alsdorf et al 1988. methods for characterization and their influence on the structure of...

7/28/2019 Alsdorf Et Al 1988. Methods for Characterization and Their Influence on the Structure of Silicon-rich Zeolites

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Journal of Thermal Analysis Vol. 33 (1988) 691-698M E T H O D S F O R C H A R A C T E R I Z A T I O NA N D T H E I R I N F L U E N C E O N T H E S T R U C T U R EO F S I L I C O N - R I C H Z E O L I T E S

E. Alsdorf, M. Feist*, Ho Fichtner-Schmittler,H.-H. Jerschkewitz, U. Lohse a n d B. ParlitzCENTRA L INSTITUTE OF PHY SICAL CHEMISTRY, ACADEMYOF SCIENCES OF THE G.D.R., BERL IN-ADL ERSH OF, 1199 G.D.R.*CHEMISTRY DEP ARTM ENT, H UMB OLDT U NIVERSITY , BERLIN , 1040, G.D.R.

H, Li, Na, C s, NH+, Mg and A1-ZSM 5 zeolites and H and N H,-mordenites were studied byDTA, X-ray diffraction, TPD and adsorption measurements. The stability relating todealumination and structure destruction depe nds on the nature of the cation.

H an d NH4 -ZS M 5 were strongly dealuminated to silicalitelike phases in the temperaturerange 973-1273 K during the course of the DTA measurement. NH4-mordenite wasdealuminated below 873 K in the T PD experiment on the deamm onization.The thermal destruction ofZ SM 5 containing N a +, Mg2 AP + and Cs + ions begins at about1400 K. Excess sodium ions present in the-original Na- ZS M 5 decreased the thermal stability.Fo r H a nd N H4-mordenites, complete amorphization was found at 1270 K.

T h e c a t a l y t ic p r o p e r ti e s o f Z S M 5 c a n b e m o d i f i ed b y i o n - e x c h an g e . I n t hi s p ap e r ,d a t a o n t h e t h e r m a l s t a b i l i t y , t h e a c i d s i t e s a n d t h e p o r e v o l u m e a r e p r e s e n t e d f o rZS M 5 z e o l i te s c on t a in in g d i f f e r e n t me t a l i ons .

ExperimentalSample preparation

T h e s a m p l e s a re l is te d i n T a b l e 1. F r o m c o m m e r c i a l N a - Z S M 5 ( s a m p l e 6 : H S - 3 0 ,V E B C K B i t t e r f e l d ) , s a m p l e s 4, 5 a n d 7 - 9 w e r e p r e p a r e d b y io n - e x c h a n g e i n 0 .1 Ns a lt s o lu t i o n . S a m p l e 1 0 w a s o b t a i n e d b y t r e a t m e n t w i t h H N O 3 . T h e d e a l u m i n a t i o no f s a m p l e 4 l e a d t o sa m p l e s 1 - 3 . T h e p a r e n t s a m p l e 6 w a s f u r t h e r m o d i f i e d b yw a s h i n g t o e l im i n a t e t h e e xc e ss s o d i u m , a n d a s e c o n d N a - Z S M 5 z e o li te w a sp r e p a r e d b y N a + - e x c h a n g e o f s a m p l e 4 ( T a b l e 2 ).

John Wiley& Sons, Limited, ChichesterAkaddmiai Kiad6, Budapest


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692 ALSDORF et al.: METHODS FOR CHARAC TERIZATI ONTable 1 Composition of the samples and TPD results

Sample Al/u.c.TPD peak area,Cation mmol/g

degree of exchange, radius,% A 520 K 720 K1 HZSM 5 4.9 100 1.25 0.62 HZSM 5 1.5 1003 HZSM 5 0.8 1004 NH~ZSM 5 5.4 100 1.43. 0.655 LiZSM 5 5.4 * 0.60 1.18 0.146 NaZSM 5 5.4 100 0.95 0.747 CsZSM 5 5.4 * 1.69 08 M gZSM 5 5.4 66 0.65 1.11 0.319 A1ZSM 5 5.4 66 0.50 , 1.0 0.32

10 HZSM 5 5.4 10t)I l modernite

H + form 3.0 100NH + form 6.4 100* probably I00%.

