DBH VII. Oxidative dehydrogenation of alkylaromatics

~

A PT PA LE IY DSS CA L I A: GENERAL

Applied Catalysis A: General 142 (1996) 19-29

ELSEVIER

Gas phase oxygen oxidation of alkylaromatics over CVD Fe/Mo/borosilicate molecular sieve, Fe/Mo/DBH VII. Oxidative dehydrogenation of alkylaromatics Jin S. Y o o l Amoco Research Center, Mail station H-2, P.O. Box 3011, Naperville, IL 60566, USA

Received 5 September 1995; revised 24 January 1996; accepted 25 January 1996

Abstract

Over the chemical vapor deposited (CVD) F e / M o / D B H catalyst, alkylaromatics such as ethylbenzene, p-diethylbenzene, p-ethyltoluene and p-(t-butyl)ethylbenzene were dehydrogenated to the corresponding alkenylaromatics by O 2 gas phase oxidation with or without CO 2. The resulting alkenyl group was further oxidized to oxygenates such as aldehyde, ketone and carboxylic acid by secondary oxidation. Carbon dioxide promoted hydrogen abstraction from the alkylaromatic substrates, but it adversely affected oxidation of the resulting alkenyl group to oxygenates in the secondary reaction. The para-selective nature of the catalyst defined reactivities of these substrates for the oxidative dehydrogenation reaction. Keywords: CVD Fe/Mo/DBH; Oxidative dehydrogenation; Ethylbenzene; p-Diethylbenzene; p-Ethyltoluene; p-(t-Butyl)ethylbenzene

1. I n t r o d u c t i o n

The non-oxidative dehydrogenation of ethylbenzene to styrene is commercially practised on a large scale. Styrene is one of the key products in the

I Correspondence address: 2315 Mast Court, Flossmoor, IL 60422, Tel.and fax. (+ 1-708) 798 4998. 0926-860X/96/$15.00 © 1996 Elsevier Science B.V. All rights reserved. PH S0926- 860X(96)00064-6

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J.S. Yoo / Applied Catal~'sis A: General 142 (1996) 19-29

petrochemical industry, and used as the starting monomer for polystyrene, ABA resin, and synthetic rubber. An F e - K double oxide system, which was found to maintain high activity and stability under steam, has been commercially used for the production of styrene [1-6]. Muller et al. [3] and Hirano [7,8] suggested that KFeO 2 is the active catalytic species for the reaction. Efforts have been made to improve the catalyst by adding a third component such as A1, Cr, Ca, V, Ce, Mo, and Mg, and the resulting ternary oxides consisting of K - F e - A 1 (1:3:3) and Ba-Fe-A1 (1:6:6) exhibited stable high activity for the synthesis of divinylbenzene from diethylbenzene [9]. However, these non-oxidative dehydrogenation reactions require high temperatures (580-650°C) and are endothermic and reversible. Their reversibility thermodynamically limits the yields of the products. The thermodynamic limitation is generally overcome by lowering the partial pressure of the reactant by diluting it in steam at higher temperature, 700°C. Thus, it has long been sought to find an effective oxidative dehydrogenation process for overcoming the thermodynamic limitations associated with the equilibrium of the non-oxidative dehydrogenation reaction. Oxidative dehydrogenation of ethylbenzene was first reported at the beginning of the 1960s. Since then, many catalysts have been studied with ethylbenzene and other alkylaromatics for this reaction. Oxides of Mo, Sb, Sn, Sn, Fe, V, Bi, and C o - M o [10] are among them. The promising initial results over phosphate of cerium and lanthanum led to the study of a whole series of condensed phosphate catalysts with typical inert support such as alumina, silica and diatomaceous earths. Phosphates of rare earths, Ca, Mg, Ni, Ca-Ni and M g - N i exhibited similar catalytic activity with ethylbenzene that is very selective for styrene at 500-600°C with very little combustion [11]. An F e / M o / p a r t i a l l y deboronated borosilicate molecular sieve (DBH) catalyst prepared by the chemical vapor deposition method from FeC13, MoOzC12 and borosilicate molecular sieve, HAMS-1B-3, has been reported to exhibit para-selective oxidation of polymethylaromatics to terephthaldehyde derivatives in the gas phase [12-15]. In the course of pursuing the selective oxidation of p-xylene in the xylene isomer mixture containing ethylbenzene over the same CVD F e / M o / D B H catalyst, we found that it was an excellent catalyst for oxidative dehydrogenation of ethylbenzene, and that its activity was dramatically enhanced by the presence of the para-oriented alkyl group. In short, if the alkyl groups in alkylaromatics are ethyl or higher, oxidative dehydrogenation of the alkyl group to produce alkenylaromatics becomes the primary reaction with the catalyst under oxidation conditions similar to those for polymethylaromatics [16]. This finding prompted us to look into a variety of alkylaromatics with different para-substituents in the O2-containing feed with and without CO 2. In this paper, gas phase O 2 oxidations of alkylaromatics over CVD F e / M o / D B H are reported using ethylbenzene, p-diethylbenzene, p-ethyltoluene and p-(tbutyl)ethylbenzene as representative substrates.

