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25 pages, 5837 KiB

Open AccessArticle

Hybrid Materials Based on Imidazo[4,5-b]porphyrins for Catalytic Oxidation of Sulfides

by Inna A. Abdulaeva, Kirill P. Birin, Remi Chassagnon and Alla Bessmertnykh-Lemeune

Catalysts 2023, 13(2), 402; https://doi.org/10.3390/catal13020402 - 13 Feb 2023

Cited by 9 | Viewed by 2071

Heterogenized metalloporphyrin catalysts for oxidation reactions are extensively explored to improve chemical production. In this work, manganese meso-tetraarylporphyrins were immobilized on hydrated mesoporous titanium dioxide (S_BET = 705 m² g⁻¹) through carboxylate or phosphonate anchoring groups separated from [...] Read more.

Heterogenized metalloporphyrin catalysts for oxidation reactions are extensively explored to improve chemical production. In this work, manganese meso-tetraarylporphyrins were immobilized on hydrated mesoporous titanium dioxide (S_BET = 705 m² g⁻¹) through carboxylate or phosphonate anchoring groups separated from the macrocycle by the 2-arylimidazole linker fused across one of the pyrrolic rings of the macrocycle. The element composition of two mesoporous hybrid materials thus obtained were investigated and the integrity of the immobilized complexes was shown by different physicochemical methods. Finally, the catalytic efficiency of the more stable material Mn(TMPIP)/TiO₂ with the phosphonate anchor was evaluated in the selective oxidation of sulfides to sulfoxides by molecular oxygen in the presence of isobutyraldehyde (IBA). The heterogenized complex has shown excellent catalytic activity exhibiting a turnover (TON) of ~1100 in a single catalytic run of the sulfoxidation of thioanisole. The catalyst was successfully reused in seven consecutive catalytic cycles. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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11 pages, 2921 KiB

Open AccessArticle

Promotion Effect of Ce Doping on Catalytic Performance of LaMnO₃ for CO Oxidation

by Nan Wang, Shan Wang, Jie Yang, Ping Xiao and Junjiang Zhu

Catalysts 2022, 12(11), 1409; https://doi.org/10.3390/catal12111409 - 10 Nov 2022

Cited by 8 | Viewed by 1788

Abstract

In this paper, Ce-doped La_1-xCe_xMnO₃ perovskite catalysts are prepared by the sol–gel method, and the promotion effect of Ce doping on LaMnO₃ catalysts for CO oxidation is investigated. The catalysts are characterized by X-ray diffractograms, Raman, [...] Read more.

In this paper, Ce-doped La_1-xCe_xMnO₃ perovskite catalysts are prepared by the sol–gel method, and the promotion effect of Ce doping on LaMnO₃ catalysts for CO oxidation is investigated. The catalysts are characterized by X-ray diffractograms, Raman, N₂ physisorption isotherms, temperature-programed reduction with H₂, transmission electron microscopy, and X-ray photoelectron spectroscopy. The results show that the Ce doping greatly improves the catalytic activity of LaMnO₃ for CO oxidation. Among the La_1-xCe_xMnO₃ catalysts, La_0.8Ce_0.2MnO₃ shows the best CO catalytic activity, with 100% CO conversion obtained at 180 °C. The characteristic results show that the LaMnO₃ perovskite phase exists in all Ce-doped catalysts, and the CeO₂ crystalline phase begins to appear at x ≥ 0.1. The high activity of La_0.8Ce_0.2MnO₃ for CO oxidation could be that: (1) it possesses large surface area (25.8 m²/g) to contact with reactants; (2) it has a high surface Ce³⁺/(Ce³⁺ + Ce⁴⁺) ratio of 0.27, which means high content of oxygen vacancies used for O₂ adsorption and activation; and (3) it exhibits strong reducibility that is beneficial to CO activation. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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16 pages, 8762 KiB

Open AccessArticle

A Study of the Degradation of LEV by Transparent PVA/NCD-TiO₂ Nanocomposite Films with Enhanced Visible-Light Photocatalytic Activity

by Anhua Jiang, Xinwen Huang, Geshan Zhang and Wanquan Yang

Catalysts 2022, 12(11), 1336; https://doi.org/10.3390/catal12111336 - 1 Nov 2022

Cited by 4 | Viewed by 1489

Abstract

In recent years, antibiotics (such as levofloxacin (LEV)) have been detected widely in the environment. Semiconductor photocatalysis has been recognized as a promising technology for removing pollutants in the environment. In this work, nitrogen and carbon codoped titanium dioxide nano-catalyst (NCD-TiO₂) [...] Read more.

