Showing papers by "Tanya Tsoncheva published in 2012"

Optimization of the preparation procedure of cobalt modified silicas as catalysts in methanol decomposition

Abstract: Novel modified “chemisorption–hydrolysis” technique and conventional “incipient wetness impregnation” procedure were compared for loading of cobalt species on mesoporous silica supports. Effect of cobalt amount, pH of the precursor solution, duration of the “chemisorption” procedure and pre-treatment medium, as well as topological characteristics of the mesoporous silica support were investigated. The state of the loaded cobalt species was studied by XRD, FTIR, FTIR of adsorbed pyridine, UV–vis, XPS and TPR methods and their catalytic properties were elucidated in methanol decomposition to hydrogen and carbon monoxide. The “incipient wetness impregnation” technique facilitates the formation of finely dispersed spinel cobalt oxide species. Their catalytic activity could be significantly increased by hydrogen pretreatment, but the effect is more pronounced when mesoporous silica with ordered pseudo 1D pore structure (SBA-15) is used as a support. The modified “chemisorption–hydrolysis” procedure facilitates the formation of strongly interacting with the support cobalt species, which are stable under the reduction conditions. Their properties could be regulated during the modification procedure, by varying the cobalt content and pH of the impregnated solution as well as by the duration of the “chemisorption” procedure.

Size controlled copper nanoparticles hosted in mesoporous silica matrix: Preparation and characterization

Abstract: A novel preparation strategy was performed to obtain uniform and size controlled, in a large scale, copper nanoparticles, hosted into mesoporous silica matrix. The method includes the initial deposition of finely dispersed copper nanoparticles, using a conventional incipient wetness impregnation of silica matrix with small amount of nitrate precursor and consecutive pretreatment in oxidation and reduction atmosphere. The further controlled growing of the loaded copper particles was performed in rotary bed reactor by step-wise deposition of copper over them by OMCVD techniques, using bis- (hexafluoroacetylacetonate) copper (II) hydrate as a precursor. A complex of physicochemical methods (TEM, Nitrogen physisorption, TPR and TPRD-MS measurements, UV-Vis and FTIR spectroscopy of adsorbed CO) was used for characterization of the samples. The catalytic properties of the obtained materials were investigated in methanol decomposition to CO and hydrogen. A mechanism of the copper particles growing was discussed. Size dependent effects of the redox and catalytic properties of the loaded copper particles which are strongly affected by their location in the silica porous structure are assumed.

11C-Radiolabeling study of methanol decomposition on chromium modified SBA-15 silica

Abstract: Chromium modified mesoporous SBA-15 silica was prepared by incipient wetness impregnation of the silica support with toluene solution of chromium acetylacetonate. Powder X-ray diffraction, Nitrogen physisorption, FTIR, UV–Vis and XPS techniques as well as temperature programmed reduction with hydrogen were used for the characterization of the obtained materials. The catalytic behaviour of the samples was tested in methanol decomposition to CO and hydrogen. Novel catalytic radio isotopic based method was applied for the elucidation of the role of different chromium surface species in the catalytic process. This approach is based on the selective coverage of the surface active sites with 11C- and 12C-methanol and simultaneous observation of the products of their conversion. It was found that the supported active phase represents a complex mixture of chromium oxide nanoparticles (mainly Cr2O3, CrO3) and anchored to the silica surface mono- and polychromate structures. It was established that these species differ significantly in their catalytic behavior during the methanol decomposition and the reaction mechanism of the formation of different products was discussed.