Vapor-phase Oxidation Of Benzyl Alcohol Research Articles

Tuning surfactant-templates of nanorod-like cryptomelane synthesis towards vapor-phase selective oxidation of benzyl alcohol

In this study, nanorod-like cryptomelane was prepared via reduction of potassium permanganate in the presence of Tergitol (S1) and cetyltrimethylammonium bromide (CTAB, S2) as surfactant-templates. X-ray powder diffraction, scanning electron microscopy and N2 adsorption–desorption isotherms indicated the microporous nanorod-like cryptomelane structure. Element analysis revealed 7.5 wt% (S1) and 4.5 wt% (S1) of potassium while thermal gravimetricanalysis and temperature program desorption of oxygen revealed more active oxygen species over S2 catalyst, consisting to a lower H2 consumption over S2 (3.04 mmolH2/g) than that over S1 (3.55 mmolH2/g). Both Tergitol and CTAB surfactant-templates contributed to significant enhancement of their catalytic reactivity in vapor-phase oxidation of benzyl alcohol to benzaldehyde (rPhCHO = 68.6 and 74.6 mmolPhCHO/g.h at 280 °C over S1 and S2 catalysts, respectively). S1 catalyst possesses unique properties such as uniform nano-rod morphology, high thermal stability and considerable rPhCHO at 240–280 °C, adapting the industrial processes to produce chlorine-free benzaldehyde.

황이 포함된 중형기공성 탄소에 화학적으로 고정화된 H5PMo10V2O40촉매 상에서 Benzyl Alcohol 산화반응

황이 포함된 중형기공성 탄소 담체(S-MC)에 화학적으로 고정화된 <TEX>$H_5PMo_{10}V_2O_{40}$</TEX> (<TEX>$PMo_{10}V_2$</TEX>) 촉매를 제조하고, 이를 Benzyl alcohol 산화반응에 적용해보았다. 먼저 주형물질로 SBA-15, 탄소 전구체로 p-Toluenesulfonic acid를 이용하여 S-MC 지지체를 제조하였다. 이후, <TEX>$PMo_{10}V_2$</TEX> 촉매가 화학적으로 고정화될 수 있는 위치를 제공하기 위해 S-MC 지지체의 표면이 양전하를 띠도록 개질시켰다. 전체적으로 음전하를 띠는 <TEX>$[PMo_{10}V_2O4_{40}</TEX><TEX>]</TEX><TEX>^{5-}$</TEX>를 이용함으로써 <TEX>$PMo_{10}V_2$</TEX>를 양이온을 띠는 S-MC 표면에 화학적으로 고정화하였다. 화학적 고정화를 통해 <TEX>$PMo_{10}V_2$</TEX>가 분자수준으로 균일하게 분산되었음을 확인하였다. Benzyl alcohol의 기상 산화반응에서 <TEX>$PMo_{10}V_2$</TEX>/S-MC 촉매는 무담지 상태의 <TEX>$PMo_{10}V_2$</TEX>보다 높은 전화율 및 수율을 나타냈다. <TEX>$PMo_{10}V_2$</TEX>/S-MC 촉매의 반응 활성이 향상된 이유는 화학적 고정화를 통해 <TEX>$PMo_{10}V_2$</TEX>이 S-MC 지지체에 고르게 분산되었기 때문이다. <TEX>$H_5PMo_{10}V_2O_{40}$</TEX> (<TEX>$PMo_{10}V_2$</TEX>) catalyst chemically immobilized on sulfur-containing mesoporous carbon (S-MC) was prepared, and it was applied to the benzyl alcohol oxidation reaction. S-MC was synthesized by a templating method using SBA-15 and p-toluenesulfonic acid as a templating agent and a carbon precursor, respectively. S-MC was then modified to have a positive charge, and thus, to provide sites for the immobilization of <TEX>$PMo_{10}V_2$</TEX>. By taking advantage of the overall negative charge of <TEX>$[PMo_{10}V_2O4_{40}</TEX><TEX>]</TEX><TEX>^{5-}$</TEX>, <TEX>$PMo_{10}V_2$</TEX> catalyst was immobilized on the S-MC support as a charge matching component. It was revealed that <TEX>$PMo_{10}V_2$</TEX> species were finely and molecularly dispersed on the S-MC via chemical immobilization. In the vapor-phase oxidation of benzyl alcohol, <TEX>$PMo_{10}V_2$</TEX>/S-MC catalyst showed higher conversion of benzyl alcohol and higher yield for benzaldehyde and benzoic acid than unsupported <TEX>$PMo_{10}V_2$</TEX> catalyst. The enhanced catalytic performance of <TEX>$PMo_{10}V_2$</TEX>/S-MC was due to fine dispersion of <TEX>$PMo_{10}V_2$</TEX> species on the S-MC via chemical immobilization.

Scanning tunneling microscopy investigation of nano-structured α-K5PW11(M x OH2)O39(M = Mn(II), Co(II), Ni(II), and Zn(II)) Keggin heteropolyacid catalyst monolayers.

Nano-structured α-K5PW11(M x OH2)O39 (M = Mn(II), Co(II), Ni(II), and Zn(II)) Keggin heteropolyacids (HPAs) were investigated by scanning tunneling microscopy (STM) and tunneling spectroscopy (TS) measurements in order to elucidate their redox property and oxidation catalysis. HPA molecules formed two-dimensional self-assembled monolayer arrays on highly oriented pyrolytic graphite (HOPG) surface. Furthermore, HPAs exhibited a distinctive current-voltage behavior referred to as negative differential resistance (NDR) phenomenon. The measured NDR peak voltage of HPAs was correlated with the reduction potential and the absorption edge energy determined by electrochemical method and UV-visible spectroscopy, respectively. NDR peak voltage of HPAs appeared at less negative voltage with increasing reduction potential and with decreasing UV-visible absorption edge energy. The correlations strongly suggested that NDR phenomenon was closely related to the redox property of HPAs. Vapor-phase oxidation of benzyl alcohol to benzaldehyde was carried out as a model reaction to track the oxidation catalysis of HPAs. NDR peak voltage appeared at less negative voltage with increasing yield for benzaldehyde.

