Copper Oxide Species Research Articles

Green Synthesis of Copper and Copper Oxide Nanoparticles From Brown Algae Turbinaria Species' Aqueous Extract and Its Antibacterial Properties.

Background Copper and copper oxide nanoparticlessynthesized by green methods have attracted considerable attention due to their environmentally friendly properties and potential applications. Green synthesis involves non-hazardous and sustainable techniques used in the production of a wide range of substances, including nanoparticles, pharmaceuticals, and chemicals. These methods often use different organisms, including bacteria, fungi, algae, and plants, each offering different advantages in terms of simplicity, cost-effectiveness, and environmental sustainability. The environmentally friendly nature of these green synthesis methods responds to the growing need for sustainable nanotechnologies. Brown algae have gained popularity due to their distinct morphological characteristics and diverse biochemical composition. This research focuses on the process of synthesizing copper and copper oxide nanoparticlesfrom the brown algae Turbinaria. It emphasizes the natural ability of the bioactive compounds contained in the algae extract to reduce and stabilize the nanoparticles. The green synthesis of copper and copper oxide nanoparticlesfrom brown algae has demonstrated a wide range of applications, including antibacterial activity. Materials and methods Fresh Turbinaria algae were collected from marine environments to ensure that they were free of contaminants. The algae underwent a purification process to remove impurities and were dried. An aqueous extract was prepared by pulverizing the dried algae and mixing them with distilled water. A copper salt solution utilizing copper nitrate was prepared. The algae extract was mixed with the copper salt solution. There are bioactive compounds in the algae extract that help reduce copper ions, which makes copper and copper oxide nanoparticles come together. The reaction mixture was incubated in a controlled environment to facilitate the growth and enhance the stability of the nanoparticles. To separate the nanoparticles from the reaction mixture, centrifugation was employed, or filtration was done with Whatman filter paper (Merck, Burlington, MA). The nanoparticles were dried to yield a stable powder. Results Copper and copper oxide nanoparticles derived from brown algae extract showed antibacterial effects against Streptococcus mutans,Klebsiella sp.,andStaphylococcus mutans. The scanning electron microscopy (SEM) analysis verified the irregular shape and elemental content of the synthesized copper and copper oxide nanoparticles. The X-ray diffraction (XRD) analysis indicated that the synthesized nanoparticles exhibited a crystallinity nature and were composed of a mixture of copper and copper oxide species, namely face-centered cubic and monoclinic structures. The transmission electron microscopy (TEM) images showed copper and copper oxide nanoparticles that were evenly distributed and had a rectangular shape. They exhibited substantial antimicrobial activity against both Gram-positive and Gram-negative bacteria. Conclusions This study enhances the field of green synthesis techniques by showcasing the adaptability of Turbinaria brown algae to synthesize copper and copper oxide nanoparticles. It underscores the potential advantages of these nanoparticles in terms of their antibacterial properties.

The chemical state and Cu+ stability for three-way catalytic performance of Cu-added Al2O3 catalysts

Cu-added γ-Al2O3 (CuAl) catalysts having varying Cu loadings (3, 5, 8, and 10 mol%) were prepared at 900 °C. The effects of the copper oxidation states and the stability of these states under oxidizing and reducing atmospheres were examined. The use of these materials as three-way catalysts (TWCs) was also assessed. Analyses by X-ray diffraction and transmission electron microscopy indicated that copper oxide species were well dispersed and formed a solid solution in a surface layer of the γ-Al2O3. The TWC activity was found to increase with the addition of copper, and the 8 mol% CuAl catalyst showed very high performance despite being heat-treated at high temperatures. In the case of the 10 mol% CuAl catalyst, the excess Cu loading resulted in the precipitations of copper species on the γ-Al2O3 surface, which decreased catalytic activity. The oxidation states also differed between these catalysts. X-ray absorption fine structure and temperature-programmed reduction data demonstrated variations in copper oxidation states among the catalysts before and after oxidation and reduction treatments. The 8 mol% CuAl catalyst had a high Cu+/Cu2+ ratio and contained stable Cu+ species during both oxidation and reduction trials. The stability of the copper oxidation states is evidently a factor affecting catalytic activity.

