Chul Wee Lee

Synthesis of SAPO-11 and AIP04-11 molecular sieves in the presence of Cu(ll)

Abstract The possible incorporation of Cu(II) into SAPO-11 (CuSAPO-11) and AIPO 4 -11 (CuAPO-11) by adding Cu(II) compounds during synthesis in the presence of di- n -propylamine or diisopropylamine templates has been assessed. The location of Cu(ll) is identified by electron spin resonance and electron spin echo modulation spectroscopies. Cu(ll) ions do not incorporate into framework positions of SAPO-11 and AIPO 4 -11, i.e., Cu(II) in CuSAPO-11 is located in the same position as Cu(ll) introduced byaqueous ion-exchange and Cu(ll) in CuAPO-11 is located in an extraframework position of AlPO 4 -11. It is of ancillary interest that in the presence of Cu(ll) the SAPO-5 phase can be obtained as a major product by varying the temperature and time of crystallization.

Wetness method preparation of catalysts for selective catalytic reduction of NO by propane

A wetness method preparation of Co/ZSM-5 catalysts for selective catalytic reduction of NO by propane is shown to be comparable to ion-exchange preparation at the optimum catalytic conversion temperature of 450°C and superior to ion-exchange preparation at lower temperatures. Modification of Co/ZSM-5 catalysts with Ca2+ or Sr2+ significantly improves the catalytic activity.

Characterization and catalytic properties of Ti-ZSM-5 prepared by chemical vapor deposition

Ti‐ZSM‐5 is prepared via a chemical vapor deposition method by reacting HZSM‐5 with TiCl4 at temperatures of 200–400°C. Ti‐ZSM‐5 is characterized by skeletal‐ and surface hydroxy‐FT‐IR, XPS, and XANES spectroscopy. It seems that Ti is incorporated in the zeolite surface with tetrahedral coordination. Contents of incorporated Ti atoms in Ti‐ZSM‐5 zeolite increase with increasing SiO2/Al2O3 ratio and a CVD reaction temperature of 400°C is optimal. Cyclohexanone ammoximation was used as test reaction and Ti‐ZSM‐5 catalysts show similar catalytic activities compared to TS‐1.

Determination of ion-exchanged Co2+ cation in Co-ZSM-5 by temperature-programmed desorption

Abstract It is shown that temperature-programmed desorption of adsorbed NO on Co-ZSM-5 zeolite used in selective catalytic reduction can accurately measure the amount of Co2+ cation for Co/Al ratios from 0 to 0.42 where the 0.42 limit corresponds to 84% maximum exchange. Evidence is also shown for the formation of cobalt oxide particles in Co-ZSM-5 for Co/Al ratios above 0.42.

Comparison of cupric ion location and adsorbate interactions in Cu(II)-exchanged H-SAPO-5 and H-SAPO-11 molecular sieves determined by electron spin resonance and electron spin echo modulation spectroscopies

The locations and interactions of cupric ion exchanged into H-SAPO-11 and H-SAPO-5 molecular sieves with water, methanol, ethanol, ammonia, ethylene and pyridine have been compared by electron spin resonance and electron spin echo modulation spectroscopies. After dehydration, equilibration with ethylene and pyridine adsorbates was slower compared with that for more polar adsorbates. One major difference between these two molecular sieves in cupric ion coordination to adsorbates is that two waters are coordinated in CuH-SAPO-11 while three waters are coordinated to cupric ion in CuH-SAPO-5. This indicates different coordination sites for the cupric ion in these two molecular sieves of rather similar structure. By considering a particular location of the cupric ion, these coordination numbers can be understood, however. Another major difference involves coordination to ammonia; four ammonias are coordinated to cupric ion in CuH-SAPO-11 consistent with the cupric ion being located in the center of a 10-ring channel, while only three ammonias are coordinated in cupric ion to CuH-SAPO-5. This indicates a different coordination site for cupric ion between these two molecular sieves also with ammonia adsorbate. The coordination site in the SAPO-5 material for cupric ion is suggested to be the same for ammonia coordination and water coordination and is different from the site for water coordination in the SAPO-11 material.

