Synthesis and characterization of zeolite Nu-1 prepared from near-neutral fluoride aluminosilicate gels

Synthesis and characterization of zeolite Nu-1 prepared from near-neutral fluoride aluminosilicate gels j.. Patarin,* P. Caullet,* B. Marler, + A.C. Faust,* and J.L. Guth* Laboratoire de Mat~iaux Ming'raux URA-CNRS 428 ENSCMU-UHA, Mulhouse, France tlnstitut fiir Mineralogie, Ruhr Universittit Bochum, Bochum, Germany The preparation of zeolite Nu-1 from near-neutral (pH - 8-10) fluoride containing media is difficult and only possible in a very narrow range of experimental conditions. Cocrystallization of other phases (e.g., MTN-type and AST-type clathrasils and FER-type zeolite) is often observed. Formation of pure Nu-1 could, nevertheless, be achieved at 170°C in 5 d from a reaction mixture of the following molar composition: 16.7 SiO= : 1 AI2Oz : 0.5 Me4NCI : 1 NH4F : 9 H20. The "crystals" display a pseudocubic morphology, with, in some cases, a size up to 40 pm and consist, in fact, of small micrometric crystallites. Zeolite Nu-1 was characterized by XRD, chemical analysis, thermal analysis, and lzc, lSF, 27AI, and assi MAS n.m.r, spectroscopy. Although the occluded organic species are mainly Me4N + ions, some Me3NH ÷ ions are also present. Three lSF n.m.r, signals may be assigned to fluoride ions incorporated into the structure of zeolite Nu-l. Although undetected by XRD, the presence of (NH4)3AIF6 as an impurity is systematically revealed by lSF and 27AI MAS n.m.r, spectroscopy. Keywords: Nu-1; synthesis; d.t.a.; t,g.; n.rn.r, spectroscopy

INTRODUCTION Zeolite Nu-1 is a highly siliceous product (SiO2/A120~ molar ratio from 20 to 150) that was first synthesized in 1977 from basic aqueous aluminosilicate gels with sodium and tetramethylammonium cations as the structuring agents. 1 After Bellussi et al., 2 the presence of sodium ions is only optional. The crystallization occurs in a few days (ca. 1-12 d) in the 150200°C temperature range. According to several authors, 3'4 the preparation of zeolite Nu-1 is only possible under quiescent conditions and, furthermore, the reproducibility is poor. Boron, iron, and gallium derivatives of zeolite Nu-1 were also prepared. 2's So far, no determination of the structure of Nu-1 has been published due to the small crystal size (1-5 Ixm) and due to the fact that Nu-1 materials always show indication of a disordered structure. Nevertheless, the available adsorption data might suggest that Nu-1 has apertures close to 0.6 nm while possessing a dual pore system based on 10- and 8-rin~ openings or a 10-ring opening with extensive faults. ~ This paper deals with the synthesis and characterization of zeolite Nu-1 from near-neutral synthesis

media containing F- ions. The organic templating agent is the Me4N + ion. The F - ions replace here the usual O H - ions as the mineralizing agent, according to the method developed in our laboratory. 6 As these fluoride synthesis media are known to lead to large crystals, 6 one aim of this work was the production of crystals of suitable size for structure determination.

EXPERIMENTAL Reactants Silica and alumina were introduced either in the form of an amorphous ammonium aluminosilicate (prepared from the sodium form of Tixolex 28 from Rh6ne-Poulenc: SiO2: 80%; A1203: 9.3%; Na20: 5.7%, by exchanges with an ammonium nitrate solution; the residual sodium content is close to 0.1%) or in the form of separate sources, i.e., pseudoboehmite (Catapal B from Vista Corporation with 25 weight % H2 O) and precipitated silica (from Merck, Si/AI molar ratio - 300). The other reactants were tetramethylammonium chloride (TMACI, Fluka purum > 98%), ammonium fluoride (NH4F, Prolabo rectapur > 97%), and triethanolamine (Fluka purissimum).

Synthesis procedure Address reprint requests to Dr. Patarin at the Laboratoire de Matdriaux Mindraux URA-CNRS 428 ENSCMU - UHA, 3, rue Alfred Werner, 68093 Mulhouse Cedex, France. Received 11 March 1994; accepted 11 May 1994

© 1994 Butterworth-Heinemann

The starting mixture was prepared by first dissolving TMACI and NH4F in water. The combined or separated sources of alumina and silica, and in some

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Synthesis of zeofite Nu-1: J. Patarin et al.

