Catalysts

2191 KiB

Open AccessArticle

Formic Acid Modified Co₃O₄-CeO₂ Catalysts for CO Oxidation

by Ruishu Shang, Yiping Duan, Xinyan Zhong, Wei Xie, Yan Luo and Lihong Huang

Catalysts 2016, 6(3), 48; https://doi.org/10.3390/catal6030048 - 17 Mar 2016

Cited by 12 | Viewed by 5807

A formic acid modified catalyst, Co₃O₄-CeO₂, was prepared via facile urea-hydrothermal method and applied in CO oxidation. The Co₃O₄-CeO₂-0.5 catalyst, treated by formic acid at 0.5 mol/L, performed better in CO [...] Read more.

A formic acid modified catalyst, Co₃O₄-CeO₂, was prepared via facile urea-hydrothermal method and applied in CO oxidation. The Co₃O₄-CeO₂-0.5 catalyst, treated by formic acid at 0.5 mol/L, performed better in CO oxidation with T₅₀ obtained at 69.5 °C and T₁₀₀ obtained at 150 °C, respectively. The characterization results indicate that after treating with formic acid, there is a more porous structure within the Co₃O₄-CeO₂ catalyst; meanwhile, despite of the slightly decreased content of Co, there are more adsorption sites exposed by acid treatment, as suggested by CO-TPD and H₂-TPD, which explains the improvement of catalytic performance. Full article

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1152 KiB

Open AccessArticle

Homo-Polymerization of 1-Hexene Catalysed by O^N^N (Salicylaldimine)Iron(III) Pre-Catalysts to Branched Poly(1-hexene)

by Margaret Yankey, Collins Obuah and James Darkwa

Catalysts 2016, 6(3), 47; https://doi.org/10.3390/catal6030047 - 17 Mar 2016

Cited by 3 | Viewed by 7521

Abstract

Five new iron(III) 1-hexene polymerisation catalysts were prepared from the reactions of 2,4-di-tert-butyl-6-(2-(1H-imidazol-4-yl)ethylimino)methylphenol (L1), or 4-tert-butyl-6-(2-(1H-imidazol-4-yl)ethylimino)methylphenol (L2) or 2,4-di-tert-butyl-6-[(2-pyridin-2-yl-ethylimino)-methyl-phenol (L3) with anhydrous iron(II) halides to form [FeCl₂(L1)] (1), [FeBr₂(L1)] (2), [FeI₂(L1)] [...] Read more.

Five new iron(III) 1-hexene polymerisation catalysts were prepared from the reactions of 2,4-di-tert-butyl-6-(2-(1H-imidazol-4-yl)ethylimino)methylphenol (L1), or 4-tert-butyl-6-(2-(1H-imidazol-4-yl)ethylimino)methylphenol (L2) or 2,4-di-tert-butyl-6-[(2-pyridin-2-yl-ethylimino)-methyl-phenol (L3) with anhydrous iron(II) halides to form [FeCl₂(L1)] (1), [FeBr₂(L1)] (2), [FeI₂(L1)] (3), [FeBr₂(L2)] (4) and [FeCl₂(L3)] (5). All the iron(III) complexes 1–5 were activated with EtAlCl₂ to produce active catalysts for the polymerisation of 1-hexene to low molecular weight poly(1-hexene) (M_n = 1021–1084 Da) and very narrow polydispersity indices (1.19–1.24). ¹H and ¹³C{¹H} NMR analysis showed the polymers are branched with methyl, butyl and longer chain branches. The longer chain branches are dominant indicating that 2,1-insertion of monomer is favoured over 1,2-insertion in the polymerisation reaction. Full article

(This article belongs to the Special Issue Molecular Catalysis for Precise Olefin Polymerization and ROP 2015)

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1654 KiB

Open AccessFeature PaperArticle

Mechanistic Investigation of the Reduction of NO_x over Pt- and Rh-Based LNT Catalysts

by Lukasz Kubiak, Lidia Castoldi, Luca Lietti, Stanislava Andonova and Louise Olsson

Catalysts 2016, 6(3), 46; https://doi.org/10.3390/catal6030046 - 15 Mar 2016

Cited by 14 | Viewed by 5227

Abstract

The influence of the noble metals (Pt vs. Rh) on the NO_x storage reduction performances of lean NO_x trap catalysts is here investigated by transient micro-reactor flow experiments. The study indicates a different behavior during the storage in that the Rh-based [...] Read more.

