Selective Oxidation Of Hydrocarbons Research Articles

Efficient and selective oxidation of alcohols and hydrocarbons catalyzed by oxovanadium(IV) unsymmetrical salophen complex supported on silica-coated CoFe2O4 magnetic nanoparticles

Efficient and selective oxidation of alcohols and hydrocarbons catalyzed by oxovanadium(IV) unsymmetrical salophen complex supported on silica-coated CoFe2O4 magnetic nanoparticles

Selective oxidation and removal of hydrocarbons from carbon nanotubes using reactive yttrium films

Wrapping polymers are useful for sorting high purity suspensions of semiconducting carbon nanotubes (CNTs) in organic solvents, but for many microelectronic applications the wroapping polymer needs to be removed. Coating wrapped CNTs with yttrium metal, followed by oxidation and removal with dilute aqueous acid, has been used to etch wrapping polymer, but the mechanism, selectivity, extent of etching, and range of conditions over which etching occurs have not been reported. We use spectroscopic and physical measurements to characterize this process on thin films of an archetypical conjugated wrapping polymer (PFO-BPy), its amorphous char residue, CNTs (average diameter 1.5 nm), graphene, and other organic films. Exposure of a yttrium overcoated film of PFO-BPy to ambient air at 20 °C oxidizes a ∼0.5 nm layer of polymer, forming carbonate, carboxylate, and/or carbonyl groups that dissolve in dilute acid. Thicker layers of polymer are removed by repeated cycles. Similar results are observed for other organic films at 20 °C whereas CNTs and graphene are unaltered, providing the selectivity needed to remove carbon-based contaminants from sp2 carbon based nanostructures. Increasing temperature to 250 °C increases polymer oxidation and removal to ∼2.5 nm per cycle; however, the CNTs and graphene are damaged.

Hybridizing engineering strategy of decatungstate III: Transition metal modified carbon quantum dot-regulated photo-catalytic oxidation performance of decatungstate

The selective oxidation of hydrocarbons (RH) by dioxygen (O2) is a very important method for industrial production of bulk oxygen-containing compounds, However, due to the high chemical inertness of RH and O2, achieving this reaction under mild conditions still faces significant challenges. This paper discloses an efficient hybridizing engineering (HE) strategy of decatungstate (DT) with 3d transition metal ions (Mn+=Ni2+, Co2+ or Cu2+)-modified carbon quantum dots (Mn+/CQD) as the dopants. Compared to pure CQD, The Mn+/CQD can more efficiently combine with DT anion to fabricate a high-quality hybrid via electrostatic interactions, thereby bestowing the hybrid with an enhanced visible light response especially the separation efficiency of photo-generated charge pairs. Furthermore, the above hybridization effects of Mn+/CQD on DT anion can be fine-tuned and gradually improved with a change of the metal ion from Cu2+, Co2+ to Ni2+, along with a continuous enhancement of the hybrid's photo-catalytic efficiency in the visible light- triggered selective oxidation of ethylbenzene with O2 in acetonitrile. The best Ni2+/CQD-doped TBADT can achieve ca. 48% ethylbenzene conversion and 87.6% acetophenone selectivity in the presence of 2 M HCl, and it also shows a much higher photo-catalytic activity for the photo-oxidation of toluene, cyclohexane and benzyl alcohol compared to pure TBADT. The HE strategy with Mn+/CQDs as the cationized hybridizers is much superior to that with pure CQD or Ni2+ as the hybridizer in hoisting the photo-catalytic performance of DT.

Photocatalytic Selective Oxidation of Toluene over Chlorine-Coordinated MIL-101(Fe) under Ambient Conditions.

The activation of an inert C(sp3)-H bond in selective oxidation of hydrocarbons under mild conditions is a critical and challenging process. Herein, we report a stable chlorine-coordinated metal-organic framework (MOF) photocatalyst, MIL-101(Fe), for efficient visible-light-driven photocatalytic selective oxidation of toluene to benzaldehyde in air under ambient conditions. Encouragingly, a benzaldehyde formation yield of 3.11 mmol·g-1·h-1 with a selectivity of 92.1% is achieved in 5 h, which is superior to most of the reported works. Based on the experimental results and characterizations, the high catalytic performance is mainly due to the promoted rate-limiting step of C(sp3)-H bond activation by a chlorine radical (Cl·) from the coordinated -Cl in the MIL-101(Fe) structure. In addition, the present photocatalyst possesses good substrate tolerance for photocatalytic selective oxidation of various toluene derivatives under optimized conditions.

