An XPS study of the oxidation of noble metal particles evaporated onto the surface of an oxide support in their reaction with NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The interaction of the model catalysts Rh/Al₂O₃, Pd/Al₂O₃, Pt/Al₂O₃, and Pt/SiO₂ with NO _x (mixture of 10 Torr of NO and 10 Torr of O₂) was studied by X-ray photoelectron spectroscopy (XPS). Samples of the model catalysts were prepared under vacuum conditions as oxide films ≥100 Å in thickness on tantalum foil with evaporated platinum-group metal particles. According to transmission electron microscopic data, the platinum-group metal particle size was several nanometers. It was found by XPS that the oxidation of Rh and Pd nanoparticles in their interaction with NO _x occurs already at room temperature. The particles of platinum were more stable: their oxidation under the action of NO _x was observed at elevated temperatures of ～300°C. At room temperature, the interaction of platinum nanoparticles with NO _x hypothetically leads to the dissolution (insertion) of oxygen atoms in the bulk of the particles with the retention of their metallic nature. It was found that dissolved oxygen is much more readily reducible by hydrogen than the lattice oxygen of the platinum oxide particles.     

Multi‐instrument characterization of the surfaces and materials in microfabricated,carbon nanotube‐templated thin layer chromatography plates. An analogy to ‘The Blind Men and the Elephant’

We apply a suite of analytical tools to characterize materials created in the production of microfabricated thin layer chromatography plates. Techniques used include X‐ray photoelectron spectroscopy (XPS), valence band spectroscopy, time‐of‐flight secondary ion mass spectrometry (ToF‐SIMS) in both positive and negative ion modes, Rutherford backscattering spectroscopy (RBS), and helium ion microscopy. Materials characterized include: the Si(100) substrate with native oxide: Si/SiO₂, alumina (35 nm) deposited as a diffusion barrier on the Si/SiO₂: Si/SiO₂/Al₂O₃, iron (6 nm) thermally evaporated on the Al₂O₃: Si/SiO₂/Al₂O₃/Fe, the iron film annealed in H₂ to make Fe catalyst nanoparticles: Si/SiO₂/Al₂O₃/Fe(NP), and carbon nanotubes (CNTs) grown from the Fe nanoparticles: Si/SiO₂/Al₂O₃/Fe(NP)/CNT. The Fe films and nanoparticles appear in an oxidized state. Some of the analyses of the CNTs/CNT forests appear to be unique: (i) the CNT forest appears to exhibit an interesting ‘channeling’ phenomenon by RBS, (ii) we observe an odd–even effect in the SIMS spectra of C_n^‐ species for n = 1 – 6, with the n ≥ 6 ions showing a steady decrease in intensity, and (iii) valence band characterization of CNTs using X‐radiation is reported. Initial analysis of the CNT forest by XPS shows that it is 100 at.% carbon. After one year, only ca. 0.25 at.% oxygen is observed. The information obtained from the combination of the different analytical tools provides a more complete understanding of our materials than a single technique, which is analogous to the story of ‘The Blind Men and the Elephant’. The raw XPS and ToF‐SIMS spectra from this study will be submitted to Surface Science Spectra for archiving. Copyright © 2013 John Wiley & Sons, Ltd.     

Synthesis of Fe2O3 Species Embedded in a Silica Xerogel Matrix: A Comparative Study

In this work we report composites of -Fe₂O₃/SiO₂ and -Fe₂O₃/SiO₂ starting from three different iron precursors: iron nitrate, iron chloride and nanometric Fe particles prepared by aqueous chemical reduction. The composite samples were prepared by the sol-gel method and were ground in order to produce powders, heat treated at different temperatures under atmospheric conditions. The powder samples were characterized by X-Ray diffraction, IR absorption, and UV-visible spectroscopy. A specific composite can be produced depending on the temperature used for reaction.     

