CuZSM-5 Zeolites Research Articles

Glycerol valorization: The effect of Cu on the HZSM5 catalyst structure and increased selectivity towards allyl alcohol

The valorization of glycerol modified with impregnated Cu nanoparticles was investigated. Significant enhancement in the rate of formation and yield of the allyl alcohol and acrolein is observed in the gas-phase conversion of glycerol. Concerning characterization results, Cu showed low interaction with the ZSM-5 support, resulting in minor changes in the structure of materials. ZSM-5 samples showed higher selectivity to acrolein and the CuZSM-5 ones showed higher selectivity to allyl alcohol. Due to agglomeration of Cu clusters and, consequently, conversion of Cu2+ into Cu0 species during glycerol reaction, liquid product selectivity was shifted from acrolein to allyl alcohol. Analysis of the glycerol valorization of the studied processes shows that the CuZSM-5 zeolite catalyst has greater selectivity for allyl alcohol, also has better performance in terms of added value than HZSM-5 catalyst, since allyl alcohol has a higher market value than acrolein.

Basic thermodynamic characteristics of toluene adsorption in Cu2+ZSM-5 Zeolite

This paper presents the results of isotherms and basic (ΔH, ΔF and ΔS) thermodynamic characteristics of toluene adsorption in CuZSM-5 zeolite. For measurements of isotherms and differential heat of adsorption, a system consisting of a universal high-vacuum adsorption unit and an attached differential modified Tian-Calve microcalorimeter DAC-1-1A was used to provide direct quantitative and qualitative characteristics of the nature and forces of adsorption interaction. The correlation between the adsorption-energy characteristics wasfound and the molecular mechanismof toluene adsorption in CuZSM-5 zeolite in the whole filling region was revealed. Toluene adsorbed in CuZSM-5 zeolite is located in the first coordination sphere with Cu2+ cation, forming two-dimensional complexes. It was found that the charge density significantly affects the mechanism, the energy of adsorption and the number of adsorbed molecules. It was determined that the average molar entropy of toluene adsorption in CuZSM5 zeolite indicates that the mobility of toluene molecules in zeolite is below the liquid phase and close to that of the solid phase, indicating that the mobility of toluene molecules on cations is strongly inhibited. This work shows how calorimetric data can be used to complement crystal structure results and detect subtle adsorbent/adsorbate interactions at the molecular level.

Automotive Internal Combustion Gas Reduction using CuZSM-5 in a Catalytic Converter

Toxic gases emitted by internal automotive combustion are responsible for air pollution and deterioration of human health. Therefore, in this study modified zeolite was evaluated as an alternative catalyst for reducing automotive gases in a catalytic converter. For the study, the CuZSM-5 zeolite was synthesized by the hydrothermal method, exchanged with copper ions and then installed in the exhaust of a T3 Bi-Fuel engine. The experiments were carried out on an auto model 1984 Toyota, with and without a catalytic converter at different revolutions per minute (rpm) as idle, average and maximum, using the HGA 400 4GR gas analyser to measure hydrocarbon (HC) and carbon monoxide (CO). The results showed a significant reduction in LPG engine of Hydrocarbon Propane (78 %) and CO (60 %) at high rpm; while in gasoline engine was reduced at Hexane (29 %) and carbon monoxide (68 %) at low rpm. This showed that Cu-zeolite is efficient in reducing gases and more economical than the commercial converter.

