Copper Ion-exchanged ZSM-5 Zeolite Research Articles

ChemInform Abstract: Novel Preparation Method of Highly Copper Ion-Exchanged ZSM-5 Zeolites and Their Catalytic Activities for NO Decomposition.

Copper(II) ion-exchanged ZSM-5 zeolites with 100% or more exchange levels were readily prepared by addition of basic compounds such as ammonia and Mg(OH)2 to the mother solution. The catalytic activities of the resulting zeolites for decomposition of nitrogen monoxide are dependent on pH of the solution and the additive.

Direct decomposition of nitrogen monoxide over Cu-MFI containing rare-earth elements: Sm and Gd as promoter

The decomposition activities of nitrogen monoxide (NO) were investigated for the copper ion-exchanged ZSM-5 zeolites (Cu-MFI) containing the rare-earth elements: La, Ce, Pr, Nd, Sm, and Gd. It was found that Sm and Gd acted as promoter for NO decomposition over Cu-MFI with 60–70% of the exchange level of copper ion, while the addition of the other rare-earth elements to Cu-MFI showed no positive effect on NO decomposition activity. The introduction of Sm and Gd to Cu-MFI had little influence on the effectiveness of each copper ion for NO adsorption in the MFI zeolite. The presence of Sm and Gd stabilized Cu + as an active center.

Calorimetric study of room temperature adsorption of N 2O and CO on Cu(II)-exchanged ZSM5 zeolites

Copper ion-exchanged ZSM5 zeolites have been prepared with different cooper loadings from under- to over-exchanged levels. The adsorptions of N 2O and CO at 303 K have been studied using calorimetric method and infrared spectroscopy. The samples were additionally characterised by ammonia adsorption at 423 K. The active sites for both N 2O and CO are Cu(I) ions, which were formed as a result of pre-treatment in vacuum at 673 K. Room temperature adsorption of nitrous oxide at low equilibrium pressures (up to 66.7 Pa) resulted in small amounts of chemisorbed N 2O (<0.2 molecule per one Cu ion). Differential heats of N 2O adsorption between 80 and 30 kJ/mol were obtained. Differential heats of CO adsorption between 140 and 40 kJ/mol were obtained. The obtained amounts of chemisorbed species in the investigated systems and the values of differential heats of both nitrous oxide and carbon monoxide demonstrate the dependence on the copper content.

Anomalous valence changes and specific dinitrogen adsorption features of copper ion exchanged in ZSM-5 zeolite prepared from an aqueous solution of [Cu(NH3)2

Direct ion-exchange of monovalent copper ions into a ZSM-5-type zeolite was carried out using an aqueous solution of diammine–copper(I) ions, [Cu(NH3)2]+, to prepare a copper ion-exchanged ZSM-5 zeolite including only monovalent copper ions, and the effect of monovalent copper ions on the zeolite's adsorption properties for dinitrogen (N2) was examined. Strangely enough, the reoxidation of monovalent copper-ion exchanged in ZSM-5 took place in the evacuation process at around 473 K. The changes in valence and structure of the exchanged copper-ions during the evacuation process and the interaction with N2 molecules at room temperature have been investigated by using spectroscopic techniques such as X-ray absorption fine structure (XAFS), IR and photoemission spectroscopy, as well as by measurements of adsorption isotherms and adsorption heats. On the basis of X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) analyses, it has become apparent that the Cu+ species exchanged in ZSM-5 zeolite is oxidized by water to form a divalent species having a CuO-like structure through heat-treatment in vacuo at 473 K. Further heat-treatment at temperatures above 673 K caused a reduction of the divalent species to a monovalent one that exhibits a pronounced adsorption feature for N2 even at room temperature. XANES and photoemission data clearly indicated that the Cu+ species in an 873 K-treated CuZSM-5 sample has a three-coordinate structure with lattice oxygen atoms and interacts strongly with an N2 molecule at room temperature. The strong interaction with N2 was also verified through the adsorption heat and IR data: an initial adsorption energy of 85 kJ mol−1 and an absorption band at 2295 cm−1. A prominent feature of this system is that some of the adsorbed species survives after evacuation at 300 K, indicative of a strong interaction between N2 and the three-coordinate copper ion.