J.S. Yoo /Applied Catalysis A: General 142 (1996) 19-29

21

2. Experimental

2.1. Catalyst preparation Catalysts A - G were prepared from FeC13, MoO2C12 (or WOC14) and borosilicate molecular sieve matrix, HAMS-1B-3, by the chemical vapor deposition (CVD) technique according to the procedure described elsewhere [12,13]. Their physical properties are summarized in Table 1.

2.2. Catalyst evaluation The evaluation of the catalyst was carried out in a quartz micro-reactor (I.D. 0.5-1 cm) loaded with 0.5 g catalyst or a larger quartz reactor (I.D. 2 - 4 cm) loaded with 5-10 g catalysts, equipped with an on-line gas chromatograph. The mass balance of carbon (_+ 3%) and oxygen (_+ 1%) was maintained by quantitatively tracking every component including CO and CO 2 present in the effluent throughout the runs, according to the procedure described elsewhere [13,15]. As a feed gas stream, a premixed gas as well as a synthesized gas was used. The synthesized gas was made by pumping liquid feed into a gas stream of desired composition containing nitrogen as an internal standard. When the reactor reached the desired reaction temperature under the flow of the purge gas, the purge gas flow was stopped and the feed gas was passed through the catalyst bed in the reactor under the following standard range of conditions: Molecular ratio of O2/substrate Concentration of a substrate in feed Weight hourly space velocity Contact time Reactor temperature

1-56 0.1-0.2 mol% 0.1-1.1 h J 0.1-2.2 s 250-550°C

Table 1 Physical properties of catalysts A - G Catalyst Mo

(%) A B C D E F G

Fe

B

(%)

(ppm)

7.0 2.22 540 6.8 1.88 540 5.5 1.16 720 5.7 1.54 6.2 1.9 5.2 1.5 8.4(W) c 1.09 9.4 2.7

a Cumulative pore volume. b Average pore radius. CVD F e / W / D B H .

M o / F e S.A.

1.8 2.1 2.8 2.0 1.9 2.1 2.3 2.0

Pore volume a Pore radius b Micropore area Volume

(mZ/g) (cm3/g)

(A)

(m2/g)

(cm3/g)

283 280 ll8 305 270

0.11

27

196

0.090

271

0.09

27

212

0.096

22

J.S. Yoo /Applied Catalysis A." General 142 (1996) 19-29

3. Results and discussions In the course of studying the preferential oxidation of p-xylene from its isomer mixture containing ethylbenzene over the CVD F e / M o / D B H , it was found that ethylbenzene was initially dehydrogenated to styrene, which was immediately oxidized to oxygenates. This finding led to the examination of other alkylaromatics.

3.1. Ethylbenzene The commercially available xylene feed usually contains ethylbenzene at a substantial level, 15-20%. In the selective synthesis of terephthaldehyde and p-tolualdehyde from a commercial p-xylene feed by gas phase O 2 oxidation over CVD F e / M o / D B H in the previous work [13], the ethylbenzene component followed a reaction path which was different from that for the xylene isomers. In order to elucidate the reaction mechanism, pure ethylbenzene was studied under the standard gas phase O 2 oxidation described above. Ethylbenzene was subjected to gas phase 0 2 oxidation over catalyst A, which had already been proven to be an active catalyst. Ethylbenzene was fed at a WHSV of 0.575 h -~ into the catalyst bed packed with 0.5 g of catalyst A in a micro-reactor, and gas phase O 2 oxidation was carried out under the standard conditions. The results are shown as a function of temperature in Table 2. The products indicate that the ethyl group is dehydrogenated to form styrene as an initial product, and the resulting vinyl group was immediately oxidized further to produce benzaldehyde and benzoic acid, some of which were ultimately converted to carbon oxides via maleic anhydride, as shown in Scheme 1. To improve the selectivity of styrene, the secondary oxidation of the resulting styrene should be suppressed. For this purpose, modification of the catalyst surface and study of process variables are required. In comparison, the non-oxidative dehydrogenation of ethylbenzene [1] was carried out in steam (steam/ethylbenzene = 11/1) over the K - F e double oxide system at 600°C, and showed excellent catalytic performance, 23-26% ethyl-