Efficient hole extraction to reactive oxidation sites over a Co3O4/Cs3Sb2Br9 p-n heterojunction for enhanced benzylic C(sp3)-H bond oxidation

Photocatalytic selective oxidation of aromatic hydrocarbons plays an important role in the production of value-added chemicals. A key step in this process is the activation of C(sp3)-H bond by photogenerated holes. However, the inadequate hole generation and lack of surface adsorption-activation sites severely hinders the improvement in photocatalytic C-H bond oxidation. In particular, the random charge migration to the surface impedes the effective capture of holes by surface active sites to dissociate the C(sp3)-H bond. Here, we design and fabricate a Co3O4/Cs3Sb2Br9 p-n heterojunction that effectively addresses these challenges. The p-n heterojunction forms strong built-in electric fields (BEF) facilitating spatial charge separation. Holes are accumulated on Co3O4, while electrons are accumulated on Cs3Sb2Br9, thereby offering abundant active holes and electrons. Moreover, Co3O4 shows stronger adsorption and activation capacity for the C(sp³)-H bond, enabling the C(sp3)-H bond dissociation with low reaction energy barrier. Consequently, the holes are directionally extracted from photoactive Cs3Sb2Br9 to catalytically active Co3O4 under visible light irradiation, thereby accelerating the toluene oxidation. The optimized 5 % Co3O4/Cs3Sb2Br9 exhibits a benzyl aldehyde (BAD) evolution rate of 5044 μmol g−1 h−1 and a benzyl alcohol (BA) production rate of 1820 μmol g−1 h−1, which are 12 and 17 times higher than that of blank Cs3Sb2Br9, respectively.

Triazine Frameworks for the Photocatalytic Selective Oxidation of Toluene

AbstractInvestigations into the selective oxidation of inert sp3 C−H bonds using polymer photocatalysts under mild conditions have been limited. Additionally, the structure‐activity relationship of photocatalysts often remains insufficiently explored. Here, a series of thiophene‐based covalent triazine frameworks (CTFs) are used for the efficient and selective oxidation of hydrocarbons to aldehydes or ketones under ambient aerobic conditions. Spectroscopic methods conducted in situ and density functional theory (DFT) calculations revealed that the sulfur atoms within the thiophene units play a pivotal role as oxidation sites due to the generation of photogenerated holes. The effect of photogenerated holes on photocatalytic toluene oxidation was investigated by varying the length of the spacer in a CTF donor‐acceptor based photocatalyst. Furthermore, the manipulation of reactive oxygen species was employed to enhance selectivity by weakening the peroxidative capacity. As an illustrative example, this study successfully demonstrated the synthesis of a precursor of the neurological drug AMG‐579 using a photocatalytic protocol.

Triazine Frameworks for the Photocatalytic Selective Oxidation of Toluene.

Investigations into the selective oxidation of inert sp3 C-H bonds using polymer photocatalysts under mild conditions have been limited. Additionally, the structure-activity relationship of photocatalysts often remains insufficiently explored. Here, a series of thiophene-based covalent triazine frameworks (CTFs) are used for the efficient and selective oxidation of hydrocarbons to aldehydes or ketones under ambient aerobic conditions. Spectroscopic methods conducted in situ and density functional theory (DFT) calculations revealed that the sulfur atoms within the thiophene units play a pivotal role as oxidation sites due to the generation of photogenerated holes. The effect of photogenerated holes on photocatalytic toluene oxidation was investigated by varying the length of the spacer in a CTF donor-acceptor based photocatalyst. Furthermore, the manipulation of reactive oxygen species was employed to enhance selectivity by weakening the peroxidative capacity. As an illustrative example, this study successfully demonstrated the synthesis of a precursor of the neurological drug AMG-579 using a photocatalytic protocol.

Selective Oxidation of Hydrocarbons by Molecular Iron Catalysts Based on Molecular Recognition through π–π Interaction in Aqueous Medium

Selective Oxidation of Hydrocarbons by Molecular Iron Catalysts Based on Molecular Recognition through π–π Interaction in Aqueous Medium

Chemical Looping Technology for Energy Storage and Carbon Emissions Reductions

Chemical looping (CL) technology, initially developed as an advanced combustion method, has been widely applied in various processes, including the selective oxidation of hydrocarbons (e [...]

