Efficient Oxidation Catalysts Research Articles

One-step synthesis of efficient manganese-based oxide catalyst for ultra-rapid CO2 absorption in MDEA solutions

The objective of this study is to develop a promising and feasible technique to significantly increase in the CO2 absorption rate of tertiary amine solutions. Here, for the first time, a manganese-based oxide (MnOx) with four different oxides, including Mn3O4, Mn2O3, MnOOH, and MnO2, is prepared using a one-step synthesis approach, and utilized to catalytically accelerate CO2 absorption in a typical tertiary amine, MDEA solution. The results reveal that the MnOx catalyst improves the CO2 absorption rate and amount as high as 360% and 132%, respectively. The MnOx also outperforms various single manganese-based oxides and their physical mixture, as well as most of the reported catalysts in terms of catalytic enhancement of CO2 absorption in the MDEA solution. The FT-IR analysis is used to confirm the catalytic promotion effect of CO2 absorption, and a catalytic mechanism is proposed. The remarkable catalytic enhancement effect of MnOx might primarily result from both plentiful basic sites and unsaturated Mn sites as well as the synergistic interaction between various oxides. Furthermore, the MnOx also has a favorable effect on CO2 desorption and exhibits outstanding recyclability. This work not only demonstrates a workable strategy for improving the CO2 absorption rate by incorporating a low-cost and high-efficiency solid base catalyst into tertiary amine solutions but also provides guidance for developing more effective catalysts to promote CO2 absorption.

Construction of surface oxygen vacancy active sites upon MnOx/AC composite catalysts for efficient coupling adsorption and oxidation of toluene

Activated carbon (AC) has been widely used as adsorbent and support of noble metal catalysts for the elimination of VOCs, owing to its high specific surface area and effective regulation of interfacial properties of catalysts via metal-support interaction. Herein, a series of MnOx/AC composite catalysts are prepared by in-situ redox precipitation method using KMnO4 as manganese source, ethylene glycol (EG) as reducing agent and coconut shell-based AC as active carrier. The obtained MnOx/AC catalysts have been fully characterized by XRD, SEM, TEM, N2 adsorption-desorption, FT-IR, XPS, EPR, H2-TPR, TPD-MS and toluene-TPSR-Ms (with and without O2) and their catalytic properties are evaluated for low temperature oxidation of toluene. It is found that the introduction of AC support significantly enhanced the adsorption capacity of toluene upon the MnOx/AC composite catalysts. Amongst, the MnOx/AC-0.3 shows excellent low-temperature catalytic activity (T90 = 193 °C), which can be related to highly efficient synergy of AC and MnOx species in toluene combustion. Especially, the construction of efficient MnOx/AC interfaces with more oxygen vacancy active sites, better lattice oxygen mobility, and stronger molecular oxygen activation ability, makes MnOx/AC-0.3 composite catalyst possess the best coupling adsorption oxidation capacity of toluene, and thus resulting in significant improvement in catalytic performance. Additionally, the obtained MnOx/AC-0.3 catalyst has also exhibited good catalytic stability and water resistance (5 vol%). This work deepens the understanding of the metal-support interaction in MnOx/AC composite catalysts and provides new ideas for the design of environmentally friendly catalysts.

Lacunary silicotungstic heteropoly salts as high-performance catalysts in oxidation of cyclopentene

• Development of lacunary Keggin heteropoly anions by one-pot simplified process. • Functionalized ionic liquid-based catalysts for efficient oxidation of cyclopentene. • The di-lacunary heteropoly anions shows higher intramolecular oxidative capacity and stability. • In situ FT-IR reveals the reaction trend of intermediates and active species. The development of polyoxometalates for olefin oxidation is critical to achieving the green chemical process of the C5 fraction further processing. Di-lacunary silicotungstic anions were easily obtained by continuously adjusting the pH instead of the traditional step-by-step method, which exhibited excellent performance in the catalytic oxidation of cyclopentene to aldehydes or alcohols. The 93.69% CPE conversion and 97.15% total product selectivity (41.38% for GA and 55.77% for 1,2-diol) were achieved by using H 2 O 2 as the oxidant and acetonitrile as the solvent. Through complementary characterization, it was found that the optimized di-lacunary silicotungstic polyoxometalate retained a complete Keggin structure, and exhibited better catalytic activity and stability than the mono-lacunary or saturated silicodecatungstate because it exposed more catalytic active centers. Furthermore, in situ FT-IR spectra was utilized to monitor the reaction process, revealing the formation of the active species W(O 2 ) on the di-lacunary silicotungstic polyoxometalate and the intermediate epoxycyclopentane during the catalytic oxidation of cyclopentene.

