J. Phys. Chem. 1994,98, 1217-1221
1217
Electron Spin Resonance Study of Ni(1) in Silicoaluminophosphate Type 11: Adsorbate Interactions and Evidence for Framework Incorporation of Ni(1) Naoto Azuma, Cbul Wee Lee, and Larry Kevan' Department of Chemistry, University of Houston, Houston, Texas 77204-5641 Received: June 24, 1993; I n Final Form: October 25, 1993'
The various Ni(1) species formed by reduction and adsorbate interactions in silicoaluminophosphate-11, synthesized by incorporation of Ni(I1) in the synthesis mixture (NiAPSO-11) and formed by partial ion exchange of H(1) by Ni(I1) (NiHSAPO-1 l ) , were studied by electron spin resonance. After dehydration at temperatures above 773 K one Ni(1) species is observed in NiAPSO-11, while this treatment does not generate any Ni(1) species in NiHSAPO-11. Two distinct Ni(1) species, assigned as isolated Ni(1) and Ni(I)-(H2),,, are observed in both NiAPSO-11 and NiH-SAPO-11 after reduction in hydrogen at 573 K. Ni(I)-(Oz),, species are produced both in hydrogen-reduced NiAPSO-11 and in NiH-SAPO-11 after adsorption of water, indicating water decomposition on the Ni-containing oxide surface. Ni(1) complexes with methanol show some differences in the g parameters between NiAPSO- 11 and NiH-SAPO- 11. A more significant difference between NiAPSO- 11 and NiHSAPO-1 1 in nickel ion coordination to adsorbates is seen with nonpolar adsorbates. The adsorption of carbon monoxide onto NiAPSO-11 and NiHSAPO-11 produces Ni(1)-(CO),, with n = 1-3. The Ni(I)-(CO)I species is not observed in NiH-SAPO-11. The rate of ethylene adsorption onto NiAPSO-11 is 1000-fold more rapid than onto NiHSAPO-11. The contrasting ESR characteristics of Ni(1) in NiAPSO-11 and NiHSAPO-11 suggest that Ni(1) in NiAPSO-11 is in a framework site.
Introduction The aluminophosphate(AlP04-n) and silicoaluminophosphate (SAPO-n) molecular sieves belong to a new class of microporous materials.'J The modification of these materials by isomorphous replacement of framework cations by transition-metal ions or by incorporationof such ions into extraframeworkpositions can play a significant role in many catalytic reactions. Since the location and oxidation state of transition-metalions can affect the catalytic activity, it is important to study the chemical environments and location of such transition-metal ions. Nickel-modified molecular sieves are quite useful in industrial processes such as hydrocracking, isomerization, and hydrogenation. Recently, Inui et al.3 reported that nickel substitution into SAPO-34 results in highly selective conversion of methanol to ethene. Ni(I1) has been reported to occupy framework positions in AlPO4-12, -214and SAPO-5, -34,5but the characterization of actual framework position is not unambiguous and no comparisons were made with known nonframework preparations of these materials. There are no electron spin resonance (ESR) studies on nickel ion incorporation into AlP04-n and SAPO-ncompounds. In this study we have synthesized NiAPSO-11 where Ni(I1) was added to the synthesis mixture and report spectroscopic evidence for Ni incorporation into the SAPO-11 framework. The Ni(1) species formed in NiAPSO-11 by reduction and interaction with several adsorbates are compared to Ni(1) speciesformed in NiHSAPO-11whereNi(I1) is incorporated by solid-state ion exchange into known nonframework sites. Experimental Section Sample Preparation. The following chemicals were used without further purification: 85% H3P04(Mallinckrodt), aluminum isopropoxide (Aldrich), 30 wt % Si02 (colloidal silica LUDOX LS, DuPont), diisopropylamine (Aldrich), Ni(OCOCH3)y4Hz0 (Aldrich), and NiC12.6H20 (Aldrich). As-synthesized NiAPSO- 11 was prepared by hydrothermal reaction with addition of Ni(OCOCH3)y4H20 in the synthesis mixture for SAPO-1 1?,7 Finely ground aluminum isopropoxide e
Abstract published in Advance ACS Abstracts, January 1, 1994.
