Benzaldehyde Selectivity Research Articles

Mixed-Metal Metal–Organic Frameworks as Catalysts for Liquid-Phase Oxidation of Toluene and Cycloalkanes

A series of isostructural mixed-metal metal–organic frameworks (MM-MOFs) of 1,3,5-benzenetricarboxylate (BTC), M–Zn–BTC, where M = Cu(II), Co(II) and Fe(II) have been synthesized using the post-synthetic exchange method. The catalytic activities of the M–Zn–BTC have been investigated for the oxidation of toluene and cycloalkanes in the presence of hydrogen peroxide as oxidant. The M–Zn–BTC catalysts show improved activity and selectivity for toluene oxidation. The introduction of the second metal to the node of the MOFs improved the toluene conversion from 22 to 70% and the selectivity of benzaldehyde improved from 22 to 57%. The Fe–Zn–BTC showed the best activity in terms of benzaldehyde selectivity for the oxidation of toluene. However, Cu–BTC gave the highest conversion for cyclohexane and methylcyclohexane oxidation.

Tuning the Synthesis of Manganese Oxides\xa0Nanoparticles for Efficient Oxidation of Benzyl Alcohol

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 {mathrm{O}}_2^{-} 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.

Selective liquid phase oxidation of benzyl alcohol to benzaldehyde by tert-butyl hydroperoxide over γ-Al2O3 supported copper and gold nanoparticles

Benzyl alcohol oxidation to benzaldehyde was performed by tert-butyl hydroperoxide (TBHP) in the absence of any solvent using γ-Al2O3 supported copper and gold nanoparticles. Li2O and ionic liquids were used as additive and stabilizers for the synthesis of the catalysts. The physico-chemical properties of the catalysts were characterized by atomic absorption spectroscopy (AAS), X-ray diffraction spectroscopy (XRD), N2 absorption/desorption (BET), transmission electron microscopy (TEM), scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and temperature programmed reduction (TPR), whereas, the oxidation reaction was followed by gas chromatography with a flame ionization detector (GC-FID). The as prepared catalysts exhibited good catalytic performance in terms of conversion and selectivity towards benzaldehyde. The performance of the Au-based catalysts is significantly higher than that of the Cu-based catalysts. For both Cu and Au catalysts, the conversion of benzyl alcohol increased as the reaction proceeds, while the selectivity for benzaldehyde decreased. Moreover, the catalysts can be easily recycled and reused with neither significant loss of activity nor selectivity. A kinetic study for the Cu and Au-catalyzed oxidation of benzyl alcohol to benzyldehyde is reported. The rate at which the oxidation of benzyl alcohol is occurring as a function of catalyst and oxidant amounts was investigated, with the apparent rate constant, kapp being proportional to the amount of nano catalyst and oxygen present in the system.

Structure‐Dependent Base‐Free Aerobic Oxidation of Benzyl Alcohol over High‐Surface‐Area Mg‐Doped ZnAl2O4 Spinel Supported Gold Nanoparticles

A facile and economical strategy to synthesize high surface area Mg-doped ZnAl2 O4 spinels is developed. These materials are employed as catalyst supports to prepare supported gold catalysts for the aerobic oxidation of benzyl alcohol by using molecular oxygen in the absence of additional alkali. The as-fabricated supported Au catalyst with the Mg/(Mg+Zn) molar ratio of 0.15 was found to show good catalytic activity with high benzaldehyde selectivity (>99 %) and a high turnover frequency of 5382 h-1 . The relationship between the surface properties of the supported Au catalysts and their catalytic performances reveals that the high catalytic efficiency is mainly attributable to surface cooperative effects between the abundant basic sites and favorable active Au species, including metallic Au and cationic Auδ+ ions. A possible mechanism for selective oxidation of benzyl alcohol is tentatively proposed. Moreover, the as-fabricated supported Au catalyst could be reused at least four times without significant loss of its catalytic performance. The present finding provides a new route for designing high-performance supported noble or non-noble metal catalysts by using high surface area ZnAl2 O4 -based spinels.