Redox Properties and Catalytic Oxidation Activities of Polyatom-Substituted H n PW11M1O40 (M = V, Nb, Ta, and W) Keggin Heteropolyacid Catalysts

Redox properties and catalytic oxidation activities of polyatom-substituted H n PW11M1O40 (M = V, Nb, Ta, and W) Keggin heteropolyacids (HPAs) were examined. Reduction potentials and UV–visible absorption edge energies of H n PW11M1O40 (M = V, Nb, Ta, and W) HPA catalysts in solution were determined by an electrochemical method and UV–visible spectroscopy measurements, respectively. It was observed that reduction potentials of H n PW11M1O40 (M = V, Nb, Ta, and W) HPA catalysts increased and UV–visible absorption edge energies of the HPA catalysts decreased with decreasing electronegativity of substituted polyatom. It was also found that the lower absorption edge energy corresponded to the higher reduction potential of the HPA catalyst. Vapor-phase oxidation of benzyl alcohol was carried out as a model reaction to probe the redox properties of H n PW11M1O40 (M = V, Nb, Ta, and W) HPA catalysts. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalyst, and in turn, with decreasing electronegativity of substituted polyatom. Reduction potential of H n PW11M1O40 (M = V, Nb, Ta, and W) HPA catalysts measured by an electrochemical method and absorption edge energy of the HPA catalysts measured by UV–visible spectroscopy could be utilized as a probe of oxidation catalysis of the HPA catalysts.

Redox properties of H3PMoxW12−xO40 and H6P2MoxW18−xO62 heteropolyacid catalysts and their catalytic activity for benzyl alcohol oxidation

Abstract Reduction potentials of H 3 PMo x W 12− x O 40 ( x = 0, 3, 6, 9, and 12) Keggin heteropolyacid (HPA) and H 6 P 2 Mo x W 18− x O 62 ( x = 0, 3, 9, 15, and 18) Wells-Dawson HPA catalysts were measured by an electrochemical method in solution. UV–visible spectra of H 3 PMo x W 12− x O 40 and H 6 P 2 Mo x W 18− x O 62 catalysts in solution were then obtained in order to explore the reduction potentials of the HPA catalysts. Reduction potentials increased and UV–visible absorption edge energies shifted to lower values with increasing molybdenum substitution in both families of H 3 PMo x W 12− x O 40 and H 6 P 2 Mo x W 18− x O 62 catalysts. It was revealed that the lower absorption edge energy corresponded to the higher reduction potential of the HPA catalyst. In order to correlate the redox property (reduction potential and absorption edge energy) with the catalytic oxidation activity of H 3 PMo x W 12− x O 40 and H 6 P 2 Mo x W 18− x O 62 catalysts, vapor-phase oxidation of benzyl alcohol was carried out as a model reaction. Yield for benzaldehyde increased with increasing reduction potential and with decreasing absorption edge energy of the HPA catalyst, regardless of the identity of HPA catalyst (without HPA structural sensitivity). The absorption edge energies measured by UV–visible spectroscopy could be utilized as a correlating parameter for the reduction potentials (oxidizing powers) of H 3 PMo x W 12− x O 40 and H 6 P 2 Mo x W 18− x O 62 catalysts, and furthermore, as a probe of oxidation catalysis of the HPA catalysts.

Preparation of H 5PMo 10V 2O 40 catalyst immobilized on nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) and its application to the vapor-phase oxidation of benzyl alcohol

Nitrogen-containing mesostructured cellular foam carbon (N-MCF-C) was synthesized by a templating method using mesostructured cellular foam silica (MCF-S) and polypyrrole as a templating agent and a carbon precursor, respectively. The N-MCF-C was then modified to have a positive charge, and thus, to provide a site for the immobilization of [PMo 10V 2O 40] 5−. By taking advantage of the overall negative charge of [PMo 10V 2O 40] 5−, H 5PMo 10V 2O 40 (PMo 10V 2) catalyst was chemically immobilized on the N-MCF-C support as a charge-matching component. Characterization results showed that the PMo 10V 2 catalyst was finely dispersed on the N-MCF-C support via strong chemical interaction, and that the pore structure of N-MCF-C was still maintained even after the immobilization of PMo 10V 2. In the vapor-phase oxidation of benzyl alcohol, the PMo 10V 2/N-MCF-C catalyst showed a higher conversion and a higher oxidation activity (formation of benzaldehyde) than the unsupported PMo 10V 2 and PMo 10V 2/MCF-S catalysts.

Catalysis of copper(II)-NaZSM-5 zeolites during benzyl alcohol oxidation

The vapor-phase oxidation of benzyl alcohol over copper(II) ion-exchanged NaZSM-5 type zeolites (Cu(II)-NaZSM-5) was studied. The major products were benzaldehyde and carbon oxides (CO 2 +CO). The Cu(II)-NaZSM-5 catalysts showed higher catalytic activity for benzyl alcohol oxidation than the corresponding Y type zeolites.

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

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, CO 2, 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 ( r φCHO = k · [O 2] 1[ φCH 2OH] −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.