Table 2 Gas phase 0 2 oxidation of ethylbenzene over catalyst A Temp.(°C) Conv.(%)

Product selectivi~' (%) Styrene Benzaldehyde Benzoic acid Maleic anhydride CO CO 2

250 0.59

275 1.00

300 1.84

325 5.15

350 10.3

375 22.6

400 38.1

425 70.4

450 79.6

74.8

73.8

52.2 24.2

25.3 37.9

14.2 33.6

7.2 16.3

12.4 24.4

21.1 11.4 19.7

7.1 28.1 11.6 24.7 10.7 17.8

4.2 25.3 9.1 29.6 12.0 19.2

1.5 21.0 4.8 39.6 12.1 21.0

1.1 18.6 1.9 39.5 14.7 23.9

25.2

26.2

Flow rate: 400 sccm, WHSV: 0.575 h L, 02/ethylbenzene = 7.51/1.

J.S. Yoo /Applied Cata~sis A." General 142 (1996) 19-29

O

-CH2CH

~

23

O-CH-CHa initial product

~

-CHO

~

~-COOH

0

HC II

-

C /"o

+

CO 2

+

H20

HC - C 0

Scheme 1.

benzene conversion with 93-95% styrene selectivity. However, 22.6% of ethylbenzene was converted to styrene, benzaldehyde, benzoic acid, maleic anhydride and CO x in the respective selectivities of 7.1, 28.1, 11.6, 24.7 and 28.5% at 375°C in gas phase O 2 oxidation over the CVD F e / M o / D B H . The oxidative dehydrogenation process over CVD F e / M o / D B H merits further study because it required a much lower reaction temperature to give comparable level of ethylbenzene conversion than the commercial K - F e oxide catalyst, and it provided four products including styrene in the absence of steam.

3.2. Styrene In order to confirm that the oxidation products obtained in the oxidation of ethylbenzene were derived from the further oxidation of styrene produced in the initial stage, pure styrene was subjected to the identical oxidation conditions used in the oxidation of ethylbenzene above with catalyst A in Table 2. The gas phase 0 2 oxidation of styrene was conducted in a larger quartz reactor loaded

Table 3 Oxidation of styrene over catalyst C Temp.(°C)

275

Feed type Conv. (%)

1 14.4

2 12.3

300 1 34.5

2 26.5

325 1 73.3

2 51.1

22.2 53.4 3.4 9.2 6.3 5.5

24.0 56.6 4.2 9.7 5.5

19.9 57.3 1.9 6.5 6.6 5.6

21.7 60.5 2.5 7.7 5.7

18.9 58.8 0.9 3.8 7.9 5.9

21.2 62.5 1.5 5.2 6.2

Product selectiviO, (%) Benzaldehyde Benzoic acid Phenylacetaldehyde Acetophenone CO CO 2

Feed 1:0.17 vol% styrene, 5.0 vol% vol% N~ in CO~.

02,

18.3 vol% N 2 in He. Feed 2:0.17 vol% styrene. 5.0 vol% O,, 18.4

24

J.S. Yoo /Applied Catalysis A: General 142 (1996) 19-29

Table 4 Oxidation of p-ethyltoluene over catalyst B (10 g) Temp. (°C)

350

Feed type Conversion (%0

1 4.7

2 11.9

375 1 39.0

2 69.9

400 I 70.0

2 81.1

Product selectil:i O, (%) p-Methylstyrene p-Tolualdehyde p-Toluic acid p-Me-acetophenone Terephthaldehyde CO CO 2

14.7 14.8 23.0 5.6 0.3 12.3 24.6

19.4 22.5 29.0 8.4 0.8 14.4

7.3 17.2 23.0 6.9 0.6 14.8 24.9

6.4 20.0 34.8 6.7 1.2 22.0

2.7 16.7 15.8 5.6 1.3 19.1 29.8

2.8 22.6 21.3 6.7 2.4 28.9

Feed 1:0.16% p-ethyltoluene (3.5 g/h), 5.5% 02, 20% N 2 in He. Feed 2:0.16% p-ethyltoluene (3.5 g/h), 5.6% 02, 20% N 2 in CO 2. WHSV: 0.36-0.37 h - ~, contact time: 0.21 s.