Catalysts based on cordierite modified with transition metal oxides

Catalysts active in ammonia oxidation have been obtained by the substitution of transition metal (Mn, Fe, Co, Ni, and Cu) ions for Mg ions in the cordierite structure 2MgO · 2Al₂O₃ · 5SiO₂ at 1100°C. Their phase composition, texture, and activity depend on the type and amount of introduced transition metal oxide. The Mn- and Cu-containing catalysts, which consist of substituted cordierites 2(Mg_{1 ? x} M _x )O · 2Al₂O₃ · 5SiO₂ and Mn₂O₃ or CuO crystallites located on their surface, are most active in ammonia oxidation. The catalysts are characterized by a small specific surface area and have large pores, whose total volume is small. The Fe-containing catalysts consist of the Fe-substituted cordierite phase and particles of an iron oxide phase. These particles are mostly located in internal pores of the catalysts and are, therefore, hardly accessible to ammonia molecules. The introduction of Co or Ni oxide leads to the formation of a low-active spinel phase rather than the cordierite phase.     

Synthesis of novel mesoporous Al2O3 microspheres with flower-like structure

Using glucose as a structuring additive and aluminium nitrate as the Al precursor, a novel kind of mesoporous Al₂O₃ microspheres with flower-like structure were synthesized hydrothermally at 180°C for 20 h. When the synthesis temperature was lowered to 140°C, the carambola-like Al₂O₃ can be synthesized. This approach is convenient and simple, and flower-like Ce-Al₂O₃ and La-Al₂O₃ spheres have also been prepared in this way. It may be applied to synthesize other metal oxides when suitable precursor salts are used. From an analysis of the experimental results, a mechanism for the formation of the flower-like Al₂O₃ spheres has been proposed and discussed.      

Stoichiography in the study of spatial heterogeneity of the chemical composition and structure of thin films and nanostructured systems

We present the principles of stoichiography and a reference-free stoichiographic differential (separating) dissolution method used to study the composition and structure of thin films and nanostructured systems: HTS films with 123 different compositions, Al–Au–Sn–Co–Mn, Si/SiO₂/Ni(Cr)–Cu–Cu2S, Cr–Cu–S, and Cu–S multilayer films, Bi–Ti–O films on Ru/SiO₂/Si, Mn_1–xZn _x S, and ZnS–EuS supports, and also nanostructured manganese ferrite in borate glass matrices, nanodisperse composite sorbents and the Co–Si–Pt–O/Al₂O₃ catalyst modified by Pt nanoparticles, and oxide catalyst precursor Fe₂Co/Al₂O₃ for the synthesis of carbon nanotubes.     

Propane combustion over supported Pd catalysts

We prepared Pd catalysts supported on various metal oxides, viz. γ-Al₂O₃, α-Al₂O₃, SiO₂–Al₂O₃, SiO₂, CeO₂ and TiO₂ by an incipient wetness method and applied them to propane combustion. Several techniques: N₂ physisorption, inductively coupled plasma-atomic emission spectroscopy (ICP-AES), CO chemisorption, temperature-programmed reduction (TPR) and temperature-programmed oxidation (TPO) were employed to characterize the catalysts. Pd/SiO₂–Al₂O₃ showed the least catalytic activity at high temperatures among Pd catalysts supported on irreducible metal oxides, viz. SiO₂, Al₂O₃ and SiO₂–Al₂O₃. Pd/γ-Al₂O₃ was much superior for this reaction to Pd/α-Al₂O₃. The Pd catalyst supported on reducible metal oxides (CeO₂ and TiO₂) with a less specific surface area showed the higher catalytic activity compared with that supported on reducible metal oxides with a higher specific surface area, even though the former had a less Pd dispersion than the latter. In the case of Pd/SiO₂–Al₂O₃, the initially reduced Pd catalyst was superior to the fully oxidized one. The oxidation of metallic Pd occurred in the presence of O₂ with increasing reaction temperature, which resulted in the change in the catalytic activity.     

Catalytic reduction of nitrogen dioxide with propene in the presence and absence of oxygen over various metal oxides

Over metal oxides (SiO₂, ZrO₂, Al₂O₃, MgO, La₂O₃, and CaO) with-H values of metal oxide formation higher than 700 kJ/mol, C₃H₆ reacts with NO₂ in preference to O₂.     

