Nanoporous carbons (NPC) or carbogenic molecular sieves (CMS) are unique materials that are able to produce shape selectivity for very precise molecular separations, such as that of oxygen from nitrogen on the basis of size. Surprisingly, the structure of NPC is globally amorphous. This seems at first irreconcilable, since regular transport behavior is expected to arise from regular porous solids such as zeolites and other crystalline molecular sieves. With this problem in mind as motivation, in this paper we describe some of the more intriguing aspects of the nanopore formation process. It is argued that at the nanoscale the NPC are both regular and structurally self similar, consisting of curved aromatic nanodomains that arise from the broken symmetry of hexagonal arrays. The symmetry breaking process is a direct result of the dissipation that takes place during pyrolysis leading to small molecules and a defect-laden carbogenic solid. In this context, some preliminary results illustrating how these NPC structures can be used to stabilize cesium for base catalysis and to prepare supported molecular sieve membranes for small molecule separations.

Activated carbon filaments of diameter ∼0.1 μm, main pore size (BJH) 55 Å, specific surface area 1310 m2/g and yield 36.2% were obtained by activating carbon filaments of diameter ∼ 0.1 urn in C02 + N2 (1:1) at 970°C for 80 min. Prior to this activation, the filaments were surface oxidized by exposure to ozone.

A mixed-valent oxide-catalytic carbonization (MVOCC) process is described for synthesizing monodispersed carbon spheres (or tubes) in macroscopic quantities at low cost. The technique uses natural gas and reusable catalysts and produces no environmental waste or pollution. The product is controlled to be either all of spheres (∼ 210 nm) or all of tubes with high purity (> 95 %). In spherical form, the product is solid and comprised of layered graphitic flakes containing paired pentagonal-heptagonal carbon-rings. In spiral tube form, the product is composed of twisted graphitic helix layers containing spherical nodes. A growth mechanism has been proposed, in which the pairing of pentagonal and heptagonal carbon-rings plays an important role. It is concluded that a change in fraction and nucleation rates of pentagonal, hexagonal and heptagonal carbon-rings results in the growth of different geometrical shapes. The success of using mixed-valence metal oxides as catalysts has opened a new field in catalysis research and applications.

In this investigation we elected to use the hydrogenation of 1-butene as probe reactions in an attempt to monitor any possible changes in catalytic behavior resulting from supporting 5 wt.% nickel on different types of carbon nanofibers compared to the performance of the same metal loading on more traditional carriers, including γ-Al2O3 and active carbon. In all cases the carbon nanofiber supported nickel particles are found to exhibit superior activity and significant changes in selectivity to that found from the same metal supported on traditional carriers.

Copper catalysts supported on different allotropie forms of carbon, such as activated carbon, graphite, pitch-based carbon fibers and diamond have been prepared and characterized using TPR, XRD, TPO, TEM and CAEM techniques. Preparation procedures were established for each support system and were dependent upon the oxidation characteristics of the particular carbonaceous solid. The ease of the reduction of copper oxide to metallic copper was found to be dependent upon the nature of the carbonaceous supports as well as the possible interactions between these two components. It was postulated that the epitaxial relationship that might exist between metallic copper and the diamond would make it easy for copper oxide to be reduced to its metallic state on this support. Attack of the graphite surface occurs in the presence of copper species in hydrogen at low temperatures. This behavior is rationalized according to the notion that dissociation of molecular hydrogen takes place on Cu2O and the active atomic species “spill-over” onto the graphite and undergo reaction with the π-electrons of the basal plane resulting in the creation of pits in the surface. In-situ electron diffraction highlighted the changes in the chemical state of copper species. Cu2O was found to be stabilized at certain stages of the reaction possibly due to its interaction with the carbonaceous supports. It is suggested that this type of copper species might exhibit some unique catalytic behavioral patterns.

High surface area (> 100 m2 · g−1) SiC doped with zirconium was prepared by the gas-solid reaction. The material was made up of three phases: β-SiC, covered by ZrO2 and an amorphous phase composed of Si, Zr and O. The characterization of the sample was performed by means of powder X-ray diffraction (XRD), surface area and porosity measurements by the BET method, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM). Preliminary catalytic tests, the standard n-C7 isomerization on supported MoOxCy showed that this new support was at least as effective as pure SiC.

