Catalysts

14 pages, 1835 KiB

Open AccessArticle

The PT/S-Box of Modular Cellulase AcCel12B Plays a Key Role in the Hydrolysis of Insoluble Cellulose

by Yuwei Li, Junling Wang, Limei Wang, Hao Tong, Mingwei Bu, Gui Gao, Weiwei Han and Zuoming Zhang

Catalysts 2018, 8(3), 123; https://doi.org/10.3390/catal8030123 - 20 Mar 2018

Cited by 1 | Viewed by 3461

Abstract

Cellulases play key roles in the degradation of lignocellulosic materials. The function and mechanism of the catalytic domain (CD) and carbohydrate-binding module (CBM) of cellulases were earlier revealed by analysis and characterization of protein structure. However, understanding of the catalytic mechanism of the [...] Read more.

Cellulases play key roles in the degradation of lignocellulosic materials. The function and mechanism of the catalytic domain (CD) and carbohydrate-binding module (CBM) of cellulases were earlier revealed by analysis and characterization of protein structure. However, understanding of the catalytic mechanism of the entire enzyme, and the analysis of the catalytic model, were inadequate. Therefore, the linker chain between CD and CBM has been extensively studied to bridge this gap. Cellulase AcCel12B and three mutants with different linker lengths (with no or 1–3 PT/S-box units) were successfully constructed and purified. Results showed that the activity of cellulases on Avicel and regenerated amorphous cellulose (RAC) increased with the number of PT/S-box units. Furthermore, the desorption of AcCel12B and its mutants from RAC and Avicel were significantly different. The energy of desorption of wild-type and mutant AcCel12B from cellulose decreased with the number of PT/S-box units. Thus, AcCel12B containing more PT/S-box units was more easily desorbed and had more opportunity to hydrolyze cellulose than other samples. The number of PT/S-box units in endocellulase affected the desorption of the enzyme, which is possibly responsible for the differences in the activity of wild-type and mutant AcCel12B on Avicel and RAC. Full article

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22 pages, 3749 KiB

Open AccessEditor’s ChoiceReview

Platinum Group Metal Phosphides as Efficient Catalysts in Hydroprocessing and Syngas-Related Catalysis

by Luis Alvarado Rupflin, Chiara Boscagli and Stephan Andreas Schunk

Catalysts 2018, 8(3), 122; https://doi.org/10.3390/catal8030122 - 20 Mar 2018

Cited by 15 | Viewed by 6293

Abstract

Platinum group metal phosphides are reviewed as catalytic materials for hydroprocessing and syngas-related catalysis. Starting from synthetic procedures leading to highly disperse nano-particular compounds, their properties in the applications are discussed and compared with relevant benchmarks, if available. Regarding their mode of action, [...] Read more.

Platinum group metal phosphides are reviewed as catalytic materials for hydroprocessing and syngas-related catalysis. Starting from synthetic procedures leading to highly disperse nano-particular compounds, their properties in the applications are discussed and compared with relevant benchmarks, if available. Regarding their mode of action, two confronting mechanistic scenarios are presented: (i) a cooperative scenario in which catalytic sites of different functionalities are active in hydroprocessing and (ii) single site catalysis, which appears to be the relevant mode of action in syngas-related catalysis and which occurs over “frustrated” active sites. Full article

(This article belongs to the Special Issue Recent Progress in Transition Metal Phosphide Catalysts for the Hydroprocessing of Petroleum or Biomass Feedstocks)

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13 pages, 2366 KiB

Open AccessArticle

Single-Atom Mn Active Site in a Triol-Stabilized β-Anderson Manganohexamolybdate for Enhanced Catalytic Activity towards Adipic Acid Production

by Jianhui Luo, Yichao Huang, Bin Ding, Pingmei Wang, Xiangfei Geng, Jiangwei Zhang and Yongge Wei

Catalysts 2018, 8(3), 121; https://doi.org/10.3390/catal8030121 - 19 Mar 2018

Cited by 27 | Viewed by 6224

Abstract

Adipic acid is an important raw chemical for the commercial production of polyamides and polyesters. The traditional industrial adipic acid production utilizes nitric acid to oxidize KA oil (mixtures of cyclohexanone and cyclohexanol), leading to the emission of N₂O and thus [...] Read more.

Adipic acid is an important raw chemical for the commercial production of polyamides and polyesters. The traditional industrial adipic acid production utilizes nitric acid to oxidize KA oil (mixtures of cyclohexanone and cyclohexanol), leading to the emission of N₂O and thus causing ozone depletion, global warming, and acid rain. Herein, we reported an organically functionalized β-isomer of Anderson polyoxometalates (POMs) nanocluster with single-atom Mn, β-{[H₃NC(CH₂O)₃]₂MnMo₆O₁₈}⁻ (1), as a highly active catalyst to selectively catalyze the oxidation of cyclohexanone, cyclohexanol, or KA oil with atom economy use of 30% H₂O₂ for the eco-friendly synthesis of adipic acid. The catalyst has been characterized by single crystal and powder XRD, XPS, ESI-MS, FT-IR, and NMR. A cyclohexanone (cyclohexanol) conversion of >99.9% with an adipic acid selectivity of ~97.1% (~85.3%) could be achieved over catalyst 1 with high turnover frequency of 2427.5 h⁻¹ (2132.5 h⁻¹). It has been demonstrated that the existence of Mn³⁺ atom active site in catalyst 1 and the special butterfly-shaped topology of POMs both play vital roles in the enhancement of catalytic activity. Full article

(This article belongs to the Special Issue Active Sites in Catalytic Reaction)

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28 pages, 8552 KiB

Open AccessReview

Recent Progress in Asymmetric Catalysis and Chromatographic Separation by Chiral Metal–Organic Frameworks

by Suchandra Bhattacharjee, Muhammad Imran Khan, Xiaofang Li, Qi-Long Zhu and Xin-Tao Wu

Catalysts 2018, 8(3), 120; https://doi.org/10.3390/catal8030120 - 19 Mar 2018

Cited by 76 | Viewed by 11165

Abstract

Metal–organic frameworks (MOFs), as a new class of porous solid materials, have emerged and their study has established itself very quickly into a productive research field. This short review recaps the recent advancement of chiral MOFs. Here, we present simple, well-ordered instances to [...] Read more.

Metal–organic frameworks (MOFs), as a new class of porous solid materials, have emerged and their study has established itself very quickly into a productive research field. This short review recaps the recent advancement of chiral MOFs. Here, we present simple, well-ordered instances to classify the mode of synthesis of chiral MOFs, and later demonstrate the potential applications of chiral MOFs in heterogeneous asymmetric catalysis and enantioselective separation. The asymmetric catalysis sections are subdivided based on the types of reactions that have been successfully carried out recently by chiral MOFs. In the part on enantioselective separation, we present the potentiality of chiral MOFs as a stationary phase for high-performance liquid chromatography (HPLC) and high-resolution gas chromatography (GC) by considering fruitful examples from current research work. We anticipate that this review will provide interest to researchers to design new homochiral MOFs with even greater complexity and effort to execute their potential functions in several fields, such as asymmetric catalysis, enantiomer separation, and chiral recognition. Full article

(This article belongs to the Special Issue Catalysis by Metal-Organic Frameworks)

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18 pages, 1784 KiB

Open AccessArticle

Catalytic Conversion of Model Tars over Carbon-Supported Ni and Fe

by Luis E. Arteaga-Pérez, Aaron M. Delgado, Mauricio Flores, Patricia Olivera, Kimberley Matschuk, Christian Hamel, Tim Schulzke and Romel Jiménez

Catalysts 2018, 8(3), 119; https://doi.org/10.3390/catal8030119 - 17 Mar 2018

Cited by 13 | Viewed by 5387

Abstract

Tar removal from gasification gases is a determinant step to guarantee the operational feasibility of gasification-to-chemicals/energy systems. This study aimed to develop novel carbon-supported catalysts for the elimination of tarry aromatics (toluene, naphthalene and benzene) from gasification gases. Effects of reaction temperature (700 [...] Read more.