Thermal behavior of Co<Subscript>x</Subscript>Fe<Subscript>3−x</Subscript>O<Subscript>4</Subscript>/SiO<Subscript>2</Subscript> nanocomposites obtained by a modified sol–gel method

The thermal behavior of Co_xFe_3?xO₄/SiO₂ nanocomposites obtained by direct synthesis starting from nonahydrate ferric nitrate and hexahydrate cobalt nitrate in different ratios with and without the addition of 1,4-butanediol was studied. For the synthesis of Co_xFe_3?xO₄ (x = 0.5–2.5) dispersed in the silica matrix a wide Co/Fe molar ratio was used. The decomposition processes, formation of crystalline phases, gases evolvement and mass changes during gels annealing at different temperatures were assessed by thermal analysis. The absence of succinate precursor and a low mass loss were observed in the case of the gel obtained in the absence of 1,4-butanediol. In case of gels obtained using a stoichiometric ratio of Co/Fe, no clear delimitation between Co and Fe succinates was observed, while for samples with a Fe or Co excess, the formation of the two succinates was observed. The evolution of the crystalline phase after annealing (673, 973 and 1273 K) investigated by X-ray diffraction analysis and Fourier transformed infrared spectrometry revealed that in samples with Fe excess, stoichiometric Fe/Co ratio or low Co excess, the cobalt ferrite (CoFe₂O₄) was obtained as a single phase, while in samples with higher cobalt excess, olivine (Co₂SiO₄) as a main phase, cobalt oxide and CoFe₂O₄ as secondary phases were obtained after annealing at 1273 K. The SEM images confirmed the nanoparticles embedding in the silica matrix, while the TEM and X-ray diffraction data showed that the obtained nanoparticles’ size was below 10 nm in most samples.     

Luminescence Properties of Mn2+-Doped Sol-Gel Glasses

Mn²⁺-doped 1Al₂O₃-99SiO₂ glasses have been prepared by a sol-gel method and their photoluminescence (PL) properties have been studied for the first time. The effect of ZrO₂ and TiO₂ on the luminescence properties has also been studied. In addition, the PL of Mn: 1Al₂O₃-99SiO₂ is compared with Mn:SiO₂. The emission spectra of all the samples containing Al₂O₃ show a band around 620 nm, and the sample without Al₂O₃ shows two bands around 620 and 650 nm. These emission bands are all assigned to the ⁴T₁ ⁶A₁ transition of octahedrally coordinated Mn²⁺ · ZrO₂ and TiO₂ have fluorescence quenching effect. The relative fluorescence intensity of Mn²⁺-doped sol-gel 1Al₂O₃-99SiO₂ is much stronger than that of Mn²⁺-doped sol-gel SiO₂. The difference of the emission wavelength between host materials is explained in terms of the ligand field effect.     

<Emphasis Type="Italic">In situ</Emphasis> XPS study of the size effect in the interaction of NO with the surface of the model Ag/Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/FeCrAl catalysts

The interaction of NO with the surface of model Ag/Al₂O₃/FeCrAl catalysts containing Ag nanoparticles of different size (1 and 3 nm) was studied. The use of the Auger parameter α_Ag (E _b(Ag3d_5/2) + E _kin(Ag MVV)) made it possible to reliably identify the change in the chemical state of silver cluster upon their interaction with О₂ and NO. The oxygen treatment leads to the oxidation of small Ag nanoparticles (1 nm) and formation of AgO _x clusters resulted in the intensive formation of nitrite—nitrate structures on the step of the interaction with NO. These structures are localized on both the silver clusters and Al₂O₃ surface. An increase in the size of Ag⁰ nanoparticles to 3 nm results in an increase in the stability of these structures and impedes the Ag⁰ → AgO _x transition, due to which the formation of surface groups NO₂ ^–/NO₃ ^– is suppressed. The data obtained make it possible to explain the dependence of the activity of the Ag/Al₂O₃ catalysts in the selective reduction of NO on the Ag nanoparticle size.     

