Synthesis of iron-MFI zeolite and its photocatalytic application for hydroxylation of phenol

Physicochemical Features and NH3-SCR Catalytic Performance of Natural Zeolite Modified with Iron—The Effect of Fe Loading

In modern dual-pressure nitric acid plants, the tail gas temperature usually exceeds 300 °C. The NH3-SCR catalyst used in this temperature range must be resistant to thermal deactivation, so commercial vanadium-based systems, such as V2O5-WO3 (MoO3)-TiO2, are most commonly used. However, selectivity of this material significantly decreases above 350 °C due to the increase in the rate of side reactions, such as oxidation of ammonia to NO and formation of N2O. Moreover, vanadium compounds are toxic for the environment. Thus, management of the used catalyst is complicated. One of the alternatives to commercial V2O5-TiO2 catalysts are natural zeolites. These materials are abundant in the environment and are thus relatively cheap and easily accessible. Therefore, the aim of the study was to design a novel iron-modified zeolite catalyst for the reduction of NOx emission from dual-pressure nitric acid plants via NH3-SCR. The aim of the study was to determine the influence of iron loading in the natural zeolite-supported catalyst on its catalytic performance in NOx conversion. The investigated support was firstly formed into pellets and then impregnated with various contents of Fe precursor. Physicochemical characteristics of the catalyst were determined by XRF, XRD, low-temperature N2 sorption, FT-IR, and UV–Vis. The catalytic performance of the catalyst formed into pellets was tested on a laboratory scale within the range of 250–450 °C using tail gases from a pilot nitric acid plant. The results of this study indicated that the presence of various iron species, including natural isolated Fe3+ and the introduced FexOy oligomers, contributed to efficient NOx reduction, especially in the high-temperature range, where the NOx conversion rate exceeded 90%.

Catalytic Performance of One-Pot Synthesized Fe-MWW Layered Zeolites (MCM-22, MCM-36, and ITQ-2) in Selective Catalytic Reduction of Nitrogen Oxides with Ammonia

The application of layered zeolites of MWW topology in environmental catalysis has attracted growing attention in recent years; however, only a few studies have explored their performance in selective catalytic reduction with ammonia (NH3-SCR). Thus, our work describes, for the first time, the one-pot synthesis of Fe-modified NH3-SCR catalysts supported on MCM-22, MCM-36, and ITQ-2. The calculated chemical composition of the materials was Si/Al of 30 and 5 wt.% of Fe. The reported results indicated a correlation between the arrangement of MWW layers and the form of iron in the zeolitic structure. We have observed that one-pot synthesis resulted in high dispersion of Fe3+ sites, which significantly enhanced low-temperature activity and prevented N2O generation during the reaction. All of the investigated samples exhibited almost 100% NO conversion at 250 °C. The most satisfactory activity was exhibited by Fe-modified MCM-36, since 50% of NO reduction was obtained at 150 °C for this catalyst. This effect can be explained by the abundance of isolated Fe3+ species, which are active in low-temperature NH3-SCR. Additionally, SiO2 pillars present in MCM-36 provided an additional surface for the deposition of the active phase.

Preparation and Photocatalytic Performance of Iron Oxide-Pillared Layered Tantalum–Tungsten Acid

Using trirutile-structure layered tantalum–tungsten acid as the layered host, [Formula: see text]-propylamin as the pre-swelling agent and aqueous solution of [Fe3(CH3COO)7(OH)(H2O)]NO3 as the pillaring solution, oligomeric polyhydroxyacetato-Fe(III) species-intercalated layered HTaWO6 was synthesized by a stepwise ion-exchange way at room temperature. Upon calcining at 673[Formula: see text]K in air atmosphere, iron oxide-pillared layered HTaWO6with nanoscale interlayer distance (denoted as Fe2O3-HTaWO[Formula: see text] was obtained. A series of Fe2O3-HTaWO6 samples with various Fe contents were prepared by using different volume of Fe(III)-pillaring solution. The layered intermediates obtained at each stage of the ions-exchange process and the final layered products were characterized by powder XRD, FT-IR, DR UV-Vis and SEM techniques. The photocatalytic performance of the Fe2O3-pillared layered HTaWO6 samples for degradation of rhodamine B was investigated. Compared with un-pillared layered HTaWO6, the Fe2O3-pillared layered HTaWO6 exhibited a significantly-improved photo-absorption performance and an enhanced photocatalytic activity. The Fe2O3-HTaWO6 sample with 5.8% (wt) iron showed the best catalytic performance in the photodegradation reaction of rhodamine B.

Advances in the synthesis, characterisation, and mechanistic understanding of active sites in Fe-zeolites for redox catalysts

The recent research developments on the active sites in Fe-zeolites for redox catalysis are discussed. Building on the characterisation of the α-Fe/α-O active sites in the beta and chabazite zeolites, we demonstrate a bottom-up approach to successfully understand and develop Fe-zeolite catalysts. We use the room temperature benzene to phenol reaction as a relevant example. We then suggest how the spectroscopic identification of other monomeric and dimeric iron sites could be tackled. The challenges in the characterisation of active sites and intermediates in NOX selective catalytic reduction catalysts and further development of catalysts for mild partial methane oxidation are briefly discussed.