Zofia Piwowarska

A series of Ni-Mg-Al hydrotalcite-derived mixed metal oxides with different Ni/Mg ratios were prepared by the coprecipitation method followed by calcination at 600 °C. The hydrotalcite-like materials, as well as their calcined forms, were characterized with respect to structure (XRD, UV-Vis DRS), chemical composition (ICP-OES), textural parameters (low-temperature N₂ sorption), dispersion of nickel species (H₂-chemisorption) and nickel species reducibility (H₂-TPR). Moreover, the process of hydrotalcite-like materials’ thermal transformation to mixed metal oxide systems in air and argon flow was studied by the TG-DTA method. The activity of the studied catalysts in the reaction of ammonia decomposition increased with an increase in nickel content in the samples. It was shown that nickel species incorporated into the Mg-Al oxide matrix segregated under conditions of reduction in a flow of H₂/Ar mixture with the formation of metallic nickel crystallites of the average size of about 10 nm. The size of nickel crystallites was practically no change in the subsequent reduction cycles and resulted in increased catalytic activity in comparison to larger crystallites of metallic nickel (20.2–23.6 nm) deposited on Al₂O₃ and MgO.

Mesoporous silicas of MCM-41 and MCM-48 types were synthesized and modified with copper by template ion-exchange (TIE) technique. A high dispersion of deposited copper species was managed by subsequent treatment of the samples with ammonia, urea, or acetonitrile solution. Copper-modified silicas were analysed in terms of their chemical composition (ICP-OES), ordering of porous structure (XRD), textural parameters (low-temperature N₂ sorption), dispersion and form of introduced copper species (UV–vis-DR, XRD, H₂-TPR, NH₃-TPD). Mesoporous silicas modified with copper exhibited promising catalytic efficiency in selective catalytic reduction of NO with ammonia (NH₃-SCR). The samples containing dispersed copper species (predominantly monomeric copper cations) presented enhanced catalytic activity compared to catalysts containing CuO aggregates. On the other hand, CuO aggregates showed greater catalytic activity in the side process of direct ammonia oxidation by oxygen present in the reaction mixture. It was demonstrated that TIE post-treatment of the samples with urea resulted in most effective improving dispersion of deposited copper and is less destructive for ordered porous structures of mesoporous silica comparing to treatment with ammonia solution. Graphical abstract

MCM-41-type mesoporous silicas were modified with alumina by the impregnation, co-condensation, and template ion-exchange (TIE) methods. The obtained materials were characterized with respect to their chemical composition (ICP-OES), textural parameters (low-temperature N₂ sorption), structure (XRD), and surface acidity (NH₃-TPD) and tested as catalysts of methanol to dimethyl ether (DME) dehydration in a flow microreactor system. The catalytic performance of the studied materials was analyzed with respect to their porous structure, as well as their density and the strength of their acid sites. It was shown that the performance of the studied catalysts depends on the contribution of the surface exposed aluminum species, as well as their aggregation. For the most active catalyst, the study of its catalytic stability under rection conditions was performed. It was shown that the catalyst can be effectively regenerated by the incineration of carbon deposits under air flow at 550 °C for 1 h.

Layered 2D zeolite MCM-22 and its delaminated derivative, ITQ-2, were modified with iron, by different methods (ion-exchange and direct synthesis), and with the use of different precursors (FeSO₄∙7H₂O, Fe(NO₃)₃∙9H₂O, and [Fe₃(OCOCH₃)₇∙OH∙2H₂O]NO₃ oligocations. The applied modifications were aimed at optimization of iron form in the samples (aggregation, amount, location, and reducibility), in order to achieve the highest catalytic activity in the N₂O decomposition. The synthesis of the samples was verified with the use of XRD (X-Ray Diffraction), N₂-sorption and ICP-OES (Inductively Coupled Plasma Optical Emission Spectroscopy) techniques, while the form of iron in the samples was investigated by UV–vis-DRS (UV–vis diffuse reflectance spectroscopy), H₂-TPR (Hydrogen Temperature-Programmed Reduction) and HRTEM (High-Resolution Transmission Electron Microscopy). The highest activity in the N₂O decomposition presented the sample Fe(O,IE)MCM-22, prepared by ion-exchange of MCM-22 with Fe3(III) oligocations. This activity was related to the oligomeric Fe_xO_y species (the main form of iron in the sample) and the higher loading of active species (in comparison to the modification with FeSO₄∙7H₂O).