Table 1 spectra

Recording conditions of the CP MAS and MAS n.m.r. 13C

19F

29Si

27AI

Standard Frequency (MHz)

TMS CFCI3 TMS AI(H20)e 3+ 75.47 282.41 59.63 78.17 Pulse width (10 -e s) 6.50 3.00 5.50 0.70 Contact time (10 -3 s) 2.00 Recycle time (s) 5.00 4 10.00 3 Spinning rate (Hz) 3500 8000 3400 8000 No. scans 50 100 800 200

cases, triethanolamine, were then added successively under stirring. For instance, in experiment no. 8, the amounts of reactants were the following: TMAC1 5.5 g; NH4F -- 3.7 g; H20 ~ 16.2 g; ammonium form of Tixolex 28 ~ 7.0 g; and triethanolamine 5.6 g. After mixing, the reaction mixture (pH -~ 8-10) was transferred into a Teflon-lined stainlesssteel autoclave and heated under static conditions at the desired temperature. The required time to reach the temperature (170-200°C) is about 4-5 h. After the reaction (pH -~ 8-10), the products were filtered and washed with water. In some cases, the separation of the two main populations, i.e., MTN and Nu-1 materials, was performed by repeated cycles of ultrasonically suspending the solid in water and subsequently decantating the resulting suspension (for experiment no. 8, the ratio between the recovered amounts of Nu-1 and MTN materials was about 0.2). The materials were dried at 80°C overnight. They were checked by optical microscopy and powder X-ray diffraction.

Powder X-ray diffraction

C h e m i c a l analysis Si and AI analysis was performed by inductively coupled plasma emission spectroscopy (accuracy close to 1%). F- was determined by using a fluoride ion-selective electrode after mineralization (accuracy close to 0.1). The amount of water and organic species was obtained by thermogravimetry. I H liquid n.m.r, spectroscopy was also used to determine the content of organic species (see below).

lSc, 19F, 27A1, and 29Si solid-state CP M A S and M A S n.m.r, spectroscopy The spectra were recorded on a Bruker MSL 300 spectrometer. The recording conditions of the CP MAS and MAS spectra are given in Table I. 1H liquid n.m.r, spectroscopy The spectra were recorded on a Bruker AC spectrometer. The recording conditions were as follows: frequency 250.13 MHz; recycle time: 8 s; and pulse width: 2.10- 6 s. The signal of water was suppressed by using the presaturation technique. For quantitative measurements (estimated accuracy close to 2 wt%), a known amount of the as-synthesized Nu-1 samples ( - 30 mg) was dissolved into a 40 weight % aqueous solution of hydrofluoric acid ( 0.3 cm3). After complete dissolution, a known amount of a solution of 1.097 wt% of dioxane in D20 was added ( - 200 mg). After homogenization, about 0.5 cm ~ of the obtained solution and a similar volume of D20 were poured into a Teflon tube (inner diameter 3 mm). The latter was then placed in a classical glass tube for the n.m.r, experiment.

The powder patterns were obtained with CuK0t radiation on a Philips PW 1800 diffractometer.

RESULTS AND DISCUSSION Influence of some crystallization parameters

Thermal analysis

For all syntheses mentioned in Table 2, the combined source of silica and alumina was used. In experiment no. 9, the latter source was previously dealuminated by acid treatment. A few syntheses (not mentioned here) were made with separate sources of

T.g. analysis was performed on a Mettler 1 thermoanalyzer by heating in air at 6°C min-1 and d.t.a, was carried out in air and in argon on a BDL-Setaram M2 apparatus with a similar heating rate. Table 2

Description of the most representative syntheses

Experiment

Starting composition (molar ratios)

Crystal size b

no.