I n s t r umen ta lTherm al analysis: an S TA 429 Netzsch G-er~itebau G m bH , F R G ; dried N 270 ml rain -1, 5-10 deg ra in-1, 30-50 mg, and a M O M derivatograph, Budapest,

Hu ngary , 5 deg min - 1, 170 mg; T PD of NH3 : 12 and 4 deg m in - 1, a stream o f He,a thermal conductivity detector; X-ray: a Guinier-type camera, CuK~ radiation.

R esails and d iscussionThermal analysis and X~ray

H -Z SM 5 did not sho w any marked effect in the DTA curves (Fig. 1) on heating to1273 K. However, X-ray investigations revealed that strong dealumination occursand silicate-likesamples are formed (Tab le 2). The dealum ination is also confirmedby the reduction in the uptake of water [I ].

Between 1370 and 1570 K, a ve ry wea k exothermic deviation fro m the base line isobserved, which corresponds to the collapse of the zeolitic structure. T he am orp hou smaterial crystallized at ab ou t 1690 K t o ~t-cristobalite, as indicated b y an exotherm icpeak in the DTA curve.

O f the ZSM 5 samples containing dif ferent cations, the or iginal N a-Z SM 5 showsJ. Thermal Anal. 33, 1988


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A L S D O R F e t a l. : M E T H O D S F O R C H A R A C T E R I Z A T I O N

Table 2 X-ray and DTA resultsTreatment, Products

Sample KD T A ,

exothermic

6 9 3

1 HZ SM 5 1273 ZSM 5 dealuminated1610 a-, B-cristobalite, amo rph.1700 ~-, p-cri stob alite

I0 HZ SM 5 as 1 as 12 HZSM 53 HZSM 56 NaZSM 5

original

N a Z S M 5washedN a Z S M 5exchang.

7 CsZSM 5

8 MgZSM 5

9 AIZSM 5

11 H-mordenlte

1273 ZSM 5 dealumiuated1273 ZSM 5 dealum inatcd1170 residual ZSM 5, amo rphou s1273 ~t-quartz, a-cri stob alite

fl-cristobalite-like(tetragonal)

1540 ~t-, fl-cristobalite -likeNa6Al4Si,,O7

1720 a-, fl-cristoba lite-like1 2 7 3 m a inly ZSM 51273 ZS M 51273 ZS M 514 73 residual ZSM 51718 residual ZS M 5, fl-cristob.q273 ZSM 51423 residual ZS M 5, fl-cristob.1573 ~t-, fl-cr isto bali tr1273 ZS M 514 58 residual ZSM 5, f l-cr istob.1720 ~t-, fl-cr istob alitr1 2 7 3 am o r p h o u si 573 mullite, ~-cristobalite1700 mull ite, ~-, fl-cristobal.

1 1 7 0 - 1 4 4 0 weak1682 Tp*

-1170-1520 weak1665 Tp

1290 Tp

> 1540 sintering

> 1375 sintering> 1420 sinte ring

> 1490 sintering

1465 Tp

> 1477 sintering1280 Tp1470 Tp> 1620 sintering

* Tp = temperature of the peak maximum.

the lowes ttherm al stability. A partial structural destruction w as already observed at1170 K. A sharp exothermic peak at 1290 K marked the complete transformationinto ~t- and fl-cristobalite. Since the thermal stability increases after wash ing of thesample, the relative instability is due to the excess o f sodiu m in this sample(Na/Al -- 1.13).

The fhermal desctruction of ZSM 5 containing M g 2 + , AI a+ and CS + ions(transformation into ~t- and fl-cristobalite) begins at about 1400 K.

9 J. Thermal Anal . 33, 1988


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6 9 4 A L S D O R F e t a l. : M E T H O D S F O R C H A R A C T E R I Z A T I O N

I 1 I l1273 1373 1473 1573 1673Temperature,KFig. 1 DTA curves on HZS M 5 , ca t ion exchanged ZSM 5 and mordeni te

60 .8 , v - - . - - J

0 2 F ~ "1 I I 1 I1 l O l O z l o ' I o 'p , l ~Fig. 2 Adsorp t ion iso therms ofn-hexane on ca t ion exchanged ZSM 5

J. Thermal Anal. 33, 1988


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A L S D O R F e t a l. : M E T H O D S F O R C H A R A C T E R I Z A T I O N 6 95

Fo r mordenite, a wea k exothermic peak is fou nd at 1270-1280 K in the DT A. TheX-ray investigation revealed the complete amorphization of the sample. A furtherexothermic peak (1470 K) and sintering (a bove 1560 K) m ark the formation ofmuUite an d small am ou nts o f ct-cristobalite, respectively. Ab ov e 1700 K, fl-cristobalite too is formed.