The influence of the noble metals (Pt vs. Rh) on the NO_x storage reduction performances of lean NO_x trap catalysts is here investigated by transient micro-reactor flow experiments. The study indicates a different behavior during the storage in that the Rh-based catalyst showed higher storage capacity at high temperature as compared to the Pt-containing sample, while the opposite is seen at low temperatures. It is suggested that the higher storage capacity of the Rh-containing sample at high temperature is related to the higher dispersion of Rh as compared to Pt, while the lower storage capacity of Rh-Ba/Al₂O₃ at low temperature is related to its poor oxidizing properties. The noble metals also affect the catalyst behavior upon reduction of the stored NO_x, by decreasing the threshold temperature for the reduction of the stored NO_x. The Pt-based catalyst promotes the reduction of the adsorbed NO_x at lower temperatures if compared to the Rh-containing sample, due to its superior reducibility. However, Rh-based material shows higher reactivity in the NH₃ decomposition significantly enhancing N₂ selectivity. Moreover, formation of small amounts of N₂O is observed on both Pt- and Rh-based catalyst samples only during the reduction of highly reactive NO_x stored at 150 °C, where NO_x is likely in the form of nitrites. Full article

(This article belongs to the Special Issue Automotive Emission Control Catalysts)

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147 KiB

Open AccessEditorial

Catalysts Best Paper Award 2016

by Keith L. Hohn

Catalysts 2016, 6(3), 44; https://doi.org/10.3390/catal6030044 - 15 Mar 2016

Viewed by 3553

Abstract

Catalysts has established a new award, to be given annually, for the best original and review articles published in Catalysts.[...] Full article

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6274 KiB

Open AccessArticle

Low-Temperature Catalytic Performance of Ni-Cu/Al₂O₃ Catalysts for Gasoline Reforming to Produce Hydrogen Applied in Spark Ignition Engines

by Le Anh Tuan, Nguyen The Luong and Keiichi N. Ishihara

Catalysts 2016, 6(3), 45; https://doi.org/10.3390/catal6030045 - 14 Mar 2016

Cited by 16 | Viewed by 6998

Abstract

The performance of Ni-Cu/Al₂O₃ catalysts for steam reforming (SR) of gasoline to produce a hydrogen-rich gas mixture applied in a spark ignition (SI) engine was investigated at relatively low temperature. The structural and morphological features and catalysis activity were observed [...] Read more.

The performance of Ni-Cu/Al₂O₃ catalysts for steam reforming (SR) of gasoline to produce a hydrogen-rich gas mixture applied in a spark ignition (SI) engine was investigated at relatively low temperature. The structural and morphological features and catalysis activity were observed by X-ray diffractometry (XRD), scanning electron microscopy (SEM), and temperature programmed reduction (TPR). The results showed that the addition of copper improved the dispersion of nickel and therefore facilitated the reduction of Ni at low temperature. The highest hydrogen selectivity of 70.6% is observed over the Ni-Cu/Al₂O₃ catalysts at a steam/carbon ratio of 0.9. With Cu promotion, a gasoline conversion of 42.6% can be achieved at 550 °C, while with both Mo and Ce promotion, the gasoline conversions were 31.7% and 28.3%, respectively, higher than with the conventional Ni catalyst. On the other hand, initial durability testing showed that the conversion of gasoline over Ni-Cu/Al₂O₃ catalysts slightly decreased after 30 h reaction time. Full article

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3336 KiB

Open AccessArticle

Low-Temperature Oxidation of Dimethyl Ether to Polyoxymethylene Dimethyl Ethers over CNT-Supported Rhenium Catalyst

by Qingde Zhang, Wenfeng Wang, Zhenzhou Zhang, Yizhuo Han and Yisheng Tan

Catalysts 2016, 6(3), 43; https://doi.org/10.3390/catal6030043 - 14 Mar 2016

Cited by 24 | Viewed by 8664

Abstract

Due to its excellent conductivity, good thermal stability and large specific surface area, carbon nano-tubes (CNTs) were selected as support to prepare a Re-based catalyst for dimethyl ether (DME) direct oxidation to polyoxymethylene dimethyl ethers (DMM_x). The catalyst performance was tested [...] Read more.

