Marek Rotko

A series of ERI‐type zeolite materials of different properties was prepared, which led to the obtaining of Cu‐containing ERI materials of distinct catalytic properties in the selective catalytic reduction of NO _x with ammonia (NH ₃ ‐SCR‐DeNO _x ) and the selective catalytic oxidation of ammonia (NH ₃ ‐SCO). Various characterization techniques were employed to describe the copper species in the synthesized ERI zeolite in order to understand its NH ₃ ‐SCR‐DeNO _x and NH ₃ ‐SCO activity as well as N ₂ selectivity. Cu‐ERI_1 and Cu‐ERI_2 possess the highest amount of active sites (i.e., Cu ²⁺ species) and thus enhanced activity in the low‐temperature range of NH ₃ ‐SCR‐DeNO _x (with NO conversion of 83%–93% and N ₂ selectivity of 93%–95% at 250 °C). Especially, Cu‐ERI_2 possesses easily reducible Cu ²⁺ species that are responsible for activation and oxidation of NH ₃ . Indeed, steady‐state isotopic transient kinetic analysis of NH ₃ ‐SCO revealed the shortest average surface lifetime and the lowest surface concentration of NH ₃ over the Cu‐ERI_2 sample. Further, modulation excitation experiments confirmed that NO preferentially consumes NH ₃ adsorbed on the Brønsted acid sites on this sample. For other samples, the experiments of NO absorption followed by NH ₃ + O ₂ exposure and around (NH ₃ adsorption and NO + O ₂ exposure) indicated that NH ₃ adsorbed on Lewis acid sites is preferentially consumed during the reaction process.

A key challenge facing modern society, fueled by the relentless growth in energy and food requirements, is meeting rising energy needs without exacerbating greenhouse gas emissions. Nevertheless, fossil fuel combustion remains the primary contributor to human-induced pollution. As environmental concerns intensify and fossil resources become increasingly scarce, there is a growing push within the research community to identify alternative energy carriers and to advance more sustainable, low-impact technologies. Thus, this review focuses on catalytic CH₄ decomposition (CDM) for hydrogen production over Ni-, Fe, and Co-metal-based catalysts. Fe-based catalysts have received considerable attention for CDM due to their low cost and environmental sustainability. Furthermore, a discussion of deactivation and regeneration, along with the identified reaction mechanisms of CH₄ decomposition over these catalysts, is presented.

The reaction mechanism of soot oxidation on Mn (Mn₃O₄), Mn-Ce (Mn₃O₄-CeO₂), and Ce (CeO₂) catalysts in tight contact conditions was investigated using ITKA (isotopic transient kinetic analysis). The obtained results suggest that lattice-bulk oxygen from all studied catalysts takes part in the soot oxidation process but with varying relative contributions: for the Ce catalyst, this contribution is practically 100%, whereas with decreasing Ce content in Mn-Ce catalysts, the significance of lattice-bulk oxygen for soot oxidation diminishes. For the Mn catalyst, it is estimated to be below 50%. Moreover, strong interactions between Mn and Ce ions were observed, increasing oxygen mobility in the catalyst crystal lattice and affecting the activity of Mn-Ce catalysts.

Fe-modified Cu catalysts with CeO₂ support, prepared by the impregnation method, were subjected to physicochemical analysis and catalytic tests in the steam reforming of methanol (SRM). Physicochemical studies of the catalysts were carried out using the XRF, TEM, STEM-EDS, XRD, TPR and nitrogen adsorption/desorption methods. XRD, TEM studies and catalytic tests of the catalysts were carried out at two reduction temperatures, 260 °C and 400 °C, to determine the relationship between the form and oxidation state of the active phase of the catalysts and the catalytic properties of these systems in the SRM. Additionally, the catalysts after the reaction were analysed for the changes in the structure and morphology using TEM methods. The presented results show that the composition of the catalysts, morphology, structure, form and oxidation state of the Cu and Fe active metals in the catalysts and the reaction temperature significantly impact their activity, selectivity and stability in the SRM process. The gradual deactivation of the studied catalysts under SRM conditions could result from the forming of carbon deposits and/or the gradual oxidation of the copper and iron phases under the reaction conditions.

ERI and SSZ-13 were subjected to post-synthetic treatments (depending on the zeolite topology) to create micro-/mesoporous materials. The results in terms of NH₃-SCR-DeNO_x show that the applied treatments improved the catalytic activity of the Cu-containing ERI-based materials; however, the NO conversion did not vary for the different materials treated with NaOH or NaOH/HNO₃. For the micro-/mesoporous Cu-containing SSZ-13, a lower NO conversion in NH₃-SCR-DeNO_x was observed. Thus, our findings challenge the current paradigm of enhanced activity of micro-/mesoporous catalysts in NH₃-SCR-DeNO_x. The modification of the supports results in the presence of different amounts and kinds of copper species (especially isolated Cu²⁺ and aggregated Cu species) in the case of ERI- and SSZ-13-based samples. The present copper species further differentiate the formation of reactive reaction intermediates. Our studies show that besides the μ-η²,η²-peroxo dicopper(II) complexes (verified by in situ DR UV-Vis spectroscopy), copper nitrates (evidenced by in situ FT-IR spectroscopy) also act as reactive intermediates in these catalytic systems.