Isolated CuO and medium strong acid on CuO/Nb2O5-H catalyst for efficient enhancement of triethylamine selective catalytic oxidation

The selective catalytic oxidation (SCO) of triethylamine (TEA) to harmless N2, CO2, and H2O is an appropriate elimination technology. It is necessary to develop the catalysts capable of working under mild condition and with excellent N2 selectivity for this reaction. In this article, the CuO/Nb2O5-H catalysts with various loadings were characterized and employed for the SCO of TEA. The 15 %CuO/Nb2O5-H demonstrated the most noticeable catalytic performance. At 220 °C, the conversion of TEA reached 100.0 %, and the selectivity of N2 was 96.0 %. XPS, UV–vis results demonstrated the presence of isolated CuO species in the catalyst and auger electron energy spectra proved the content of Cu2+ species over 85 %. Pyridine-IR and NH3-TPD demonstrated the presence of a substantial number of acidic sites in Nb2O5-H. Based on the in-situ DRIFTs results, the adsorption of TEA on the acidic sites of Nb2O5-H at low temperature is considered as the initial step in the process, followed by C-N bond activation, cleavage, and adsorption of the -NH* intermediates. The -NH* was oxidized to N2 by highly dispersed copper oxide species on the catalyst surface at 220 °C.

Cu/SiO2 CATALYSTS OBTAINED BY CATIONIC ADSORPTION FROM DIFFERENT PRECURSOR SALTS

In this work the effect of different copper precursor salts (acetate, nitrate, sulfate) on the physicochemical characteristics of Cu/SiO2 catalysts is studied. The catalysts were prepared by the cationic adsorption method and analyzed by several characterization techniques (TGA, DSC, FTIR, XRD, AAS, SEM-EDS, N2-sorptometry and TPR). The results showed that the copper acetate precursor generated highly dispersed nano-sized copper oxide species on the silica surface, while the copper nitrate precursor leaded to bulk-type copper oxide strongly interacting with the silica, and the copper sulfate precursor did not decompose completely during the catalyst preparation. Besides, the acetate precursor produced the highest copper content, due to lower acidity of its solution, which generated a higher density of negative charge on the silica surface and a higher affinity for cupric ions. In conclusion, the great influence of the nature of the precursor salt on the physicochemical characteristics of silica-supported copper catalysts is established.

Copper–Cerium–Tin Oxide Catalysts for Preferential Oxidation of CO in Hydrogen: Effects of Synthesis Method and Copper Content

Copper was incorporated into the Ce-Sn and comparative Ce-Zr oxide supports by one-pot precipitation in the presence of CTAB template and by the impregnation of templated Ce-Sn and Ce-Zr oxides. The synthesized Cu-Ce-Sn and Cu-Ce-Zr catalysts were tested in the continuous-flow preferential oxidation of CO in hydrogen excess. The one-pot synthesized tin- and zirconium-doped catalysts demonstrated better CO conversion and CO2 selectivity than their impregnated counterparts. For the tin-modified ternary system that showed the best catalytic performance, the copper content was further optimized. The structure, reducibility, surface chemical state and textural properties of the catalysts were analyzed by SEM-EDX, XRD, H2-TPR, Raman spectroscopy, XPS and TEM. The nonmonotonic changes in the specific surface area, Cu+/Cu2+ ratio and ratio of lattice and non-lattice oxygen with increasing the Cu content are discussed in terms of copper distribution in the catalysts. The influence of the interaction between copper oxide species and the cerium–tin/cerium–zirconium oxide support on the performance of the ternary catalysts was thoroughly analyzed and discussed.

