Momtchil Dimitrov

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.

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.

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.

Methanol decomposition on Fe2O3/MCM-48 silica catalyst

Fe2O3/MCM-48 silica samples are characterized by high catalytic activity and methane selectivity in methanol decomposition. The catalytically active phase is substantially changed by the reaction medium and/or hydrogen pretreatment.

Silica supported copper and cerium oxide catalysts for ethyl acetate oxidation

The formation of active sites in the silica supported copper and cerium oxide bi-component catalysts for total oxidation of ethyl acetate was studied by Nitrogen physisorption, XRD, XPS, UV-Vis, Raman, FTIR of adsorbed CO spectroscopies and TPR. It was found that the interaction between the copper oxide nanoparticles and the supported on the silica ceria ones is realized with the formation of interface layer of penetrated into ceria lattice copper ions in different oxidative state. This type of interaction improves the dispersion of copper oxide particles and provides higher accessibility of the reactants to the copper active sites even at low copper amount.

Iron modified mesoporous carbon and silica catalysts for methanol decomposition

Iron modified silica and carbon mesoporous materials with similar textural characteristics are compared in methanol decomposition to H2, CO and CH4. The influence of the support on the phase composition and reductive properties of the catalysts is studied by Mössbauer spectroscopy and TPR with hydrogen.

Transition metal modified activated carbons from biomass and coal treatment products as catalysts for methanol decomposition

Copper, iron and cobalt supported on activated carbon materials are compared as catalysts in methanol decomposition in view of their potential application as intelligent carriers of hydrogen. The activated carbon supports were obtained from renewable agriculture waste (peach shell) or coal treatment by-products (coal tar pitch). The parent activated carbons and their transition metal modifications were characterized by nitrogen physisorption, XRD, UV–Vis, FTIR, Mössbauer spectroscopy and TPR in hydrogen, and the surface functional groups were determined by the Böhm method. It was assumed that the formation of transition metal modified activated carbon catalysts is a complex process which proceeds during the preparation procedure with the activity of the support and also during the catalysis by the influence of the reaction medium. The decisive effect of carbon basal planes over the texture and surface functionality of the support on the formation of transition metals active phase was assumed. Among the studied materials, cobalt modifications exhibited excellent catalytic activity and selectivity in methanol decomposition to H2 and CO despite the nature of the activated carbons used.

Autoreduction of Copper on Silica and Iron‐Functionalized Silica Nanoparticles with Interparticle Mesoporosity

Copper‐supported catalysts are of industrial importance in many catalytic processes. Mesoporous silica materials are of particular interest as green heterogeneous catalyst supports. In the present study we demonstrate the nature and reduction properties of copper oxide species, which are influenced by the peculiarity of the silica nanoparticles with interparticle mesoporosity (KIL family) and the presence of a second metal (iron) in the silica matrix. The copper‐containing KIL‐2 and FeKIL‐2 samples are prepared by incipient wetness impregnation. The reduction of copper oxide species is easier on the FeKIL‐2 supported sample in comparison to its KIL‐2 supported analogue, whereas the copper‐containing KIL‐2 sample shows higher catalytic activity in total toluene oxidation. The presence of iron in the FeKIL‐2 structure leads to autoreduction of copper followed by the redispersion and oxidation of metallic copper in the reaction medium; this results in the formation of different types of finely dispersed copper oxide species (<100 nm). The later species possess lower catalytic activity in toluene oxidation in comparison to species that are 100 nm in size and formed on KIL‐2.

Effect of support pore size on the structural and catalytic properties of iron and cobalt oxides modified SBA-1, SBA-15, MCM-41 and MCM-48 silica materials

Abstract Structural, reductive and catalytic properties of iron and cobalt oxides, supported on different mesoporous silicas have been characterized and compared by N 2 physisorption, XRD, EXAFS/XANES, Moessbauer spectroscopy, TPR and methanol decomposition as catalytic test. Different effect of the support pore size on the dispersion and the catalytic behaviour of the loaded metal oxides have been established.

Cobalt and iron modified activated carbon from coal tar pitch: preparation and application as catalysts for methanol decomposition

Activated carbons were prepared from waste coal treatment by-products by different preparation and activation procedures and applied as a host matrix of nanodispersed cobalt and iron species. Thus obtained composites were characterized by nitrogen physisorption, XRD, UV–Vis, FTIR, TPR and tested as catalysts in methanol decomposition to hydrogen and CO. It was established that the activated carbon, prepared from waste coal treatment by-products could be successfully used for the preparation of highly active catalysts for methanol decomposition. The facilitated effect of surface functionality decrease on the dispersion and catalytic activity of loaded metal species was demonstrated.