Selective Oxidation Of Benzene Research Articles

Selective oxidation of benzene by an iron oxide carbonaceous nanocatalyst prepared from iron perchlorate salts and hydrogen peroxide in benzene and acetonitrile

Direct benzene hydroxylation under mild conditions using hydrogen peroxide can be essential in producing phenol. A new iron oxide-carbonaceous nanocatalyst (Fe-oxide CNC) is prepared in situ using a precursor of Fe(ClO4)2 and H2O2 in benzene and CH3CN. The obtained Fe-oxide CNC can efficiently catalyze benzene oxidation to phenol using H2O2(aq) in CH3CN. The highest phenol production was achieved with the turnover number (TON) of 122 in unit iron content and selectivity of 96% at 60 °C. The catalyst was characterized by SEM, TEM, XAS, XPS, Raman, XRD, BET, and TGA techniques.Interestingly, materials identification and characterization of the Fe-oxide CNC provided evidence to support the presence of Fe2O3. In addition, the carbonaceous moieties mainly consisted of branched aliphatic hydrocarbons on the iron oxide surface, which enhance the catalytic performance for benzene oxidation to phenol. The Fe-oxide CNC can be recycled three times with comparable catalytic efficiency. Using H218O2 as an oxidant, the phenol product with highly enriched 18O-atom indicates that the reactive oxygen species (ROS) activated by H2O2(aq) is crucial for aromatic oxidation. Time-resolved spin trapping experiments displayed the formation of the intermediate adducts consisting of 5,5-dimethyl-1-pyrroline N-oxide (DMPO) and reactive oxygenated radicals. For 3‒24 h durations, higher steady-state concentrations of the oxygenated intermediates observed at 25 °C than 60 °C indicate that the catalytic oxidation of benzene mediated by Fe-oxide CNC performs much faster kinetics at 60 °C than the ambient condition.

Photoreactive Solid Phase Based on N-Doped Tio2 Embedded into Syndiotactic Polystyrene Aerogel for Selective Oxidation of Benzene to Phenol

Photoreactive Solid Phase Based on N-Doped Tio2 Embedded into Syndiotactic Polystyrene Aerogel for Selective Oxidation of Benzene to Phenol

Eco-efficiency and techno-economic analysis for maleic anhydride manufacturing processes

Maleic anhydride may be obtained from different technological routes, being the selective oxidation of benzene and oxidation of butane the only ones that are currently in operation and, hence, represent competitive alternatives. In this paper, the said technologies are compared with regard to their economics and ecological performances in order to assert which one corresponds to the cleanest technology. The economics of each process was estimated on the basis of their respective cash flows, while the environmental comparison was carried out through the Eco-efficiency Comparison Index method by estimating six different categories of eco-indicators and seven life cycle metrics. To the best of our knowledge, such technologies have not been compared in terms of a joint evaluation of life cycle and eco-efficiency metrics, let alone considering the design of their respective utility plants. Finally, a sensitivity analysis was performed in order to analyze how the heuristic parameters for the utility plants considered in this work affect the estimation of the said indicators. The butane technology was shown to be more sustainable than the benzene process, since it was approximately 72% more profitable and 38% more eco-efficient than the latter.

Dry gel conversion of organosilane templated mesoporous silica: from amorphous to crystalline catalysts for benzene oxidation

Mesoporous silica grown using [3-(trimethoxysilyl)propyl]octadecyldimethylammonium chloride as the mesoporogen in the presence of Fe and Al is X-ray amorphous, but contains very small domains with features of MFI zeolite as evidenced by IR and Raman spectroscopy. When applied as a catalyst, this amorphous sample shows good performance in the selective oxidation of benzene using nitrous oxide. Addition of tetrapropylammonium as structure directing agent to the as-synthesized mesoporous silica and subsequent dry gel conversion results in the formation of hierarchical Fe/ZSM-5 zeolite. During dry gel conversion the wormhole mesostructure of the initial material is completely lost. A dominant feature of the texture after crystallization is the high interconnectivity of micropores and mesopores. Substantial redistribution of low-dispersed Fe takes place during dry gel conversion towards highly dispersed isolated Fe species outside the zeolite framework. The catalytic performance in the oxidation of benzene to phenol of these highly mesoporous zeolites is appreciably higher than that of the parent material.

