Activity For Toluene Oxidation Research Articles

Simultaneously Enhanced Activity and Selectivity for C(sp3)\u2013H Bond Oxidation Under Visible Light by Nitrogen Doping

Selective oxidation of saturated C(sp3)–H bonds in hydrocarbon to target chemicals under mild conditions remains a significant but challenging task because of the chemical inertness and high dissociation energy of C(sp3)–H bonds. Semiconductor photocatalysis can induce the generation of holes and oxidative radicals, offering an alternative way toward selective oxidation of hydrocarbons under ambient conditions. Herein, we constructed N-doped TiO2 nanotubes (N-TNTs) that exhibited remarkable activity and selectivity for toluene oxidation under visible light, delivering the conversion of toluene and selectivity of benzaldehyde of 32% and > 99%, respectively. Further mechanistic studies demonstrated that the incorporation of nitrogen induced the generation of N-doping level above the O 2p valance band, directly contributing to the visible-light response of TiO2. Furthermore, hydroxyl radicals generated by photogenerated holes at the orbit of O 2p were found to be unselective for the oxidation of toluene, affording both benzaldehyde and benzoic acid. The incorporation of nitrogen was able to inhibit the generation of hydroxyl radicals, terminating the formation of benzoic acid.

Efficient catalytic combustion of toluene at low temperature by tailoring surficial Pt0 and interfacial Pt-Al(OH)x species

SummaryExploring highly efficient and low-cost supported Pt catalysts is attractive for the application of volatile organic compounds (VOCs) combustion. Herein, efficient catalytic combustion of toluene at low temperature over Pt/γ-Al2O3 catalysts has been demonstrated by tailoring active Pt species spatially. Pt/γ-Al2O3 catalyst with low Pt-content (0.26 wt%) containing both interfacial Pt-Al(OH)x and surficial metallic Pt (Pt0) species exhibited super activity and water-resistant stability for toluene oxidation. The strong metal-support interaction located at the Al-OH-Pt interfaces elongated the Pt-O bond and contributed to the oxidation of toluene. Meanwhile, the OH group at the Al-OH-Pt interfaces had the strongest adsorption and activation capability for toluene and the derived intermediate species were subsequently oxidized by oxygen species activated by surficial Pt0 to yield carbon dioxide and water. This work initiated an inspiring sight to the design of active Pt species for the VOCs combustion.

Lattice oxygen and surface states dual modulation of manganese oxide with remarkably enhanced catalytic activity for toluene oxidation

The manganese oxide catalysts were synthesized by the hydrothermal method and applied for the catalytic oxidation of VOCs. The effects of lattice oxygen and surface states for enhancing the catalytic oxidation properties of toluene were investigated over MnOx with the different hydrothermal temperatures. MnOx prepared at 140 °C owned plenty of lattice oxygen, the highest content of surface Mn3+ species, excellent low-temperature reducibility and outstanding mobility of oxygen species, resulting in the improvement of catalytic performance.

In-situ atmosphere thermal pyrolysis of spindle-like Ce(OH)CO3 to fabricate Pt/CeO2 catalysts: Enhancing Pt–O–Ce bond intensity and boosting toluene degradation

In this work, a series of spindle-like CeO2 supports with different contents of surface oxygen vacancies were fabricated by an in-situ atmosphere thermal pyrolysis method. Due to the unique surface physicochemical properties of the modified CeO2 supports, the interaction between Pt and CeO2 can be regulated during the synthesis of the Pt/CeO2 catalyst. The abundant oxygen vacancies on the CeO2 support could preferentially trap Pt2+ ions in solution during the Pt impregnation process and enhance the Pt–CeO2 interaction in the subsequent reduction process, which results in the strongest Pt–O–Ce bonds formed on the PCH catalysts successfully (0.6% Pt loading on the CH support, which generated by thermal pyrolysis of Ce(OH)CO3 under H2 atmosphere). The strong Pt–O–Ce bond would trigger abundant surface oxygen species generated and enhanced the lattice oxygen species transfer from CeO2 supports to Pt nanoparticles. It was crucial to boosting the toluene catalytic activity. Therefore, the PCH catalyst exhibits the highest activity for toluene oxidation (T10 = 120 °C, T50 = 138 °C, and T90 = 150 °C with WHSV = 60,000 mL g−1 h−1) and remarkable durability and water resistance among all catalysts. We also conclude that the Pt–O–Ce bond may be the active site for toluene oxidation by calculating the turnover frequencies (TOFPt-O-Ce) value for all Pt/CeO2 catalysts. Moreover, the DFT calculation indicates that the Pt/CeO2 catalyst with a strong Pt–O–Ce bond possesses the lowest oxygen absorption energy and higher CO tolerance ability, which leads to excellent catalytic performance for toluene and CO catalytic oxidation.