Si02/AI203

Me4NCI/Si02

NH4F/Si02

H20/Si02

Temp. (°C)

Time (d)

Products a (from XRD)

(pro)

1 2 3 4 5 6 7c 8c 9 10 11

16.7 16.7 16.7 16.7 16.7 16.7 16.7 16.7 ~>25.0 16.7 16.7

0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5

1 1 1 1 1 1 1 1 1 1 1

9 9 17 30 30 30 9 9 9 9 9

170 170 170 170 170 170 170 170 170 200 200

5 9 9 5 9 56 15 42 6 1 3

Nu-1 Nu-1 + MTN MTN + (Nu-1) + FER Gel MTN + ((NU-1)) FER + MTN + (NU-1) MTN + (NU-1) MTN + (NU-1) MTN + ((AST)) MTN + ((NH4)zAIF6) FER + MTN

20 20 20 20 5 30 40 -

a Minor phases in parentheses; traces in double parentheses b Largest crystal size of Nu-1 in micrometers CTriethanolamine (0.38 mole) was added to the reaction mixture

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ZEOLITES, 1994, Vol 14, November~December

Synthesis of zeofite Nu-l : J. Patarin et al.

¢o.

C0) Figure 1 Scanning electron micrographs of Nu-1 (sample no. 8): (a) 10 p,m = 2 m m ; (b) 10 I~m = 8 m m ; (c) 10 p.m = 10 mm).

silica and alumina but led to conclusions similar to those discussed thereafter. Zeolite Nu-1 could be synthesized as a pure phase (experiment no. 1) after 5 days of reaction at 170°C. The value of the SiO2/A120.~ molar ratio in the synthesis medium is close to the one generally used for zeolite Nu-1 synthesis;l'2 on the other hand, the water content of the starting gel is rather low. Under similar conditions, but with longer reaction times (experiment nos. 2, 7, and 8), a mixture of Nu-1 and MTN-type clathrasil is obtained, the latter phase being preponderant. In this system, the MTN-type material appears to be more stable than is Nu-1. It should also be noted that the size of the "crystals" of Nu-1 increases with the crystallization time. In fact, as it is mentioned in Table 2, sample nos. 7 and 8 corresponding to the longest reaction times were obtained in the additional presence of triethanolamine. Thus, the presence of this molecule may also play a role in the increase of the crystal size. Such a phenomenon has been shown previously in other systems. 7 The "crystals" of Nu-1 obtained here are significantly larger than the ones prepared from alkaline fluoride-free gels. Figure la shows large twinned crystals of Nu-1 obtained in experiment no. 8. The morphology is pseudocubic, with a dimension close to 40 I~m. However, higher magnifications (Figure lb and c) reveal that each "crystal" is, in fact, an aggregate of small crystallites with a corresponding size near 3 F~m. Such observations hold for the other samples of Nu-1 prepared in this work. When the water content of the synthesis medium is increased and for short crystallization times (experiment nos. 3-5), the Nu-1 content of the product decreases whereas the MTN content increases. The

decrease of the concentrations of the soluble species with dilution, and especially of the aluminum species, favors the formation of the more stable and completely siliceous MTN-type material. When the reaction ume is prolonged up to 56 d (experiment no. 6), FER-type zeolite forms together with the MTN-type clathrasil. Increase of the reaction temperature (experiment nos. 10 and 11) or of the SIO2/A1203 molar ratio (experiment no. 9) prevents the formation of Nu-1. At 200°C, the major phase obtained after 1 d of reaction is the MTN-type material (experiment no. 10); as already mentioned before, FER-type zeolite appears also with an increase of the reaction time (experiment no. 11). From an aluminum-poorer gel (experiment no. 9), the same MTN-tvpe solid is again obtained with traces of octadecasil°(AST-type clathrasil). Finally, all these observations are consistent with Nu-1 being a more metastable phase than is the MTN-type phase. It is quite surprising to observe that in some cases the increase of the reaction time leads to the formation of FER-type zeolite (as a mixture with the MTN-type phase). Indeed, open structures (here of the FER type) are generally less stable than are closed structures (here of the MTN type). All the characterizations made and described thereafter were performed on sample nos. 1, 7, and 8. In the last two cases, the "crystals" of Nu-1 had to be separated from those of the MTN-type phase through successive cycles of sonication and decantation. Such operations are easy because the size of the particles of the type MTN (spherulitic aggregates) is much larger (several hundreds of micrometers) than the size of the aggregates of Nu-1.

