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Hydrothermal stability of US-Ex
Hydrothermal stability of US-Ex Akira Yoshida, Kouzou Inoue, and Yoshio Adachi Government Industrial Research Institute, Kyushu, Saga-ken, Japan USY samples, which were prepared from sodium Y whose Si/AI atomic ratios were in the range of 2.5 to 3.0, were treated hydrothermally under deep-bed conditions and with steam. The nonframework and framework aluminum was extracted with HCI solutions. The hydrothermal stabilities under 100% steam of US-Ex were examined in relation with the unit cell dimensions, chemical analyses, M A S n.m.r., t.g., and i.r. observations. The hydrothermal stability of US-Ex was affected mainly by the amounts of framework and nonframework aluminum and the retention of crystallinity, but not by the amounts of residual alkali metal oxides and the amount of 4-OH nest. Some of Si (3AI) and Si (2AI) units converted to nonframework Si (4AI), Si (3AI), and Si (2AI) units and left the vacancies larger than four OH nests in zeolite framework. It was confirmed that the population of Si (4AI), Si (3AI), and Si (2Si) in parent sodium Y affects the retention of crystallinity of US-Ex.
Keywords: US-Ex; MAS n.m.r.; hydrothermal stability
INTRODUCTION For the complete dealumination of zeolite Y, three methods have been proposed. 1-3 Scherzer ~ treated the dealuminated Y with HC1 solution and obtained highly siliceous zeolite Y with SIO2/A1203 = 192. This method was reinvestigated by Lohse et al., 4 who named the highly siliceous and highly stabilized zeolite Y prepared by acid leaching as US-Ex. The subsequent studies by several authors established the complete dealumination of Y without significant collapse of crystalline structure. 4-v The formation of a secondary pore system 6'8'9 and its properties s--t° have been reported. However, the literature contains limited information on the hydrothermal stability of highly siliceous zeolite Y. Patzelova et al.tl reported that extralattice AI clusters contribute to the decrease of thermal stability, though Breck and Skeels lz mentioned the contribution of wtrioxotrialuminum cations to the increased stability of the dealuminated structure. These two studies suggest the complicated contributions of extralattice alumina to the hydrothermal stability of dealuminated Y. We already reported the partial destruction of USY and its effect on the hydrothermal stability.13 In this study, we examined the relation between the hydrothermal stability of US-Ex and Si/AI ratio of parent sodium Y in relation to 29Si n.m.r, spectra, i.r. spectra, t.g. XRD, and chemical analyses.
Address reprint requests to Dr. Yoshida at the Government Industrial Research Institute, Kyushu, Shuku-machi, Tosu-shi, Saga-ken 841, Japan. Received 4 August 1989; accepted 27 June 1990
© 1991 Butterworth-Heinemann
EXPERIMENTAL Preparation of US-Ex Zeolite sodium Y samples used were LZ-Y52 (U.C.C.), two reference catalysts (JRC-Z-Y4.8, JRC-ZY5.6), supplied from Catalysis Society of Japan, four sodium Y samples, i.e., 3-3-101, 3-3-102, 3-3-103, and 3-3-203, prepared from silica sol. The crystallinities, unit cell dimensions, and Si/A1 molar ratios obtained by chemical analyses and MAS n.m.r, of the NaY samples are showin in Table I. Zeolite sodium Y (3-3-n) and USY were prepared as previously reported. 13 d-USY (prepared by deep-bed method) and s-USY (steaming) were heated in a capsule or with steam at 500-750°C for 1-4 h; then, dd-USY (prepared by two times of deep-bed treatments), ds-USY (first step was deep bed, second treatment was steaming), and ssUSY (two times of steaming) were obtained, dd-, dsand ss-USY samples were treated with 0.096 -0.95 N Table 1 Crystallinities, unit cell dimensions, and Si/AI atomic ratios of parent Nay Si/AI Sample
I/Io
U.d. (nm)
N.m.r.
Chemical
LZ-Y52 JRC-Z-Y4.8 JRC-Z-Y5.6
1.00 1.03 1.01
2.4690 2.4671 2.4650
2.52 2.61 2.74
2.51 2.60 2.73
3-3-101 3-3-102 3-3-203 3-3-103
1.05 1.04 0.98 1.05
2.4644 2.4635 2.4634 2.4630
2.77 2.94 2.88 2.99
2.87 2.94 2.99 2.98
/ means the sum of peak heights of 10 lines in the range of 6°32°; Io means the sum of peak heights of LZ-Y52
ZEOLITES, 1991, Vol 11, March
223
Hydrothermal stability of US-Ex: A. Yoshida et al.
HCI solutions (V/P = 66.7 cm 3 g-l) at reflux for 1 h, and dd-, ds-, and ss-US-Ex samples were obtained. As for the. treatment with 0.096 N HC1 solution, the value of HC1/(Na + + 3A1) mole/mole was about 0.5; Na + and AI were those in the USY samples. These samples were designated as ss-USY (JRC-Z-Y4.8) or dd-US-Ex (LZ-Y52, 0.096 N), showing the parent sodium Y and the concentration of HCI solution used for extraction in parentheses, if necessary. Some USY samples (0.1 g) were treated with 0.0960.95 N HCI solutions (V/P = 66.7 cm 3 g-X) at 100°C for I h in a glass test tube and then filtered. The filtr.ates were analyzed chemically.
Characterization The evaluations of the retention of crystallinity and unit cell dimensions, hydrothermal stability test, chemical analyses, and 29Si MAS n.m.r, observations were performed as previously reported. ~3 From the specific gravity obtained using a pycnometer with distilled water, and the weight of sample mounted in the cavity of holder for XRD, the fractional solid volume of sample was calculated. The 52.148 MHz 27A1MAS n.m.r, spectra of USY and US-Ex samples were obtained using a spectra width of 62.5 kHz, on a narrow-bore Bruker AC 200 spectrometer. The rotor, made of zirconia, was spun at about 4 kHz. A pulse-FT technique with a 2 ~ts pulse width and 2 s pulse repetition time was applied; 256 free-induction decays were accumulated. Data were acquired in 2048 data points, which were zerofilled to 4 K before using line broadening of 30 Hz. The peak intensity was evaluated using an integration subroutine. 27 A1 MAS n.m.r, spectra of USY and US-Ex contain three distinct kinds of signals. 14 Two
2.438
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,
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I /: 2.430]
2"4280
,~
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0.4 0[6 0'.8 I/Ie OF US-Ex(0,95N)
1.0
Figure 1 Correlations between the unit cell dimensions of USY and US-Ex (0.95 N) and the retentions of US-Ex (0.95 N). (Q), 0 ) LZ-Y52; (A, A) JRC-Z-Y5.6; (O, O ) 3-3-203. Empty symbols: USY; filled symbols: US-Ex (0.95 N). I means the sum of peak heights of six lines in the range of 16o32 °. Io means the sum of peak heights of LZ-Y52
224
ZEOLITES, 1991, Vol 11, March
of them are sharp and assigned to tetrahedrally and octahedrally coordinated alumina. The third one is broad (not sharpened) because of the second-order quadrupolar-broadening and overlaps with the two sharp peaks and contributes to the integrated intensity. We also evaluated the sharpened peak area (ASP) divided by appropriate base lines. Infrared spectra were recorded on an IR-810 infrared spectrophotometer (Japan Spectrscopic Co., Ltd.). T h e sample was pressed into a wafer of about 4.3-4.8 mg cm -2 and evacuated for 2 h at 389°C under a pressure of 8 x 10 -3 Pa, then cooled to 192°C and observed. Next, excess pyridine was adsorbed on the sample at room temperature for 30 min. The spectrum of the adsorbate was obtained after the sample-adsorbate had been evacuated at 282°C for 30 min. and observed at 282°C and at room temperature. The amount of hydroxyl groups were detected by thermogravimetric analysis from 400 to 1400°C.
RESULTS A N D D I S C U S S I O N The retentions of dd-, ds-, and ss-USY (LZ-Y52, JRC-Y5.6, 3-3-n) samples were in the range of 0.660 to 0.774 (LZ-Y52), 0.769 to 0.866 (JRC-Z-Y5.6), and 0.778 to 0.905 (3-3-n), respectively. T h e more severe the second hydrothermal treatment was, the lower was the retention and the smaller was the unit cell dimension of USY sample. Correlations between the unit cell dimensions ofss-US-Ex (0.95 N), those of the starting ss-USY, and the retentions of ss-US-Ex (0.95 N) are shown in Figure 1. As for dd-USY (LZ-Y52), whose unit cell dimension was 2.4405 nm, the retention ofdd-US-Ex (0.95 N) decreased from 0.774 down to 0.317, though that of dd-US-US-Ex (0.096 N) increased up to 0.875. From these results, the following general observations can be made: The larger the unit cell dimension of USY was, the smaller was the unit cell dimension of US-Ex (0.95 N) and the lower was the crystallinity of US-Ex (0.95 N). The unit cell dimensions of some US-Ex (0.95 N), whose retentions were decreased remarkably, were smaller than those of reported as constants 15-x9 for aluminum-free faujasite, i.e., in the range of 2.411719 to 2.425 nm. 17 The unit cell dimension of USY should be shrunk down to 2.434-2.436 or less in order to get the highly crystalline US-Ex (0.95 N). This optimum unit cell dimension of USY for HC1 treatment is independent of Si/A1 atomic ratio of starting NaY. As shown in Figure 2, the retentions of US-Ex after steaming tests were affected mainly by the retentions of US-Ex. As for the well-shrunk and highly crystalline US-Ex, the higher the Si/AI molar ratio of parent NaY was, the slightly higher was the retentions after the steaming tests. The retentions of US-Ex (0.096 N) were about one-third of those for US-Ex (0.95 N). T h e optimum unit cell dimension of USY for the hydrothermally stable US-Ex (0.95 N) is the same with that for HCI treatment. Consequently, it was concluded that heating of s- or d-USY, at least up to 650°C for 4 h with steam, is
Hydrothermal stability of US-Ex: A. Yoshida et al.