Due to its excellent conductivity, good thermal stability and large specific surface area, carbon nano-tubes (CNTs) were selected as support to prepare a Re-based catalyst for dimethyl ether (DME) direct oxidation to polyoxymethylene dimethyl ethers (DMM_x). The catalyst performance was tested in a continuous flow type fixed-bed reactor. H₃PW₁₂O₄₀ (PW₁₂) was used to modify Re/CNTs to improve its activity and selectivity. The effects of PW₁₂ content, reaction temperature, gas hourly space velocity (GHSV) and reaction time on DME oxidation to DMM_x were investigated. The results showed that modification of CNT-supported Re with 30% PW₁₂ significantly increased the selectivity of DMM and DMM₂ up to 59.0% from 6.6% with a DME conversion of 8.9%; besides that, there was no CO_x production observed in the reaction under the optimum conditions of 513 K and 1800 h⁻¹. The techniques of XRD, BET, NH₃-TPD, H₂-TPR, XPS, TEM and SEM were used to characterize the structure, surface properties and morphology of the catalysts. The optimum amount of weak acid sites and redox sites promotes the synthesis of DMM and DMM₂ from DME direct oxidation. Full article

(This article belongs to the Special Issue Catalysts for Selective Oxidation)

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10530 KiB

Open AccessFeature PaperCommunication

Effect of Porphyrin Molecular Structure on Water Splitting Activity of a KTaO₃ Photocatalyst

by Hidehisa Hagiwara, Kohei Higashi, Motonori Watanabe, Ryota Kakigi, Shintaro Ida and Tatsumi Ishihara

Catalysts 2016, 6(3), 42; https://doi.org/10.3390/catal6030042 - 10 Mar 2016

Cited by 23 | Viewed by 7211

Abstract

Photocatalytic water splitting is one of the ideal methods for solving the global energy crisis and its associated environmental problems. In this study, the effect of altering the molecular structure of porphyrins was investigated to improve the water splitting activity of Zr-doped KTaO [...] Read more.

Photocatalytic water splitting is one of the ideal methods for solving the global energy crisis and its associated environmental problems. In this study, the effect of altering the molecular structure of porphyrins was investigated to improve the water splitting activity of Zr-doped KTaO₃ (KTa(Zr)O₃) modified with porphyrin dyes. UV-vis spectra indicated that porphyrins with long alkoxy chains tended to form well-developed H-aggregates on the KTa(Zr)O₃ surface. The photocatalytic activity of Pt-loaded KTa(Zr)O₃ was improved by using porphyrins with longer alkoxy chains because of the improvement in the charge migration between porphyrin dye molecules. While the charge transfer between the inorganic semiconductor and porphyrin dye interface is important, it was found that the formation of H-aggregation was more effective in improving the water splitting activity of the porphyrin-modified photocatalysts. Full article

(This article belongs to the Special Issue Photocatalytic Water Splitting-1)

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1548 KiB

Open AccessArticle

Vanadium Oxide Supported on MSU-1 as a Highly Active Catalyst for Dehydrogenation of Isobutane with CO₂

by Guosong Sun, Qingze Huang, Shiyong Huang, Qiuping Wang, Huiquan Li, Haitao Liu, Shijie Wan, Xuewang Zhang and Jinshu Wang

Catalysts 2016, 6(3), 41; https://doi.org/10.3390/catal6030041 - 9 Mar 2016

Cited by 9 | Viewed by 5281

Abstract

Vanadium oxide supported on MSU-1, with VO_x loading ranging from 2.5 to 17.5 wt. %, was developed as a highly active catalyst in dehydrogenation of isobutane with CO₂. The obtained catalysts of VO_x/MSU-1 were characterized by X-ray diffraction [...] Read more.