A series of γ-Al2O3 and SiO2 supported tungsten carbides was synthesized by the temperature programmed reaction of supported tungstates with CH4/H2 mixtures. The three known phases, W2C, WC and WC1−x, were evaluated as butane dehydrogenation catalysts. The microstructure and composition of the supported carbides depended on the loading and final synthesis temperature. The low and medium loaded materials were x-ray amorphous suggesting highly dispersed carbide domains on the support. The high loaded materials possessed small crystallites of W2C, WC or WC1-x. The supported carbides were as active as a commercial dehydrogenation catalyst with comparable selectivities in several cases. The butane conversion activity decreased in the following order: W2C > WC > WC1-x. The dehydrogenation selectivity decreased as the activity increased. The results suggest that there were two different types of sites, those catalyzing the selective dehydrogenation of butane and those capable of butane hydrogenolysis. The activity of these latter sites declined significantly with time on stream. We believe the hydrogenolysis activity was due to acid sites on the supported carbides.

Early transition metal carbides and nitrides have been shown to be active for the hydrotreatment of model compounds and petroleum crudes. In this paper we describe our investigations of the structural and compositional properties of γ-Al2O3-supported molybdenum carbides and efforts to correlate these properties with their pyridine and quinoline hydrodenitrogenation (HDN) activities. The HDN activities of the materials scaled linearly with the loading and oxygen chemisorptive uptake. Oxygen chemisorption results also suggested that the molybdenum carbide particles were highly dispersed and perhaps raft-like. Using temperature programmed desorption and infrared spectroscopy of carbon monoxide, we were able to identify two types of sites on the carbides; sites “on top” of the particle and sites at the perimeter. We have tentatively concluded that the most active sites for HDN were “on top” of the supported carbide particles.

Free-standing aluminum nitride (AlN) films were prepared by ammonia heat-treatment of pseudoboehmite [AIO(OH)] gels derived from an alumina sol. Supported films on sapphire substrates were also made by spin-coating the alumina sol, followed by ammonia nitridation. The conversion of the specimens to AIN as a function of heat-treatment temperature was studied using various characterization techniques.

For the free-standing films, X-ray diffraction (XRD) showed that upon ammonia treatment, the specimens were first transformed from pseudoboehmite to η-alumina and finally to A1N above 1000°C. 27Al magic-angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy confirmed the appearance of Al[N]4 coordination at 1000°C, indicative of AlN. Complete conversion to AlN was achieved after 5 hour nitridation at 1200°C. The 1200°C heat-treated films consisted of crystallites of AlN in the size range 0.01 − 0.15 μm, with pores between 0.03 − 0.25 μm in diameter, as observed by TEM/electron diffraction analyses. These films had BET surface areas of approximately 25 m2/g. Nitridation of the supported films to AlN occurred at lower temperatures (∼900°C), as shown by secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS).

A nanostructured aluminum nitride powder prepared by sol-gel type chemical synthesis is analyzed by Fourier transform infrared spectrometry. The surface acidic and basic sites are probed out by adsorption of several organic molecules. Resulting from the unavoidable presence of oxygen, the aluminum nitride surface is an oxinitride layer in fact, and its surface chemistry should present some analogies with alumina. Therefore, a thorough comparison between the acido-basicity of aluminum nitride and aluminum oxide is discussed. The remaining nitrogen atoms in the first atomic layer modify the acidity-basicity relative balance and reveals the specificity of the aluminum nitride surface.