Enhanced water-gas shift reaction performance of MOF-derived Cu/CeO2 catalysts for hydrogen purification

The water-gas shift (WGS) reaction has received renewed interest because it is one of the key reactions for producing hydrogen and renewable energy in contemporary technologies like fuel cells and bio-refineries. Catalysts play an important role in WGS reaction for achieving high CO conversion and hydrogen generation activity. Thus, the performance and stability of catalysts are vital for the WGS reaction. In the present work, the CuCe metal-organic framework (MOF) is used as a template to derive the nanostructured Cu/CeO2 catalyst. The influence of CuCe-MOF templated approach on the WGS activity of Cu/CeO2 has been established. Different Cu doping levels had a significant impact on WGS activity. Amongst, the Ce0.8Cu0.2O2 (Cu2Ce) catalyst had a highest CO conversion (96%). The long-term stability tests further prove that the Cu2Ce catalyst had maintained high CO conversion over 100 h reaction time. XRD and TEM results suggest that different loadings of Cu content have a distinct impact on the dispersion of Cu and the catalytic properties. N2O chemisorption results suggest that 20 wt.% of Cu loading resulted in high Cu dispersion (52%) compared to other loadings. The H2-temperature programmed reduction (TPR) revealed that the superior catalytic activity of Cu2Ce catalyst could be attributed to the strong reducibility (i.e. lower redox temperature) derived from CuCe-MOF template. It further suggests well-dispersed copper oxide species at low Cu loadings and crystalline copper oxide species at high Cu loadings. This work emphasizes the significance of Cu/CeO2 catalysts with exceptional catalytic activity and stability for the WGS process with MOF-precursor.

Thermal transformation of copper incorporated hydrotalcite-derived oxides and their catalytic activity for ethanol dehydrogenation

Thermal transformation of copper incorporated hydrotalcite-derived oxides is investigated in ethanol dehydrogenation. Among the copper supported catalyst c-10Cu/HT600 prepared by impregnation of thermally treated hydrotalcite at 600 °C with Cu(NO3)2 solution followed by a calcination provides a high catalytic activity, selectivity and stability. XRD, DR-UV, TGA, H2-TPR, CO2-TPD, TEM and XPS techniques reveal that the nature of the copper species depended on the thermal treatment process and support. Such treatment at high temperatures yields a homogeneous dispersion mixed metal oxide. After copper incorporation generated CuAl2O4 spinel structure linked to the copper oxide species can suppress copper agglomeration leading to the catalytic stability. Moreover, the c-10Cu/HT600 catalyst can provide a high activity and high selectivity to acetaldehyde even at low reaction temperatures (200 °C). However, the copper species may agglomerate to form relatively larger clusters upon increasing metal loading leading to the deactivation.

Synthesis and antimicrobial studies of nano-copper doped carbon substrates; activated carbon, reduced graphene oxide, and carbon nanofiber

Copper oxides (CuxO) have received considerable attention as a result of their biological activity. Nanoparticles (NPs) of CuxO attached to different substrates exhibit a wide spectrum of antimicrobial activity against bacteria and viruses, with similar properties to silver. The antimicrobial activity of CuxO-NPs doped on distinctive carbon materials was investigated for three carbon substrates: apricot stone activated carbon (AAC), reduced graphene oxide (rGO) and carbon nanofiber (CNF). The CuxO-NPs (5 wt%) doped AAC and rGO substrates were prepared by impregnation of copper nitrate followed by a thermal treatment process, while a similar weight of CuxO-NPs doped CNF was fabricated by electrospinning copper nitrate with polyacrylonitrile precursor, followed by carbonization. The CuxO species and chemical functions were characterized by X-ray diffraction and Fourier transform infrared spectroscopy, respectively. Surface morphology was measured using scanning electron microscopy. The antimicrobial activities of the substrates were evaluated by inhibition zone measurement of Staphylococcus aureus and Escherichia coli. The results demonstrated significant inhibition distances for different carbon substrates. Interestingly, CuxO-NPs doped over both AAC and rGO surfaces revealed clear zones against bacteria, whereas the inhibition zone was not recorded for CuxO-NPs doped over a CNF substrate. Various parameters such as carbon substrates, particle size, and copper oxide species were investigated.