with l0 g of catalyst C in two feed streams under the conditions of WHSV:0.429-0.485 h-~, and contact time:0.187 second. The results are summarized in Table 3. It should be noted that the presence of carbon dioxide adversely affected the oxidation of styrene contrary to the oxidation reaction of other alkylaromatic substrates, in which the conversion level was increased in the presence of CO 2. The conversion levels of styrene in feed 2 containing 0 2 plus CO 2 were generally lower than the corresponding values in feed 1 containing 0 2 alone. Catalyst C has already proven to be very effective for promoting the O z oxidations of p-xylene to aldehydes with CO 2 [15]. These findings suggest that the presence of CO 2 in the 0 2 stream promotes the initial hydrogen abstraction step to produce free radicals in the case of ethylbenzene, but adversely affects the subsequent oxidation steps, as observed in the styrene oxidation reaction.

3.3. p-Ethyltoluene In order to examine the effect of a para-oriented pair of ethyl and methyl groups on the oxidation reaction, p-ethyltoluene was oxidized in a larger quartz reactor loaded with 10 g of catalyst B in two feed streams, O 2 and O 2 plus CO 2, at 350-400°C. These results are summarized in Table 4. p-Ethyltoluene was converted to p-methylstyrene via the oxidative dehydrogenation reaction, and the vinyl group in the resulting p-methylstyrene was further oxidized to aldehyde and carboxylic acid while the methyl group remained intact. The oxidative dehydrogenation reaction proceeded faster than the oxidation of methyl groups in p-xylene to aldehydes. As shown in Scheme 2, the ethyl group was preferentially oxidized over the methyl group in p-ethyltoluene. This phenomenon was particularly evident in feed 2 containing CO 2 in 0 2, even at lower temperatures, p-Methylstyrene, the initial dehydrogenation product, was mainly oxidized to form p-tolualdehyde,

J.S. Yoo /Applied Catalysis A: General 142 (1996) 19-29

©

H3C-

-CHaCH3

-"°© ~ Oa

HsC-

39.9%

-CH-CH2

~

7.3%

25

©

H3C-

-COCH3

6.9%

H3C-&-CHO 17.2% Z

N OHC-&-CHO

HsC-&-COOH

23.0%

0.6% Scheme 2.

and then to p-toluic acid. A substantial amount (5.6%-8.4%) of p-methylacetophenone was also produced. This was formed from the attack on the c~-carbon of the vinyl group of p-methylstyrene, while p-tolylacetaldehyde found in trace quantity was formed from the [3-carbon attack of the vinyl group. The results obtained in the oxidation of styrene and p-xylene in O 2 plus CO 2 lead to an identical conclusion regarding the promoting role of CO 2. The presence of CO 2 induced higher substrate conversion by promoting the formation of p-methylstyrene via oL,[3-hydrogen abstraction. The p-ethyltoluene conversion increased from 39.0 mol% to 69.9 mol%, and selectivity to ptolualdehyde and p-toluic acid increased from 17.2 mol% to 20.0 mol%, and 23.0 mol% to 34.8 mol%, respectively, at 375°C in the presence of CO 2. Selectivity to p-methylacetophenone and terephthaldehyde remained roughly the same in feed streams 1 and 2. Selectivity to an initial product, p-methylstyrene, remained at about 6-7 tool% in both streams indicating that p-methylstyrene was very rapidly oxidized to p-tolualdehyde and then to p-toluic acid under the conditions employed in this study. A similar phenomenon was observed in the liquid phase oxidation of styrene with Fe and Rh complex catalysts [17]. In contrast, KFeO 2, the active species, of the commercial non-oxidative dehydrogenation catalyst, was decomposed above 600°C in the presence of CO 2, higher than the equilibrium partial pressure of CO 2 (ca. 0.29 psi at 600°C, 1 p.s.i. = 6894.76 Pa), and consequently the catalyst deactivated very rapidly [1].