Vanadium oxide supported on MSU-1, with VO_x loading ranging from 2.5 to 17.5 wt. %, was developed as a highly active catalyst in dehydrogenation of isobutane with CO₂. The obtained catalysts of VO_x/MSU-1 were characterized by X-ray diffraction (XRD), N₂ adsorption-desorption, and H₂-temperature programmed reduction (H₂-TPR) methods and the results showed that the large surface area of MSU-1 was favorable for the dispersion of VO_x species and the optimal loading of VO_x was 12.0 wt. %. Meanwhile, the catalytic activity of VO_x/MSU-1 was investigated, and VO_x/MSU-1 with 12.0 wt. % VO_x content was found to be the best one, with the conversion of isobutane (58.8%) and the selectivity of isobutene (78.5%) under the optimal reaction conditions. In contrast with the reaction in the absence of CO₂, the presence of CO₂ in the reaction stream could obviously enhance the isobutane dehydrogenation, which raised the conversion of reaction and the stability of VO_x/MSU-1. Full article

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3398 KiB

Open AccessArticle

Effect of Ce and Co Addition to Fe/Al₂O₃ for Catalytic Methane Decomposition

by Ahmed Sadeq Al-Fatesh, Ashraf Amin, Ahmed Aidid Ibrahim, Wasim Ullah Khan, Mostafa Aly Soliman, Raja Lafi AL-Otaibi and Anis Hamza Fakeeha

Catalysts 2016, 6(3), 40; https://doi.org/10.3390/catal6030040 - 8 Mar 2016

Cited by 31 | Viewed by 6779

Abstract

Catalytic methane decomposition is studied in a fixed bed reactor. Two sets of bimetallic catalysts are employed, namely: 30%Fe-X%Ce/Al₂O₃ and 30%Fe-X%Co/Al₂O₃, and compared with monometallic 30%Fe/Al₂O₃ catalyst. The effect [...] Read more.

Catalytic methane decomposition is studied in a fixed bed reactor. Two sets of bimetallic catalysts are employed, namely: 30%Fe-X%Ce/Al₂O₃ and 30%Fe-X%Co/Al₂O₃, and compared with monometallic 30%Fe/Al₂O₃ catalyst. The effect of promoting Fe with Ce and Co and reduction temperature are investigated. The results reveal that Ce addition has shown a negative impact on H₂ yield while a positive effect on H₂ yield and catalyst stability are observed with Co addition. In terms of number of moles of produced hydrogen per active sites, Fe/Al₂O₃ has shown a higher number of moles of hydrogen compared to bimetallic catalysts. The catalyst reduced at 500 °C exhibits better activity as compared to the catalyst reduced at 950 °C. Carbon nano-tubes are deposited on the catalyst within the range of 14–73 nm diameter. Two types of carbon nanotubes are detected: Cα and Cγ. Full article

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4864 KiB

Open AccessFeature PaperArticle

Hydrogen Production by Ethanol Steam Reforming (ESR) over CeO₂ Supported Transition Metal (Fe, Co, Ni, Cu) Catalysts: Insight into the Structure-Activity Relationship

by Michalis Konsolakis, Zisis Ioakimidis, Tzouliana Kraia and George E. Marnellos

Catalysts 2016, 6(3), 39; https://doi.org/10.3390/catal6030039 - 8 Mar 2016

Cited by 75 | Viewed by 10431

Abstract

The aim of the present work was to investigate steam reforming of ethanol with regard to H₂ production over transition metal catalysts supported on CeO₂. Various parameters concerning the effect of temperature (400–800 °C), steam-to-carbon (S/C) feed ratio (0.5, 1.5, [...] Read more.

The aim of the present work was to investigate steam reforming of ethanol with regard to H₂ production over transition metal catalysts supported on CeO₂. Various parameters concerning the effect of temperature (400–800 °C), steam-to-carbon (S/C) feed ratio (0.5, 1.5, 3, 6), metal entity (Fe, Co, Ni, Cu) and metal loading (15–30 wt.%) on the catalytic performance, were thoroughly studied. The optimal performance was obtained for the 20 wt.% Co/CeO₂ catalyst, achieving a H₂ yield of up to 66% at 400 °C. In addition, the Co/CeO₂ catalyst demonstrated excellent stability performance in the whole examined temperature range of 400–800 °C. In contrast, a notable stability degradation, especially at low temperatures, was observed for Ni-, Cu-, and Fe-based catalysts, ascribed mainly to carbon deposition. An extensive characterization study, involving N₂ adsorption-desorption (BET), X-ray diffraction (XRD), Scanning Electron Microscopy (SEM/EDS), X-ray Photoelectron Spectroscopy (XPS), and Temperature Programmed Reduction (H₂-TPR) was undertaken to gain insight into the structure-activity correlation. The excellent reforming performance of Co/CeO₂ catalysts could be attributed to their intrinsic reactivity towards ethanol reforming in combination to their high surface oxygen concentration, which hinders the deposition of carbonaceous species. Full article

