Catalytic activity of X and Y nickel zeolites in hydrogenation of ethylene and benzene

Catalytic activity of X and Y nickel zeolites in hydrogenation of ethylene and benzene

CATALYTIC ACTIVITY OF. X AND Y N I C K ~ ZEOLITES IN HYDROGENATION OF ETHYLENE AND BENZENE* V. :P. P A R A N O S E N K O V and Z. V. GRYAZI~OVA M. V...

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CATALYTIC ACTIVITY OF. X AND Y N I C K ~ ZEOLITES IN HYDROGENATION OF ETHYLENE AND BENZENE* V. :P. P A R A N O S E N K O V

and Z. V. GRYAZI~OVA

M. V. Lomonosov State University, Moscow

(Received 29 .May 1973) T ~ catalytic activity of metal-zeolite catalysts in hydrogenation has been little studied. The effect of the type of metal and zeolite structure, metal dislocation in the zeolite lattice and other factors in relation to the hydrogenation activity of zeolites, up to now, remains obscure. During the reduction of iron-exchange forms of zeolites containing nickel, cobalt and rhodium ions, the atoms formed migrate to the external surface of zeolite crystals where metal crystals of up to 100 A in size [1-4] may form over a period of time, Authors of previous papers [5-7] came to the conclusion that the catalytic activity of reduced forms of zeolites is related to the presence of a metal phase, the initial ion-exchange forms under these conditions being inactive [6]. The hydrogenation activity of various ion-exchange forms of Y type zeolites and mordenite was described in former papers [8, 9]. Their activity, however, was variable, required special treatment of catalysts and fairly strict conditions of experiments. In the hydrogenation of propylene [10] Y zeolites were examined in sodium, yttrium, lanthanum and chromium forms. The authors came to the conclusion that the zeolite frame has hydrogenating properties. It was noted that all forms of zeolites have to be treated at high temperature with hydrogen, in order to obtain a .high and stable activity and it was found that activity increased on adding trivalent cations to the zeolite. An attempt was made [11] to evaluate the participation of active centres in macro- and micropores of zeolites. According to results, 70% ethylene and isobutylene molecules on NaA zeolite with 0.22% Pt are converted in the micropores of zeolites. The predominant role of structural factors in catalysis on zeolites was noted in numerous studies. The authors of previous papers [12, 13] indicated this, for example, for hydrogenation. It follows from results that the catalytic activity of reduced forms, of zeolites in hydrogenation depends on many parameters, namely zeolite struc* 1~eftekhimiya 14, 1~o. 4, 576-581, 1974. 146

Catalytic activity of X and Y nickel zeolites

147

ture, metal ions and chemical properties of the metal phase, the latter being, apparently, of decisive importance. Their interaction is probably also of significance. CHARACTERISTICS OF ZEOLITES STUDIED

Degree Zeolite*

NaNiYI NaNiYe NaNiX6

Me% of ion ex%wt. 3.3

8-5 9-6

Eapp, k c a l / m o l e , hydrogenation

change, ethylene benzene % 22.0 56"8 58-8

--

11.7

7"8 12.1 10"5

* The number after the catalyst index characterizes the rate of ion exchange.

This paper is concerned with the catalytic activity of X and Y zeolites with varying nickel contents in hydrogenation of ethylene and benzene, of which the molecules have very different dimensions (4.25 and 6.0 A, respectively). EXPERIMENTAL

Hydrogenation of ethylene and benzene was studied on NaNiYx, NaNiYe and NaNiXe zeolites. Results concerning catalysts are tabulated. Initial ion-exchange forms were calcined in dry air for 2 hr at 400 °. Reduction was carried out with purified hydrogen for 2.5 hr at the same temperature. T h e maintenance of the crystalline lattice before and after reduction was controlled by X-ray. Catalytic properties of zeolites were studied by a pulse method under non-chromatographic conditions. Hydrogen was used as carrier gas and hydrogenating component, with a rate of flow for hydrogenation of ethylene of 100 ml/min and for hydrogenation of benzene--40 ml/min. Catalyst samples weighed between 0.02 and 0-07 g. After hydrogenation of benzene, reaction products were frozen at --196 ° in a quartz trap for 10 min and then analysed chromatographically at 52 ° in a column 150 em long, 0.4 cm in diameter containing zeolite-545 with a stationary phase; 10~ glycerine and 10% wt. tricresylphosphate. In the case of ethylene hydrogenation, freezing lasted for 2 min and reaction products were chromatographically analysed in a column 150 cm long, 0.5 cm in diameter, filled with chromosorb-1 and a carrier gas velocity of 30 ml/min. The ethylene and benzene doses introduced were 0.4 ml and 3.3 ~1, respectively. Peaks of ethylene and ethane, benzene and cyclohexane were recorded on chromatograp~c curves of reaction products obtained at a temperature lower ~han 160 °. On 'increasing the temperature of the reactor to 160-200 °, reaction products of hydrogenation of benzene contained traces of methylcyclopentane. Kinetic experiments on determining the dependence of ethane and cyclohexane yields on

