Promotion Effect of Alkali Metal Added to Impregnated Cobalt

Ind. Eng. Chem. Res. 2004, 43, 6021-6026

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Promotion Effect of Alkali Metal Added to Impregnated Cobalt Catalysts in the Gas-Phase Catalytic Oxidation of Benzyl Alcohol Yonghao Li,† Daisuke Nakashima,† Yuichi Ichihashi,§ Satoru Nishiyama,‡ and Shigeru Tsuruya*,§ Division of Molecular Science, Graduate School of Science and Technology, Kobe University, Nada, Kobe 657-8501, Japan, Department of Chemical Science and Engineering, Faculty of Engineering, and Center for Environmental Management, Kobe University, Nada, Kobe 657-8501, Japan

The effect of the addition of alkali metals on the catalytic activity of cobalt catalysts (Co/NaY, Co/SiO2, etc.) impregnated on inorganic oxides including NaY and SiO2 was studied using the gas-phase catalytic oxidation of benzyl alcohol. The partial oxidation activities, measured by the yield of benzaldehyde, of the supported Co catalysts were selectively promoted by adding alkali metal, with keeping the yield of CO2 low. The amount of added alkali metal under a constant amount of the impregnated cobalt had an optimal value for the catalytic activity of the benzaldehyde formation. The influences of the supporting method of Co, the inorganic oxide support, the amount of supported Co, and the kind of the added alkali metal on the partial oxidation activity were investigated to explore the supported Co catalysts for high catalytic activity. The sorpted oxygen species, rather than gaseous oxygen, were suggested to participate in the formation of benzaldehyde on the basis of a transient response experiment. The addition of alkali metal caused the increase in the amount of O2 uptake of the prereduced Co/NaY catalysts. A correlation was observed between the amount of O2 uptake and the amount of alkali metal added to the catalyst. The comparison between the diffuse-reflectance spectra of the Co/ NaY catalysts with and without added alkali metal definitely revealed that the added alkali metal enhanced the affinity of the supported Co species toward oxygen to form the cobalt oxides (Co3O4≡Co2+(Co3+)2O4). The cobalt oxides were suggested to be responsible for the partial oxidation of benzyl alcohol and the formation of benzaldehyde. 1. Introduction The oxidation of alcohols is one of the key chemical processes to obtain important compounds with a functional oxygen containing group, aldehydes or ketones. To meet an international protocol for lower loading in the global environment, an existing chemical process should be improved from an environmental harmony point of view. Catalysts have so far played a crucial role for low-loading processes in the environment (green sustainable processes). The liquid-phase oxidation of alcohols with a toxic inorganic oxidant will place a heavy load against the environment.1 The liquid- or the gasphase catalytic oxidation of alcohols using gaseous O2 as the oxidant, in place of stoichiometric oxidation with an inorganic oxidant, will be an alternative having harmony with the environment. Recently, the efficient and selective liquid-phase oxidation of alcohols to the corresponding carbonyl compounds in the presence of gaseous oxygen as an oxidant has been reported using Ru/Al2O32 and Pd/hydroxyapatite3 catalysts. The liquidphase oxidation of alcohols over Fe3+/montmorilloniteK10 was carried out using hydrogen peroxide, an environmentally friendly oxidant.4 We have reported that an alkali metal added to supported Cu catalysts * To whom correspondence should be addressed. Tel. and fax: +81-78-803-6171. E-mail: [email protected]. † Division of Molecular Science, Graduate School of Science and Technology. § Department of Chemical Science and Engineering, Faculty of Engineering. ‡ Center for Environmental Management.