In this paper we describe the synthesis, morphologies, and catalytic properties of vanadium nitrides prepared via the temperature programmed reaction (TPR) of V2O5 (7 m2/gr) with ammonia. This reaction yielded VN with surface areas up to 60 m2/gr. Among the synthesis parameters, the molar hourly space velocity had the most significant influence on the BET surface areas, crystallite sizes, and pore size distributions. Thermal gravimetric analysis (TGA) and x-ray diffraction indicated that the solid state reaction of V2O5 with NH3 occurred as follows: V2O5 → V4O9 → VO2 → V2O3 → VO0.9 → V.N. Scanning electron microscopy revealed that the surface roughness increased as the transformation proceeded, which corresponds to the increase in surface area. The vanadium nitrides were exceptionally active for the dehydrogenation of butane with selectivities greater than 98 % to C4 olefins. The deactivation was very slow for these catalysts. The reaction rates increased with increasing surface area and were comparable to that of a commercial Pt-Sn/Al2O3 dehydrogenation catalyst.

Controlled desilication of ZSM-5 zeolite increases the acid site density of its acid form. A subsequent treatment with steam at 300 °C results in a material with single-sized and slightly larger micropores when compared to the parent zeolite. This is likely the cause of a second increase of the yields of MTBE (methyl terbutyl ether) and ethylene when the steamed desilicated zeolite is used as catalyst in the MTBE synthesis and ethanol dehydration, respectively. Steam appears to be capable of “healing” the zeolite framework at a temperature much lower than that normally required when the desilicated ZSM-5 zeolite is solely heated in air.

In this work a series of [Zn1−xAlx(OH)2](CO3)x/2·mH2O; x=0.25−0.66 were prepared at constant pH in order to study the effect of the thermal treatment on their crystalline srtucture. It was found that is possible to obtain pure Zn-Al hydrotalcite materials within a x = 0.25−0.50 range in comparison with Mg-Al hydrotalcites which yield pure phases in more restricted x ranges (0.25−0.33). All Zn-Al hydrotalcites lost their layered structure at temperatures above 473 K being less stable than their parental Mg-Al hydotalcite (623 K). Specific surface areas of these materials depended strongly on the Zn/Al ratio and calcination temperature, ranging from 280 to 20 m2/g. ZnO and ZnAl2O4 compounds were detected as the calcination products at temperatures higher than 873 K.

A titanium-boron binary oxide has been prepared by the sol-gel method and characterized using SEM, TEM, UV-VIS reflectance, and X-ray diffraction spectroscopies. These measurements indicated that the obtained Ti/B gel with no treatment exhibited an amorphous structure. After calcination in O2, the crystalline structure of titanium oxide species in the Ti/B binary oxide was changed while boron oxide species maintained in the state of amorphous. Titanium oxide species in the Ti/B binary oxide calcined at 673 K showed an anatase phase of TiO2, and changed with the calcination temperatures from anatase phase to rutile phase. The Pt loaded Ti/B photocatalysts in aqueous suspension system decomposed water stoichiometrically under UV-irradiation. Their photocatalytic activities decreased with increasing the calcination temperature, indicating the photocatalytic activities of the Ti/B binary oxides were depended on the crystal phase of titanium oxide in the Ti/B photocatalysts.

Systems containing metal ions stabilized in Si-O matrix are perspective for the development of new selective oxidation catalysts. The comparative study of the following catalysts were performed to elucidate the influence of structural factors on the catalytic properties of iron systems in the reactions H2O oxidation, H2O2 decomposition, N2O decomposition and 16O2 ⇔ O18O2 exchange. The following catalysts were used: A) carbon-supported polyhedral silsesquioxanes (PhSiO1.5)12(MO)nL ((MO)n = (FeO)6, Fe2Ni4O6, (NiO)6; L=ROH, H2O); B) Fe-containing zeolites ZSM-5 (0.1−3.5 wt.% Fe); C) hydroxocomplexes Fe4(OH)10SO4 and NaFe3(OH)6(SO4)2). Fe silsesquoxanes in contrast to Fe-ZSM5 do not activate N2O decomposition and isotopie oxygen exchange. However, they are active in H2O oxidation and H2O2 decomposition. It was found that both reactions proceed via nonradical mechanism in the presence of Fe heterogeneous catalysts. For H2O oxidation active site contains at least two Fe atoms situated at appropriate distance from each other. H2O2 decomposition can proceed with participation either one and two metal active sites.