Photooxidation of Benzene to Phenol by Al2O3-Supported Fe(III)-5-Sulfosalicylic Acid (ssal) Complex

Selective oxidation of benzene with H2O2 to phenol has been developed using a novel Fe(III) complex bearing 5-sulfosalicylic acid ligands immobilized alumina catalyst under visible light irradiation. The catalyst activity was evaluated by the photooxidation of benzene to phenol. The results indicate the best result with 100% conversion of benzene and 27.64% selectivity for phenol at low catalyst loading (0.7 mmol/g alumina). The catalyst was used for at least 4 cycles without any appreciable loss of activity.

How does the strength of exchange interactions in iron oxides influence the EPR line intensity and the catalytic activity?

Fe(III) ions may form ordered domains wherein the EPR resonance extends to the whole particle volume, leading to a major increase of spectral line intensities. This phenomenon of “strong exchange“ is known as ferromagnetic resonance (fmr). The authors observed another type of exchange, a weak one, characterized by drastically reduced resonances. Interestingly, both exchanges run parallel (up- or downwards) with the catalytic activity of iron oxide nano-particles as catalysts in the N2O-mediated selective oxidation of benzene.

Comparing two new routes for benzene hydroxylation

The vapour phase hydroxylation of benzene to phenol by two different methods has been investigated. In the first, a mixture of oxygen and hydrogen using a Pd membrane tubular reactor with and without second catalyst was used. Hydrogen dissociated on the palladium layer and reacted with oxygen to give active oxygen species, which reacted with benzene to produce phenol. The slow step in the overall reaction is the formation of usable hydrogen peroxide. Using a second catalyst changed the productivity, and conversion of benzene was increased by changing the length and diameter of porous reactor tubes. Low phenol productivity and selectivity was observed and showed that hydroxylation of benzene using a Pd membrane reactor is a far from economic method. In the second, selective oxidation of benzene with N 2O on iron zeolite of different SiO 2/Al 2O 3 composition, with concentration of iron rating from 50 to 2000 ppm was investigated. The effects of temperature, reactant mole ratio, and contact time were investigated. Phenol was formed with near 97% selectivity and average productivity of 5 mmol g −1 h −1.

One-step production of phenol by selective oxidation of benzene in a biphasic system

Phenol production through the direct hydroxylation of benzene with hydrogen peroxide using a catalytic membrane reactor has been studied. The reaction was carried out in a biphasic system separated by a membrane. This new system showed a high selectivity to phenol, minimizing its over-oxidation in over-oxygenated by-products. The effect of various reaction parameters such as the addition of hydrogen peroxide mode, amount of hydrogen peroxide, type of membrane, type of catalyst and organic acid was investigated. The results showed that iron(II) sulphate as the catalyst, 18 mmol of hydrogen peroxide pumped for 4 h in the aqueous phase as oxidant feeding, acetic acid and polypropylene hydrophobic porous support gave the best system performance in terms of produced phenol (17.42 mmol), selectivity to phenol (99.94%), benzene conversion to phenol (1.20%), and hydrogen peroxide conversion to phenol (96.78%).

Direct Phenol Synthesis by Selective Oxidation of Benzene with Molecular Oxygen on an Interstitial-N/Re Cluster/Zeolite Catalyst

Direct Phenol Synthesis by Selective Oxidation of Benzene with Molecular Oxygen on an Interstitial-N/Re Cluster/Zeolite Catalyst

Direct Phenol Synthesis by Selective Oxidation of Benzene with Molecular Oxygen on an Interstitial‐N/Re Cluster/Zeolite Catalyst

Direct Phenol Synthesis by Selective Oxidation of Benzene with Molecular Oxygen on an Interstitial‐N/Re Cluster/Zeolite Catalyst

A semiconductor gas sensor system for high throughput screening of heterogeneous catalysts for the production of benzene derivatives

