Journal of Molecular Catalysis, 49 (1989) L43 - L46 L43

Enhancement of Ethylene Metathesis Rate by Adsorbate Interaction between Ethylene and Carbon Monoxide

TAKASHI SUZUKI*, SADAO HAYASHI, TOSHIHIRO HIRAI

Department of Chemistry, Faculty of Textile Science and Technology, Shinshu University. 3-15-1, Tokida, Ueda-shi, Nagano-ken 386 (Japan)

KATSUMI TANAKA and ISAMU TOYOSHIMA

Research Institute for Catalysis, Hokkaido University. Kita-ku, Sapporo 060 (Japan)

(Received September 2,1988; accepted October, 5,1988)

Introduction It has been proved that olefin metathesis proceeds via metal alkylidene

and metallacyclobutane intermediates in homogeneous systems [ 1 - 51. These are also demonstrated species in olefin metathesis on heterogeneous catalysts [ 61. In general, CO decreases the olefin metathesis activity of both a reduced heterogeneous [ 7, 81 and a homogeneous metathesis catalyst [ 91. In contrast to these, the metathesis activity of a homogeneous tungsten halide complex with EtAIClz is enhanced in the presence of CO and the formation of tungsten carbonyl derivatives is assumed [lo].

In this paper, it is reported that adsorbed CO increases the ethylene metathesis rate ( C2H,- 12C2 + C2Hc13C2 - 2C2H,-13C1) due to an electronic effect induced by the adsorbate interaction between ethylene and CO on a reduced molybdena silica catalyst. This may be the first case in which a metathesis rate has been enhanced by CO on a heterogeneous catalyst.

Experimental Commercial grade silica gel, Si02 (Kieselgel 60, Merck) with surface

area of 465 m2gw1 was used. The Si02 was immersed in an aqueous solution of ammoniumparamolybdate, (NH,)&l0,0~~*4H,0 (Wako Chemical), to contain 2.8 mol% of MO to Si02, and was dried in an oven at 120 “C for 12 h. The starting material was activated by evacuation and reduction with H, (ca. 150 torr, 1 ton = 133.3 Pa) at 500 “C for 1 h. Finally the catalyst was evacuated at 500 “C for 1 h, to yield the reduced Mo0,/Si02. Partially reduced Mo0,/Si02 was prepared by reoxidation of MoO,/SiO, using a 1 :l mixture of N,O and H, (total 60 torr) at 200 “C for 30 min. The catalyst was then subjected to ethylene metathesis at 25 “C. Catalyst activation and

*Author to whom correspondence should be addressed.

0304-5102/89/$3.50 0 Elsevier Sequoia/Printed in The Netherlands

L44

reaction were carried out in a circulation system with a volume of 280 ml. The rate of formation of CzH4-‘% 1 (metathesis) was measured with a 1 :l mixture of C2H,- 12C2 and -13C2 (total 7.5 torr) on 20 mg of a catalyst. Deter- mination of C2H,- 13C1 in ethylene was carried out by mass spectrometry with 10 - 14 V ionization voltage to measure parent ion peaks. Temperature programmed desorption (TPD) was carried out on MoO,/SiO, and MOO,/ Si02 (1 g) under flowing He with a linear heating rate of 5 “C mm-’ and the desorbed gas was analyzed by quadrupole mass spectrometry. C2H, (10 torr), CO (10 torr) and a 1:l mixture of C2H, and CO (total 20 torr) were con- tacted on the catalyst surface at 25 “C for 30 min, followed by evacuation at the same temperature, before the TPD experiment.

Results and discussion When a 1:l mixture of C2H4-12C2 and -13C2 (total 7.5 torr) was reacted

on Mo0,/Si02 (20 mg) at 25 “C, C2H,- 13C1 was formed by metathesis with a rate constant of 5.0 X 10M2 min-‘. As shown in Fig. 1 (0) the rate constant of metathesis on the catalyst was increased in the presence of 9 torr of CO(g) (7.7 X 10e2 min-‘). After 20 min of the reaction, ethylene was trap- ped at liquid nitrogen temperature and CO(g) was removed by the evacua- tion. The metathesis was then continued at 25 “C; interestingly, the rate again increased to 11.8 X low2 min -l. From these results, it can be concluded that the rate of ethylene metathesis was enhanced in the presence of CO(a) on the catalyst by a factor of 2.4.

