Maciej Trejda

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.

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.

Incorporation of group five elements into the faujasite structure

Niobium and tantalum were incorporated into the faujasite aluminosilicate structure in one-pot synthesis and also by post-synthesis method, i.e. solid-state ion exchange. One-pot synthesized zeolites exhibit Nb and Ta incorporated into the zeolite skeleton as evidenced by different methods. The efficiency of metal incorporation examined by XPS measurements was found to be higher for tantalum than for niobium.

Development of basicity in mesoporous silicas and metallosilicates

We report herein an experimental study on the development of basicity on mesoporous silicas and metallosilicates (Nb- and Ce-) on SBA-15 and MCF porous structures. Our results demonstrated that the role of the catalyst structure (hexagonally ordered mesoporous SBA-15 vs. mesoporous cellular foam MCF), the effect of the amount and nature of metal in the supports (different acidic/redox properties), and the effect of the type of nitrogen-containing organic modifier (imidazole, triazole and aminotriazole) play an important role on the activity and selectivity in Knoevenagel condensation, which is a well-known probe reaction to determine the basicity of inorganic solids. We demonstrate that niobium Lewis acidity is determinant for the Knoevenagel condensation and, also, redox properties of cerium play an important role in the basicity. In fact, acid–base cooperation plays a positive role in promoting the Knoevenagel condensation via the ion-pair mechanism. These mesoporous silicas and metallosilicates are interesting catalysts for production of fine chemicals due to their thermal stability and controllable acid–base catalytic properties.

FTIR study of FE-doped MCM-41 mesoporous molecular sieves

Abstract Iron has been introduced into MCM-41 samples in two ways: i) during the synthesis together with either Si or Si+Al, or Si+Nb and ii) via impregnation or CVD (post-synthesis methods) on MCM-41, AlMCM-41, and NbMCM-41. All the materials exhibit well hexagonal ordered mesoporous MCM-41 structure. Iron species formed were identified by FTIR spectra of adsorbed NO and estimated as follows: i) iron isolated cations in extra framework sites, ii) iron in the skeleton, iii) Fe 2+ -O-Fe 3+ clusters. The relationship between their content depends on the chemical composition of MCM-41 samples and the Fe-doping procedure.

Relationship between basicity, reducibility and partial oxidation properties of chromium containing MCM-41

MCM-41 mesoporous solids were modified with chromium species using Cr(NO3)3 and CrO3 as precursors. The impact of metal amount and metal sources on the structural and textural parameters of the materials obtained was investigated. Their surface properties were analyzed using XRD, UV-Vis, H2-TPR (the state of Cr species) as well as test reactions (2-propanol decomposition and cyclization and dehydration of 2,5-hexsanedione). The catalytic activity of Cr/MCM-41 materials was tested in methanol partial oxidation. The relationships of reducibility, kind of chromium species, basicity of material surface and the catalysts performance in partial oxidation of methanol were examined and discussed. The impact of basicity on methanol oxidation was clearly documented. Di- and polychromate species were found to be responsible for high yields of formaldehyde.

Generation of iron active species in MCM-41 materials

A new method, the immobilisation of ferroceneacetic acid (FAA) on various MCM-41 mesoporous molecular sieves (containing Si or Si+Al) followed by calcination at 773 K has been applied for the formation of ion active species. The structural, surface and catalytic properties of these materials, characterised by N2 adsorption/desorption, XRD, 27Al NMR, ESR, and Mossbauer spectroscopy as well as test reactions, were compared with those of materials prepared via commonly used impregnation methods. Contrary to Fe-impregnated samples, Fe oxides species were only slightly detected in the solids modified by FAA followed by calcination. It is evidenced that the new technique applied for Fe-modification gives rise to the significantly higher activity (in isopropanol decomposition and acetonylacetone cyclization) reached thanks to a better isolation and/or dispersion of Fe3+ species. The presence of Al, in the sample influences the Fe3+ reduction under vacuum.

Structure and Reactivity of Zeolites Containing Group Five Elements (V, Nb, Ta)

This chapter is devoted to the inclusion of group five metals (vanadium, niobium and tantalum) into different zeolite structures (mainly AFI, AM-11, BEA, FAU, LTA, MEL, MFI, MOR, MWW) in order to achieve zeolites with novel catalytic and photocatalytic properties. The focus is on the achievement in the last two decades in the field of methods of metal incorporation and characterization of structure of species formed by different modification methods and their acid-base and redox properties. Special attention is paid to the reactivity of metal species in zeolites with reagents in selected catalytic processes. Their catalytic activity is considered in oxidation processes (in liquid and gas phases), reduction and acid-catalysed reactions as well as photocatalytic processes. From among liquid-phase oxidation processes, hydroxylation of benzene and oxidation of olefins and sulphides with hydrogen peroxide are considered. As examples of gas-phase redox processes, propane and methanol oxidation and catalytic reduction of nitrogen oxide are presented. The tandem reaction, ethanol to 1,3-butadiene, and transformation of glycerol to acrolein are discussed in details as examples of acid-catalysed reactions. The use of zeolites as supports for group five metals is demonstrated to be a good solution for designing attractive photocatalysts.