(This article belongs to the Special Issue Surface Chemistry and Catalysis)

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4053 KiB

Open AccessArticle

Heterogeneous Asymmetric Oxidation Catalysis Using Hemophore HasApf. Application in the Chemoenzymatic Deracemization of sec-Alcohols with Sodium Borohydride

by Hiroyuki Nagaoka

Catalysts 2016, 6(3), 38; https://doi.org/10.3390/catal6030038 - 8 Mar 2016

Cited by 3 | Viewed by 7772

Abstract

This study aims to demonstrate the coordination of oxygen regarding the hemophore HasApf expressed by Escherichia coli cells, which appears to create an unlikely oxygen-activating system in HasA due to the already-coordinated iron. In the asymmetric oxidation of rac-1-(6-methoxynaphthalen-2-yl)ethanol (rac-1) [...] Read more.

This study aims to demonstrate the coordination of oxygen regarding the hemophore HasApf expressed by Escherichia coli cells, which appears to create an unlikely oxygen-activating system in HasA due to the already-coordinated iron. In the asymmetric oxidation of rac-1-(6-methoxynaphthalen-2-yl)ethanol (rac-1) using dissolved oxygen, the signals at g-values of 2.8, 2.22, and 1.72 in the electron spin resonance (ESR) spectra disappeared in conjunction with the promotion of oxoferric (Fe^III−O–O⁻) species in the distal site. These results suggest that the iron of porphyrin/Fe may be oxidized in water, leading to exhibition of greater asymmetric oxidation activity in the promotion of oxoferryl (Fe^IV=O) species. A ketone (~50% chemical yield) produced from (R)-(−)-sec-alcohol can be desymmetrized by NaBH₄ in aqueous medium at 40 °C (>99% enantiomer excess, ee, >90% chemical yield) in the absence of NAD(P). Therefore, HasA can be regenerated via successive asymmetric catalytic events through an incorporated iron electron-transfer system in the presence of oxygen: Fe^II + O₂ → Fe^III−O–O⁻ → Fe^IV=O (oxidizing rac-1) → Fe^II + H₂O. This process is similar to a Fenton reaction. The use of a HasA-catalytic system with an incorporated redox cofactor for asymmetric oxidation overcomes the apparent difficulties in working with pure dehydrogenase enzyme/redox cofactor systems for biotransformations. Full article

(This article belongs to the Special Issue Enzyme Catalysis)

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5691 KiB

Open AccessArticle

Gold-Iron Oxide Catalyst for CO Oxidation: Effect of Support Structure

by Hui-Zhen Cui, Yu Guo, Xu Wang, Chun-Jiang Jia and Rui Si

Catalysts 2016, 6(3), 37; https://doi.org/10.3390/catal6030037 - 7 Mar 2016

Cited by 14 | Viewed by 7626

Abstract

Gold-iron oxide (Au/FeO_x) is one of the highly active catalysts for CO oxidation, and is also a typical system for the study of the chemistry of gold catalysis. In this work, two different types of iron oxide supports, i.e., hydroxylated [...] Read more.

Gold-iron oxide (Au/FeO_x) is one of the highly active catalysts for CO oxidation, and is also a typical system for the study of the chemistry of gold catalysis. In this work, two different types of iron oxide supports, i.e., hydroxylated (Fe_OH) and dehydrated iron oxide (Fe_O), have been used for the deposition of gold via a deposition-precipitation (DP) method. The structure of iron oxide has been tuned by either selecting precipitated pH of 6.7–11.2 for Fe_OH or changing calcination temperature of from 200 to 600 °C for Fe_O. Then, 1 wt. % Au catalysts on these iron oxide supports were measured for low-temperature CO oxidation reaction. Both fresh and used samples have been characterized by multiple techniques including transmission electron microscopy (TEM) and high-resolution TEM (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) and temperature-programmed reduction by hydrogen (H₂-TPR). It has been demonstrated that the surface properties of the iron oxide support, as well as the metal-support interaction, plays crucial roles on the performance of Au/FeO_x catalysts in CO oxidation. Full article

(This article belongs to the Special Issue Surface Chemistry and Catalysis)

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4513 KiB

Open AccessFeature PaperArticle

Study of N₂O Formation over Rh- and Pt-Based LNT Catalysts

by Lukasz Kubiak, Roberto Matarrese, Lidia Castoldi, Luca Lietti, Marco Daturi and Pio Forzatti

Catalysts 2016, 6(3), 36; https://doi.org/10.3390/catal6030036 - 1 Mar 2016

Cited by 17 | Viewed by 5688

Abstract

In this paper, mechanistic aspects involved in the formation of N₂O over Pt-BaO/Al₂O₃ and Rh-BaO/Al₂O₃ model NO_x Storage-Reduction (NSR) catalysts are discussed. The reactivity of both gas-phase NO and stored nitrates was investigated by [...] Read more.