Selective oxidation of styrene catalyzed by cerium-doped cobalt ferrite nanocrystals with greatly enhanced catalytic performance

The rare earth metal Ce-doped cobalt ferrite samples CexCo1−xFe2O4 (x=0.1, 0.3, 0.5) were prepared by the sol–gel autocombustion route. The as-prepared samples were characterized by X-ray diffractometry, scanning electron microscopy, transmission electron microscopy, ICP–atomic emission spectroscopy, and N2 physisorption. Their catalytic performance was evaluated in oxidation of styrene using hydrogen peroxide (30%) as oxidant. Compared with pristine CoFe2O4, the Ce-doped samples were found to be more efficient catalysts for the oxidation of styrene to benzaldehyde, with greatly enhanced catalytic performance. Especially, when Ce0.3Co0.7Fe2O4 was used as catalyst, 90.3% styrene conversion and 91.5% selectivity for benzaldehyde were obtained at 90°C for 9h reaction. The catalyst can be magnetically separated easily for reuse, and no obvious loss of activity was observed when it was reused in five consecutive runs.

Highly efficient N-doped magnetic cobalt-graphene composite for selective oxidation of benzyl alcohol

We developed a graphene-directed assembly route to synthesize a hybrid composite by assembling cobalt based framework material ZIF-67 on the graphene oxide (GO). The hybrid composite exhibited excellent catalytic performance in selective oxidation of benzyl alcohol by oxygen molecule with 89.5% conversion and 97.3% benzaldehyde selectivity. The catalyst can be magnetically separated and reused four times without obvious loss in the catalytic activity and selectivity.

Ag-doped 4A-zeolite as an efficient catalyst in the epoxidation of styrene

Silver nanoparticles (Ag NPs) were successfully immobilized onto the 4A-zeolite by a facile, environmentally friendly method, which combined the ion exchange and hydration hydrazine reduction. Several techniques were used to characterize the synthesized Ag NPs/4A-zeolite composite catalyst. The results indicated that Ag NPs have the excellent dispersion on the 4A-zeolite, and it can be pulled to the surface of carrier. Then, the Ag NPs/4A-zeolite composite catalyst was utilized to catalyze styrene epoxidation in order to test the catalytic performances, and excellent catalytic activity and catalytic selectivity of the composite catalyst were revealed when tert-butyl hydroperoxide (TBHP) was used as oxidizing agent. The selectivity of styrene oxide (SO) has been maintained at a high value (>89 %), and the joint selectivity of SO and Benzaldehyde (BZ) also had been maintained at more than 96 %.

Studies of styrene oxidation by catalyst based on zeolite-Y nanohybrid materials

Metal complexes of VO(IV), Mn(II), Fe(II), Co(II), Ni(II), Cu(II) and HNIMMPP (4-(((2-hydroxy-5-nitrophenyl)imino)methyl)-3-methyl-1-phenyl-1H-pyrazol-5-ol) schiff base ligand have been synthesized within zeolite-Y along with neat one. Synthesized compounds were characterized by physico-chemical techniques such as elemental analysis of catalysts, BET, XRD, SEM, FT-IR, UV–vis, ICP-OES and TGA. Synthesized zeolite-Y based nanohybrid materials and their uncovered complexes were used in styrene oxidation with TBHP as an oxidizing agent. Oxidation reaction of styrene furnished benzaldehyde as the major product and styrene glycol, chalcone and 2-phenyloxirane as minor products. Amongst all catalysts, [VO(HNIMMPP)(H2O)]-Y produced the highest conversion at 93.35% and selectivity of benzaldehyde (45.70%) was the greatest. These nanohybrid materials can be easily reprocessed and recovered within these reaction parameters. The reaction mechanism for catalytically oxidized styrene is discussed in the present paper.

Novel conjugated nanoporous alkynyl metalloporphyrin framework as effective catalyst for oxidation of toluene with molecular oxygen

A porous alkynylporphyrin conjugated organic polymer (MnE‐TPP) was synthesized by Sonogashira coupling reaction with Mn(II) 5,10,15,20‐tetrakis(4′‐ethynylphenyl)porphyrin and Mn(II) 5,10,15,20‐tetrakis(4′‐bromophenyl)porphyrin as building blocks. The polymer was characterized using nitrogen adsorption–desorption isotherms, field‐emission scanning electron microscopy, high‐resolution transmission electron microscopy, Fourier transform infrared and UV–visible spectroscopies, X‐ray diffraction, thermogravimetry and inductively coupled plasma atomic emission spectrometry. The electrochemical behaviors of MnE‐TPP were investigated by cyclic voltammetry. MnE‐TPP was developed as a heterogeneous catalyst for the activation of molecular oxygen to oxidize toluene under mild conditions. The selectivity of total benzaldehyde and benzyl alcohol remained above 70.0% with a conversion of toluene up to 10.2%. The turnover number was as high as 13 653. Also, MnE‐TPP remained structurally stable and the toluene conversion rate hardly decreased after 5 h of reaction and five cycles of reuse.