Effect of the nature of the salt precursor of an oxide-hydroxide sorbent on the sorption of oxalate ions

Generalizations are made on the effect of the nature of a precursor (the original salt of a metal) on the sorption activity of hydrogels of oxidehydroxides (OHes) towards oxalate ions using the example of an OH obtained by the alkaline hydrolysis of chloride, perchlorate, and sulfate of Fe(III); chloride, sulfate, and nitrate of Al; and nitrate of Zr(IV). It is established that the sorption of C₂O ₄ ^2? on the studied OHes is described by the Langmuir equation. We find that the sorption activity depends on the nature of the precursor: Al₂(SO₄)₃ > Al(NO₃)₃ > AlCl₃ > ZrO(NO₃)₂ > Fe₂(SO₄)₃ > FeCl₃ > Fe(ClO₄)₃.     

Influence of calcination and lithium promotion on the surface properties of oxide supports

Thermal treatment and the addition of lithium influence the surface area of the oxides SiO₂, Al₂O₃ and MgO. A calcination temperature 1073 K causes a significant decrease of the surface area of SiO₂ and Al₂O₃; the same is not observed in case of MgO. Systems Li/MgO and Li/SiO₂ are characterized by a much smaller specific surface area than pure oxides thermally treated at the same temperature.     

Monolithic FeO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for ammonia oxidation and nitrous oxide decomposition

(1.2–8.3)%FeO_х/Al₂O₃ monolith catalysts have been prepared by impregnating alumina with aqueous solutions of iron(III) nitrate and oxalate and have been tested in NH₃ oxidation and in the selective decomposition of N₂O in mixtures resulting from ammonia oxidation over a Pt–Rh gauze pack under conditions of nitric acid synthesis (800–900°C). In the case of the support calcined at 1200°C, the catalyst is dominated by bulk Fe₂O₃ particles localized on the Al₂O₃ surface. The activity of these samples in both reactions decreases with a decreasing active component content, thus limiting the potential of Fe₂(C₂O₄)₃ · 5H₂O, an environmentally friendlier but poorly soluble compound, as a substitute for Fe(NO₃)₃ · 9H₂O. Decreasing the support calcination temperature to 1000°C or below leads to the formation of a highly defective Fe–Al–O solid solution in the (1.2–2.7)%FeO_х/Al₂O₃ catalysts. The surface layers of the solid solution are enriched with iron ions or stabilize ultrafine FeO_х particles. The catalytic activity of these samples in both reactions is close to the activities measured for ~8%FeO_х/Al₂O₃ samples prepared using iron nitrate.     

Complex specific heat capacity of two nanocomposite systems

Thermal investigations on two selected model-nanocomposites have been made. They differ with regard to the type of the anorganic nanoparticles that have been filled into an organic oligomer matrix. The properties of nanocomposites may vary between those of a simple mixture of independent components and those of a system, where specific interfacial interactions between the constituting parts lead to ‘new’ properties. Depending on the type of the nanoparticles filled into the matrix, the resulting properties might be closer to one or to the other extreme. We used temperature modulated differential scanning calorimetry (TMDSC) to investigate a matrix of the oligomer diglycidyl ether of bisphenol A (DGEBA) filled either with SiO₂- or Al₂O₃-nanoparticles. The dependence of the complex specific heat capacity () on the concentration of nanoparticles shows a clear difference between the two systems as far as the glass transition of the oligomer is concerned. The SiO₂ composite seems to behave more like a simple mixture, whereas the Al₂O₃ composite shows ‘new’ properties.     

The influence of the method of addition of Al2O3 to 3YSZ material on its thermal and electrical properties

The properties of tetragonal yttria-stabilized zirconia composites with the small addition of alumina (Al₂O₃?Y₂O₃?ZrO₂ composite) obtained on two ways of synthesis were studied in terms of usability for anode materials in solid oxide fuel cell. Both methods were based on citric synthesis: in the first one, Al₂O₃ was coprecipitated with the tetragonal ZrO₂ in the form of citrate by citric acid, while in the second Al₂O₃ was impregnated in the form of aluminium nitrate precursor on tetragonal ZrO₂ matrix. The obtained materials were analysed by X-ray diffraction, dilatometry and impedance spectroscopy. The results of measurements show that regardless of synthesis method, the addition of Al₂O₃ influences the conductivity of samples by increasing their grain boundaries conductivity as an effect of removing of SiO₂ and decreasing of conductivity activation energy. The impregnation of Al₂O₃ on tetragonal ZrO₂ and sintering of this material above shrinking temperature cause, however, radical decrease of porosity of materials, which disqualifies these samples as anode materials. In the case of samples obtained by coprecipitation the significant decrease of porosity is not observed.     

