Shigeru Tsuruya

Formation of Cu-supported mesoporous silicates and aluminosilicates and liquid-phase oxidation of benzene catalyzed by the Cu-mesoporous silicates and aluminosilicates

Mesoporous silicates (MCM-41 and Al-containing MCM-41) were applied to catalyst supports for liquid-phase benzene oxidation paying attention to their remarkable features, such as large surface area, ordered mesopores and high thermal stability. The MCM-41-supported Cu catalysts were prepared by the method of impregnation (Cu/MCM-41) and ion-exchange treatment (Cu–Na·MCM-41, Cu–H·MCM-41). The liquid-phase oxygenation of benzene to phenol over the MCM-41-supported Cu catalysts was studied using molecular oxygen as an oxidant and ascorbic acid as a reducing reagent for the Cu species. The MCM-41-supported Cu catalysts, particularly the Cu ion-exchanged H·MCM-41 (Cu–H·MCM-41), were more active than the corresponding Cu catalysts supported on SiO2, TiO2, MgO, NaZSM-5, NaY, or KL zeolites. The accumulation of hydrogen peroxide (H2O2) was confirmed during the liquid-phase oxidation of benzene catalyzed by the Cu-supported MCM-41.

Oxidation of benzyl alcohol over Co(II)NaY zeolites

Abstract Benzyl alcohol oxidation was carried out with a Y-type zeolite catalyst ion-exchanged with cobalt(II) ion (Co(II)NaY) in a flow system operated at atmospheric pressure and temperatures of 320 to 390 °C. The Co(II)NaY catalyst was found to have high selectivity for benzaldehyde, a partial oxidation product, in comparison with that of Cu(II)NaY catalyst. The catalytic activity was proportional to the degree of Co(II) ion exchange up to a level of about 65 to 70%. This dependence of the oxidation activity of Co(II)NaY catalyst upon cobalt(II) ion content emphasizes the importance of this exchanged cobalt(II) ion as the main active site for benzyl alcohol oxidation. The rate of formation of benzaldehyde was second order in benzyl alcohol and 0.5 order in oxygen ( r φCHO = k · [ φCH 2 OH ] 2 · [ O 2 ] 1 2 ). An activation energy of 25.6 kcal/mole was observed in the temperature range 320 to 390 °C. The effect of amine addition in the Co(II)NaY catalytic system was investigated by the variation of the amount of amine addition. The addition of pyridine or piperidine increased the oxidation activity, while the addition of ethylenediamine decreased the oxidation activity. Increased concentrations of ethylenediamine resulted in the complete deactivation of Co(II)NaY catalyst for this oxidation. Cobalt(II)-pyridine or -piperidine adduct formation within the large cavities of a Co(II)NaY catalyst was demonstrated by infrared measurements. A mechanism for benzaldehyde formation over Co(II)NaY catalyst, in which dissociative oxygen species participate as a form of [CoO], is proposed on the basis of the kinetic result obtained here. The presence of the dissociative oxygen species adsorbed on cobalt ions was suggested to contribute to the high selectivity for benzaldehyde, a partial oxidation product of benzyl alcohol.

One-step gas-phase catalytic oxidation of benzene to phenol with molecular oxygen over Cu-supported ZSM-5 zeolites

The gas-phase catalytic oxidation of benzene was carried out using molecular oxygen as an oxidant over Cu-supported catalysts. Phenol was formed only when using Cu-supported high-silica-type zeolites as catalysts. The Cu-supported H-ZSM-5 zeolite (CuH-ZSM-5) was the most active among those tested. Deep oxidation products (CO and CO2) were also produced together with phenol and they were suggested to form either via phenol or directly from benzene, based on the activity test experiments by varying the contact time. The yield and selectivity of phenol had a maximum with respect to the Cu contents in the CuH-ZSM-5, and were optimized with ca. a 0.77 wt.% Cu loading (phenol yield ∼4.9%). The calcination of the CuH-ZSM-5 at the higher temperature of around 1123 K was found to be effective for the phenol formation. The H-ZSM-5 with lower Si/Al atomic ratios was an effective support for the phenol formation. The EPR study revealed that the increase in the square-pyramidal Cu2+ species was brought about when the CuH-ZSM-5 was calcined at higher temperatures or when HZSM-5 with lower Si/Al atomic ratios was used as a support. The isolated square-pyramidal Cu2+ species was suggested to be the active species for the phenol formation.