Highly efficient V-Mo-Fe-O catalysts for selective oxidation of toluene to benzaldehyde

The V-Mo-Fe-O catalysts were synthesized by a sol-gel method, characterized and used for the selective oxidation of toluene to benzaldehyde with hydrogen peroxide. The results show that V-Mo-Fe-O catalyst is an effective catalyst, exhibiting a toluene conversion of 40.3%, and a benzaldehyde selectivity of 84.5% at 80°C. Scanning electron microscopy (SEM) shows that the catalyst has nanorod structure with a thin layer compound, which may be constitutive of iron molybdate while the main compound of catalyst is MoV2O8. Furthermore, the catalyst can be easily recycled and reused for four times without significant changes in its activity.

Ultrafine MnO2 nanoparticles decorated on graphene oxide as a highly efficient and recyclable catalyst for aerobic oxidation of benzyl alcohol

The highly active and selective aerobic oxidation of aromatic alcohols over earth-abundant, inexpensive and recyclable catalysts is highly desirable. We fabricated herein MnO2/graphene oxide (GO) composites by a facile in-situ growth approach at room temperature and used them in selective aerobic oxidation of benzyl alcohol to benzaldehyde. TEM, XRD, FTIR, XPS and N2 adsorption/desorption analysis were employed to systematically investigate the morphology, particle size, structure and surface properties of the catalysts. The 96.8% benzyl alcohol conversion and 100% benzaldehyde selectivity over the MnO2/GO (10/100) catalyst with well dispersive ultrafine MnO2 nanoparticles (ca. 3nm) can be obtained within 3h under 383K. Simultaneously, no appreciable loss of activity and selectivity occurred after recycling use up to six times. Due to their significant low cost, excellent catalytic performance, the MnO2/GO composites have huge application prospect in organic synthesis.

Gold-catalyzed selectivity-switchable oxidation of benzyl alcohol in the presence of molecular oxygen

A selectivity-switchable oxidation of benzyl alcohol by molecular oxygen is achieved with the iron doped graphene (FeGr) supported gold catalysts. The oxidative esterification process is dominant with Au/FeGr and K2CO3 as the catalyst in methanol where a 96.2% conversion of benzyl alcohol and 99.9% selectivity of methyl benzoate were obtained. While, the oxidation of benzyl alcohol is orientated to produce benzaldehyde in n-butanol using AuPd/FeGr as the catalyst, in which an 89.1% conversion and 87.5% selectivity of benzaldehyde was attained. Moreover, the effects of the additive, reaction medium and reaction time were investigated. Also, the oxidation of different benzylic alcohols was successfully performed under the optimal conditions. Furthermore, the used catalysts were characterized by XRD, NH3-TPD, SEM, Roman, TG-DTA and BET techniques. Based on the experimental results and phenomena, a possible reaction mechanism is proposed for the selective oxidation of benzyl alcohol with molecular oxygen in which alkyl benzoate is produce through the hemiacetal intermediate of benzaldehyde with short chain alcohol, and the generation rate of hemiacetal decides the selectivity of product.

Solvent-free benzyl alcohol oxidation reaction over Sm-CeO2 supported gold nanoparticle using tert-butyl hydroperoxide (TBHP) as an oxidant

In this work, liquid phase oxidation of benzyl alcohol under solvent-free condition is carried out using tert-butyl hydroperoxide (TBHP) as an oxidant over CeO2, Sm-CeO2, Au/CeO2, and Au/Sm-CeO2 catalysts. The Au/Sm-CeO2 catalyst shows higher activity compared to Au/CeO2 catalyst but in every case, almost 100% selectivity of benzaldehyde is observed. From CO2-temperature programmed desorption results, it is observed that the amount of basic sites increase after samarium doping and these basic sites play a crucial role for benzyl alcohol oxidation reaction. From these above experimental results, superior catalytic activity was observed for 2.33 wt% Au/Sm-CeO2 catalyst (Sm/Ce = 4/100).