Tar removal from gasification gases is a determinant step to guarantee the operational feasibility of gasification-to-chemicals/energy systems. This study aimed to develop novel carbon-supported catalysts for the elimination of tarry aromatics (toluene, naphthalene and benzene) from gasification gases. Effects of reaction temperature (700 < T < 900 °C) and catalyst nature (Fe⁰ and Ni⁰) on the activity were assessed by considering thermo-catalytic conversion and steam reforming, under a simulated gasification gas. The catalysts (Ni and Fe) and support (AC) were characterized by X-ray diffraction (XRD), N₂ physisorption, thermogravimetric analysis (TGA), transmission electron microscopy (TEM) and compositional analyses. Both catalysts and support, presented a mesoporous-like texture with a considerable high surface area (690 < S_BET < 743 m²/g). Furthermore, dispersion of the metal nanoparticles (active phase) was uniform as confirmed by TEM images. Results from activity tests suggest that Ni/AC has higher effectivity for converting tars than Fe/AC, as confirmed by the low apparent activation energies (34 < E_app < 98 kJ/mol) for naphthalene and benzene conversion between 700 and 900 °C. The conversion was 100% above 850 °C; nevertheless; below 750 °C, a sharp reduction in benzene conversion was observed, which was attributed to reversible carbon deposition. Full article

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14 pages, 4511 KiB

Open AccessArticle

Photocatalytic Performance and Degradation Mechanism of Aspirin by TiO₂ through Response Surface Methodology

by Lezhuo Li, Qiuling Ma, Sanfan Wang, Sanxiang Song, Bo Li, Ruonan Guo, Xiuwen Cheng and Qingfeng Cheng

Catalysts 2018, 8(3), 118; https://doi.org/10.3390/catal8030118 - 16 Mar 2018

Cited by 21 | Viewed by 5452

Abstract

In the present work, the photocatalytic performance of P25TiO₂ was investigated by means of the degradation of aspirin, while the reaction system was systematically optimized by central composite design (CCD) based on the response surface methodology (RSM). In addition, three variables of [...] Read more.

In the present work, the photocatalytic performance of P25TiO₂ was investigated by means of the degradation of aspirin, while the reaction system was systematically optimized by central composite design (CCD) based on the response surface methodology (RSM). In addition, three variables of initial pH value, initial aspirin concentration and P25 concentration were selected to assess the dependence of degradation efficiencies of aspirin. Meanwhile, a predicted model of degradation efficiency was estimated and checked using analysis of variance (ANOVA). The results indicated that the PC removal of aspirin by P25 was significantly influenced by all these variables in descending order as follows: P25 concentration > initial aspirin concentration > initial pH value. Moreover, the parameters were optimized by the CCD method. Under the conditions of an initial pH value of 5, initial aspirin concentration of 10 mg/L and P25 concentration of 50 mg/L, the degradation efficiency of aspirin was 98.9%with 60 min of Xenon lamp irradiation. Besides, based on the liquid chromatography-mass spectrometry measurements, two main PC degradation pathways of aspirin by TiO₂ were deduced and the tentative degradation mechanism was also proposed. Full article

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9 pages, 1701 KiB

Open AccessCommunication

Functional Analysis of Methylomonas sp. DH-1 Genome as a Promising Biocatalyst for Bioconversion of Methane to Valuable Chemicals

by Anh Duc Nguyen, In Yeub Hwang, Ok Kyung Lee, Dong Hoon Hur, Young Chan Jeon, Susila Hadiyati, Min-Sik Kim, Sung Ho Yoon, Haeyoung Jeong and Eun Yeol Lee

Catalysts 2018, 8(3), 117; https://doi.org/10.3390/catal8030117 - 16 Mar 2018

Cited by 19 | Viewed by 7212

Abstract

Methylomonas sp. DH-1, newly isolated from the activated sludge of a brewery plant, has been used as a promising biocatalytic platform for the conversion of methane to value-added chemicals. Methylomonas sp. DH-1 can efficiently convert methane and propane into methanol and acetone with [...] Read more.

Methylomonas sp. DH-1, newly isolated from the activated sludge of a brewery plant, has been used as a promising biocatalytic platform for the conversion of methane to value-added chemicals. Methylomonas sp. DH-1 can efficiently convert methane and propane into methanol and acetone with a specific productivity of 4.31 and 0.14 mmol/g cell/h, the highest values ever reported, respectively. Here, we present the complete genome sequence of Methylomonas sp. DH-1 which consists of a 4.86 Mb chromosome and a 278 kb plasmid. The existence of a set of genes related to one-carbon metabolism and various secondary metabolite biosynthetic pathways including carotenoid pathways were identified. Interestingly, Methylomonas sp. DH-1 possesses not only the genes of the ribulose monophosphate cycle for type I methanotrophs but also the genes of the serine cycle for type II. Methylomonas sp. DH-1 accumulated 80 mM succinate from methane under aerobic conditions, because DH-1 has 2-oxoglutarate dehydrogenase activity and the ability to operate the full TCA cycle. Availability of the complete genome sequence of Methylomonas sp. DH-1 enables further investigations on the metabolic engineering of this strain for the production of value-added chemicals from methane. Full article

(This article belongs to the Special Issue Biocatalysis and Biotransformations)

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14 pages, 9356 KiB

Open AccessArticle

Catalytic Oxidation of Chlorobenzene over Ruthenium-Ceria Bimetallic Catalysts

by Meng Ye, Li Chen, Xiaolong Liu, Wenqing Xu, Tingyu Zhu and Guanyi Chen

Catalysts 2018, 8(3), 116; https://doi.org/10.3390/catal8030116 - 16 Mar 2018

Cited by 17 | Viewed by 5742

Abstract

A series of Ru-based mono and bimetallic materials were prepared and evaluated in the catalytic oxidation of chlorobenzene. Among the different Ru-based catalysts, 1Ru/TiO₂(P25) was the most active catalyst and contributed the lowest complete oxidation temperature, suggesting that commercial P25 TiO [...] Read more.

