5959
J . Phys. Chem. 1992, 96, 5959-5962 clues about catalyst surface chemistry when combined with spectroscopic probes in the study of alkali-promoted supported metals.
Acknowledgment. Support from the National Science Foundation through the Presidential Young Investigator Program (CBT-8552656) is gratefully acknowledged. Regtry
NO. (CH,),C-CHCHO, 107-86-8; Ru, 7440-18-8; K,
7440-09-7.
References and Notes (1) (a) Heterogentous Catalysis and Fine Chemicals. Proceedings from the 1st International Symposium, 1987; Guisnet, M., et al. Eds.; Elsevier: Amsterdam, 1988. (b) Heterogeneous Catalysis and Fine Chemicals 11. Proceedings from the 2nd InrernafionalSymposium, 1990; Guisnet, M., et al., Eds.; (Elsevier, Amsterdam, 1991). (2) See, for example, the following patents: Cordier, G.; Fouilleux, P.; Grosselin, J. M. French Patent App. No.882919, 1988. Homer, M.; Irgang, M. German Patent No.81-313805,1981. Ichikawa, Y.; Suzuki, M.; Sawaki, T. Japanese Patent No. 52084193, 1977. (3) Blackmond, D. G.;Oukaci, R.; Blanc, B.; Gallezot, P. J . Catal. 1991, 131, 401. (4) Vannice, M. A,; Sen, B. J . Catal. 1989, 115, 65. (5) Poltarzewski, A.; Galvagno, S.;Pietropaolo, R.; Staiti, P. J . Catal. 1986, 102, 190. (6) Giroir-Fendler, A.; Richard, D.; Gallezot, P. In Heterogeneous Caralysis and Fine Chemicals; Guisnet, M., et ai., Eds.; Elsevier: Amsterdam, 1988, p 171. (7) Campelo, J. M.; Garcia, A,; Luna, D.; Marinas, J. M. J . Catal. 1988, ’ 113, 172. (8) (a) Simonik, J.; Beranek, P. J . Catal. 1972,24,348. (b) Simonik, J.; Beranek, P. Collect. Czech. Chem. Commun. 1972, 37, 353. (9) (a) Nitta, Y.; Ueno, K.; Imanaka, T. Appl. Catal. 1989, 56, 9. (b) Nitta, Y.; Hiramatsu, Y.; Imanaka, T. J. Caral. 1990, 126. (10) Jenck, J.; Germain, J. E. J. Catal. 1980, 65, 14. (1 1) Hubaut, R.; Daage, M.; Bonnelle, J. P. Appl. Catal. 1986, 22, 231.
(12) Beccat, P.; Bertolini, J. C.; Gauthier, Y.; Massardier, J.; Ruiz, R. J . Catal. 1990, 126, 451. (13) Cavalcanti, F. A. P.; Blackmond, D. G.; Oukaci, R.; Sayari, A.; Erdem-Senatalar, A,; Wender, I. J . Caral. 1988, 113, 1. (14) Oukaci, R.; Sayari, A.; Goodwin, J. G . J . Catal. 1986, 102, 126. (15) Ke-sraoui, S.;Oukaci, R.; Blackmond, D. G. J . Cafal.1987,105,432. (16) McClory, M. M.; Gonzalez, R. D. J. Catal. 1984.89, 392. (17) Uram, K. J.; Ng, L.; Yates, J. T., Jr. Surf. Sci. 1986, 177, 253. (18) DePaola, R. D.; Hrbek, J.; Hoffmann, F. M. J. Chem. Phys. 1985, 82, 2484. (19) Ertl, G.; Weiss, M.; Lee, S. B. Chem. Phys. Lett. 1979, 60, 391. (20) Lang, N. D.; Holloway, S.;Norskov, J. K. Surf. Sci. 1985, 150,24. (21) Falconer, J. L.; Schwarz, J. A. Coral. Reu.-Sci. Eng. 1983,25, 141. (22) Little, L. H. infrared Spectra ofAdsorbed Species; Academic Press: London, 1966; Chapter 10. (23) Dalla Betta, R. A. J . Phys. Chem. 1975, 79, 2519. (24) Robbins, J. L. J. Caral. 1989, 115, 120. (25) Yokomizo, G. H.; Louis, C.; Bell, A. T. J . Caral. 1989, 120, 1. (26) Solymosi, F.; Rasko, J. J . Catal. 1989, 115, 107. (27) van Hardeveld, R.; Hartog, F. Adu. Catal. 1975, 22, 75. (28) Van’t Blik, H. F. J.; van Zon, J. B. A. D.; Huizinga, T.; Vis, J. C.; Konigsberger, D. C.; Prins, R. J . Am. Chem. SOC.1985, 107, 3139. (29) Bergeret, G.; Gallezot, P.; Gelin, P.; Ben Taarit, Y.; Lefebvure, F.; Naccache, C.; Shannon, R. D. J . Catal. 