Synergy of oxygen vacancy and Mn-substitution on SrTiO3 perovskites supported copper nanocatalysts for enhanced cyclohexylbenzene oxidation

Aiming at the main challenge of poor atomic economy for selective oxidation of hydrocarbons, synergistic catalysis on heterogenous catalysts has been focused on precisely regulating oxidation of specific chemical bonds in organic substrates. Here, a series of copper nanocatalysts loaded on Mn-substituted SrTiO3 perovskite-type oxides with varying Mn/Ti ratios for cyclohexylbenzene (CHB) oxidation to form cyclohexylbenzene-1-hydroperoxide (CHBHP) were successfully synthesized by coprecipitation method assisted by a micro-liquid-film reactor. It was found that the introduction of manganese created numerous oxygen vacancies in nanocatalysts, promoting the activation of oxygen molecules. Moreover, both copper and manganese ions enhanced the activated adsorption of CHB substrate. In particular, as-constructed Cu-based nanocatalyst with a substitution of 15% Mn into Ti sites showed superior catalytic oxidation efficiency with a ∼30% yield of CHBHP product, which is at the highest level compared with previously reported heterogenous catalysts, mainly attributable to the favorable synergy between copper, manganese, and oxygen vacancies. This work sheds light on the importance of multi-active site synergistic catalysis in advanced alkane oxidation processes.

Photothermal catalytic selective oxidation of isobutane to methacrylic acid over keggin-type heteropolyacid

Thermal and photothermal catalytic selective oxidation of isobutane to methacrylic acid (MAA) are comparatively studied over a keggin-type Cs2.9Cu0.34V0.49PMo12O40 heteropolyacid acid. An introduction of light was observed to enhance both the i-C4H10 conversion and the MAA selectivity, and consequently the MAA formate rate, particularly at low temperatures. Characterization results show that oxidation of methacrolein (MAL) to MAA is the rate-limiting step while UV light illumination promotes the oxidation of σ-bonded MAL with OH groups to σ-bonded MAA on the catalyst surface. These results demonstrate a synergistic effect of thermal catalysis and photocatalysis in selective oxidation of isobutane to MAA, which suggests photothermal catalysis as a promising strategy to catalyze the selective oxidation of higher hydrocarbons at relative mild reaction conditions.

Single Metal Atoms on Oxide Surfaces: Assessing the Chemical Bond through 17O Electron Paramagnetic Resonance.

ConspectusEven in the gas phase single atoms possess catalytic properties, which can be crucially enhanced and modulated by the chemical interaction with a solid support. This effect, known as electronic metal-support interaction, encompasses charge transfer, orbital overlap, coordination structure, etc., in other words, all the crucial features of the chemical bond. These very features are the object of this Account, with specific reference to open-shell (paramagnetic) single metal atoms or ions on oxide supports. Such atomically dispersed species are part of the emerging class of heterogeneous catalysts known as single-atom catalysts (SACs). In these materials, atomic dispersion ensures maximum atom utilization and uniform active sites, whereby the nature of the chemical interaction between the metal and the oxide surface modulates the catalytic activity of the metal active site by tuning the energy of the frontier orbitals. A comprehensive set of examples includes fourth period metal atoms and ions in zeolites on insulating (e.g., MgO) or reducible (e.g., TiO2) oxides and are among the most relevant catalysts for a wealth of key processes of industrial and environmental relevance, from the abatement of NOx to the selective oxidation of hydrocarbons and the conversion of methane to methanol.There exist several spectroscopic techniques able to inform on the geometric and electronic structure of isolated single metal ion sites, but either they yield information averaged over the bulk or they lack description of the intimate features of chemical bonding, which include covalency, ionicity, electron and spin delocalization. All of these can be recovered at once by measuring the magnetic interactions between open-shell metals and the surrounding nuclei with Electron Paramagnetic Resonance (EPR) spectroscopy. In the case of oxides, this entails the synthesis of 17O isotopically enriched materials. We have established 17O EPR as a unique source of information about the local binding environment around oxygen of magnetic atoms or ions on different oxidic supports to rationalize structure-property relationships. Here, we will describe strategies for 17O surface enrichments and approaches to monitor the state of charge and spin delocalization of atoms or ions from K to Zn dispersed on oxide surfaces characterized by different chemical properties (i.e., basicity or reducibility). Emphasis is placed on chemical insight at the atomic-scale level achieved by 17O EPR, which is a crucial step in understanding the structure-property relationships of single metal atom catalysts and in enabling efficient design of future materials for a range of end uses.

Precisely Tailoring Heterometallic Polyoxotitanium Clusters for the Efficient and Selective Photocatalytic Oxidation of Hydrocarbons.

