Piotr Decyk

Oxidative properties of niobium-containing mesoporous silica catalysts

Abstract Oxidative properties of MCM-41 molecular sieves containing niobium in the framework or/and in the extra framework positions were studied by means of H2-TPR, FTIR+NO, ESR techniques and were tested in the oxidation of dibutyl sulphide with hydrogen peroxide. The application of various Nb-sources in the synthesis of NbMCM-41 materials allows the estimation of a role of oxalate ions in the generation of active centres. The activity of Nb-containing mesoporous molecular sieves in the oxidation of thioethers with H2O2 requires the presence of Nb–O− species in the framework. The growth of a concentration of niobium (from Si/Nb=32 to Si/Nb=16) results in the decrease of the number of active centres due to the release of oxygen during the activation procedure. Niobium species in the extra framework positions of MCM-41 catalysts are not active in the dibutyl sulphide oxidation with H2O2 unless they are leached to the solution. Oxidative centres on the catalyst surface cause the formation of nitrite/nitrate species after the adsorption of NO.

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.

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).

NO adsorption and decomposition on Cu-containing mesoporous molecular sieves - comparison with CuZSM-5

Nitric oxide adsorption and decomposition on CuAlMCM-41 mesoporous molecular sieves and CuZSM-5 zeolites (as reference materials) were studied by means of ESR, FTIR and a catalytic test. It was indicated that the Cu-sites reducibility and Cu+(NO) complex stability controlled by the Cu/Al/Si compositon are important parameters in NO decomposition on mesoporous materials. The Cu+(NO) species was well detectable only on the overexchanged CuAlMCM-41-32-132 mesoporous sieve and various CuZSM-5 zeolites. On the other samples Cu2+(NO2−)(NO) was the main complex registered and it was active in NO decomposition.

Characterisation of iron containing molecular sieves—the effect of T-element on Fe species

Surface properties of Fe-modified micro-(ZSM-5) and mesoporous (MCM-41) molecular sieves exhibiting various T elements (Si, Al, Nb) in the framework have been studied by means of XRD, adsorption of N 2 , ESR, and FTIR spectroscopy combined with the adsorption of NO. Fe oxide species, tetrahedral coordinated Fe 3+ and isolated Fe 2+ cations have been identified depending on the kind of the matrix. The presence of niobium in the mesoporous framework enhances the oxidative properties of iron modified samples.

Synthesis and characterisation of multi-element (Nb, V, Mo) MCM-41 molecular sieves

Abstract This work describes the syntheses, the textural and structural characterisation of NbVSi, NbVMoSi MCM-41 type materials in comparison with NbSiMCM-41. It is evidenced that the second transition metal used (V or Mo) during the synthesis affects the location of the elements in the extra framework or framework position (on the walls or inside the walls). The role of each metal for texture and surface properties is discussed.

Zeolites as catalysts for decomposition of sulfur organic compounds

Decomposition of ethanethiol (EtSH) and diethyl sulfide (Et 2 S) on X, Y and ZSM-S zeolites in hydrogen forms and the forms modified with alkali metal cations was studied by means of GC analysis and IR spectroscopy. Bronsted acid sites were described as active centres in elimination of H 2 S from EtSH and of ethene from Et 2 S. The electronegativity of the alkali-metal-exchanged forms of zeolites influences mainly the formation of thiophene in transformation of EtSH and ethene in decomposition of Et 2 S.

Catalytic decomposition of organic sulfur compounds—effect of zeolite acidity

Decomposition of ethanethiol, diethyl sulfide and thiophene on Y zeolites modified with ammonium and alkali metal cations as well as on dealuminated Y and ZSM-5 zeolites was studied by means of GC analysis. The acidity of zeolites was measured using TPD/MS of ammonia or pyridine and a test reaction. The influence of the nature of the alkali metal cations on the strength of neighbouring acidic hydroxyls was determined. The catalytic studies have shown that the nature of the alkali metal cation and the strength of Bronsted acid centres strongly influence the activity and selectivity in ethanethiol and diethyl sulfide conversion. Thiophene did not decompose on M I Y and ZSM-5 zeolites. Its transformation required the presence of strong Bronsted acid centres and large pore zeolites.

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.