Copper Ion-exchanged Zeolites Research Articles

Copper ion-exchanged zeolite X from fly ash as an efficient adsorbent of phosphate ions from aqueous solutions

Zeolite X derived from fly ash was modified with Cu(NO3)2∙3 H2O solutions of various initial concentrations (0.01, 0.05, 0.10, 0.15, and 0.20 M). The obtained materials were investigated by means of XRD, XRF, N2 adsorption-desorption, and pHpzc. The concentration of Cu(NO3)2∙3 H2O significantly affected both the textural and chemical surface properties of the obtained zeolites. The materials were subjected to a series of adsorption experiments to remove phosphate ions from aqueous solutions. The highest adsorption capacity was obtained for zeolite X modified with 0.05 M Cu(NO3)2∙3 H2O solution, and the obtained adsorption capacity was 87.7 mg (PO43-) g−1. The adsorption mechanism was investigated by means of XPS analysis and correlated with the assumptions of kinetic adsorption models. The interaction between phosphate ions and Cu species on the zeolite surface was found to be the guiding mechanism of adsorption. Additional mechanisms, including precipitation as calcium phosphate and electrostatic attraction, should also be taken into account. A single-point adsorption of phosphate ions was also studied to evaluate the effects of adsorbent dose (1, 2, and 3 g L−1) and adsorption temperature (18, 25 and 40 °C). Increased adsorbent dose resulted in a significantly greater removal of phosphate ions for zeolite Cu0.05X (up to 65.4%). The temperature of 25 °C was found to be the most suitable for conducting adsorption of phosphate ions. Leaching test was performed in water to investigate the risk of applying the investigated zeolites in aqueous solutions as potential adsorbents.

Copper Ion-Exchanged Zeolite X Derived from Fly Ash for Enhanced Phosphate Removal from Aqueous Solutions

Copper Ion-Exchanged Zeolite X Derived from Fly Ash for Enhanced Phosphate Removal from Aqueous Solutions

Micro-structured Cu-ZSM-5 catalyst on aluminum microfibers for selective catalytic reduction of NO by ammonia

Selective catalytic reduction of NOx with NH3 (NH3-SCR) is one of the most efficient technologies to remove NOx emissions. The copper ion-exchanged zeolites with broad temperature windows and high N2 selectivity are very promising for this process. In this work, we synthesized a series of microfibrous-structured Cu-ZSM-5/Al-fiber catalysts for SCR reaction by changing the Si/Al molar ratios. The in-situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) of NH3 adsorption results show that the Cu-ZSM-5/Al-fiber catalysts with higher Si/Al molar ratios have higher NH3 adsorption capacity. The subsequent NO adsorption results show that the amount of adsorbed bridged nitrates species is in accordance with the enhanced NOx degradation activity. At moderate temperature, Cu-ZSM-5/Al-fiber catalyst shows better NH3-SCR performance under higher gas hourly space velocity (GHSV), indicating microstructured Cu-ZSM-5 catalysts are more active at high-throughout conditions due to the enhanced mass transfer.

Copper-exchanged Y zeolites for gasoline deep-desulfurization

Adsorptive desulfurization is one of the most efficient methods to remove recalcitrant sulfur compounds from transportation fuels. Two π-complexation-based sorbents were studied for desulfurization of synthetic gasoline. The sorbents were obtained by ion exchanging Y zeolites with copper cations using different techniques, which includes liquid phase ion exchange (CuY1) and vapor phase ion exchange (CuY2). Preliminary kinetic and equilibrium experiments for sulfur adsorption in batch system showed that CuY1 has the greatest desulfurization capacity and selectivity. The best adsorbent, CuY1 pellet, had a dynamic adsorption and equilibrium capacity of 2.97 and 4.14 mg S/g for fixed bed column assays, respectively. Experimental data obtained to batch reactor and packed bed column have been interpreted by means of a pore diffusion model in which the mass balance to the pellets are emphasized. The model proposed was able to fit well to the experimental data. After the first thermal regeneration, the copper ion-exchanged zeolite presented a maximum recovery of 91.5%. The copper-exchanged zeolite (in pellet form) has shown good uptake rate and regenerability for desulfurization of synthetic gasoline.