promotes the catalytic activity for the partial oxidation in the gas-phase catalytic oxidation of benzyl alcohol.5-11 The activation of the oxygen molecule by metal ions or their complexes has synthetic potential for various oxygenated compounds. Cobalt complexes, such as typical cobalt Shiff base complexes (simple dioxygenase models), have been known12,13 to form the corresponding cobalt-dioxygen complex in the activation process of an oxygen molecule, to have catalytic activity in the oxidation of hydrocarbons, and also to function as oxygen carriers. The immobilization of cobalt ions or their complexes on a support will provide ease of separation between the products and the catalyst and also the prevention of the contamination of catalyst in the products after or during the catalytic oxidation. The influence of the alkali metal added to the Co ionexchanged NaX and NaY catalysts on the oxidation activity was reported in the gas-phase catalytic oxidation of benzyl alcohol.14 The added alkali metal promoted the partial oxidation activity of the Co ionexchanged catalysts. We herein report the oxidation activity of the supported Co catalysts prepared by an impregnation method, in place of an ion-exchange method, with and without added alkali metal in the gas-phase catalytic oxidation of benzyl alcohol with a focus on both the promotion effect and the role of the added alkali metal on the catalytic activity. The alkali metals added to the impregnated Co catalysts play an important role as a promoter for the supported Co catalysts with comparatively low loadings of Co. The role of the added alkali metals on the supported Co species is discussed on the

10.1021/ie040078e CCC: $27.50 © 2004 American Chemical Society Published on Web 08/11/2004

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basis of the results of the O2 uptake of the prereduced supported Co catalysts and the diffuse reflectance (DR) spectra. 2. Experimental Section 2.1. Catalysts. The supported Co catalysts were prepared by a conventional impregnation method (Co/ support) at 358-373 K using Co(NO3)‚6H2O (Nacalai tesque, guaranteed reagent) as a cobalt source followed by drying at 393 K overnight and calcining at 773 K for 5 h in flowing air. NaY (Tosoh, Si/Al ) 2.5), SiO2 (JRCSiO-8), NaZSM-5 (prepared according to ref 15), MCM41 (prepared according to ref 16), Al2O3 (JRC-ALO-4), and MgO (Nacalai tesque) were used as the inorganic supports. The alkali metal-added supported Co catalysts (alkali metal/Co/support) were prepared by impregnating the alkali metal acetate (CH3COOLi‚2H2O, CH3COONa, CH3COOK, CH3COORb, and CH3COOCs) on the corresponding supported Co catalysts at 358-373 K followed by drying at 393 K overnight and calcining at 773 K for 5 h in flowing air. 2.2. Gas-Phase Catalytic Oxidation of Benzyl Alcohol. Benzyl alcohol (Nacalai tesque, guaranteed reagent) was used without further purification after confirming by GLC that no impurity was detected. The gas-phase catalytic oxidation was carried out under atmospheric pressure using a continuous flow fixed-bed reactor (Pyrex glass, 15 mm i.d.) vertically located in an electronic furnace. After the precalcination of a catalyst (usually 0.2 g) packed in the reactor at 773 K for 2 h in flowing air, the reaction was started by supplying benzyl alcohol through a microfeeder. The typical reaction conditions are as follows: reaction temperature, 623 K; W/F ) 8.68 (g-cat‚mol/min) [W, catalyst weight ) 0.2 (g-cat); F, total mole flow ) 0.023 (mol/min)]; benzyl alcohol:O2:N2 ) 1:3:32 (mole ratio). The liquid products and the unconverted benzyl alcohol, collected using a refrigerant consisting of diethyl malonate and liquid N2, were analyzed, after adding 1 cm3 dimethylformamide as an internal standard, using a GLC (Shimazu GC-8A, FID) equipped with a 1-m glass column packed with PEG HD Uniport HP 5% under a H2 carrier (35 cm3/min). The gaseous products introduced to a 1-cm3 gas sampler through a six-way bulb were analyzed by an intermediate method17 using gas layer chromatography (GLC) (Shimazu GC-6A, thermal conductivity detector (TCD)) equipped with two 1-m stainless columns packed with silica gel and molecular sieve 5A, respectively, under a N2 carrier (20 cm3/min). 2.3. XRD Measurement of the Supported Co Catalysts. The XRD patterns of the supported Co catalysts were observed at room temperature using X-ray diffraction equipment (Rigaku RINT 2100) with a Cu-KR source. 2.4. BET Surface Measurement of the Supported Co Catalysts. The BET surface areas of the supported Co catalysts, which were preheated at 473 K for 2 h, were measured using a static gas-adsorption apparatus equipped with a digital manometer. 2.5. Measurement of the Amount of O2 Uptake of the Prereduced Impregnated Co Catalysts. The measurement of the amount of O2 uptake of the supported Co catalyst pretreated with carbon monoxide (CO) was performed using a semi-microgas-adsorption apparatus equipped with a capillary sample tube. A 0.01 g portion of the catalyst sample was calcined at 773 k for 1 h under O2 at 20 kPa followed by degassing at