Metal-organic frameworks-derived hierarchical Co3O4/CoNi-layered double oxides nanocages with the enhanced catalytic activity for toluene oxidation

The development of active transition-metal oxide (TMO) catalysts for the abatement of volatile organic compounds (VOCs) remains a great challenge. Controllable synthesis of TMOs with specific morphology and suitable composition is a promising way for acquiring efficient oxidation catalysts. Herein, a series of hierarchical Co3O4/CoNi-layered double oxides (CoNi-LDO) nanocages covered by interlaced nanosheets were synthesized using a cobalt metal-organic framework (Co-MOF)-based strategy. The textural properties, morphology, surface chemical state, and reducibility of the CoNi-LDO catalysts were systematically characterized by various techniques. The catalytic activity toward toluene oxidation and the stability performance was investigated. Results demonstrated that the morphology, composition, and textual properties can be controlled by tuning the post-synthetic etching reaction conditions. Benefiting from the structural and compositional merits, as well as the superior low-temperature reducibility, the CoNi-LDO-1 catalyst (Ni/Co molar ratio was 0.39) with core-shell structure exhibited excellent activity toward toluene oxidation. Our work offers a new strategy for the design of high-performance oxidation catalysts for the abatement of VOCs.

Enhancement of toluene oxidation performance over Cu–Mn composite oxides by regulating oxygen vacancy

Oxygen vacancy plays an important role in regulating the chemical and catalytic properties of catalysts. In this paper, Cu-Mn composite oxide catalyst was firstly synthesized by hydrothermal method and then modified by urea solid reaction treatment to obtain CM-X catalysts (X = 2, 4, 6, where × represents the weight ratio of urea/CM catalyst) with different oxygen vacancy concentrations. The relationship between the structure and catalytic performance of these catalysts was analyzed by a variety of characterization techniques. The CM-4 sample showed the maximum specific surface area, which enhanced the adsorption capacity of the catalyst to the reactants. Moreover, there existed a large number of oxygen vacancies in CM-4 samples, leading to the amount increase of adsorbed oxygen species on the surface and high migration ability of lattice oxygen, which can improve the catalyst reducibility and oxygen species activity. Therefore, the CM-4 catalyst showed the excellent catalytic activity and stability for toluene oxidation, and toluene could be completely oxidized into CO2 and H2O at 215 °C under the equivalent gas hourly space velocity (GHSV) of 22,500 mLg-1h−1. And it was found by in situ DRIFTS experiment that the oxidation of toluene occurs via the benzyl alcohol-benzoate-anhydride reaction pathway on CM-4 catalyst.

Achieving toluene efficient mineralization over K/ɑ-MnO2via oxygen vacancy modulation

Oxygen vacancy plays an important role in adsorption and activation of oxygen species and therefore promotes the catalytic performance of materials in heterogeneous oxidation reactions. Here, a series of K-doped ɑ-MnO2 materials with different K loadings were synthesized by a reproducible post processing process. Results show that the presence of K+ enhances the reducibility and oxygen vacancy concentration of ɑ-MnO2 due to the break of charge balance and the formation of low valence Mn species. 4-K/MnO2 material exhibits the highest toluene oxidation activity and satisfied long-term stability and water resistance owing to its superior reducibility and abundant surface absorbed oxygen (Oads). In situ DRIFTS demonstrate that Oads greatly accelerates toluene dehydrogenation rate and promotes benzoate formation, enhancing the activation and decomposition of toluene molecules. Moreover, the CC cleavage of benzene ring (forming maleic anhydride) is the rate-determining step of toluene oxidation, which can be easily occurred over 4-K/MnO2.