Investigation of the robust hydrothermal stability of Cu/LTA for NH3-SCR reaction

Recently copper ion-exchanged LTA zeolites were proved to be robust for NH3-SCR reaction. In this study, Cu/LTA catalysts with Si/Al = 15 and Cu/Al = 0.4 were synthesized via incipient wetness impregnation (IWI) method, following degreening/hydrothermal aging at different temperatures (750, 800, 850, 900 °C), and used to catalyze standard SCR, fast SCR and NH3/NO oxidation reactions. Catalysts were characterized with surface area/pore volume, powder X-Ray diffraction (XRD), nuclear magnetic resonance (NMR), H2-temperature programmed reduction (H2-TPR) and in situ Diffuse Reflectance Infrared Fourier Transform Spectra (DRIFTS). Through the BET surface areas, XRD and NMR results, it can be found that the framework structure stability of Cu/LTA catalysts during hydrothermal aging was outstanding, even after harsh aging at 900 °C. Moreover, various Cu species, including Z-Cu2+, Z-[Cu(OH)]+ and CuOx clusters, were quantified for Cu/LTA catalysts hydrothermally aged under various temperatures with H2-TPR and in situ DRIFTS. An imperative finding in this study is the exceptional hydrothermal stability of [Cu(OH)]+ and the gradual conversions of both Cu2+ and CuOx clusters to [Cu(OH)]+ with increasing aging temperature. It is worth noting that this phenomenon is exactly the opposite of Cu/SSZ-13. As it is known from the literature (Song et al., 2017), the formation of CuOx not only decreases the selectivity of NOx conversion, but also can cause deterioration of zeolite structure, since the ion-exchanged copper stabilizes the zeolite. This may also explain why the hydrothermal stability of Cu/LTA samples is outstanding.

Effect of pretreatment on carbon oxidation activity over copper ion-exchanged zeolite catalysts

The carbon oxidation over copper ion-exchanged zeolites (Cu-MFI, Cu-MOR, Cu-FAU, and Cu-BEA) pretreated at 700 °C was investigated. The catalytic activities of Cu-MFI, Cu-MOR, and Cu-FAU pretreated at 700 °C were higher for carbon oxidation in NO + O2 atmosphere than that of Cu-BEA. The TEM results demonstrated that Cu fine particles were formed on the external surface of Cu-MFI, Cu-MOR, and Cu-FAU, showing high activity. In addition, it was suggested that the coexisting NO plays an important role in enhancing the catalytic activity of Cu-MFI for carbon oxidation.

Direct Information on Structure and Energetic Features of Cu+−Xe Species Formed in MFI-Type Zeolite at Room Temperature

The interacted species of Xe with metal ions that are stable at room temperature are not known and are a subject of interest for fundamental chemistry. We have experimentally found a new and stable Xe species, XeCu+, which was formed at room temperature in a copper ion-exchanged MFI-type zeolite. The presence of a prominent interaction between Cu+ in MFI and Xe, which has a covalent nature, was for the first time evidenced from experimental in situ synchrotron X-ray absorption fine structure and heat of adsorption measurements: the Cu+−Xe bond length of 2.45 Å and the bonding energy of ca. 60 kJ mol−1. The bonding nature between Xe and Cu+ in the MFI zeolite was discussed utilizing density functional theory; the observed significant stabilization comes from the d(Cu+ in MFI)−p(Xe) orbital interaction. These new findings may pave a new way to developing fundamental chemistry of Xe compounds.

Improvement of the carbon oxidation activity of Cu-MFI by high-temperature pretreatment

The carbon oxidation was investigated over copper ion-exchanged MFI zeolite (Cu-MFI) as a function of pretreatment temperature. Cu-MFI pretreated at 700 °C exhibited high activity for carbon oxidation in NO + O2 atmosphere. The activity of Cu-MFI pretreated at 700 °C increased with increasing the amount of copper ion exchanged. XRD and ESR measurements suggest that the CuO fine particles as an active site for carbon oxidation were formed on the surface of MFI zeolite by pretreatment at 700 °C.