0022-365419412098-1217$04.50/0
(9.191 g) was added slowly to 13.0 mL of HzO while stirring for 1 h to obtain a homogeneous mixture. To this mixture was added 5.128 g of H3P04 (85 wt %) drop by drop while stirring for about 1 h. Then 1.OOOg of 30 wt % Si02 and 1.O mL of H20 were added drop by drop. Finally, 7.0 mL of 0.71 M Ni(OCOCH3)y4HaO and 2.555 g of diisopropylamine were added drop by drop to this mixture. The mixture was aged with stirring at room temperatureovernight to form a uniform gel. The reaction mixture was placed in a stainless steel pressure vessel lined with Teflon and heated in an oven at 493 K at autogenous pressure for 3 days. Calcined NiAPSO- 11 was prepared by heating the as-synthesized sample in air at 823 K for 48 h. Upon calcination at 823 K, the specimen turned from violet to light green. The chemical composition of this calcined sample was Ho.os(Nio.olSi0.04Al0.~oP0.45)02 based on electron probe microanalysis. HSAPO-11 was synthesized according to previous work.7 NiHSAPO- 11 was prepared by solid-state ion exchange by using NiC1~6Hz0and HSAPO-11, where Ni ions exist in extraframework positions in the SAPO- 11structure.8 NiCb6Hz0 (0.01 g) and 1.0 g of calcined HSAPO-11 were mixed with a mortar and pestle. This solid mixture was pressed in a steel die with 1500 kg cm-2 for 20 min to make a disc. Then the disc was heated in a muffle furnace at 873 K in air for 12 h, and the reaction product was cooled to room temperature slowly. The chemical composition of this sample was N~o.wIHo.o~~(S~O.OSAlo.5oPo.45)02based on electron probe microanalysis. After the ion exchange of NiHSAPO-11, the samples remained white. We also prepared liquid-state ion-exchanged samples with calcined HSAPO-11 and an aqueous solution of NiC12.6H20, but the ESR signal intensities of Ni(1) in these samples are much smaller for unknown reasons. Ni-AlP04-11 was prepared by impregnation, in contrast to ion exchange, by using NiC1~6H20and AIPO4-11 according to the following procedure where AlPO4- 1 1 was prepared as done previo~sly.~ One gram of calcined AlP04-11 was added to 20 mL of 1 X l t 3M NiC12.6H20 solution and stirred at 363 K until the water was completely evaporated. Then, this sample was washed with deionized water at room temperature in order to remove any nickel ion on the surface. 0 1994 American Chemical Society
1218 The Journal of Physical Chemistry, Vol. 98, No. 4, 1994 Sample Treatments. Calcined and hydrated samples were loaded into 3-mm-0.d. by 2-mm4.d. Suprasil quartz tubes and gradually heated in vacuo ( < 1 V Torr) to 773 K for 12 h. Then the samples were contacted with dry oxygen (500 Torr) after cooling the samples to room temperature and heated at 823 K for 5 h. The excess oxygen was pumped off for 10 min in vacuo at 773 K. After oxidation with static oxygen the color of N M S O 11 changed to light brown, but the color of NiHSAPO-11 remained white. In order to prepare Ni(1) species, the samples were treated by two different reduction methods after the above dehydration and oxidation procedures. In one reduction method the samples were evacuated in vacuo at temperatures above 773 K for several hours (denoted throughout as “thermal reduction”). In another reduction method the samples were reduced by static dry hydrogen (100 Torr) at 573 K for only 1 h to avoid formation of metallic nickel (denoted as “hydrogen reduction”). After both reduction treatments, the color of NiAPSO-11 remained light brown and the color of NiHSAPO-11 remained white. In order to prepare Ni(1) complexes with various adsorbates, the hydrogen-reduced samples were evacuated at 573 K for 10 min and then were adsorbed with D20, CHjOD, CO, and C2D4 from Stohler Isotope Chemicals and Aldrich Chemical Co., for 1 min at ambient vapor pressure at room temperature. These samples were frozen in liquid nitrogen and sealed. Ni(1) complexes were also prepared with the thermally reduced samples, but the ESR signal intensity was much smaller. During these sample treatments it is important not to contaminate the sample with trace amounts of water from a vacuum line or elsewhere because the efficiency of Ni(I1) reduction is affected by water and Ni(1) in these samples is very reactive toward water. Measurements. The structures of as-synthesized NiAPSO- 11 and NiHSAPO-11 were examined by powder X-ray diffraction (XRD) with a Philips PW 1840 diffractometer using Cu Ka radiation and a 20 range of 4-55O. The compositions of the samples were measured by electron probe microanalysis with a JEOL JXA-8600 spectrometer. Thermogravimetric measurements of the as-synthesized NiAPSO- 11 and H S A P O - 11 were made by heating them from room temperature to 1073 K at a temperature elevating rate of 10K m i d under dry air atmosphere using a Dupont 95 1 thermal analyzer. X-band ESR spectra were recorded at 77 K with a modified Varian E-4 spectrometer interfaced to a Tracor Northern TN- 1710signal averager.I0Each spectrum was obtained by multiple scans to achieve a satisfactory signal-to-noise ratio. The magnetic field was calibrated with a Varian E-500 gaussmeter. The microwave frequency was measured by a Hewlett Packard HP 5342A frequency counter.