Investigation into the roles of different oxygen species in toluene oxidation over manganese-supported platinum catalysts

With the aim to elucidate the roles of different oxygen species, the catalytic oxidation of toluene over Pt/Mn3O4 synthesized by a facile reduction method was investigated. Compared with the Pt/Mn3O4-C using the commercial Mn3O4 as the support, Pt/Mn3O4-R was found to possess more surface oxygen vacancies, exhibit better redox properties and dispersion of platinum particles, leading to its higher activity for toluene oxidation (T90 = 183 ℃). Through toluene-TPD, toluene-TPSR and in-situ DRIFTS, it was found that toluene oxidation over Pt/Mn3O4-R catalyst might follow the Mars–van Krevelen (MVK) mechanism and the pathway of toluene oxidation over Pt/Mn3O4-R was possible toluene → benzoate → carbonate → CO2. The lattice oxygen species on the surface of catalysts was directly involved in the oxidation of toluene and played an important role in the formation of key intermediate such as carbonate, resulting in the difference of the reaction mechanism and pathway between Pt/Mn3O4-R and Pt/Mn3O4-C. In addition, the degradation of the surface carbonate was demonstrated to be the rate-controlling step at 180℃ to 200℃.

Acid treated Sr-substituted LaCoO3 perovskite for toluene oxidation

For A-site substituted AA'BO3 perovskite, the doped A' element is easy to migrate to the surface and form segregation of A'Ox, which could partially block active B sites and thus reduce catalytic activity. In the present work a La0.8Sr0.2CoO3-δ perovskite-type solid was first prepared and then treated with acetic acid to eliminate SrO segregation on its surface. The obtained catalyst (LCSO-a) possessed a significantly enhanced catalytic activity for toluene oxidation in the 220–260 °C range. This promotion effect might be attributed to the increase in the concentration of active surface oxygen species and the reduction in their binding strength. In addition, the LCSO-a catalyst showed very good stability and water resistance.

Insight into the effect of manganese substitution on mesoporous hollow spinel cobalt oxides for catalytic oxidation of toluene

The cobalt oxides and manganese oxides have high-activity potential for catalytic oxidation of volatile organic compounds (VOCs), while the mesoporous hollow morphology is crucial to the mass transfer of reactant and product. Therefore, it is worth investigating the effect of manganese substitution in mesoporous hollow cobalt oxides on catalytic oxidation. Herein, a partially disordered spinel structure is formed by the Mn substitution in Co3O4 and the mesoporous hollow microsphere is improved in morphology homogeneity with the decrease of Co/Mn ratio in the range of 1.8–28.8. The 5Co1Mn (Mn-substituted Co3O4 with Co/Mn at 5.4) exhibits outstanding catalytic activity for toluene oxidation with 50% CO2 generation at 237 °C, which is 21 °C lower than Co3O4. Moreover, the 5Co1Mn displays satisfactory stability in reusability, lifetime, and water resistance. The small defective crystallite, mesoporous hollow morphology, and high specific surface area endow Mn-substituted Co3O4 with more surface chemical adsorbed oxygen, enhancing the catalytic oxidation of toluene. Theoretical calculation on (311) plane of Co3O4 reveals that Mn2+ or Mn3+ substitution increases the formation energy of oxygen vacancy and makes it difficult to adsorb gaseous oxygen on the defective surface. The interaction between Co and Mn impedes the improvement of toluene oxidation because the mobility of lattice oxygen, the surface distribution of Co3+, and the ratio of surface adsorbed oxygen to surface lattice oxygen are hindered by Mn substitution. The chemical adsorbed oxygen is more active than lattice oxygen in the oxidation of adsorbed intermediates (phenolate, benzoate species, etc.). The Langmuir-Hinshelwood mechanism dominates in the catalytic oxidation at 200–250 °C, while the catalytic oxidation follows both the Langmuir-Hinshelwood mechanism and Mars-van Krevelen mechanism above 250 °C. This work provides some enlightenment for exploring the role of surface oxygen species in VOCs oxidation and uncovering the interaction in binary spinel oxides.