A series of Ru-based mono and bimetallic materials were prepared and evaluated in the catalytic oxidation of chlorobenzene. Among the different Ru-based catalysts, 1Ru/TiO₂(P25) was the most active catalyst and contributed the lowest complete oxidation temperature, suggesting that commercial P25 TiO₂ was the best support for Ru catalysts. After ceria oxides were introduced into the Ru catalytic system, the catalytic activity of 1Ru-5Ce/TiO₂(Rutile) dramatically improved and that of P25 supported catalysts was decreased. Comparing the chlorobenzene consumption rates for 1Ru/TiO₂ and 1Ru-5Ce/TiO₂ at 280 °C, it could be concluded that monometallic Ru catalytic system was appropriate for P25 support, and the Ru-Ce bimetallic catalytic system was suitable for the rutile TiO₂ support. At 280 °C, for 1Ru-5Ce/TiO₂(Rutile) and 1Ru-5Ce/TiO₂(P25), the chlorobenzene conversion was stabilized at approximately 91% and 86%, respectively. According to the physicochemical properties of the catalysts as characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), and Hydrogen temperature programmed reduction (H₂-TPR), it can be concluded that (a) electrophilic O_ads species play an important role in VOCs oxidation; (b) abundant RuO₂ nanoparticles on the surface of 1Ru-5Ce/TiO₂(Rutile) result in higher catalytic activity and stability; and (c) dispersion is not the major factor for the catalytic activity, rather the unique structure greatly facilitated the catalytic activity and stability. Full article

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9 pages, 1191 KiB

Open AccessFeature PaperArticle

Solvent-Free Mizoroki-Heck Reaction Applied to the Synthesis of Abscisic Acid and Some Derivatives

by Geoffrey Dumonteil, Marie-Aude Hiebel and Sabine Berteina-Raboin

Catalysts 2018, 8(3), 115; https://doi.org/10.3390/catal8030115 - 15 Mar 2018

Cited by 9 | Viewed by 5075

Abstract

Abscisic acid (ABA) is a natural product, which is a well-known phytohormone. However, this molecule has recently exhibited interesting biological activities, emphasizing the need for a simple and direct access to new analogues based on the ABA framework. Our strategy relies on a [...] Read more.

Abscisic acid (ABA) is a natural product, which is a well-known phytohormone. However, this molecule has recently exhibited interesting biological activities, emphasizing the need for a simple and direct access to new analogues based on the ABA framework. Our strategy relies on a pallado-catalyzed Mizoroki-Heck cross-coupling as key reaction performed in solvent and ligand free conditions. After a careful optimization, we succeeded in accessing various (E/Z)-dienes and (E/E/Z)-trienes in moderate to good yields without isomerization and applied the same approach to the synthesis of ABA in an environmentally sound manner. Full article

(This article belongs to the Special Issue Catalyzed Mizoroki–Heck Reaction or C–H activation)

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16 pages, 3938 KiB

Open AccessArticle

Highly Active and Selective Supported Rhenium Catalysts for Aerobic Oxidation of n-Hexane and n-Heptane

by Gopal S. Mishra, Elisabete C. B. A. Alegria, Armando J. L. Pombeiro and Luísa M. D. R. S. Martins

Catalysts 2018, 8(3), 114; https://doi.org/10.3390/catal8030114 - 15 Mar 2018

Cited by 7 | Viewed by 5428

Abstract

A series of derivative C-scorpionate rhenium complexes, i.e., [ReCl₂{NNC(O)C₆H₅}(Hpz)(PPh₃)₂] (A) (where Hpz is pyrazole), [ReCl₂{NNC(O)C₆H₅}(Hpz)₂(PPh₃)] (B), [ReClF{NNC(O)C₆H [...] Read more.

A series of derivative C-scorpionate rhenium complexes, i.e., [ReCl₂{NNC(O)C₆H₅}(Hpz)(PPh₃)₂] (A) (where Hpz is pyrazole), [ReCl₂{NNC(O)C₆H₅}(Hpz)₂(PPh₃)] (B), [ReClF{NNC(O)C₆H₅}(Hpz)₂(PPh₃)] (C), and their precursor [ReOCl₃(PPh₃)₂] (D), immobilized on 3-aminopropyl-functionalized silica have been prepared and used for neat O₂ oxidation of n-hexane and n-heptane mainly to the corresponding alcohols and, in lower amounts, ketones. The supported catalyst C, with fluoro- and diazenido-ligands, exhibits the highest activity for both alkanes (overall turnover numbers (TONs) up to 3.8 × 10³ and 2.5 × 10³, for n-hexane and n-heptane, respectively) and can be reused in consecutive catalytic cycles. Improved conversion was observed after addition of hetero-carboxylate co-catalysts. A free-radical-based mechanism is proposed to explain the product formation. Full article

(This article belongs to the Special Issue New Trends in Scorpionate Catalysts)

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16 pages, 4183 KiB

Open AccessReview

Waste into Fuel—Catalyst and Process Development for MSW Valorisation

by Izabela S. Pieta, William S. Epling, Alicja Kazmierczuk, Pawel Lisowski, Robert Nowakowski and Ewa M. Serwicka

Catalysts 2018, 8(3), 113; https://doi.org/10.3390/catal8030113 - 14 Mar 2018

Cited by 34 | Viewed by 10188

Abstract

The present review paper highlights recent progress in the processing of potential municipal solid waste (MSW) derived fuels. These wastes come from the sieved fraction (∅ < 40 mm), which, after sorting, can differ in biodegradable fraction content ranging from 5–60%. The [...] Read more.

The present review paper highlights recent progress in the processing of potential municipal solid waste (MSW) derived fuels. These wastes come from the sieved fraction (∅ < 40 mm), which, after sorting, can differ in biodegradable fraction content ranging from 5–60%. The fuels obtained from these wastes possess volumetric energy densities in the range of 15.6–26.8 MJL⁻¹ and are composed mainly of methanol, ethanol, butanol, and carboxylic acids. Although these waste streams are a cheap and abundant source (and decrease the fraction going to landfills), syngas produced from MSW contains various impurities such as organic compounds, nitrogen oxides, sulfur, and chlorine components. These limit its use for advanced electricity generation especially for heat and power generation units based on high temperature fuel cells such as solid oxide fuel cells (SOFC) or molten carbonate fuel cells (MCFC). In this paper, we review recent research developments in the continuous MSW processing for syngas production specifically concentrating on dry reforming and the catalytic sorbent effects on effluent and process efficiency. A particular emphasis is placed on waste derived biofuels, which are currently a primary candidate for a sustainable biofuel of tomorrow, catalysts/catalytic sorbents with decreased amounts of noble metals, their long term activity, and poison resistance, and novel nano-sorbent materials. In this review, future prospects for waste to fuels or chemicals and the needed research to further process technologies are discussed. Full article

(This article belongs to the Special Issue Novel Enzyme and Whole-Cell Biocatalysis)

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16 pages, 9094 KiB

Open AccessArticle

Fabrication of a Z-Scheme g-C₃N₄/Fe-TiO₂ Photocatalytic Composite with Enhanced Photocatalytic Activity under Visible Light Irradiation

by Zedong Zhu, Muthu Murugananthan, Jie Gu and Yanrong Zhang

Catalysts 2018, 8(3), 112; https://doi.org/10.3390/catal8030112 - 13 Mar 2018

Cited by 44 | Viewed by 6006

Abstract

In the present study, a nanocomposite material g-C₃N₄/Fe-TiO₂ has been prepared successfully by a simple one-step hydrothermal process and its structural properties were thoroughly studied by various characterization techniques, such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) [...] Read more.

