °C. All these features make the synthesized nickel-carbon composites attractive materials for adsorption, catalysis, energy storage, and environmental applications.     

Gas adsorption on heterogeneous surfaces: A detailed computation of adsorption energy distribution

A new numerical method is proposed for solving the integral equation for the overall adsorption isotherm, with respect to the energy distribution function. This method can be applied for an arbitrary function, taken as the local adsorption isotherm, and for arbitrary integration limits.     

Influence of analysis conditions on low pressure adsorption measurements and its consequences in characterization of energetic and structural heterogeneity of microporous carbons

Nitrogen adsorption isotherms on nonporous and microporous carbons were thoroughly studied at low relative pressures. For nonporous carbons low pressure measurements seem to be unaffected by analysis conditions. However, these measurements on microporous solids may be affected by analysis conditions at relative pressures below 10^–4. It was shown that selection of proper equilibration time is crucial for correct measurements of equilibrium pressures during adsorption on microporous carbons. The isotherm shift induced by insufficient equilibration of the system may affect the surface heterogeneity and microporosity analysis. A comparison of the adsorption energy and pore volume distribution functions calculated from low pressure nitrogen adsorption isotherms measured at different equilibration times on a microporous carbon shows that this effect is smaller than it was expected.     

Thin-layer adsorption chromatography with mixed mobile phases. 3. Correlation between parameters characterizing the chromatographic systems with binary and ternary mobile phases

TLC experimental data have been measured for polycyclic hydrocarbons in binary and ternary mobile phases on silica gel. These data have been interpretated using the equation discussed by us in Part 1 of this series [HRC & CC 2 (1979) 236]. The heterogeneity parameter appearing in this equation has been evaluated and compared for different ternary and binary mobile phases.     

Adsorption of gas mixtures on heterogeneous solid surfaces II. Adsorption isotherms for gaseous mixtures whose pure-gas isotherms show the Freundlich,Tóth and Langmuir behaviours

Summary In this paper the problem of determining adsorption from binary gaseous mixtures on the basis of pure-gas adsorption parameters has been theoretically discussed. The author analysed adsorption systems whose adsorption from pure gases is in agreement with the equation ofTóth, Freundlich orLangmuir.

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Zusammenfassung In der vorliegenden Arbeit wurde das Problem zur Ermittlung der Adsorption aus binären Gasmischungen auf der Basis von Adsorptionsparametern der reinen Gase theoretisch diskutiert. Es wurden nur solche Adsorptionssysteme analysiert, bei denen die Adsorption der reinen Gase mit der Gleichung vonTóth, Freundlich oderLangmuir übereinstimmt.

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With 1 table     

An improved methodology for adsorption characterization of unmodified and modified silica gels

An improvement in the adsorption characterization of the surface and structural properties of unmodified and modified mesoporous silica gels is presented. This improvement was achieved by selection of proper macroporous silica as the reference solid for adsorption characterization of porous silica gels. Experimental illustration is provided for unmodified and n-octyl-modified silica gels of different bonding density. The surface and structural properties of these silica gels were characterized by utilizing the standard adsorption data for both unmodified and octyl-modified LiChrospher Si-1000 macroporous silica gels. It was shown that the standard nitrogen adsorption data have an appreciable influence on the analysis of the pore size and surface properties of silica gels. This analysis can be improved by selecting the reference solid of the surface properties close to those of the silica gel studied.     

The solution of adsorption integral equations by means of the regularization method

An overall adsorption quantity for a heterogeneous solid is usually expressed by an integral equation, which contains a distribution function that describes heterogeneous properties of this solid. The calculation of this distribution function is an ill-posed problem. The current article shows that the difficulties arising from the ill-posed nature of an adsorption equation can be overcome with the regularization method. This work presents general principles of regularization for solving the ill-posed problems without detailed mathematical considerations. The application of the regularization method to calculate a distribution function from any overall adsorption functions is illustrated with both simulated and experimental adsorption isotherms.