1987, 104, 279. (30) Basu, P.; Panayotov, D.; Yates, J. T., Jr. J . Am. Chem. SOC.1988, 110, 2074. (31) Zaki, M. J.; Ballinger, T. H.; Yates, J. T., Jr. J . Phys. Chem. 1991, 95, 4028. (32) Hammaker, R. M.; Francis, S.A.; Eischens, R. P. Spectrochim. Acta 1965, 21, 1295. (33) Crossley, A.; King, D. A. Surf. Sci. 1977, 68, 528. (34) Nunan, J. G.; Bogdan, C. E.; Klier, K.; Smith, K. J.; Young, C. W.; Herman, R. G . J. Caral. 1989, 116, 195. (35) Horvitz, C. P.; Shriver, D. F. Adu. Orgonomet.Chem. 1984,23,219. (36) Okuhara, T.; Tamaru, H.; Misono, M. J . Carol. 1985, 95, 41. (37) Hoost, T. E.; Goodwin, J. G., Jr. J . Caral. 1991, 130, 283. (38) Goupil, D. Ph.D. dissertation, University of Lyon, France, 1986. (39) Waghray, A.; Oukaci, R.; Blackmond, D. G. Caral. Lett. 1992, 14, 115. (40) Waghray, A.; Blackmond, D. G., unpublished results.
Study of Photoreduction of PtQ2- on CdS Qinglin Li,* Zhengshi Chen, Xinbua Zheng, and Zhensheng Jin* Lanzhou Institute of Chemical Physics, Chinese Academy of Sciences, Lanzhou 730000, P. R. China (Received: December 23, 1991; In Final Form: March 18, 1992)
The photoinduced reduction of PtCb2-on CdS was investigated by means of XPS,DTA, and TEM. The experimental results indicate that the photoreduced product of PtCl,” on CdS is PtS in acidic solution and Pt(OH)2 in basic solution. PtS can be converted to Pto by further treatment in air at high temperature. But the photoreduced product of PtCh2-on high-temperature air-treated CdS is Pt(0H)’ in both acidic and basic solution. Pt(0H)’ can be dehydrated to PtO at high temperature under ultra-high-vacuum conditions.
1. Introduction Some new findings have led to the recent surge of interest in the photoinduced reduction of PtC16’-. Bocarsly observed that the formation of platinum metal (PtO) occurs only when ca. 90% of PtC1,2- is formed on photoreduction of PtC1,’- in aqueous i-PrOH solution and suggested that PtC16’- acts as an inhibitor in Roformation.’ Shagisultanova found the presence of Pt(II1) species in cryogenic ESR studies of the photolysis of PtClS2-ions in organic glaws.2 Using ESR and spin trapping technique, Kemp confirmed that the photoreduction of PtCb2- by alcohols involves a photoredox process yielding R(II1) and a hydroxyalkyl r a d i ~ a l . ~ The photodepasition of Ptoon some semiconductor oxide powders in acidic PtC162-solution is now a method for the preparation of photocatalysts, such as Pt/TiOz and Pt/W03.4*5The photoreduction product Ptois mainly determined by XPS. But there are arguments on the photoreduced product of ptc16’- over powder CdS. Some researchers considered it as Pt0:6*7
Reber inferred that the photodeposit is a mixture of Pt0/Pt+/Pt2+? By means of XPS and DTA, Jin and Li discovered that the photoreduced product of PtC16z-in acidic solution is PtS which can be converted to Pto in high-temperature air9 PtS + 02 PtO so2 In this paper, the effects of the surface property of CdS and the pH of solution on the forms of photoreduced product are reported and the mechanism discussed.