New Analysis of Oxidation State and Coordination Environment of Copper Ion-Exchanged in ZSM-5 Zeolite

The changes of structure and electronic state of copper ion species during the heat treatment of copper ion-exchanged ZSM-5 zeolite (CuZSM-5) as well as the interaction with CO molecules have been investigated by using various spectroscopic techniques such as infrared (IR) and emission spectroscopy (ES), electron spin resonance (ESR), and X-ray absorption fine structure (XAFS) consisting of a XANES (X-ray absorption near edge structure) and an EXAFS (extended X-ray absorption fine structure) and through the measurements of heat of adsorption and adsorption isotherm. About 70% of the divalent copper ions (Cu2+) exchanged in CuZSM-5 were found to be reduced to the monovalent copper ions (Cu+) during the heat treatment at 873 K in vacuo, the latter species having a linear or a planar coordination structure with a coordination number of 2 or 3 with respect to the nearest-neighboring oxygen atoms at a distance of 1.98 A. It was found from the ES data that the Cu+ species strongly interact with CO molecules at ...

Experimental study of the formation and the reaction of an intermediate during the lean NO χ reaction over Cu-ZSM-5

Two-step experiments were conducted to investigate the mechanism of NO χ reduction over copper ion-exchanged ZSM-5 zeolites. The first step was the formation of a reactive intermediate and the second one the reaction of this intermediate during a transient regime without any hydrocarbon injection. The presence of NO or NO 2 appears to be mandatory to obtain such an intermediate. In contrast, the presence of oxygen is not necessary. The intermediate reacts only with NO 2 as well as with O 2. The role of oxygen could be to oxidize NO to NO 2 in a first reaction step.

NOx Emission Control in Oxygen-Rich Exhaust Through Selective Catalytic Reduction by Hydrocarbon

Selective catalytic reduction of nitrogen monoxide by hydrocarbon in the presence of oxygen and sulphur dioxide has very recently been found on copper ion-exchanged ZSM-5 zeolite (Cu-ZSM-5). The reaction proceeds even in the oxidizing atmosphere at temperatures as low as 573 K. Addition of oxygen to the reactant stream is necessary to achieve the selective reduction of nitrogen monoxide. The increment of concentration of hydrocarbon increased the conversion into nitrogen and expanded the active temperature region. After summarizing the new findings on Cu-ZSM-5, the present review introduces catalytic activities of various metal-ion exchanged zeolites and metal-loaded aluminas. Based on the temperature dependence of each catalyst and the change of conversion of nitrogen monoxide into nitrogen with space velocity, Cu-ZSM-5 is suggested as one of the strong candidates for catalysts applicable to lean-burn gasoline and diesel engines, though several problems such as durability to water and overheating remain to be solved.

Silver ion-exchanged zeolites as highly effective adsorbents for removal of NO x by pressure swing adsorption

The increasing global concern in recent years over air pollution problems caused by nitrogen oxides (NOx) has brought extensive research on catalytic NOx decomposition and reduction [1, 2]. Adsorption is one of the most suitable techniques for removal of dilute adsorbates [3]. In particular, pressure swing adsorption (PSA) is expected to be an effective method to remove or concentrate NOx exhausted into air. In a previous paper, we reported that the copper ion-exchanged ZSM-5 zeolite is the most effective adsorbent for PSA at 273 K among the various cation-exchanged zeolites [4]. However, the adsorptive properties were tested only at 273 K. The optimum temperature of adsorption for PSA depends on adsorbent and adsorbate; for example, the optima for CO2 adsorption were 230 K and 323 K for activated carbon and zeolite, respectively [5]. In this study, the adsorption properties of metal ion-exchanged zeolites were examined as a function of adsorption temperature, and it was found that silver ion-exchanged ZSM-5 and mordenite zeolites with exchange level of around 100% have greater capacity at 195-273 K for reversible adsorption of NO than copper ion-exchanged zeolites. The concentration of NO was set at 1000 ppm in this work to enable quick evaluation of the adsorption properties of adsorbents; the concentration is much lower under practical conditions. Parent zeolites, ZSM-5 (SIO2/A1203=23.3), mordenite (15.0), ferrierite (12.3), offretite/erionite (7.7), Y-(5.6), L-(6.0), X-(2.6), and A-type (2.0) were supplied by Tosoh Corporation and denoted as MFI, MOR, FER, OFF/ERI, FAU, LTL, FAU, and LTA, respectively. Copper and silver ionexchanged zeolites were prepared as described previously [6]. The exchange levels of metal ions were determined by atomic absorption spectroscopy. Hereafter the samples are abbreviated as Ag-MFI(23.3)-100 (cation-zeolite structure (SiO2/ A120 3 ratio)-degree of exchange). The adsorption and desorption measurements were carried out in a fixed bed adsorption apparatus [4]. The adsorbent (0.5 g) was placed in a stainless steel column and heated at 773 K for 5 h under a helium stream (50 cm 3 min -1) just before the adsorption run. In the adsorption experiment, 1000 ppm of NO in He was introduced at a rate of 100 cm 3 min -1 into the column. After the adsorption run, He