Synthesis of an efficient VPO catalyst for the selective oxidation of n-butane to the MA product: Mechanism of crystal transformation

Serial VPO catalysts with different crystal structures were prepared by adjusting the ratios of air and N2 in the calcination process. The precursors and vanadium phosphorus oxide (VPO) catalysts were characterized by various measurements. As the air and N2 ratios were lower than 1:1, the ordered VOHPO4·0.5H2O phase was mainly formed in the precursors during calcination. However, as the ratio of air to N2 reached 3:1, amorphous VOPO4 phases were formed over the surface of the precursor during calcination, which prevented the formation of ordered V5+ species over the surface of the VPO catalyst after activation. Meanwhile, a high proportion of VOHPO4·0.5H2O in the precursor could facilitate more formation of the ordered α1-VOPO4 phase over the surface of the VPO catalyst. Interestingly, the crystal structure over the surface of active VPO catalysts was totally different from the core of VPO catalysts. There were more P species and V species with 5+ existing over the surface of the VPO catalysts. The evaluation results of n-butane oxidation showed that when the ratio of air to N2 was 1:3, the corresponding VPO-1A catalyst presented the highest conversion of n-butane and yield of the MA product (57.6 m% at 412 °C). The reason should be related to the fact that the VPO-1A catalyst possessed the highest acidity and proportions of surface V5+ species and Sur-O species. As the ratio of air to N2 reached 3:1, the VPO-3A catalyst showed the poorest performance in the oxidation of n-butane, which could be due to the formation of inactive and amorphous VOPO4 phases over the surface of the VPO catalyst. Finally, kinetic and thermodynamic models were established and calculated to investigate the characteristics of n-butane oxidation reactions for various VPO catalysts.

Iron nanoparticles supported ordered mesoporous CeO2, an efficient catalyst for photo-Fenton oxidation of phenol under irradiation

Iron nanoparticles supported ordered mesoporous CeO2, an efficient catalyst for photo-Fenton oxidation of phenol under irradiation

Ruthenium(III) Chloride as an Efficient Catalyst for the Selective Oxidation of Fatty Alcohols to Aldehydes

AbstractThe oxidation of a series of fatty alcohols to yield the corresponding aldehydes is performed using RuCl3 ⋅ (H2O)x as a homogeneous catalyst and inexpensive trimethylamine N‐oxide (TMAO) as the oxygen source. The reaction conditions were optimized for both high conversion and high selectivity.

Transition Metal (Fe2O3, Co3O4 and NiO)-Promoted CuO-Based α-MnO2 Nanowire Catalysts for Low-Temperature CO Oxidation

As a toxic pollutant, carbon monoxide (CO) usually causes harmful effects on human health. Therefore, the thermally catalytic oxidation of CO has received extensive attention in recent years. The CuO-based catalysts have been widely investigated due to their availability. In this study, a series of transition metal oxides (Fe2O3, Co3O4 and NiO) promoted CuO-based catalysts supported on the α-MnO2 nanowire catalysts were prepared by the deposition precipitation method for catalytic CO oxidation reactions. The effects of the loaded transition metal type, the loading amount, and the calcination temperature on the catalytic performances were systematically investigated. Further catalyst characterization showed that the CuO/α-MnO2 catalyst modified with 3 wt% Co3O4 and calcined at 400 °C performed the highest CO catalytic activity (T90 = 75 °C) among the investigated catalysts. It was supposed that the loading of the Co3O4 dopant not only increased the content of oxygen vacancies in the catalyst but also increased the specific surface area and pore volume of the CuO/α-MnO2 nanowire catalyst, which would further enhance the catalytic activity. The CuO/α-MnO2 catalyst modified with 3 wt% NiO and calcined at 400 °C exhibited the highest surface adsorbed oxygen content and the best normalized reaction rate, but the specific surface area limited its activity. Therefore, the appropriate loading of the Co3O4 modifier could greatly enhance the activity of CuO/α-MnO2. This research could provide a reference method for constructing efficient low-temperature CO oxidation catalysts.