The Effect of Water on the Oxidation of Toluene Catalyzed by Molybdenum Manganese Complex Oxide

Molybdenum manganese complex oxide was prepared and applied to the oxidation of toluene. The influences of various factors on the oxidation were observed and large amounts of benzyl acetate were formed in the reaction. When 30 mL water was added into the feed, the conversion of toluene and the maximum yield of benzaldehyde increased. Benzaldehyde was synthesized by the oxidation of toluene. The influences of various factors on the oxidation were observed and large amounts of benzyl acetate were formed in the reaction. To suppress the formation of benzyl acetate and increase the selectivity of benzaldehyde, water was added into the feed. It indicated that water not only increased the conversion of toluene, but improved the selectivity of benzaldehyde. The redox potential theory was used to explain the phenomenon.

Mechanochemical Synthesis of TiO₂ Nanocomposites as Photocatalysts for Benzyl Alcohol Photo-Oxidation.

TiO2 (anatase phase) has excellent photocatalytic performance and different methods have been reported to overcome its main limitation of high band gap energy. In this work, TiO2-magnetically-separable nanocomposites (MAGSNC) photocatalysts with different TiO2 loading were synthesized using a simple one-pot mechanochemical method. Photocatalysts were characterized by a number of techniques and their photocatalytic activity was tested in the selective oxidation of benzyl alcohol to benzaldehyde. Extension of light absorption into the visible region was achieved upon titania incorporation. Results indicated that the photocatalytic activity increased with TiO2 loading on the catalysts, with moderate conversion (20%) at high benzaldehyde selectivity (84%) achieved for 5% TiO2-MAGSNC. These findings pointed out a potential strategy for the valorization of lignocellulosic-based biomass under visible light irradiation using designer photocatalytic nanomaterials.

Hybrids of [C4mim]3+xPMo12−xVxO40: A new catalyst for oxidation of benzyl alcohol to benzaldehyde in water with greatly improved performances

A series of hybrid materials ([C4mim]3+xPMo12−xVxO40, x=0, 1, 2) based on V-substituted phosphomolybdic acid H3+xPMo12−xVxO40 (x=0, 1, 2) and ionic liquid 1-butyl-3-methyl imidazolium bromide ([C4mim]Br) have been prepared by anion-exchange method. The samples were well characterized by X-ray diffraction, Fourier transform infrared spectrophotometry and UV–Vis diffuse reflectance spectra analysis. The catalytic performances of the samples were tested in oxidation of benzyl alcohol to produce benzaldehyde using H2O2 as oxidant in water. The results have shown that the hybrids [C4mim]3+xPMo12−xVxO40 exhibit much higher catalytic properties than both the corresponding moieties. Especially, under the optimized conditions, 34% of benzyl alcohol conversion and 99% of selectivity for benzaldehyde have been obtained in the case of [C4mim]4PMo11VO40. The sample also exhibits good reusability and has been reused five runs without much decrease in conversion and selectivity.

Magnetic Core–Shell Nanostructured Palladium Catalysts for Green Oxidation of Benzyl Alcohol

Multifunctional catalysts are highly attractive for green oxidation process integrating excellent conversion and selectivity with high separability and recyclability. In this regards, a facile method is developed to fabricate yolk–shell microspheres consisting of Fe3O4 cores, mesoporous CeO2 shells and loaded Pd nanoparticles. Microspheres with 2.6 % Pd loading exemplify excellent catalytic activity for solvent-free, selective oxidation of benzyl alcohol to benzaldehyde by molecular oxygen at 373 K and atmospheric pressure, resulting in 80.5 % conversion of benzyl alcohol with 94.8 % selectivity for benzaldehyde. The catalyst can be magnetically separated and recycled without significant loss of catalytic efficiency even after seven catalytic runs.