Copper(II) ionic species in CuII-exchanged K-offretite aluminosilicate and comparison with CuII-exchanged K-offretite gallosilicate determined by electron paramagnetic resonance and electron spin echo modulation spectroscopies

The location of Cu II and its interaction with deuteriated adsorbates in Cu II -exchanged K-offretite aluminosilicate zeolite have been investigated by electron paramagnetic resonance (EPR) and electron spin echo modulation (ESEM) spectroscopies and compared with those in Cu II -exchanged K-offretite gallosilicate. Basically similar Cu II locations to those in CuK-offretite gallosilicate are observed in CuK-offretite aluminosilicate, but there are some interesting differences. It is found that in the fresh hydrated sample, Cu II is, in the main channel, coordinated to three water molecules and three framework oxygens in a six-ring window of an e-cage to form a distorted octahedral complex. Upon evacuation at increasing temperature, Cu II ions move from the main channel through the e-cages to hexagonal prism sites. However, the water coordinated to Cu II is more tightly bound in the aluminosilicate than in the gallosilicate. Dehydration produces two different Cu II species in the aluminosilicate, both believed to be located in recessed sites owing to the lack of broadening of its EPR lines by oxygen, while only one Cu II species is located in a recessed site in the gallosilicate. Adsorption of polar molecules such as water, alcohols, dimethyl sulfoxide, acetonitrile and ammonia cause changes in the EPR spectrum of the Cu II indicating migration into cation positions in the main channels where adsorbate coordination can occur. However, non-polar ethene does not cause migration of Cu II . Cu II forms complexes with two molecules of methanol, ethanol and propanol, and one molecule of dimethyl sulfoxide based on ESEM data. Cu II forms a trigonal bipyramidal complex with two ammonias in axial positions and three framework oxygens in a six-ring window of an e-cage based on EPR parameters and ESEM data, which is the same for Cu II in CuK-offretite gallosilicate.

Anionic coordination involvement in solid-state ion-exchanged CuH-SAPO-n(n= 5, 11 and 34) molecular sieves

High-temperature solid-state ion exchange has been performed with H-SAPO-5 and various copper(II) compounds. Electron paramagnetic resonance (EPR) shows that this technique introduces CuII cations by ion exchange into H-SAPO-5, producing (S)Cu(F)H-SAPO-5 and (S)Cu(O)H-SAPO-5, where (S) indicates solid-state ion exchange and the subscripts F and O indicate the copper sources CuF2 and CuO used in the solid-state reaction. The EPR parameters for both hydrated and dehydrated samples of (S)Cu(F)H-SAPO-5 and (S)Cu(O)H-SAPO-5 vs.(L)CuH-SAPO-5, where (L) indicates liquid-state ion exchange, show differences which are suggested to be due to anion involvement in the coordination of copper(II). This is supported by electron spin echo modulation data which show that the distances between CuII and several adsorbates in (S)Cu(F)H-SAPO-5 are shorter than those for (L)CuH-SAPO-5 by 0.02–0.04 nm. Similar differences are observed for (S)Cu(F)H-SAPO-34 and (S)Cu(Cl)H-SAPO-34 vs.(L)CuH-SAPO-34 and for (S)Cu(O)H-SAPO-11 vs.(L)CuH-SAPO-11. The g anisotropy also supports a decrease in symmetry owing to anion involvement.