Removal of nitrogen monoxide through a novel catalytic process. 2. Infrared study on surface reaction of nitrogen monoxide adsorbed on copper ion-exchanged ZSM-5 zeolites

The authors have studied the adsorption of NO onto copper loaded ion-exchanged zeolites by means of infrared spectroscopy coupled with isotopic techniques. Such zeolites have been reported to be catalytically active for the decomposition of NO, and the development of such catalysts for exhaust gas treatments is a major factor behind this work. The authors studied the molecular form that NO took when it was adsorbed, and the nature of the sites which would bind NO. They found bound forms of the nature, NO{sup {delta}+}, NO{sup {delta}{minus}}, and (NO){sub 2}{sup {delta}{minus}}. They also observed the formation of N{sub 2} and N{sub 2}O.

Adsorption-desorption Properties of Nitrogen Monoxide on Metal Ion-exchanged Zeolites

Among the samples tested, the amounts of reversible and irreversible adsorption of NO were the largest on copper ion-exchanged ZSM-5 zeolite and cobalt ion-exchanged ZSM-5 zeolite, respectively. In the former case, the amounts of reversible and irreversible adsorption of NO were dependent on the aluminum content of zeolite and linearly increased with increasing the exchange level.

Reduction of Nitrogen Oxides by Cooper Ion-exchanged Zeolite Catalyst in Diesel Engine Exhaust.

Copper ion-exchanged ZSM-5 zeolite catalyst, which deoxidizes nitrogen oxides (NOx) in the presence of oxygen and hydrocarbons, was applied to actual diesel engine exhaust. Copper ionexchanged ZSM-5 zeolite effectively reduced NOx by 25% in normal engine operation, and by 80% when hydrocarbons in the exhaust were increased. Water in the exhaust gas decreased the NOx reduction rate, but oxygen and sulfur appeared to have only a small effect. Maximum NOx reduction was observed at 400°C irrespective of hydrocarbon species, and did not decrease with space velocity up to values of 200001/h.

Influence of cocations on catalytic activity of copper ion-exchanged ZSM-5 zeolite for reduction of nitric oxide with ethene in the presence of oxygen

The coexistence of alkaline earth (Ca and Sr) and transition metal (Fe, Co and Ni) cations with Cu ions in ZSM-5 zeolite is effective in the promotion of the maximum activity and the expansion of the active temperature range for the reduction of nitric oxide with ethene in the presence of excess oxygen.

Removal of nitrogen monoxide through a novel catalytic process. 1. Decomposition on excessively copper-ion-exchanged ZSM-5 zeolites

Repeated ion exchange of the ZSM-5 zeolite using aqueous copper(II) acetate solution was found to bring about excess loading of copper ions above an exchange level of 100%. The high activity of the resulting catalyst for NO decomposition was consistent for at least 30 h even at short contact time and low NO pressure. The number of copper ions that can adsorb NO molecules has been determined by a temperature-programmed desorption technique combined with IR measurement; 94% of Cu{sup 2+} ions in ZSM-5 were active for the adsorption. The activity of excessively copper ion exchanged ZSM-5 zeolite was slightly reduced by the oxygen in the feed gas while that of zeolite, of which the loading amount of copper was less than 100%, was greatly diminished under the same condition. SO{sub 2} completely poisons the activity at 673-923 K, but the activity can be regenerated at the higher temperature treatment.

Cocation Effect in Catalytic Property of Copper Ion-Exchanged ZSM-5 Zeolites for the Direct Decomposition of Nitrogen Monoxide

Abstract The coexistence of metal cations such as alkaline earth and transition metal cations with Cu ions in ZSM-5 zeolites promoted the catalytic activity of Cu ion for the direct decomposition of nitrogen monoxide at temperatures above 450 °C. The promotion effect was found to depend on the ion exchange mode.

