Abstract:a b s t r a c tInverse micelle templated mesoporous manganese oxide (University of Connecticut mesoporous material, UCT-1) and ion promoted mesoporous manganese oxides (UCT-18-X, X = Mg 2+ , Ca 2+ , K + , Na + and Cs + ) having trace amount of alkali metal ions as promoters with tunable porosity and crystallinity were synthesized. The synthesis was based on the use of inverse micelles as soft templates and unique NO x chemistry as established for recently discovered UCT materials. The materials were tested for… Show more
“…The defects promoted the adsorption of the oxygen as indicated by O 2 -TPD, which would enhance the catalytic activity. Furthermore, the structure and crystallinity of samples obtained were similar to what Sourav and his group reported recently [6], and the manganese oxides they made still have good performance in benzyl alcohol oxidation after being recycled four times. So we believe that our catalysts could also have excellent reusability.Fig.…”
Section: Resultssupporting
confidence: 84%
“…Both products can act as versatile intermediates for the synthesis of fine chemicals or perfume [2–7]. In the past few years, numerous catalytic systems have been developed to perform this chemo-selective oxidation of alcohols [6]. Both homogeneous and heterogeneous catalysts can perform this benzyl alcohol oxidation.…”
Section: Introductionmentioning
confidence: 99%
“…Both homogeneous and heterogeneous catalysts can perform this benzyl alcohol oxidation. Traditional homogeneous catalytic systems for the oxidation of benzyl alcohols use stoichiometric chemicals such as chromium (VI) reagents, dimethyl sulfoxide, hydrogen peroxide, tert-butyl hydroperoxide (TBHP), nitric acid, and permanganates or other inorganic oxidants [6, 8]. Homogeneous catalysis normally has excellent reactivity and selectivity in a small scale reaction since in homogeneous catalysts every single catalytic entity can act as a single active site [9–12].…”
The liquid phase oxidation of benzyl alcohol is an important reaction for generating benzaldehyde and benzoic acid that are largely required in the perfumery and pharmaceutical industries. The current production systems suffer from either low conversion or over oxidation. From the viewpoint of economy efficiency and environmental demand, we are aiming to develop new high-performance and cost-effective catalysts based on manganese oxides that can allow the green aerobic oxidation of benzyl alcohol under mild conditions. It was found that the composition of the precursors has significant influence on the structure formation and surface property of the manganese oxide nanoparticles. In addition, the crystallinity of the resulting manganese nanoparticles was gradually improved upon increasing the calcination temperature; however, the specific surface area decreased obviously due to pore structure damage at higher calcination temperature. The sample calcined at the optimal temperature of 600 °C from the precursors without porogen was a Mn3O4-rich material with a small amount of Mn2O3, which could generate a significant amount of species on the surface that contributed to the high catalytic activity in the oxidation. Adding porogen with precursors during the synthesis, the obtained catalysts were mainly Mn2O3 crystalline, which showed relatively low activity in the oxidation. All prepared samples showed high selectivity for benzaldehyde and benzoic acid. The obtained catalysts are comparable to the commercial OMS-2 catalyst. The synthesis–structure–catalysis interaction has been addressed, which will help for the design of new high-performance selective oxidation catalysts.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1777-y) contains supplementary material, which is available to authorized users.
“…The defects promoted the adsorption of the oxygen as indicated by O 2 -TPD, which would enhance the catalytic activity. Furthermore, the structure and crystallinity of samples obtained were similar to what Sourav and his group reported recently [6], and the manganese oxides they made still have good performance in benzyl alcohol oxidation after being recycled four times. So we believe that our catalysts could also have excellent reusability.Fig.…”
Section: Resultssupporting
confidence: 84%
“…Both products can act as versatile intermediates for the synthesis of fine chemicals or perfume [2–7]. In the past few years, numerous catalytic systems have been developed to perform this chemo-selective oxidation of alcohols [6]. Both homogeneous and heterogeneous catalysts can perform this benzyl alcohol oxidation.…”
Section: Introductionmentioning
confidence: 99%
“…Both homogeneous and heterogeneous catalysts can perform this benzyl alcohol oxidation. Traditional homogeneous catalytic systems for the oxidation of benzyl alcohols use stoichiometric chemicals such as chromium (VI) reagents, dimethyl sulfoxide, hydrogen peroxide, tert-butyl hydroperoxide (TBHP), nitric acid, and permanganates or other inorganic oxidants [6, 8]. Homogeneous catalysis normally has excellent reactivity and selectivity in a small scale reaction since in homogeneous catalysts every single catalytic entity can act as a single active site [9–12].…”
The liquid phase oxidation of benzyl alcohol is an important reaction for generating benzaldehyde and benzoic acid that are largely required in the perfumery and pharmaceutical industries. The current production systems suffer from either low conversion or over oxidation. From the viewpoint of economy efficiency and environmental demand, we are aiming to develop new high-performance and cost-effective catalysts based on manganese oxides that can allow the green aerobic oxidation of benzyl alcohol under mild conditions. It was found that the composition of the precursors has significant influence on the structure formation and surface property of the manganese oxide nanoparticles. In addition, the crystallinity of the resulting manganese nanoparticles was gradually improved upon increasing the calcination temperature; however, the specific surface area decreased obviously due to pore structure damage at higher calcination temperature. The sample calcined at the optimal temperature of 600 °C from the precursors without porogen was a Mn3O4-rich material with a small amount of Mn2O3, which could generate a significant amount of species on the surface that contributed to the high catalytic activity in the oxidation. Adding porogen with precursors during the synthesis, the obtained catalysts were mainly Mn2O3 crystalline, which showed relatively low activity in the oxidation. All prepared samples showed high selectivity for benzaldehyde and benzoic acid. The obtained catalysts are comparable to the commercial OMS-2 catalyst. The synthesis–structure–catalysis interaction has been addressed, which will help for the design of new high-performance selective oxidation catalysts.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1777-y) contains supplementary material, which is available to authorized users.