Table 1. Influence of Inorganic Support on the Oxidation Activitya yield of benzaldehyde (%) support

support only

Co/support

K/Co/support

NaZSM-5 MCM-41 NaY SiO2 Al2O3 MgO

1.0 0.78 0.27 0.54 3.2 1.2

4.6 2.6 1.1 1.1 4.6 6.5

14.6 4.5 18.5 11.4 12.5 7.2

a Loading of Co, 1 wt %; added K/Co atomic ratio, 8; reaction temperature, 623 K.

773 K for 1 h under less than 0.1 Pa. The catalyst was then treated at 773 K for 1 h under CO at 20 kPa followed by degassing at 773 K for 1 h. After introducing He at 1.3 kPa, the dead volume was measured at 623 K followed by degassing. After introducing the O2 at 5.2 kPa and confirming the attainment of adsorption equilibrium, the amount of O2 uptake was measured at 623 K. The reversible amount of O2 uptake was measured at 623 K after degassing at 623 K for 1 h under less than 0.1 Pa. The irreversible amount of O2 uptake was defined as the difference between the amount of O2 uptake and the corresponding reversible amount. 2.6. Diffuse Reflectance (DR) Spectra of the Impregnated Co Catalysts. The DR spectra of the supported Co catalysts were measured at room temperature using an electronic absorption spectrophotometer (Hitachi U-3210D) equipped with an integral sphere (Hitachi 150-0902). The catalyst sample packed in the treatment portion of an in-situ cell, connected to a vacuum line, was pretreated under various conditions before transferring for the DR measurement. The obtained DR data were transformed to the KubelkaMunk function [F(R)] using an application program (Hitachi U-3210/U-3410). 3. Results and Discussion The conversion of benzyl alcohol, the yields of benzaldehyde and CO2, and the selectivity for benzaldehyde were defined elsewhere.6,7 The carbon balances obtained in this study were usually more than 90%. No oxidation products were obtained at 623 K over only silica sand, a diluent, and benzyl alcohol was almost quantitatively recovered. The main oxidation products over the supported Co catalysts both with and without the added alkali metal were benzaldehyde and CO2. Trace amounts of benzene and toluene (less than 0.1%) were obtained depending on both the catalysts and the reaction conditions. The yields of both benzyl alcohol and CO2 were estimated as the average values at the process times of 2-4 h. The added alkali metal of the alkali metal/Co/ support catalysts precalcined at 773 K for 5 h in flowing air is thought to be substantially present as the corresponding oxide.7 3.1. Oxidation Activity of the Impregnated Co Catalysts with and without Added Alkali Metal. The influence of the inorganic support of the impregnated Co catalysts (Co, 1 wt %) with and without added K (K/Co atomic ratio, 8) on the oxidation activity was investigated using some oxide supports (Table 1). The impregnated Co caused an increase in the yield of benzaldehdye, irrespective of the utilized support. The K added to the Co/support catalysts promoted the partial oxidation activity of the Co/support catalysts,

Ind. Eng. Chem. Res., Vol. 43, No. 19, 2004 6023 Table 2. Influence of Alkali Metal Added to Co(1)/NaY on the Oxidation Activitya catalyst

yield of benzaldehyde (%)

yield of CO2 (%)

1% Co/NaY 2.0% Li/1% Co/NaY 4.0% Na/1% Co/NaY 6.0% K/1% Co/NaY 11% Rb/1% Co/NaY 16% Cs/1% Co/NaY

1.1 3.8 5.6 18.4 9.8 14.4

0.3 0.5 0.4 0.9 0.7 0.8

a Catalyst, 0.2 g; loaded Co, 1 wt %; added alkali metal/Co atomic ratio, 8; reaction temperature, 623 K.

