Showing papers by "Tanya Tsoncheva published in 2011"

Structure and catalytic activity of hosted in mesoporous silicas copper species: Effect of preparation procedure and support pore topology

Abstract: Copper modifications of ordered mesoporous materials with different pore topology (SBA-15 and KIT-6) were prepared by incipient wetness impregnation and “chemisorption–hydrolysis” methods and further oxidative or consecutive oxidative/reductive treatment. The samples were characterized by nitrogen physisorption, XRD, XPS, FTIR, UV–vis and TPR–TG techniques. The ordered structures and the “chemisorption–hydrolysis” post synthetic method provide the formation of homogeneously dispersed in the mesopores copper species. The “chemisorption–hydrolysis” modification of the silicas with more opened 3D ordered structure (KIT-6) provides the formation of highly active catalysts, but their activity could be easily suppressed after the treatment under the reduction medium.

Structure sensitivity of methanol decomposition on Ni/SiO2 catalysts

Abstract: Three different silica-supported nickel samples were prepared by successive adsorption, reduction, and passivation (SARP) of nickel. The materials obtained were characterized by various techniques (TEM, XRD, H2 chemisorption, FTIR spectroscopy of adsorbed CO, FMR). Metal nickel particles were uniformly distributed by size with all samples. With increasing the number SARP cycles (1, 3, and 5, respectively) the metal concentration (3.6, 7.6, and 12.6 wt%, respectively) and the mean particle size (4–5, ca. 6 and ca. 7 nm, respectively) also increased without substantial increase of the number of metal particles. The samples were tested as catalysts in methanol decomposition to CO and H2. It was found that this reaction was structure sensitive and the turn-over frequency decreased with the particle size increase. In contrast, the secondary interaction between the reaction products, i.e., CO methanation (occurring above 515 K) appears to be structure insensitive.

Coordination state of Cu+ ions in Cu-[Al]MCM-41

Abstract: A Cu-[Al]MCM-41 sample was studied by FTIR spectroscopy of probe molecules (CO and NO) and methanol conversion test reaction. It was found that the parent MCM-41 material was characterized by the practical absence of strongly acidic hydroxyl groups (typical of zeolites), but possessed some hydroxyls with a moderate acidity. Introduction of copper to the material by a procedure typical of ion-exchange did not affect the OH groups of MCM-41. However, reduction of the deposited Cu2+ ions resulted in formation of Cu+ ions with a high coordinative unsaturation (typical of Cu+ in zeolites): they were able to adsorb up to three CO molecules each. Adsorption of 12C16O–13C18O mixtures was used to prove the polycarbonyl structures. The possible application of Cu-[Al]MCM-41 in environmental catalysis is discussed.