“…The new evidence of ion induced promotion of activity enhancement of inverse micelle templated mesoporous manganese oxides for aerobic oxidation reactions has been revealed in [16]. Ion promoted mesoporous manganese oxides (UCT-18-X, X= Mg 2+ , Ca 2+ , K + , Na + and Cs + ) having trace amount of alkali metal ions were tested for selective aerobic alcohol oxidation and the catalytic activity following the order of UCT-1 <UCT-18-Mg <UCT-18-Ca <UCT-18-K<UCT-18-Na <UCT-18-Cs.…”
The ionic dopant additives have different mechanisms of their influence upon MnO2 electrocrystallisation process and depending on dopants added the following polymorphs are stabilised: α-MnO2 (hollandite, I4/m) -NH + 4 ; γ-MnO2 (ramsdellite, P bnm) -Co 2+ , Fe 2+ ; layered polymorph δ-MnO2 (birnessite, C2/m) -Cr 3+ . The defect states of intergrowth method in ramsdellite matrix and twinning, OH groups studied by X-ray diffraction and the Fourier transform infrared mtehod, respectively, indicate their high content in case of Fe 2+ and Co 2+ -doped manganese dioxide. CVA oxygen reduction reaction peaks were established after experiments in alkaline electrolytes and dioxygen (argon, air) atmosphere. Activity of doped samples studied is comparable with other published data. Both doped with Co 2+ and Fe 2+ samples display maximal currents and some distinctive features in oxygen reduction reaction.
“…Cation promoted mesoporous manganese oxides show increased catalytic activity while maintaining the structural characterization of traditional UCT material. However, one system that has been studied extensively in catalytic reactions involves doping with Cs + ions [2]. The levels of dopants like Cs + can be very small, perhaps 1 in 100 metal ions.…”
UCT (University of Connecticut) mesoporous transition metal oxide materials are synthesized using an inverse micelle soft template and unique NOx chemistry. The resulting aggregated nanoparticles exhibit tunable pore structures, excellent thermal stability, and easily accessible oxidation states which contribute to a wide range of organic catalytic transformations [1]. Among the variety of transition metal oxide systems, mesoporous manganese oxides have proven to be efficient catalysts in the oxidation of alcohols to carboxylic acids. In addition to organic catalysis, there is interest in using the various mesoporous metal oxides in other fields such as energy and advanced separations.Doping of UCT materials is still in its infancy. Cation promoted mesoporous manganese oxides show increased catalytic activity while maintaining the structural characterization of traditional UCT material. However, one system that has been studied extensively in catalytic reactions involves doping with Cs + ions [2]. The levels of dopants like Cs + can be very small, perhaps 1 in 100 metal ions. In addition there has been some doping with transition metal systems such as iron doped manganese, cobalt doped iron, nickel doped titanium, and similar systems. These materials have interesting magnetic properties. Very few details of the location of these dopant ions are available.Typically, catalyst morphology is examined using SEM and TEM techniques. A dilute solution drop onto carbon film copper grid sample preparation for TEM is adequate to analyze the electron transparent particles along the edges of the aggregate. FIB has been employed in many cases to analyze cross sections of nanoparticles. This is typically done by first immobilizing the particles in a matrix (epoxy, metal, etc.) or on a substrate in order to obtain an adequate lamella without the loss of material due to structural instability [3][4][5]. In this work, lamella preparation of a variety of doped UCT materials is performed using an FEI Helios Nanolab 460F1 FIB without the use of bulk matrix immobilization in order to determine if the centers of these aggregates reflect the morphology and pore structure confirmed along the edges. TEM-EDS (FEI Talos S/TEM) of these cross sectioned particles can also be utilized to verify even distribution of detectable dopant amounts in the center of the aggregate [6].
References:[1] A.
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