Table 3. Influence of Alkali Metal Added to Co(1)/SiO2 on the Oxidation Activitya catalyst

yield of benzaldehyde (%)

yield of CO2 (%)

1% Co/SiO2 2.0% Li/1% Co/SiO2 4.0% Na/1% Co/SiO2 6.0% K/1% Co/SiO2 11% Rb/1% Co/SiO2 16% Cs/1% Co/SiO2

1.1 2.7 2.8 11.4 5.8 8.4

0.18 0.10 0.12 0.10 0.20 0.12

a Catalyst, 0.2 g; loaded Co, 1 wt %; added alkali metal/Co atomic ratio, 8; reaction temperature, 623 K.

though the extent of the promotion differed with respect to each support. The influence of alkali metal (added alkali metal/Co atomic ratio, 8) added to both the 1% Co/NaY and 1% Co/SiO2 catalysts on both the yields of benzaldehdye and CO2 is shown in Table 2 and Table 3, respectively. All the alkali metals added to both the 1% Co/NaY and 1% Co/SiO2 catalysts were confirmed to promote the oxidation activity, particularly the activity of the partial oxidation, though the extent of the promotion depends on the kind of the added alkali metal. One of the reasons seems to be that the optimum value of the added alkali metal/Co atomic ratio on the partial oxidation varies from one alkali metal to another. The added alkali metal was thus found to act as a promoter of the impregnated Co catalysts in the gas-phase catalytic oxidation of benzyl alcohol. The influence of the amount of the added K on the yields of both benzaldehyde and CO2 was investigated using both the 1% Co/NaY and the 1% Co/SiO2 catalysts (Figure 1). The yield of benzaldehyde (Figure 1a, b, b) increased with the increase in the added K/Co atomic ratio and passed through a maximum value at a ratio of around 8 for both catalysts. Further increase in the added K/Co atomic ratio of both the catalysts inversely caused a decrease in the yield of benzaldehyde. The yield of CO2 (Figure 1a, b, O) over both the catalysts hardly varied, keeping the yield low, with the increase in the added K/Co atomic ratio. The results obtained in Figure 1 indicate that the K added to both the Co/NaY and the Co/SiO2 catalysts selectively promote the catalytic activity of the partial oxidation, keeping the yield of CO2 low. To investigate whether the added alkali metal promotes the catalytic activity of the partial oxidation separately or corporately with Co species, the oxidation was attempted over a catalyst consisting of a physical mixture of Co/NaY and K/NaY, in which the Co species are kept away from the added K, in contrast to the K/Co/ NaY catalyst in which the supported Co species are vicinal to the added K. The results of the oxidation activity of the physically mixed catalyst are revealed in Table 4, together with the results over 6.0% K/1% Co/NaY (K, 6.0 wt %; added K/Co atomic ratio, 8), 1%

Figure 1. Influence of added K/Co atomic ratio on the yields of benzaldehyde and CO2. Catalyst, 0.2 g; reaction temperature, 623 K; b, yield of benzaldehyde; O, yield of CO2; (a) K/1% Co/NaY catalyst; (b) K/1% Co/SiO2 catalyst. Table 4. Comparison of K/Co/NaY Catalyst and the Physically Mixed Catalyst of K/NaY and Co/NaYa catalyst

yield of benzaldehyde (%)

yield of CO2 (%)

K/NaYb 1% Co/NaY 6.0% K/1% Co/NaY 1% Co/NaY + K/NaYb

1.2 1.1 18.5 1.3

0.15 0.26 0.99 0.25

a Catalyst, 0.2 g; loaded Co, 1 wt %; added alkali metal/Co atomic ratio, 8; reaction temperature, 623 K. b Loaded K, same as the K amount added to the 6.0% K/1% Co/NaY catalyst.