INVESTIGATION OF PERFORMANCE AND EMISSION CHARACTERISTICS OF AN SI ENGINE FITTED WITH ZEOLITE-COATED CATALYTIC CONVERTER FOR VARIOUS ETHANOL-GASOLINE BLENDS

Ethanol blended in gasoline will produce more NOx emissions, compared to the conventional engine working under a stoichiometric air-fuel ratio. But, the emission control regulatory bodies tightened the emission level year by year. So, in our present work, a new metal-doped zeolite (as a catalyst)-coated monolith catalytic converter (CC) is developed and tested in the twin-cylinder multipoint fuel injection (MPFI) petrol engine using ethanol-gasoline blended fuels (P100, P95, P90, P85, and P80) (the numbers following P indicate percentage of the volumetric amount of gasoline). Initially, the engine was tested without a catalytic converter at various designated speed levels (2200, 2400, 2600, 2800, and 3000 rpm) and the emissions such as CO, HC, NOx, CO2, and O2 were calculated by an AVL 444 Di-gas analyzer at each speed level. The emission levels were compared and it was found that P80 blended fuel gives less emission. So, P80 blended fuel alone was taken for further investigation. Then, the market available catalytic converter was linked immediately to the exhaust gas outflow and a similar procedure was continued. Likewise, the testing was conducted with a new in-house-made Cu-ZSM5 zeolite catalytic converter. Outcomes from these experiments revealed that Cu-ZSM5 zeolite-based catalytic converter reduces NOx emission by 29% more effective than the market available catalytic converter for all the speeds.

Investigation of Cu-ZSM5 catalyst for the Emission Reduction in ethanol-gasoline blends using iso-butanol as an additive in SI engine

In this experimental work, the Gasoline engine was used to find out the effects of Cu-ZSM5 zeolite coated catalytic convertor on the emission characteristics of iso-butanol additive in ethanol-gasoline blends. The engine was tested under three speeds namely 2000rpm, 3000rpm, and 4000rpm. The volumetric proportion of the fuel samples taken for testing were gasoline (pure gasoline), E10 (90% gasoline, 10%ethanol), IB5 (95% E10, 5% Iso-butanol) and IB10 (90% E10, 10% Iso-butanol). The physiochemical properties of the fuels like heating value, kinematic viscosity, and density were analyzed for these samples as these values influence the emission formation characteristics. The heating value of the samples was decreased with the gasoline concentration in the fuel samples. E10, IB5, and IB10 produced the heating values of 2.34%, 3.13% and 5.05% respectively less than that of the gasoline. However the fuel properties like density, kinematic viscosity tens to increase with the alcohol concentration in the samples. From the performance results, the Brake specific fuel consumption decreased for E10, IB5 and IB10 of about 3.57%, 5.14%, and 7.13% respectively when compared to gasoline. Brake thermal efficiency of the fuel increased to a noticeable level with the addition of the alcohol in gasoline. Initially, the engine was tested by fitting the commercially purchased catalytic converter in the exhaust system and the emissions values were measured with the help of AVL 444 gas analyzer. Then the engine was fitted with the Cu-ZSM5 coated in-house fabricated catalytic convertor and the emission values were measured. At 3000rpm, it has been found that the zeolite coated catalytic convertor reduces HC, CO and NOX emissions by 33%, 9% and 8.3% more than that of the commercial catalytic convertor.

Adsorption and Photocatalytic Degradation of Methyl Orange on TiO<sub>2</sub> and CuZSM-5 Mixture

TiO2 and CuZSM-5 were mixed together as photocatalyst in dealing with photocatalytic degradation of methyl orange. Adsorption and photocatalytic degradation properties of the CuZSM-5 zeolite and mixture of TiO2 and CuZSM-5 were investigated. The CuZSM-5 zeolite has no photocatalytic activity under the experimental conditions. Methyl orange decoloration rate was 65.4%, which was 9.60% higher than that without using CuZSM-5, when TiO2 and CuZSM-5 were at the optimum ratio of 3.13:1. An optimum TiO2 concentration of 250 mg/l occurred when using pure TiO2. However, when using TiO2-CuZSM-5 mixture, the decoloration rate continuously increased with increasing photocatalyst concentration. After 70 min of irradiation, 98.4% of the initial methyl orange decoloration was found using TiO2-CuZSM-5 mixture at TiO2 concentration of 250 mg/l.