We used a semiconductor gas sensor system developed for odour discrimination for a rapid quantification of benzene derivatives which can be formed as the product of a catalytic reaction. Phenol can be obtained by the selective oxidation of benzene. The sensor system shows higher sensitivity to phenol than benzene. In particular, a SnO2 sensor sensitized with ZrO2 responds selectively to phenol. Aniline is provided as a reaction product between ammonia and benzene. The output signal of the gas sensor system increases when it is exposed to air containing aniline at the ppm level; on the other hand, the sensor output resulting from 1% ammonia in air does not increase so much. Cumene formation can be observed by the reaction of propane and benzene. The sensitivity of a SnO2 sensor sensitized with 12%SiO2–Al2O3 to cumene was about ten times higher than that to benzene. These results indicate that the semiconductor gas sensor system is useful for rapid screening of the catalyst for benzene functionalization.

Effect of high-temperature treatment on Fe/ZSM-5 prepared by chemical vapor deposition of FeCl 3: II. Nitrous oxide decomposition, selective oxidation of benzene to phenol, and selective reduction of nitric oxide by isobutane

The catalytic performance (nitrous oxide decomposition, hydroxylation of benzene to phenol with nitrous oxide, and selective reduction of nitric oxide by i-butane) was evaluated for a set of HZSM-5 and sublimed Fe/ZSM-5 catalysts, which have been extensively characterized in an earlier contribution (J. Catal. (2003)). Nitrous oxide decomposition rates for the sublimed samples strongly increase after high-temperature calcination and particularly, after high-temperature steaming. Only a small fraction of the total iron content is active in this decomposition. For benzene hydroxylation the initial phenol productivity also increases with increasing severity of treatment. It is concluded that similar catalytic sites are important. Nevertheless, Fe/ZSM-5 and Fe/ZSM-5(HTC) exhibit relatively low phenol selectivities due to significant hydrocarbon combustion. The steamed Fe/ZSM-5, however, produces phenol with high selectivity. The stability of the sublimed samples is relatively low due to the large coke make, attributable to the large number of active sites. Commercial HZSM-5 with an iron content of 0.024 wt% and its steamed counterpart are also active and have a better stability, the latter one having the highest phenol productivity after prolonged reaction times. The beneficial effect of severe activation treatments to sublimed Fe/ZSM-5, where iron is introduced at extraframework positions, is taken as an indication that removal of lattice aluminum is important for the generation of active sites. The different activity order in NO reduction by i-butane suggests that the active sites for this reaction are different from those for nitrous oxide decomposition and selective benzene oxidation.

Benzene Selective Oxidation with N 2 O on Fe/MFI Catalysts: Role of Zeolite and Iron Sites on the Deactivation Mechanism

The catalytic performances of Fe-zeolites having MFI structures and in which the Fe introduced either by ion exchange or during the hydrothermal synthesis has undergone partial framework to extra-framework migration induced by controlled heat treatment are reported. In particular, the catalytic behavior as function of time-on-stream and the formation of carbonaceous species were studied. The results suggest that only a small fraction of the iron is active in the selective oxidation of benzene to phenol in the presence of N2O. It is suggested that the active fraction is formed by isolated iron ions in a pseudo-octahedral configuration with the sites positioned in hydroxyl nests (defects) of the zeolite and is selective in phenol formation as a result of in situ reduction during the catalytic tests. Two possible pathways of carbonaceous species were identified, the first through the intermediate further hydroxylation of phenol and the second through the coupling of phenol with benzene or another phenol molecule. This second pathway is the dominant mechanism of formation of carbonaceous species, although the relative rate of the two pathways depends on the zeolite characteristics and iron loading. It is also suggested that the second pathway depends on the strong chemisorption of phenol, probably on Lewis acid sites, which hinders the fast back-desorption of phenol out from the zeolite channels and thus favors the formation of carbonaceous species. Catalysts prepared by hydrothermal treatment show a lower rate of deactivation than those prepared by ion exchange, although the latter show a comparable productivity to phenol for amounts of iron in extra-framework positions around 20 to 30 times lower. The results also indicate that the presence of Al in the zeolite framework is beneficial for reducing the rate of deactivation as compared to that of Fe-silicalite samples.