X-ray photoelectron spectroscopy of pure and K chemisorbed VxOy/TiO2 powders are reported. Core-line and valence band spectra suggest the presence of vanadium open shell ions on the pure VxOy/TiO2 interface, whereas potassium vanadate seems to form after K chemisorption. That results in the presence of a significant amount of gap states, with vanadium character, just above the O2p band edge, for the pure VxOy/TiO2 powder, while K chemisorption, reducing significantly the open shell vanadium ions, quenches the gap emission in the XPS valence band spectra.

Heteropoly acids, HPA are well known solid acid and oxidation catalysts that find application in hetergeneous and homogeneous reactions. In the former, surface area and stability problems are diminshed by supporting the HPA. Typical supports include oxide substrates and porous carbon materials. The HPA's show some instability on these supports however. In this work, we demonstrate that HPA encapsulated in sol-gel silica matrices show enhanced catalytic performance without compromising the catalytic activity of the HPA. In addition, the specific role of the support in the catalytic process is described as well.

The synthesis of MCM-41 in a highly acidic medium has been optimised. It was found that the relatively low-cost synthesis gave a material with extremely high surface areas (more than 1500 m2/g) compared to that obtained in conventional alkaline synthesis (ca 1100 m2/g). Judged by the short synthesis time, high yield, enhanced adsorption capacity, large particle size and thermal stability, the acid route to MCM-41 appears promising from an industrial point of view. Additional cost-reducing steps, such as the recycling of the “acid matrix” and the reduction of the volume of the water/acid mixture were successfully applied.

The MCM-41 family of surfactant templated materials were used as model mesoporous sorbents for storage of light hydrocarbon vapors, by utilizing the phenomenon of capillary condensation. The experimental data show that, because of the fine tunability of MCM-41 type materials (mesopore diameter was controlled between 20 and 40 Å), the onset of capillary condensation can be controlled, and from here the point of achieving liquid-like fluid density in the pores. Such a unique characteristic makes the MCM-41 family of materials a potential media for sorptive fractionation.

This paper reports on the synthesis of four series of mesoporous aluminosilicate molecular sieves (Al-MCM-41) and their catalytic applications. Four different aluminum compounds were examined as Al source in the hydrothermal synthesis of the mesoporous aluminosilicates of MCM-41 type, including pseudo boehmite (alumina), aluminum sulfate, aluminum isopropoxide, and sodium aluminate. Each Al source was examined at three different feed Si/Al ratios in the synthesis. XRD results show that there are differences in the dioo-spacings for the samples prepared with different Al sources: sodium aluminate > Al isopropoxide > Al sulfate > pseudo boehmite. Such differences reveal that Al incorporation in the framework increases in the following order: pseudo boehmite < Al sulfate < Al isopropoxide < sodium aluminate. XRD also indicates that the synthesized Al-MCM-41 samples have different crystallinity. 27Al NMR and 29Si NMR reveal that most of the Al species in the samples prepared with pseudo boehmite were present in octahedral coordination, whereas in other samples nearly all the Al species are tetrahedral (in the framework). The acid characteristics of the synthesized molecular sieves were characterized by temperature-programmed desorption of n-butylamine, and by using 1,3,5-triisopropylbenzene hydrocracking as probe reaction. The results of TPD and probe reaction clearly indicate that the Al source used for synthesis has a major impact on the acidic and catalytic properties of Al-MCM-41. The samples prepared with Al isopropoxide and sodium aluminate are better as catalysts than those with Al sulfate and pseudo boehmite. We also explored the potential of mesoporous molecular sieves as support for noble metal hydrogenation catalysts and metal sulfide-based hydrotreating catalysts. Pd and Pt-loaded mesoporous molecular sieves were prepared and applied for hydrogenation of naphthalene and phenanthrene. The results show that mesoporous molecular sieve-supported catalysts are much more active than alumina- and titania-supported catalysts. The data for dibenzothiophene hydrodesulfurization suggest that Al-MCM-41 supported Co-Mo may be effective for deep desulfurization of distillate fuels.