Potential for C−H Activation in CH4Utilizing a CuMFI-Type Zeolite as a Catalyst

We have found that a copper ion-exchanged MFI (Mobil Five)-type zeolite, having an ion exchange capacity of 112% (CuMFI-112), exhibits a specific interaction with CH4, even at room temperature. The observed properties are very remarkable compared with those found in the adsorbed amount of sodium ion-exchanged MFI and in the interaction with the sodium ion in MFI as well as in the adsorbed amounts for other types of copper ion-exchanged zeolites. The specificity of Cu+ in MFI is clearly evident. The most remarkable feature of the present system is the distinct appearance of infrared bands (IR) at 2661 and 2619 cm−1 due to adsorbed CH4 at 300 K and the change in the X-ray absorption fine structure spectra of CuMFI before and after CH4 adsorption at 300 K, indicating the existence of substantial and specific interaction in this system. In addition, calculations based on the density functional theory were carried out by utilizing a Cu−AlSi91O151H66 cluster model, which is made up of a 10-membered ring of CuMF...

Preparation of CuNaY zeolites with microwave irradiation and their application for removing thiophene from model fuel

To produce ultralow-sulfur fuels, copper ions have been introduced into the framework of Y zeolite by a novel, simple liquid-phase ion exchange method taking advantage of microwaves irradiation. Removal of thiophene from model fuels were studied over activated copper ion-exchanged zeolite samples using column breakthrough experiments at ambient temperature and pressure. The effects of the microwave irradiating power, duration time and the copper ion concentration in aqueous solutions on the ion exchange level and the structure of copper ion-exchanged zeolite samples were investigated by atomic absorption spectrophotometer, X-ray powder diffraction, N 2 adsorption and scanning electron microscope and X-ray photoelectron spectroscopy. The results demonstrated that ion exchange under microwave irradiation was a more attractive zeolite preparation method compared with conventional ion-exchange process. The maximum exchange level of 75% could be obtained after only 10 min irradiation while the exchange level was 71% after conventional ion exchange for twice and the copper can be better dispersed in zeolite framework under microwave irradiation. Microwave-irradiated CuNaY zeolites could efficiently remove thiophene from model fuel with a high sulfur removal capacity of 1.22 mmol/g.

New Information Related to the Adsorption Model of N2 on CuMFI at Room Temperature

The N2 adsorption occurring at temperatures around room temperature is a particularly surprising phenomenon given by the copper ion-exchanged MFI-type zeolite (CuMFI). However, the assignment of the active sites for N2 adsorption on CuMFI at room temperature is controversial: which ones act as the real active center, the dimeric or monomeric Cu+ sites? We have analyzed the real active site for N2 adsorption by studying the adsorption of CO and N2, and also by spectroscopic methods, such as photoluminescence, X-ray absorption fine structure, and IR measurements. Clear evidence was observed for the adsorption of N2 molecules on the monomeric Cu+ ions exchanged in the MFI-type zeolite at temperatures around room temperature, which puts to an end the dispute regarding the dimeric state made up of the monovalent copper ions as being a potential adsorption site.

Copper ion-exchanged zeolite in plant nutrition

Copper ion-exchanged zeolite in plant nutrition

Nitric oxide adsorbed on zeolites: EPR studies

CW-EPR studies of NO adsorbed on sodium ion-exchanged zeolites were focused on the geometrical structure of NO monoradical and (NO) 2 biradical formed on zeolites. The EPR spectrum of NO monoradical adsorbed on zeolite can be characterized by the three different g-tensor components and the resolved y-component hyperfine coupling with the 14 N nucleus. Among the g-tensor components, the value of g zz is very sensitive to the local environment of zeolite and becomes a measure of the electrostatic field in zeolite. The temperature dependence of the g-tensor demonstrated the presence of two states of the Na–NO adduct, in rigid and rotational states. The EPR spectra of NO adsorbed on alkaline metal ion-exchanged zeolite and their temperature dependency are essentially the same as that on sodium ion-exchanged zeolite. On the other hand, for NO adsorbed on copper ion-exchanged zeolite it is known that the magnetic interaction between NO molecule and paramagnetic copper ion are observable in the spectra recorded at low temperature. The signals assigned to (NO) 2 biradical were detected for EPR spectrum of NO adsorbed on Na-LTA. CW-EPR spectra as well as their theoretical calculation suggested that the two NO molecules are aligned along their NO bond axes. A new procedure for automatical EPR simulation is described which makes it possible to analyze EPR spectrum easily. In the last part of this paper, some instances when other nitrogen oxides were used as a probe molecule to characterize the zeolite structure, chemical properties of zeolites, and dynamics of small molecules were described on the basis of selected literature data reported recently.