In the present study, a nanocomposite material g-C₃N₄/Fe-TiO₂ has been prepared successfully by a simple one-step hydrothermal process and its structural properties were thoroughly studied by various characterization techniques, such as X-ray diffraction (XRD), Fourier Transform Infrared (FTIR) spectroscopy, electron paramagnetic resonance (EPR) spectrum, X-ray photoelectron spectroscopy (XPS), and UV-vis diffuse reflectance spectrometry (UV-vis DRS). The performance of the fabricated composite material towards the removal of phenol from aqueous phase was systematically evaluated by a photocatalytic approach and found to be highly dependent on the content of Fe³⁺. The optimum concentration of Fe³⁺ doping that showed a dramatic enhancement in the photocatalytic activity of the composite under visible light irradiation was observed to be 0.05% by weight. The separation mechanism of photogenerated electrons and holes of the g-C₃N₄/Fe-TiO₂ photocatalysts was established by a photoluminescence technique in which the reactive species generated during the photocatalytic treatment process was quantified. The enhanced photocatalytic performance observed for g-C₃N₄-Fe/TiO₂ was ascribed to a cumulative impact of both g-C₃N₄ and Fe that extended its spectrum-absorptive nature into the visible region. The heterojunction formation in the fabricated photocatalysts not only facilitated the separation of the photogenerated charge carriers but also retained its strong oxidation and reduction ability. Full article

(This article belongs to the Special Issue Photocatalysts for Organics Degradation)

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22 pages, 4592 KiB

Open AccessArticle

A Comparative Study of Mn/Co Binary Metal Catalysts Supported on Two Commercial Diatomaceous Earths for Oxidation of Benzene

by Marco Tomatis, Honghui Xu, Chaohui Wei, Matthew Thomas Bishop, Jun He, Chengjun Wang, Ming Zhao, Hang Xiao, Huan Yu, Sailesh N. Behera and Bencan Tang

Catalysts 2018, 8(3), 111; https://doi.org/10.3390/catal8030111 - 12 Mar 2018

Cited by 9 | Viewed by 5828

Abstract

Two commercial diatomaceous earths were used as supports for the preparation of Mn/Co binary metal catalysts at different metal loads (5 to 10 wt % Mn and 5 to 15 wt % Co) by incipient wetness deposition. The activity of the prepared catalysts [...] Read more.

Two commercial diatomaceous earths were used as supports for the preparation of Mn/Co binary metal catalysts at different metal loads (5 to 10 wt % Mn and 5 to 15 wt % Co) by incipient wetness deposition. The activity of the prepared catalysts towards the complete oxidation of benzene to CO₂ and water was investigated between 100 and 400 °C. Raw supports and synthesized catalysts were characterized by XRD, N₂ physisorption, SEM-EDS, H₂-TPR, and TPD. The purification treatment of food-grade diatomite significantly affected the crystallinity of this support while reducing its specific surface area (SSA). A loss of SSA, associated with the increase in the metal load, was observed on samples prepared on natural diatomite, while the opposite trend occurred with food-grade diatomite-supported catalysts. Metal nanoparticles of around 50 nm diameter were observed on the catalysts’ surface by SEM analysis. EDS analysis confirmed the uniform deposition of the active phases on the support’s surface. A larger H₂ consumption was found by TPR analysis of natural diatomite-based samples in comparison to those prepared at the same metal load on food-grade diatomite. During the catalytic oxidation experiment, over 90% conversion of benzene were achieved at a reaction temperature of 225 °C by all of the prepared samples. In addition, the formation of coke during the oxidation tests was demonstrated by TGA analysis and the soluble fraction of the produced coke was characterized by GC-MS. Full article

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18 pages, 3442 KiB

Open AccessReview

Recent Scientific Progress on Developing Supported Ni Catalysts for Dry (CO₂) Reforming of Methane

by Hyun Ook Seo

Catalysts 2018, 8(3), 110; https://doi.org/10.3390/catal8030110 - 11 Mar 2018

Cited by 95 | Viewed by 9632

Abstract

Two major green house gases (CO₂ and CH₄) can be converted into useful synthetic gas (H₂ and CO) during dry reforming of methane (DRM) reaction, and a lot of scientific efforts has been made to develop efficient catalysts for [...] Read more.

Two major green house gases (CO₂ and CH₄) can be converted into useful synthetic gas (H₂ and CO) during dry reforming of methane (DRM) reaction, and a lot of scientific efforts has been made to develop efficient catalysts for dry reforming of methane (DRM). Noble metal-based catalysts can effectively assist DRM reaction, however they are not economically viable. Alternatively, non-noble based catalysts have been studied so far, and supported Ni catalysts have been considered as a promising candidate for DRM catalyst. Main drawback of Ni catalysts is its catalytic instability under operating conditions of DRM (>700 °C). Recently, it has been demonstrated that the appropriate choice of metal-oxide supports can address this issue since the chemical and physical of metal-oxide supports can prevent coke formation and stabilize the small Ni nanoparticles under harsh conditions of DRM operation. This mini-review covers the recent scientific findings on the development of supported Ni catalysts for DRM reaction, including the synthetic methods of supported Ni nanoparticles with high sintering resistance. Full article

(This article belongs to the Special Issue Conversion of CO₂ into CO Using Heterogeneous Catalysis)

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14 pages, 2207 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Use of Lactobacillus rhamnosus (ATCC 53103) as Whole-Cell Biocatalyst for the Regio- and Stereoselective Hydration of Oleic, Linoleic, and Linolenic Acid

by Stefano Serra and Davide De Simeis

Catalysts 2018, 8(3), 109; https://doi.org/10.3390/catal8030109 - 9 Mar 2018

Cited by 19 | Viewed by 7364

Abstract

Natural hydroxy fatty acids are relevant starting materials for the production of a number of industrial fine chemicals, such as different high-value flavour ingredients. Only a few of the latter hydroxy acid derivatives are available on a large scale. Therefore, their preparation by [...] Read more.

Natural hydroxy fatty acids are relevant starting materials for the production of a number of industrial fine chemicals, such as different high-value flavour ingredients. Only a few of the latter hydroxy acid derivatives are available on a large scale. Therefore, their preparation by microbial hydration of unsaturated fatty acids, affordable from vegetable oils, is a new biotechnological challenge. In this study, we describe the use of the probiotic bacterium Lactobacillus rhamnosus (ATCC 53103) as whole-cell biocatalyst for the hydration of the most common unsaturated octadecanoic acids, namely oleic acid, linoleic acid, and linolenic acid. We discovered that the addition of the latter fatty acids to an anaerobic colture of the latter strain, during the early stage of its exponential growth, allows the production of the corresponding mono-hydroxy derivatives. In these experimental conditions, the hydration reaction proceeds with high regio- and stereoselectivity. Only 10-hydroxy derivatives were formed and the resulting (R)-10-hydroxystearic acid, (S)-(12Z)-10-hydroxy-octadecenoic acid, and (S)-(12Z,15Z)-10-hydroxy-octadecadienoic acid were obtained in very high enantiomeric purity (ee > 95%). Although overall conversions usually do not exceed 50% yield, our biotransformation protocol is stereoselective, scalable, and holds preparative significance. Full article

(This article belongs to the Special Issue Enzyme-Mediated Stereoselective Synthesis)

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10 pages, 1976 KiB

Open AccessArticle

High Performance of Manganese Porphyrin Sensitized p-Type CuFe₂O₄ Photocathode for Solar Water Splitting to Produce Hydrogen in a Tandem Photoelectrochemical Cell

by Xia Li, Aijuan Liu, Dongmei Chu, Chunyong Zhang, Yukou Du, Jie Huang and Ping Yang

Catalysts 2018, 8(3), 108; https://doi.org/10.3390/catal8030108 - 9 Mar 2018

Cited by 40 | Viewed by 6381

Abstract

A novel composite composed of (5, 10, 15, 20-tetraphenyl) porphinato manganese sensitized p-type CuFe₂O₄ was developed for constructing the photocathode of a tandem photoelectrochemical (PEC) cell. The prepared material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray [...] Read more.