Unraveling the decisive role of surface CeO2 nanoparticles in the Pt-CeO2/MnO2 hetero-catalysts for boosting toluene oxidation: Synergistic effect of surface decorated and intrinsic O-vacancies

The synergistic effect of surface decorated and intrinsic O-vacancies through an oxygen replenishment-migration pathway is the key to boost the remarkable catalytic activity for deep toluene oxidation. • The Pt-CeO 2 /MnO 2 hetero-nanostructures can be fine-manipulated via a novel synthesis method. • The synergistic effect of dual O-vacancies is the key to enhance the deep toluene oxidation. • The Pt-CeO 2 /MnO 2 exhibited more O-vacancies, well redox ability and well dispersion of Pt. • DRIFTS study revealed that toluene was adsorbed directly on surface adsorbed oxygen species. Oxygen vacancy engineering has been verified as an important approach to achieve the efficient degradation of VOCs in nanomaterials. Herein, a synthetic strategy of Pt-CeO 2 /MnO 2 hetero-catalysts is developed to fine-manipulate the surface oxygen vacancies and catalytic activities through surface CeO 2 decoration as a surface O-vacancy donor. Among these Pt-based catalysts, the optimal Pt-0.15Ce-Mn catalyst exhibits the greatest catalytic activity for toluene oxidation (T 99 = 155 °C), which is attributed to more oxygen vacancies, outstanding redox ability and well dispersion of Pt. Combined with experiments and DFT calculations, it has been demonstrated that the special role of introducing CeO 2 NPs is to induce the generation of more O-vacancies, new structure defects (Mn 3+ and Ce 3+ species), and the lower formation energy of oxygen vacancy. Furthermore, the synergistic effect of dual O-vacancies (surface decorated and intrinsic O-vacancies) via an oxygen replenishment-migration pathway is the key to boost the remarkable catalytic activity for deep toluene oxidation. Finally, in situ DRIFTS reveals that partial toluene molecules can be adsorbed directly on surface adsorbed oxygen species replenished by gas-phase oxygen, and these catalysts with richer O-vacancies can effectively reduce the accumulation of by-product (phenolate, C 6 H 5 –OH).

Selective Catalytic Oxidation of Toluene to Benzaldehyde: Effect of Aging Time and Calcination Temperature Using CuxZnyO Mixed Metal Oxide Nanoparticles

Oxidation is an important organic transformation, and several catalysts have been reported for this conversion. In this study, we report the synthesis of mixed metal oxide CuxZnyO, which is prepared by a coprecipitation method by varying the molar ratio of Cu and Zn in the catalytic system. The prepared mixed metal oxide CuxZnyO was evaluated for catalytic performance for toluene oxidation. Various parameters of the catalytic evaluation were studied in order to ascertain the optimum condition for the best catalytic performance. The results indicate that aging time, calcination temperature, reaction temperature, and feed rate influence catalytic performance. It was found that the catalyst interfaces apparently enhanced catalytic activity for toluene oxidation. The XRD diffractograms reveal the crystalline nature of the mixed metal oxide formed and also confirm the coexistence of hexagonal and monoclinic crystalline phases. The catalyst prepared by aging for 4 h and calcined at 450 °C was found to be the best for the conversion of toluene to benzaldehyde while the reactor temperature was maintained at 250 °C with toluene fed into the reactor at 0.01 mL/min. The catalyst was active for about 13 h.

Selective aerobic oxidation of toluene to benzaldehyde catalyzed by covalently anchored N-hydroxyphthalimide and cobaltous ions

Abstract Selective oxidation of toluene to benzaldehyde via dioxygen is of great significance industrially but suffers from a severely low selectivity due to a much higher reactivity of the desired product than the reactant. A combination of homogeneous N-hydroxyphthalimide (NHPI) and cobaltous ions was found active and selective for the transformation from toluene to benzaldehyde in the presence of hexafloropropan-2-ol. In this work, homogeneous NHPI was covalently anchored onto the surface of commercial mesoporous SiO2 to facilitate the separation and recovery of the catalyst, aiming at a possible industrial application. The grafting bonds were well confirmed by FT-IR, TGA and XP spectra, and the density of > N OH groups anchored was up to 0.6 mmol/g in the immobilized NHPI catalysts. The resulting catalysts exhibited an excellent activity for selective oxidation of toluene to benzaldehyde, and there was no appreciable loss in catalytic activity observed after repeated evaluations, suggesting a promising prospect for its further investigation and possible application.