In recent years, antibiotics (such as levofloxacin (LEV)) have been detected widely in the environment. Semiconductor photocatalysis has been recognized as a promising technology for removing pollutants in the environment. In this work, nitrogen and carbon codoped titanium dioxide nano-catalyst (NCD-TiO₂) was immobilized in polyvinyl alcohol (PVA) matrix to form PVA/NCD-TiO₂ films through solution casting and thermal treatment, which exhibited good photocatalytic efficiency for LEV degradation. The results showed that about 42% LEV can be degraded after 2 h in the presence of PVA/NCD-TiO₂ nanocomposite film (the weight ratio of NCD-TiO₂ to PVA is 8% and thermal treatment is 120 °C) under visible light. Moreover, possible pathways of photocatalytic degradation of LEV according to the detected intermediates are proposed, which provide insight into the degradation mechanism of LEV by using PVA/NCD-TiO₂ photocatalytic films. Finally, the synthesized PVA/NCD-TiO₂ films exhibited excellent reusability and stability in photocatalysis. This work provides fundamental support for the design of a high-stability, excellent photocatalyst for practical application. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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10 pages, 1670 KiB

Open AccessArticle

Integrated CO₂ Capture and Hydrogenation to Produce Formate in Aqueous Amine Solutions Using Pd-Based Catalyst

by Lichun Li, Xiangcan Chen, Chu Yao and Meng Xu

Catalysts 2022, 12(8), 925; https://doi.org/10.3390/catal12080925 - 21 Aug 2022

Cited by 5 | Viewed by 2670

Abstract

Integrated CO₂ capture and hydrogenation to produce formate offers a sustainable approach for reducing carbon dioxide emissions and producing liquid hydrogen carriers (formate) simultaneously. In the current study, three different types of aqueous amine solutions including monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine [...] Read more.

Integrated CO₂ capture and hydrogenation to produce formate offers a sustainable approach for reducing carbon dioxide emissions and producing liquid hydrogen carriers (formate) simultaneously. In the current study, three different types of aqueous amine solutions including monoethanolamine (MEA), diethanolamine (DEA) and triethanolamine (TEA) were investigated as CO₂-capturing and hydrogenation agents in the presence of a Pd/NAC catalyst. The effect of amine structures on the CO₂ absorption products and formate yield was investigated thoroughly. It was found that the formate product was successfully produced in the presence of all three aqueous amine solutions, with tertiary amine TEA accounting for the highest formate yield under the same CO₂ loadings. This is due to the fact that primary and secondary amine moieties in MEA and DEA are responsible for the formation of CO₂ adducts of carbamate and bicarbonate, whereas the tertiary amine moiety in TEA is responsible for the formation of hydrogenation-favorable bicarbonate as the solo CO₂ absorption product. A high yield of formate of 82.6% was achieved when hydrogenating 3 M TEA with 0.3 mol CO₂/mol amine solution in the presence of a Pd/NAC catalyst. In addition, the physio-chemical properties of the Pd/NAC catalyst analyzed using TEM, XRD and XPS characterization were applied to rationalize the superior catalytic performance of the catalyst. The reaction mechanism of integrated CO₂ capture and hydrogenation to produce formate in aqueous amine solutions over Pd/NAC catalyst was proposed as well. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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10 pages, 3219 KiB

Open AccessArticle

Selective Synthesis of 1,4-Dioxane from Oxirane Dimerization over ZrO₂/TiO₂ Catalyst at Low Temperature

by Yinan Wang, Qingrong Yu, Lijun Xue, Qingyue Yu and Xinbao Zhu

Catalysts 2022, 12(8), 832; https://doi.org/10.3390/catal12080832 - 29 Jul 2022

Cited by 2 | Viewed by 2900

Abstract

We report a route to produce 1,4-dioxane from oxirane by using ZrO₂/TiO₂ as catalyst. The composite oxide ZrO₂/TiO₂ was prepared by a coprecipitation method and the catalytic performance was tested through the synthesis of 1,4-dioxane from oxirane [...] Read more.