A novel composite composed of (5, 10, 15, 20-tetraphenyl) porphinato manganese sensitized p-type CuFe₂O₄ was developed for constructing the photocathode of a tandem photoelectrochemical (PEC) cell. The prepared material was characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflectance spectroscopy (DRS). Light-driven water splitting to produce hydrogen can be achieved through the PEC cell, and the results show that H₂ and O₂ can be collected separately at low applied bias. This work demonstrates that manganese porphyrin sensitized CuFe₂O₄ is an effective hybrid material for building the photocathode of a PEC cell for solar water splitting to produce H₂. Full article

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

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18 pages, 9762 KiB

Open AccessArticle

Synthesis of Rectorite/Fe₃O₄/ZnO Composites and Their Application for the Removal of Methylene Blue Dye

by Huanhuan Wang, Peijiang Zhou, Rui Guo, Yifei Wang, Hongju Zhan and Yunfei Yuan

Catalysts 2018, 8(3), 107; https://doi.org/10.3390/catal8030107 - 9 Mar 2018

Cited by 35 | Viewed by 5353

Abstract

A novel series of rectorite-based magnetic zinc oxide (ZnO) photocatalysts (REC/Fe₃O₄/ZnO) was synthesized and characterized in the present work. The fabricated REC/Fe₃O₄/ZnO composite possessed a high specific surface area and high capacity of adsorption and [...] Read more.

A novel series of rectorite-based magnetic zinc oxide (ZnO) photocatalysts (REC/Fe₃O₄/ZnO) was synthesized and characterized in the present work. The fabricated REC/Fe₃O₄/ZnO composite possessed a high specific surface area and high capacity of adsorption and photocatalysis toward methylene blue (MB) dye. The adsorption isotherm of the dye on the composite fitted well to the Langmuir model, with a maximum adsorption of 35.1 mg/g. The high adsorption capacity increased the interactions between the dye and the REC/Fe₃O₄/ZnO, which enabled efficient decomposition of the dye under simulated solar radiation using REC/Fe₃O₄/ZnO as the photocatalyst. The degradation kinetics of MB dye followed the Langmuir–Hinshelwood model. More importantly, the degradation of MB dye and the mass loss of REC/Fe₃O₄/ZnO after three repetitive experiments were quite small. This suggests that the magnetic composite has great potential as an effective, stable, and easily recovered catalyst. Four major intermediates were detected during the degradation of MB dye and the degradation pathway was proposed. Full article

(This article belongs to the Special Issue Nanomaterials for Environmental Purification and Energy Conversion)

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8 pages, 1477 KiB

Open AccessArticle

Effects of Mesopore Internal Surfaces on the Structure of Immobilized Pd-Bisphosphine Complexes Analyzed by Variable-Temperature XAFS and Their Catalytic Performances

by Ken Motokura, Takuma Fukuda, Yohei Uemura, Daiju Matsumura, Marika Ikeda, Masayuki Nambo and Wang-Jae Chun

Catalysts 2018, 8(3), 106; https://doi.org/10.3390/catal8030106 - 9 Mar 2018

Cited by 4 | Viewed by 3682

Abstract

In this study, mesoporous and nonporous silica-supported Pd complexes were synthesized and characterized. Variable-temperature XAFS measurements and a curve-fitting analysis showed a slightly larger contribution of σ²_static when the Pd complexes were on a nonporous support in comparison to a mesoporous [...] Read more.

In this study, mesoporous and nonporous silica-supported Pd complexes were synthesized and characterized. Variable-temperature XAFS measurements and a curve-fitting analysis showed a slightly larger contribution of σ²_static when the Pd complexes were on a nonporous support in comparison to a mesoporous support. In contrast, the catalytic performance of the attached Pd complex in the Suzuki-Miyaura cross-coupling reaction was not affected by such small differences in the static disorder of the Pd complex. Full article

(This article belongs to the Special Issue Porous Materials in Catalysis)

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11 pages, 1574 KiB

Open AccessArticle

Synthesis of Tetrahydropyran from Tetrahydrofurfuryl Alcohol over Cu–Zno/Al₂O₃ under a Gaseous-Phase Condition

by Fengyuan Zhang, Bin Zhang, Xincheng Wang, Long Huang, Dekun Ji, Songsong Du, Lei Ma and Shijing Lin

Catalysts 2018, 8(3), 105; https://doi.org/10.3390/catal8030105 - 6 Mar 2018

Cited by 5 | Viewed by 4705

Abstract

Tetrahydropyran (THP) represents an O-containing hetero-cyclic compound that can be used as a promising solvent or monomer for polymer synthesis. In this work, Cu–ZnO/Al₂O₃ catalysts have been prepared by a facile precipitation–extrusion method and used for the synthesis of THP [...] Read more.

Tetrahydropyran (THP) represents an O-containing hetero-cyclic compound that can be used as a promising solvent or monomer for polymer synthesis. In this work, Cu–ZnO/Al₂O₃ catalysts have been prepared by a facile precipitation–extrusion method and used for the synthesis of THP through gaseous-phase hydrogenolysis of tetrahydrofurfuryl alcohol (THFA). The effect of the molar ratio of Cu/Zn/Al, reaction temperature, and hydrogen pressure was investigated. An 89.4% selectivity of THP was achieved at 270 °C and 1.0 MPa H₂. Meanwhile, the optimum molar ratio of Cu/Zn/Al was determined to be 4:1:10. The Cu–ZnO/Al₂O₃ catalyst exhibited high catalytic activity and stability for 205 h on-stream. A possible reaction mechanism involving several consecutive reactions was proposed: THFA was firstly rearranged to 2-hydroxytetrahydropyran (2-HTHP), followed by the dehydration of 2-HTHP to 3,4-2H-dihydropyran (DHP) over acid sites; finally, the DHP was hydrogenated to THP. The synergy of acid sites and metal sites of Cu–ZnO/Al₂O₃ played an important role during the production of THP. Full article

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13 pages, 4396 KiB

Open AccessArticle

Selective Hydrogenation of Benzene to Cyclohexene over Ru-Zn Catalysts: Mechanism Investigation on NaOH as a Reaction Additive

by Haijie Sun, Zhihao Chen, Chenggang Li, Lingxia Chen, Zhikun Peng, Zhongyi Liu and Shouchang Liu

Catalysts 2018, 8(3), 104; https://doi.org/10.3390/catal8030104 - 2 Mar 2018

Cited by 6 | Viewed by 5074

Abstract

Ru-Zn catalysts were synthesized via a precipitation method, and the mechanism of NaOH modifying Ru-Zn catalysts on the selective hydrogenation of benzene to cyclohexene was thoroughly investigated. Fresh as well as used catalysts were characterized via X-ray diffraction (XRD), X-ray Fluorescence (XRF), transmission [...] Read more.