Copper ion-exchanged zeolite catalysts in deNO x reaction

Copper ion-exchanged zeolites have widely been studied as the catalysts for NO x emission control. Cu-MFI zeolites, especially over-exchanged Cu-MFI, are very active for the catalytic decomposition of NO. The reaction mechanisms and the active sites suggested are summarized. The newly developed selective catalytic reduction of NO with hydrocarbons in the presence of excess oxygen is then introduced. The role of oxygen and the deactivation of the zeolite catalysts are discussed. In the last chapter, the high ability of Cu-zeolites for NO adsorption is overviewed. Here, some fundamental aspects of the bonding and the molecular diffusion of NO or NO 2 molecules in zeolites are also summarized.

The characteristics of a copper-exchanged natural zeolite for NO reduction by NH 3 and C 3H 6

The catalytic performance of the natural zeolite mined from Youngil, Korea was investigated when two types of reductant such as NH 3 and hydrocarbons were employed for the reduction of NO. The determination of the structure of the natural zeolite has also been made to identify the type of zeolite and to examine its use as a catalytic material for NO removal reaction. The elementary analysis and electron probe microanalysis of the zeolite revealed that it typically consisted of an aluminosilicate. Although it mainly contains mordenite-type zeolite, heulandite was also included as well as the phases of quartz and feldspar as an impurity in the zeolite. This result could be also confirmed by the X-ray diffraction (XRD) and differential scanning calorimetry (DSC) analyses. It should be noted that the acid treatment of the natural zeolite for its use as a catalytic material is essential for the high performance of NO reduction by selective catalytic reduction (SCR) technology. Copper ion-exchanged natural zeolite catalyst (CuNZA) exhibits a competitive NO reducing activity for the reduction of NO by NH 3 as well as hydrocarbons. It can be regarded as a promising catalytic system by NH 3 and hydrocarbons for the removal of NO x from stationary and mobile sources.

Conversion and in situ FTIR studies of direct NO decomposition over Cu-ZSM5

Copper ion-exchanged zeolites ZSM5 with SiO 2:Al 2O 3 molar ratios 33 and 53 have been subjected to activity tests for direct decomposition of NO (2000 ppm, GHSV 560–5400 h −1). In situ infrared measurements were used to follow the reaction and surface and gas phase compositions. IR studies were also done in excess oxygen with rapid NO 2 formation in the gas phase. A high level of overexchange of copper in the zeolite in combination with a low concentration of acid sites, concurrent with a high SiO 2:Al 2O 3 ratio, enhances the conversion of NO. A vibrational band at 1631 cm −1 is observed below the light-off temperature and interpreted as a bridged nitrato group bound to Cu 2+–O–Cu 2+ dimers. This band disappears above the light-off temperature but the intensity below this temperature correlates with the catalytic activity. We interpret that these bridge bound nitrato groups act as siteblockers on the active sites for NO conversion and that a tentative reaction intermediate, N 2O 3, also binds in a bridge configuration to the same Cu 2+–O–Cu 2+ dimers. A second nitrato group with unidentate coordination and vibrational bands at 1598/1575 cm −1 probes isolated copper ions. A third infrared band at 2130 cm −1 confirms previous observations of NO + 2-ions bound to the zeolite. We conclude that these species are coordinated to deprotonated and negatively charged sites on the zeolite and that these sites for NO + 2 adsorption are blocked by Cu 2+ ion-exchange. The 2130 cm −1 species appear to have no role in direct NO decomposition but the adsorption sites are crucial for the stability of the zeolite and intimately related to ion mobility in the lattice. Prolonged immersion of the zeolite in dilute solutions of copper ions improves the catalyst performance by copper hydroxylation leading to enhanced formation of the above dimers. A high SiO 2:Al 2O 3 ratio leads to more stable catalysts, particularly in combination with a modest overexchange of copper ions. Excessive amounts of copper escalates the deactivation of the Cu-ZSM5 catalyst through the migration and sintering of cupric oxide crystallites.