We report a route to produce 1,4-dioxane from oxirane by using ZrO₂/TiO₂ as catalyst. The composite oxide ZrO₂/TiO₂ was prepared by a coprecipitation method and the catalytic performance was tested through the synthesis of 1,4-dioxane from oxirane in a pipe reactor. The X-ray diffraction (XRD) shows that ZrO₂ and TiO₂ are in crystal form. When the mass percentage of ZrO₂ is 25%, the composite oxide ZrO₂/TiO₂ presents as an amorphous form. The sample 25%ZrO₂/TiO₂ exhibits a specific surface area of 269.5 m²·g⁻¹ and pore volume of 1.34 mL·g⁻¹. The catalyst has 670 µmol·g⁻¹ of NH₃-TPD acid, and the characterization of ammonia infrared spectroscopy (NH₃-FTIR) shows that both Brønsted and Lewis acids are present on the surface of the catalyst. The reaction mechanism was analyzed according to the distribution of product. The test of catalytic performance showed 100.0% conversion of oxirane and 86.2% selectivity of 1,4-dioxane at the optimal operation conditions: atmospheric pressure, reaction temperature 75 °C and gaseous hourly space velocity of 1200.0 h⁻¹. The catalyst exhibits good catalytic performance stability after continuous use for 720 h. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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9 pages, 1221 KiB

Open AccessArticle

F⁻@d4r, a New Type of Acidic Catalytic Site in Zeolite

by Yukai Zhao, Weichi Liang, Yihan Wang, Yan Tong, Zhanhong Li, Yuqian Liang, Xiaolong Liu and Jiuxing Jiang

Catalysts 2022, 12(8), 809; https://doi.org/10.3390/catal12080809 - 24 Jul 2022

Viewed by 1756

Abstract

As a solid acid, zeolite has been widely used in many fields such as tail gas treatment, petrochemical engineering, and the fine chemical industry. F⁻ has been widely used in the synthesis of pure silica or high silica zeolites. To balance the [...] Read more.

As a solid acid, zeolite has been widely used in many fields such as tail gas treatment, petrochemical engineering, and the fine chemical industry. F⁻ has been widely used in the synthesis of pure silica or high silica zeolites. To balance the charge of organic structure directing agents (OSDA), F⁻ is often found located at the center of the double-4-rings (d4r) of the as-made zeolites. During calcination, fluorine ion is removed with the OSDA. We screened a series of composition building units and found that d4r is capable to retain F⁻ in zeolite structure. We introduce the F⁻ back after the calcination to create an unprecedented type of acid site, i.e., F⁻@d4r in pure silica zeolites ITQ-12. The F⁻@d4r species is thermal stable up to 300 °C. ITQ-12 with F⁻@d4r shows substantial catalytic activity in Biginelli reaction. Furthermore, the catalytic performance is proved to be positive correlated with the presence of F⁻@d4r, indicating the mild acid catalytic property of F⁻@d4r. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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15 pages, 4700 KiB

Open AccessArticle

Substituent’s Effects of PNP Ligands in Ru(II)-Catalyzed CO₂ Hydrogenation to Formate: Theoretical Analysis Considering Steric Hindrance and Promotion of Hydrogen Bonding

by Xiangyang Feng, Jun Li and Zhuhong Yang

Catalysts 2022, 12(7), 760; https://doi.org/10.3390/catal12070760 - 8 Jul 2022

Cited by 2 | Viewed by 1961

Abstract

This paper investigates the effects of substituents in PNP-type ruthenium complexes in the catalytic hydrogenation of CO₂ to formate using the DFT method. Six groups were considered as substituents linked to the P atom of the PNP ligand: hydrogen, methyl, iso-propyl, [...] Read more.

This paper investigates the effects of substituents in PNP-type ruthenium complexes in the catalytic hydrogenation of CO₂ to formate using the DFT method. Six groups were considered as substituents linked to the P atom of the PNP ligand: hydrogen, methyl, iso-propyl, tert-butyl, cyclopentyl, and cyclohexyl. The substituent effects were analyzed from the perspectives of steric hindrance and promotion of hydrogen bonding. With the joint functions of steric hindrance and hydrogen bonding promotion during the CO₂ coordination step, hydride addition step, and HCOO⁻ rotation step, these groups exhibited very different substituent effects. The results showed that the methyl group was the most favorable substituent when the solvent’s effects were not included, as it formed hydrogen bonding with relatively weak steric hindrance. The second favorable substituent was the iso-propyl group, while the tert-butyl group was the most unfavorable one, due to remarkable steric hindrance. When the substituent was cyclopentyl or cyclohexyl, the complex provided a wider open space for the reaction compared with the tert-butyl-substituted complex, because cyclopentyl and cyclohexyl are cyclic groups. Therefore, the principle for choosing the substituent in PNP-type complexes allowing the design of highly efficient catalysts for CO₂ hydrogenation indicates that more hydrogen atoms but wider open space are ideal. In addition, the substituent’s effects can be markedly impacted by the solvent used. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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17 pages, 5212 KiB