Characterization o f zeolite Nu- 1

X-ray diffraction results The powder XRD pattern and the d values of a Nu-1 sample prepared in this work (sample no. 8) are reported in Figure 2 and Table 3. The pattern is similar to the one previously published for Nu-l.1 I , ~o2 7 O0

6 30 5 GO 4 90 4 20 3 50 2 80 2 10 I 40 0 70

5 o

lo o

15 o

20 o

a5 o

30 o

35 o 2 0 ( o i o

o

Figure 2 Powder X-ray diffraction pattern of as-synthesized Nu-1 (sample no. 8) (variable slit opening on the diffractometer).

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Synthesis of zeolite Nu-l : J. Patarin et al. Table 3 Powder X-Ray diffraction data of an as-synthesized zeolite Nu-1 (sample no. 8)

dh,i (A)

I/Io"

dhkl (A)

I/Io"

8.900 8.320 6.560 6.210 5.720 5.650 5.400 4.650 4.460 4.330 . 4.170 4.130 4.070 4.010 3.975 3.882

13 100 24 55 1 9 9 5 37 38 8 22 83 31 77 40

3.836 3.802 3.728 3.597 3.534 3.458 3.290 3.202 3.116 3.042 3.024 2.981 2.945 2.881 2.813 2.779 2.693

44 5 11 4 19 7 18 2 12 4 6 5 7 14 6 15 6

C

~'.5

aThe I/Io values were corrected for constant slit opening

Figure 3

Chemical analysis Table 4 summarizes the data for sample nos. 1, 7, and 8. The Si/A1 molar ratio ranges from about 12 to 14. The content of organic species is close to 10 wt% as shown by 1H liquid n.m.r, and thermogravimetric analysis. The molar ratio organic species/framework T atoms is close to 0.1 (T = Si + A1). According to the IH n.m.r, spectra (Figure 3), the occluded organic species are the Me4N + and Me3NH + ions, the latter arising from the thermal decomposition of the initially present Me4 N+ ions. These Me4N + ions remain preponderant with a molar ratio Me4N+/Me3NH + ranging from about 4 to 5. The molar ratio organic species/A1 is much larger than 1. Part of the alkylammonium cations are probably present as ion-pairs with F- anions. The fluoride content is much higher (1.4 wt%) for sample no. 7 than for sample nos. 1 and 8 (0.8 wt%). The discrepancy may result from the presence of some impurity. This impurity is probably (NH4)~A1F6 and is present in small amounts in all prepared samples (see the paragraphs about the 19F'and 27A1 MAS n.m.r, spectroscopy).

Thermal analysis The d.t.a, and t.g.a, curves of as-synthesized Nu-1 (sample no. 8) are given as an example in Figure 4. Table 4

~i0

2 .'5

PPM

1 7 8

1H liquid n.m.r, spectrum of Nu-1 (sample no. 8), after

Under inert atmosphere, three broad d.t.a, endotherms were observed at 400, 590, and 660°C (Figure 4c). The thermal effects found by d.t.a, under 02 or air occur in the same temperature ranges. The exothermic components consist of a broad drift (T -~ 350°C) that is related to the first endotherm of curve c, followed by two broad signals at 570 and 650°C corresponding to the second and the third endotherms, respectively. These exothermic peaks may be attributed to the thermal decomposition of the organic species occluded in the structure. On the t.g. curve (Figure 4a), three main different steps are observed between 25 and 450°C (weight loss -~ 1.9%), 450 and 600°C (weight loss -~ 0.8%), and 600 and 850°C (weight loss 2.1%). After calcination in air at 950°C for 2 h, the weight loss is close to 9.7%. The resulting product is black, showing that some organic material remains occluded in the structure after such a thermal treatment. Besides, the XRD pattern of this calcined product reveals a partial collapse of the structure. 13C M A S n.m.r, spectroscopy As an example, the ~C MAS n.m.r, spectrum of sample no. 8 is reported in Figure 5. Only one single signal located at 57.6 ppm is observed. This signal

Chemical composition of sample nos. 1, 7, and 8 of zeolite Nu-1 Molar ratios

SiO2

AI2Oz

F

Me4N + a

MezNH + a

Weight loss from t.g. b

79 80 81

5.6 4.8 5.2

0.8 1.4 0.8

9.5 8.3 9.4

1.62 1.44 1.81

10.0 9.2 9.7

Si/AI

R/AI

R/(Si + AI)

F/(Si + AI)

12.0 14.2 13.3

1.44 1.54

0.09 O.11

0.030 0.047 0.030

a Determined from 1H liquid n.m.r, spectroscopy (after dissolution in HF; dioxane was used as an internal standard) u Under air up to 950°C R = organic species (Me4N + + MezNH +)

678

1.5 '

dissolution in HF: (a) dioxane; (b) Me4N+; (c) Me3NH +.