Photocatalysis is a promising yet challenging approach for the selective oxidation of hydrocarbons to valuable oxygenated chemicals with O2 under mild conditions. In this work, we report an atomically precise material model to address this challenge. The key to our solution is the rational incorporation of Fe species into polyoxotitanium cluster to form a heterometallic Ti4 Fe1 cocrystal. This newly designed cocrystal cluster, which well governs the energy and charge transfer as evidenced by spectroscopic characterizations and theoretical calculations, enables the synergistic process involving C(sp3 )-H bond activation by photogenerated holes and further reactions by singlet oxygen (1 O2 ). Remarkably, the cocrystal Ti4 Fe1 cluster achieves efficient and selective oxidation of hydrocarbons (C5 to C16 ) into aldehydes and ketones with a conversion rate up to 12 860 μmol g-1 h-1 , 5 times higher than that of Fe-doped Ti3 Fe1 cluster. This work provides insights into photocatalyst design at atomic level enabling synergistic catalysis.

Precisely Tailoring Heterometallic Polyoxotitanium Clusters for the Efficient and Selective Photocatalytic Oxidation of Hydrocarbons

AbstractPhotocatalysis is a promising yet challenging approach for the selective oxidation of hydrocarbons to valuable oxygenated chemicals with O2 under mild conditions. In this work, we report an atomically precise material model to address this challenge. The key to our solution is the rational incorporation of Fe species into polyoxotitanium cluster to form a heterometallic Ti4Fe1 cocrystal. This newly designed cocrystal cluster, which well governs the energy and charge transfer as evidenced by spectroscopic characterizations and theoretical calculations, enables the synergistic process involving C(sp3)−H bond activation by photogenerated holes and further reactions by singlet oxygen (1O2). Remarkably, the cocrystal Ti4Fe1 cluster achieves efficient and selective oxidation of hydrocarbons (C5 to C16) into aldehydes and ketones with a conversion rate up to 12 860 μmol g−1 h−1, 5 times higher than that of Fe‐doped Ti3Fe1 cluster. This work provides insights into photocatalyst design at atomic level enabling synergistic catalysis.

Interface engineered Ca–Co mixed oxide heterostructures for boosting the aerobic and solvent-free selective oxidation of ethybenzene

Exploration of a high-performance, low-cost and easy-to-prepare solid catalyst is a permanent goal to advance the selective oxidation of hydrocarbons to high-value-added oxygenated products. Herein, we demonstrated for the first time that Ca–Co mixed oxide with abundant strongly interacting heterointerfaces for advanced ethylbenzene oxidation performance under solvent-free conditions and using molecular oxygen as the only oxidant. The interface engineering strategy contributes to the formation of weakened Co–O bonds, enhanced oxygen vacancy concentration and boosted reactivity of lattice oxygen, facilitating the generation of superoxide radical anions for driving the ethylbenzene (EB) oxidation catalysis. In addition, the CaxCoyOz catalyst exhibits good recyclability and high stability. This study provides a paradigm for the rational construction of metal oxides with hybrid interfaces towards a lab as well as a large-scale green oxidation of EB and beyond.

Photoreactive polymer composite for selective oxidation of benzene to phenol

In this work, the photocatalytic hydroxylation of benzene to phenol in presence of H2O2 is studied using, for the first time, a photoreactive polymer composite based on N-doped TiO2 (N-TiO2) embedded into a monolithic syndiotactic polystyrene aerogel (N-TiO2/sPS, 10/90 w/w). N-TiO2/sPS is able to enhance the phenol selectivity and yield compared to bare N-TiO2. The best results in terms of selectivity (98%) and phenol yield (57%) are achieved under visible light in acidic conditions (pH=2), preserving a high benzene conversion (58%). In addition, N-TiO2/sPS is recovered from the aqueous solution containing the reaction products and reused several times without significant loss of photoreactivity and reduction of phenol yield. The described photoreactive solid phase represents a "proof of concept" that could allow a significant leap forward in the development of innovative green processes for the selective oxidation of aromatic hydrocarbons under mild conditions.