3.4. p-Diethylbenzene p-Diethylbenzene was chosen to study how para-oriented ethyl groups influence the oxidative dehydrogenation reaction, p-Diethylbenzene was pumped at a rate of 0.49 g / h into a micro-reactor and was oxidized over catalyst E in a flow (200 cm3/min) of the feed gas consisting of 6% 0 2 and 6% N 2 in He at 350°C. Considerable exothermicity was observed, and the catalyst bed temperature

26

J.S. Yoo /Applied Catalysis A: General 142 (1996) 19-29

Table 5 Gas phase oxidation of p-diethylbenzene over catalyst E: composition of the reaction effluent Components

Area % a

p-Diethylbenzene o-Diethylbenzene b p-Ethylstyrene p-Divinylbenzene Terephthaldehyde p- vinylbenzaldehyde p-Ethylbenzaldehyde p-Ethylhenzoic acid Unidentified

72.9 2.7 7.2 0.43 6.4 1.5 2.1 5.7 1.1

Temperature 325°C. a Excluding CO X. b May be the isomerized product.

climbed up to 411°C. The catalyst bed temperature was lowered to 325°C and the flow rate of the feed gas was increased to 800 cm3/min. The reaction effluent was collected in an ice trap, and the collected solid was soluble in acetone except for an extremely small portion which remained insoluble. The resulting acetone solution was analyzed by GC and the products were identified by GC and mass spectrometry. The results summarized in Table 5 lead to the conclusion that p-diethylbenzene was far more reactive than p-ethylbenzene in gas phase O 2 oxidation over CVD F e / M o / D B H . Very little p-divinylbenzene was collected in reaction effluent. As is shown

C2Hs-~-C2H5 02 C2Hs-~CH-CH 2

+

02

H2C-CH-~-CH-CH 2 ,I. 02

C2Hs-~-CHO

H2C-CH-~-CHO

J. 02

~ 02

C2Hs-G-COOH

OHC-~-CH0 Scheme 3.

J.S. Yoo / Applied Catalysis A: General 142 (1996) 19-29

27

Table 6 Oxidation of p-diethylbenzene in CO 2 in the absence of 02 over catalyst H Temp. (°C) Conversion (%)

250 3.3

275 4.2

300 1.1

325 1.6

375 3.4

400 3.8

100 0 0 0

100 0 0 0

93.0 0.9 0.5 5.5

94.0 1.3 0.7 4.0

92.9 3.2 0.6 3.4

93.0 3.8 0.6 2.5

Product selectiL,iD' (%) a p-Ethylstyrene p-Divinylbenzene m-Ethylstyrene b m-Divinylbenzene ~

Excluding CO~. b May be the isomerized product.

in Scheme 3, it appears that it was further oxidized to p-vinylbenzaldehyde and terephthaldehyde as soon as it was formed, and the resulting aldehydes were slowly oxidized further to the insoluble product, most likely, p-ethylbenzoic acid and terephthalic acid. When just one ethyl group in p-diethylbenzene substrate interacted with the "single" site of the catalyst in the stand-on manner [13,14], p-ethylstyrene was produced as a result of single a,[3-hydrogen elimination reaction. Once p-ethylstyrene was formed, the remaining ethyl group became much more difficult to be oxidized, and only the vinyl group in p-ethylstyrene was oxidized further to p-ethylbenzaldehyde, which eventually converted to p-ethylbenzoic acid. On the other hand, p-divinylbenzene, which was formed on the " p a i r " sites via two a,[3-hydrogen abstraction in a concerted manner [13,14], was extremely reactive and likely to produce terephthaldehyde and p-vinylbenzaldehyde in the subsequent oxidation. In another run, p-diethylbenzene was pumped into the micro-reactor loaded with 0.509 g of catalyst G and oxidized in CO 2 (400 cm3/min) in the absence of 02. The main product was p-ethylstyrene in more than 90% selectivity and p-divinylbenzene was present only as a minor product, as shown in Table 6. As is expected, CO and H 2 0 were also produced. Conversion of the substrate was limited to 3-4% under the conditions employed. The formation of terephthaldehyde was completely suppressed, and p-tolualdehyde became a sole product. The same phenomenon was also observed in the p-xylene oxidation in CO 2 alone [15]. The yields of terephthaldehyde and p-tolualdehyde were remarkably increased when gas phase O 2 oxidation of p-xylene was carried out in the presence of CO~ over the CVD F e / M o / D B H catalyst. It should be pointed out that the ternary catalysts such as K-Fe-AI(1:3:3) and Ba-Fe-A1 (1:6:6) showed excellent catalytic performance, high activity and selectivities to ethylvinylbenzene and divinylbenzene for the non-oxidative dehydrogenation of divinylbenzene [9].