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necessary in order to get the well-shrunk USY samples, which are stable for the treatment with excess acid. There was no difference between the hydrothermal stabilities ofdd-, ds-, and ss-US-Ex when the unit cell dimensions and the retentions were similar. In Figure 3, correlations between the retentions after the hydrothermal stability test at 870°C, the amount of A1203, the amount of Na20, and the unit cell dimensions of US-Ex (LZ-Y52, 0.096-0.95 N) are shown. All the exchangeable sodium ions were extracted first as shown by Patzelova et al., 2° then probably nonframework aluminum, and, finally, framework aluminum atoms were extracted with excess amount of hydrochloric acid. By the extraction of about one-half of nonframework aluminum, the unit cell dimension decreased from 2.4305 _+ 0 . 0 0 0 3 nm to 2.4299 +_ 0.0002 nm. However, the unit cell dimension of US-Ex (0.192 N), whose nonframework alumina was extracted almost completely, was also 2.4298 _+ 0.0001 nm. These results strongly suggest that the first shrinkage must be due to the collapse of nonframework alumina species that probably made the unit cell larger than it would be expected without nonframework aluminum species as shown by Klinowski et al. m and that almost no framework alumina was extracted in this region. The slight decrease of unit cell dimension from 2.4298 nm (US-Ex [0.192 N]) to 2.4278 _+ 0.0003 nm (US-Ex [0.95 N]), however, shows the gradual extraction of framework aluminum. The retention of US-Ex increased with the decrease of nonframework aluminum and remained relatively constant d u r i n g f u r t h e r extraction of framework aluminum (Figure 4). This result, at first sight, seems to suggest that the removal of amorphous nonframework species as impurities merely enhanced the intensity of XRD powder pattern.
0.8
0.15
1.0
Figure 2 Correlations between I/Io of US-Ex and I/Io after steaming test. Blank marks steamed at 810°C; solid marks steamed at 870°C. (~) US-Ex (LZ-Y52, 0.096 N) steamed at 870°C; ( 0 , 0 ) US-Ex (LZ-Y52, 0.95 N); (rq, II) US-Ex (JRC-Z-Y4.8, 0.95 N); (A, &) US-Ex (JRC-Z-Y5.6, 0.95 N); (O, 0 ) US-Ex (3-3-n, 0.95 N). For identification of I/Io, see Figure 1 legend
fl
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2
0.10
0.4
0.05
0.2 0
O 2,427
2,428
2,429
2.430
2.431
UNIT CELL DIMENSION OF US-Ex(NM)
Figure 3 Correlations between the amounts of AI2Oz, the amounts of Na20 in US-Ex (LZ-Y52, 0.096-0.95 N), the retentions after steaming test at 870°C, and the unit cell dimensions of US-Ex (LZ-Y52). The molar ratio of HCI/(Na + + 3AI); 1 = 0, 2 = 0.5, 3 = 1.0, 4 = 2.0, 5 = 3.0, 6 = 4.0, 7 = 4.96. Na + and AI are those in USY
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0,8 0,7
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I
5
10
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AMOUNT OF AL203 (G/G)
Figure 4 Correlations between the amount of AI2Oz, the fractional solid volume in the XRD sample holder, and the retentions of USY (LZ-Y52)and US-Ex (LZ-Y52).Vs = volume of solid powder; Vt = volume of cavity of sample holder; (~) dd-USY and dd-US-Ex; (O) ss-USY and ss-US-Ex. For identification of I/Io, see Figure 1 legend
ZEOLITE& 1991, Vol 11, March
225
Hydrothermal stability of US-Ex: A. Yoshida et al. 1,0
I
i
,
,
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However, the total amount dissolved from dd-USY with 0.096 N HCI was 0.126 g/g, i.e., 0.0323 g/g of SiO2 and 0.0936 g/g of A1903. Then, the calculated intensity should be 0.851 for dd-US-Ex (0.096 N) prepared from dd-USY, whose intensity was 0.738. This calculated value was lower than the observed one, i.e., 0.906. As for ss-USY, the total amount dissolved was 0.122 g/g, i.e., 0.0256 g/g of SiO2 and 0.0959 g/g of A1203. The calculated value for ss-USEx (0.096 N) should be 0.754, which was also slightly lower than the observed one, i.e., 0.774. In addition, the fractional solid volume of sample mounted in the holder decreased with an increasing dealumination ratio of HC1 solution. These results suggest that the enhancement of XRD intensity by extraction of nonframework alumina was due to the disapl~earance of distortion caused by polymerized A1203, -2-25 which probably has edge-shared boehmitelike structure, 26 as well as the removal of amorphous nonframework species as impurities. The hydrothermal stability was improved by the extraction of nonframework aluminum as shown by Patzelova et al. 11 and framework aluminum. The amounts of Na20 in US-Ex (0.096 N) and US-Ex (0.19 N) were 0.00050 g/g and 0.00066 g/g, respectively. On the other hand, the retentions of US-Ex (0.096 N) and US-Ex (0.19 N) after the steaming test were 0.215 and 0.349, respectively. Correlation between the amounts of Na20 in US-Ex (0.95 N) and the retentions after the steaming tests are shown in Figure 5. These results show that the amount of Na20 in US-Ex (0.95 N) did not affect the hydrothermal stability. The amount of K20 in US-Ex (0.95 N) were in the range of 0.000036 g/g to 0.000084 g/g. These results sugg.est that the amount of alkali metal oxides remaining m US-Ex samples are too small to affect the hydrothermal stability of US-Ex. 27A1 MAS n.m.r, spectra of d-USY, ss-USY, and ss-US-Ex prepared from LZ-Y52 are show in Figure 6. Table 2 shows the integrated intensities of 27A1 MAS
ZEOLITES, 1991, Vol 11, March
" -,~,
,,
,
,1
l=
1
i',
',,
!
x 10 -4
Figure 5 Correlations between the amounts of Na20 and the retentions of US-Ex (0.95 N) after steaming tests. For identification of symbols and I/Io, see Figure 1 legend
226
I
150
L~ 100
;,i 50
i 0
-50
-100
PPH
27AI MAS n.m.r, of d-, ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52, 0.096-0.95 N). Numbers are the same with those in
Figure 6
Figure 3
n.m.r, spectra. Figure 7 gives a set of i.r. spectra for some of the samples. The suppressed i.r. spectra for ss-USY (LZ-Y52) show no distinct b a n d s for A I ( O H ) , (3-')+ species 2'27'28 located in the nonframework position or distinct bands for bridging hydroxyl groups at 3650 cm -l and at 3550 cm -123
Table 2
The integrated intensities of 27AI MAS n.m.r, spectra of LZ-Y52, USY (LZ-Y52) and ss-US-Ex (LZ-Y52, 0.096-0.95 N)
Sample LZ-Y52 d-USY (LZ-Y52) ss-USY (LZ-Y52) ss-US-Ex (0.096 N) ss-US-Ex (0.192 N) ss-US-Ex (0.38 N) ss-US-Ex (0.57 N) ss-US-Ex (0.76 N) ss-US-Ex (0.95 N) LZ-Y52a ss-US-Ex (0.76 N) a
Integrated range (ppm - ppm)
Intensity
Relative intensity
110 20 110 20 110 20 110 20 110 20 110 20 110 20 110 21 110 20
22 -54.5 20 -57 22 - 55 21 -57 22 -55 21 -55 21 -54 21 -58 21 -55
72.76 2.23 21.85 7.63 10.34 7.14 8.365 6.473 4.831 0.994 2.899 0.599 2.665 0.722 2.278 0.608 1.482 0.934
1.000 0.0306 0.300 0.105 0.142 0.098 0.040 0.115 0.0667 0.0137 0.0397 0.00823 0.0366 0.00992 0.0313 0.00836 0.0204 0.0129
110 20 110 20
21 - 54 21 - 54
71.61 1.68 2.200 0.470
1.000 0.023 0.0307 0.00656
a Integrated another day from same spectra
Hydrothermal stability of US-Ex: A. Yoshida et al.
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I
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1300 1800
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]_
1300
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Figure 7 I.r. spectra of USY (LZ-Y52) and US-Ex (LZ-Y52). (A): After evacuation at 389°C for 2 h and measured at 192°C; wavenumber (a) 3740 cm -~, (b) 3710 cm-t; (B) and (C): after addition of pyridine at room temperature and desorption at 282°C for 30 rain and measured at 282°C (B) and at room temperature. (C); wavenumber (c) 1542 cm -1, (d) 1446 cm -~. Numbers are the same as in Figure 3
(Refs. 29-31), which were almost completely diminished during the second hydrothermal treatment by dehydroxylation. The peak height of signal at 57 ppm of ss-USY (LZ-Y52) was less than one-fourth of that of d-USY, in contrast to the results reported by Ray et al. 32 Ai(OH),,(3-")+s~ecies seem to polymerize and form neutral AI,~O&, "- being responsible for the raised base line of 27 A1 spectra.7 4 • 21 •2 5 The integrated intensities of 27A1 spectra, therefore, consi.st of two parts, i.e., the sharp one and the overlapped broad line. Then, ASP at 58.9-55.6 ppm were estimated (Figure 8). By extraction of about one-half of nonfralaework aluminum, the peak assigned for the octahedrally coordinated aluminum (0.33 ppm) was remarkably increased. In addition, ASP also slightly increased. Bosacek et al. 33 reported that the remarkable increase of the signal intensity at 0 ppm was caused by the remaining hexaquo- or/and hydroxoaquoaluminum complex cations in the lattice. However, we would like to stress the possibility that the increased intensity was due to the disappearance of distortion caused by the long aluminum-hydroxo-oxide chains. The remarkable increase of the signal intensity at ca. 57 ppm was also observed by partial extraction of nonframework aluminum ofdUSY with dilute NaOH solution. The details of this phenomenon will be reported elsewhere. Consequently, the number of AI atoms at the framework position in the unit cell, NA~ (Aln.m.r.), for US-Ex (0.38 N) was estimated as 2.1