Construction of Pt-MnO2 interface with strong electron coupling effect for plasma catalytic oxidation of aromatic VOCs

The design of efficient catalysts with desirable active sites is an important direction for the plasma catalytic oxidation of VOCs. In this research, a combination of hydrothermal and impregnation methods was used to load Pt nanoparticles on MnO2 with different crystalline phases. The effect of Pt/MnO2 catalysts with different interactions between Pt and MnO2 on the plasma catalytic oxidation of o-xylene under ambient conditions was investigated. The plasma catalytic performance of different Pt/MnO2 varied greatly due to the different physicochemical properties of MnO2 with different crystalline phases. Among them, Pt/α-MnO2 showed the best catalytic performance with 100% o-xylene conversion and 93% CO2 selectivity at room temperature and 100 J/L energy density. The characterization results showed that the most electron transfer from Mn to Pt at the Pt/α-MnO2 interface produced the most oxygen vacancies and afforded the highest oxygen migration ability. The construction of Pt-MnO2 interface with strong electron coupling effect led to the excellent plasma catalytic efficiency as well as stability towards VOCs oxidation. This work provides inspiration for the design of efficient catalyst for the plasma catalytic oxidation of aromatic VOCs.

Hollow Ag/Mn(btc): As highly efficient catalyst for oxidation of sulfides to sulfoxides

Hollow Ag/Mn(btc): As highly efficient catalyst for oxidation of sulfides to sulfoxides

Oxygen vacancies engineering of Fe doped LaCoO3 perovskite catalysts for efficient H2S selective oxidation

Fe-doped LaCoO3 perovskite catalysts synthesized via a facile citric acid-assisted sol-gel route have been applied for the H2S selective oxidation. The as-synthesized LaFexCo1−xO3 perovskites exhibit a randomly macroporous structure formed by the accumulation of nanoparticles. Characterization studies reveal that appropriate Fe substitution effectively enhances the formation of oxygen vacancies, and thus improves the lattice oxygen mobility and H2S adsorbability, respectively. The obtained LaFe0.4Co0.6O3 exhibited remarkable catalytic activity, with the H2S conversion and sulfur yield of 100% at 190 °C. A combined approach of in-situ FT-IR and in-situ Raman experiments disclosed that the plausible reaction pathway of H2S selective oxidation over LaFexCo1−xO3 perovskites follows the Mars-van Krevelen mechanism. The density functional theory calculations revealed that Fe-doping improves the formation of oxygen vacancy and enhances the adsorption of H2S. This study offers new insights for the design of highly efficient perovskites for the selective oxidation of H2S.

Pt–Co bimetals supported on UiO-66 as efficient and stable catalysts for the catalytic oxidation of various volatile organic compounds

Bimetallic catalysts exhibit excellent synergistic catalytic performance for volatile organic compounds (VOCs) oxidation. However, it remains challenging to design more active, selective, and stable bimetallic catalytic systems for the practical oxidation of various VOCs. Here, by integrating porous metal-organic frameworks as support, platinum as catalytic center, and cobalt as promoter, we obtained a synergistic and stable Pt–Co/UiO-66 catalytic system, with highly dispersed active sites for various VOCs oxidation. Pt–Co/UiO-66 exhibited better catalytic performances than monometallic constituents in toluene, n-hexane, and ethyl acetate oxidation. Besides, Pt–Co/UiO-66 showed high reusability, water or CO2 resistance, long-term activity over 120 h, and structural stability. Furthermore, the reaction pathway and mechanism of toluene oxidation were investigated by in-situ diffuse reflectance infrared Fourier transform spectroscopy and online gas chromatography-mass spectrometer. We believe that this work will provide a useful idea for developing effective bimetallic catalysts in environmental catalysis.