Reductive amination of cyclohexanol/cyclohexanone to cyclohexylamine using SBA-15 supported copper catalysts

Amination of cyclohexanol was investigated in vapour phase over copper catalysts supported on mesoporous SBA-15. The different products identified during reductive amination of cyclohexanol reaction were cyclohexanone, cyclohexylamine, along with small amounts of N-Cyclohexylidinecyclohexylamine and dicyclohexylamine. Among several catalysts tested for the reductive amination, 5% Cu supported on SBA-15 exhibited better catalytic performance than other catalysts with 36% selectivity towards cylclohexylamine at 80% cyclohexanol conversion. The optimum reaction conditions employed to achieve the best catalyst performance were at 250 °C, 0.1 MPa of H2/NH3, TOS-10h. The active Cu sites, acidity of the catalyst, and effect of reaction parameters play a pivotal role in the reductive amination reaction. The prepared catalysts were characterized by XRD, BET, SEM, H2-TPR and NH3-TPD. The dispersion of Cu, particle size, and metal surface area (m2/g) calculated from pulse N2O decomposition method. TPR findings reveal the presence of substantially dispersed copper oxide species at lower loadings which is easily reducible than the bulk copper oxide species found at higher Cu loadings. The acidity measurements by NH3-TPD analysis suggest that the maximum acidic strength was obtained at 5 wt% copper on porous SBA-15, and decreased with Cu loadings. The catalytic properties are well in agreement with the findings of catalysts characterization.

Design Control of Copper-Doped Titania–Zirconia Catalysts for Methanol Decomposition and Total Oxidation of Ethyl Acetate

This study is focused on the design control of Cu–Zr–Ti oxide composites by the variation of the Zr/Ti ratio and the copper deposition procedure used. For the first time, these ternary composites were obtained by a combination of template-assisted hydrothermal techniques for the preparation of mesoporous ZrO2–TiO2 mixed oxides with diverse compositions, followed by the consecutive chemisorption and hydrolysis of copper ammonia complexes on them. The nitrogen physisorption, XRD, SEM, HRTEM, TPR, XPS, UV-Vis, and Raman spectroscopies were applied for the catalysts’ characterization. Methanol decomposition and the total oxidation of ethyl acetate, both of which with potential for sustainable environmental protection, were used as catalytic tests. The complex relationship between the phase composition, structure, and morphology of titania–zirconia mixed oxides and the state and catalytic behavior of the copper oxide species supported on them was investigated. In comparison with the conventional impregnation technique, the novel preparation procedure revealed the generation of more uniform and homogeneously dispersed needle-like copper oxide crystallites in the mesoporous TiO2–ZrO2 host matrix, which typically ensure improved catalytic performance. The synergistic activity between the loaded copper species and TiO2–ZrO2 support was discussed. All ternary composites exhibited superior catalytic activity in total oxidation of ethyl acetate. The specific behavior of the catalysts in methanol decomposition was related to the irreversible phase transformations by the influence of the reaction medium.

Cu‐Fe/activated carbon catalyst for low‐temperature CO‐selective catalytic: Modification and denitration mechanism

AbstractTo study the Cu‐Fe modification and CO denitration mechanism of carbon‐based sorbent, coconut‐husk activated carbon (AC), which was activated via air thermo‐oxidation and modified using Cu(NO3)2 and Fe(NO3)2 was examined. In addition, the denitration activity was evaluated. The effects of air thermo‐oxidative activation, as well as Cu(NO3)2 and Fe(NO3)2 immersion on the pore texture and surface characteristics of the carbon materials, were examined by scanning electron microscopy (SEM), Brunauer–Emmett–Teller (BET) analysis, X‐ray powder diffraction (XRD) and Fourier‐transform infrared (FTIR) spectroscopy. The reduction performance and CO adsorptive property of xCu‐yFe/AC catalyst was measured using hydrogen temperature‐programmed reduction (H2‐TPR) and carbon monoxide temperature‐programmed desorption (CO‐TPD). The xCu‐yFe/AC's denitration activity showed that physical adsorption is a priority, then chemical adsorption recovers the denitration activity after physical adsorption saturation. The modification mechanism showed that higher loading of Cu and Fe resulted in enhanced dispersivity and more active sites but decreased specific surface area and pore volume. Then, the capability of physical adsorption decreased. Moreover, higher Fe loading was conducive to improved dispersivity of copper oxide species. The effects of Cu and Fe modification on the majority of functional groups were insignificant. The reduction peak at approximately 150°C indicated that the xCu‐yFe/AC catalyst has strong reduction characteristics. The number of CO active adsorption sites increased by high loading quantity at high‐temperature. The CO‐selective catalytic reduction (SCR) denitration conforms to Langmuir–Hinshelwood mechanism. The reciprocal transformation between Fe2+ and Fe3+, Cu+ and Cu2+, which is conducive to the rapid progress of the CO‐SCR reaction.