from the integrated intensity (Table 2). NA| (Aln.m.r.) for ss-USY was estimated as 3.0-4.5 from ASP; 4.5 was obtained by linear extrapolation using the values of ss-US-Ex (0.096--0.96 N) on the assumption that the shrinkage of unit cell dimension from 2.4305 nm (ss-USY) to 2.4299 nm (ss-US-Ex [0.096 N]) was due to the extraction of framework aluminum. Then, the value, 4.5, seems to be upper limit for NAI in ss-USY (LZ-Y52). I.r. spectra of dealuminated zeolite Y have been reported by several authors. 2"5'12'20'22'2::L29-31 The spectra of US-Ex (0.38 N-0.95 N) in the hydroxyl stretching region were closely similar to those reported for highly dealuminated zeolite Y prepared with SIC14,34 with HCI, 5 and for Al-deplete NaY prepared with H,tEDTA. 2'19 Ward 22':~° assigned a band at 3742 cm- f to the silanol group on the surface of the zeolite crystals. Anderson and Klinowski34 assigned a band at 3734 cm -1 to terminating silanol groups. Other authors '''23'35'36 also have reported similar conclusions. However, Kubelkova et al. 37 assigned this band to hydroxyls on structural defects, though Anderson and Klinowski3'I and Patzelova et al. 2O assigned the band at 3675 cm- 1 to framework Si-OH groups at defect sites. Bennett et al., 3s Skeels and Breck 2 and Bosacet et al. 5 assi_~ned the broad adsorption band at 3750-3000 c m - ' to hydrogenbonded OH groups at the defect site (4 OH nest) that remained in the framework without the insertion of silicon atoms. Skeels and Breck 2 evaluated the amounts of 4 OH nests with the absorbance value at 3710 cm -l. As for US-Ex samples of this study, no distinct band except at 3740 cm -1 was detected between 3800 and 3000cm-1. The amount of 4 OH nests of our US-Ex (0.95 N) evaluated by Skeels and 1,2 1,0
0.8
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20427 ~.428 2.429 2.430 2.431 UNIT CELL DIMENSION OF USEx(NM)
the amounts
Figure 8 Changes of of 40H nest and framework alumina evaluated from ~;AI MAS n.m.r. (ASP) and chemical analysis. Sample numbers are the same with those in Figure 3. (O) 40H nest: as for sample 7, the relative intensity .was regarded as unity; (Q) framework alumina measured from the peak areas divided by appropriate base lines: as for sample 1, the relative intensity was regarded as unity; (A) framework alumina obtained from chemical analysis: as for sample 3, relative intensity was regarded as unity and was regarded as zero for sample 7
ZEOLITES, 1991, Vol 11, March
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Hydrothermal stability of US-Ex: A. Yoshida et al. A
B
:0
,0
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Figure 9 agSi MAS n.m.r, spectre for ss-USY and ss-US-Ex and their deconvolutions. (A) Solid line = ss-USY (LZ-Y52), dotted line = ss-US-Ex (0.38 N); (B and C): ss-USY (LZ-Y52), B = Gau§sian, C = Lorentzian; numbers are " n " in Si(0AI).(0Si)4_., U = unknown; A m - l , -2, -3 = a m o r p h o u s parts
Breck's method is larger than that of HY (u.d. = 2.427 nm) prepared by repeated mild, compared with our conditions, hydrothermal treatments and ion exchanges by Fukushima et al., 39 though the intensity of band at about 3740-3750 cm-= is similar. After the extraction of almost all nonframework aluminum with 0.192 N HC1, the intensity of band at about 3740-3750 c m - l was enhanced remarkably, suggesting the existence of bondings between zeolite framework and nonframework aluminum species. By treatment with excess acid (nos. 4 and 7 in Figure 6), the broad band between 3740 cm-1 and about 3200 c m - i increased significantly. The peak areas of broad i.r. bands in the range of 3800 to 3200 cm- 1 involving a narrow band at 3740 cm-I show behaviour similar to those given by Skeels and Breck's method. The behavior of this band in relation to adsorption and desorption of pyridine closely resembles those reported by Anderson and Klinowski34 showing the lower desorption temperature, which means lower acidity. After desorption of excess p~,ridine at 289°C, two well-defined peaks at 1542 c m - " (Br6nsted acid sites) and 1446 cm -a (Lewis acid sites) were detected in the US-Ex (0.096 N) sample and a detectable peak at 1542 cm -l was also found in US-Ex (0.95 N). However, as for the other samples, no detectable peak was found at 289°C, though the slight peaks were detected after cooling down to room temperature under a pressure of 8 × 10 -3 Pa. The intensity of this two peaks did not associate with the increased intensities of bands at 3740 cm-1 and between 3800 and 3200 cm -~. The slight peak at 1540 cm -l for US-Ex (LZ-Y52, 0.95 N) might be due to that for amorphous aluminum silicate, because this sample has no framework or nonframework alumina (see no. 7 in Figure 6), though 1.84% of alumina still remains. The two peaks at 1542 and 1446 cm -I for US-Ex (0.096 N) should be assigned to nonframework alumina species. These results show that the severe acidic conditions for extraction of framework aluminum formed the less acidic silanol groups with the broad i.r. bands at 3800-3200 cm -l. T h e broad bands at 3800-3200 cm-X show the irregularity of the 4 OH nest. It also
228
ZEOLITE& 1991, Vol 11, March
seemed that the rather sharp peak at about 3740 cm -I should be assigned to terminating hydroxyls that were produced during the extraction of nonfi'amework and framework aluminum. The spectra of 2'~Si MAS n.m.r, of the USY and US-Ex samples show the interesting experimental evidence for the partial dissociation of framework silica to the nonframework position during dealumination. We already suggested the dissociation of Si (3AI) during dealumination previously. 13 We noticed that Si (2A1) also has the same possibility of dissociation under severe hydrothermal treatment. 4° The deconvolution of - $1MAS n.m.r, spectrum has been carried out using lorentzian profiles as well as Gaussian profiles (Figures 9 and 10 and Table 3). In both cases, broad peaks for Si (4A1), Si (3A1), and almost all of Si (2A1) disappeared by means of the extraction with 0.38 N HCI. However, the decrease of unit cell dimension by this treatment was only 0.0013 nm. Using constants for unit cell dimension presented by several authors,~5-~° the number of AI atoms in a unit cell, NAI (XRD), of USY and US-Ex samples was calculated. With different constants, NAI (XRD) for ss-USY (LZ-Y52) shows rather wide scattering in the range of 19.8 to 6.3. However, the differences between ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52, 0.38 N) and that between ss-US-Ex (LZ-Y52, 0.38 N) and ss-US-Ex (LZ-Y52, 0.95 N) are less than 2.0, in good agreement with N A I (Aln.m.r.). The number of A1 in ss-US-Ex (0.95 N) should be 0. As shown by Kerr, 41 most of observed values for the unit cell dimensions of zeolite X, Y, and dealuminated Y lie between the lines reported by Breck and Flanigen ~5 and Sohn et al. Is The deviations of the unit cell dimension of aluminum-free ss-US-Ex (0.95 N) from these two values were +0.0086 and +0.0040 nm, respectively. The deviations correspond to 10 to 4.3 atoms/unit cell. These deviations might be caused by the formation of secondary pores 6-9'42--44 and 4 OH nests, which seem to prohibit the complete shrinkage to idealized values. When we used the Gaussian peak profiles, one or two unknown peaks between those for Si (1A1) and Si (0AI) and three amorphous peaks in the high magnetic field should be divided for ss-USY (LZ-Y52) and •
9 9
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U-2~
4'0
-i~o PPM
-i~o
-60
-100 PPM
-lqO
-90 -lO0 -llO -120 PPM
Figure 10 z~Si MAS n.m.r, spectra for ss-US-Ex and their deconvolutions. (A) ss-US-Ex (LZ-Y52, 0.38 N), (B) and (C): ss-US-Ex (LZ-Y52, 0.95 N), U-l, -2, -3 = unknown. For identification of other symbols, see Figure 9 legend
Hydrothermal stability of US-Ex: A. Table 3
Yoshida
et al.
RSM error
29Si MAS n.m.r, spectra of ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52) samples
Sample
G/L
Si(4AI)
Si(3AI)
Si(2AI)
Si(1AI) Si(3Si)OH
ss-USY
G
3.1 -82.9
4.1 -89.2
5.4 -95.2
10.8 -102.3
L
2.3 -82.2
3.9 -88.5
4.9 -94.5
cs
ss-USY cs
ss-U$-Ex (0.38 N)
G
0.0
cs
.
ss-US-Ex (0.38 N)
L
0.0
cs
.
ss-US-Ex (0.95 N)
G L
.
.
.
Si(0AI)-2
am-1
am-2
am-3
0.0 -
20.7 -106.8
39.1 -107.7
8.0 -109.0
6.4 -111.4
2.4 -116.5
4.5%
7.2 -101.3
0.0 -
0.0 -
74.2 -107.7
0.0 -
7.5 -112.8
0.0 -
2.6%
0.0
8.8 101.7
2.8 -105.1
13.4 -106.9
42.0 -107.7
14.0 -108.4
13.0 -110.2
6.0 -114.3
3.8%
0.0
6.2 101.1
0.0 -
0.0 -
79.2 -107.7
0.0 -
14.6 -111.3
0.0 -
2.0%
3.2 -97.2
9.2 -102.0
8.2 -105.9
12.2 -107.1
31.7 -107.6
16.6 -108.1
15.0 -110.6
3.9 -116.0
3.1%
0.0
10.2 101.2
0.0 -
0.0 -
76.3 -107.6
0.0 -
13.5 -111.5
0.0 -
1.7%
.
0.0 .
Unknown
.
0.0 -
0.0
cs
.
0.0 .
0.0 -
cs
ss-US-Ex (0.95 N)
0.0 .
.
Unknown
G/L: G means Gaussian profiles were used for deconvolution; L means Lorentzian profiles were used
ss-US-Ex (LZ-Y52). The assignments for Si (4AI), Si (3A1), Si (2AI), Si (1A1), and am-2 were already reported. 13A4'23'~6'45"46 The assignment of 298i M A S n.m.r, signals in the range of - 103 to - 107 ppm has yet to be established. 2''45 Engelhardt et al. 46 confirmed the presence of Si-OH groups by a considerable increase of the - 1 0 0 ppm signal from the CP spectrum of ultrastable Y. Ray et al. 32 assigned the peaks at -101, - 103, and - 1 0 4 ppm to Si-OH groups associated with defect sites or amorphous materials, though Grobet et al. 45 assigned the peak at 104.2 ppm to crystallographically inequivalent Si (0A1) sites. As shown in Figure IOA and B, the peak profiles of 29Si M A S n.m.r, did not change notably by the extraction of remaining framework aluminum and formation of new defect sites. Then, the peak location of Si (3Si) OH seems to be nearly the same as that for Si (1A1), in agreement with Engelhardt et al.'s results. 46 For the calculation of the Si/A1 ratio, Si (3Si) OH can be estimated as Si (0A1). From the spectrum of 27A1 M A S n.m.r., the peak at -101 - 1 0 2 ppm for ss-US-Ex (0.95 N) should be assigned to Si (3Si) OH. However, the peak at -101 - 1 0 2 ppm for ss-USY and ss-US-Ex (0.38 N) should be divided into two sections. To determine the amounts of OH groups, thermogravimetric analysis was carried out (Table 4). Supposing that all of the A1 atoms are in the form of A1-OH, the ratios of Si-OH/Sitot~l were estimated. As for ss-USY, the ratio of Si-OH was not clear. Then, it Table 4 Amounts of OH groups and Si-OH calculated from thermogravimetry
Sample ss-USY ss-US-Ex ss-US-Ex ss-US-Ex s$-US-Ex ss-US-Ex ss-US-Ex
(0.096 N) (0.192 N) (0.38 N) (0.57 N) (0.76 N) (0.95 N)
400-1400°C (t.g.)