A theoretical study of the Pd10Sb3 single-atom alloy cluster for CO oxidations

Inspired by the experimental synthesis of Pd-based single-atom alloy (SAA) catalysts which display high performance for reactions in the chemical industry. In this work, we have designed a Pd10Sb3 SAA alloy cluster as an efficient catalyst for CO oxidation. It is stable at 400 K for 3 ps under the ab-initio molecular dynamic simulation. Compared with Pd13, the Sb atom transfers electrons to the neighbour Pd atom, which induces its 4d states near the fermi level reduced much more. As a result, Pd10Sb3 show much weaker adsorptions of CO and O2. In addition, CO and O2 prefer to be adsorbed on the Pd site rather than on the Sb site. Thus, we have considered the full path for CO oxidation on the pure Pd site on Pd13 and Pd10Sb3 clusters. Compared with Pd13, on Pd10Sb3 the barrier of the rate-limiting step, that is the peroxide-like OO-CO intermediate formation, decreases by 0.54 eV which indicates Pd10Sb3 can be a potential catalyst for CO oxidation.

CeO2-Supported TiO2-Pt Nanorod Composites as Efficient Catalysts for CO Oxidation.

Supported Pt-based catalysts have been identified as highly selective catalysts for CO oxidation, but their potential for applications has been hampered by the high cost and scarcity of Pt metals as well as aggregation problems at relatively high temperatures. In this work, nanorod structured (TiO2-Pt)/CeO2 catalysts with the addition of 0.3 at% Pt and different atomic ratios of Ti were prepared through a combined dealloying and calcination method. XRD, XPS, SEM, TEM, and STEM measurements were used to confirm the phase composition, surface morphology, and structure of synthesized samples. After calcination treatment, Pt nanoparticles were semi-inlayed on the surface of the CeO2 nanorod, and TiO2 was highly dispersed into the catalyst system, resulting in the formation of (TiO2-Pt)/CeO2 with high specific surface area and large pore volume. The unique structure can provide more reaction path and active sites for catalytic CO oxidation, thus contributing to the generation of catalysts with high catalytic activity. The outstanding catalytic performance is ascribed to the stable structure and proper TiO2 doping as well as the combined effect of Pt, TiO2, and CeO2. The research results are of importance for further development of high catalytic performance nanoporous catalytic materials.

Barium carbonate promoted cobalt oxide as highly efficient catalyst for the total oxidation of vinyl chloride

Co-based catalyst has excellent chlorine resistance, so it is an effective catalyst to degrade VC at present. A series of high-performance CoxBa1 catalysts were prepared by doping Ba into Co3O4 and changing the Ba/Co mol ratio. Under the condition of space velocity of 15,000 ml·g−1·h−1, the conversion rate of VC reached 90% at 199 °C in Co19Ba1, the temperature is much lower than T90 of pure Co3O4 (309 °C), and the catalysis activity of Co19Ba1 was higher than that of the other alkali metal-doped Co19M1 (M = Sr, Ca). Ba species in CoxBa1 mainly exist in the form of BaCO3. With the addition of BaCO3, the particle size of CoxBa1 decreases, resulting in the increase of active site of CoxBa1. BaCO3 can also make CoxBa1 obtain better low-temperature reducibility and more active components. In addition, the increase of BaCO3 content will also increase the basic sites of CoxBa1, and more basic sites can effectively protect Co3O4 from Cl poisoning. When Ba/Co is 1/19, the content of BaCO3 is the highest, so Co19Ba1 also shows the best activity.

Rational Design of NiZnx@CuO Nanoarray Architectures for Electrocatalytic Oxidation of Methanol.