Azuma et al. TABLE l: XRD Data of As-Synthesized SAPO-11 and NiAPSO-11’ SAPO-1 1 NiAPSO-1 1 ref 6 28
iooi/io
20
iooi/i0
20
loOI/Io
8.1 9.4 13.2 15.7
46 58 21 33
8.1 9.4 13.2 15.6
39 54 22 37
19.0 20.5 21.0 22.1 22.5 22.7 23.2 24.7 26.4 26.7
9 41 100 55 48 58 68 10 17 16
19.0 20.5 21.1 22.1
7 46 100 53
8.05-8.3 9.4-9.65 13.1-1 3.4 15.6-15.85 16.2-16.4 18.95-19.2 20.3-20.6 21.0-21.3 22.1-22.35 22.5-22.9”
20-42 36-58 12-16 23-38 3-5 5-6 36-49 100 47-59 55-60
22.7 23.2 24.6 26.3 26.6
58 I5 9 15 21
23.1 5-23.35 24.5-24.9, 26.4-26.8’
64-14 7-10 11-19
28.6
14
28.6
16
29.5 31.5 32.9 34.2 35.7 36.6
10 9 12 8 4
11 3 2
16 17 11 4 5 10 10 3
0-1 11-17 0-3 5-7 7-9 11-14 7-9 0-3 3 4 10-13
37.9 39.4 40.5
31.6 32.9 34.2 35.7 36.6 37.5 37.9 39.3
27.2-27.3 28.3-28.5 * * 29.0-29.2 29.45-29.65 3 1.45-3 1.7 32.8-33.1 34.1-34.4 35.7-36.0 36.3-36.7 37.5-38.0*
42.9 45.0
5 4
42.2 42.8 44.8
3 5 8
48.9 50.7 54.7
3 3 3
48.8 50.6 54.7
3 4 3
3 9.3-3 9 * 55 40.3 42.2-42.4 42.843.1 44.845.2’ 45.9-46.1 46.8-47.1 48.7-49.0 50.5-50.8 54.6-54.8 55.4-55.7
2-3 0-2 0-2 3-6 3-5 0-2 0-1 2-3 3-4 2-3 0-2
5
Key: *doublet; **shoulder.
Temp., K
.-0
Results and Discussion X-ray Powder Diffraction. The structures of as-synthesized NiAPSO- 11and HSAPO-11 werecharacterized by XRD. Table 1 shows the powder XRD pattern of synthesized NiAPSO-11 and H-SAPO-11. There are no significant differences in the XRD patterns between synthesized NiAPSO-11 and H-SAPO11. These XRD patterns agree reasonably with the patent literature6 to identify the product (Table 1). They indicate that NiAPSO-11 has the same structure as SAPO-11. No peak broadening was observed. Such a similarity of the XRD pattern has been demonstrated for MnAPSO-ll.ll Thus, it is not surprising that the XRD does not give definitive information on possible Ni(I1) locations in NiAPSO- 1 1. A significant color difference depending on the position of transition-metal ions in tetrahedral framework sites or in ionexchanged sites has been demonstrated for c 0 A P 0 - 5 ~and ~ MnAPSO-1 1.13 When Ni(I1) is added during synthesis to form NiAPSO- 11,the product is violet. After calcination of the sample at 823 K, the color changed to light green. However, when Ni-
1
g61 94
9 2 90
273
,q:: /-
p
-
473
673 073 1073 Temp., K Figure 1. Thermogravimetric analysis curves for (a) as-synthesized HSAPO-11 and (b) as-synthesized NiAPSO-11.