Imidazolate-mediated synthesis of hierarchical flower-like Co3O4 for the oxidation of toluene

Abstract Cobalt oxide (Co3O4) materials with specific structure have shown great potential as highly efficient catalysts in the oxidation reactions. In this work, a novel hierarchical flower-like Co3O4 was synthesized by the imidazolate-induced hydrothermal and subsequent thermolysis method. The effect of reaction parameters as well as the phase evolution of the flower-like structure was investigated in detail. For comparison, a rod-like Co3O4 was also prepared with urea under similar conditions. The morphology-dependent effect of Co3O4 towards toluene oxidation was studied. Moreover, the physicochemical properties of Co3O4 were analyzed by various characterization techniques. The flower-like Co3O4 catalyst presented a higher catalytic activity for toluene oxidation than the rod-like Co3O4, which was associated with hierarchical flower-like morphology, reactive exposed planes, abundant adsorbed oxygen species at surface and better low-temperature reducibility.

Efficient catalytic degradation of toluene at a readily prepared Mn-Cu catalyst: Catalytic performance and reaction pathway

Fabricating of economical transitional metal oxide-based materials with satisfied low-temperature catalytic performance and application perspective is still a challenge in deep degradation of VOCs. Here, Mn-Cu bimetallic oxides were facilely prepared by one-step hydrothermal-redox method, which displayed much higher catalytic activity in toluene oxidation than those synthesized by hydrolysis-driven redox-precipitation or co-precipitation approach. It is shown that the lattice defect and oxygen vacancy concentration over prepared materials can be tuned by controlling Cu/Mn molar ratio. Amongst, spinel structured MnCu0.5 exhibited the highest catalytic activity, superior durability and water resistance in toluene total oxidation owing to abundant surface adsorbed oxygen species, excellent low-temperature reducibility, and high amounts of Cu+ and Mn3+. In detail, the reaction rate of MnCu0.5 was over 9.0 times higher than that of MnCu0.75, MnCu0.75-P and MnCu0.75-H2O2 at relative low temperature of 210 °C. The cyclic redox process with easier oxygen species mobility played a key role in the catalytic oxidation of toluene. Typical reaction intermediates as benzyl alcohol, benzaldehyde, benzene, phenol, and benzoquinone could be detected by PTR-MS, which further decomposed to acetone, ethanol, ketone, acetic acid, methanol, formaldehyde and acetaldehyde species by ring opening before total mineralization.

Bimetallic Pt-Co Nanoparticle Deposited on Alumina for Simultaneous CO and Toluene Oxidation in the Presence of Moisture

Carbon monoxide (CO) and hydrocarbons (HCs) generally have competitive adsorption on the active site of noble-metal nano-catalysts, thus developing an effective way to reduce the passivation of competitive reaction with each other is an urgent problem. In this study, we successfully synthesized transition metal-noble metal (Pt-M) alloys via introducing inexpensive metal elements (M = Ni, Co and Cu) into Pt particles and then deposited on alumina support to form Pt-based catalysts. Subsequently, we choose CO and toluene as polluting gases to evaluate the catalytic activities of Pt-M/Al2O3 catalysts. Introducing inexpensive metal elements (M = Ni, Co, and Cu) significantly changed the physicochemical properties and catalytic activities of these Pt-based catalysts. It can be found that the Pt-Co/Al2O3 catalyst exhibited outstanding catalytic activity for CO and toluene oxidation under mixed gas atmosphere, compared with other Pt-based catalysts, which is due to the higher dispersity, more surface adsorption oxygen, and well redox ability. Surprisingly, H2O could promote the catalytic activities for CO/toluene co-oxidation over the Pt-Co/Al2O3 catalyst. Thus, the present synthetic strategy not only opens an avenue towards the synthesis of noble metal-based catalysts, but also provides an excellent tolerance to H2O in the catalytic process.

Effect of strong interaction between Co and Ce oxides in CoxCe1-xO2-δ oxides on its catalytic oxidation of toluene

A series of CoxCe1-xO2-δ (x = 0.05−0.6) oxides were synthesized through non-ionic surfactant hydrothermal method and applied for catalytic toluene oxidation. Various characterizations were performed to investigate the relation between structure and activity of the catalysts, including XRD, N2 adsorption-desorption, Raman spectra, TEM, H2-TPR, O2-TPD, XPS and in situ DRIFTS. CoxCe1-xO2-δ shows higher catalytic performance than pure Co3O4 and CeO2, meanwhile Co0.2Ce0.8O2-δ exhibits the best catalytic activity for toluene oxidation in the presence and absence of water, moreover, no obvious difference in activity among three successive testing runs. This good activity can be mainly attributed to the strong interaction between Co and Ce oxides to form Co0.2Ce0.8O2-δ solid solution, leading to abundant surface active oxygen species, more surface Co3+ and Ce3+ species. In situ DRIFTS is used to probe the catalytic reaction process, which reveals that toluene can be rapidly adsorbed and transferred to benzoate species, finally oxidized into CO2 and H2O.