In this paper, mechanistic aspects involved in the formation of N₂O over Pt-BaO/Al₂O₃ and Rh-BaO/Al₂O₃ model NO_x Storage-Reduction (NSR) catalysts are discussed. The reactivity of both gas-phase NO and stored nitrates was investigated by using H₂ and NH₃ as reductants. It was found that N₂O formation involves the presence of gas-phase NO, since no N₂O is observed upon the reduction of nitrates stored over both Pt- and Rh-BaO/Al₂O₃ catalyst samples. In particular, N₂O formation involves the coupling of undissociated NO molecules with N-adspecies formed upon NO dissociation onto reduced Platinum-Group-Metal (PGM) sites. Accordingly, N₂O formation is observed at low temperatures, when PGM sites start to be reduced, and disappears at high temperatures where PGM sites are fully reduced and complete NO dissociation takes place. Besides, N₂O formation is observed at lower temperatures with H₂ than with NH₃ in view of the higher reactivity of hydrogen in the reduction of the PGM sites and onto Pt-containing catalyst due to the higher reducibility of Pt vs. Rh. Full article

(This article belongs to the Special Issue Surface Chemistry and Catalysis)

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1983 KiB

Open AccessArticle

Characterization of a Metagenome-Derived β-Glucosidase and Its Application in Conversion of Polydatin to Resveratrol

by Zhimao Mai, Hongfei Su and Si Zhang

Catalysts 2016, 6(3), 35; https://doi.org/10.3390/catal6030035 - 1 Mar 2016

Cited by 21 | Viewed by 5413

Abstract

For the beneficial pharmacological properties of resveratrol, there is increasingly interest in enzymatic conversion of polydatin to resveratrol. The metagenomic technique provides an effective strategy for mining novel polydatin-hydrolysis enzymes from uncultured microorganisms. In this study, a metagenomic library of mangrove soil was [...] Read more.

For the beneficial pharmacological properties of resveratrol, there is increasingly interest in enzymatic conversion of polydatin to resveratrol. The metagenomic technique provides an effective strategy for mining novel polydatin-hydrolysis enzymes from uncultured microorganisms. In this study, a metagenomic library of mangrove soil was constructed and a novel β-glucosidase gene MlBgl was isolated. The deduced amino acid sequences of MlBgl showed the highest identity of 64% with predicted β-glucosidase in the GenBank database. The gene was cloned and overexpressed in Escherichia coli BL21(DE3). Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) assay demonstrated the purified recombinant β-glucosidase r-MlBgl with a molecular weight approximately of 71 kDa. The optimal pH and temperature of purified recombinant r-MlBgl were 7.0 and 40 °C, respectively. r-MlBgl could hydrolyze polydatin effectively. The k_cat and k_cat/K_m values for polydatin were 989 s⁻¹ and 1476 mM⁻¹·s⁻¹, respectively. These properties suggest that -r-MlBgl has potential application in the enzymatic conversion of polydatin to resveratrol for further study. Full article

(This article belongs to the Special Issue Enzyme Catalysis)

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4945 KiB

Open AccessArticle

Charge Transfer Mechanism in Titanium-Doped Microporous Silica for Photocatalytic Water-Splitting Applications

by Wendi Sapp, Ranjit Koodali and Dmitri Kilin

Catalysts 2016, 6(3), 34; https://doi.org/10.3390/catal6030034 - 29 Feb 2016

Cited by 9 | Viewed by 5623

Abstract

Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, [...] Read more.