Ru-Zn catalysts were synthesized via a precipitation method, and the mechanism of NaOH modifying Ru-Zn catalysts on the selective hydrogenation of benzene to cyclohexene was thoroughly investigated. Fresh as well as used catalysts were characterized via X-ray diffraction (XRD), X-ray Fluorescence (XRF), transmission electron microscope (TEM), scanning electron microscope (SEM), Auger electron spectroscopy (AES), X-ray photoelectron spectroscopy (XPS), and density functional theory (DFT), respectively. Before catalytic experiments, metallic Ru and rodlike ZnO were detected from fresh Ru-Zn catalysts. Notably, with the increasing concentration of NaOH added into the reaction medium (e.g., from 0 to 0.6 mol·L⁻¹), the dispersion of ZnO on the Ru surface significantly improved, resulting in the enhancement Ru^δ+ species of electron deficiency. The catalytic activity towards benzene conversion was therefore retarded and the selectivity towards cyclohexene was improved. When the added NaOH concentration reached 0.6 mol·L⁻¹, the atomic ratio of Zn/Ru decreased from 0.27 (when no NaOH was added) to 0.16, benzene conversion of 45.3%, and cyclohexene selectivity of 89.3% was achieved using a batch reactor after 25 min of reaction time. However, with continually increasing the NaOH concentration, i.e., to 1.2 mol·L⁻¹, parts of ZnO could react with the over-added NaOH, leading to the unfavorable consumption of uniformly dispersed ZnO. This causes the increasing of catalytic activity towards benzene conversion, as well as the decreasing of the selectivity towards cyclohexene. Moreover, no loss of catalytic activity and selectivity towards cyclohexene formation from selective hydrogenation of benzene was observed after 10 times of catalytic experiments without any regeneration. Full article

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19 pages, 2224 KiB

Open AccessReview

Designing Multifunctionality into Single Phase and Multiphase Metal-Oxide-Selective Propylene Ammoxidation Catalysts

by James F. Brazdil

Catalysts 2018, 8(3), 103; https://doi.org/10.3390/catal8030103 - 2 Mar 2018

Cited by 14 | Viewed by 5714

Abstract

Multifunctionality is the hallmark of most modern commercial heterogeneous catalyst systems in use today, including those used for the selective ammoxidation of propylene to acrylonitrile. It is the quintessential principle underlying commercial catalyst design efforts since petrochemical process development is invariably driven by [...] Read more.

Multifunctionality is the hallmark of most modern commercial heterogeneous catalyst systems in use today, including those used for the selective ammoxidation of propylene to acrylonitrile. It is the quintessential principle underlying commercial catalyst design efforts since petrochemical process development is invariably driven by the need to reduce manufacturing costs. This is in large part achieved through new and improved catalysts that increase selectivity and productivity. In addition, the future feedstocks for chemical processes will be invariably more refractory than those currently in use (e.g., replacing alkenes with alkanes or using CO₂), thus requiring a disparate combination of chemical functions in order to effect multiple chemical transformations with the fewest separate process steps. This review summarizes the key chemical phenomena behind achieving the successful integration of multiple functions into a mixed-metal-oxide-selective ammoxidation catalyst. An experiential and functional catalyst design model is presented that consists of one or both of the following components: (1) a mixed-metal-oxide–solid solution where the individual metal components serve separate and necessary functions in the reaction mechanism through their atomic level interaction in the context of a single crystallographic structure; (2) the required elemental components and their catalytic function existing in separate phases, where these phases are able to interact for the purposes of electron and lattice oxygen transfer through the formation of a structurally coherent interface (i.e., epitaxy) between the separate crystal structures. Examples are provided from the literature and explained in the context of this catalyst design model. The extension of the model concepts to the design of heterogeneous catalysts in general is also discussed. Full article

(This article belongs to the Special Issue New Developments in Heterogeneous Partial and Total Oxidation Catalysis)

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10 pages, 1901 KiB

Open AccessFeature PaperArticle

A New Approach to Deep Desulfurization of Light Cycle Oil over Ni₂P Catalysts: Combined Selective Oxidation and Hydrotreating

by Gwang-Nam Yun, Kye-Syng Cho, Yong-Su Kim and Yong-Kul Lee

Catalysts 2018, 8(3), 102; https://doi.org/10.3390/catal8030102 - 1 Mar 2018

Cited by 11 | Viewed by 4966

Abstract

Amphiphilic phosphotungstic acid (A-PTA) and Ni₂P/SBA-15 catalysts were prepared to apply for selective oxidation of refractory sulfur compounds in light cycle oils and hydrotreating of the oxidized S compounds, respectively. Physical properties of the catalyst samples were analyzed by BET, CO [...] Read more.

Amphiphilic phosphotungstic acid (A-PTA) and Ni₂P/SBA-15 catalysts were prepared to apply for selective oxidation of refractory sulfur compounds in light cycle oils and hydrotreating of the oxidized S compounds, respectively. Physical properties of the catalyst samples were analyzed by BET, CO uptake chemisorption, and TEM. Structural properties for the supported Ni₂P catalysts were analyzed by X-ray diffraction (XRD) and extended X-ray absorption fine structure (XAFS) spectroscopy. The selective oxidation of S compounds in the LCO feed was conducted in a batch reactor at H₂O₂/S ratio of 10, atmospheric pressure and 353 K and then the products were fed to a continuous flow fixed-bed reactor for hydrotreating at 623 K, 3.0 MPa, and LHSV’s of 0.5–2.0 h⁻¹. A-PTA catalyst showed a high oxidation conversion of 95% for a real LCO feed. The following hydrotreating led to a hydrodesulfurization (HDS) conversion of 99.6% and a hydrodenitrogenation (HDN) conversion of 94.7% over Ni₂P/SBA-15, which were much higher than those of direct hydrotreating results which gave an HDS conversion of 63.5% and an HDN conversion of 17.5% based on the same LHSV of 2.0 h⁻¹. It was revealed that the reduction in refractory nitrogen compounds after oxidative treatment contributed to the increase of the following HDS activity. Full article

(This article belongs to the Special Issue Recent Progress in Transition Metal Phosphide Catalysts for the Hydroprocessing of Petroleum or Biomass Feedstocks)

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12 pages, 2662 KiB

Open AccessArticle

Methyl Chloride Synthesis over Metal Chlorides-Modified Mesoporous Alumina Catalyst

by Yuwen Ji, Feilong Zhang, Feng Yu, Jianshu Zhang and Jinli Zhang

Catalysts 2018, 8(3), 99; https://doi.org/10.3390/catal8030099 - 28 Feb 2018

Cited by 9 | Viewed by 6700

Abstract

Mesoporous alumina has been successfully prepared using sucrose as templates. Mesoporous alumina-based catalysts, neat and impregnated with metal chlorides, were tested for gas phase methyl chloride synthesis from methanol and HCl. The catalysts were characterized with Transmission electron microscope (TEM), N₂-physisorption, [...] Read more.

Mesoporous alumina has been successfully prepared using sucrose as templates. Mesoporous alumina-based catalysts, neat and impregnated with metal chlorides, were tested for gas phase methyl chloride synthesis from methanol and HCl. The catalysts were characterized with Transmission electron microscope (TEM), N₂-physisorption, X-ray diffraction (XRD), Fourier Transform infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) to identify the relationship between the catalyst characteristics and their activity and selectivity. Experimental studies revealed that the alumina acidity decreases with increasing calcination temperature, and the catalytic activity is strongly related to the acidity. The catalytic activity of mesoporous alumina (named as Al₂O₃-500 °C) is higher than that of the commercial alumina under the same experimental conditions. The metal chlorides-modified alumina has more Lewis acid sites than the neat alumina. Impregnation by alcohol is more effective for increasing the amount of Lewis acid sites than impregnation by water. The total Lewis acid concentration of the modified alumina decreases in the following order: ZnCl₂/Al₂O₃-E > ZnCl₂/Al₂O₃-W > FeCl₃/Al₂O₃-E > FeCl₃/Al₂O₃-W, Where E and W respectively indicate that the catalyst impregnation solution is ethanol and water, which agrees well with the catalytic performance order. The effect of ethanol as a solvent in the impregnation could be due to the inhibition of the hydrolysis of metal chloride. The catalyst delivered a stable performance during a 100 h test that was significantly higher than that of commercial alumina. Full article

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10 pages, 7730 KiB

Open AccessArticle

Kinetics of CO Oxidation over Unloaded and Pd-Loaded α-Fe₂O₃ Spherical Submicron Powder Catalysts: Photoacoustic Investigations at Low Pressure

by Joong-Seok Roh, Ji-Yeong Kim, Joong-Gill Choi and Sung-Han Lee

Catalysts 2018, 8(3), 98; https://doi.org/10.3390/catal8030098 - 28 Feb 2018

Cited by 1 | Viewed by 3828

Abstract

In this study, α-Fe₂O₃ spherical particles with an average diameter of approximately 200 nm were synthesized by a solvothermal method for use as both a catalyst and medium for a Pd catalyst. The kinetics of CO oxidation over powders of [...] Read more.