Co/NaY, and K/NaY catalysts. The potassium supported on NaY zeolite hardly promotes the benzyl alcohol oxidation under the present reaction conditions. The yield of benzaldehyde obtained over the physically mixed catalyst of 1% Co/NaY + K/NaY (the loaded K, same as the K amount added to the 6.0% K/1% Co/NaY catalyst) was considerably lower than that over the 6.0% K/1% Co/NaY catalyst. This indicates that the added K can promote the oxidation activity in contact with the Co species. Both the Co species and the added K must be spatially next to each other to function cooperatively to obtain high activity for the partial oxidation. The promotion effect of the potassium is thus induced only when the alkali metal directly interacted with the cobalt species which is supposed to be active catalytic species. 3.2. Behavior of the Oxidation Activity of the K-Added Co/NaY Catalyst in the Absence of Gaseous O2. The influence of gaseous oxygen on the yields of both benzaldehyde and CO2 over the 6.0% K/1% Co/ NaY (added K/Co atomic ratio, 8) catalyst were investigated using a transient response method (Figure 2). After the gas-phase catalytic oxidation of benzyl alcohol reached a steady state (Region I), the only O2 supply was halted and the behavior of the oxidation product

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Figure 2. Behaviors of the yields of both benzaldehyde and CO2 in the absence of gaseous O2. Catalyst, 0.2 g of 6.0% K/1% Co/ NaY; reaction temperature, 623 K; b, yield of benzaldehyde; O, yield of CO2.

was observed with respect to the time on stream (Region II). The production of benzaldehdye was detected despite the stoppage of the O2 supply, although the yield was not high; the yield of benzaldehyde continuously decreased with the time on stream. The formation of benzaldehyde is thought to involve the participation of the O2 species adsorbed on the catalyst. In contrast, CO2 immediately disappeared after gaseous O2 flow was stopped. Benzaldehyde was thus produced even in the absence of gaseous O2; on the other hand, gaseous oxygen is essential for the formation of CO2. The reactivation (Region III) of the 6.0% K/1% Co/NaY catalyst caused the almost perfect recovery of the oxidation activity (Region IV). No benzaldehyde, together with CO2, was detected when only N2 was supplied (Region V). The Region V result suggests that benzaldehyde formed in Region II is not due to the elution of the adsorbed benzaldehyde formed in the Region I. The transient response experiment over the 6.0% K/1% Co/SiO2 catalyst exhibited similar results as in Figure 2, that is, benzaldehyde continued to be formed even after the stoppage of gaseous O2, but CO2 disappeared immediately after halting O2 flow (figure not depicted). The formation of benzaldehyde over the impregnated Co catalysts under the absence of gaseous O2 suggests that the oxygen species sorbed on the supported Co catalysts are responsible for the oxidation of benzyl alcohol to benzaldehyde. 3.3. Amount of O2 Uptake of the Prereduced K-Added Impregnated Co Catalysts. The participation of the O2 species sorbed on the impregnated Co catalysts in the formation of benzaldehyde was suggested from the transient response experiment in the absence of gaseous O2 (Section 3.2). The storage capacities of the O2 species by the impregnated Co catalysts were estimated from the amount of O2 uptake of the catalysts prereduced by CO. The influence of the alkali metal added to the impregnated Co catalysts on the amount of O2 uptake was studied. The dependence of the amount of irreversible O2 uptake per Co on the K/Co atomic ratio was investigated using the K/1% Co/NaY catalyst, as illustrated in Figure 3. The amount of irreversible O2 uptake increased with the added K/Co atomic ratio and passed through a maximum at a ratio of 8. Further increase in the added K/Co ratio declined the amount of irreversible O2 uptake. The comparison of the variations of the yield of benzaldehyde (Figure 1a, b) and the amount of irreversible O2 uptake (Figure 3) with respect to the added K/Co atomic ratio reveals that both the yield of benzaldehyde and the amount of irreversible O2 uptake have a maximum value at the

Figure 3. Dependence of the amount of irreversible O2 uptake on the added K/Co atomic ratio. Catalyst, K/1% Co/NaY; measured temperature, 623 K.