H20 (in A I - O H )
H20 (in SiOH)
Si-OH Sitotal
0.0123 0.0123 0.0153 0.0131 0,0124 0.0127 0.0127
0.0421 0.0221 0.0072 0.0047 0.0042 0.0035 0.0032
0.0081 0.0083 0.0082 0.0092 0.0095
0.0574 0.0572 0.0568 0.0634 0.0643
was assumed that the peak at -101 - 1 0 2 ppm belongs to Si (1A1) units. As for ss-US-Ex (0.38 N), Si-OH was evaluated as 0.0572 mole/mole. From NA= (Aln.m.r.), Si (1A1) for US-Ex (0.38 N) can be evaluated as 8.4 atoms/unit cell. It corresponds to 0.044 mole/mole of SiO2. Another problem was whether it was the crystalline part or not. From the retention ofss-US-Ex (LZ-Y52, 0.38 N), i.e., about 0.851, it was concluded that the peaks at -110.2 and - 114.3 ppm seem to be amorphous states, then the peaks at -105.1, - 106.9, and -108.4 ppm should be assigned to crystalline units. On the basis of these assumptions, NAI (Sin.m.r.) were calculated (Table 5). The value for NA= (Sin.m.r.) was affected several factors, such as the amount of Si-OH groups, evaluation of amorphous fraction, and the profiles of signals. However, the most important factor was assignment of Si (4AI), Si (3A1), and Si (2A1) to crystalline parts or not. From the results of NA! (Aln.m.r.) and NA! (XRD), NAI for ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52), 0.38 N) were calculated as 2.0-2.1 and 3.0-4.5. Then, Si (4AI) and Si (3AI) should be nonframework units in ss-USY (LZ-Y52). The greater part ofSi (2A1) also seem to be at the nonframework position. The sum of relative intensities of Si (4AI), Si (3AI), and Si (2A1) units in ss-USY (LZ-Y52) was 0.126 mole/mole (Gaussian) - 0.111 mole/mole (Lorentzian). The amount of SiO2 dissolved from ss-USY (LZ-Y52) with 0.95 N HC1 was 0.0487 mole/mole, corresponding to the sum of Si (4A1) and one-half of Si (3A1). The greater part of SiO2 species dissolved in acidic solution accompanied with nonframework alumina probably precipitated as amorphous silica with the 29Si n.m.r, signal of higher magnetic field, which increased from 0.088 mole/mole to 0.189 mole/mole (Gaussian) and 0.075 mole/mole to 0.135 mole/mole (Lorentzian). RSM errors for the deconvolution with Lorentzian profiles were smaller than those with Gaussian profiles. The number of signals divided with Lorentzian profiles also seems to be reasonable. However, the
ZEOLITES, 1991, Vol 11, March
229
Hydrothermal stability of US-Ex: A. Yoshida et al. Table 5
N u m b e r of AI atoms in unit cell calculated from the intensities of divided 29Si MAS n.m.r, signals
Deconvolution
Gauss-1
Gauss-2
Gauss-3
Lorentz-1
-d
19.9 15.4 10.5 5.8
21.6 16.8 11.6 6.4
23.4 18.4 12.7 7.1
16.6 13.3 8.4 3.8
ss-US-Ex (0.38 N)-e -f -g
4.2 2.0 1.5
5.1 2.6 1.9
6.2 3.1 2.3
ss-USY (LZ-Y52) -a -b -c
2.9 2.1 0.25
Lorentz-2 17.8 14.2 9.0 4.2 3.4 2.4 0.29
Gauss-1 = am-1 - 3 are regarded as crystalline part; Gauss-2 = am-1 is regarded as crystalline part; Gauss-3 = am1 - 3 are regarded as a m o r p h o u s part; Lorentz-1 = am-2 is regarded as crystalline part; Lorentz-2 = am-2 is regarded as a m o r p h o u s part; a = Si(4AI), Si(3~l), and Si(2AI) are regarded as f r a m e w o r k unit; b = Si(4AI) is regarded as n o n f r a m e w o r k unit; c = Si(4AI) and Si(3AI) are regarded as n o n f r a m e w o r k units; d = Si(4AI), Si(3AI), and Si(2A.I) are regarded as n o n f r a m e w o r k units; e = Si(3Si)OH was evaluated 0; f = Si(1AI) was calculated from NA,(AIn.m.r.); g = Si(3Si)OH was calculated f r o m t.g.
value for Si (1Al) + Si (3Si) O H of US-Ex (0.38 N), 0.062 mole/mole, was smaller than the sum of Si (IAl) calculated from N,xi (Aln.m.r.) and Si (3Si) O H obtained from t.g.i.e., 0.1012 mole/mole. On the other hand, the value for Si (3Si) O H of US-Ex (0.95 N), 0.102 mole/mole, was larger than that obtained from t.g.i.e., 0.0643 mole/mole. These deviations seems to be caused by greater allotment to main peak, Si (0A1), with Lorentzian profiles decreasing the relative intensities for neighboring peaks, and by the existence of amorphous silica contained alumina with extremely broad lines of 29Si n.m.r., which can be partly observed for US-Ex (0.95 N). Correlations between the sum of relative populations of Si (hA1) in parent sodium Y, i.e., 2 × Si (4A1) + 1.5 × Si (3A1) + Si (2AI), the retentions ofss-US-Ex (0.95 N); and the retentions after the steaming tests are shown in Figure 11. These results evidently show
that Si (nAl) units with greater n value tend to dissociate from framework positions during dealumination and decrease the hydrothermal stability of US-Ex. CONCLUSION Hydrothermal stability of US-Ex increased by the extraction of nonframework and framework aluminums. Nonframework aluminum species in dd-, ds-, and ss-USY seem to distort the framework and decrease the hydrothermal stability. T h e removal of aluminum accompanies the partial dissociations of Si (4A1), Si (3AI), and, probably, Si (2A1) units. The decrease of retentions and hydrothermal stability of US-Ex prepared from well-shrunk USY with excess acid might be due to this silicon dissociation. 298i n.m.r, signals of ss-USY and ss-US-Ex seem to deviate CONCLUSION
1.1 1.0
SI I
AL I
I
I
0
o
0
SI J
SI |
0
0
I
i
SI-0-AL-0-SI-O-AL-O-S!-O
0.9 0.8
I
e-~ll.
I
I
Q
0
0
SI
SI
SI
SI
S=
~L
oI
SI H~
Sll
o'I
•
I
I
"" 0.7
0
~
OH 0 Si
~I
SI
SI SUBSEOUENT
S,_O_A,_0_SI_ON H' 0-SI-0 0.4
0.3
0
o.~o
o.'4s
o.~o
o.~s
0.60
Figure 11 Correlation between the sum of relative p o p u l a t i o n s and the retentions of US-Ex after the h y d r o t h e r m a l stability tests. Xs=(nAj) = 2 Si(4AI) + 1.5 Si(3AI) + Si(2AI); (©) US-Ex; ( & ) after the h y d r o t h e r m a l stability test at 810°C for 6 h; (Q) after the h y d r o t h e r m a l stability test at 870°C for 6 h. For identification of I//o, see Figure I legend
ZEOLITES, 1991, Vol 11, March
0
~=
)~"XsI(NAL)
230
FORMATION OF 40H NEST
I
S=
0.5
o
,0-!i-0
SI
t
SI
0.6
/
Sx I
H0 Si-0 H , OIH
SI
Figure 12
H0
Sz I
0
H0-SI-0 ' (~H SI
DEALUMINATION
I
OH 0
OIH SI
I 0 SI
COMIGRATION OF SI(3AL)
FORMATION OF SECONDARY PORES
Schematic representation of the m e c h a n i s m of hydrothermal d e a l u m i n a t i o n of the faujasite f r a m e w o r k
Hydrothermal stability of US-Ex: A. Yoshida et al.
from Gaussian profiles and have some portion of Lorentzian character. The mechanism of the silicon dissociation might be as shown in Figure 12.