-
+
2. Experimental Section 1. Preparation of Specimen. Two grams of CdS powder was added into 20 mL of deionized water containing 0.66 mL of 7.72
0022-3654/92/2096-5959%03.00/00 1992 American Chemical Society
5960 The Journal of Physical Chemistry, Vol. 96, No. 14, 1992 TABLE I. ho~ertiesof CdS av size, surface area, purity, % m m2/g CdS, 98 0.5 11 4.1' heating loss, 1 Fe, 0.0005 c u , 0.001
so:-,
Li et al.
hP
crystalline hexagonal
color orange
v
2130 4
c,
mean p a r t i c l e s i z e 2.9 nm
m
20
CL w
0.2
mean p a r t i c l e s i z e 3.5 nm
0
+
"After treatment at 520 OC in air.
0
::
IO
a,
P a r t i c l e s i z e (nm)
Figure 2. Distribution curves of Pt particle sizes (photodeposited 0.5 wt % Pt/CdS, pH 2.3, UV): (0)before hot air treatment, (A)after hot air
treatment.
18
71
76
15
74
n
72
71
m
M E b lev1
Figure 1. XPS spectra of photodeposited Pt on CdS in acidic solution and platinum metal: (a) photoreduced, pH 2.3, UV light; (b) treated at 600 OC in UHV chamber for 30 min; (c) treated at 520 O C in air for 5 min; (d) metal platinum. X M H2PtCl&H20 aqueous solution. The pH of the solution was adjusted to 2.3 or 13 using 0.5 M HCl or 1 N NaOH, respectively. Then, high-purity N2 was bubbled through the solution for 20 min prior to irradiation. The photoreduction of PtC1:- on the CdS powder surface was performed under UV light for 3 h or in visible light for 6 h with stirring. After irradiation, the powder was filtered and washed to remove residual C1- and dried in a vacuum oven at 100 OC for 12 h. Further treatment of the s e e n was camed out at 520 OC in air. The specification of CdS (Beijing Chemical Factory) used in this work is listed in Table I. 2. XPS Analysis. XPS spectral measurements were performed on a PHI-550 multifunctional spectrometer (P-E Co., U.S.A.) with Mg Km radiation (power 320 W, energy 1253.6 eV). The powder specimen was pressed into a disk (diameter 10 X 1 mm) and mounted on a heatable sample holder. The specimen desorbed for 30 min at 1.3 X Pa prior to XPS analysis in ultrahigh-vacuum (UHV) chamber. The voltage of argon ion sputtering was 4 kV, and the sputtered area was 10 X 10 mm. The relative atomic concentrationon CdS surface was determined using X P S sensitivity correcting factors provided by P-E Co. The binding energy was calibrated by S, line of CdS (Eb = 161.8 eV). The error in binding energy measurements is ca. fO.l eV. 3. Measurementsof H+/OH- Adsorption Isotberm and PZC (Point of Zero Charge). Potentiometric titration was performed in a 100-mL electrochemical cell under N2 flow at 25 f 1 OC. Solutions for titration were 0.1 N NaOH and 0.1 N HCl. NaCl served as a supporting electrolyte. The pH value was measured by SPM-1OA digital pH meter (Xiaoshan Xinjie Instrument Factory, China). The amount of sample used was 1 g. The drawing of H+/OH- adsorption isotherm curves and determination of PZC were done in accordance with ref 10. 4. "EM and DTA. The dispersity of platinum particles on CdS surface was determined from the pictures taken by JEM-7 electron microscope (Japan) and DTA was measured on a LCT-1 differential thermal analyzer (China).
3. Results and Discussion 1. Wotoreductioa of ptcbs- on CdS -ace in Acidic Solution. Figure 1 shows the XPS spectra of platinum species under different conditions. The binding energy Eb(Pt41,,2)of the photoreduced
Figure 3. DTA curves of CdS, Pt/CdS, and air-treated Pt/CdS: (a) CdS; (b) photodeposited Pt/CdS (pH 2.3, UV); (c) photodeposited Pt/CdS (pH 2.3, UV), after air-treatment.