Oxygen vacancy engineering in Fe doped akhtenskite-type MnO2 for low-temperature toluene oxidation

To clarify the discrepancies between oxygen vacancies (VO) types and concentrations, we designed two types of VO by substituting Mn4+ in akhtenskite-type MnO2 with low-valence manganese (e.g. Mn3+) or iron (e.g. Fe3+), denoted as VO (MM) and VO (FM), respectively. The concentration of VO was adjustable by the varied sample calcination temperature. The catalysts with more VO (FM) achieved higher toluene specific reaction rate and better stability than those of Mn3+ doped MnO2, ascribing to the chemical and reactive difference of their different Vo types. Toluene specific reaction rate have been quantitatively calculated to estimate the contribution of VO on catalytic performance and followed the order of F1M4 (2.73 mmol/(g h)) > F2M13 (2.29 mmol/(g h)) > F1M14 (1.52 mmol/(g h)) > Mn (0.91 mmol/(g h)) > F1M2 (0.89 mmol/(g h)) at 200 °C (Mn, F1M14, F2M13, F1M4 and F1M2 represented pure MnO2 and Fe doped MnO2 with Fe/Mn = 1/14, 2/13, 1/4, and 1/2, respectively). Additionally, the VO concentrations of as-prepared catalysts decreased with the increasing calcination temperature, which then led to the declining activity for toluene oxidation. Furthermore, in situ DRIFTS spectra demonstrated that the higher concentrations of VO (FM) sites accelerated the transformation of intermediates from benzaldehyde to benzoate, which was the intermediate to be further oxidized into CO2 and H2O.

Layer MnO2 with oxygen vacancy for improved toluene oxidation activity

Volatile organic compounds (VOCs) is known as global air pollutant, which urgent needs to be removed. It is necessary to obtain an efficient catalyst with high activity to achieve completely oxidize VOCs into CO2 and H2O at low temperature. The catalytic reaction on the catalyst surface usually requires active sites, which are closely related to structure defects. In this paper, the MnO2 sample treated with TMAOH and TPAOH shows higher activity, and the MnO2-P catalyst has the best catalytic performance (T50 = 207 °C, T90 = 223 °C). The formation of irregular pores on the surface of MnO2−M and MnO2-P results in the increase of the surface area, pore volume and amount of oxygen vacancy. And the MnO2-P has the highest content of oxygen vacancy. Therefore the improved adsorption of toluene (toluene-TPD) together with the enhanced reducibility and mobility of lattice oxygen (H2-TPR and XPS) causes the outstanding catalytic performance of MnO2-P sample.

TiO2@UiO‐66 Composites with Efficient Adsorption and Photocatalytic Oxidation of VOCs: Investigation of Synergistic Effects and Reaction Mechanism

AbstractTiO2@UiO‐66 composite with intimate contact interfaces is fabricated by in situ solvothermal methods. Compared with other UiO‐based composites, TiO2@UiO‐66 exhibits superior photocatalytic activity for oxidation of toluene into CO2 during long‐time reaction under flowing conditions. This is because (1) the intimate contact interface and well‐matched band structure between TiO2 and UiO‐66 can effectively separate and transfer photogenerated electrons; (2) the synergistic effect between UiO‐66 and TiO2 promotes the adsorption of toluene and desorption of CO2 and provides sufficient active sites for photocatalytic reaction. The toluene conversion and CO2 production on 4TiO2@U are 3.27 and 4.10 times higher than that on UiO‐66, respectively. 4TiO2@U also shows the highest activity for formaldehyde and rhodamine B degradations. The in situ FTIR results exhibit that toluene can be oxidized by .O2− and h+ to benzaldehyde and benzoic acid, then further oxidized to oxalic acid, and finally mineralized into CO2 and H2O.