Liquid-phase hydrogenation of car☐ylic acid on supported bimetallic RuSn-Alumina catalysts

Abstract Heterogeneous Ru Sn catalysts are effective for the liquid-phase hydrogenation of C O group in car☐ylic acids. Hydrogenation activity was affected by the kind of tin compounds used for the preparation of the Ru Sn catalyst. Bis-tributyl tin oxide ((Bu 3 Sn) 2 O), K 2 SnO 3 and Na 2 SnO 3 were found to be the appropriate materials for the hydrogenation of C O group over the Ru Sn catalysts. The C O hydrogenation activity for the hydrogenation of car☐ylic acids increased with the increasing amount of Sn added whereas, the C C hydrogenation activity decreased. Effect of activation temperature was also studied. The C O hydrogenation activity was increased by calcinating the catalyst precursor, Sn/alumina, before impregnation with Ru solution. The calcination of the Sn/alumina at 973 K was quite effective for the hydrogenation of car☐ylic acids over the resultant Ru Sn/alumina catalysts. The Ru Sn/alumina catalysts reduced at 723 K were also effective for the hydrogenation of car☐ylic acids. We have also studied the hydrogenation in a continuously flowing system. The Ru Sn/alumina catalysts showed high and stable activity under mild conditions in the flowing system.

Benzyl alcohol oxidation over Y-type zeolite ion-exchanged with copper(II) ion

Abstract The vapor-phase oxidation of benzyl alcohol catalyzed by Y-type zeolite, in which the Na+ had been replaced by copper(II) ion, has been investigated in a flow system with reaction temperature between 300 to 390 °C. The main oxidation products were benzaldehyde, CO2, and CO. The main active site for this oxidation was found to be Cu(II) ion in the zeolite. The rate for benzaldehyde formation was best described as first order in oxygen and reciprocal first order in benzyl alcohol, respectively (rφCHO = k · [O2]1[φCH2OH]−1), and an apparent activation energy of 13.6 kcal/mol was observed on this basis in the temperature range 330 to 390 °C. The catalytic activity for the oxidation of benzyl alcohol was found to be affected by the addition of amine. Piperidine addition increased the oxidation activity, while pyridine addition decreased the oxidation activity. The bonding parameters obtained from ESR measurement of Cu(II)NaY-amine systems indicate that covalent bonding strength between Cu(II) and piperidine is stronger than that with pyridine. A reaction mechanism for the oxidation of benzyl alcohol to benzaldehyde over Cu(II)NaY was proposed on the basis of the results obtained.

The oxidative coupling reaction of 2,6-dimethylphenol with heterogeneous basic copper(II) catalysts

The oxidation of 2,6-dimethylphenol by heterogeneous basic copper (II) catalyst (CuCl2KOH system) without amine such as pyridine under an oxygen atmosphere resulted in the formation of the corresponding coupling products, polyphenylene oxide (CO coupling product) and diphenoquinone (CC coupling product). The KOHCuCl2 ratio was found to be the main factor which controls the coupling manner, namely, the increase of this ratio was favorable for CO coupling, whereas CC coupling product was liable to be preferentially obtained under a low KOHCuCl2 ratio. The effect of the variation in base and copper(II) salt on the product yield and/or the reaction rate were discussed in terms of the catalytic activity of the basic copper(II) system formed. In contrast to hitherto reported homogeneous copper complex catalysts, it was found that the heterogeneous basic copper (II) system in the absence of oxygen could not catalyze the oxidative coupling reaction of 2,6-dimethylphenol. The role of oxygen was discussed on the basis of esr spectra of the mixed system consisting of the catalyst and 2,6-dimethylphenol. From the esr measurement of the mixed system under an oxygen atmosphere, the corresponding polymer radical was observed.

Effect of alkali-metal promoter on silica-supported copper catalysts in benzyl alcohol oxidation

The effect of alkali metals, such as Na, added to silica-supported copper (Cu/SiO2) catalysts has been studied in the gas-phase catalytic oxidation of benzyl alcohol. The main products were benzaldehyde as a partial oxidation product and carbon dioxide as a complete oxidation product. The silica-supported copper catalysts were prepared using both ion-exchange and impregnation methods. The catalyst prepared by the impregnation method (Cuimp/SiO2) had a higher oxidation activity than (Cuex/SiO2) prepared by the ion-exchange method. The effects of reaction temperature and the amount of supported Cu on the oxidation activity were investigated using the catalysts both with and without added Na. The addition of alkali metal to the silica-supported copper catalysts prepared by both methods was found to promote the oxidation activity, particularly the partial oxidation activity. The coordination and redox properties of the Cu/SiO2 catalysts, with and without alkali metal, were investigated using diffuse reflectance (DR) spectroscopy and temperature-programmed reduction (TPR) measurements. It is suggested, based on the DR spectra, that the alkali-metal added to the Cu/SiO2 catalysts decreases the electronegativity of the supported Cu species; this decrease makes dissociative oxygen adsorption easier. The other role of the added alkali metal was thought to be to remove the oxidic Cu species which do not have catalytic activity for the partial oxidation.