Performance of Zeolite-Supported Catalysts for Selective Catalytic Reduction of Nitric Oxide and Oxidation of Methane

The selective catalytic reduction of nitric oxide by methane over copper ion-exchanged natural zeolites was investigated in a packed-bed tubular reactor. The catalytic activity of Cu−N and Cu−H−N catalysts was confirmed as NO, CH4, and O2 displayed very little reaction in the absence of any catalyst and zeolite without ion exchange was totally inactive. A maximum NO conversion of 33% at 650 °C for Cu−N-66 was achieved with 2% NO and 1% CH4 and a contact time of 0.9 g s cm-3, but the introduction of 2% O2 reduced the NO conversion to only 12%. Ion exchange for the H-form prior to copper ion exchange was essential for oxygen to promote catalytic activity over the temperature range 250−650 °C, with a maximum conversion of 30% at 450 °C with O2 present. The direct reduction of NO by methane was ruled out as a possible reaction pathway.

Remarkable Difference between the Kinetic Parameters of a Selective Catalytic Reduction of NO by Ethene on a Copper Ion-Exchanged MFI Zeolite and Al2O3

Abstract The kinetic parameters have been determined in reaction systems of NO + O2 + C2H4, NO2 + O2 + C2H4, NO + O2, and O2 + C2H4 over a copper ion-exchanged MFI zeolite (Cu-MFI) and Al2O3. The rate equations for the N2 formation in the NO + O2 + C2H4 system on Cu-MFI (553—593 K) and Al2O3 (673—773 K) were expressed by exp (−168000/RT) and exp (−294000/RT), respectively. The significant difference between the equations reveals that the reaction mechanisms or rate-determining steps on Cu-MFI and Al2O3 greatly differ. In addition, the rate equations for N2 and CO2 production were the same on Cu-MFI, while they were different on Al2O3. The reaction mechanism is discussed based on the equations.

Assignment of the 2177 cm−1 Absorption Band Appearing upon Admission of CO on a Copper Ion-exchanged MFI Zeolite

Abstract The titled absorption band was attributable to νsym of a dicarbonyl species adsorbed on a Cu+ ion. The monocarbonyl species at 2158 cm−1 and the dicarbonyl species at 2177 and 2151 cm−1 have reversibly changed each other dependent on the partial pressure of CO.

Assignment of Nonclassical [Cu(CO)(n)](+) (n = 1, 2) Complex Ions in Zeolite Cages.

A time-resolved FT-IR technique combined with an isotopic tracer method has been applied to study CO adsorbates on Cu(+) ions in copper ion-exchanged zeolites. Three kinds of monocarbonyl species were found to adsorb strongly on Cu-zeolite samples after admission and subsequent evacuation of gas phase CO at room temperature. Their absorption bands were observed at 2146-2160, 2128-2150, and 2097-2129 cm(-1), respectively, dependent on the zeolite structures. In the presence of gaseous CO, the monocarbonyl species at 2146-2160 cm(-1) (so called nonclassical [Cu(CO)](+) complexes) could react with a CO molecule to form a dicarbonyl species [Cu(CO)(2)](+) with nu(sym) bands at 2169-2180 cm(-1). The reactivity of the nonclassical [Cu(CO)](+) complexes was dependent on the zeolite structures, ferrierite > mordenite > ZSM-5 > X-type left harpoon ovet right harpoon offretite/erionite left harpoon ovet right harpoon Y-type > L-type. The remaining two types of monocarbonyl species have little been affected by gas phase CO.