(11) is incorporated by solid-state ion exchange to form NMSAPO- 11,the product is white, which may indicate a lower nickel content. ThermogravimetricAnalysis. The TGA curves of as-synthesized H S A P O - 11 and as-synthesized NiAPSO-11 are shown in Figure 1. They show four stages of weight loss: 295-399,399578, 578-778, and 778-840 K for HSAPO-11 and 295-430, 430409,609-726, and 726-1053 K for NiAPSO-11. The first
ESR of Ni(1) in SilicoaluminophosphateType 11
The Journal of Physical Chemistry, Vol. 98, No. 4, 1994 1219
100 G
(4
(b)
-
[-
s;:o1-
1
NiH-SAPO-11
Figure 2. ESR spectra at 77 K after thermal reduction at 823 K for 20 h of (a) NiAPSO-11 and (b) NiH-SAPO-11. TABLE 2 ESR g Values at 77 K of Ni(1) in NMPSO-11 and NM-SAPO- 11 NiAPSO-11 NiHSAPO-11 reduction method species gl' gl" thermal reduction6 Ni(1) 2.463 2.099 c 2.463 2.099 2.460 2.099 hydrogen reductionb Ni(1) 2.061 Ni(I)-(H& 2.334 2.061 2.334 Estimated uncertainty is *0.004. Before this treatment the sample was activated by 0 2 (500 Torr) at 823 K. No ESR signal. stage of weight loss is due to the desorption of physically adsorbed water on HSAPO-11 and NiAPSO-11. The other losses are due to the decomposition of the organic templating agent, diisopropylamine. The temperatures of these decomposition stages for the as-synthesized NiAPSO-11 are higher than those of as-synthesized HSAPO-11. The second stage of weight loss is assigned to the physically adsorbed diisopropylamine, and the third stage of weight loss is assigned to protonated diisopropylamine, which indicates the presence of acid sites.I3 The last stage of weight loss is assigned to diisopropylamine interacting with acid sites. The higher decompositiontemperatureand greater weight losses in the third and fourth weight-loss stages for assynthesized NiAPSO-11 indicate the presence of additional acid sites compared to the case for H S A P O - 1 1. Electron Spin Resonance. Calcined and oxidized samples of NiAPSO- 11 and NiHSAPO- 11 do not show any ESR signal at 77 K. Thus, the Ni species exist in the form of Ni(I1). Figure 2 shows ESR spectra of thermally reduced NiAPSO-11 and NiHSAPO-11 at 823 K. Thermal reduction of NiAPSO-11 at temperatures above 773 K after oxidation leads to the formation of one Ni(1) species assigned to isolated Ni(1) with axially symmetricgvalues (Figure 2 and Table 2). Similar ESR spectra have been reported for NiCa-X, NiNa-X, and NiCa-Y photoreduced and thermally reduced in H2.I4 In contrast, detectable amounts of Ni(1) are not obtained by the high-temperature evacuation of NiHSAPO- 11. Kasai et al.Is suggested that the reduction of Cu(I1) ions in Cu-exchanged mordenite-type zeolite that occurs upon heating in vacuum is caused by reduction by residual water. Michalik et a1.16 also showed that retained water in PdCa-X zeolite plays a significant role in the reduction of Pd upon heating in vacuum. Thus, the formation of Ni(1) species in NiAPSO-11 after evacuation at temperatures above 773 K is suggested to be due to reduction by residual water in NiAPSO-11. The fact that similar reduction is not observed for NiH-SAPO- 11 suggests that the Ni(I1) is in a different site. Figure 3 shows the ESR spectra of NiAPSO-11 and NiHSAPO-11 after hydrogen reduction at 573 K. Two distinct Ni(I) species (Figure 3a,c) are observed in both NiAPSO-l l and NiHSAPO-11 in the presence of hydrogen gas. The g values of species A in NiAPSO-11 is the same as that of isolated Ni(1) observed in NiAPSO- 1 1 after evacuation at temperatures above 773 K. There are slight differences in the gl values of isolated Ni(1) between NiAPSO- 11 and NiHSAPO- 11 (Table 2). This species remains after hydrogen outgassing at room temperature