TABLE II: Binding Energy of PtM,,,in Several Plptinum Compounds Pt PtS Pt(OH)2 PtO PtOz KzPtC14 K2PtCI6 ref 11.0 11.2 10.9 10.1 11.1
12.4 12.4
12.2 12.5 12.2
14.4 14.6 14.2 13.2
15.1
11 12 13 14 5
product of PtC162-is 72.4 eV (Figure la), and after heating at 600 OC for 30 min in the UHV chamber, no change in E,, is observed (Figure lb). When the specimen is exposed to 520 OC air for 5 min, however, Eb shifts to 71.0 eV (Figure IC) which is the binding energy of platinum metal (Figure Id). TEM determination shows that average size of the platinum particle increases slightly after high-temperature treatment in air (Figure 2). The DTA experiments demonstrate that a surplus exothermic peak appears at 500 "C for the platinum-loaded CdS by photoreduction of PtC16*- as compared with the naked CdS (Figure 3a,b). But the peak at 500 OC disappears when the specimen is pretreated in air at 520 OC prior to the DTA test (Figure 3c). As to the decrease of temperature of the exothermic peak, it is probably due to the catalysis of Pt on oxidation of CdS in air. Referring to the binding energy of platinum compounds given in refs 5 and 11-14 (Table 11), we suggest that the photoreduced product of PtC16" on CdS in acidic solution is PtS which is undecomposable under UHV condition at high temperature. But in air PtS is easily converted to Pto at high temperature. PtS + 0
500 'C
2
a11
PtO + so2
It is, therefore, reasonable for the appearance of a surplus exothermic peak at 500 OC in Figure 3b.
Study of Photoreduction of PtC1,2- on CdS R4t
1
.
The Journal of Physical Chemistry, Vol. 96, No. 14, 1992 5961
I
Pt 4f *b
,
77 16
, 75
.
74
. 73
72
, 71
, 70
~b
(.v)
Figure 4. XPS spectra of photodeposited Pt on CdS in basic solution: (a) pH 13,visible; (b) pH 13, visible, 600 'C, UHV, 30 min; (c) pH 13, UV; (d) pH 13,UV, 600 OC, UHV, 30 min.
I
10
30
?o
IO
0
50
60
sputtering t i m e b i n )
Figure 6. O/S atomic ratio of CdS versus argon sputtering time: (a) 520 OC, air, 5 min; (b) 520 OC, air, 45 min; (c) 520 OC, air, 90 min.
ql
\
-4
-6
Figure 5. Adsorption isotherm of CdS and CdO suspension in water (electrolyte: NaCl lW3M):(a) untreated cds,(b) air-treated CdS, 520 OC, 5 min; (c) air-treated CdS, 520 OC, 90 min; (d) pure CdO powder. TABLE IIk Pro& treating time. min
of CdS Treated at 520 O C in Air re1 atom concn, at surface, 96 S Cd 0 PZC"
1.6+/1.2-
~~
0 45 90
34.4 24.8 22.5
49.3 39.4 31.4
16.5 35.1 40.1
5.1
9.2
0 0.19 0.24
'PZC of powder CdO is 11.2.
2. Photoreduction of PtQz- on CdS in Basic Solution. The photoreduction of PtC1;- on CdS in basic solution differs much from that in acidic solution under either UV light or visible light illumination (Figure 4a,c). The binding energy Eb of Pt4n/2,72.7 eV, is 0.3-0.4 eV higher than the Eb in acidic condition. It is interesting to note that after specimen heating at 600 OC for 30 min in the UHV chamber, Eb of Ptdnp shifts to 72.1 eV (Figure 4b,d) which is in agreement with PtO (Table 11). From these, we p r o p that the photoredud prcduct of PtC&> in basic solution is Pt(OH)2. 3. Pbotoredsction of on Air-TreatedCdS at High Temperature. We reported earlier that a composite surface layer of Cd(OH),-CdO-CdS is formed on the air-treated CdS surface at 520 OC and the relative atomic oxygen concentration at CdS surface and surface alkalinity (is., PZC) of CdS increases with the increasing of treating time (Table I11 and Figure 5). The argon ion sputtering experiments reveal that molecular oxygen may m u s einto the CdS lattice and oxidize CdS to CdO and the relative atomic oxygen concentration below the surface layer of cds correspondingly increases with the increasing of treating time (Figure 6 ) . XPS examination indicates that photoredud prcduct of PtCb2on air-treated CdS is Pt(OH)2 (.Eb = 72.7 eV) both in acidic solution and in basic solution (Figure 7a,c). After heating the specimen in the UHV chamber for 30 min at 600 OC the peak
lb
5
1.1 x 1od
76
75
14
73
72
71
70
69
Eb(e~,
Figure 7. XPS spectra of photodeposited F? on air-treated Cds: (a) pH 13, visible; (b) pH 13,visible, 600 OC, UHV, 30 min; (c) pH 2.3,UV; (d) pH 2.3,UV, UHV, 30 min.