Adsorption isothermsAdsorption isotherms of n-hexane on ZSM 5 exchanged with Li Na Cs

M g 2+ and A13+ are given in Fig. 2. the a dsorp tion capacity of 1.2 mm ol g- i(0.16 cm a g -l ) lies in the range o f the usual values. In the case of Cs -Z SM 5, onlyhalf of this value is found. The large Cs ion probab ly blocks par t of the channelsystem in the ZSM 5 structure [2].Temperature-programmed N H a desorption

In agreement with the l iterature [3] , the TP D curves of H -Z SM 5 show twomaxima (a t abou t 520 and 720 K; Fig. 3) . In the thermal decomposit ion o fNH 4-Z SM 5, a unique peak a t 720 K corresponds to the chemisorption o f N H a onBrfnsted acid sites [1]. The TP D curves of H -Z SM 5 are completely reproducible inrepeated runs, i.e. no changes are detectable.

r te tI II ; A1 t , , 1 ~ .: " I : , ' 1 1i I # Ii t, , , I " II t I I bi . t O l t

l V l I

~ i/ / " l- - J - I / I I I ~ k l ID473 573 673 773 873

Ternpero tu re , KFig. 3 TPD of NH a on ZSM 5

a ) th e r m a l d ecom p o s i ti o n o f NH ,ZS M 5 to HZSM 5 "b ) NH a d eso rp t io n o n HZSM 5 /NH4 ZSM 5

(adsorption at 390 K, heating rate 12 deg rain -1, 100 rag)

9* J. Thermal Anal. 33, 1988


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6 96 A L S D O R F e t a l. : M E T H O D S F O R C H A R A C T E R I Z A T I O N

" \ i . . . . . . . . N ~- - , F - ~

E o ig :

" . . . . .,~176 ~

/.'73 57 3 67 3 773 873Tem perature, K

Fig. 4 TP D of NH 3 On ca t ion exchanged ZSM 5(Conditions as in Figure 3b),

A

l!T ~

~ J i .I4 7 3 5 7 3 6 7 3

: %. , > . . . . . u: ~ , ? . . . . . . . . . Mg

% , , . \% I

" '%ei~o"

' . , ' , , , , . . . . .7 7 3 8 7 3 9 7 3TemperQture, K

--D,

Fig. 5 TP D of NH 3 on ca t ion exchanged ZSM 5

~n

"D !i

I/&73

C t

\573 673 773 873 973

Temperature, K"Fig. 6 T PD of NH 3 on m ordeni te

a) thermal decomposi t ion o f N H 4mordeni te to H m ordeni teb) NH 3 dcsorp t ion on H mordeni tc(conditions as in Figure 3b)

D

._ g

S ,473 573G

bt%1 %

||ttI |II

I%[ I \1673 773 873 973Temperoture, K

Fig. 7 Comparison of the thermal decompositionof NH4-mordeni te (a ) and N H, ZS M 5 (b)

J . T h e r m a l A n a l . 3 3 , 1 9 8 8


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A L S D O R F e t a l.: M E T H O D S F O R C H A R A C T E R I Z A T I O N 6 97

T he 520 K peak reflects the interaction o f NI-I3 with centres weaker than thezeolitic cations. T he'influence of the radius and ch arge o f the cation is demonstratedin Fig s 4 and 5 and in Tab le 1. In the alkali metal series, th e peak area decreases w ithincreasing cation radius, in accordance with the results reported by Derewinski etal. [4].

In contrast to H -Z S M 5, mordenite is already c hang ed during th e thermaldecomposition of the N H 2 form. Fig ure 6 demonstrates the reduction o f the high-temperature peak d ue to dealumination. T he b roader distribu tion of the acid strengthfor mordenite as compared with Z S M 5 follows from F igs 7 and 8 [5].