REFERENCES 1 Scherzer, J. J. Catal. 1978, 54, 285 2 Skeels, G.W. and Breck, D.W., in Proceedings of the Sixth International Zeolite Conference (Eds. D. Olson and A. Bisio) Butterworths, Guildford, UK, 1984, p. 87 3 Bayer, H.K. and Belenkaya, I., in Catalysis by Zeolites (Eds. B. Imelik et al.) Elsevier, Amsterdam, 1980, p. 203 4 Lohse, U., Alsdorf, E., and Stach, H.Z. Anorg. AIIg. Chem. 1978, 447, 64 5 Bosacek, V., Patzelova, V., Tvaruzkova, Z., Freude, D., Lohse, U., Schirmer, W., Stach, H. and Thamm, H. J. Catal. 1980, 61, 435 6 Lynch, J., Raatz, F., and Dufrensne, P. Zeolites 1987, 7, 333 7 Fukushima, T., Kamiyama, K., and Igawa, K. Poster Abstracts of 7th International Zeolite Conference, Japan Association of Zeolite, 1986, p. 93 8 Stach, H., Lohse, U., Thamm, H. and Shirmer, W, Zeolites 1986, 6, 74 9 Patzelova, V. and Jaeger, N.J. Zeolites 1987, 7, 240 10 Ogata, M., Masuda, T., Nishimura, Y., Satoh, G. and Egashira, S. Sekiyu Gakkaishi 1985, 29(29), 105 11 Patzelova, V., Lohse, U., Engelhardt, E., Altsdorf, E. and Koelsch, P. Rope Uhlie 1986, 28(6), 343 12 Breck, D.W. and Skeels, G.W. Molecular Sieves-II, Am. Chem. Soc., Washington, DC, 1977, p. 271 13 Yoshida, A. and Adachi, Y. Zeolites 1989, 9, 111 14 Klinowski, J., Thomas, J.M., Fyfe, C.A. and Gobbi, G.C. Nature 1982, 296(8), 533 15 Breck, D.W. and Flanigen, E.M. Molecular Sieves, Soc. Chem. Ind., London, 1968, p. 47 16 Fichtner-Schmittler, H., Lohse, U., Engelhardt, G. and PatzeIova, V. Cryst. Res. Technol. 1984, 19(1), K1-K3 17 Beyer, H.K., Belenykaja, IM., Hange, F., Tielen, M., Grobet, P.J. and Jacobs, P.A.J. Chem. Soc., Faraday Trans. 1 1985, 81, 2889 18 Sohn, J.R., Decanio, S.J., Lunsford, J.H. and O'Donnell, D.J. Zeolites 1986, 7, 225 19 Zi, G. and Yi, T. Zeolites 1988, 8, 232 20 Petzelova, V., Drahoradova, E., Tvaruzkova, Z. and Lohse, U. Zeolites 1989, 9, 74 21 Klinowski, J., Fyfe, C.A. and Gobbi, G.C., J. Chem. Soc., Faraday Trans. 1 1985, 81, 3003
22 Ward, J.W.J. Catal. 1970, 19, 348 23 Lohse, V., Loffeler, E., Hunger, M., Stockner, J. and Patzelova, V. Zeolites 1987, 7, 11 24 Gross, Th., Lohse, U., Engelhardt, G., Richter, K.H. and Patzelova, K.H. Zeolites 1984, 4, 25 25 Freude, D., Frohlich, T., Pfeifer, H. and Scheler, G. Zeolites 1983, 3, 171 26 Shannon, R.D., Gardner, K.H., Staley, R.H., Bergeret, G., Gallezot, P. and Auroux, A. J. Phys. Chem. 1985, 89, 4778 27 Maher, P.K., Hunter, F.D. and Scherzer, J. Adv. Chem. 1971, 101,266 28 Peri, J.B., in Proceedings of the 5th International Congress on Catalysis (Ed. J. Hightower) Elsevier, New York, 1973, p. 329 29 Uytterhoeven, J.B., Christner, L.G. and Hall, W.K.J. Phys. Chem. 1965, 69(6), 2117 30 Ward, J.W.J. Catal. 1967, 9, 225 31 Jacobs, P.A. and Uytterhoeven, J.B.J. Chem. Soc., Trans. 1 1973, 68, 359 32 Ray, G.J., Meyer, B.L. and Marshall, C.L. Zeolites 1987, 7, 307 33 Bosacek, V. and Mastikhin, V.M.J. Phys. Chem. 1987, 91, 260 34 Anderson, M.V. and Klinowski, J. Zeolites 1986, 6, 455 35 Uytterhoeven, J.B., Christner, L.G. and Hall, W.K.J. Phys. Chem. 1965, 69, 3463 36 Ray, G.J., Nerheim, A.G. and Donohue, J.A. Zeolites 1988, 8, 458 37 Kubelkova, L., Beran, S., Malecka, A. and Mastikhin, V.M. Zeolites 1989, 9, 12 38 Bennet, J.M., Breck, D.W. and Skeels, G.W., presented at the Fifth North American Meeting of the Catalysis Society, Pittsburgh, April 1977 39 Fukushima, T., Kamiyama, K. and Igawa, K. Scientific Report of Toyo Soda Manufacturing Company, Ltd. 1987, Vol. 31, No. 1, p. 3 40 Yoshida, A., Inoue, K. and Adachi, Y. Reports of the Government Industrial Research Institute, Kyushu, 1989, Vol 43, p. 2745 41 Kerr, G.T. Zeolites 1989, 9, 350 42 Lohse, U. and Mildebrath, M. Z. Anorg. AIIg. Chem. 1981, 476, 126 43 Zukal, A., Patzelova, V. and Lohse, U. Zeolites 1986, 6, 133 44 Horikoshi, H., Kasahara, S., Fukushima, T., Itabashi, K., Okada, T. and Terasaki, O. Nippon Kagaku Kaishi 1989, 3, 398 45 Grobet, P.J., Jacob, P.A. and Beyer, H.K. Zeolites 1986, 6, 47 46 Engelhardt, G., Lohse, U., Samoson, A., Magi, M., Tamak, T. and Lippmaa, E. Zeolites 1982, 2, 59
ZEOLITES, 1991, Vol 11, March
231
Keywords: US-Ex; MAS n.m.r.; hydrothermal stability
INTRODUCTION For the complete dealumination of zeolite Y, three methods have been proposed. 1-3 Scherzer ~ treated the dealuminated Y with HC1 solution and obtained highly siliceous zeolite Y with SIO2/A1203 = 192. This method was reinvestigated by Lohse et al., 4 who named the highly siliceous and highly stabilized zeolite Y prepared by acid leaching as US-Ex. The subsequent studies by several authors established the complete dealumination of Y without significant collapse of crystalline structure. 4-v The formation of a secondary pore system 6'8'9 and its properties s--t° have been reported. However, the literature contains limited information on the hydrothermal stability of highly siliceous zeolite Y. Patzelova et al.tl reported that extralattice AI clusters contribute to the decrease of thermal stability, though Breck and Skeels lz mentioned the contribution of wtrioxotrialuminum cations to the increased stability of the dealuminated structure. These two studies suggest the complicated contributions of extralattice alumina to the hydrothermal stability of dealuminated Y. We already reported the partial destruction of USY and its effect on the hydrothermal stability.13 In this study, we examined the relation between the hydrothermal stability of US-Ex and Si/AI ratio of parent sodium Y in relation to 29Si n.m.r, spectra, i.r. spectra, t.g. XRD, and chemical analyses.
Address reprint requests to Dr. Yoshida at the Government Industrial Research Institute, Kyushu, Shuku-machi, Tosu-shi, Saga-ken 841, Japan. Received 4 August 1989; accepted 27 June 1990
© 1991 Butterworth-Heinemann
EXPERIMENTAL Preparation of US-Ex Zeolite sodium Y samples used were LZ-Y52 (U.C.C.), two reference catalysts (JRC-Z-Y4.8, JRC-ZY5.6), supplied from Catalysis Society of Japan, four sodium Y samples, i.e., 3-3-101, 3-3-102, 3-3-103, and 3-3-203, prepared from silica sol. The crystallinities, unit cell dimensions, and Si/A1 molar ratios obtained by chemical analyses and MAS n.m.r, of the NaY samples are showin in Table I. Zeolite sodium Y (3-3-n) and USY were prepared as previously reported. 13 d-USY (prepared by deep-bed method) and s-USY (steaming) were heated in a capsule or with steam at 500-750°C for 1-4 h; then, dd-USY (prepared by two times of deep-bed treatments), ds-USY (first step was deep bed, second treatment was steaming), and ssUSY (two times of steaming) were obtained, dd-, dsand ss-USY samples were treated with 0.096 -0.95 N Table 1 Crystallinities, unit cell dimensions, and Si/AI atomic ratios of parent Nay Si/AI Sample
I/Io
U.d. (nm)
N.m.r.
Chemical
LZ-Y52 JRC-Z-Y4.8 JRC-Z-Y5.6
1.00 1.03 1.01
2.4690 2.4671 2.4650
2.52 2.61 2.74
2.51 2.60 2.73
3-3-101 3-3-102 3-3-203 3-3-103
1.05 1.04 0.98 1.05
2.4644 2.4635 2.4634 2.4630
2.77 2.94 2.88 2.99
2.87 2.94 2.99 2.98
/ means the sum of peak heights of 10 lines in the range of 6°32°; Io means the sum of peak heights of LZ-Y52
ZEOLITES, 1991, Vol 11, March
223
Hydrothermal stability of US-Ex: A. Yoshida et al.
HCI solutions (V/P = 66.7 cm 3 g-l) at reflux for 1 h, and dd-, ds-, and ss-US-Ex samples were obtained. As for the. treatment with 0.096 N HC1 solution, the value of HC1/(Na + + 3A1) mole/mole was about 0.5; Na + and AI were those in the USY samples. These samples were designated as ss-USY (JRC-Z-Y4.8) or dd-US-Ex (LZ-Y52, 0.096 N), showing the parent sodium Y and the concentration of HCI solution used for extraction in parentheses, if necessary. Some USY samples (0.1 g) were treated with 0.0960.95 N HCI solutions (V/P = 66.7 cm 3 g-X) at 100°C for I h in a glass test tube and then filtered. The filtr.ates were analyzed chemically.
Characterization The evaluations of the retention of crystallinity and unit cell dimensions, hydrothermal stability test, chemical analyses, and 29Si MAS n.m.r, observations were performed as previously reported. ~3 From the specific gravity obtained using a pycnometer with distilled water, and the weight of sample mounted in the cavity of holder for XRD, the fractional solid volume of sample was calculated. The 52.148 MHz 27A1MAS n.m.r, spectra of USY and US-Ex samples were obtained using a spectra width of 62.5 kHz, on a narrow-bore Bruker AC 200 spectrometer. The rotor, made of zirconia, was spun at about 4 kHz. A pulse-FT technique with a 2 ~ts pulse width and 2 s pulse repetition time was applied; 256 free-induction decays were accumulated. Data were acquired in 2048 data points, which were zerofilled to 4 K before using line broadening of 30 Hz. The peak intensity was evaluated using an integration subroutine. 27 A1 MAS n.m.r, spectra of USY and US-Ex contain three distinct kinds of signals. 14 Two
2.438
~-" 2.42
2.436I
"
!
2.434[
,
2.41 ~~.
I /: 2.430]
2"4280
,~
2.39 0.'2
0.4 0[6 0'.8 I/Ie OF US-Ex(0,95N)
1.0
Figure 1 Correlations between the unit cell dimensions of USY and US-Ex (0.95 N) and the retentions of US-Ex (0.95 N). (Q), 0 ) LZ-Y52; (A, A) JRC-Z-Y5.6; (O, O ) 3-3-203. Empty symbols: USY; filled symbols: US-Ex (0.95 N). I means the sum of peak heights of six lines in the range of 16o32 °. Io means the sum of peak heights of LZ-Y52
224
ZEOLITES, 1991, Vol 11, March
of them are sharp and assigned to tetrahedrally and octahedrally coordinated alumina. The third one is broad (not sharpened) because of the second-order quadrupolar-broadening and overlaps with the two sharp peaks and contributes to the integrated intensity. We also evaluated the sharpened peak area (ASP) divided by appropriate base lines. Infrared spectra were recorded on an IR-810 infrared spectrophotometer (Japan Spectrscopic Co., Ltd.). T h e sample was pressed into a wafer of about 4.3-4.8 mg cm -2 and evacuated for 2 h at 389°C under a pressure of 8 x 10 -3 Pa, then cooled to 192°C and observed. Next, excess pyridine was adsorbed on the sample at room temperature for 30 min. The spectrum of the adsorbate was obtained after the sample-adsorbate had been evacuated at 282°C for 30 min. and observed at 282°C and at room temperature. The amount of hydroxyl groups were detected by thermogravimetric analysis from 400 to 1400°C.