ERI and SSZ-13 were subjected to post-synthetic treatments (depending on the zeolite topology) to create micro-/mesoporous materials. The results of NH3-SCR-DeNOx show that the applied treatments improved the catalytic activity of the Cu-containing ERI-based materials; however, the NO conversion does not vary for the different materials treated with NaOH or NaOH/HNO3. For the micro-/mesoporous Cu-containing SSZ-13, a lower NO conversion in NH3-SCR-DeNOx is observed. Thus, our findings challenge the current paradigm of enhanced activity of micro-/mesoporous catalysts in NH3-SCR-DeNOx. The modification of the supports results in the presence of different amounts and kinds of copper species (especially isolated Cu2+ and aggregated Cu species) in the case of ERI- and SSZ-13-based samples. The present copper species further differentiate the formation of reactive reaction intermediates. Our studies approved that besides the -2,2-peroxo dicopper(II) complexes (verified by in situ DR UV-Vis spectroscopy), also copper nitrates (evidenced by in situ FT-IR spectroscopy) act as reactive intermediates in these catalytic systems.

The promotional effect of potassium (~1.25 wt%) on a Co/MnO_x catalyst was studied for samples prepared by the impregnation method in the steam reforming of ethanol (SRE) process at 420 °C for a H₂O/EtOH molar ratio of 12/1. The catalysts were characterized using physicochemical methods to study their textural, structural, and redox properties. The XRD studies revealed that, during the treatment of both cobalt-based catalysts under a hydrogen atmosphere at 500 °C, Co⁰ and MnO phases were formed by the reduction in Co₃O₄ and Mn₂O₃/Mn₃O₄ phases, respectively. Potassium doping significantly improved stability and ability for the C–C bond cleavage of the Co/MnO_x catalyst. The enhancement of activity (at ~25%) and selectivity to hydrogen (at ca. 10%) and the C1 product, mainly carbon dioxide (at ~20%), of the Co/MnO_x catalyst upon potassium doping was clarified by the alkali promoter’s impact on the reducibility of the cobalt and manganese oxides. The microscopic observations revealed that fibrous carbon deposits are present on the surface of Co/MnOx and KCo/MnOx catalysts after the SRE reaction and their formation is the main reason these catalysts deactivate under SRE conditions. However, carbon accumulation on the surface of the potassium-promoted catalyst was ca. 12% lower after 18 h of SRE reaction compared to the unpromoted sample.

The effect of a potassium promoter on the stability of and resistance to a carbon deposit formation on the Ni/MnO_x catalyst under SRE conditions was studied at 420 °C for different H₂O/EtOH molar ratios in the range from 4/1 to 12/1. The catalysts were prepared by the impregnation method and characterized using several techniques to study their textural, structural, and redox properties before being tested in a SRE reaction. The catalytic tests indicated that the addition of a low amount of potassium (1.6 wt.%) allows a catalyst with high stability to be obtained, which was ascribed to high resistance to carbon formation. The restriction of the amount of carbon deposits originates from the potassium presence on the Ni surface, which leads to (i) a decrease in the number of active sites available for methane decomposition and (ii) an increase in the rate of the steam gasification of carbon formed during SRE reactions.

The influence of Ce and W promoters on the performance of alumina-supported nickel catalysts in the CO₂ methanation reaction was investigated. The catalysts were obtained by the co-impregnation method. Nitrogen low-temperature adsorption, temperature-programmed reduction, hydrogen desorption, transmission electron microscopy, X-ray diffraction, and photoelectron spectroscopy studies were used for catalyst characterization. An introduction of Ce and W promoters (1–5 wt %) led to the decrease in mean Ni crystallite size. Gradual increase in the active surface area was observed only for Ce-promoted catalysts. The increase in CO₂ conversion in methanation reaction at low-reaction temperatures carried out over Ce-promoted catalysts was attributed to the increase in the active surface area and changes in the redox properties. The introduction of small amounts of tungsten led to an increase in the activity of catalysts, although a decrease in the active surface area was observed. Quasi in situ XPS studies revealed changes in the oxidation state of tungsten under CO₂ methanation reaction conditions, indicating the participation of redox promoter changes in the course of surface reactions, leading to an improvement in the activity of the catalyst.

In this paper, a screen-printed boron-doped electrode (aSPBDDE) was subjected to electrochemical activation by cyclic voltammetry (CV) in 0.1 M NaOH and the response to rifampicin (RIF) oxidation was used as a testing probe. Changes in surface morphology and electrochemical behaviour of RIF before and after the electrochemical activation of SPBDDE were studied by scanning electron microscopy (SEM), CV and electrochemical impedance spectroscopy (EIS). The increase in number and size of pores in the modifier layer and reduction of charge transfer residence were likely responsible for electrochemical improvement of the analytical signal from RIF at the SPBDDE. Quantitative analysis of RIF by using differential pulse adsorptive stripping voltammetry in 0.1 mol L⁻¹ solution of PBS of pH 3.0 ± 0.1 at the aSPBDDE was carried out. Using optimized conditions (E_acc of −0.45 V, t_acc of 120 s, ΔE_A of 150 mV, ν of 100 mV s⁻¹ and t_m of 5 ms), the RIF peak current increased linearly with the concentration in the four ranges: 0.002–0.02, 0.02–0.2, 0.2–2.0, and 2.0–20.0 nM. The limits of detection and quantification were calculated at 0.22 and 0.73 pM. The aSPBDDE showed satisfactory repeatability, reproducibility, and selectivity towards potential interferences. The applicability of the aSPBDDE for control analysis of RIF was demonstrated using river water samples and certified reference material of bovine urine.