Modification of siliceous zeolites using phosphorus pentachloride

Modification of siliceous zeolites using phosphorus pentachloride M. Kojima,* F. Lefebvre, and Y. Ben Tafirit Institut de Recherches sur la Catalyse, CNRS, Villeurbanne, France Phosphorus pentachloride was reacted under static conditions at 423-873 K with dealuminated Y, small and large port mordenite, and ZSM-5. 31p and 27AI MAS n.m.r, spectra were taken to identify the location of phosphorus and aluminum subsequent to reaction. Isomorphous substitution of phosphorus into the zeolite framework appeared to be possible only with sodium forms of zeolites, H forms giving rise to reaction with hydroxyl groups. Small port Na mordenite was unreactive at 773 K. ZSM-5 behaved differently in that a considerable amount of aluminum was dislodged from the framework of NaZSM-5 without phosphorus substitution. Keywords: Phosphorus pentachloride; mordenite; dealuminated Y; ZSM-5

INTRODUCTION In a previous study, reaction of PC15 with NaY and HY was examined in a static system, x Phosphorus reacted rapidly with NaY and the amount of PC15 contacted with NaY had to be reduced significantly for the zeolite crystallinity to be preserved. Controlling the extent of framework aluminum removal by changing the reaction temperature in a static system was limited because of apparent realumination by AICIa. A alp MAS n.m.r, peak at - 2 9 ppm was ascribed to framework-substituted P, in accordance with the data published on aluminophosphate-based molecular sieves, 2 whereas those at higher ppm were attributed to extraframework P. Characterization of the product obtained by reacting PCI3 with NaY has been published previously. 3 Dealumination of mordenite using PCI3 and PC15 has been reported by Fejes et al. 4 Using chemical analysis for the determination of aluminum content, they reported that it decreased slightly after reaction with PCIs at 773 K. No data were given for the reaction of PC15 with mordenite. They did not investigate the possibility of isomorphous substitution of phosphorus for aluminum or silicon. In the present work, PCI5 was reacted with dealuminated NaY, Na-mordenite, NaZSM-5, and their hydrogen counterparts under various conditions. The choice of zeolites enabled an investigation into the effect of varying the Si/A1 ratio and zeolite pore geometry on the nature of reaction with PCIs. In

* On leave from the Dept. of Chemical Engineering, University of Cape Town, Rondebosch 7700, South Africa. Address reprint requests to Dr. Kojima at UOP Research Center, 50E Alquonquin Rd., P.O. Box 5016, Des Plaines, IL 60017-5016, USA. Received 29 October 1990; accepted 9 January 1992 ~) 1992 Butterworth-Heinemann 724

ZEOLITES, 1992, Vol 12, July~August

particular, alp MAS n.m.r, analysis of the reaction products was performed to examine whether or not the previous peak assignments are consistent with the new data.

EXPERIMENTAL Materials Dealuminated Y was obtained by reacting LZY-52 from Union Carbide in a dynamic system for 1 h at 620 K with SiCI4 (vapor pressure at 273 K) and washing with deionized water. Its Si/AI ratio was determined by 2°Si MAS n.m.r, to be 7.7. Three types of mordenite were used: small port NaM and large port HM supplied by Soci~t~ Chimique de la Grande Paroisse and NaM (Z-900-Na) from Norton. NaZSM5 was synthesized in this laboratory according to the procedure specified by MobiP and had a Si/AI ratio of 16. PCI5 (purity > 99%) and SiCI4 (98% purity) were obtained from Merck. Dealuminated Y and NaZSM-5 were also ion-exchanged repeatedly with NH4CI to yield NH4 zeolites.

Reaction procedure A static procedure was adopted in this study. The reaction apparatus and procedure have been described previously. 1 Approximately 800 mg of catalyst in powd6r form was calcined overnight in flowing oxygen and then evacuated to a final pressure of less than 10 -s Pa for 8 h at 750 K. After cooling, the catalyst was contacted with PCI5 at the desired temperature, and subsequent to the reaction, the cell was evacuated at or below the reaction temperature to remove volatile substances.