RESULTS A N D D I S C U S S I O N The retentions of dd-, ds-, and ss-USY (LZ-Y52, JRC-Y5.6, 3-3-n) samples were in the range of 0.660 to 0.774 (LZ-Y52), 0.769 to 0.866 (JRC-Z-Y5.6), and 0.778 to 0.905 (3-3-n), respectively. T h e more severe the second hydrothermal treatment was, the lower was the retention and the smaller was the unit cell dimension of USY sample. Correlations between the unit cell dimensions ofss-US-Ex (0.95 N), those of the starting ss-USY, and the retentions of ss-US-Ex (0.95 N) are shown in Figure 1. As for dd-USY (LZ-Y52), whose unit cell dimension was 2.4405 nm, the retention ofdd-US-Ex (0.95 N) decreased from 0.774 down to 0.317, though that of dd-US-US-Ex (0.096 N) increased up to 0.875. From these results, the following general observations can be made: The larger the unit cell dimension of USY was, the smaller was the unit cell dimension of US-Ex (0.95 N) and the lower was the crystallinity of US-Ex (0.95 N). The unit cell dimensions of some US-Ex (0.95 N), whose retentions were decreased remarkably, were smaller than those of reported as constants 15-x9 for aluminum-free faujasite, i.e., in the range of 2.411719 to 2.425 nm. 17 The unit cell dimension of USY should be shrunk down to 2.434-2.436 or less in order to get the highly crystalline US-Ex (0.95 N). This optimum unit cell dimension of USY for HC1 treatment is independent of Si/A1 atomic ratio of starting NaY. As shown in Figure 2, the retentions of US-Ex after steaming tests were affected mainly by the retentions of US-Ex. As for the well-shrunk and highly crystalline US-Ex, the higher the Si/AI molar ratio of parent NaY was, the slightly higher was the retentions after the steaming tests. The retentions of US-Ex (0.096 N) were about one-third of those for US-Ex (0.95 N). T h e optimum unit cell dimension of USY for the hydrothermally stable US-Ex (0.95 N) is the same with that for HCI treatment. Consequently, it was concluded that heating of s- or d-USY, at least up to 650°C for 4 h with steam, is
Hydrothermal stability of US-Ex: A. Yoshida et al.
1.0
0.003
of
0.8 LU
-$ v"$
0.002 0.001
0.6 U4
/.
~-0,4 @
-
%
0.2
0
0
0.2"
0.4
0.6
0.8
7
0.20
0,6 5 ~
I/Io OF US-Ex
necessary in order to get the well-shrunk USY samples, which are stable for the treatment with excess acid. There was no difference between the hydrothermal stabilities ofdd-, ds-, and ss-US-Ex when the unit cell dimensions and the retentions were similar. In Figure 3, correlations between the retentions after the hydrothermal stability test at 870°C, the amount of A1203, the amount of Na20, and the unit cell dimensions of US-Ex (LZ-Y52, 0.096-0.95 N) are shown. All the exchangeable sodium ions were extracted first as shown by Patzelova et al., 2° then probably nonframework aluminum, and, finally, framework aluminum atoms were extracted with excess amount of hydrochloric acid. By the extraction of about one-half of nonframework aluminum, the unit cell dimension decreased from 2.4305 _+ 0 . 0 0 0 3 nm to 2.4299 +_ 0.0002 nm. However, the unit cell dimension of US-Ex (0.192 N), whose nonframework alumina was extracted almost completely, was also 2.4298 _+ 0.0001 nm. These results strongly suggest that the first shrinkage must be due to the collapse of nonframework alumina species that probably made the unit cell larger than it would be expected without nonframework aluminum species as shown by Klinowski et al. m and that almost no framework alumina was extracted in this region. The slight decrease of unit cell dimension from 2.4298 nm (US-Ex [0.192 N]) to 2.4278 _+ 0.0003 nm (US-Ex [0.95 N]), however, shows the gradual extraction of framework aluminum. The retention of US-Ex increased with the decrease of nonframework aluminum and remained relatively constant d u r i n g f u r t h e r extraction of framework aluminum (Figure 4). This result, at first sight, seems to suggest that the removal of amorphous nonframework species as impurities merely enhanced the intensity of XRD powder pattern.
0.8
0.15
1.0
Figure 2 Correlations between I/Io of US-Ex and I/Io after steaming test. Blank marks steamed at 810°C; solid marks steamed at 870°C. (~) US-Ex (LZ-Y52, 0.096 N) steamed at 870°C; ( 0 , 0 ) US-Ex (LZ-Y52, 0.95 N); (rq, II) US-Ex (JRC-Z-Y4.8, 0.95 N); (A, &) US-Ex (JRC-Z-Y5.6, 0.95 N); (O, 0 ) US-Ex (3-3-n, 0.95 N). For identification of I/Io, see Figure 1 legend
fl
.4
@
2
0.10
0.4
0.05
0.2 0
O 2,427
2,428
2,429
2.430
2.431
UNIT CELL DIMENSION OF US-Ex(NM)
Figure 3 Correlations between the amounts of AI2Oz, the amounts of Na20 in US-Ex (LZ-Y52, 0.096-0.95 N), the retentions after steaming test at 870°C, and the unit cell dimensions of US-Ex (LZ-Y52). The molar ratio of HCI/(Na + + 3AI); 1 = 0, 2 = 0.5, 3 = 1.0, 4 = 2.0, 5 = 3.0, 6 = 4.0, 7 = 4.96. Na + and AI are those in USY
0.4 ..__._---e 0.3 -O0,2 0,9
@
0,8 0,7
0.6
0
!
I
5
10
15
2'0
25
AMOUNT OF AL203 (G/G)
Figure 4 Correlations between the amount of AI2Oz, the fractional solid volume in the XRD sample holder, and the retentions of USY (LZ-Y52)and US-Ex (LZ-Y52).Vs = volume of solid powder; Vt = volume of cavity of sample holder; (~) dd-USY and dd-US-Ex; (O) ss-USY and ss-US-Ex. For identification of I/Io, see Figure 1 legend
ZEOLITE& 1991, Vol 11, March
225
Hydrothermal stability of US-Ex: A. Yoshida et al. 1,0
I
i
,
,
,
v
I
I
,I ii [I
0,8
o rl ii
i i I
II
ii
0.6 O
o-usY ,:~
I
,, I
0.4
II
~
f
,,
I
,
0.2 ,I
0
0
i
i
=
i
1
2
3
4
N^20(G/G )
4
5
'
However, the total amount dissolved from dd-USY with 0.096 N HCI was 0.126 g/g, i.e., 0.0323 g/g of SiO2 and 0.0936 g/g of A1903. Then, the calculated intensity should be 0.851 for dd-US-Ex (0.096 N) prepared from dd-USY, whose intensity was 0.738. This calculated value was lower than the observed one, i.e., 0.906. As for ss-USY, the total amount dissolved was 0.122 g/g, i.e., 0.0256 g/g of SiO2 and 0.0959 g/g of A1203. The calculated value for ss-USEx (0.096 N) should be 0.754, which was also slightly lower than the observed one, i.e., 0.774. In addition, the fractional solid volume of sample mounted in the holder decreased with an increasing dealumination ratio of HC1 solution. These results suggest that the enhancement of XRD intensity by extraction of nonframework alumina was due to the disapl~earance of distortion caused by polymerized A1203, -2-25 which probably has edge-shared boehmitelike structure, 26 as well as the removal of amorphous nonframework species as impurities. The hydrothermal stability was improved by the extraction of nonframework aluminum as shown by Patzelova et al. 11 and framework aluminum. The amounts of Na20 in US-Ex (0.096 N) and US-Ex (0.19 N) were 0.00050 g/g and 0.00066 g/g, respectively. On the other hand, the retentions of US-Ex (0.096 N) and US-Ex (0.19 N) after the steaming test were 0.215 and 0.349, respectively. Correlation between the amounts of Na20 in US-Ex (0.95 N) and the retentions after the steaming tests are shown in Figure 5. These results show that the amount of Na20 in US-Ex (0.95 N) did not affect the hydrothermal stability. The amount of K20 in US-Ex (0.95 N) were in the range of 0.000036 g/g to 0.000084 g/g. These results sugg.est that the amount of alkali metal oxides remaining m US-Ex samples are too small to affect the hydrothermal stability of US-Ex. 27A1 MAS n.m.r, spectra of d-USY, ss-USY, and ss-US-Ex prepared from LZ-Y52 are show in Figure 6. Table 2 shows the integrated intensities of 27A1 MAS
ZEOLITES, 1991, Vol 11, March
" -,~,
,,
,
,1
l=
1
i',
',,
!
x 10 -4
Figure 5 Correlations between the amounts of Na20 and the retentions of US-Ex (0.95 N) after steaming tests. For identification of symbols and I/Io, see Figure 1 legend
226
I
150
L~ 100
;,i 50
i 0
-50
-100
PPH
27AI MAS n.m.r, of d-, ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52, 0.096-0.95 N). Numbers are the same with those in
Figure 6
Figure 3
n.m.r, spectra. Figure 7 gives a set of i.r. spectra for some of the samples. The suppressed i.r. spectra for ss-USY (LZ-Y52) show no distinct b a n d s for A I ( O H ) , (3-')+ species 2'27'28 located in the nonframework position or distinct bands for bridging hydroxyl groups at 3650 cm -l and at 3550 cm -123
Table 2
The integrated intensities of 27AI MAS n.m.r, spectra of LZ-Y52, USY (LZ-Y52) and ss-US-Ex (LZ-Y52, 0.096-0.95 N)
Sample LZ-Y52 d-USY (LZ-Y52) ss-USY (LZ-Y52) ss-US-Ex (0.096 N) ss-US-Ex (0.192 N) ss-US-Ex (0.38 N) ss-US-Ex (0.57 N) ss-US-Ex (0.76 N) ss-US-Ex (0.95 N) LZ-Y52a ss-US-Ex (0.76 N) a
Integrated range (ppm - ppm)
Intensity
Relative intensity
110 20 110 20 110 20 110 20 110 20 110 20 110 20 110 21 110 20
22 -54.5 20 -57 22 - 55 21 -57 22 -55 21 -55 21 -54 21 -58 21 -55
72.76 2.23 21.85 7.63 10.34 7.14 8.365 6.473 4.831 0.994 2.899 0.599 2.665 0.722 2.278 0.608 1.482 0.934
1.000 0.0306 0.300 0.105 0.142 0.098 0.040 0.115 0.0667 0.0137 0.0397 0.00823 0.0366 0.00992 0.0313 0.00836 0.0204 0.0129
110 20 110 20
21 - 54 21 - 54
71.61 1.68 2.200 0.470
1.000 0.023 0.0307 0.00656
a Integrated another day from same spectra
Hydrothermal stability of US-Ex: A. Yoshida et al.
I
¢
/ / /
v
/
/
\
!