Figure 4. Diffuse reflectance (DR) spectra of Co/NaY and K/Co/ NaY catalyst. (a) Catalyst, 1% Co/NaY; s, oxidized form (calcined at 773 K for 1 h under 150 Torr O2); - - -, reduced form (treated at 773 K for 1 h under 150 Torr CO). (b) Catalyst, 6.0% K/1% Co/ NaY; s, oxidized form (calcined at 773 K for 1 h under 150 Torr O2); - - -, reduced form (treated at 773 K for 1 h under 150 Torr CO).

added K/Co atomic ratio of around 8. A correlation between the yield of benzaldehyde and the amount of irreversible O2 uptake is reasonable when taking into consideration the role of the O2 sorbed on the impregnated Co catalysts as suggested previously. Thus, the increase in the amount of O2 uptake, related to sorbed O2 species suggested to be involved in the partial oxidation of benzyl alcohol, will bring about an increase in the yield of benzaldehyde. In turn, the O2 species sorbed on the impregnated Co catalyst are thought to play a crucial role in the partial oxidation of benzyl alcohol. 3.4. Diffuse Reflectance (DR) Spectra of the K-Added Impregnated Co Catalysts. To examine the structures and the valence states of the Co species impregnated on the NaY zeolite, the diffuse reflectance

Ind. Eng. Chem. Res., Vol. 43, No. 19, 2004 6025 Scheme 1

(DR) spectra of the Co/NaY catalysts with and without added alkali metal were observed making note of the difference in the DR spectra in both the presence and the absence of the added alkali metal. Figure 4a illustrates the DR spectra of both the oxidized and the reduced Co/NaY catalysts. Both 1% Co/NaY catalysts were pretreated at 773 K for 1 h under oxygen and under carbon monoxide, respectively. The DR spectra of the oxidized 1% Co/NaY showed three peaks at around 520, 580, and 680 nm, together with a broad DR band at around 400-450 nm (Figure 4a, s). Three DR peaks at around 520, 580, and 640 nm were observed in the reduced 1% Co/NaY sample (Figure 4a, - - -). The DR peaks located at 510 and 550-650 nm of supported Co species were identified18,19 as Co2+ ions coordinated with an octahedral and a tetrahedral configuration, respectively. The DR broad peaks at 450 nm, characteristic of a charge-transfer band of Co3O4, and 700 nm were identified18,19 as cobalt oxide (Co3O4≡Co2+(Co3+)2O4). The Co species on the oxidized 1% Co/NaY catalyst are mainly present as Co2+ species but the Co oxide species are thought to be present also because of the broad DR peak at around 400-450 nm. The Co species on the reduced 1% Co/NaY catalyst are substantially present as Co2+ species from the DR peaks at around 520-640 nm. The DR spectra of the K-added counterparts (the oxidized and the reduced 6.0% K/1% Co/NaY catalysts) are illustrated in Figure 4b. The addition of K to the oxidized 1% Co/NaY catalyst caused a dramatic increase in the intensities of the comparatively broad DR peaks at around 440 and 700 nm (Figure 4b, s). The reduction of the oxidized 6.0% K/1% Co/NaY catalyst resulted in significant decrease in the two DR peaks at around 440 and 700 nm and the appearance of the DR peaks at around 520-640 nm (Figure 4b, - - -). The variation in the DR spectra of the 6.0% K/1% Co/NaY catalyst by the oxidizing and the reducing treatments (Figure 4b) indicates that the Co species on the 6.0% K/1% Co/NaY catalyst had redox behavior. From the difference in the