Chemical composition (in weight loss %) Sample no.

210

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Synthesis o f zeolite N u - l : J. Patarin et al.

TG wt loss (%)

(a)

,J

[

J

/

~endo (b)

I

-100

I

-110

I

-120

gppm/TMS Figure 6

,

0

,

,

,

200

400

,

,

,

600

T('C)

I,

800

Figure 4 Thermal analysis of Nu-1 (sample no. 8): (a) t.g. under air; (b) d.t.a, under air; (c) d.t.a, under argon. For clarity, the zero A T levels for the d,t.a, curves were shifted.

corresponds to the carbon atoms of the tetramethylammonium ions. Probably due to its lower sensitivity (in comparison to ]H liquid nmr spectroscopy), this technique does not reveal the presence of the Me3NH + ions. According to the empirical relation established by Hayashi et al., 9 the approximate diameter of the zeolite cage occluding the Me4N + is close to 0.8 nm.

I

I

60

50

oeppm/TMS Figure 5 13C MAS n.m.r, spectrum of Nu-1 (sample no. 8) (the signal at 57.6 ppm corresponds to Me4N + cations).

29Si MAS n.m.r, spectrum of Nu-1 (sample no. 8).

29Si MAS n.m.r, spectroscopy The 29Si MAS n.m.r, spectrum of Nu-1 (sample no. 8) shows a broad and poorly resolved signal, whose maximum is located at about - 1 1 3 ppm (Figure 6). Several overlapping signals may be distinguished and correspond probably to various chemical environments and crystallographic sites of the silicon atoms. In the absence of a structure determination, no assignment can be given.

27Al MAS n.m.r, spectroscopy According to the literature, 2 all A1 atoms are tetracoordinated in Nu-1 with a corresponding chemical shift around 50 ppm. The 2VA1MAS n.m.r, spectrum of sample no. 8 reported in Figure 7 displays two signals: the main asymmetric signal at 51.4 ppm (with a shoulder at low field) corresponds to tetracoordinated A1. The very small signal located at -0.3 ppm can be attributed to hexacoordinated AI. The proportion of hexacoordinated AI is less than 5% for sample no. 8 and slightly higher (ca. 10%) in sample nos. 1 and 7. Taking also into account the 19F MAS n.m.r. spectra (see next paragraph), this hexacoordinated AI may be attributed to the presence of a (NH4)3AIF6 impurity. This impurity is not detectable by X-ray diffraction but is systematically present. 19F MAS n.m.r, spectroscopy All samples of Nu-1 prepared in this work display a ~gF MAS n.m.r, spectrum analogous to the one shown in Figure 8a for sample no. 8. The signals always have the same chemical shifts but various relative intensities. The broad signal at -140.7 ppm with its sidebands (*) is probably due to (NH4)3AIF6 .1° As mentioned before, the presence of such an impurity is responsible for the signal of hexacoordinated AI detected by 27A1 MAS n.m.r, spectroscopy. It should be noted that

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Synthesis of zeolite Nu-l: J. Patarin et al.

100

0

ppm/Al%O) +

Figure 7 27AI MAS n.m.r, spectrum of Nu-1 (sample no. 8) (the signals at 50.0 and -0.3 ppm correspond to tetra- and hexacoordinated AI atoms, respectively).

Nu-1 [except for a minor (NH4)s AIF6 impurity] is possible in a quite narrow range of experimental conditions. The "crystals" of Nu-1 are large with a size up to 40-50 ~tm and display a pseudocubic morphology. Each "crystal" consists, in fact, of an aggregate of small crystallites (ca. 3 ~tm). Thus, the expected preparation of large single crystals was unsuccessful. The thermal behavior of the Nu-1 samples prepared in near-neutral fluoride medium is analogous to the one previously described by other authors. The complete removal of the organic species (by calcination under air) cannot be achieved without a partial collapse of the framework. The SiO2/A1203 molar ratio of the Nu-1 samples is close to 25. The main occluded organic species is the MeaN + cation, a small amount of Me3NH + (arising from the hydrothermal decomposition of Me4N +) being also detected. Several peaks on the lOF MAS n.m.r, spectrum might be specifically attributed to the Nu-1 structure. A clear assignment would obviously require the structure to be determined.

