J. Kujawa

Nb-containing mesoporous molecular sieves — a possible application in the catalytic processes

Abstract Nb-containing MCM-41 mesoporous molecular sieves were modified with ammonium and copper cations and characterised by ESR, FTIR and H 2 -TPR techniques. The prepared materials were tested in the following catalytic reactions: NO decomposition, reduction of NO with NH 3 , hydrosulphurisation of methanol, and oxidation of thioethers with hydrogen peroxide. The oxidising character of the NbMCM-41 mesoporous molecular sieves was revealed, which induces their application as very active and selective catalysts in the oxidation of thioethers with H 2 O 2 to sulphoxides. HNbMCM-41 samples, which exhibit Lewis acidity after dehydroxylation, are selective catalysts in the methanethiol synthesis in the reaction between methanol and hydrogen sulphide. Copper modified NbMCM-41 sieves indicate the higher reducibility of cupric cations than that observed when AlMCM-41 matrix for copper is used. The higher reducibility of cupric ions does not cause a higher activity in the catalytic NO decomposition.

Influence of sulfur dioxide adsorption on the surface properties of metal oxides

The effect of SO2 chemisorption at 623 K on various metal oxides (CeO2, MgO, Al2O3, ZrO2, TiO2 anatase and rutile) has been studied by IR spectroscopy and catalytic tests: cumene cracking and isopropanol decomposition, IR spectroscopic studies of lutidine and pyridine adsorbed on SO2 treated metal oxides surfaces show the increase or the creation of Bronsted acidity. Test reactions evidence that the strength of such sites depends on the metal oxide, being very weak on MgO and important on TiO2. Formation of hydrogensulfite species or modification of the redox character of surface properties explains the SO2 chemisorption effects.

Influence of hydrogen sulfide adsorption on the catalytic properties of metal oxides

Abstract The effect of sulfidation by H 2 S at 623 K of various metal oxides (MgO, TiO 2 rutile and anatase, ZrO 2 , CeO 2 , Al 2 O 3 ) on their catalytic properties towards isopropanol decomposition, cumene decomposition and methanol hydrosulfurization has been studied. The results are discussed according to the H 2 S adsorption modes. H 2 S coordination mainly occurs on TiO 2 samples and generates strong acid sites. The dissociative adsorption of H 2 S on alumina does not significantly influence its acidity. Replacement of O 2− by S 2− ions as in the case of MgO, ZrO 2 and CeO 2 mainly affects their basic or redox properties.

Physicochemical and catalytic properties of iron-doped silica—the effect of preparation and pretreatment methods

Chemical vapor deposition (1wt% of iron) and wet and wetness impregnations (both giving Fe loading of 1.6 and 2.9 wt%) have been applied for the formation of iron-doped silica. The obtained materials were characterized by means of low-temperature N2 adsorption, XRD, TEM, H2-TPR, ESR, and chemisorption of CO and O2. Their catalytic activity was tested in isopropanol decomposition and oxidation of methanol to formaldehyde. Depending on the preparation procedure various levels and strengths of Fe–silica interactions were observed. The activation conditions determine the nature of the Fe species formed. Fe3+ isolated species are active in isopropanol dehydration whereas Fe–oxide centers exhibit very high selectivity in methanol oxidation to methylformate and formaldehyde.

Physico-chemical and catalytic properties of MCM-41 mesoporous molecular sieves containing transition metals (Cu, Ni, and Nb)

Publisher Summary This chapter describes recent works concerning the physicochemical and catalytic properties of Nb-containing mesoporous sieves. The behavior of NbMCM-41 materials is compared with the one of AlMCM-41 molecular sieves. Moreover, the chapter discusses how the mesoporous matrices (i.e. aluminosilica (AlMCM-41) and niobiosihca (NbMCM-41)) affect the properties of the protons-, nickel-, and copper-exchanged materials. The choice of the transition metals incorporated to the mesoporous sieves depended on the fixture use of the materials either as sorbents or catalysts in the transformation of sulfur compounds (Nb- and Ni-materials), or in the catalytic redox reactions (Cu- and Nb-sieves).

Reactions of alcohols with hydrogen sulphide on zeolites. Part 7: the effect of Brønsted acidity of faujasite type zeolites on methanol hydrosulphurisation

The reaction between methanol and hydrogen sulphide towards methanethiol and dimethyl sulphide was studied on MNaY, MNaX HNaX and MHNaY zeolites (M=Li, K, Rb, Cs). A substantial influence of the nature and strength of active centres on the activity of zeolites and the yield of products was found. A low Bronsted acidity and a high basicity of catalysts favour the hydrosulphurisation process. A decrease of the zeolite acidity strength causes the growth of thiol and the decrease of sulphide formation. High strength of Bronsted acid sites leads to high conversion of methanol to hydrocarbons and low activity in the hydrosulphurisation reaction. An FT IR spectroscopic study showed the difference in the reagents and by-products adsorption depending on the strength of the acidic centres and its influence on the reaction pathways.

Effect on the reaction between methanol and hydrogen sulphide of Na or Mo doping on zirconia and alumina

Abstract The effect of sodium doping on alumina and zirconia activity in methanethiol formation from hydrosulphurisation of methanol by H 2 S was studied. It provoked an activity decrease and a selectivity increase in agreement with the catalysts basicity increase. By contrast, molybdenum doped zirconia samples presented a higher activity but a lower selectivity than pure zirconia, as expected from their higher acidity. Increase of the CH 3 OH/H 2 S ratio in the reaction mixture improved both activity and CH 3 SH selectivity. It was found that zirconia loaded with small amounts of molybdenum working under H 2 S excess shows good performances towards CH 3 SH production.

27-P-09-Niobium leaching from the catalysts applied in the sulfoxidation of thioethers with hydrogen peroxide

Publisher Summary This chapter presents the study of micro- and mesoporous materials containing niobium (Nb) in the framework or extra framework positions in the oxidation of dibutyl sulphide with hydrogen peroxide (H 2 O 2 ). Leaching of Nb from the solid to the liquid phase is considered. Some of the catalysts prepared through the impregnation with Nb salts show some leaching of Nb to the liquid phase and the oxidation partially occurs homogeneously in the liquid phase. The reaction proceeds mainly on the catalyst surface when the mesoporous molecular sieves containing Nb in the framework are used.

Application of modified zeolites and mesoporous materials for deodorization

Abstract The high pore volume nanomaterials (zeolites and mesoporous MCM-41) modified with active components (Ni, Cu, Mn, Au) were prepared to obtain adsorbents able to concentrate a maximum amount of pollutants in a minimum volume of solids. Butyl amine (BuNH 2 ) and dibutyl sulphide (Bu 2 S) were adsorbed on these materials in the presence and absence of humidity atmosphere. It is evidenced the attractiveness of Au/MCM-41 samples for the selective adsorption of both odour compounds (much higher for the sulphide) and possible further oxidation of adsorbates during the recovery of adsorbents. The highest protection from moisture adsorption was found for Au/NbMCM-41.