Rational Catalyst Design for Higher Propene Partial Electro-oxidation Activity by Alloying Pd with Au

Selective partial oxidation of hydrocarbons to oxygenates plays a large role in the chemical industry, while falling prices for electricity from renewable sources make electrification of such industrial chemical processes relevant. The oxidation of propene is an interesting model system as propene can be oxidized in two different positions, allowing for insights into the reaction mechanism. On Pd, a layer of adsorbates formed in situ governs the reaction by steering reactant adsorption to achieve high selectivity for allyl oxidation, albeit largely inhibiting the reaction rate. Through rational catalyst design, we demonstrate that alloying reactive Pd with inert Au influences the adsorbate layer formation, enhancing activity while maintaining high selectivity toward allyl oxidation. We obtain mechanistic insights with a combination of ab initio computational modeling and electrochemical measurements with ex situ product quantification and online mass spectrometry. Using a statistical approach, we explore the correlation of the Au:Pd ratio with Pd surface cluster size and density, which determine the properties of the adsorbate layer and thus the reaction outcome. We report an activity enhancement by a factor 2.4 with 10% Au in Pd and propose that (i) activity is maximized at potentials just before Pd cluster oxidation and (ii) the optimal catalyst surface contains approximately one Au every six Pd atoms, statistically most frequent at the nominal alloy composition Au14Pd86.

Oxidation of methane and ethylene over Al incorporated N-doped graphene: A comparative mechanistic DFT study

It is generally recognized that developing effective methods for selective oxidation of hydrocarbons to generate more useful chemicals is a major challenge for the chemical industry. In the present study, density functional theory calculations are conducted to examine the catalytic partial oxidation of methane (CH4) and ethylene (C2H4) by nitrous oxide (N2O) over Al-incorporated porphyrin-like N-doped graphene (AlN4-Gr). Adsorption energies for the most stable configurations of CH4, C2H4, and N2O molecules over the AlN4-Gr catalyst are determined to be −0.25, −0.64, and −0.40 eV, respectively. According to our findings, N2O can be efficiently split into N2 and Oads species with a negligible activation energy on the AlN4-Gr surface. Meanwhile, CH4 and C2H4 molecules compete for reaction with the activated oxygen atom (Oads) that stays on the surface. The energy barriers for partial methane oxidation through the CH4 + Oads → CH3° + HOads and CH3° + HOads → CH3OH reaction steps are 0.16 eV and 0.27 eV, respectively. Furthermore, the produced CH3OH may be overoxidized by Oads to give formaldehyde and water molecules by overcoming a relatively low activation barrier. The activation barriers for C2H4 epoxidation are small and comparable to those for CH4 oxidation, implying that AlN4-Gr is highly active for both reactions. The high energy barrier for the 1,2-hydrogen shift in the OCH2CH2 intermediate, on the other hand, makes the production of acetaldehyde impossible under normal conditions. According to the population analysis, the AlN4-Gr serves as a strong electron donor to aid in the charge transfer between the Al atom and the Oads moiety, which is necessary for the activation of CH4 and C2H4. The findings of the present study may pave the way for a better understanding of the catalytic oxidation the CH4 and C2H4, as well as for the development of highly efficient noble-metal free catalysts for these reactions.

Relay catalysis of hydrocarbon oxidation using O2 in the confining domain of 3D metalloporphyrin-based metal-organic frameworks with bimetallic catalytic centers

To realize efficient and selective oxidation of hydrocarbons with O2, 3D MOFs possessing bimetallic centers were prepared to construct confining domains and relay catalysis sites. Applied to oxidation of hydrocarbons, optimum performance was observed in PCN-224(Co&Ni) as catalyst. Both of conversion and selectivity towards partial oxidation products were enhanced. In the significant cyclohexane oxidation, conversion increased from 5.89% to 7.26% with selectivity rose from 81.5% to 85.2%. Superior performance of PCN-224(Co&Ni) was attributed to suppressed free radical diffusion in confining domains of PCN-224(Co&Ni), enhanced oxidation of C-H bonds with oxidation intermediate R-OOH in relay catalysis, and decreased contact between partial oxidation products and catalytic centers. The relay catalysis mode and catalytic mechanism were also studied. The relay catalysis in confining domains herein provided a novel and effective strategy for selective and efficient oxidative functionalization of hydrocarbons, but also an intelligent and valuable idea for other chemical transformations involved free radicals.

Guiding questions for catalyst synthesis and use in selective catalytic oxidation reactions

This paper presents a brief history of catalysis, as well as of the processes of selective oxidation of hydrocarbons. On the other hand, the basic concepts involved in heterogeneous catalysis are mentioned, emphasizing the role of catalytic materials in chemical oxidation processes and posing a series of guiding questions to be followed when approaching a process catalyzed by solid materials. In the same way, the methods of synthesis of catalysts called in the literature as sol-gel and impregnation are shown, identifying the influence of each stage of preparation with the physical and chemical properties of the materials. Finally, a case study applied to the selective catalytic oxidation of methane and methanol using iron, molybdenum and vanadium catalytic materials synthesized by the sol-gel method is presented.