In this study, α-Fe₂O₃ spherical particles with an average diameter of approximately 200 nm were synthesized by a solvothermal method for use as both a catalyst and medium for a Pd catalyst. The kinetics of CO oxidation over powders of α-Fe₂O₃ spherical particles and 14 wt % Pd/α-Fe₂O₃ spherical particles were measured in a static reactor by using a CO₂ laser-based photoacoustic technique. The total pressure was fixed at 40 Torr for the CO/O₂/N₂ mixture for temperatures in the range of 225–350 °C. The variation in the CO₂ photoacoustic signal with the CO₂ concentration during CO oxidation was recorded as a function of time, and the CO₂ photoacoustic data at the early reaction stage was used to estimate the rates of CO₂ formation. Based on plots of ln(rate) vs. 1/T, apparent activation energies were calculated as 13.4 kcal/mol for the α-Fe₂O₃ submicron powder and 13.2 kcal/mol for the 14 wt % Pd/α-Fe₂O₃ submicron powder. Reaction orders with respect to CO and O₂ were determined from the rates measured at various partial pressures of CO and O₂ at 350 °C. The zero-order of the reaction with respect to Po₂ was observed for CO oxidation over α-Fe₂O₃ submicron powder, while 0.48 order to Po₂ was observed for CO oxidation over Pd/α-Fe₂O₃ submicron powder. The partial orders with respect to P_CO were determined as 0.58 and 0.54 for the α-Fe₂O₃, and the Pd/α-Fe₂O₃ submicron powders, respectively. The kinetic results obtained from both catalysts were compared with those for the α-Fe₂O₃ fine powder catalysts and were used to understand the reaction mechanism. Full article

(This article belongs to the Special Issue Conversion of CO₂ into CO Using Heterogeneous Catalysis)

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9 pages, 1367 KiB

Open AccessReview

A SET Approach to the Interplay of Catalysts and Reactants

by Ragnar Larsson

Catalysts 2018, 8(3), 97; https://doi.org/10.3390/catal8030097 - 28 Feb 2018

Cited by 5 | Viewed by 3099

Abstract

Research within the area of selective energy transfer (SET) on how resonance develops between a specific vibration within a catalyst system and a corresponding vibration within a reacting system that resonates with it is discussed here. The catalyst system is assumed to donate [...] Read more.

Research within the area of selective energy transfer (SET) on how resonance develops between a specific vibration within a catalyst system and a corresponding vibration within a reacting system that resonates with it is discussed here. The catalyst system is assumed to donate one or more vibrational quanta to the reacting system. The term ‘specific vibration’ refers to vibration of a type involving bending or stretching that, when transferred resonantly to the reacting system, serves to drive the reactant molecules involved to assume the basic structure of the molecules of the catalyst system. Regardless of whether the catalyst is a pure metal surface or a complex polymolecular system (an enzyme), its role is seen to be that of transferring energy to corresponding vibrations of the reactant system. Examples are here presented of vibrators of various types that can act as catalysts. Full article

(This article belongs to the Special Issue Catalysis Assisted by Calculations: From Organic and Metal Catalysts to Enzymes)

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14 pages, 7247 KiB

Open AccessArticle

X-Shaped ZIF-8 for Immobilization Rhizomucor miehei Lipase via Encapsulation and Its Application toward Biodiesel Production

by Miaad Adnan, Kai Li, Li Xu and Yunjun Yan

Catalysts 2018, 8(3), 96; https://doi.org/10.3390/catal8030096 - 28 Feb 2018

Cited by 101 | Viewed by 7127

Abstract

This study presents a one-step encapsulation method for synthesizing X-shaped zeolitic imidazolate frameworks (ZIF-8) and immobilizing Rhizomucor miehei lipase (RML). We proved that the morphological structure of ZIF-8 had changed after immobilization with enhanced characterization using a field-emission scanning electron microscope, an energy-dispersive [...] Read more.

This study presents a one-step encapsulation method for synthesizing X-shaped zeolitic imidazolate frameworks (ZIF-8) and immobilizing Rhizomucor miehei lipase (RML). We proved that the morphological structure of ZIF-8 had changed after immobilization with enhanced characterization using a field-emission scanning electron microscope, an energy-dispersive spectrometer, a transmission electron microscope, a Fourier transform infrared spectrometer, and powder X-ray diffraction. The surface area and pore size of the carrier were investigated before and after immobilization using Brunauer–Emmett–Teller and Barrett–Joyner–Halenda methods, respectively. RML@ZIF-8 exhibited high recovery activity of up to 2632%, representing a 26-fold increase in its free lipase. Encapsulated RML was used for biodiesel production from soybean oil in an isooctane system with a conversion yield of 95.6% under optimum conditions. The resulting reusability of the immobilized enzyme indicated no substantial decline in the conversion yield, which remained at 84.7% of the initial activity after 10 cycles. The stability and high performance of the immobilized enzyme are attributed to the harmony between RML and ZIF-8 based on the easy synthesis of ZIF-8 and the short time required to immobilize RML. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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15 pages, 3954 KiB

Open AccessArticle

Cost-Effective and Facile Preparation of Fe₂O₃ Nanoparticles Decorated N-Doped Mesoporous Carbon Materials: Transforming Mulberry Leaf into a Highly Active Electrocatalyst for Oxygen Reduction Reactions

by Tingting Zhang, Lihao Guan, Changqing Li, Junfeng Zhao, Manchao Wang, Lin Peng, Jiahui Wang and Yuqing Lin

Catalysts 2018, 8(3), 101; https://doi.org/10.3390/catal8030101 - 28 Feb 2018

Cited by 14 | Viewed by 5816

Abstract

Herein, a promising method to prepare efficient N-doped porous carbon-supported Fe₂O₃ nanoparticles (Fe₂O₃/N-PCs) ORR electrocatalysts is presented. The porous carbon was derived from a biomass i.e., mulberry leaf through a cost-effective approach. The existence of diverse [...] Read more.