Removal of nitrogen oxides under visible light irradiation by copper phthalocyanine/MOR zeolite composite

A novel copper phthalocyanine/mordenite zeolite (CuPcs/MOR) photocatalyst was synthesized and tested to be a good photocatalyst for NOx removal. With CuPcs0.85/MOR2 composite as catalyst, the degradation rate of NO2 can reach 71.4% under irradiation for 2 h than that of pure CuPcs, attributing to the synergistic effect between them. The process of NOx photocatalytic degradation was discussed, indicating that the MOR with adsorption property not only increased the active sites of CuPcs but also accelerated the charge transfer. A small amounts of copper oxide species are produced during the synthesis, forming co-catalyst with copper phthalocyanine in the system to eliminate nitrogen oxides.

The effect of copper oxide on the CuO–NiO/CeO2 structure and its influence on the CO-PROX reaction

The effect of copper oxide species on the CuO–NiO/CeO 2 structure and the influence on the preferential CO oxidation in H 2 excess (CO-PROX) reaction at low and high temperatures were investigated. Temperature-programmed surface reaction (TPSR), In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and X-ray photoelectron spectroscopy (XPS) results allowed determining the surface species. The maximum temperature of CO 2 formation or selectivity decreased about 40 °C for the CuO–NiO/CeO 2 catalyst compared to the NiO/CeO 2 , which suggests that the addition of Cu + species increases the active sites due to interaction with the Ni–Ce structure. Therefore, the activity of the catalyst was closely related to the oxygen in vacancies and the formation of Cu + -carbonyl species of the redox mechanism. Besides, the superior selectivity towards CO 2 below 150 °C depends on the carbonyl stabilization at the surface, inhibiting the adsorption and subsequent oxidation of H 2 . Using TPSR and spectroscopic analyzes by DRIFTS and XPS allowed us to propose the reaction mechanisms for low and high temperatures. • Synergistic interaction between dispersed CuO species and Ni–Ce–O solid solution. • The presence of Ce 3+ in CeO 2 indicate formation of oxygen vacancies on the surface. • The activity was closely related to oxygen vacancies and Cu + -carbonyl species. • The temperature of CuNiCeO catalyst decreased about 40 °C compared to the NiCeO. • The oxygen vacancies and Cu + -carbonyl species suggest a multiple-step process.

Insight into enhanced hydrogen evolution of single-atom Cu1/TiO2 catalysts from first principles

Developing efficient catalysts of low-cost transition metals for hydrogen production is of great importance but remains a huge challenge. Motivated by the idea of engineering local atomic configuration, we propose to focus on single metal atom confined in the lattice oxygen environment, as a class of non-Pt catalysts for hydrogen production. By first principles calculations, we study the characteristics and mechanism of hydrogen evolution reaction of single-atom Cu supported on anatase TiO2 catalysts, Cu1/TiO2. Cu preferentially sits on the bridge-centre site between two 2-fold coordinated O atoms (O2c) on the surface. Cu and coordinated O2c function as copper oxide species (-Cu-O-) in the reaction. The reaction starts with two isolated H respectively positioned on Cu and O2c, proceeds with a transfer of H from O2c to Cu, and eventually forms a H2 molecule. The free energy profiles indicate that Cu1/TiO2 exhibits excellent hydrogen evolution activity even better than Pt and MoS2. This study not only shows that single-atom Cu1/TiO2 is an excellent hydrogen evolution catalyst, but also expands the understanding of oxide species in single-atom catalysis and proposes an engineering local atomic configuration strategy for optimizing the design of single-atom catalysts for enhanced hydrogen production.

Catalytic activity of Cu/η-Al2O3 catalysts prepared from aluminum scraps in the NH3-SCO and in the NH3-SCR of NO.

