The copper zeolites used in previous studies were prepared by
liquid-phase ion exchange (LPIE) of Na-Y with copper(II) nitrate
(followed by reduction to Cu+) and had a unit cell composition of
Cu21Na14[Al56Si136O384]. If all the copper is reduced to Cu+, then
38% of the charge compensation comes from cuprous ions, and
the other 62% comes from sodium ions and free hydroxyl groups
or extra lattice oxygen (ELO).9,10 Complete ion exchange in aqueous
phase is usually difficult because of the hydration state of the cupric
ions and because of complex hydrolysis mechanisms that arise
during the process. Thus, other means of introducing copper(I) ions
directly are essential. Guidry and Price11 and Spoto et al.12,13 used
vapor-phase ion exchange (VPIE) techniques to fully exchange
ZSM-5 (MFI) zeolites with copper(I) ions. Afterward, the zeolite
needed to be oxidized to a Cu2+ state before exposing it to
atmospheric air. This avoids disproportionation of Cu+ to Cu2+ and
Cu0.11 The Cu+ species are then recovered by traditional reduction
methods. Here we report the use of these techniques to synthesize
a faujasite zeolite containing almost 57 copper ions per unit cell
and use of the same to desulfurize a commercial diesel fuel.
H-Y was first obtained by heating a NH4-Y zeolite powder
(Si/Al ) 2.40, Strem Chemicals) in air at 450 °C at 1 °C/min.
Layers of the proton-form zeolite and CuCl (99.99%, Sigma-
Aldrich) were loaded into a reactor each separated by thin quartz
wool walls. Direct contact of the zeolite and salt is not desired
because of hydrolysis of the copper species in the presence of
adsorbed water. The reactor was then heated in an inert, dry
atmosphere, from room temperature to 200 °C at 1 °C/min and the
temperature held at that point for 4-6 h. Afterward, the temperature
was slowly increased above the normal melting point of CuCl (430
°C) and kept at a specific temperature for another 10 h. The zeolite
was then treated in oxygen at 200 °C for 4 h before cooling down
to room temperature. During the oxidation stage the cupric ions
react to form oxonium ions [Cu-O-Cu]2+, which could further
interact with moist air to form stable [Cu(OH)]+ ions.11 After
recovery, all the as-prepared zeolites were analyzed for elemental
composition using neutron activation analysis (NAA). In addition,
liquid nitrogen adsorption at -196 °C provided sorbent surface area
information.
The copper zeolites used in previous studies were prepared by
liquid-phase ion exchange (LPIE) of Na-Y with copper(II) nitrate
(followed by reduction to Cu+) and had a unit cell composition of
Cu21Na14[Al56Si136O384]. If all the copper is reduced to Cu+, then
38% of the charge compensation comes from cuprous ions, and
the other 62% comes from sodium ions and free hydroxyl groups
or extra lattice oxygen (ELO).9,10 Complete ion exchange in aqueous
phase is usually difficult because of the hydration state of the cupric
ions and because of complex hydrolysis mechanisms that arise
during the process. Thus, other means of introducing copper(I) ions
directly are essential. Guidry and Price11 and Spoto et al.12,13 used
vapor-phase ion exchange (VPIE) techniques to fully exchange
ZSM-5 (MFI) zeolites with copper(I) ions. Afterward, the zeolite
needed to be oxidized to a Cu2+ state before exposing it to
atmospheric air. This avoids disproportionation of Cu+ to Cu2+ and
Cu0.11 The Cu+ species are then recovered by traditional reduction
methods. Here we report the use of these techniques to synthesize
a faujasite zeolite containing almost 57 copper ions per unit cell
and use of the same to desulfurize a commercial diesel fuel.
H-Y was first obtained by heating a NH4-Y zeolite powder
(Si/Al ) 2.40, Strem Chemicals) in air at 450 °C at 1 °C/min.
Layers of the proton-form zeolite and CuCl (99.99%, Sigma-
Aldrich) were loaded into a reactor each separated by thin quartz
wool walls. Direct contact of the zeolite and salt is not desired
because of hydrolysis of the copper species in the presence of
adsorbed water. The reactor was then heated in an inert, dry
atmosphere, from room temperature to 200 °C at 1 °C/min and the
temperature held at that point for 4-6 h. Afterward, the temperature
was slowly increased above the normal melting point of CuCl (430
°C) and kept at a specific temperature for another 10 h. The zeolite
was then treated in oxygen at 200 °C for 4 h before cooling down
to room temperature. During the oxidation stage the cupric ions
react to form oxonium ions [Cu-O-Cu]2+, which could further
interact with moist air to form stable [Cu(OH)]+ ions.11 After
recovery, all the as-prepared zeolites were analyzed for elemental
composition using neutron activation analysis (NAA). In addition,
liquid nitrogen adsorption at -196 °C provided sorbent surface area
information.
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