Experimental and theoretical studies of sonically prepared Cu-Y, Cu-USY and Cu-ZSM-5 catalysts for SCR deNO(x)

The objective of our study was to prepare Y-, USY- and ZSM-5-based catalysts by hydrothermal synthesis, followed by copper active-phase deposition by either conventional ion-exchange or ultrasonic irradiation. The resulting materials were characterized by XRD, BET, SEM, TEM, Raman, UV-Vis, monitoring ammonia and nitrogen oxide sorption by FT-IR and Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS). XRD data confirmed the purity and structure of the Y/USY or ZSM-5 zeolites. The nitrogen and ammonia sorption results indicated that the materials were highly porous and acidic. The metallic active phase was found in the form of cations in ion-exchanged zeolites and in the form of nanoparticle metal oxides in sonochemically prepared catalysts. The latter showed full activity and high stability in the SCR deNO(x) reaction. The faujasite-based catalysts were fully active at 200-400 degrees C, whereas the ZSM-5-based catalysts reached 100% activity at 400-500 degrees C. Our in situ DRIFTS experiments revealed that Cu-O(NO) and Cu-NH3 were intermediates, also indicating the role of Bronsted sites in the formation of NH4NO3. Furthermore, the results from our experimental in situ spectroscopic studies were compared with DFT models. Overall, our findings suggest two possible mechanisms for the deNO(x) reaction, depending on the method of catalyst preparation (i.e., conventional ion-exchange vs. ultrasonic irradiation).Web of Science117art. no. 82

Nano-design of Zeolites Biomass Wastes Valorization: Dehydration of Lactic Acid into Acrylic Acid

The valorization of waste from biomass currently arouses great interest. In the present study we concentrate on the design of innovative BEA zeolite catalysts with applied metal nanoparticles - copper, vanadium and manganese for the dehydration of lactic acid to acrylic acid. The ab initio method based on density functional theory (DFT) was used to calculate the electron structure of the analyzed molecules. The non-local generalized gradient corrected functionals GGA-RPBE was used to in order to account for electron exchange and correlation. The cluster model was represented by a hierarchical zeolite M2Al2Si12O40H22 (M = Cu, V, Mn). The stabilization of the M-Ob-M dimer complex in the hierarchical structure of BEA, mechanism of adsorption of lactic acid on BEA zeolite with applied metal dimers and formation of acrylic acid on these zeolites were investigated. The examined metals form stable dimers interconnected by a bridge oxygen (Ob). Adsorption of lactic acid takes place in the vicinity of a dimer of M-Ob-M. The dehydration of lactic acid to acrylic acid in all cases consists in the separation of the hydroxyl group and creating a connection with a metal center of dimer and disconnection of a single hydrogen atom from the methyl group and its interaction with bridge oxygen of dimer.Waloryzacja odpadów z biomasy cieszy się obecnie dużym zainteresowaniem. W niniejszych badaniach koncentrujemy się na projektowaniu innowacyjnych katalizatorów zeolitowych BEA z nanocząstkami metali - miedzi, wanadu i manganu w celu odwodnienia kwasu mlekowego do kwasu akrylowego. Metoda ab initio oparta na teorii funkcjonalności gęstości (DFT) została wykorzystana, przy użyciu nielokalnego funkcjonału korelacyjno-wymiennego GGA-RPBE, do obliczenia struktury elektronowej analizowanych cząsteczek. Hierarchiczny zeolite BEA był reprezentowany przez model klasterowy M2Al2Si12O40H22 (M = Cu, V, Mn). Badano stabilizację dimeru M-Ob-M w hierarchicznej strukturze BEA, mechanizm adsorpcji kwasu mlekowego na zeolicie BEA z zastosowanymi dimerami metali i tworzenie kwasu akrylowego na tych zeolitach. Badane metale tworzą stabilne dimery połączone wzajemnie tlenem mostkowym (Ob). Adsorpcja kwasu mlekowego odbywa się w pobliżu dimeru M-Ob-M. Odwodnienie kwasu mlekowego do kwasu akrylowego we wszystkich przypadkach polega na oddzieleniu grupy hydroksylowej i utworzeniu połączenia z jednym z metali dimeru i odłączeniem pojedynczego atomu wodoru od grupy metylowej kwasu mlekowego i jego oddziaływaniem z tlenem mostkowym dimeru

Modelling of porous metal-organic framework (MOF) materials used in catalysis

This paper presents a review of modern modelling of porous materials such as metal-organic frameworks used in catalysis. The authors’ own research approach using the nano-design of metal-organic frameworks is included in this review

Theoretical Studies on the Mechanism of deNOx Process in Cu–Zn Bimetallic System—Comparison of FAU and MFI Zeolites

In the present study we propose a more promising catalyst for the deNOx process to eliminate harmful nitrogen oxides from the environment. The study was performed with a computer calculation using density functional theory (DFT) based on an ab initio method. Two zeolite catalysts, FAU and MFI, were selected with additional Cu–O–Zn bimetallic dimer adsorbed inside the pores of both zeolites. Based on the analysis of preliminary studies, the most probable way of co-adsorption of nitric oxide and ammonia was selected, which became the initial configuration for the reaction mechanism. Two types of mechanisms were proposed: with hydroxyl groups on a bridged position of the dimer or a hydroxyl group on one of the metal atoms of the dimer. Based on the results, it was determined that the FAU zeolite with a bimetallic dimer and an OH group on the zinc atom was the most efficient configuration with a relatively low energy barrier. The real advantage of the Cu–Zn system over FAU and MFI in hydrothermal conditions has been demonstrated in comparison to a conventional Cu–Cu catalyst

Change in the Nature of ZSM-5 Zeolite Depending on the Type of Metal Adsorbent—The Analysis of DOS and Orbitals for Iron Species

Transition-metal-modified zeolites have recently gained the greatest interest among scientists. Ab initio calculations within the density functional theory were used. The exchange and correlation functional was approximated with the Perdew–Burke–Ernzerhof (PBE) functional. Cluster models of ZSM-5 (Al2Si18O53H26) zeolites were used with Fe particles adsorbed above aluminum. The adsorption of three iron adsorbates inside the pores of the ZSM-5 zeolite—Fe, FeO and FeOH—was carried out with different arrangements of aluminum atoms in the zeolite structure. The DOS diagram and the HOMO, SOMO and LUMO molecular orbitals for these systems were analyzed. It has been shown that depending on the adsorbate and the position of aluminum atoms in the pore structure of the zeolite, the systems can be described as insulators or conductors, which significantly affects their activity. The main aim of the research was to understand the behavior of these types of systems in order to select the most efficient one for a catalytic reaction