Methanol oxidation reaction (MOR) in anodes is one of the significant aspects of direct methanol fuel cells (DMFCs), which also plays a critical role in achieving a carbon-neutral economy. Designing and developing efficient, cost-effective, and durable non-Pt group metal-based methanol oxidation catalysts are highly desired, but a gap still remains. Herein, we report well-defined hierarchical NiZnx@CuO nanoarray architectures as active electrocatalysts for MOR, synthesized by combining thermal oxidation treatment and magnetron sputtering deposition through a brass mesh precursor. After systematically evaluating the electrocatalytic performance of NiZnx@CuO nanoarray catalysts with different preparation conditions, we found that the NiZn1000@CuO (thermally oxidized at 500 °C for 2 h, nominal thickness of the NiZn alloy film is 1000 nm) electrode delivers a high current density of 449.3 mA cm-2 at 0.8 V for MOR in alkaline media as well as excellent operation stability (92% retention after 12 h). These outstanding MOR performances can be attributed to the hierarchical well-defined structure that can not only render abundant active sites and a synergistic effect to enhance the electrocatalytic activity but also can effectively facilitate mass and electron transport. More importantly, we found that partial Zn atoms could leach from the NiZn alloy, resulting in rough surface nanorods, which would further increase the specific surface area. These results indicate that the NiZn1000@CuO nanoarray architecture could be a promising Pt group metal alternative as an efficient, cost-effective, and durable anode catalyst for DMFCs.

Unraveling the role of OH groups over CeO2 derived from methanol modification for enhancing toluene oxidation: Experimental and theoretical studies

Developing efficient catalysts for catalytic oxidation of toluene at low temperatures is challenging. Herein, the OH groups and oxygen vacancies are introduced into CeO2 by methanol modification and applied in catalytic oxidation of toluene. CeO2-T-M, one of the modified CeO2, displays the greatest catalytic activity for toluene oxidation with T90 of 235 oC. In situ characterizations and theoretical calculations show that abundant OH groups and oxygen vacancies on the CeO2-T-M are well correlated with the catalytic activity. The OH groups facilitate the adsorption and activation of gaseous oxygen into adsorbed active oxygen species (O22-) and lattice oxygen (O2-) over oxygen vacancies. And the toluene and key intermediates (benzyl alcohol, benzaldehyde, benzoate, and maleic anhydride) are more easily adsorbed and oxidized on CeO2-T-M. Meanwhile, the consumed OH groups will be regenerated with activated lattice oxygen by dehydrogenation, thus the catalytic activity and stability for toluene oxidation are enhanced over modified CeO2.

Sustainable design of co-doped ordered mesoporous carbons as efficient and long-lived catalysts for H2S reutilization

Selective catalytic oxidation of H2S into elemental sulfur has been recognized as the optimal route for H2S reutilization, but traditional metal catalysts show poor sulfur resistance. Herein, we report a solvent-free route for designing nitrogen and defects co-doped, ordered mesoporous carbons (ND-OMCs) from co-assembly of block copolymer template with nitrogen-containing oligomers and silica defects directing agent. Through thermal curing, carbonization and etching of silica, the microporosity tandem ordered mesopores, abundant nitrogen sites (6.13 wt%) and structural defects were introduced into ND-OMCs. The ND-OMCs were successfully applied as efficient and long-lived metal-free catalysts for H2S selective oxidation to sulfur, giving nearly 100 % H2S conversion and sulfur selectivity at only 150 °C. Their remarkable activities of ND-OMCs can be well-maintained over 157 h of continuous reaction, exhibiting the sulfur capacity as high as 3295 mg/g, which were much better than mostly desulfurizes such as commercial Fe2O3, g-C3N4, and nitrogen-containing, ordered mesoporous carbons.

Evolution of Carbonate-Intercalated γ-NiOOH from a Molecularly Derived Nickel Sulfide (Pre)Catalyst for Efficient Water and Selective Organic Oxidation.