Copper-loaded η-alumina catalysts with different copper contents were prepared by impregnation/evaporation method. The catalysts were characterized by XRD, FTIR, BET, UV-Vis, and H2-TPR and evaluated, for the first time, in the selective catalytic reduction of NO by NH3 and in the selective catalytic oxidation of NH3. The characterization techniques showed that the impregnation/evaporation method permits to obtain highly dispersed copper oxide species on the η-alumina surface when a low amount of copper is used (1wt. % and 2 wt.%). The wet impregnation method made it possible to reach a well dispersion of the copper species on the surface of the alumina for the low copper contents Cu(1)-Al2O3 and Cu(2)-Al2O3. The latter justifies the similar behavior of Cu(1)-Al2O3) and Cu(2)-Al2O3 in the selective catalytic oxidation of NH3 where these catalysts exhibit a conversion of NH3 to N2 of the order of 100% at T> 500 °C.

Effects of Fe+2 and Fe+3 in Pretreatment and Leaching on a Mixed Copper Ore in Chloride Media

A study of the pretreatment stage and subsequent leaching of a mixed copper ore with different chloride solutions containing iron was carried out. The first stage considered pretreatment tests to decide the best conditions. Two levels of each factor were analyzed, 20 and 50 kg/t of NaCl, 17 and 25 kg/t of H2SO4, 0 and 25 kg/t of Fe2(SO4)3·9.2H2O, 0 and 25 kg/t of Fe2SO4·7H2O, and a curing time of 15 and 30 days. The results showed a significant effect of NaCl and curing time on the extraction, and less effect was found with the variation of acid and iron salts. The second stage included column leaching using a solution with 0.5 g/L of Cu+2, 80 g/L of Cl−, 10 g/L of H2SO4, and variable concentrations of ferric and ferrous ions (0 and 2 g/L). The best copper extraction of 80.2% was found considering a pretreatment of 30 days, 25 kg/t of H2SO4, 50 kg/t of NaCl, and a leaching solution concentration described previously with 2 g/L of Fe+2. The results showed the leaching of all copper oxide species and 20% of the copper sulfide species. In addition, there was a reduction in the acid consumption as the resting time increases. Furthermore, to evaluate a possible decrease in time and acid in pretreatment and chloride in leaching, tests including 10 and 25 kg/t of H2SO4 and 1, 15, and 30 days of curing and a diminution of the NaCl concentration to 20 g/L (content from seawater) were executed. The results showed a significant effect on curing time below 15 days. Furthermore, the slight influence of the decrease of acid on copper extraction gives cost reduction opportunities. The diminution of chloride concentration (80 to 20 g/L) in leaching solution decreases the extraction from 79% to 66.5%. Finally, the Mellado leaching kinetic model was successfully implemented.

Spherical Al-MCM-41 Doped with Copper by Modified TIE Method as Effective Catalyst for Low-Temperature NH3-SCR.

Aluminum containing silica spherical MCM-41 was synthesized and modified with copper by the template ion-exchange method (TIE) and its modified version, including treatment of the samples with ammonia solution directly after template ion-exchange (TIE-NH3). The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD), texture (low temperature N2 sorption), morphology (SEM-EDS), form and aggregation of deposited copper species (UV-vis DRS), reducibility of copper species (H2-TPR), and surface acidity (NH3-TPD). The deposition of copper by the TIE-NH3 method resulted in much better dispersion of this metal on the MCM-41 surface comparing to copper introduced by TIE method. It was shown that such highly dispersed copper species, mainly monomeric Cu2+ cations, deposited on aluminum containing silica spheres of MCM-41, are significantly more catalytically effective in the NH3-SCR process than analogous catalysts containing aggregated copper oxide species. The catalysts obtained by the TIE-NH3 method effectively operated in much broader temperature and were less active in the side process of direct ammonia oxidation by oxygen.