/
/
/
" I,
\
/
/
\ •~ 4000
I
-V(CM-I )
I
~doo tsoo
l
l
1300 1800
V(CM-1)
]_
1300
V(CM-I)
Figure 7 I.r. spectra of USY (LZ-Y52) and US-Ex (LZ-Y52). (A): After evacuation at 389°C for 2 h and measured at 192°C; wavenumber (a) 3740 cm -~, (b) 3710 cm-t; (B) and (C): after addition of pyridine at room temperature and desorption at 282°C for 30 rain and measured at 282°C (B) and at room temperature. (C); wavenumber (c) 1542 cm -1, (d) 1446 cm -~. Numbers are the same as in Figure 3
(Refs. 29-31), which were almost completely diminished during the second hydrothermal treatment by dehydroxylation. The peak height of signal at 57 ppm of ss-USY (LZ-Y52) was less than one-fourth of that of d-USY, in contrast to the results reported by Ray et al. 32 Ai(OH),,(3-")+s~ecies seem to polymerize and form neutral AI,~O&, "- being responsible for the raised base line of 27 A1 spectra.7 4 • 21 •2 5 The integrated intensities of 27A1 spectra, therefore, consi.st of two parts, i.e., the sharp one and the overlapped broad line. Then, ASP at 58.9-55.6 ppm were estimated (Figure 8). By extraction of about one-half of nonfralaework aluminum, the peak assigned for the octahedrally coordinated aluminum (0.33 ppm) was remarkably increased. In addition, ASP also slightly increased. Bosacek et al. 33 reported that the remarkable increase of the signal intensity at 0 ppm was caused by the remaining hexaquo- or/and hydroxoaquoaluminum complex cations in the lattice. However, we would like to stress the possibility that the increased intensity was due to the disappearance of distortion caused by the long aluminum-hydroxo-oxide chains. The remarkable increase of the signal intensity at ca. 57 ppm was also observed by partial extraction of nonframework aluminum ofdUSY with dilute NaOH solution. The details of this phenomenon will be reported elsewhere. Consequently, the number of AI atoms at the framework position in the unit cell, NA~ (Aln.m.r.), for US-Ex (0.38 N) was estimated as 2.1
from the integrated intensity (Table 2). NA| (Aln.m.r.) for ss-USY was estimated as 3.0-4.5 from ASP; 4.5 was obtained by linear extrapolation using the values of ss-US-Ex (0.096--0.96 N) on the assumption that the shrinkage of unit cell dimension from 2.4305 nm (ss-USY) to 2.4299 nm (ss-US-Ex [0.096 N]) was due to the extraction of framework aluminum. Then, the value, 4.5, seems to be upper limit for NAI in ss-USY (LZ-Y52). I.r. spectra of dealuminated zeolite Y have been reported by several authors. 2"5'12'20'22'2::L29-31 The spectra of US-Ex (0.38 N-0.95 N) in the hydroxyl stretching region were closely similar to those reported for highly dealuminated zeolite Y prepared with SIC14,34 with HCI, 5 and for Al-deplete NaY prepared with H,tEDTA. 2'19 Ward 22':~° assigned a band at 3742 cm- f to the silanol group on the surface of the zeolite crystals. Anderson and Klinowski34 assigned a band at 3734 cm -1 to terminating silanol groups. Other authors '''23'35'36 also have reported similar conclusions. However, Kubelkova et al. 37 assigned this band to hydroxyls on structural defects, though Anderson and Klinowski3'I and Patzelova et al. 2O assigned the band at 3675 cm- 1 to framework Si-OH groups at defect sites. Bennett et al., 3s Skeels and Breck 2 and Bosacet et al. 5 assi_~ned the broad adsorption band at 3750-3000 c m - ' to hydrogenbonded OH groups at the defect site (4 OH nest) that remained in the framework without the insertion of silicon atoms. Skeels and Breck 2 evaluated the amounts of 4 OH nests with the absorbance value at 3710 cm -l. As for US-Ex samples of this study, no distinct band except at 3740 cm -1 was detected between 3800 and 3000cm-1. The amount of 4 OH nests of our US-Ex (0.95 N) evaluated by Skeels and 1,2 1,0
0.8
o
\
0,4
0~ { 0.2
:" ,/
/
~
o\
\
20427 ~.428 2.429 2.430 2.431 UNIT CELL DIMENSION OF USEx(NM)
the amounts
Figure 8 Changes of of 40H nest and framework alumina evaluated from ~;AI MAS n.m.r. (ASP) and chemical analysis. Sample numbers are the same with those in Figure 3. (O) 40H nest: as for sample 7, the relative intensity .was regarded as unity; (Q) framework alumina measured from the peak areas divided by appropriate base lines: as for sample 1, the relative intensity was regarded as unity; (A) framework alumina obtained from chemical analysis: as for sample 3, relative intensity was regarded as unity and was regarded as zero for sample 7
ZEOLITES, 1991, Vol 11, March
227
Hydrothermal stability of US-Ex: A. Yoshida et al. A
B
:0
,0
C
AM-I
1 i(/AM_2
-GO
-100 ppl4
-lgO
-60
-100
-lgO
PPM
1
-60
-lO0
AM-2
-140
PPM
Figure 9 agSi MAS n.m.r, spectre for ss-USY and ss-US-Ex and their deconvolutions. (A) Solid line = ss-USY (LZ-Y52), dotted line = ss-US-Ex (0.38 N); (B and C): ss-USY (LZ-Y52), B = Gau§sian, C = Lorentzian; numbers are " n " in Si(0AI).(0Si)4_., U = unknown; A m - l , -2, -3 = a m o r p h o u s parts
Breck's method is larger than that of HY (u.d. = 2.427 nm) prepared by repeated mild, compared with our conditions, hydrothermal treatments and ion exchanges by Fukushima et al., 39 though the intensity of band at about 3740-3750 cm-= is similar. After the extraction of almost all nonframework aluminum with 0.192 N HC1, the intensity of band at about 3740-3750 c m - l was enhanced remarkably, suggesting the existence of bondings between zeolite framework and nonframework aluminum species. By treatment with excess acid (nos. 4 and 7 in Figure 6), the broad band between 3740 cm-1 and about 3200 c m - i increased significantly. The peak areas of broad i.r. bands in the range of 3800 to 3200 cm- 1 involving a narrow band at 3740 cm-I show behaviour similar to those given by Skeels and Breck's method. The behavior of this band in relation to adsorption and desorption of pyridine closely resembles those reported by Anderson and Klinowski34 showing the lower desorption temperature, which means lower acidity. After desorption of excess p~,ridine at 289°C, two well-defined peaks at 1542 c m - " (Br6nsted acid sites) and 1446 cm -a (Lewis acid sites) were detected in the US-Ex (0.096 N) sample and a detectable peak at 1542 cm -l was also found in US-Ex (0.95 N). However, as for the other samples, no detectable peak was found at 289°C, though the slight peaks were detected after cooling down to room temperature under a pressure of 8 × 10 -3 Pa. The intensity of this two peaks did not associate with the increased intensities of bands at 3740 cm-1 and between 3800 and 3200 cm -~. The slight peak at 1540 cm -l for US-Ex (LZ-Y52, 0.95 N) might be due to that for amorphous aluminum silicate, because this sample has no framework or nonframework alumina (see no. 7 in Figure 6), though 1.84% of alumina still remains. The two peaks at 1542 and 1446 cm -I for US-Ex (0.096 N) should be assigned to nonframework alumina species. These results show that the severe acidic conditions for extraction of framework aluminum formed the less acidic silanol groups with the broad i.r. bands at 3800-3200 cm -l. T h e broad bands at 3800-3200 cm-X show the irregularity of the 4 OH nest. It also
228
ZEOLITE& 1991, Vol 11, March
seemed that the rather sharp peak at about 3740 cm -I should be assigned to terminating hydroxyls that were produced during the extraction of nonfi'amework and framework aluminum. The spectra of 2'~Si MAS n.m.r, of the USY and US-Ex samples show the interesting experimental evidence for the partial dissociation of framework silica to the nonframework position during dealumination. We already suggested the dissociation of Si (3AI) during dealumination previously. 13 We noticed that Si (2A1) also has the same possibility of dissociation under severe hydrothermal treatment. 4° The deconvolution of - $1MAS n.m.r, spectrum has been carried out using lorentzian profiles as well as Gaussian profiles (Figures 9 and 10 and Table 3). In both cases, broad peaks for Si (4A1), Si (3A1), and almost all of Si (2A1) disappeared by means of the extraction with 0.38 N HCI. However, the decrease of unit cell dimension by this treatment was only 0.0013 nm. Using constants for unit cell dimension presented by several authors,~5-~° the number of AI atoms in a unit cell, NAI (XRD), of USY and US-Ex samples was calculated. With different constants, NAI (XRD) for ss-USY (LZ-Y52) shows rather wide scattering in the range of 19.8 to 6.3. However, the differences between ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52, 0.38 N) and that between ss-US-Ex (LZ-Y52, 0.38 N) and ss-US-Ex (LZ-Y52, 0.95 N) are less than 2.0, in good agreement with N A I (Aln.m.r.). The number of A1 in ss-US-Ex (0.95 N) should be 0. As shown by Kerr, 41 most of observed values for the unit cell dimensions of zeolite X, Y, and dealuminated Y lie between the lines reported by Breck and Flanigen ~5 and Sohn et al. Is The deviations of the unit cell dimension of aluminum-free ss-US-Ex (0.95 N) from these two values were +0.0086 and +0.0040 nm, respectively. The deviations correspond to 10 to 4.3 atoms/unit cell. These deviations might be caused by the formation of secondary pores 6-9'42--44 and 4 OH nests, which seem to prohibit the complete shrinkage to idealized values. When we used the Gaussian peak profiles, one or two unknown peaks between those for Si (1A1) and Si (0AI) and three amorphous peaks in the high magnetic field should be divided for ss-USY (LZ-Y52) and •
9 9
•
A
B
fO
...-----0
fO
U-3. ~AM-I
U-2~
4'0
-i~o PPM
-i~o
-60
-100 PPM
-lqO
-90 -lO0 -llO -120 PPM
Figure 10 z~Si MAS n.m.r, spectra for ss-US-Ex and their deconvolutions. (A) ss-US-Ex (LZ-Y52, 0.38 N), (B) and (C): ss-US-Ex (LZ-Y52, 0.95 N), U-l, -2, -3 = unknown. For identification of other symbols, see Figure 9 legend
Hydrothermal stability of US-Ex: A. Table 3
Yoshida
et al.
RSM error
29Si MAS n.m.r, spectra of ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52) samples
Sample
G/L
Si(4AI)
Si(3AI)
Si(2AI)
Si(1AI) Si(3Si)OH
ss-USY
G
3.1 -82.9
4.1 -89.2
5.4 -95.2
10.8 -102.3
L
2.3 -82.2
3.9 -88.5
4.9 -94.5
cs
ss-USY cs
ss-U$-Ex (0.38 N)
G
0.0
cs
.
ss-US-Ex (0.38 N)
L
0.0
cs
.
ss-US-Ex (0.95 N)
G L
.
.
.
Si(0AI)-2
am-1
am-2
am-3
0.0 -
20.7 -106.8
39.1 -107.7
8.0 -109.0
6.4 -111.4
2.4 -116.5
4.5%
7.2 -101.3
0.0 -
0.0 -
74.2 -107.7
0.0 -
7.5 -112.8
0.0 -
2.6%
0.0
8.8 101.7
2.8 -105.1
13.4 -106.9
42.0 -107.7
14.0 -108.4
13.0 -110.2
6.0 -114.3
3.8%
0.0
6.2 101.1
0.0 -
0.0 -
79.2 -107.7
0.0 -
14.6 -111.3
0.0 -
2.0%
3.2 -97.2
9.2 -102.0
8.2 -105.9
12.2 -107.1
31.7 -107.6
16.6 -108.1
15.0 -110.6
3.9 -116.0
3.1%
0.0
10.2 101.2
0.0 -
0.0 -
76.3 -107.6
0.0 -
13.5 -111.5
0.0 -
1.7%
.