148

V. ]~. PARANOSE~KOV a n d Z. V. GRYAZNOVA

! 1 doses of ethylene and benzene added and the dependence of -- In - - on the ,m 1- - y inverse rate of hydrogen flow established that both reactions using ethylene and benzene were of first order. Since under our conditions the reaction took place with considerable hydrogen excess, according to results of a former study [14] the order in respect of this component was zero. The first overall order in both cases enabled us to use the Basset and Habgood [15] equation for the analysis of kinetic results. Apparent activation energies [E~pp±0.5 kcal/mole, Table) were calculated when analysing results in Arrhenius coordinates. Initial ion-exchange forms of zeolites were inactive under the reaction conditions indicated, whereas reduced forms showed considerable hydrogenating properties (Figs. 1 and 2). NaNiYe zeolite showed maximum activity in hydrogenation of benzene,. Extremal dependence of activity on tem10erature was observed for all zeolites studied. According to the Balandin [16] theory of hydrogenation, inhibition begins to take effect when the heat of adsorption of hydrogen becomes greater than the adsorption heats of hydrogenated materials and reaction products. The activity of all zeolites studied in hydrogenation of ethylene considerably exceeds their activity in the reaction with benzene. In hydrogenation of ethylene on NaNiXs zeolite activity suddenly changes in a narrow range o f temperature, thus hindering the calculation of E~pp for this catalyst. The activity of NaNiY6 zeolite in the temperature range studied is described only by the ascending branch of the curve and up to 400 ° 100~"o conversion is observed. NaNiY 1 zeolite is unstable in this reaction, however, the dependence of activity on temperature and the extremal nature of this relation could still be shown for this sample. The temperature range of hydrogenation of ethylene on NaNiY1 zeolite and maximum activity coincide with the values obtained for NaNiX6 zeolite (Fig. 1). As with hydrogenation of benzene, the activity of NaNiY6 zeolite exceeds the activities of two other catalysts; however, the difference in the activities of zeolites in hydrogenation of ethylene is much lower than in hydrogenation of benzene. This combination of experimental results and values of Eapp suggests t h a t the metal phase is active under the conditions indicated. I t follows from the Table t h a t for the two zeolites studied, NaNiXe and NaNiY6 values of Ear p are close, while for NaNiY 1 zeolite, this value is somewhat lower. The value of Eapp in hydrogenation of ethylene on NaNiYe zeolite is close to the Ea~p value of hydrogenation of benzene. Commensurate values of Eapp were also obtained previously [17] during hydrogenation of ethylene and benzene on NaNiX 8 and NaNiA5 zeolites. The hydrogenation properties of these zeolites were examined by the same method and it was shown that the metal phase was active. W e established previously [18] that on metal-zeolite eat-

Catalytic activity of X and Y nickel zeolites

149

alysts under similar conditions benzene was hydrogenated by the system:

Commensurate values of Eapp obtained during hydrogenation of ethylene and benzene on various zeolites containing nickel, apparently, support the view that hydrogenation of benzene, like hydrogenation of ethylene, takes place in stages on a doublet active centre [19]. A considerably higher activity of zeolites studied in hydrogenation of e t h y l e n ~ compared with hydrogenation of benzene, is probably due t o the fact that a larger number of active centres and higher energy consumption of hydrogenation of benzene characterize ethylene molecules of smaller size. Since values of Eapp in hydrogenation of benzene on NaNiY n and NaNiX e zeolites are similar, proving the same efficiency of active centres of these catalysts [19], the higher activity of NaNiY e zeolite in this reaction may be due to a higher dispersion of nickel in NaNiY6 zeolite, i.e. the presence in this zeolite of a large number of active centres accessible to benzene. A study of o-p-conversion of hydrogen on nickel zeolites shows that at temperatures of hydrogenation of hydrocarbons the ion-exchange and decationized forms of zeolites are inactive in this process. On reduced forms of nickel-zeolite catalysts o-p-conversion of hydrogen is observed, which also suggests that the metal phase is active in this process. NaNiXe and NaNiYe zeolites showed practically identical activities in ortho-para-conversion of hydrogen. Bearing in mind the absence of steric hindrances for small hydrogen molecules (2.4 A) and the high nickel content of NaNiX s zeolite, the same activity of both zeolites also proves a higher dispersion of nickel in a NaNiY e catalyst, compared with NaNiX~. In addition to results derived in our study for NaNiY1, NaNiY~ and NaNiX s zeolites, Fig. 2 shows the dependence on temperature of the specific activity of hydrogenation of benzene for NaNiX 8 zeolite [17]; it follows from this Figure that NaNiX 3 zeolite is more active in this reaction, although the content of nickel metal, according to former results [17], is lower in NaNiX6 zeolite. It is known [6] that the metal phase ,was recorded in this zeolite by X-ray, while in a NaNiX 3 sample this phase was not detected by X-ray. However, nickel metal was detected in this sample by chemical analysis [17], from which it was concluded that the metal phase in NaNiX3 zeolite was more dispersed, compared with NaNiX e zeolite. Therefore, a lower activity of NaNiX8 zeolite in: hydrogenation of benzene was apparently, explained by two factors: 1) the formation of small metal crystals, which reduced the number of active centres, 2) crystalline nickel formations, which created steric hindrances to benzene molecules. The latter is also confirmed by the following results. A NaNiYI~ sample, in which 63.5~/o of sodium ions are exchanged by

150

V.P.

PARANOSENKOV and Z. V. GRYAZNOVA

nickel cations, after 2 hr in hydrogen during reduction and hydrogenation of benzene, became fully inactive in this reaction. The retention volume for benzene also changed from 389 ml (300 °) to zero, while for ethylene, from 455 (50 °) to 167 ml. This suggests that the small nickel crystals formed are situated near the openings of zeolite and hinder the penetration of benzene inside large cavities, but do not impede smaller ethylene molecules. It is known that at a temperature of 0.3-0-4 m.p. surface mobility of metal atoms is observed. It is shown [20] that if a platinum catalyst is kept at 700 ° and then rapidly cooled to room temperature ("quenched"), as a result of atomization, i.e. changing the number and quality of active centres, catalyst activity and selectivity alters. We used this method for metal-zeolite systems. A NaNiY1s catalyst was kept for 1 hr at 550 ° and then "quenched" by cooling for a few seconds to room temperature--this catalyst fully recovered its activity. y/m

yaw

30

8

20 q /O 2 I

I

100

lO0 FIG. 1

I

180~°0

I

I

too

I

I

I

t¢o

I

180

I

I

22~T, °C

Fro. 2

FIG. 1. Temperature dependence of the activity of zeolites in hydrogenation of ethylene: © --NaNiY6 ; • --NaNiX6, ~TaNiY1. Fro. 2. Temperature dependence of the a c t i v i t y of zeolites in hydrogenation of benzene: (3--NaNiYe; A - - N a N i X s ; 0 - - N a N i Y ~ ; ~ - - N a N i X 3 , according to results previously obtained [17].

It is indicated [21] that with a reduction in the degree of exchange in zeolites containing nickel, maximum activities in hydrogenation of benzene are displaced to the high temperature region, which is observed in our case. The proportion of metal phase decreases in the same direction [17]. Zeolites obtained by reduction of ion-exchange forms and containing a variable amount of metal phase are distinguished by ion density and degrees of decationation, i.e. the substrate of the metal phase shows a marked variation. Results confirm that the zeolite substrate is not inert and determines the state of the metal in the zeolite and energy conditions of the process. This is also confirmed by the fact that the degree of reduction of nickel zeolites depends on the type of zeolite and varies in the order A > X > Y, the distribution of the metal being different in different types of zeolite structure. Thus, in NaNiXs in which the degree of exchange of sodium ions by nickel ions is close to NaaNiY12 {58-8

Catalytic activity of X and Y nickel zcolites

151

a n d 6 3 . 5 ~ , respectively), t h e c o n t e n t o f nickel m e t a l in N a N i X e b e i n g cons i d e r a b l y higher owing to a high ionic d e n s i t y a n d degree o f reduction, for b e n z e n e molecules t h e openings of zeolite are n o t fully screened b y m e t a l , as o b s e r v e d in a NaNiY12 sample. SUMMARY