Solar energy conversion into chemical form is possible using artificial means. One example of a highly-efficient fuel is solar energy used to split water into oxygen and hydrogen. Efficient photocatalytic water-splitting remains an open challenge for researchers across the globe. Despite significant progress, several aspects of the reaction, including the charge transfer mechanism, are not fully clear. Density functional theory combined with density matrix equations of motion were used to identify and characterize the charge transfer mechanism involved in the dissociation of water. A simulated porous silica substrate, using periodic boundary conditions, with Ti⁴⁺ ions embedded on the inner pore wall was found to contain electron and hole trap states that could facilitate a chemical reaction. A trap state was located within the silica substrate that lengthened relaxation time, which may favor a chemical reaction. A chemical reaction would have to occur within the window of photoexcitation; therefore, the existence of a trapping state may encourage a chemical reaction. This provides evidence that the silica substrate plays an integral part in the electron/hole dynamics of the system, leading to the conclusion that both components (photoactive materials and support) of heterogeneous catalytic systems are important in optimization of catalytic efficiency. Full article

(This article belongs to the Special Issue Surface Chemistry and Catalysis)

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3047 KiB

Open AccessArticle

Methanol Reforming over Cobalt Catalysts Prepared from Fumarate Precursors: TPD Investigation

by Eftichia Papadopoulou and Theophilos Ioannides

Catalysts 2016, 6(3), 33; https://doi.org/10.3390/catal6030033 - 24 Feb 2016

Cited by 5 | Viewed by 7085

Abstract

Temperature-programmed desorption (TPD) was employed to investigate adsorption characteristics of CH₃OH, H₂O, H₂, CO₂ and CO on cobalt-manganese oxide catalysts prepared through mixed Co-Mn fumarate precursors either by pyrolysis or oxidation and oxidation/reduction pretreatment. Pyrolysis temperature [...] Read more.

Temperature-programmed desorption (TPD) was employed to investigate adsorption characteristics of CH₃OH, H₂O, H₂, CO₂ and CO on cobalt-manganese oxide catalysts prepared through mixed Co-Mn fumarate precursors either by pyrolysis or oxidation and oxidation/reduction pretreatment. Pyrolysis temperature and Co/Mn ratio were the variable synthesis parameters. Adsorption of methanol, water and CO₂ was carried out at room temperature. Adsorption of H₂ and H₂O was carried out at 25 and 300 °C. Adsorption of CO was carried out at 25 and 150 °C. The goal of the work was to gain insight on the observed differences in the performance of the aforementioned catalysts in methanol steam reforming. TPD results indicated that activity differences are mostly related to variation in the number density of active sites, which are able to adsorb and decompose methanol. Full article

(This article belongs to the Special Issue Surface Chemistry and Catalysis)

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1554 KiB

Open AccessArticle

Production of Resveratrol by Piceid Deglycosylation Using Cellulase

by Chia-Hung Kuo, Bao-Yuan Chen, Yung-Chuan Liu, Jiann-Hwa Chen and Chwen-Jen Shieh

Catalysts 2016, 6(3), 32; https://doi.org/10.3390/catal6030032 - 24 Feb 2016

Cited by 19 | Viewed by 6079

Abstract

Resveratrol is a dietary polyphenolic compound widely used in medicine, food, and cosmetic products. The glycoside form of resveratrol, piceid, is also present in several plant materials but is less bioavailable. In this study, enzymatic transformation of piceid into resveratrol using inexpensive cellulase [...] Read more.

Resveratrol is a dietary polyphenolic compound widely used in medicine, food, and cosmetic products. The glycoside form of resveratrol, piceid, is also present in several plant materials but is less bioavailable. In this study, enzymatic transformation of piceid into resveratrol using inexpensive cellulase was investigated. Response surface methodology was used to evaluate the effect of reaction parameters, including reaction temperature, reaction time, enzyme amount and pH. The optimal conditions for biotransformation of piceid to resveratrol are: a reaction temperature of 50 °C, reaction time of 4.75 h, enzyme amount of 2.5 fungal β-glucanase (FBG) units and pH of 4.3. In addition, the extracts from Polygonum cuspidatum root contained high amounts of piceid were treated with cellulase in order to deglycosylation that increased resveratrol yield. After treatment, the resveratrol yield significantly increased from 2.72 to 9.49 mg/g, while the piceid contents decreased from 8.60 to 0 mg/g. The result provides an efficient method to convert piceid in the extracts of P. cuspidatum root into resveratrol by cellulase. Full article

(This article belongs to the Special Issue Enzyme Catalysis)

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