0.0 .
Unknown
.
0.0 -
0.0
cs
.
0.0 .
0.0 -
cs
ss-US-Ex (0.95 N)
0.0 .
.
Unknown
G/L: G means Gaussian profiles were used for deconvolution; L means Lorentzian profiles were used
ss-US-Ex (LZ-Y52). The assignments for Si (4AI), Si (3A1), Si (2AI), Si (1A1), and am-2 were already reported. 13A4'23'~6'45"46 The assignment of 298i M A S n.m.r, signals in the range of - 103 to - 107 ppm has yet to be established. 2''45 Engelhardt et al. 46 confirmed the presence of Si-OH groups by a considerable increase of the - 1 0 0 ppm signal from the CP spectrum of ultrastable Y. Ray et al. 32 assigned the peaks at -101, - 103, and - 1 0 4 ppm to Si-OH groups associated with defect sites or amorphous materials, though Grobet et al. 45 assigned the peak at 104.2 ppm to crystallographically inequivalent Si (0A1) sites. As shown in Figure IOA and B, the peak profiles of 29Si M A S n.m.r, did not change notably by the extraction of remaining framework aluminum and formation of new defect sites. Then, the peak location of Si (3Si) OH seems to be nearly the same as that for Si (1A1), in agreement with Engelhardt et al.'s results. 46 For the calculation of the Si/A1 ratio, Si (3Si) OH can be estimated as Si (0A1). From the spectrum of 27A1 M A S n.m.r., the peak at -101 - 1 0 2 ppm for ss-US-Ex (0.95 N) should be assigned to Si (3Si) OH. However, the peak at -101 - 1 0 2 ppm for ss-USY and ss-US-Ex (0.38 N) should be divided into two sections. To determine the amounts of OH groups, thermogravimetric analysis was carried out (Table 4). Supposing that all of the A1 atoms are in the form of A1-OH, the ratios of Si-OH/Sitot~l were estimated. As for ss-USY, the ratio of Si-OH was not clear. Then, it Table 4 Amounts of OH groups and Si-OH calculated from thermogravimetry
Sample ss-USY ss-US-Ex ss-US-Ex ss-US-Ex s$-US-Ex ss-US-Ex ss-US-Ex
(0.096 N) (0.192 N) (0.38 N) (0.57 N) (0.76 N) (0.95 N)
400-1400°C (t.g.)
H20 (in A I - O H )
H20 (in SiOH)
Si-OH Sitotal
0.0123 0.0123 0.0153 0.0131 0,0124 0.0127 0.0127
0.0421 0.0221 0.0072 0.0047 0.0042 0.0035 0.0032
0.0081 0.0083 0.0082 0.0092 0.0095
0.0574 0.0572 0.0568 0.0634 0.0643
was assumed that the peak at -101 - 1 0 2 ppm belongs to Si (1A1) units. As for ss-US-Ex (0.38 N), Si-OH was evaluated as 0.0572 mole/mole. From NA= (Aln.m.r.), Si (1A1) for US-Ex (0.38 N) can be evaluated as 8.4 atoms/unit cell. It corresponds to 0.044 mole/mole of SiO2. Another problem was whether it was the crystalline part or not. From the retention ofss-US-Ex (LZ-Y52, 0.38 N), i.e., about 0.851, it was concluded that the peaks at -110.2 and - 114.3 ppm seem to be amorphous states, then the peaks at -105.1, - 106.9, and -108.4 ppm should be assigned to crystalline units. On the basis of these assumptions, NAI (Sin.m.r.) were calculated (Table 5). The value for NA= (Sin.m.r.) was affected several factors, such as the amount of Si-OH groups, evaluation of amorphous fraction, and the profiles of signals. However, the most important factor was assignment of Si (4AI), Si (3A1), and Si (2A1) to crystalline parts or not. From the results of NA! (Aln.m.r.) and NA! (XRD), NAI for ss-USY (LZ-Y52) and ss-US-Ex (LZ-Y52), 0.38 N) were calculated as 2.0-2.1 and 3.0-4.5. Then, Si (4AI) and Si (3AI) should be nonframework units in ss-USY (LZ-Y52). The greater part ofSi (2A1) also seem to be at the nonframework position. The sum of relative intensities of Si (4AI), Si (3AI), and Si (2A1) units in ss-USY (LZ-Y52) was 0.126 mole/mole (Gaussian) - 0.111 mole/mole (Lorentzian). The amount of SiO2 dissolved from ss-USY (LZ-Y52) with 0.95 N HC1 was 0.0487 mole/mole, corresponding to the sum of Si (4A1) and one-half of Si (3A1). The greater part of SiO2 species dissolved in acidic solution accompanied with nonframework alumina probably precipitated as amorphous silica with the 29Si n.m.r, signal of higher magnetic field, which increased from 0.088 mole/mole to 0.189 mole/mole (Gaussian) and 0.075 mole/mole to 0.135 mole/mole (Lorentzian). RSM errors for the deconvolution with Lorentzian profiles were smaller than those with Gaussian profiles. The number of signals divided with Lorentzian profiles also seems to be reasonable. However, the
ZEOLITES, 1991, Vol 11, March
229
Hydrothermal stability of US-Ex: A. Yoshida et al. Table 5
N u m b e r of AI atoms in unit cell calculated from the intensities of divided 29Si MAS n.m.r, signals
Deconvolution
Gauss-1
Gauss-2
Gauss-3
Lorentz-1
-d
19.9 15.4 10.5 5.8
21.6 16.8 11.6 6.4
23.4 18.4 12.7 7.1
16.6 13.3 8.4 3.8
ss-US-Ex (0.38 N)-e -f -g
4.2 2.0 1.5
5.1 2.6 1.9
6.2 3.1 2.3
ss-USY (LZ-Y52) -a -b -c
2.9 2.1 0.25
Lorentz-2 17.8 14.2 9.0 4.2 3.4 2.4 0.29
Gauss-1 = am-1 - 3 are regarded as crystalline part; Gauss-2 = am-1 is regarded as crystalline part; Gauss-3 = am1 - 3 are regarded as a m o r p h o u s part; Lorentz-1 = am-2 is regarded as crystalline part; Lorentz-2 = am-2 is regarded as a m o r p h o u s part; a = Si(4AI), Si(3~l), and Si(2AI) are regarded as f r a m e w o r k unit; b = Si(4AI) is regarded as n o n f r a m e w o r k unit; c = Si(4AI) and Si(3AI) are regarded as n o n f r a m e w o r k units; d = Si(4AI), Si(3AI), and Si(2A.I) are regarded as n o n f r a m e w o r k units; e = Si(3Si)OH was evaluated 0; f = Si(1AI) was calculated from NA,(AIn.m.r.); g = Si(3Si)OH was calculated f r o m t.g.
value for Si (1Al) + Si (3Si) O H of US-Ex (0.38 N), 0.062 mole/mole, was smaller than the sum of Si (IAl) calculated from N,xi (Aln.m.r.) and Si (3Si) O H obtained from t.g.i.e., 0.1012 mole/mole. On the other hand, the value for Si (3Si) O H of US-Ex (0.95 N), 0.102 mole/mole, was larger than that obtained from t.g.i.e., 0.0643 mole/mole. These deviations seems to be caused by greater allotment to main peak, Si (0A1), with Lorentzian profiles decreasing the relative intensities for neighboring peaks, and by the existence of amorphous silica contained alumina with extremely broad lines of 29Si n.m.r., which can be partly observed for US-Ex (0.95 N). Correlations between the sum of relative populations of Si (hA1) in parent sodium Y, i.e., 2 × Si (4A1) + 1.5 × Si (3A1) + Si (2AI), the retentions ofss-US-Ex (0.95 N); and the retentions after the steaming tests are shown in Figure 11. These results evidently show
that Si (nAl) units with greater n value tend to dissociate from framework positions during dealumination and decrease the hydrothermal stability of US-Ex. CONCLUSION Hydrothermal stability of US-Ex increased by the extraction of nonframework and framework aluminums. Nonframework aluminum species in dd-, ds-, and ss-USY seem to distort the framework and decrease the hydrothermal stability. T h e removal of aluminum accompanies the partial dissociations of Si (4A1), Si (3AI), and, probably, Si (2A1) units. The decrease of retentions and hydrothermal stability of US-Ex prepared from well-shrunk USY with excess acid might be due to this silicon dissociation. 298i n.m.r, signals of ss-USY and ss-US-Ex seem to deviate CONCLUSION
1.1 1.0
SI I
AL I
I
I
0
o
0
SI J
SI |
0
0
I
i
SI-0-AL-0-SI-O-AL-O-S!-O
0.9 0.8
I
e-~ll.
I
I
Q
0
0
SI
SI
SI
SI
S=
~L
oI
SI H~
Sll
o'I
•
I
I
"" 0.7
0
~
OH 0 Si
~I
SI
SI SUBSEOUENT
S,_O_A,_0_SI_ON H' 0-SI-0 0.4
0.3
0
o.~o
o.'4s
o.~o
o.~s
0.60
Figure 11 Correlation between the sum of relative p o p u l a t i o n s and the retentions of US-Ex after the h y d r o t h e r m a l stability tests. Xs=(nAj) = 2 Si(4AI) + 1.5 Si(3AI) + Si(2AI); (©) US-Ex; ( & ) after the h y d r o t h e r m a l stability test at 810°C for 6 h; (Q) after the h y d r o t h e r m a l stability test at 870°C for 6 h. For identification of I//o, see Figure I legend
ZEOLITES, 1991, Vol 11, March
0
~=
)~"XsI(NAL)
230
FORMATION OF 40H NEST
I
S=
0.5
o
,0-!i-0
SI
t
SI
0.6
/
Sx I
H0 Si-0 H , OIH
SI
Figure 12
H0
Sz I
0
H0-SI-0 ' (~H SI
DEALUMINATION
I
OH 0
OIH SI
I 0 SI
COMIGRATION OF SI(3AL)
FORMATION OF SECONDARY PORES
Schematic representation of the m e c h a n i s m of hydrothermal d e a l u m i n a t i o n of the faujasite f r a m e w o r k
Hydrothermal stability of US-Ex: A. Yoshida et al.
from Gaussian profiles and have some portion of Lorentzian character. The mechanism of the silicon dissociation might be as shown in Figure 12.
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