Cu-ZSM-5 zeolite as highly active catalyst for removal of nitrogen monoxide from emission of diesel engines

Copper ion-exchanged ZSM-5 zeolite is the most active for the selective reduction of nitric oxide by ethene in the presence of oxygen at temperatures as low as 437–<Zn (873 K). The activity of copper ion-exchanged ZSM-5 zeolite did not decrease much even in a high gas hourly space velocity (GHSV) region of more than 10 000 h −1 while those of proton-exchanged zeolites and Al 2O 3 greatly decreased in such high GHSV regions.

Influence of sulfur dioxide on catalytic removal of nitric oxide over copper ion-exchanged ZSM-5 zeolite

The catalytic activity of copper ion-exchanged ZSM-5 zeolites, used for the selective reduction of nitric oxide by propene in the presence of oxygen was only slightly decreased by the addition of sulfur dioxide; for example, the conversion of nitric oxide into nitrogen was changed from ca. 100% in the absence of sulfur dioxide to 85% (773 K) upon the introduction of sulfur dioxide. In contrast, the catalytic activity for nitric oxide decomposition completely disappeared upon addition of sulfur dioxide. These results show that the selective reduction of nitric oxide by hydrocarbon may be practical.

Removal of Nitrogen Monoxide over Copper Ion-exchanged Zeolite Catalysts.

Direct decomposition and selective reduction of nitrogen monoxide over copper ion-exchanged zeolite catalysts are proposed as new methods for removal of NO. The copper ion-exchanged ZSM-5 zeolite (Cu-Z) was the most active catalyst for decomposition of NO. The activity of Cu-Z zeolites increased with increase in the exchange level. The zeolites with copper ion-excange levels of 100% or more, which could be prepared by repeating ion exchange of the ZSM-5 zeolite using aqueous copper(II) acetate solution or addition of ammonia into the aqueous copper(II) nitrate solution, showed significantly high activity even in the presence of oxygen and at high GHSV region. It was clarified concerning Cu-Z, by using IR, ESR, phosphorescence, TPD, and CO adsorption measurements that (1) the Cu2+ ions exchanged into zeolite were reduced to Cu+ and/or Cu+-Cu+ through evacuation at elevated temperature, (2) after exposure to oxygen at 773K and subsequent evacuation, about 40% copper ions in zeolite existed as Cu+ ions, (3) the NO- species formed by adsorption of NO on Cu+ would be an intermediate in the NO decomposition, and (4) redox cycle of Cu+_??_Cu2+ in the zeolite is probably a key step to achieve the decomposition reaction. Selective reduction of NO by hydrocarbon in the presence of oxygen was first found by the authors and Cu-Z was remarkably effective for NO removal at temperatures as low as 523-673K. The activity for this selective reduction in NO+C3H6+O2 system was not poisoned very much by addition of SO2. The conversion into N2 was changed to 85% (773K) in the presence of SO2, from 100% in the absence of SO2, which is in contrast with the fact that the catalytic activity for direct decomposition NO was completely lost on adding the same amount of SO2. Furthermore, the reduction rate over Cu-Z at 573K was higher than those over H-zeolite and alumina catalysts at 723 and 773K, respectively, which have been reported to be active, after findings by the authors.

Novel Preparation Method of Highly Copper Ion-exchanged ZSM-5 Zeolites and Their Catalytic Activities for NO Decomposition

Abstract Copper(II) ion-exchanged ZSM-5 zeolites with 100% or more exchange levels were readily prepared by addition of basic compounds such as ammonia and Mg(OH)2 to the mother solution. The catalytic activities of the resulting zeolites for decomposition of nitrogen monoxide are dependent on pH of the solution and the additive.

XANES and EXAFS analysis of copper ion-exchanged ZSM-5 zeolite catalyst used for nitrogen monoxide decomposition

XANES and EXAFS analysis of Cu ion-exchanged ZSM-5 zeolite, a highly active catalyst for NO decomposition, is performed. The copper species in the zeolite are Cu(II) ions in the zeolite cages. The contribution of Cu-Cu local structure is suggested for high loading samples. The Cu atoms in the zeolite are more ionic than CuO. The analysis of the catalyst deactivated by SOx treatment suggests the presence of Cu atoms surrounded by SO4 ions which blocks the adsorption of NO molecules.