The development of a competent (pre)catalyst for the oxygen evolution reaction (OER) to produce green hydrogen is critical for a carbon-neutral economy. In this aspect, the low-temperature, single-source precursor (SSP) method allows the formation of highly efficient OER electrocatalysts, with better control over their structural and electronic properties. Herein, a transition metal (TM) based chalcogenide material, nickel sulfide (NiS), is prepared from a novel molecular complex [NiII (PyHS)4 ][OTf]2 (1) and utilized as a (pre)catalyst for OER. The NiS (pre)catalyst requires an overpotential of only 255mV to reach the benchmark current density of 10mAcm-2 and shows 63h of chronopotentiometry (CP) stability along with over 95% Faradaic efficiency in 1m KOH. Several ex situ measurements and quasi in situ Raman spectroscopy uncover that NiS irreversibly transformed to a carbonate-intercalated γ-NiOOH phase under the alkaline OER conditions, which serves as the actual active structure for the OER. Additionally, this in situ formed active phase successfully catalyzes the selective oxidation of alcohol, aldehyde, and amine-based organic substrates to value-added chemicals, with high efficiencies.

PtRuFe/Carbon Nanotube Composites as Bifunctional Catalysts for Efficient Methanol Oxidation and Oxygen Reduction.

The design of bifunctional catalysts with high performance and low platinum for the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR) is of significant implication to promote the industrialization of fuel cells. In our work, Pt/carbon nanotube (CNT), Pt3Ru/CNT, and PtRu/CNT catalysts were synthesized by plasma heat treatment, in which the pyrolysis reduction of organometallic salts and the dispersion of CNTs were achieved simultaneously, and catalytic nanoparticles with uniform particle size were anchored on the dispersed CNT surface. Later, Fe was further introduced, and PtFe/CNT, Pt3RuFe/CNT, and PtRuFe/CNT catalysts were synthesized by calcination, and the structure and electrochemical properties in both MOR and ORR of all as-synthesized catalysts were investigated. The results indicated that plasma thermal treatment has the advantage of rapidness and immediacy in the synthesis of catalysts, and the Pt/CNT, Pt3Ru/CNT, and PtRu/CNT catalysts exhibited better electrocatalytic properties than commercial platinum (JM-Pt/C) catalysts. Meanwhile, the introduction of Fe during the calcination further changed the surface electronic properties of catalytic nanoparticles and enhanced the graphitization degree of catalysts; the PtRuFe/CNT catalyst exhibited outstanding electrocatalytic properties with a mass activity of 834.3 mA mg-1 for MOR and a half-wave potential of 0.928 V in alkaline media for ORR. The combination of plasma thermal treatment and calcination puts forward a novel strategy for the optimization of catalysts, and the synthesis method based on plasma dispersion needs to be further optimized to achieve its large-scale promotion.

Enhanced toluene oxidation by photothermal synergetic catalysis on manganese oxide embedded with Pt single-atoms

The degradation of volatile organic compounds (VOCs) at low temperature remains a big challenge. Photothermal catalysis coupling the advantages of photocatalysis and thermocatalysis is promising to address this issue. However, there is still a long way to construct highly active catalysts and deeply understand the mechanism of photothermal catalysis. Herein, maganese oxide (MnO2)catalysts embedded with Pt single-atoms (0.11 wt% Pt) have achieved greatly enhanced toluene conversion of 95%, far surpassing most supported Pt photothermal catalysts. The excellent catalytic activity has been disclosed to derive from the synergetic effect oflight-driven thermocatalysis and photocatalysis. The light-driven thermocatalysis predominates and the strong electron transfer from Pt single-atoms to MnO2 improves the activity of surface lattice oxygen to boost the generation of benzoic acid and the mineralization of toluene. Meanwhile, in photocatalytic process, Pt single-atoms accelerate the generation of superoxide radicals (O2−), which facilitate the ring-opening and deep oxidation of toluene. This understanding on the photothermal synergetic mechanism will inspire the design of highly efficient catalysts for VOCs oxidation.