g,: = 2.460 gIlB= 2.334
V'
N~H-SAPO-1 1
gLB= 2.061
Figure 3. ESR spectra at 77 K of (a) NiAPSO-11 after reduction with H2 for 1 h at 573 K, (b) NiAPSO-11 after 10-min evacuation of (a) at room temperature, (c) NiHSAPO-11 after reduction with H2 for 1 h at 573 K, and (d) NiHSAPO-11after 10-min evacuation of (c) at room temperature. (Figure 3b,d), and the ESR signal intensity does not change even after evacuation at 573 Kin both NiAPSO- 11 and NiHSAPO11. Thus, this species is assigned to isolated Ni(1). On the other hand, species B is lost after evacuation of the hydrogen at room temperature (Figure 3b,d) but is readily regenerated after exposure to hydrogen. Thus, species B is assigned to Ni(1)(H&. ESR shows no difference for the Ni(I)-(H& species between NiAPSO- 11 and NiHSAPO- 11. Before an adsorbate is added, the hydrogen-reduced samples are evacuated at 573 K for 10 min so only isolated Ni(1) remains. The adsorbate is then exposed to the sample for a short time (1 min) at room temperature, and the reaction is quenched at 77 K. After D20 adsorption (vapor pressure -23 Torr) species C with a rhombic g tensor is observed in both NiAPSO-11 and NiHSAPO-11 (Figure 4a,b). The ESR parameters of species C are almost the same in NiAPSO- 11 and NiHSAPO- 11. An ESR signal with similar g values and line shape is observed in NiAPSO- 11 and NiHSAPO- 11 after adsorption of oxygen. Thus, we assign species C to Ni(I)-(02)"17 where n is probably below 2 considering the kinetic diameter of 0 2 (0.346 nm)le and the free diameter of the largest 10-membered ring channel (0.39 X 0.63 nm) in SAPO-1 1.I9 The formation of Ni(I)-(02)n species suggests that DzO is decomposed on Ni(1) sites to produce 02. Interestingly, such water decomposition has not been reported on zeolites containing Ni cations. After D2O adsorption, species A is destroyed completely in NiAPSO-11 but still remains to about 15% in NiHSAPO-11. Furthermore, an 0 2 - radical species with gll = 2.009 and gl = 1.998 assigned to Ni(II)-02- 2o is observed after adsorption of D2O onto NiHSAPO-11 but not onto NiAPSO-11. This substantiates the decomposition of water by Ni(1). In order to confmwhether thedifferenceofreactivityofNi(1)speciestoward water molecules is dependent upon a difference of the Ni(1) location in these materials, the effect of water adsorption on paramagnetic nickel species in Ni-AlP04-11, whereNi ions were introduced by impregnation with NiC12.6H20, was studied. The results for Ni-AlP04- 11 are shown in Figure 4c,d. A broad ESR signal is observed around g = 1.920 in Ni-AlP04- 11after thermal reduction (Figure 4c). Nickel species in Ni-AlPO4-11 may aggregate during thermal reduction, because AlPO4- 11 has no ion-exchange capacity. The broad ESR signal at g = 1.92 might be due to Ni(1) clusters or Ni(0) clusters. The production of
-
1220 The Journal of Physical Chemistry, Vol. 98, No. 4, 1994
Azuma et al. NiAPSO-11
100 G
50 G
NiAPSO-11 1 min
+ D,O/
v
NiH-SAPO-11
(b)
+ D,O
%PPH
b
/ 1 min
NiH-SAPO-11
1
(c)
(4
therm. reduct Ni-AIP04-11 x 1/2000
Ni-AIP04-11 + D,O / 1 min
RT/40 h
(f)
Figure 4. ESR spectra at 77 K of (a) H2-reduced NiAPSO-11 after D2O
Figure 5. ESR spectra at 77 K of (a) H2 reduced NiAPSO-11 after D20
adsorption for 1 min at room temperature, (b) H2-reduced N i H S A P O 11 after DzO adsorption for 1 min at room temperature, (c) Ni-AIP0411 after thermal reduction by evacuation at 823 K, and (d) thermal reduced Ni-AlP04-11 after D2O adsorption for 1 min a t room temperature.