Characterizations The infrared spectra of all the samples were

PCIs modification of zeolites: M. Kojima et al. Table 1

Reaction of PCIs with dealuminated LZY-52 (Si/AI = 7.7); reaction time length 0.5 h

Code

PCIs/ u.c.a

T (K)

Evacuation

5 5 5 5

423 473 573 673

373 423 473 500

8

573

500-670 K, 2.5 h

procedure

Na-dealuminated Y

I.r. wavenumber (cm-1) 1058

DY1 DY2 DY3 DY4

K, K, K, K,

1 1 1 1

h h h h

NH4-dealuminated Y

1058 1059 1063 1061 1060

DY5

1070

a Rough estimates of mol PCIs/zeolite u.c. transferred to the reaction cell

recorded on a Perkin-Elmer 580 spectrophotometer using the KBr pellet as well as the wafer technique. To study the hydroxyl bands, spectra were recorded after exchanging Na zeolites with ammonium ions and evacuating wafers (2.5 - 4.5 mg cm -2) at 623 K for 2 h. Powder XRD patterns of certain samples were taken to determine if the crystallinity of the zeolite varied during the reaction. For this purpose, the moisture content of the zeolites was not controlled. 31p and 27A1 magic angle spinning (MAS) n.m.r. spectra were recorded at a magnetic field strength of 7.05 Tesla on a Bruker MSL-300 spectrometer equipped with a commercial double-bearing probehead with zirconia rotors. T h e spinning rates varied between 2.5 and 4 kHz depending on the sample. To obtain 27A1 spectra as quantitatively as possible, short pulses were used (below 10°) and the recycle delay was adjusted allowing a complete relaxation of the nuclei. However, as in the case of most n.m.r, spectra of quadrupolar nuclei, the possibility of not observing all the aluminum species cannot be excluded. The 27A1 chemical shifts were referenced to an external 1 ~l aluminum sulfate solution. Their values were not corrected for quadrupolar interactions. For 31p n.m.r, studies, a small pulse angle (15 °) was also used, and the recycle delay allowing complete relaxation Table 2

Reaction of PCIs with mordenite; reaction time length

4h Code

PCIs/ u.c.

T (K)

Evacuation procedure

Zeolon NaM M1 M2a M2b a M3

1058 3 3 3 3

673 773 873 873

473 K, 1 h 573 K, 1 h 673 K, 1 h

3 3 3

673 773 873

473 K, 1 h 573 K, 1.5 h No evacuation

HM M4 M5 M6

1058 1060 1060 1068 1068

Small port NaM M7

I.r. wavenumber (cm -1)

1075 1078 1082 1056

3

773

470-520 K, 1 h

1055

Prepared by heating sample M2a at 873 K under flowing N2 saturated with water vapor at room temperature

was typically 10 s. For all the spectra, the number of scans was 360. The chemical shifts are reported relative to 85% HsPO4.

RESULTS Infrared data The results using dealuminated Na-Y are shown in Table 1. No changes in i.r. band positions could be detected after reaction below 575 K. However, when the reaction was carried out at higher temperatures, the absorption band at 1058 cm -1 shifted to 1062 _+ 1 cm -1 and the bands at 397, 517, and 598 cm -x broadened slightly, indicating a small decrease in zeolite crystallinity. In addition, a small peak developed at 925 cm - l . The loss of crystallinity was supported by the XRD spectrum. Reaction of PC15 with ammonium-exchanged dealuminated Y resulted in a larger shift of the band initially at 1060 cm -1, a peak at 938 cm -1, and a partial loss of zeolite crystallinity. As seen from Table 2, mordenite was much more stable in the presence of PCI5 and, hence, required more severe reaction conditions to dealuminate than did Y zeolite. In the runs on large port NaM and HM, increasing the reaction temperature resulted in a shift to a higher frequency (indicative of dealumination) in the position of the i.r. internal asymmetric stretching band initially presented near 1058 and 1068 cm - ' , respectively. In addition, the positions and/or intensities of bands characteristic of external vibrations changed slightly in the case of NaM. Reaction at 873 K led to the XRD-detectable presence of NaCI. M2a (reaction temperature of 773 K) was heated at 873 K for 2 h in flowing nitrogen saturated with water at the ambient temperature. No changes in the i.r. spectrum could be detected, suggesting that the crystallinity of the sample did not vary. There was no evidence from the i.r. spectrum that dealumination occurred at 773 K in small port NaM. The results obtained using ZSM-5 are shown in Table 3. Both Na- and NH4-ZSM-5 had the same wavenumber shift from 1090 to 1100 cm -1. Infrared spectra of hydroxyl bands of ammoniumexchanged dealuminated LZY-52 and DY3 showed that upon reaction both low-frequency and highfrequency band intensities decreased in size. More-

