Christo Minchev

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.

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).

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.

Influence of the Lewis acidity of indium-modified beta zeolite in the m-xylene transformation

Abstract The catalytic performance of NH4-beta zeolite containing different amounts of indium, introduced as In+ cations by the method of reductive solid-state ion exchange (RSSIE), has been studied in the m-xylene conversion. It has been shown that In cations regarded as coordinatively unsaturated species possessing Lewis acidity substantially change the catalyst stability and the selectivity of the reaction when performed in an inert atmosphere. An acceleration of the side reactions of disproportionation and coking has been observed on the In-modifications of zeolite beta and a mechanism of hydride ion abstraction and faster benzylic cation formation on them have been supposed. In presence of H2 these reactions are strongly suppressed at the expense of the main reaction of isomerisation. On the completely In-exchanged beta zeolite a partial bimolecular mechanism of isomerisation is suggested.

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.

Infrared-spectroscopic detection and distinction of indium cations of different oxidation states in zeolites

In+ cations introduced by reductive solid-state ion exchange into zeolites (Y, ZSM-5, mordenite) and cationic InO+ species created by oxidation of the incorporated univalent cations were found to be detectable and distinguishable by IR spectroscopy using pyridine as probe molecule. Relatively weak interactions of In+ lattice cations with pyridine give rise, after degassing at temperatures not higher than 370 K, to typical bands at 1446 and 1599 cm−1. After oxidation to InO+, these bands are shifted to 1452 and 1610 cm−1, being significantly more resistant towards degassing. Because of restrictions in the accessibility of InO+ to pyridine, the respective bands are absent in the spectra of mordenite.

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.

Incorporation of cationic indium species into zeolite beta by template-induced reductive solid-state ion exchange

Reductive solid-state ion exchange (RSSIE) was found to proceed in mechanical mixtures of crystalline In2O3 and as-synthesized precursors of zeolite beta (TEA-beta) during thermal decomposition of the template (TEA) in an inert gas atmosphere or high vacuum. It was evidenced that gaseous decomposition products of the template play the decisive role as reductants in this process, which results in the incorporation of univalent indium cations into the zeolite structure. Accordingly, no reaction between In2O3 and the zeolitic component was observed during template decomposition in an oxidizing atmosphere. After RSSIE associated with thermal template decomposition both In+ and InO+ lattice cations could be detected by typical IR spectroscopic bands attributed to interactions of these ions with adsorbed pyridine. The trivalent indium species are probably formed by a redox process involving the reduction of protons (internal silanol groups) to H2 and oxidation of In+ into InO+. In line with this conclusion is the finding that part of the In+ cations are converted into InO+ upon contact with water.

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.