ACKNOWLEDGEMENTS the same broad signal is present on the spectrum (Figure 8b) of the MTN-type clathrasil. A very small signal located at about - 1 2 8 ppm is visible on both spectra and is indicative of the presence of SiF 2 anions. 1 1 In Figure 8a, three other signals can be detected. These signals may correspond to F- anions incorporated into the structure of Nu-1. The chemical shift of the sharp one, i.e., about - 116 ppm, is close to the chemical shift characteristic of a free fluoride anion m an aqueous solution; 12 this signal corresponds, thus, to a mobile fluoride ion. The two other broad signals located at about - 5 8 and - 7 3 ppm might correspond to less mobile F- anions. These differences in mobility could be related to the presence of F- anions inside framework cavities of various sizes. Indeed, the usual chemical shifts of fluoride anions incorporated in zeolite frameworks range from about - 6 0 to - 8 0 ppm. ]° This is the case for MFI-, MTT-, and TON-type zeolites that display 10-membered ring channels. By contrast, octadecasil is characterized by fluoride anions trapped in double fourmembered rings (very small cavities), the 19F n.m.r. chemical shift being close to - 3 8 ppm. 8 Finally, the deconvolution of the spectrum allows to estimate that the three signals located at - 1 1 6 , - 5 8 , and - 7 3 ppm (with the sidebands) correspond approximately to half of the fluoride amount detected by n.m.r. CONCLUSION The preparation of pure zeolite Nu-1 from a fluoride synthesis medium is difficult. In most cases, the additional formation of other phases such as the MTN- and AST-type clathrasils and the FER-type zeolite was observed. However, the synthesis of pure

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ZEOLITES, 1994, Vol 14, November~December

The authors thank Dr. H. Kessler for fruitful discussions, Drs. L. Delmotte and D. Le Nouen for running the n.m.r, spectra, and S. Einhorn for taking the photographs.

a

i

I

-40

I

q

i

-80

-120 - 160 8pprn/CFCI 3

Figure 8 19F MAS n.m.r, spectra of (a) Nu-1 and (b) the MTN-type clathrasil (separated from sample no. 8); (*) and (©) correspond to sidebands of the peaks at - 1 4 0 and - 7 3 ppm, respectively.

Synthesis of zeolite Nu-l: J. Patarin et aL

REFERENCES 1 Whittam, T.V. and Youll, B. US Pat. 4 060 590 (1977) (to ICI) 2 Bellussi, G., Millini, R., Carati, A., Maddinelli, G. and Gervasini A. Zeolites 1990, 10, 642 3 Dewing, J., Spencer, M°S. and Whittam, T.V. Catal. Rev. Sci. Eng. 1985, 27, 461 4 Whittam, T.V. Ger. Offenl. 2 643 928 (1978) (to ICI) 5 Taramasso, M., Perego, G. and Notari, B., in Proceedings of the Fifth International Conference on Zeolites (Ed. L.C.V. Rees) Heyden, Naples, 1980, p. 40 6 Guth, J.L., Kessler, H. and Wey, R., in New Developments in

7 8 9 10 11 12

Zeolite Science and Technology (Eds. Y Murakami, A. lijima and J.W. Ward) Elsevier, Amsterdam, 1986, p. 121 Charnell, J.F.J. Cryst. Growth 1971, 3, 291 Caullet, P., Guth, J.L., Hazm, J. and Lamblin, J.M. Eur. J. Solid State Inorg. Chem. 1991, 28, 345 Hayashi, S., Suzuki, K., Shin, S., Hayamizu, D. and Yamamoto, O. Chem. Phys. Lett. 1985, 113(4), 368 Delmotte, L., Soulard, M., Guth, F., Seive, A., Lopez, A. and Guth, J.L. Zeolites 1990, 10, 778 Dean, P.A.W. and Evans, D.F.J. Chem. Soc. A. 1967, 698 Tong, J.P.K., Langford, C.H. and Stengle, T.R. Can. J. Chem. 1974, 52, 1721

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