Characterization of CuY zeolites after dehydration,oxidation and reduction with carbon monoxide An adsorption and 129Xe nuclear magnetic resonance spectroscopy study |
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| Affiliation: | 1. Institute of Chemical Engineering, Ural Federal University, Mira St., 19, 620002 Yekaterinburg, Russia;2. Department of Inorganic and General Chemistry, Ural State Forest Engineering University, Siberian Highway, 37, 620100 Yekaterinburg, Russia;3. Erlangen Catalysis Resource Center (ECRC), Friedrich-Alexander Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058 Erlangen, Germany;4. Institute of Organic Chemistry, Siberian Branch of the Russian Academy of Sciences, Akad. Lavrent’ev Av., 9, 630090 Novosibirsk, Russia;1. School of Chemical Engineering, University of Queensland, St. Lucia 4072, QLD, Australia;2. School of Chemical Engineering, Suranaree University of Technology, Nakhon 30000, Ratchasima, Thailand;3. Department of Chemical Engineering, Curtin University, Perth 6102, WA, Australia;1. Institute of Arts and Sciences, Yamagata University, Yamagata 990-8560, Japan;2. Tokyo Institute of Technology, Nagatsuta, Yokohama 226-8503, Japan;3. MO Device Corporation, Kanazawa 920-0335, Japan;4. Institute for Molecular Science, Okazaki 444-8585, Japan |
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| Abstract: | The adsorption isotherms and 129Xe nuclear magnetic resonance (NMR) chemical shifts of xenon and the adsorption isotherms of carbon monoxide of Cu(II)- and Cu(I)-exchanged zeolites NaY were measured. The former zeolites of 53, 75, and 95% exchange degrees were investigated after various pretreatment steps comprising dehydration, oxidation and reduction with CO at 420°C as well as long-term CO reduction at 470°C. The Cu(I)Y zeolite of 70% exchange degree was prepared via a solid-state exchange procedure with CuCl and subjected to dehydration at 420°C. In all cases, except the dehydrated zeolites, almost linear xenon adsorption isotherms and linear 129Xe NMR chemical shift versus xenon concentration curves running parallel to each other are obtained. In contrast, the chemical shift curves for the dehydrated zeolites are non-linear at low xenon concentrations turning towards negative chemical shift values at very low pressures. The whole body of the experimental xenon data can be explained quantitatively with a unifying approach on the basis of a site adsorption model where the sites are (i) two types of cuprous ions of much different adsorption strength and 129Xe chemical shift, (ii) Na+ cations, (iii) Lewis acid sites generated through autoreduction and reduction of Cu2+ by CO, and (iv) framework sites free of cations. These five types of sites are each characterized by Langmuir adsorption isotherm constants and local 129Xe NMR chemical shifts. The adsorption site concentrations in the various zeolites are evaluated. The supercage Cu(I) concentration values are in nice agreement with the results deduced from the CO adsorption isotherm measurements. |
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