/ 1 i 1t- A t i :,.Q

/.73 573 673 773 873Temperoture,KF'~g. 8 Comp arison of NH 3 TP D on H-mo rdenite (a) and HZ SM 5 (b)

R e f e r e n c e s

1 E. Alsdorf, M. Feist, H. Fichtner-Schmittler,Th. Gross, H .J . Jerschkewitz, U. Lo hse and B.Parlitz, Adsorption Science and Technology,submitted.

2 Pingdong Wu and Yi Hua Ma, 6 th Interna-tional Zeolite Conference, Reno 1983.

3 N. Topsoe, K. Petersen and E. Derouane, J .Catal., 70 (1981) 41.

4 M. Derewinski, J. Haber, J; PtaszyBski, J. A.Lerscher and G. Rumplmayr, Proceedings ofthe 7th International Zeolite Conference (ed. byM urakami et al.) Tokyo 1986, 957.

5 D. Kall6, I . Bankbs and J. Papp, ProceedingsInternational S ympo sium on Zeolite Catalysis ,Si6fok, Hungary 1985, 329.

J . Therm al Ana l . 33 , 1988


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698 ALSDORF et al.: METHODS FOR CHARACT ERIZATI ON

Zmammtenfassa~g--H-, Li-, Na-, Cs-, NH4-, Mg- und A1-Ze01ithe ZSM 5 sowie H- und NH4-Mordenitwurden durch DTA, Rbntgenbeugung, temperaturprogrammierte Desorption (TPD) und Adsorp-tionsmessungen untersuchL Die Stabilitfit gegeni iber Dealuminierung und Strukturzusammenbruchh/ingt yon der Art des Kations ab. H- und NH4-ZSM 5 werden im Verlauf der DTA-Messungen imBereich 97Y-1273 K zu Silicalit-/ihnlichen Phasen dealuminiert. NH,-Mordenit wird unterhalb 873 Kbei der Ammoniakabspaltung im TPD-Experiment dealuminiert. Der thermische Zusammenbruch vonNa-, Mg-~ AI- und Cs-ZSM 5 beginnt um 1400 K. Im urspriinglichen NaZSM 5 vorhande nefiberschfissige Natriumionen verringem seine thermische Stabilitfit. Fiir H- und NH4-Morden it wird bei1270 K vollstgndige Amorphisie rung gefunden.

P e 3 ~ e - - MeTo~aM~ ~[TA,. pe/iTrenoqba3osoro aHa.aaaa H a~cop6nna HayqeHI~IH, Li, Na, Cs, NH 4,Mg, AI ZSM 5 HOD21HTIaI H H-, NH4-M0p/IeHRTbL YC'FOfiqHBOCTb C ~eamoMnnHpoBaanHm n xapaxTep~ecTpytny~ 3aeMcsrr OT Tuna raTl~Otta. MeTO~OM~[TA ycTanoaaeno, qTO o6p aau~ H- H NH4---ZSM 5B unTepaa~e TOMlIepaTyp 973---1273 no~epra~oTcg anTeacnanoMy ~eaamsmHxpoaaamo c o6-pa3onaHtteM C~aTOnO2106HI, IX dpa3. rIpH npo~e~emm TI-I~[ a~cnepaMeaToa ycTanosaeno, aTO NH 4-Mop~ICmtT lea.~oM~tnnpyeTca aaxe TeMnepaTypbl 873 K. Tep~aaecKaa ~eCTpyKtmao6pa3IIoa ZSM 5IleozmTo~, co~ep~aml4x ~ou~ naTpHa, tleana, Marana a a~mManas, nasmHacTca ap a TCMllCpaTyprOXOaO 1400 K. Haaaqae g36bZTO~ab~x aOHOB aaTpaa n aCXO~OM o6paaur IIr NaZSM 5yMeasmacT cro TepMoycTofiqHnOCTb. Flo:maa aMop#pa3auaa H/NH4-Mop~ea~Ta npogcxoaHT npa1270 K.

J . T herma l Ana l . 33 , 1988

alsdorf et al 1988. methods for characterization and their influence on the structure of...

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