for Pt+* shifts ca. 0.6 eV, which denotes the conversion of Pt(OH),to PtO (Eb 72.0 eV) (Figure 7b,d). This result implies that strong interaction between PtC&2-and air-treated CdS occurs. 4. M e c W of Photoinduced Reduction of P a z - on CdS Surface. We propose that the mechanism of photoinduced reduction of PtC12- on CdS in different conditions is as follows: (i) Photoreduction of PtCb2- on CdS in acidic solution. Since CdS dissolved slightly in water (Table IV)
wz-
TABLE Iv: sdubllity of CdS in Water 3 pH (25 "C) solubility, mol/L 1.0 x 104
77
CdS
+ HzO
-.*
Cd(OH)+ + SH-
(2)
PtCIt- adsorbed on CdS surface can be reduced by the conduction band electrons of excited CdS. PtC162-(a) + 2e-cb
hv
+ 2C1-
(3)
+ H+ + 4Cl-
(4)
PtC14,-(a)
and thus PtCId2-(a) + SH-(a)
CdS
PtSl
(ii) Photoreduction of PtC162-on CdS in basic solution. CdS with a weak acidic surface (PZC = 5.7, Figure 5 ) adsorbed OHions in basic solution. The photogenerated electrons reduce PtC&>
I 1.5 X
9 1.1 x lo-"
11
1.1 x 10-12
5962
J. Phys. Chem. 1992,96, 5962-5965
to PtC14z-which react further with adsorbed OH- to form Pt(OH),. PtC162-(a) + 2e-cb PtC142-(a) + 20H-(a)
hv
PtC142-(a) + 2Cl-
CdS
pH = 13
Pt(OH),l
+ 4C1-
(3) (5)
(iii) Photoreduction of PtCb2- on high-temperature air treated CdS. As mentioned earlier, the CdO formed on the CdS surface when treated in high-temperature air can further react with the moisture in air to form Cd(OH),. Cd(OH)2, depending on the acidity of solutions, dissociates into two different kinds of complexes. in acidic solution: Cd(OH),(s) in basic solution:
+ H+(a)
-
Cd(OH)+(a) + H 2 0
+
(6)
+
Cd(OH),(s) OH-(a)- HCd(0H)-(a) H 2 0 (7) Since XPS spectra reveal that the photoreduced product of PtCl& on high-temperature air-treated CdS is Pt(OH)2 (Figure 6b,c) in either acidic solution or basic solution. Therefore PtCl,,-(a) PtC14,-(a)
+ 2e-cb
+ 20H-(a)
hv
PtC142-+ 2Cl-
Cd(OH)+
Pt(OH),i
+ 4C1-
(3) (8)
respectively. 4. Conclusions PtS or Pt(OH), is formed after photoreduction of PtClS2-on a CdS surface due to the different initial properties of CdS and
to the solutions of different pH values. PtS is not decomposable in UHV at 600 OC, but can be converted to Ptoin air a t 500 O C . Pt(OH)2 can be dehydrated in the UHV chamber at 600 OC and the dehydrated product is PtO.