DR spectra of the 1% Co/NaY catalysts with and without added K, the addition of K to the 1% Co/NaY catalyst will make the interaction of the supported Co species with O2 stronger followed by facilitating the formation of Co oxides (Co3O4≡Co2+(Co3+)2O4). The O2 species sorbed on the supported Co species and the correspondingly formed oxides are thought to play a crucial role for the formation of benzaldehyde as suggested previously. The results of the DR spectra obtained in this study are thus consistent with the deduction obtained from the results of both the transient response experiment and the O2 uptake experiment that the role of the added alkali metal is to strengthen the affinity of the supported Co species with gaseous O2. 3.5. The Role of the Added Alkali Metal and the Scheme of the Benzyl Alcohol Oxidation. The electron density of the supported Co species has been reported to increase20,21 by the electron transferred from the added alkali metal which is located as a nearest neighbor to the Co species. The electron-rich Co species will more easily interact with gaseous O2 because of its strong electron affinity. This will result in the easy formation of Co3O4 (Co2+(Co3+)2O4) of which Co species and their sorbed oxygen species present are thought to participate in the formation of benzaldehyde, from the isolated Co2+ species as evidenced from the difference in the DR spectra of the Co/NaY catalysts both with and without added K. A plausible scheme of the benzyl alcohol oxidation over K-added Co/NaY catalyst is thought to be similar to one proposed using the alkali metal-added Co ion-exchanged NaY and NaX catalysts.14 4. Conclusions An alkali metal added to Co catalysts impregnated on various inorganic oxides promoted the catalytic activity of partial oxidation, while retaining the activity of total oxidation low, in the gas-phase catalytic oxida-

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tion of benzyl alcohol. An optimum amount of the loaded alkali metal existed for the promotion of the partial oxidation. Spatial close contact between the supported Co species and the added alkali metal was crucial for the promotion of the partial oxidation. The transient response experiment involving halting gaseous O2 flow showed that benzaldehyde continued to form even in the absence of O2 in contrast to the CO2 formation which ceased immediately after the O2 supply was halted. The amount of O2 uptake of the prereduced K/Co/NaY catalysts increased with an increase in the added K/Co atomic ratio and passed through a maximum. Both the yield of benzaldehyde and the amount of O2 implied a good correlation with the added K/Co atomic ratio. The DR spectra of both the Co/NaY and the K/Co/NaY catalysts demonstrated that the alkali metal added to the Co/NaY catalyst facilitates the formation of oxidized Co species. From the results obtained in this study, the role of the added alkali metal was suggested to be that the supported Co species facilitated the sorption of gaseous O2. Also, the O2 species sorped on the Co species are thought to play an important role in the formation of benzaldehyde. Acknowledgment The authors thank Mr. Kenji Nomura of Kobe University for his technical assistance during this work. Literature Cited (1) Sheldon, R. A.; Kochi, J. K. Metal-Catalyzed Oxidation of Organic Compounds; Academic Press: New York, 1981. (2) Yamaguchi, K.; Mizuno, N. Supported Ruthenium Catalyst for the Heterogeneous Oxidation of Alcohols with Molecular Oxygen. Angew. Chem., Int. Ed. 2002, 41, 4538. (3) Mori, K.; Yamaguchi, K.; Hara, T.; Mizugaki, T.; Ebina, K.; Kaneda, K. Controlled Synthesis of Hydroxyapatite-Supported Palladium Complexes as Highly Efficient Heterogeneous Catalyst. J. Am. Chem. Soc. 2002, 124, 11572. (4) Pillai, U. R.; Sahle-Demessie, E. Oxidation of Alcohols over Fe3+/Montmorillonite-K10 Using Hydrogen Peroxide. Appl. Catal., A: General 2003, 245, 103. (5) Hayashibara, H.; Nanbu, T.; Nishiyama, S.; Tsuruya, S.; Masai, M. In Catalysis of Alkali Added Cu(II)-NaZ Zeolites in Benzyl Alcohol Oxidation; von Ballmoos, R., Higgins, J. B., Treacy, M. M. J., Eds.; Proceedings of 9th International Zeolite Conference; Butterworth-Heinemann: London, 1993; p 575. (6) Hayashibara, H.; Nishiyama, S.; Tsuruya, S.; Masai, M. The Effect of Alkali Promoters on Cu-Na-ZSM-5 Catalysts in the Oxidation of Benzyl Alcohol. J. Catal. 1995, 153, 254.