Nature of Active Sites in the Oxidation of Benzene to Phenol with N 2O over H–ZSM-5 with Low Fe Concentrations

Selective oxidation of benzene with N 2O to phenol was investigated at 350 and 450°C on H–ZSM-5 zeolites of different Si/Al composition, with concentrations of iron ranging from 30 to 2000 ppm, and with gallium (1000 ppm). Zeolites dehydrated at 480°C, dehydroxylated at 720°C, and steamed at temperatures ranging from 500 to 780°C as well as zeolites exchanged by NaCl and treated in NaOH solution were used. IR spectra of OH groups and of adsorbed d 3-acetonitrile on zeolites were employed to determine the concentration of Brønsted and Al-Lewis sites. ESR spectra of Fe(III) ions and IR spectra of perturbed framework T–O–T bonds due to the presence of Fe(II) ions at cationic sites of the reduced zeolites were applied to determine the location of Fe ions in zeolites. The rate of phenol formation correlated with the concentration of Fe in the zeolite but was not affected by the presence of gallium. With all the steamed zeolites the rate of phenol formation increased substantially compared to that of dehydrated zeolites. In contrast, no correlation was found between the concentration of the Brønsted or Al-Lewis sites and the rate of phenol formation. The Fe ions with a complex oxo-structure were found to be the active sites for benzene oxidation with N 2O to phenol. They are reflected in the characteristic ESR signals of Fe(III) at g 6.0 and 5.6, and in the IR band at 935 cm −1 of perturbed T–O–T framework bonds due to the Fe(II) ions at cationic sites present in the reduced zeolites.

Nature of Active Sites in the Oxidation of Benzene to Phenol with N2O over H–ZSM-5 with Low Fe Concentrations

Selective oxidation of benzene with N 2 O to phenol was investigated at 350 and 450°C on H–ZSM-5 zeolites of different Si/Al composition, with concentrations of iron ranging from 30 to 2000 ppm, and with gallium (1000 ppm). Zeolites dehydrated at 480°C, dehydroxylated at 720°C, and steamed at temperatures ranging from 500 to 780°C as well as zeolites exchanged by NaCl and treated in NaOH solution were used. IR spectra of OH groups and of adsorbed d 3 -acetonitrile on zeolites were employed to determine the concentration of Brønsted and Al-Lewis sites. ESR spectra of Fe(III) ions and IR spectra of perturbed framework T–O–T bonds due to the presence of Fe(II) ions at cationic sites of the reduced zeolites were applied to determine the location of Fe ions in zeolites. The rate of phenol formation correlated with the concentration of Fe in the zeolite but was not affected by the presence of gallium. With all the steamed zeolites the rate of phenol formation increased substantially compared to that of dehydrated zeolites. In contrast, no correlation was found between the concentration of the Brønsted or Al-Lewis sites and the rate of phenol formation. The Fe ions with a complex oxo-structure were found to be the active sites for benzene oxidation with N 2 O to phenol. They are reflected in the characteristic ESR signals of Fe(III) at g 6.0 and 5.6, and in the IR band at 935 cm −1 of perturbed T–O–T framework bonds due to the Fe(II) ions at cationic sites present in the reduced zeolites.

Studies on the preparation of supported metal oxide catalysts using JRC-reference catalysts: II. Vanadia–titania catalyst: effect of starting solution and phase of titania

The effect of preparation conditions on the structure of vanadia–titania catalysts was investigated using two series of 5 wt.%V 2O 5/TiO 2 catalysts prepared by impregnation of ammonium metavanadate using JRC-TIO-3 (rutile) and JRC-TIO-4 (mainly anatase) as supports. The structure and chemical properties of supported vanadia were investigated by FT-IR, Raman, XPS, UV–VIS, NARP, and TPR. The dispersion of surface vanadia was affected by preparation conditions and by the phase of titania, i.e. the catalysts impregnated from oxalic acid solution exhibited higher dispersion of surface vanadia species. The effect of the starting solution was more drastic on the selective oxidation of benzene into maleic anhydride. The production of maleic anhydride was observed in the catalysts prepared from oxalic acid solution of ammonium metavanadate. On the contrary, V 2O 5/TiO 2(rutile) prepared without oxalic acid solution only formed carbon oxides. The correlation between preparation method and catalytic performance in the oxidation reaction was discussed on the basis of the dispersion, surface species, and chemical properties of surface vanadia species.