CuIIlocation and adsorbate interaction in CuII-exchangedsynthetic Na-omega gallosilicate EPR and electron spin echo modulation studies

The location of CuII and its interaction with adsorbates in CuII-exchanged synthetic Na-omega gallosilicate have been studied by EPR and electron spin echo modulation (ESEM) spectroscopies. These results are compared with those of CuII-exchanged Na-omega aluminosilicate and also those of L and offretite gallosilicates of similar channel type and size, and the differences are discussed. In general, similar results to those for CuNa-omega gallosilicate are obtained for CuNa-omega aluminosilicate. It is concluded that, in fresh hydrated omega material, CuII is in a main channel coordinating to three water molecules and to framework oxygens in the main channel wall. A minor CuII diaquo species not seen in the gallosilicate is observed in the aluminosilicate. Upon evacuation at increasing temperature, CuII moves from the main channel to a gmelinite cage. Dehydration at 410°C produces one CuII species located in a six-ring window of a gmelinite cage, based on a lack of broadening of its EPR lines by oxygen. In L and offretite gallosilicates, there is evidence for back migration of CuII from a hexagonal prism into a main channel to coordinate with adsorbates. However, in omega the back migration from a gmelinite cage to a main channel seems to be blocked, as shown by very slow changes in the EPR spectra and differing coordination numbers for methanol, ethanol and propanol to CuII when alcohols are adsorbed. CuII does not form a complex with propanol or larger adsorbates in omega gallosilicate. It is suggested that, in omega, small adsorbates must diffuse into a gmelinite cage where CuII is located, to form CuII–adsorbate complexes. The slow changes in the EPR spectra correspond to the time for adsorbate diffusion into a gmelinite cage. CuII interacts with one molecule each of ethylene and acetonitrile, based on EPR and ESEM analyses. CuII forms a square-planar complex containing four molecules of ammonia, based on resolved nitrogen superhyperfine coupling.

The comparative reactivity of various organic adsorbates with Cu(II) in CuH-SAPO-5 and CuH-SAPO-11 molecular sieves studied by electron spin resonance

The adsorption rates of various organic adsorbates on CuH-SAPO-5 and CuH-SAPO-11 molecular sieves have been studied from changes in the electron spin resonance (e.s.r.) spectra of Cu(II). The adsorption rate for hydrazine is much faster than for ethylene, and hydrazine coordinates to Cu(II) through its π-bond. The room-temperature adsorption of aromatic compounds (benzene; o-, m-, and p-xylene; toluene; ethylbenzene; and aniline), saturated nonpolar hydrocarbons (n-hexane, cyclohexane, methylcyclohexane, 1,2-dimethylcyclohexane, and 1,3-dimethylcyclohexane), and polar cyclohexylamine on dehydrated CuH-SAPO-5 and CuH-SAPO-11, heat-treated at 65–200°C, is evaluated. With increased pretreatment temperature, the original Cu(II) e.s.r. intensity (IA) decreases and the intensity of a sharp singlet at g = 2.003 (IB), associated with adsorbate decomposition, increases. From the variation of the IAIB ratio as a function of pretreatment temperature, the relative reactivity of Cu(II) in CuH-SAPO-5 and CuH-SAPO-11 toward the various organic adsorbates is determined. It is of particular interest that the order of reactivity differs between the SAPO-5 material with a 12-ring channel and the SAPO-11 material with a 10-ring channel.

Electron Spin Echo Modulation Spectroscopic Evidence for Framework Substitution of Ni(I) in NiAPSO-11

The various Ni(I) species formed by reduction and adsorbate interactions in silicoaluminophosphate-11, synthesized by incorporation of Ni(II) in the synthesis mixture(NiAPSO-11) and formed by partial ion exchange of H(I) by Ni(II)(NiH-SAPO-11) were studied recently for the first time by electron spin resonance(ESR). Significant differences in the ESR parameters between NiAPSO-11 and NiH-SAPO-11 for nickel ion coordination to methanol, carbon monoxide and ethylene. Adsorbates indicate that Ni(I) is in different sites in these two materials and suggests that Ni(I) in NiAPSO-11 is in a framework site. This has been confirmed here by electron spin echo modulation data on these synthesized and ion-exchanged materials. Analysis of the deuterium modulation from deuterated methanol and ethylene adsorbates gives different coordination geometries for the synthesized and ion-exchanged nickel-incorporated SAPO-11 materials and is consistent with Ni(I) being in a framework site in NiAPSO-11.