ZEOLITES, 1992, Vol 12, July/August

725

PCI5 modification of zeolites: M. Kojima et al. Table 3

Reaction of PCIs with ZSM-5; reaction time length 4 h

PCId T u.c. (K)

Code

NaZSM-5 Z1 NH4-ZSM-5 Z2

Evacuation procedure

A

B

I.r. wavenumber (cm-1)

6

773 Ambient-773 K, 4 h

6

773

1090 1100 1090 1100

No evacuation

P'+";o ....

+ . . . . -so'. . . .-lOO""

PPm'

'50 ....

0= . . . .

- 5 =0 . . . .

- 1 0=0' "

0

-50

-100

over, the shoulder at 3600 cm- 1 present in the parent material was absent in DY3. Similarly, in the case of ammonium-exchanged NaM and M3, there was a substantial reduction in the size of the band at 3600 cm -].

MAS

50

n.m.r,

results

Figures la and b show 27A1 spectra of calcined dealuminated NaY and of DY3, respectively. After dealumination with SiCI4, there was a considerable amount of octahedrally coordinated aluminum and a small peak at 39 ppm. The spectrum of DY3 was similar except that the peak corresponding to the octrahedral species (at about 0 ppm) was smaller. After ion-exchange with NH4C1, Sll~ n.m.r, spectra of DY3 were r e c o r d e d with and without crosspolarization. The results are shown in Figure 2. In the absence of cross-polarization, there was a broad signal at - 17 ppm and a shoulder at about - 3 0 ppm. Upon cross-polarization, the shoulder disappeared, showing that it was not an experimental artifact. The 27A1 n.m.r, spectrum of DY5 showed that the amount of framework aluminum had decreased considerably, in agreement with the loss of crystallinity observed from the intensities of the i.r. structural bands. Sip MAS n.m.r, showed numerous small peaks, including two broad signals at 2 and - 3 1 ppm. 27A1 n.m.r, spectra of Zeolon NaM were similar before and after reaction with PC15 and, specifically, there was no evidence of the presence of extra-

(b)

<.)

11o 1~o 5"o a -io pP"

It

0

-50

-100

50

Figure 2 31p MAS n.m.r, spectra of DY3 and Z1 (A) without and (B) with cross-polarization

framework aluminum. The Sip n.m.r, spectrum of M3 had a large peak at - 3 4 ppm, as shown in Figure 3. When this sample was ammonium-exchanged, the spectrum with cross-polarization produced only noise level signals while that recorded without crosspolarization was unchanged. Steaming had no effect on the aluminum of M2b, but 3IPMAS n.m.r, gave an additional signal near - 4 0 ppm. Figures ic and d show the ~7-A1 spectra of calcined HM and M6. Clearly, the amount of extraframework aluminum decreased upon reaction. The Sip spectrum of M6 had a broad signal centered around 0 ppm, while that of M5 gave, in addition, a signal near - 3 4 ppm. Finally, 27A1 spectra of calcined ZSM-5 and Z1, and Sip spectra of Z1 with and without cross-polarization, are shown in Figures 1 and 2, respectively. Z1 had a prominent 2]A1 peak at 40 ppm and a very large amount of octahedrally coordinated aluminum characterized by a broad signal at about - 10 ppm. Its 3]p spectrum showed many peaks between 0 and - 2 0 ppm and only a small shoulder around - 3 0 ppm. Cross-polarization showed clearly that the phosphorus peak at - 1 7 ppm corresponds to species bound to protons. The corresponding spectra for Z2 were similar.