adsorption for 1 min at room temperature, (b) NiAPSO-11 after annealing (a) at room temperature for 3 min, (c) NiAPSO-11 after annealing (a) at room temperature for 1 h, (d) H2-reduced NiHSAPO-11 followed by D20 adsorption for 1 min at room temperature, (e) NiHSAPO-11 after annealing (d) at room temperature for 10 min, and ( f ) N i H S A P O 11 after annealing (d) at room temperature for 40 h.
Ni(0) clusters is observed in silica,21NiNa- and NiCa-X,22 and NiCa-Y23 with g -2.2. The observed g = 1.92 species is tentatively assigned to Ni(1) clusters. After D20 adsorption onto Ni-AlP04-11 the g = 1.92 signal completely disappears, and a strong anion radical Ni(II)-02- is detected (Figure 4d). Thus, paramagnetic nickel species in nonframework sites react readily with water molecules to produce Ni(II)-02- species. This accounts for the observation of Ni(II)-02- in NiHSAPO-11 since nickel is in nonframework sites. This result further suggests that the Ni(1) species in NiAPSO-11 is in a different type of site from that in NiHSAPO-11 and that this different site is apparently not a nonframework site. The Ni(1) complexeswith oxygen formed after water adsorption in NiAPSO-11 and NiHSAPO-11 are not stable at room temperature,probably because they are oxidized toNi(I1). Figure 5 shows the decay of Ni(I)-(Odn species at room temperature. InNiAPSO-11 the ESRsignalintensities0fNi(I)-(02)~decrease rapidly at room temperature and disappear completely after 2 h. In contrast, in NiHSAPO-11 the Ni(1)-(0~)~ESR peak broadens after 10 min at room temperature (Figure 5e). The peak broadening of Ni(I)-(O& species with 0 2 exposure has also been reported in NiCa-Y ze01ite.I~Thus, presumably water decomposition leading to 0 2 causes the broadening by dipolar interactions with oxygen. The Ni(I)-(O& broadened ESR signal decays slowly, but some still remains after 40 h at room temperature. The Ni(II)-02- species also decays slowly. Table 3 summarizes the ESR parameters and species assignments of hydrogen-reducedNiAPSO-11 and NiHSAPO- 1 1with various adsorbates and of related Ni-containingX and Y zeolites. The ESR parametersof hydrogen-reduced NiAPSO- 11and NiHSAPO-1 1 after CH30D, CO, and C2H4 adsorption for 1 min at room temperature are given (ESR spectra not shown). Again, there are some differences between the Ni(1) parameters in NiAPSO-11 versus NiHSAPO- 1 1. Ethylene adsorption shows other significant evidence for a Ni(11) location difference between NiAPSO-1 l and NiHSAPO11. A new Ni(I)-CzDd complex is formed in NiAPSO- 1 1 after 1-min exposure to ethylene. Similar complexes have been reported in NiCa-X26 and NiLa-Y.20 On the other hand, C2D4 exposure to NiHSAPO- 1 1 for 1 min at room temperature does not show any change in the ESR spectrum. Such a change requires
TABLE 3: ESR g Values of Ni(1) in Various Matrices matrix
adsorbate
species
NiAPSO-11 NiHSAPO-11 NiCa-X NiAPSO-11 NIHSAPO-I 1 NiCa-X NiAPSO-11
D20 D20 H20 CH3OD CH3OD CH3OH CO
Ni(I)-(Oz)" Ni(I)-(O& Ni(I)-(H20)3 Ni(I)-(CH,OD),, Ni(I)-(CH3OD). Ni(I)-(CH3OH)s Ni(I)-(CO)3 Ni(I)-(CO)Z Ni(1)-(CO)I Ni(I)-(CO)I Ni(I)-(C0)2 Ni(I)-(CO)3 Ni(I)-(CO)Z Ni(I)-(CO)I Ni(I)-(CO)a Ni(I)-(C0)2 Ni(1)-(CO)I Ni(I)-(CiD4)1 Ni(I)-(QD& Ni(I)-(CzDd),
NiHSAPO-11 CO NiCa-X
CO
NiCa-Y
CO
NiAPSO-11 NiCa-X NiLa-Y
C2D4 C2H4 C2H4
gil
gi
ref