This may be the first case in which a metathesis rate has been enhanced in the presence of CO(a) on a heterogeneous catalyst. Such ethylene meta- thesis rate enhancement was not observed on Mo0,/Si02 as shown in Fig. 1 (0).

+CD 9 Torr

Fig. 1. Ethylene metathesis rate on MoO,/SiOz and MoO,/SiOz in the presence and ab- sence of CO at 25 “C. o; MoO,/SiOz (reduced), l ; MoO,/SiOz (partially reduced).

L45

TABLE 1

Temperature programmed desorption (TPD) of (&Ha(a) and CO(a) on MoO,/SiOz’and MoO,/SiOz

Catalyst Run Adsorbed Desorbed Desorbed max. Desorbed amount gas gas (Temp./X) (mol.% to MO)

MoO,/SiOa C2H4 50 3.15 (reduced) 1 CzH4 C3H6 150 2.55

C4H8 150 4.14

2 co co 70 0.29

3 co + C2H4 {Eg4 60 7.

0.25 2.44

MoO,/SiO2 I C2H4 65 0.63 (partially reduced) 4 c2H4 c$6 150 trace

C4Hs 150 trace

5 co co 70 0.15

6 co + C2H4 {g>, ;; 0.15 0.06

Catalyst: 1 g, rate of temperature increase: 5 “C min-‘, He flow rate: 40 ml min-‘.

To obtain further information of the role of CO(a) on the metathesis reaction in our system, MoO,/SiOz and MoO,/SiO, were subjected to TPD. These results are summarized in Table 1. Propylene and butenes were formed in runs 1 and 4, by homologation of ethylene and successively occurring metathesis of propylene, respectively. These reactions were completely inhibited in the presence of CO as shown in runs 3 and 6. It is significant to note that the desorption peak of CzH4 was shifted from 50 “C in the ab- sence of CO to 70 “C in the presence of CO (compare runs 1 and 3) and that the CO peak was shifted back from 70 “C to 60 “C in the presence of ethyl- ene (compare runs 2 and 3). However, such adsorbate interaction between ethylene and CO was not observed on partially reduced MoO,/SiO,, which exhibited a fair amount of desorbed C,H, in the presence of CO.

In conclusion, adsorbed CO dramatically enhances the activity of adsorbed CzH4 in metathesis and as a result increases the rate of ethylene metathesis. This is attributed to an electronic effect induced by the adsor- bate interaction between C2H, and CO.

References K. J. Ivin, Olefin Metathesis, Academic Press, New York, 1983. J. J. Rooney and A. J. Stewart, Catalysis, Specialist Periodical Reports, Vol. 1, The Royal Society of Chemistry, London, 1977, p. 277. N. Calderon, J. P. Lawrence and E. A. Ofstead, Adv. Organometall. Chem., 17 (1979) 499. R. H. Grubbs, in G. Wilkinson (ed.), Comprehensive Organometallic Chemistry, Vol. 8, Pergamon Press, Oxford, 1985, p. 499.

L46

5 C. P. Casey, in M. Jones and M. A. Moss (eds.), Reactive Intermediates, Vol. 3, Wiley, Chichester, 1985, p. 109.

6 K. Tanaka, K. Tanaka, H. Takeo and C. Matsumura, J. Am. Chem. Sot., 109 (1987) 2422.

7 R. H. Howe, D. E. Davidson and D. A. Whan, J. Chem. Sot., Faraday Trans. 1, 68 (1972) 2266.

8 A. Brenner, D. A. Hucul and S. J. Hardeick, Znorg. Chem., 18 (1979) 1478. 9 C. P. Casey and A. J. Shusterman,J. Mol. Catal., 8 (1980) 1.

10 L. Bencze and L. Marko, J. Organometall. Chem., 28 (1971) 271.