lio lOO 6"o o -io p~m DISCUSSION

(¢-)M ~

_

_

(d)

1io 1;o io

~

-ioPPm

II~0"1()0

4)

-50

5'0

ppm

|

"Z2__ +io 16o 5"o 6

-ioPP"

150 100

-II0 llpm

50

()

Figure 1 27AI MAS n.m.r, spectra of (a) calcined dealuminated NaY; (b) DY3; (c) calcined HM; (d) M6; (e) calcined NaZSM-5; (f) Z1

726

ZEOLITES, 1992, Vol 12, July~August

T h e parent dealuminated Y had much extraframework aluminum, giving rise to peaks at 39 and ca. 0 ppm. That the intensity of the latter decreased upon reaction suggests that PC15 reacted with extraframework aluminum releasing AICIs, which was al subsequently evacuated. T h e P peak at - 17 ppm is most likely due to e x t r a f r a m e w o r k P. Crosspolarization showed that this signal corresponds to species associated with protons, suggesting that they are not substituted into the zeolite framework. A peak in this region was also observed by Kfihl and Schmitt who reported the existence of a alp n.m.r, signal at ca. - 1 7 ppm in zeolites ZK-21 and ZK-22. ~ By analogy with the results published previously I and in agree-

PCIs modification of zeofites: M. Kojima et aL

'

'

I

50

. . . .

1

0

. . . .

I

-50

. . . .

i -100

. . . .

I

'

'

pprn

-150

Figure 3 31p MAS n.m.r, spectrum of M3

ment with the published data, 2'6--9 the shoulder at - 3 0 ppm is attributed to phosphorus in the framework. The shape and position of the new i.r. peak at 925 cm -1 is very similar to that observed by Fejes et al. a° upon exposure or mordenite to COCI2. Although not shown in Table 1, reacting 20 mol PCls/u.c. with dealuminated NaY resulted in near complete loss of crystallinity. Dealuminated Y, although having a Si/AI ratio comparable to that of mordenite, is evidently far less stable to PCIs. A m m o n i u m - e x c h a n g e d dealuminated Y reacted appreciably with PCI5 and much of framework aluminum was extracted. Hydrolysis of PC15 by protons in the zeolite releasing HC1 accounts for the high level of reaction and the degradation of the framework. Reaction with NaM resulted in no extraframework AI, even after steaming at 873 K. The presence of XRD-detectable NaC1 in M3 suggests that the actual temperature inside zeolite pores was much higher than 873 K during the reaction. The 31p n.m.r, peak at - 3 4 p p m may be ascribed to frameworksubstituted phosphorus not linked to protons. The appearance of a new band near - 4 0 ppm upon steaming may be due to the presence of some phosphate compound. Its chemical shift is close to those of silicophosphates ] ] and the absence of change in the 27A1 n.m.r, spectrum after steaming may indicate that the above band is due to a compound formed by the reaction of extraframework phosphorus with silica present in the pores of the zeolite after the reaction. T h e framework of small port NaM remained intact upon contact with PC15 at 733 K. This is in agreement with the observations of Klinowski et al.12 and Bodart et al. l~ who pointed out that it was more difficult to dealuminate mordenite than it was Y zeolite by SiCI4. These results were explained in terms of pore blockage by the reaction products. The lower reactivity of mordenite toward PC19 in general and the absence of reaction of small port mordenite in particular supports this hypothesis. HM, possessing a fair amount of extraframework aluminum, did not produce a well-defined Sip n.m.r. peak near - 3 0 ppm. The decrease in the amount of octahedral aluminum can be attributed, as in the case of Y zeolite, to reaction of extraframework aluminum species with PCI5 or with HC1 produced by the