Unique hydrogenation activity of supported tin catalyst: Selective hydrogenation catalyst for unsaturated aldehydes

Abstract Selective hydrogenation of unsaturated aldehydes, crotonaldehyde (CH 3 CHCHCHO) and cinnamaldehyde (C 6 H 5 CHCHCHO), has been studied over SiO 2 -supported monometallic Sn and bimetallic RhSn catalysts in the liquid phase. Over a silica-supported monometallic Rh catalyst, Rh SiO 2 , no unsaturated alcohol (crotyl alcohol or cinnamyl alcohol) was formed, whereas considerable amounts of the corresponding saturated aldehyde and saturated alcohol were obtained. The selectivity to the unsaturated alcohol was improved over the RhSn bimetallic catalyst. The selectivity to the corresponding unsaturated alcohol attained ca. 65% over the RhSn bimetallic catalysts. On the other hand, The supported Sn catalyst showed markedly high selectivity to the unsaturated alcohols. The selectivity of the Sn SiO 2 , attained 95% to crotyl alcohol and 100% to cinnamyl alcohol, respectively. Although the conversion of each unsaturated aldehyde over RhSn SiO 2 catalysts was greater than that over Sn SiO 2 catalysts, the selectivity of Sn SiO 2 catalysts to the corresponding unsaturated alcohols was superior to that over RhSn SiO 2 . The selectivity of Sn SiO 2 was also compared with that of RhSn SiO 2 at a similar conversion of the unsaturated aldehydes. The selectivity of Sn SiO 2 was significantly greater than that of the RhSn bimetallic catalyst. These results indicate that the high selectivity over Sn SiO 2 was ascribed not to low conversion but to intrinsic selectivity of the Sn catalyst.

Deactivation of zeolites in n-hexane cracking

Abstract The deactivation process of the H-type zeolites (H-mordenite, H-Y zeolite, and H-ZSM-5) in n-hexane cracking was studied using a pulse method in which the emphasis was put on the clarification of the initial stage of the deactivation of these H-type zeolites. The adsorption behaviors of n-hexane and ammonia on fresh and used zeolites were compared in order to elucidate the relationship between the micropore structure of the zeolites and the deactivation by the carbonaceous deposits (coke). The main deactivation of the H-mordenite (HM) zeolite was found to be caused by pore blockage of the deposited coke. The H-Y zeolite (HY) was suggested to be deactivated by the proton coverage of the coke. No deactivation of the H-ZSM-5 (HZ) was observed under the present pulse conditions. These deactivation behaviors of the H-type zeolites were found to be consistent with the results obtained by a gravimetric flow method. The initial activity, defined as the conversion at the first pulse, could be correlated with the strong acidity, irrespective of the micropore structure of the zeolites used. The correlation of both the initial aromatic and coke yields with the strong acidity was discussed in connection with the micropore structure of the H-type zeolites.

Ethanol conversion over ion-exchanged ZSM-5 zeolites

Abstract The activities of ZSM-5 zeolites ion exchanged with proton and Cu II for ethanol conversion were observed using an ordinary flow reaction in order to explore the role of the proton and the transition metal ion in the conversion of ethanol under an atmosphere with and without oxygen. Proton-exchanged ZSM-5 favoured the dehydration of ethanol to form ethene, irrespective of the presence or absence of oxygen. On the other hand, the transition metal ion in the ZSM-5 promoted the deep oxidation of ethanol to form a deep oxidation product (carbon dioxide + carbon monoxide) under the reaction conditions used. Increasing the concentration of the surface hydroxyl groups of the H-NaZSM-5 catalysts caused an increase in dehydration activity and a decrease in the activity for oxidation. Increased Cu II ion-exchange in Cu II -NaZSM-5 increased the activity for oxidation of ethanol. Various intermediates were observed in the situ Fourier transform IR spectra of ethanol adsorbed on HZSM-5, and Cu II -NaZSM-5. Reaction schemes for the dehydration of ethanol to ethene over HZSM-5 and the oxidation of ethanol over Cu II -NaZSM-5 are suggested.