Tunable catalytic properties of multi-metal–organic frameworks for aerobic styrene oxidation

The Cu and Co mixed metal–organic frameworks (MOFs) MOF-74(Cu/Co) with different Cu/Co ratios were prepared via a facile one-pot synthesis method and then characterized by means of various techniques. Whatever the Cu/Co ratios in the synthesized MOFs were, both Cu2+ and Co2+ could be uniformly distributed in MOF-74. The synthesized MOF-74(Cu/Co) materials were used as catalysts in styrene oxidation with O2 under solvent-free and mild reaction conditions. The results show that the catalytic properties of MOF-74(Cu/Co) can be tuned by varying the Cu/Co ratio in MOF-74. MOF-74(Cu) has a rather low catalytic activity but an absolute selectivity for benzaldehyde while MOF-74(Co) possesses a relatively higher catalytic activity, leading to the formation of benzaldehyde, styrene epoxide, and phenylacetaldehyde as well as to polystyrene. It is surprising that the incorporation of Cu2+ in MOF-74(Co) can completely inhibit the polymerization of styrene while the incorporation of Co2+ in MOF-74(Cu) can significantly enhance the conversion of styrene to benzaldehyde, styrene epoxide, and phenylacetaldehyde. In addition, by increasing the Co2+ amount in MOF-74(Cu/Co), the conversion of styrene and the selectivity for styrene epoxide and phenylacetaldehyde are increased while the selectivity for benzaldehyde is decreased. Moreover, the catalytic properties of MOF-74(Cu/Co) were compared with those of the physical mixtures of MOF-74(Cu) and MOF-74(Co), demonstrating the synergetic effects of Co2+ and Cu2+ in MOF-74(Cu/Co) on the catalytic oxidation of styrene. The current work reveals a strategy to incorporate multiple metal cations into MOFs for enhancing a specific catalytic property or achieving a new catalytic property.

Atomic level tuning of the catalytic properties: Doping effects of 25-atom bimetallic nanoclusters on styrene oxidation

Atomically precise bimetallic MxAu25-x(SR)18 (MCu and Ag, R=CH2CH2Ph) nanoclusters are investigated as oxide-supported catalysts for the catalytic oxidation of styrene. Their catalytic properties are compared with the case of homogold Au25(SR)18 nanocluster. The oxide-supported MxAu25-x(SR)18 catalysts give rise to 42–82% conversion of styrene at 70°C using (diacetoxyiodo)benzene (PhI(OAc)2) as the oxidant. The Ag and Cu dopants are found to modulate both the activity (i.e., conversion of styrene) and the selectivity to styrene epoxide or benzaldehyde (major products). The AgxAu25-x(SR)18 clusters exhibit higher activity and benzaldehyde selectivity than the homogold cluster, while the CuxAu25-x(SR)18 clusters primarily enhance the selectivity to benzaldehyde without significantly changing the activity. The results provide insights into the factors that influence the catalytic activity and selectivity in styrene oxidation.

A Simple Method to Prepare Bimetallic Ag–Cu/Cu2O Carbon Fibers Applied in the Regulation of Styrene Epoxidation Reaction

In this paper, a simple method to prepare three different catalysts was reported. Ag carbon fiber, Cu/Cu2O carbon fiber and Ag–Cu/Cu2O carbon fiber were prepared by electrospinning and high temperature carbonization. Ag nanoparticles were formed by in situ reduction of silver nitrate that DMF was used as reducing agent and got the Ag carbon fiber through the carbonization technology. Cu (NO3)2 was added into Ag/PAN/DMF solution and PAN/DMF solution, respectively, so Cu nanoparticles and Cu2O nanoparticles were got through the high temperature carbonization and the reduction. The morphologies of fibers and nanoparticles were characterized by field emission scanning electron microscopy and transmission electron microscope. The effect of three kinds of catalyst was investigated by oxidation of styrene and three different results were got. The conversation of styrene got to 99 % when Ag–Cu/Cu2O carbon fiber and Cu/Cu2O carbon fiber were used as the catalyst. When the catalyst was Ag–Cu/Cu2O carbon fiber, the selectivity of styrene oxide and benzaldehyde were 41.9 and 40.6 %, respectively. The main product was only one when Ag carbon fiber or Cu/Cu2O carbon fiber was used as the catalyst. Therefore, Cu/copper oxide-silver bimetallic catalyst provided an efficient catalyst in styrene epoxidation reaction.