hydrolysis of PCI5 by protons. AICIs, which forms as a reaction product, would be volatized during evacuation. NaZSM-5 was the only Na zeolite that gave a greatly enhanced 27A1 peak at - 12 ppm after reaction (Figure 1J'). In addition, there was a prominent 2VAl peak at 39 ppm, while most of the phosphorus was not in the framework since the intensity of the peak at - 17 ppm was very large. The 27A1 n.m.r, peaks can be attributed, as in the case of dealumination by SiCI4, to octahedral extraframework species ( - 1 2 ppm) and tetrahedral or pentacoordinated extraframework species (39 ppm). However, since this material contains phosphorus, the reaction of aluminum (extracted from the framework in the presence of PCIs) with PC15 to form an aluminophosphate phase is an alternative explanation. Indeed, in aluminophosphates, the 27A1 chemical shifts have values close to 40 and - 1 2 ppml4'lS; thus, PC15 could react with a l u m i n u m species extracted from the zeolite framework and form an aluminophosphate phase. CONCLUSIONS PC15 reacted preferentially with extraframework aluminum species and, in hydrogen forms of zeolites, with hydroxyl groups yielding A1CI3 or HCI (which can destroy the zeolite framework). Isomorphous s u b s t i t u t i o n o f p h o s p h o r u s into the zeolite framework was observed to occur with sodium forms of zeolites. Dealuminated Y reacted more easily than did mordenite, while ZSM-5 yielded extraction of aluminum without phosphorus insertion.

REFERENCES 1 Kojima, M., Lefebvre, F. and Ben Ya~rit, Y. d. Chem. Soc., Faraday Trans. 1990, 86, 757 2 Appleyard, I.P., Harris, R.K. and Fitch, F.R. Chem. Lett. 1985, 1747 3 (a) Anderson, M.W. and Klinowski, J. J. Chem. Soc., Faraday Trans. L 1986, 82, 1449; (b) Thomas, J.M., Klinowski, J., Ramdas, S., Anderson, M.W., Fyfe, C.A. and Gobbi, G.C., ACS Syrup. Ser. 218, Am. Chem. Soc., Washington, DC, 1983, p. 159 4 Fejes, P., Kiricsi, I., Hannus, I. and Schobel, G., Magy. Kern. Folyoirat 1983, 89, 264 5 Argauer, R.J. and Landolt, G.R. US Pat. 3 702 886 (1972) 6 KLihl, G.H. and Schmitt, K.D. Zeolites 1990, 10, 2 7 Martens, J.A., Janssens, C., Grobet, P.J., Beyer, H.K. and Jacobs, P.A., in Zeolites: Facts, Figures, Future (Ed, P.A. Jacobs and R.A. van Santen) Elsevier, Amsterdam, 1989, p. 215 8 Khouzami, R., Coudurier, G., Lefebvre, F., V6drine, J.C. and Mentzen, B.F. Zeolites 1990, 10, 183 9 Grimmer A.-R. and Haubenreisser, U. Chem. Phys. Lett. 1983, 99, 487 10 Fejes, P., Kiricsi, I. and Hannus, I. Acta. Phys. Chim. 1982,28, 173 11 Mudrakovskii, I.L., Mastikhin, V.M. Shmachkova, V.P. and Kotsarenko, N.S. Chem. Phys. Lett. 1985, 120, 424 12 Klinowski, J., Thomas, J.M., Anderson, M.W., Fyfe, C.A. And Gobbi, G.C. Zeofites 1983, 3, 5 13 Bodart, P., Nagy, J.B., Debras, G., Gabelica, Z. and Jacobs, P.A.J. Phys. Chem. 1986, 90, 5183 14 Coury, L., Babonneau, F., Henry, M. and Livage, J. C.R.Acad. ScL Paris. Ser. II. 1989, 309, 799 15 Sierra de Saldarriaga, L., Saldarriaga, C. and Davis, M.E.J. Am. Chem. Soc. 1987, 109, 2686

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