Acknowledgment. We thank the Natural Science Foundation of Gansu Province for financial support of this work. We are also indebted to Prof. Hanqing Wang and Zhicheng Jiang for valuable discussions and Chengyun Wu for carrying out the DTA determination. Re&@ NO. PtQ2-, 16871-54-8; CdS, 1306-23-6; PtS, 12038-20-9; Pt(OH),, 12135-23-8;CdO, 1306-19-0; Cd(OH),, 21041-95-2. References and Notes (1) Cameron, R. E.;Bocorsly, A. B. Inorg. Chem. 1986, 25, 2910. (2) Shagisultanova, G. A. Koord. Khim. 1981, 7 , 1527. (3) Fadnis, A. G.; Kemp, T. J. J. Chem. Soc., Dalron Trans. 1989, 1237. (4) Kraeutler. B.;Bard, A. J. J. Am. Chem. Soc. 1978,100,4317. ( 5 ) Koudelka, M.; Sanchez, J.; Augustynski, J. J. Phys. Chem. 1982.86, 4211. (6) Dimitrijevic, N. M.; Li, Shuben; Gritzel, M. J . Am. Chem. Sa.1984, 106,6565. (7) Mills,A,; Williams,G. J. Chem.Soc., Faraday Trans. 1 1989,85,503. (8) Buhler, Meier, K.;Reber, J. F. J . Phys. Chem. 1984, 88, 3261. (9) Zhensheng, Jin; Qinglin, Li; Liangbo, Feng; Zhengshi, Chen J. Mol. Cafa. 1989, 50, 315. (10) Jaffrezic-Renanlt, N.; Pichat, P.; Foissy, A.; Mercier, R. J . Phys. Chem. 1986, 90,2733. (1 1) Hammond, J. S.;Winograd, N. J . Elecrroanal. Chem. 1977, 78,55. (12) Allen, G. C.; Tucker, P. M. J. Eleciroanal. Chem. Interfacial Elecrrochem. 1974, 50, 335. (13) Wang, T.; Vazguez, A.; Kato, A.; Schmidt, L. D. J . Catal. 1982. 78, 306. (14) Kim. K. S.;Winograd, N.; Dairs, R. E. J. Am. Chem. Soc. 1971,93, 6296. (15) Zhensheng, Jin; Qinglin, Li; Changjuan, Xi; Zhicheng, Jiang; Zhengshi, Chen Appl. Surf. Sei. 1988, 32,218. (16) Gmelins Handbuch der Anorgamschen Chcmie;System-NR.33, Cd Erganzungsband, p 608.
Synthesis of FuHy Dehydrated Fully Zn2+-ExchangedZeolite Y and Its Crystal Structure Determined by Pulsed-Neutron Dlffractlon Petie B. Peapples-Montgomery a d Karl Sew Department of Chemistry, University of Hawaii, Honolulu, Hawaii 96822-2275 (Received: December 23, 1991; In Final Form: April 6, 1992)
Fully dehydrated, fully Zn2+-exchangedzeolite Y has been synthwized by the reduction of all H+ ions in H-Y by zinc vapor. This solvent-free ion-exchange reaction goes to completion at 420 OC with about 0.2 Torr of Zno to give Zn27,sSi137Alss0384 (a,, = 24.4688 (3) A). The crystal structure was determined in the cubic space group F&m by pulsed-neutron powder-diffraction methods at 10 K and was refined to Rp = 0.0268 and Rw = 0.0368. Two different Znz+positions were found in the structure. The Zn(1) position is located on a threefold axis in the sodalite unit adjacent to a single 6-ring (site II'), 2.183 (12) A from three nearest framework oxygens. The Zn(2) position is also on a threefold axis in the sodalite unit, but is adjacent to a double 6-ring (site I'), 2.228 (15) A from three nearest framework oxygens. It must be true, on the basis of refined fractional occupancy parameters and to avoid 3.1-A Zn( 1)-Zn(2) distances, that about half of the sodalite cavities contain about four Zn(1) ions in the four tetrahedrally arranged single 6-rings and that the other half contain about three Zn(2) ions in three of the four tetrahedrally arranged double 6-rings. Based on this crystal structure, it is proposed that Zn(2) is initially preferred Zn2+can bond to 0(3), the most electronegative oxygen) but that at higher loadings the increased number of short 3.90 intrasodalite Zn(2)-Zn(2) distances causes Zn( 1) to be the preferred site.
L
Introduction Most dipositive cations cannot be completely exchanged into zeolites by aqueous methods. The only dipositive cations reported to have exchanged completely into zeolite Y by aqueous methods at 25 OC are Mg2+and Ca2+,and at 80 O C , S?+.' The maximum extent of exchange of the ions Co2+,Ni2+, Cu2+,and Zn2+at 25 OC is 80, 70,86, and 94.5%, respectively.2 For zeolite X,Ca2+ fully exchanges at 25 OC,' Zn2+ a t 45 0C,2and Sr2+and Ba2+ 0022-3654/92/2096-5962S03 .OO/O
a t 80 O C . I Complete aqueous exchange of dipositive cations into zeolite A has been achieved for Ca2+,35S P p Ba2+PZn2+,7Cd2+,8 and Pb2+.9 Zeolite A generally accepts extra molecules (over ion exchange) of salts of Cd2+or Pb2+, or of Cd(OH)2or Pb(OH)2, from aqueous solutions of those ions. The complete ion exchange of metal ions into zeolites has been accomplished by solvent-free redox methods. Na-A,Io K-A," and Ca-AI2 successfully underwent complete ion-exchange with 0 1992 American Chemical Society