(7) Genta, M.; Nishiyama, S.; Tsuruya, S.; Masai, M. Role of Alkali-Metal Added to Cu-NaZSM-5 Catalysts in the Oxidation of Benzyl Alcohol. J. Chem. Soc., Faraday Trans. 1996, 92, 1267. (8) Arai, M.; Nishiyama, S.; Tsuruya, S.; Masai, M. Effect of Alkali-Metal Promoter on Silica-Supported Copper Catalysts in Benzyl Alcohol Oxidation. J. Chem. Soc., Faraday Trans. 1996, 92, 2631. (9) Sueto, S.; Nishiyama, S.; Tsuruya, S.; Masai, M. Catalytic Activity of NaZSM-5 Supported Cu Catalysts with or without Added metal in Benzyl Alcohol Oxidation. J. Chem. Soc., Faraday Trans. 1997, 93, 659. (10) Xu, J.; Ekblad, M.; Nishiyama, S.; Tsuruya, S.; Masai, M. Effect of Alkali Metals Added to Cu Ion-Exchanged Y-Type Zeolite Catalysts in the Gas-Phase Catalytic Oxidation of Benzyl Alcohol. J. Chem. Soc., Faraday Trans. 1998, 94, 473. (11) Konda, T.; Nishiyama, S.; Tsuruya, S. Influence and Role of Added Alkali Metals on the Gas-Phase Oxidation of Benzyl Alcohol Catalyzed by Cu Ion-exchanged NaX Zeolites. Phys. Chem. Chem. Phys. 1999, 1, 5393. (12) Simandi, L. I. Catalytic Activation of Dioxygen by Metal Complexes; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992. (13) Nishinaga, A. Non-Iron Model Studies on Dioxygenases. In Oxygenases and Model Systems; Funabiki, T., Ed.; Kluwer Academic Publishers: Dordrecht, The Netherlands, 1997. (14) Seiki, T.; Nakato, A.; Nishiyama, S.; Tsuruya, S. Effect and Role of Alkali Metals Added to Cobalt Ion-Exchanged X and Y Zeolite Catalysts in the Gas-Phase Catalytic Oxidation of Benzyl Alcohol. Phys. Chem. Chem. Phys. 2003, 5, 3818. (15) Argauer, R. J.; Landolt, G. R. Crystalline Zeolite ZSM-5 and Method of Preparing the Same. U.S. Patent 3,702,886, 1972. (16) Fujiyama, H.; Kohara, I.; Iwai, K.; Nishiyama, S.; Tsuruya, S.; Masai, M. Liquid-Phase Oxidation of 2,6-Di-tert-butylphenol with Cu-Impregnated MCM-41 Catalysts in the Presence of Alkali Metals. J. Catal. 1999, 188, 417. (17) Murakami, U. The Equipment of Gas Chromatograph. Jpn. Pat. S 37-8,447, 1962. (18) Stranick, M. A.; Houalla, M.; Hercules, D. M. The Effect of Boron on the State and Dispersion of Co/Al2O3 Catalysts. J. Catal. 1987, 104, 396. (19) Ramirez, J.; Castillo, P.; Cedeno, L.; Cuevas, R.; Castillo, M.; Palacios, J. M.; Lopez-Agudo, A. Effect of Boron Addition on the Activity and Selectivity of Hydrotreating CoMo/Al2O3 Catalysts. Appl. Catal., A: General 1995, 132, 317. (20) McLendon, G.; Martell, A. E. Inorganic Oxygen Carrier as Models for Biological Systems. Coord. Chem. Rev. 1976, 19, 1. (21) Jones, R. D.; Summerville, D. A.; Basolo, F. Synthetic Oxygen Carriers Related to Biological Systems. Chem. Rev. 1979, 79, 139.

Received for review March 8, 2004 Revised manuscript received May 19, 2004 Accepted July 1, 2004 IE040078E