Herein, a promising method to prepare efficient N-doped porous carbon-supported Fe₂O₃ nanoparticles (Fe₂O₃/N-PCs) ORR electrocatalysts is presented. The porous carbon was derived from a biomass i.e., mulberry leaf through a cost-effective approach. The existence of diverse compounds containing carbon, oxygen, nitrogen and sulfur in mulberry leaf benefit the formation and uniform dispersion of Fe₂O₃ nanoparticles (NPs) in the porous carbon. In evaluating the effects of the carbon support on the Fe₂O₃ NPs towards the ORR, we found that the sample of Fe₂O₃/N-PCs-850 (Fe₂O₃/N-PCs obtained at 850 °C) with high surface area of 313.8 m²·g⁻¹ exhibits remarkably superior ORR activity than that of materials acquired under other temperatures. To be specific, the onset potential and reduction peak potential of Fe₂O₃/N-PCs-850 towards ORR are 0.936 V and 0.776 V (vs. RHE), respectively. The calculated number of electron transfer n for the ORR is 3.9, demonstrating a near four-electron-transfer process. Furthermore, it demonstrates excellent longtime stability and resistance to methanol deactivation compared with Pt/C catalyst. This study provides a novel design of highly active ORR electrocatalysts from low-cost abundant plant products. Full article

(This article belongs to the Special Issue Catalysts for Oxygen Reduction Reaction)

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15 pages, 4497 KiB

Open AccessArticle

Enhanced Low Temperature NO Reduction Performance via MnO_x-Fe₂O₃/Vermiculite Monolithic Honeycomb Catalysts

by Ke Zhang, Feng Yu, Mingyuan Zhu, Jianming Dan, Xugen Wang, Jinli Zhang and Bin Dai

Catalysts 2018, 8(3), 100; https://doi.org/10.3390/catal8030100 - 28 Feb 2018

Cited by 47 | Viewed by 6829

Abstract

Selective catalytic reduction of NO_x by ammonia (NH₃-SCR) was the most efficient and economic technology for De-NO_x applications. Therefore, a series of MnO_x/vermiculite (VMT) and MnO_x-Fe₂O₃/VMT catalysts were prepared by an [...] Read more.

Selective catalytic reduction of NO_x by ammonia (NH₃-SCR) was the most efficient and economic technology for De-NO_x applications. Therefore, a series of MnO_x/vermiculite (VMT) and MnO_x-Fe₂O₃/VMT catalysts were prepared by an impregnation method for the selective catalytic reduction (SCR) of nitrogen oxides (NO_x). The MnO_x-Fe₂O₃/VMT catalysts provided an excellent NO conversion of 96.5% at 200 °C with a gas hourly space velocity (GHSV) of 30,000 h⁻¹ and an NO concentration of 500 ppm. X-ray photoelectron spectroscopy results indicated that the Mn and Fe oxides of the MnO_x-Fe₂O₃/VMT catalyst were mainly composed of MnO₂ and Fe₂O₃. However, the MnO₂ and Fe₂O₃ components were well dispersed because no discernible MnO₂ and Fe₂O₃ phases were observed in X-ray powder diffraction spectra. Corresponding MnO_x-Fe₂O₃/VMT monolithic honeycomb catalysts (MHCs) were prepared by an extrusion method, and the MHCs achieved excellent SCR activity at low temperature, with an NO conversion greater than 98.6% at 150 °C and a GHSV of 4000 h⁻¹. In particular, the MnO_x-Fe₂O₃/VMT MHCs provided a good SCR activity at room temperature (20 °C), with an NO conversion of 62.2% (GHSV = 1000 h⁻¹). In addition, the NO reduction performance of the MnO_x-Fe₂O₃/VMT MHCs also demonstrated an excellent SO₂ resistance. Full article

(This article belongs to the Special Issue Selective Catalytic Reduction of NO_x)

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20 pages, 4458 KiB

Open AccessFeature PaperArticle

Tungsten-Based Mesoporous Silicates W-MMM-E as Heterogeneous Catalysts for Liquid-Phase Oxidations with Aqueous H₂O₂

by Nataliya Maksimchuk, Irina Ivanchikova, Olga Zalomaeva, Yurii Chesalov, Alexandr Shmakov, Vladimir Zaikovskii and Oxana Kholdeeva

Catalysts 2018, 8(3), 95; https://doi.org/10.3390/catal8030095 - 27 Feb 2018

Cited by 10 | Viewed by 4561

Abstract

Mesoporous tungsten-silicates, W-MMM-E, have been prepared following evaporation-induced self-assembly methodology and characterized by elemental analysis, XRD, N₂ adsorption, STEM-HAADF (high angle annular dark field in scanning-TEM mode), DRS UV-vis, and Raman techniques. DRS UV-vis showed the presence of two types of tungsten [...] Read more.

Mesoporous tungsten-silicates, W-MMM-E, have been prepared following evaporation-induced self-assembly methodology and characterized by elemental analysis, XRD, N₂ adsorption, STEM-HAADF (high angle annular dark field in scanning-TEM mode), DRS UV-vis, and Raman techniques. DRS UV-vis showed the presence of two types of tungsten oxo-species in W-MMM-E samples: isolated tetrahedrally and oligomeric octahedrally coordinated ones, with the ratio depending on the content of tungsten in the catalyst. Materials with lower W loading have a higher contribution from isolated species, regardless of the preparation method. W-MMM-E catalyzes selectively oxidize of a range of alkenes and organic sulfides, including bulky terpene or thianthrene molecules, using green aqueous H₂O₂. The selectivity of corresponding epoxides reached 85–99% in up to 80% alkene conversions, while sulfoxides formed with 84–90% selectivity in almost complete sulfide conversions and a 90–100% H₂O₂ utilization efficiency. The true heterogeneity of catalysis over W-MMM-E was proved by hot filtration tests. Leaching of inactive W species depended on the reaction conditions and initial W loading in the catalyst. After optimization of the catalyst system, it did not exceed 20 ppm and 3 ppm for epoxidation and sulfoxidation reactions, respectively. Elaborated catalysts could be easily retrieved by filtration and reused several times with maintenance of the catalytic behavior. Full article

(This article belongs to the Special Issue New Developments in Heterogeneous Partial and Total Oxidation Catalysis)

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36 pages, 4326 KiB

Open AccessEditor’s ChoiceReview

The Role of Yeast-Surface-Display Techniques in Creating Biocatalysts for Consolidated BioProcessing

by Ian Dominic Flormata Tabañag, I-Ming Chu, Yu-Hong Wei and Shen-Long Tsai

Catalysts 2018, 8(3), 94; https://doi.org/10.3390/catal8030094 - 25 Feb 2018

Cited by 19 | Viewed by 8296

Abstract

Climate change is directly linked to the rapid depletion of our non-renewable fossil resources and has posed concerns on sustainability. Thus, imploring the need for us to shift from our fossil based economy to a sustainable bioeconomy centered on biomass utilization. The efficient [...] Read more.

Climate change is directly linked to the rapid depletion of our non-renewable fossil resources and has posed concerns on sustainability. Thus, imploring the need for us to shift from our fossil based economy to a sustainable bioeconomy centered on biomass utilization. The efficient bioconversion of lignocellulosic biomass (an ideal feedstock) to a platform chemical, such as bioethanol, can be achieved via the consolidated bioprocessing technology, termed yeast surface engineering, to produce yeasts that are capable of this feat. This approach has various strategies that involve the display of enzymes on the surface of yeast to degrade the lignocellulosic biomass, then metabolically convert the degraded sugars directly into ethanol, thus elevating the status of yeast from an immobilization material to a whole-cell biocatalyst. The performance of the engineered strains developed from these strategies are presented, visualized, and compared in this article to highlight the role of this technology in moving forward to our quest against climate change. Furthermore, the qualitative assessment synthesized in this work can serve as a reference material on addressing the areas of improvement of the field and on assessing the capability and potential of the different yeast surface display strategies on the efficient degradation, utilization, and ethanol production from lignocellulosic biomass. Full article

(This article belongs to the Special Issue Immobilized Biocatalysts)

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