DRIFTS evidence for the formation of binuclear Cu(I)–dinitrogen complexes upon adsorption of N 2 on CuZSM-5

The room temperature adsorption of dinitrogen on CuZSM-5 zeolite was studied using diffuse-reflectance infrared spectroscopy (DRIFTS). In addition to an intense absorption band at 2294 cm −1, a weak band at 2207 cm −1 in the region of NN stretching vibrations was also detected in the spectra. Surprisingly, this latter band increases in intensity when the dinitrogen pressure decreases. This band was assigned to internuclear bridging dinitrogen molecules in copper–dinitrogen complexes formed following the adsorption of dinitrogen on CuZSM-5. Quantum-chemical calculations of model zeolite–2Cu(I)– nN 2 compounds were performed to confirm the assignment of the bands in the DRIFT spectra of adsorbed N 2. It is suggested that at high dinitrogen pressures the formation of a binuclear zeolite–2Cu(I)–3N 2 complex containing both terminal on- top and bridging end- on dinitrogen molecules takes place. At low dinitrogen pressures the terminal molecules are removed and the complex is transformed to one containing only an internuclear dinitrogen ligand. The internuclear coordination could explain the high efficiency of CuZSM-5 for dinitrogen adsorption.

Unambiguous evidence supporting the decomposition reaction of NO on two types of monovalent copper-ion in CuZSM-5 zeolite

By combining the methods of calorimetry and spectroscopy using CO as a probe molecule, we obtained the evidence supporting the decomposition reaction of NO on two types of monovalent copper-ion (Cu +) species in CuZSM-5 zeolite. These Cu + species showed the characteristic emission bands at 21,000 and 18,500 cm −1 and, respectively, gave the CO adsorption heats of 122 and 110 kJ mol −1. Taking account of our previous EXAFS data, it was found that the former species take the two-coordinated structure involving lattice oxygen atoms, while the latter ones the three-coordinated structure. In this paper, we also emphasized the validity of our original assignment of active sites on CuZSM-5 for N 2 adsorption at room temperature; three-coordinated Cu + species adsorb N 2 molecules.

ESR and TPD Study of the Interaction of Nitromethane and Ammonia with HZSM-5 and CuZSM-5 Zeolites

The properties of complexes formed on HZSM-5 and CuZSM-5 zeolites in the course of ammonia and nitromethane adsorption are studied. Ammonia adsorbs on CuZSM-5 and forms two species, which decompose at different temperatures Tdec. One is due to the formation of the Cu2+(NH3)4 complex (Tdec = 450 K), and the other is assigned to ammonia adsorbed on copper(II) compounds, Cu2+O– and Cu2+–O2––Cu2+, or CuO clusters (Tdec = 650–750 K). Ammonia adsorption on Cu+ and Cu0 is negligible compared with that on the Bronsted acid sites and copper(II). Nitromethane adsorbed on HZSM-5 and CuZSM-5 at 400–500 K transforms into a series of products including ammonia. Ammonia also forms complexes with the Bronsted acid sites and copper(II) similar to those formed in the course of adsorption from the gas phase, but the Cu2+(NH3)4 complexes on CuZSM-5 are not observed. Possible structures of ammonia and nitromethane complexes on Bronsted acid sites and the Cu2+ cations in zeolite channels are discussed. The role of these complexes in selective NOx reduction by hydrocarbons over the zeolites is considered in connection with their thermal stability.

Decomposition and selective catalytic reduction of NO by propane on CuZSM-5 zeolites: a mechanistic study

NO decomposition and selective catalytic reduction (SCR) of NO by propane in oxygen were compared over Cu-ZSM-5 with various Si/Al ratios and extent of exchange. It was established that the turnover frequency (TOF) values referred to copper ions species characterized by NO desorption, are independent of the Si/Al ratio and the extent of exchange. The presence of propane and oxygen accelerates N 2 formation and higher conversion can be reached at lower temperature. TPD experiments indicate that the Cu 2+(O)(NO)(NO 2) surface complex, which is formed as an intermediate in the decomposition of NO, is not the active pathway in SCR. In SCR of NO by propane in the presence of oxygen, the first step is Cu(I) to Cu(II) conversion by oxygen. NO 2 formation is facilitated by Cu(II) species, which react with propane forming a nitrito–propane compound. Its result in N 2 formation at a lower temperature than what is required for decomposition of NO.