3.5. p-( t-Butyl)ethylbenzene Catalyst A (0.52 g) loaded in the microreactor had been used in a series of intermittent oxidations of various alkylaromatics including p-xylene under the

J.S. Yoo /Applied Catalysis A: General 142 (1996) 19-29

28

Table 7 Gas phase oxidation of p-(t-butyl)ethylbenzene over catalysts A and F ( F e / W / D B H ) Temp.(°C)

Feed a

Conversion (%)

Selectivity (%) h

Dealkylated prod.

A

F

A

F

A

F

350 400 450 500

1

1.9 2.5 5.1 7.7

3.2 4.1 4.3 5.6

18 14 14 16

12 12 13 15

34 48 67 65

57 54 65 64

375 400 450 500

2

4.0 4.7 l 1.8 13.0

5.7 15.8 21.8

40 62 60 68

65 73 66

4 2 3 7

4 1 13

350 400 450

3

2.5 4.0 15.0

5.8 8.9 18.6

14 14 50

34 34 65

2 2 4

2 2 1

350 400 450

4

3.5 9.0 31.0

4.4 10.9 21.4

51 43 17

66 71 59

2 1 1

5 2 1

a Feed 1: N2; Feed 2: 0.5% 02 in N2; Feed 3: 2% 02 and 2% N 2 in He; Feed 3: 4% 0 2 and 4% N 2 in He. h Selectivity to p-O-butyl)styrene.

standard conditions for a two and a half month period. The catalyst resulting from these runs was further subjected to the oxidation of p-(t-butyl)ethylbenzene. Four different gas streams consisting of 100% N 2, 0.5% 0 2 in N 2, 2% 0 2 and 2% N 2 in He, and 4% 0 2 and 4% N 2 in He were fed at a rate of 100 c m 3 / m i n while varying the reaction temperatures. The p-(t-butyl)ethylbenzene feed was pumped into these four gas streams at 0.23 m l / h . The results are shown in Table 7 along with the results obtained with catalyst F, CVD F e / W / D B H , prepared from FeC13 and WOC14. The ethyl group was dehydrogenated while the t-butyl group remained almost intact, p-(t-Butyl)styrene was formed in high selectivities (60-73%) at conversion of 12 ~ 22% of p-(tbutyl)ethylbenzene at 450-500°C in feed 2. A limited amount of debutylated product was detected in feeds 2, 3, and 4 containing 0 2. However, the debutylation of p-(t-butyl)ethylbenzene became a primary reaction with a limited amount of p-(t-butyl)styrene in N 2 under the non-oxidative conditions.

4. Conclusions When an alkyl group in alkylaromatics is ethyl or higher, it was oxidatively dehydrogenated to form an alkenyl group over CVD F e / M o / D B H under the standard gas phase 0 2 oxidation conditions. The resulting initial alkenyl groups are immediately oxidized to aldehyde, ketone and carboxylic acid in the subsequent step. Ethylbenzene, p-ethyltoluene, and p-(t-butyl)ethylbenzene were

J.S. Yoo /Applied Catalysis A: General 142 (1996) 19-29

29

initially converted to styrene, p-methylstyrene and p-(t-butyl)styrene, respectively. The vinyl groups in these products were further oxidized to the corresponding aldehydes and/or carboxylic acids. Presence of the two para-oriented ethyl groups in p-diethylbenzene enhanced the reactivity of the substrate dramatically and produced p-ethylstyrene and p-divinylbenzene. These products were subjected to the secondary oxidation reactions, p-Ethylbenzaldehyde and p-ethylbenzoic acid were derived from p-ethylstyrene, and terephthaldehyde and p-vinylbenzaldehyde were produced from p-divinylbenzene. The reactivities of ethylbenzene, p-ethyltoluene, and p-diethylbenzene over CVD F e / M o / D B H catalyst are defined by the para-selective nature of the catalyst. In the presence of CO 2, a dramatic improvement in the catalyst performance for 0 2 gas phase oxidations of these substrate was observed. It appears that carbon dioxide promotes hydrogen abstraction reaction, but it adversely affect the oxidation of the akenylaromatics to oxygenates.

Acknowledgements The author is indebted to M.S. Kleefisch, P.S. Lin and S.D. Elfline for their technical assistance.

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