1. A s t u d y was m a d e of h y d r o g e n a t i o n o f e t h y l e n e a n d b e n z e n e on X a n d Y zeolites containing nickel. I t was s h o w n t h a t h y d r o g e n a t i o n u n d e r t h e conditions selected t a k e s place on t h e a c t i v e m e t a l surface, on d o u b l e t a c t i v e centres, t h e h y d r o g e n a t i o n a c t i v i t y of zeolites d e p e n d i n g l a r g e l y on t h e dispersion o f t h e metal. 2. Zeolite is n o t a n i n e r t carrier of t h e m e t a l phase. A r e d u c t i o n in t h e c o n t e n t o f nickel cations, dispersion a n d t h e p r o p o r t i o n of t h e m e t a l p h a s e displaces to the high t e m p e r a t u r e region the a c t i v i t y m a x i m u m of m e t a l - z e o lite c a t a l y s t s in h y d r o g e n a t i o n of h y d r o c a r b o n s . REFERENCES 1. Z. V. GRYAZNOVA, A.A. BALANDIN, Z.F. GLOTOVA, G.V. PITSISHVILI, T. G.

ANDRONIKASHVILI and A. Yu. KRUPENNIKOVA, Dokh AN SSSR 175, 381, 1967 2. D. J. A. YATES, J. Phys. Chem. 69, 1976, 1965 3. A. M. RUBINSHTEIN, Kh. M. lVHNACHEV, A. A. SLINKIN, V. I. GARANIN and G. A. ASHAVSKAYA, Izv. AN SSSR, Ser. khim., 786, 1968 4. D. H. LEWIS, J. Catalysis 11, 162, 1968 5. M. SELENINA and K. WENCKE, Monatsberiehte Dtseh. Akad. Wiss. Berlin 8, 886, 1966 6. Z. F. 'GLOTOVA, Z. V. GRYAZNOVA, G. V. PITSISHVILI, T. G. ANDRONIKASHVILI and A. Yu. KRUPENNIKOVA, Soobshch. AN Gruz. SSR 54, 89, 1969 7. Kh. M. MINACHEV, V. I. GARANIN, L. I. PIGUZOVA and A. S. VITUKHINA, Izv. AN SSSR, Ser. khim., 1001, 1966 8. G. M. MINACHEV, V. I. GARANIN, T. A. ISAKOVA and V. V. KHARLAMOV, Tzv. AN SSSR, Set. khim., 481, 1969 9. Kh. M, MINACHEV, L. K. SHCHUKINA, M. A. MARKOV and R. D. DMITRIYEV, Neftekhimiya 8, 37, 1968 10. K. V. TOPCHIYEVA, L. L. SHAKHNOVSKAYA, Ye. N. ROSOLOVSKAYA, S. P. ZHDANOV and N. N. SAMULEVICH, Kinetika i kataliz 18, 1453, 1972 11. Y. BERNARD, C. CLAUDE and L. PIERRE, Bull. Soc. Chim. France 2, 709, 1966 12. Z. V. GRYAZNOVA and Ye. V. KOLODIYEVA, Dokl. AN SSSR 190, 1383, 1970 13. Z.V. GRYAZNOVA, Ye. V. KOLODIYEVA, A. Yu. KRUPENNIKOVA, T. G. ANDRONIKASHVILI and V. P. PARANOSENKOV, Soobshcheniya AN GruzSSR 68, 85, 1972 14. "T. A. DENISOVA, K. P. LAVROVSKII and A. A. ROZENTAL', Neftekhimiya 8, 326, 1968 15. D. M. BASSET and H. W. HABGOOD, J. Phys. Chem. 64, 769, 1960 16. A. A. BALANDIN, Zh. obshch, khimii 15, 608, 1945 17. Ye. V. KOLODIYEVA, Kand. dis. MGU, 1972 18. Z. V. GRYAZNOVA and V. P. PARANOSENKOV, Dokl. AN SSSR 212, 104, 1973 19. V. P. LEBEDEV, Sovremennye problemy fizicheskoi khimil 8, Moscow, 1969 20. V. M. GRYAZNOV, V. D. YAGODOVS~H and V. I. 8HIMYLI8, Kinetika i kataliz 2, 221, 1961 21. Z. F. YEGORUSHKINA, Kanda. dis. MGU, 1969