2.046 2.125,2.062 this work 2.048 2.135,2.062 this work 2.471 2.061 26 2.496 2.078 this work 2.463 2.084 this work 2.461 2.084 26 1.997 2.185,2.146 this work 2.209 2.050 2.019 2.429, 2.340 1.997 2.185, 2.146 this work 2.209 2.050 2.014 2.212,2.157 25 2.206 2.056, 2.071 2.020 2.425, 2.35 2.013 2.225, 2.118 24 2.212 2.065 2.015 2.39 1.947 2.705,2.497 this work 1.973 2.643,2.46 26 1.96 2.71, 2.57 20
about 2 days for equilibration with C2D4. The ESR spectrum of C2D4 interacting with Ni(1) is almost the sameas that for isolated Ni(1) except for the line intensity and width. When ethylene is adsorbed onto Ni(1) in NiCa-X and NiCa-Y, theextraframework Ni(1) species disappear rapidly with the immediate formation (within 30 min) of a species with an orthorhombic g tensor.23v26 Thus, theinteraction between Ni(1) in NiHSAPO-11 and C2D4 seems weaken than that of Ni(1) in NiAPSO-11, NiiCa-X, and NiCa-Y with C2D4. This indicates that most of the Ni(1) in NiAPSO-11 is in a more accessible site to an adsorbate than that in NiHSAPO-I 1. Weak signals A due to Ni(1) which cannot be coordinated by C2D4 are also observed in NiAPSO-I 1 with adsorbed C2D4. This signal intensity is about 20 times smaller than that of the isolated Ni(1) A species remaining after hydrogen evacuation. We assign this remaining species to Ni(1) in extraframework sites. Conclusions This work shows comparativeESR studies of Ni(I1) reduction and adsorbate interaction between synthesized NiAPSO- 1 1 and ion-exchanged NiHSAPO-11 in order to differentiate the Ni-
ESR of Ni(1) in SilicoaluminophosphateType 11 (11) location in these two preparations. While thermal reduction of NiAPSO- 1 1 above 773 K produces one isolated Ni(1) species, no Ni(1) species is detected in NiHSAPO-11. Hydrogen reduction at 573 K generates two Ni(1) species, isolated Ni(1) and Ni(I)-(H2)n in both NiAPSO- 11 and NiHSAPO-11. The isolated Ni(1) species is stable even after evacuation at 573 K. The Ni(I)-(H& complexes are stable only in the presence of hydrogen. Ni(1) species, identified as Ni(I)-(O*)n, are produced in both NiAPSO- 11and NiHSAPO-11 after adsorption of water, indicating water decomposition on the Ni-containing oxide surface. The Ni(1) complex generated in NiAPSO-11 after methanol adsorption is slightly different by electron spin resonance from that in NiHSAPO- 11. The adsorption of carbon monoxide ontoNiAPS0-11 andNiHSAPO-11 producesNi(1)-(CO),with n = 1-3. The Ni(I)-(CO)I species is not observed in NiHSAPO- 11. While the rate of ethylene adsorptiononto NiAPSO11 is quite rapid (1 min), NiHSAPO-11 requires about 2 days for full equilibrationwith ethylene. The contrastingcoordination propertiesof the Ni(1) species indicate that the local environment of Ni(I1) in synthesized NiAPSO-11 is different from that in ion-exchanged NiHSAPO-11. Since Ni(I1) in ion-exchanged NiHSAPO- 11is clearly in a nonframework position, these results support that Ni(I1) in synthesized NiAPSO- 11 is in a framework position. Acknowledgment. This result was supported by the National Science Foundation and the Robert A. Welch Foundation. We thank J. Michalik for useful discussions. References and Notes (1) Wilson, S. T.; Lok, B. M.; Flanigen, E. M. US.Patent 4,310,440, 1982. (2) Wilson, S.T.; Lok, B. M.; Messina, C. A.; Cannan, T. R.; Flanigen, E. M. J. Am. Chem. SOC.1982, 104, 1146.
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