Open AccessFeature PaperArticle

Metal Ions (Li, Mg, Zn, Ce) Doped into La₂O₃ Nanorod for Boosting Catalytic Oxidative Coupling of Methane

by Jing Xiong, Hongbin Yu, Yuechang Wei, Chengshu Xie, Kezhen Lai, Zhen Zhao and Jian Liu

Catalysts 2022, 12(7), 713; https://doi.org/10.3390/catal12070713 - 29 Jun 2022

Cited by 9 | Viewed by 2296

Abstract

A series of La₂O₃ nanorod catalysts with doping of active metal ions (Li, Mg, Zn and Ce) were synthesized successfully by the hydrothermal method. The La₂O₃ nanorods show a uniform size with the length of 50–200 nm [...] Read more.

A series of La₂O₃ nanorod catalysts with doping of active metal ions (Li, Mg, Zn and Ce) were synthesized successfully by the hydrothermal method. The La₂O₃ nanorods show a uniform size with the length of 50–200 nm and the width of 5–20 nm, and the {110} crystal facet is a preferentially exposed surface. The active metal ions (Li, Mg, Zn and Ce) doped into the lattice of La₂O₃ nanorods enhance the selectivity of the desired products during oxidative coupling of methane (OCM) and decrease the reaction temperature. Among these catalysts, the Mg-La₂O₃ catalyst exhibits the best catalytic performance during the OCM reaction, i.e., its selectivity and yield of C2 products at 780 °C is 73% and 21%, respectively. The effect of doped metal ions on catalytic activity for OCM was systematically investigated. Insight into the fabrication strategy and promoting factors of the OCM reaction indicates the potential to further design a high-efficient catalyst in the future. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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20 pages, 8787 KiB

Open AccessFeature PaperArticle

Undercooling, Thermal Stability, and Application in Exothermic Catalytic Reaction of SiO₂ Encapsulated SnZnCu Microspheres

by Haodong Tang, Xiali Zheng, Yun Yu, Jinxin Liang, Yifan Zheng and Zongjian Liu

Catalysts 2022, 12(2), 205; https://doi.org/10.3390/catal12020205 - 9 Feb 2022

Viewed by 1799

Abstract

SiO₂ encapsulated SnZnCu microspheres (several micrometers to about 30 μm in diameter) with very low undercooling, narrow freezing/melting range, and high thermal cycling stability have been produced and used as the temperature stabilizer of the packed bed in highly exothermic Fischer–Tropsch reaction. [...] Read more.

SiO₂ encapsulated SnZnCu microspheres (several micrometers to about 30 μm in diameter) with very low undercooling, narrow freezing/melting range, and high thermal cycling stability have been produced and used as the temperature stabilizer of the packed bed in highly exothermic Fischer–Tropsch reaction. The core–shell structured SnZnCu@SiO₂ microspheres are prepared in a two-step way, namely SnZnCu microspheres are firstly produced via a molten LiCl–KCl–CsCl eutectic-based metal emulsion method, and then a sol–gel approach is employed to coat them with a uniform, anti-leakage SiO₂ layer. It is found that raising the amount of Zn to 4.0 at.% is critical for achieving a very low undercooling (<5 °C for SnZn_0.04Cu_x@SiO₂ vs. about 84 °C for Sn@SiO₂) and a narrow freezing/melting peak width, and both undercooling and peak width are almost unchanged as the Cu content (x) increases from 1.5 to 3.0 at.%. However, their thermal cycling stability depends positively on the amount of Cu and can be remarkably improved when 3.0 at.% Cu is added. The results also show that low undercooling and narrow freezing/melting peak width are associated with the formation of Sn–Zn–Cu ternary eutectic and metastable phase Cu₅Zn₈, and poor thermal cycling stability of SnZn_0.04Cu_x@SiO₂ microspheres with low Cu content is related to the decomposition of Cu₅Zn₈ during thermal cycling. By embedding thermally stable SnZn_0.04Cu_0.03@SiO₂ microspheres into the Co/SiO₂ catalyst for Fischer–Tropsch synthesis, the temperature gradient in the catalyst bed can be significantly reduced by suppressing the formation of hot spots or thermal runaway and thus rapid deactivation of Co catalyst that occurs in the SnZn_0.04Cu_x@SiO₂-absent Co/SiO₂ catalyst can be avoided. Full article

(This article belongs to the Special Issue Catalysts with New Formulations/Structures: Synthesis and Applications)

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