Tanya Tsoncheva

Studies on the state of iron oxide nanoparticles in MCM-41 and MCM-48 silica materials

Phase transformations in and the reductive and catalytic properties of mesoporous MCM-41 and MCM-48 silica molecular sieves modified with iron oxide were studied by X-ray diffraction, nitrogen physisorption, Mossbauer spectroscopy, temperature-programmed reduction, and methanol decomposition as a catalytic test. Their behavior is compared to that of the related bulk materials. Various types of iron species with different properties were identified.

Toluene oxidation on titanium- and iron-modified MCM-41 materials

Iron- and titanium-modified MCM-41 materials, prepared by direct synthesis at ambient temperature or wet impregnation technique, were investigated using X-ray diffraction (XRD), transmission electron microscopy (TEM), temperature-programmed reduction (TPR), UV-vis diffuse reflectance, Mössbauer and FT-IR spectroscopies. Their catalytic behavior was studied in total oxidation of toluene. Materials with high surface area and well-ordered pore structure were obtained. The increase of the titanium content (up to 50%) in the bisubstituted, iron and titanium containing materials leads to partial structure collapse of the silica matrix. Finely dispersed anatase particles were also formed during the impregnation procedure. The catalytic activity of the bisubstituted materials was influenced by the method of their preparation, but higher catalytic stability could be achieved, compared to iron monosubstituted one. The nature of the catalytic active sites is discussed.

Characterization of Cu/MCM-41 and Cu/MCM-48 mesoporous catalysts by FTIR spectroscopy of adsorbed CO

Adsorption of CO at 85 K on Cu/MCM-48 results in formation of Cu + (CO)2 species (2162 and 2121 cm −1 ) H-bonded CO (2156 cm −1 ) and a negligible amount of Cu 2+ –CO carbonyls. Decrease of the coverage is accompanied by decomposition of the OH–CO and Cu 2+ –CO species while the Cu + (CO)2 dicarbonyls loose one ligand and are converted into Cu + –CO species (2130 cm −1 ). The assignments are proved by co-adsorption of 12 CO and 13 CO. CO adsorption on the hydrogen-reduced sample provokes formation of Cu 0 –CO species characterized by a band at 2122 cm −1 . The latter are easily decomposed upon evacuation. Low temperature CO adsorption on Cu/MCM-41 leads to formation of the same species as observed with Cu/MCM-48. In this case, the concentration of the Cu + –CO species is higher and a significant amount of Cu 2+ –CO species is detected. These results suggest a higher dispersion of copper on MCM-41. The frequencies of the Cu + (CO)2 (2163 and 2127 cm −1 ) and Cu + –CO (2134 cm −1 ) species on Cu/MCM-41 are slightly blue shifted. The frequency of the Cu 0 –CO species (2125 cm −1 ) is also a little higher. In line with the higher copper dispersion, Cu/MCM-41 is superior to Cu/MCM-48 in its catalytic activity for the methanol decomposition to hydrogen and CO. The peculiarities of the samples depending on the preparation method are discussed.

Cobalt-modified mesoporous MgO, ZrO2, and CeO2 oxides as catalysts for methanol decomposition

Cobalt oxide-modified mesoporous CeO(2), ZrO(2), and MgO oxides and their SBA-15 silica analogues were prepared and characterized by XRD, TEM, N(2) physisorption, FTIR, and TPR-TG analysis. Their catalytic activity in methanol decomposition to CO and hydrogen was tested. The support effect on the state and catalytic behavior of the loaded cobalt oxide nanoparticles is discussed. The best catalytic activity and selectivity of methanol decomposition to CO and hydrogen are registered for Co/CeO(2).

Effect of the precursor and the preparation method on copper based activated carbon catalysts for methanol decomposition to hydrogen and carbon monoxide

Copper oxide supported on activated carbon catalysts, obtained by various preparation techniques, are compared in methanol decomposition to hydrogen and carbon monoxide. The favourable role of copper deposition from ammonia solution of copper carbonate is proved. The effect of the preparation conditions on the catalysts activity and stability as well as on the nature of the catalytic active complexes is studied.

Effect of the rehydration on the acidity and catalytic activity of SAPO molecular sieves

The structural changes occurring in the template-free SAPO-5 and SAPO-34 upon the rehydration are reversible and do not affect their acidity and catalytic activity. The rehydrated SAPO-37 loses irreversibly a considerable part of its initial crystallinity, surface area, acidity and catalytic activity. Nevertheless the remaining acid centers are stable against dehydrationrehydration cycles.

Oxidized carbon as a support of copper oxide catalysts for methanol decomposition to hydrogen and carbon monoxide

Abstract Copper oxide supported on oxidized activated carbon is investigated as a catalyst for methanol decomposition to H2 and CO. The influence of the medium of the precursor deposition on the state of the active phase is observed. The role of the chemical nature of the support in the formation of catalytic active complex is discussed.

Methanol conversion to hydrocarbons on porous aluminosilicates

Abstract Methanol conversion to hydrocarbons on aluminosilicates with different structures and composition is studied. The role of the complex catalytic centers described as ‘Bronsted acid site-conjugated oxygen atom’ on the process selectivity is discussed.

Synthesis and characterization of CuO and Fe2O3 nanoparticles within mesoporous MCM-41/-48 silica

Two simple methods for the synthesis of pure siliceous MCM-41 and MCM-48 silica materials, modified with CuO or Fe2O3 nanoparticles, located almost exclusively within the mesopores are presented. The modified samples were characterized by powder X-ray diffraction, nitrogen physisorption, temperature programmed reduction, X-ray absorption spectroscopy, (XANES/EXAFS) or Mossbauer spectroscopy and methanol decomposition as a catalytic test reaction. The existence of small, slightly disordered metal oxide nanoparticles was proved. The redox and catalytic behavior of the modified samples depending on the metal oxide, the preparation method used and the type of the mesoporous support are studied and compared to the corresponding bulk oxide phases.

Physicochemical and catalytic properties of grafted vanadium species on different mesoporous silicas

Vanadium modified mesoporous silicas type MCM-41, MCM-48, and SBA-15 are obtained by a solid state method. The samples are characterized and compared at the different steps of their preparation by X-ray diffraction, N(2)-physisorption, FTIR, UV-vis, XPS, and TG-TPR. Samples catalytic activity is tested in ethylacetate oxidation. Formation of various vanadium species, mainly isolated and small oligomeric ones, grafted to the support surface silanol groups, is observed. It is found that the state and the properties of the vanadium species depend on the porous characteristics of the silica host matrix. The nature of the catalytic active center in the ethylacetate oxidation is discussed.