Ethylene and propylene adsorption and the formation of hydrocarbon complexes with NO2 upon interaction of adsorbed olefins with an NO + O2 mixture over HZSM-5 and CuZSM-5 zeolites studied by TPD and ESR

Adsorption of C2H4 and C3H6 on copper in oxidized samples of CuZSM-5 is found to increase with the copper concentration; simultaneously, olefin adsorption on the Bronsted acid sites decreases. The Cu2+ cations in the square-planar coordination exhibit higher reactivity in olefin adsorption than copper cations in the square-pyramidal coordination. Thermal treatment of CuZSM-5 with hydrogen results in regeneration of the Bronsted acid sites for olefin adsorption and the disappearance of Cu2+ cations, the active sites of adsorption, due to the reduction of Cu2+ to Cu+ and Cu0. Desorption peaks appear in the TPD spectra upon the interaction between the adsorbed hydrocarbons and NO2. These peaks are not observed upon separate adsorption of the reactants, and they are likely due to decomposition of NO2-hydrocarbon complexes over both the Bronsted and copper-containing sites of the zeolite

Hydrocarbon radicals and nitroxy complexes on the surface of HZSM-5 and CuZSM-5 zeolites: An ESR study

The conditions favorable for the formation of oligomer and benzene cation radicals upon C2H4, C6H6, and C3H6 adsorption on thermally activated HZSM-5 and CuZSM-5 zeolites were studied. In the case of isolated copper ions, the radicals were shown to be formed from C3H6 but not from C2H4 and C6H6. Paramagnetic nitroxy complexes, which were formed as a result of the interaction of adsorbed hydrocarbons C2H4, C6H6, and C3H6 with NO and NO2, were revealed on HZSM-5 zeolite and Al2O3. Hydrocarbon radicals and nitroxy complexes are localized on different zeolite sites. Nitroxy complexes are formed on aluminum cations. The role of radicals and nitroxy complexes in the process of NO x selective catalytic reduction by hydrocarbons on the zeolites was discussed on the basis of the temperature dependences of the concentrations of these species.

T–O–T skeletal vibration in CuZSM-5 zeolite: IR study and quantum chemical modeling

The location of Cu cations in CuZSM-5, properties of cationic sites and their interaction with guest molecules have been studied by quantum chemical (DFT) modeling and IR spectroscopy based on the frequency shift of antisymmetric T–O–T vibration of oxygen rings. The shift has been found sensitive both to the framework interaction with cations and to the interaction with adsorbed molecules. It has been measured and estimated theoretically from parameters characterising framework distorsion by Cu+ and Cu2+, with MgZSM-5 and NaZSM-5 used as ‘‘reference samples’’. It was found that the ordering of the cation perturbing effect was: Na+<Cu+<Mg2+<Cu2+. NO interaction with Cu cations was much stronger than that of CO and N2 . Divalent copper showed polarized 2-electron covalent bonding with NO strengthening its bond while moderate bonding ability of monovalent copper led to NO bond activation, in accordance with high catalytic activity of Cu+ZSM-5.

Ring-Opening and Dimerization Reactions of Methyl- and Dimethyloxiranes on HZSM-5 and CuZSM-5 Zeolites

Ring-opening and dimerization reactions of methyloxirane and cis- and trans-2,3-dimethyloxirane were studied on CuZSM-5, prepared by various methods, and HZSM-5 zeolites in a closed static recirculation reactor at 363 K in reductive atmosphere. On these materials two main reaction types, ring-opening and dimerization, could be observed. For methyloxirane the major transformation pathways were ring opening and dimerization, producing various dioxolane and dioxane derivatives. In addition to these routes 2,3-dimethyloxiranes underwent deoxygenation and rearrangement as well. The activities and selectivities of the transformations toward these pathways were found to be significantly different depending on the stereochemistry of the substrates as well as the nature of the catalysts. Suggestions for the active sites and transformation mechanisms are also offered.