Synthesis of Nickel Supported Catalysts for Hydrogen Production by Sol-Gel Method

SiO₂ and Al₂O₃ supported Ni catalysts were synthesized in the form of xerogels: the SiO₂ based materials were prepared starting from Ni propionate or glycolate salts and reacting them with tetraethoxysilane (TEOS) in propionic acid, Si(ethylene glycolate) or sodium silicate. The Al₂O₃ supported catalysts were prepared similarly from Ni propionate salts with Al iso-propoxide salts. Narrow metal particles and strong metal support interactions are observed in the sol-gel catalysts. The metal dispersion was higher for Al₂O₃ based materials than the SiO₂ ones and it deeply depends on the Ni precursor for the silica supported Ni. Wet impregnated oxides with similar Ni loading have higher metal surface area than those from sol-gel processing. The influence of surface differences on the catalytic activity of the materials was studied following the CH₄ and CO₂ reaction in dry reforming conditions by pulse reaction tests.     

Liquid phase selective hydrogenation of phenol to cyclohexanone over Ru/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocatalyst under mild conditions

Highly monodispersed ruthenium nanoparticles were prepared via wet impregnation technique using RuCl₃ · nH₂O as a precursor. Ru nanoparticles were supported on Al₂O₃ to synthesize Ru nanocatalyst. The nanocatalyst was characterized by various techniques like XRD, SEM, TEM and BET analysis. The catalyst was used for hydrogenation of phenol under mild condition. The activity of the catalyst was checked by varying different parameters such as reaction temperature, time, H₂ partial pressure, metal loading and catalyst amount. The catalyst was recovered from product and reused up to four times without significant loss in its catalytic activity. After a reaction time of 1 h, Ru/Al₂O₃ nanocatalyst showed high reactivity (82% conversion) and selectivity to cyclohexanone (67%) at 80°C and 20 bar hydrogen pressure.     

Synthesis and properties of mullite and cordierite aerogels

This work deals with the preparation of aluminosilicate aerogels, especially mullite (3Al₂O₃·2SiO₂) and cordierite (2MgO·2Al₂O₃·5SiO₂) aerogels, from the cohydrolysis of tetraethoxysilane and chelated aluminum-secbutylate; in the case of cordierite magnesium nitrate was added. The influence of various preparation conditions on the aerogel synthesis is described. Crystallization and sintering behavior of mullite aerogels supercritically dried in acetone or alcohol differs from that one of mullite aerogels dried in CO₂. During non-isothermal heat treatment the former show a drastically reduced shrinkage compared to the latter. This behavior can be explained by a phase separation during the high temperature autoclaving process. In cordierite aerogels the crystallization of tetragonal mullite at about 1000°C is observed, while the correspondent xerogels show the crystallization of - and - cordierite between 1000 and 1100°C. On the other hand sintering is promoted in cordierite aerogels, which is due to the content of MgO.     

Fe K‐Edge X‐ray Absorption Fine Structure Determination of γ‐Al2O3‐Supported Iron‐Oxide Species

The structure of FeO_x species supported on γ‐Al₂O₃ was investigated by using Fe K‐edge X‐ray absorption fine structure (XAFS) and X‐ray diffraction (XRD) measurements. The samples were prepared through the impregnation of iron nitrate on Al₂O₃ and co‐gelation of aluminum and iron sulfates. The dependence of the XRD patterns on Fe loading revealed the formation of α‐Fe₂O₃ particles at an Fe loading of above 10 wt %, whereas the formation of iron‐oxide crystals was not observed at Fe loadings of less than 9.0 wt %. The Fe K‐edge XAFS was characterized by a clear pre‐edge peak, which indicated that the Fe?O coordination structure deviates from central symmetry and that the degree of Fe?O?Fe bond formation is significantly lower than that in bulk samples at low Fe loading (<9.0 wt %). Fe K‐edge extended XAFS oscillations of the samples with low Fe loadings were explained by assuming an isolated iron‐oxide monomer on the γ‐Al₂O₃ surface.