Promotion effects of various oxides on oxidation of benzene over vanadium pentoxide catalysts

The effect of promoters on the activity and selectivity of the active sites was investigated in the selective oxidation of benzene over vanadium pentoxide catalysts. The activity per surface area is increased by addition of MoO 3, WO 3, P 2O 5 and SnO 2, but the activity of each redox sites, i.e., turnover frequency (TF), was not. This indicates that the promoters enhanced the activity by increasing the redox sites, such as the surface V O species. The selectivity to maleic anhydride (MA) was improved by the addition of MoO 3, WO 3 and P 2O 5, while it was lowered by SnO 2. The effect on the selectivity was discussed in the light of the electronegativity of promoter cations. The additions of MoO 3, WO 3 and P 2O 5, of which the cations are more electronegative than V 5+, decreased TF of the production of carbon oxides more seriously than that of MA. On the other hand, the addition of less electronegative cation, i.e., Sn 4+, increased TF of the production of carbon oxides at the sacrifice of MA.

Synergetic effect of silver and molybdenum (VI) oxide additives in vanadia catalysts for the selective oxidation of benzene

It has been shown that the selectivity of V2O5−MoO3 catalysts for benzene oxidation to maleic anhydride can be enhanced by small amounts of silver introduced by impregnation with AgNO3 solution. The effect of Ag2O additive is synergetic and increases with increasing concentration of MoO3 up to 28.5 mol %. The best effect was obtained when about 7 Ag atoms were introduced for 1000 (V+Mo) atoms at the surface.

Thermal stability and phase transformations in a commercial vanadia-molybdena alkali-promoted catalyst

Temperature-programmed decomposition, thermal analysis, thermogravimetry and high-temperature X-ray analysis have been used to investigate a commercial catalyst for the selective oxidation of benzene into maleic anhydride. It was shown that phase transformations took place in the vanadia-molybdena alkali-promoted catalyst. The transformations were caused either by high-temperature treatment or by catalytic work in an industrial plant. As a result, theβ-bronze phase was formed. In the high-temperature region a reversible transformation of the bronze phase was observed. This was interpreted as theβ⇋β′ phase transformation.

Analysis of the factors affecting selectivity in the partial oxidation of benzene to maleic anhydride. Part 1.—Detailed kinetics of maleic anhydride adsorption

The adsorption of maleic anhydride on a vanadium pentoxide–molybdenum trioxide catalyst has been studied using the transient techniques of temperature programmed desorption and gas adsorption chromatography. The desorption spectra obtained over a range of adsorption temperatures show two peaks having maxima at between 220 and 250 °C and 340 and 350 °C. Solution of the Redhead equation for an assumed value of 1013 s–1 for the desorption A-factor at the peak maxima gave desorption energies of between 138 and 148 kJ mol–1 and 171 and 181 kJ mol–1. In spite of the high dosages used (ca. 107 Langmuirs), the surface coverages never exceeded 6 × 1012 sites (molecules) cm–2 with the number of high energy sites remaining constant at 3 × 1012 sites cm–2 over the large range of adsorption temperatures; it is inferred that these sites are a defect property of the mixed oxide. The gas adsorption chromatographic peak shapes are also analysed in terms of two adsorption bonds from which the heats of adsorption of 79.9 and 104.2 kJ mol–1 are derived. The adsorption of maleic anhydride on the mixed oxide catalyst is therefore seen to be activated, having adsorption activation energies of 63 and 71 kJ mol–1. These not inconsiderable heats of adsorption and desorption activation energies imply the possibility of product inhibition in the selective oxidation of benzene to maleic anhydride.