Electrodeposition of Cu2O nanostructures with improved semiconductor properties

In the present research, nanocomposites based on copper (I) oxide poly(1-vinyl-2—pyrolidone-co-itaconic acid) nanostructures (Cu2O/p(NVP-co-AI)) were synthesized by the electrodeposition method using the copolymer p(NVP-co-AI) as a stabilizing agent in the reduction of Cu+2 to Cu+. The chemical and physical properties of the nanostructures were characterized by techniques such as scanning electron microscopy, infrared (IR) spectroscopy, Raman and ultraviolet-visible spectrophotometry. The obtained nanostructures are mainly a mixture of agglomerated nanospheres with a diameter of approximately 78 to 91 nm, with an alternation of nanolaminar structures, composed of copper (I) oxide species. In the case of the Cu2O/p(NVP-co-AI) nanocomposite, it was observed a decrease in the carbon-oxygen vibration links of the carbonyl groups in IR intensity for the polymer when it was dissolved in the electrolytic solution, which indicates that interactions are produced by the carbonyl groups with the Cu2O species. In addition, bandgap values of 1.80 and 1.63 eV were estimated by the Kubelka–Munk method for Cu2O and Cu2O/p(NVP-co-AI) samples, respectively.

Effect of zeolite topology on NH3-SCR activity and stability of Cu-exchanged zeolites

The catalytic activity and stability of Cu-exchanged zeolites Cu-ZSM-5 (MFI topology), Cu-TNU-9 (TUN), Cu-FER (FER) and steamed Cu-Y (FAU) were evaluated in the selective catalytic NO reduction by ammonia (NH3-SCR). The NH3-SCR activity of the investigated catalysts strongly depended on the feed composition, i.e., the presence of H2O (5.0 Vol.-% of H2O). The catalysts revealed high stability during 24 h of NH3-SCR reaction, also in the presence of water vapour. DR UV–vis and FT-IR with probe molecules (CO or NO) showed the presence of isolated Cu+/Cu2+ and aggregated copper oxide species. Although Cu-ZSM-5 is less active than Cu-TNU-9 in catalysing NO oxidation to NO2, both catalysts revealed similar activity in the NH3-SCR reaction. Applying Rapid-Scan FT-IR spectroscopy and 2D COS analysis the reaction mechanism of NH3-SCR on Cu-exchanged zeolites was investigated. It is proposed that NH3-SCR over the studied Cu-exchanged catalysts proceeds via [Cu(OH)(NH3)2(NO)]+ intermediates followed by the reduction of Cu(II) to Cu(I). The differentiated speciation of copper sites is reflected in their various susceptibility for the reduction and finally affects the catalytic activity and stability of the zeolitic catalysts. The formation of the [Cu(OH)(NH3)2(NO)]+ mixed ligand species is governed by the competition between the O2− and NH3 ligands. Also the stability of the forms initiating NH3-SCR, i.e., [Cu(NH3)4]2+, [Cu(OH)(NH3)3]+ and [Cu(NH3)2]+, is ruled by the confine interaction of ammonia molecules, which can be both adsorbed on a protonic site and ligated to copper sites with the framework oxygen atoms.

Ferrierite and Its Delaminated Forms Modified with Copper as Effective Catalysts for NH3-SCO Process.

Ferrierites and their delaminated forms (ITQ-6), containing aluminum or titanium in the zeolite framework, were synthetized and modified with copper by an ion-exchange method. The obtained samples were characterized with respect to their chemical composition (ICP-OES), structure (XRD, UV-Vis DRS), textural parameters (N2-sorption), surface acidity (NH3-TPD), form and reducibility of deposited copper species (UV-Vis DRS and H2-TPR). Ferrierites and delaminated ITQ-6 zeolites modified with copper were studied as catalysts for the selective catalytic oxidation of ammonia to dinitrogen (NH3-SCO). It was shown that aggregated copper oxide species, which were preferentially formed on Ti-zeolites, were catalytically active in direct low-temperature ammonia oxidation to NO, while copper introduced into Al-zeolites was present mainly in the form of monomeric copper cations catalytically active in selective reduction of NO by ammonia to dinitrogen. It was postulated that ammonia oxidation in the presence of the studied catalysts proceeds according to the internal-selective catalytic reduction mechanism (i-SCR) and therefore the suitable ratio between aggregated copper oxide species and monomeric copper cations is necessary to obtain active and selective catalysts for the NH3-SCO process. Cu/Al-ITQ-6 presented the best catalytic properties possibly due to the most optimal ratio of these copper species.