Use of ESR and 129Xe NMR spectroscopy to characterize CuZSM-5 zeolite synthesized in the presence of a copper–phthalocyanine complex

In the presence of a copper phthalocyanine complex (CuPc) it is possible to synthesize ZSM-5 zeolite containing the complex, and the crystallinity is good provided the amount of CuPc trapped is much lower than the number of channel intersections where it can be located without too much distortion. The crystallinity is retained after decomposition of the CuPc in a stream of air at 500°C. The copper-ZSM-5 system is characterized by the combined application of xenon adsorption, ESR and 129Xe NMR spectroscopy. These techniques allow the location and the oxidation states of the copper ions after various thermal treatments to be studied. 129Xe NMR gives evidence about the partial self-reduction of the Cu 2+ ions during the dehydration process. The ESR spectra taken after adsorption of ammonia or o-xylene confirm that the Cu 2+ ions are located in the channels. However, the NMR spectroscopy of adsorbed xenon shows that when there is no chemisorbed phase the Cu 2+ are stabilized in the crystallites but outside the channels. They return to the channels upon chemisorption of ammonia.

Investigation of Copper Carbonyl Species Formed upon CO Adsorption on Copper-Exchanged Zeolites by Diffuse Reflectance FTIR

Diffuse reflectance FTIR spectroscopy was applied to the study of the fundamental C−O bond stretching vibrations and their first overtones and combination modes of copper carbonyl species formed upon CO adsorption on aqueous ion-exchanged CuZSM-5, CuM, CuY, and CuL zeolites autoreduced at 673 K in vacuo and on Cu(I)Y (sse) zeolite prepared by solid-state ion exchange of NH4Y with CuCl. At low CO pressures, different kinds of Cu(I)(CO) monocarbonyl species are formed depending upon the types of the zeolites. With increasing the CO pressure, Cu(I)(CO)2 dicarbonyl species are formed on CuZSM-5, CuM, and CuY. After an evacuation of the preadsorbed CO at room temperature, the dicarbonyl species are transformed into monocarbonyl species. Such a transformation is reversible upon a change of the CO pressure. On the CuL zeolite, however, only one type of monocarbonyl is observed, no dicarbonyl species being detected even at high CO pressures. The frequency of the stretching vibration of the metal cation−carbon bon...

Selective catalytic reduction of NO x on Cu-beta zeolites

A series of Cu-beta zeolites with different Cu contents have been prepared. Their activity for selective catalytic reduction (SCR) of NO with C 3H 8 has been studied and compared with that of Cu-ZSM5 zeolites. Cu-beta samples are stable SCR catalysts giving activities as high as those of Cu-ZSM5 zeolites. Their behaviour toward reaction temperature and oxygen content is practically the same as that of Cu-ZSM5. Similar results were achieved when the adsorption of NO over the zeolites was followed by i.r. spectroscopy.

The desorption of O2 during NO and N2O decomposition on Cu- and Fe-zeolites

The decomposition of NO and of N2O over a CuZSM-5 zeolite and a Fe-mordenite, respectively, has been studied using tracer techniques. The results demonstrate the high mobility of the lattice oxygen ions in self-diffusion. They afford a possible explanation for the problem of how two extralattice oxygens located at positions remote from each other may combine to form the O2 molecules which are spontaneously desorbed in these redox reactions. They show that a portion of the lattice oxygen mixes into the O2 released on decomposition. The data also show that N18O and N218O undergo exchange with the catalyst oxygen under reaction conditions.