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Volume 8
Issue 12
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Catalysts, Volume 8, Issue 12 (December 2018) – 105 articles

Cover Story (view full-size image): Between environmental applications of photocatalysis, TiO2 nanoparticles composite with eco-friendly-prepared, reduced Graphene Oxide (rGO), in combination with visible light, has proved itself to be a high performing photocatalyst for the photodegradation of water pollutants. View this paper.
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18 pages, 2651 KiB  
Review
Application of Catalytic Wet Peroxide Oxidation for Industrial and Urban Wastewater Treatment: A Review
by Juan José Rueda Márquez, Irina Levchuk and Mika Sillanpää
Catalysts 2018, 8(12), 673; https://doi.org/10.3390/catal8120673 - 19 Dec 2018
Cited by 71 | Viewed by 8103
Abstract
Catalytic wet peroxide oxidation (CWPO) is emerging as an advanced oxidation process (AOP) of significant promise, which is mainly due to its efficiency for the decomposition of recalcitrant organic compounds in industrial and urban wastewaters and relatively low operating costs. In current study, [...] Read more.
Catalytic wet peroxide oxidation (CWPO) is emerging as an advanced oxidation process (AOP) of significant promise, which is mainly due to its efficiency for the decomposition of recalcitrant organic compounds in industrial and urban wastewaters and relatively low operating costs. In current study, we have systemised and critically discussed the feasibility of CWPO for industrial and urban wastewater treatment. More specifically, types of catalysts the effect of pH, temperature, and hydrogen peroxide concentrations on the efficiency of CWPO were taken into consideration. The operating and maintenance costs of CWPO applied to wastewater treatment and toxicity assessment were also discussed. Knowledge gaps were identified and summarised. The main conclusions of this work are: (i) catalyst leaching and deactivation is one of the main problematic issues; (ii) majority of studies were performed in semi-batch and batch reactors, while continuous fixed bed reactors were not extensively studied for treatment of real wastewaters; (iii) toxicity of wastewaters treated by CWPO is of key importance for possible application, however it was not studied thoroughly; and, (iv) CWPO can be regarded as economically viable for wastewater treatment, especially when conducted at ambient temperature and natural pH of wastewater. Full article
(This article belongs to the Special Issue Trends in Catalytic Wet Peroxide Oxidation Processes)
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21 pages, 3082 KiB  
Review
Photocatalyzed Transformation of Free Carbohydrates
by Mehdi Omri, Frédéric Sauvage, Séma Golonu, Anne Wadouachi and Gwladys Pourceau
Catalysts 2018, 8(12), 672; https://doi.org/10.3390/catal8120672 - 19 Dec 2018
Cited by 11 | Viewed by 4538
Abstract
In the growing context of sustainable chemistry, one of the challenges of organic chemists is to develop efficient and environmentally friendly methods for the synthesis of high-added-value products. Heterogeneous photocatalytic transformations have brought revolution in this regard, as they take advantage of an [...] Read more.
In the growing context of sustainable chemistry, one of the challenges of organic chemists is to develop efficient and environmentally friendly methods for the synthesis of high-added-value products. Heterogeneous photocatalytic transformations have brought revolution in this regard, as they take advantage of an unlimited source of energy (solar light) or artificial UV light to onset organic chemical modifications. The abundance of free carbohydrates as chemical platform feedstock offers a great opportunity to obtain a variety of industrial interest compounds from biomass. Due to their chirality and polyfunctionality, the conversion of sugars generally requires multi-step protocols with protection/deprotection steps and hazardous chemical needs. In this context, several selective and eco-friendly methodologies are currently under development. This review presents a state of art of the recent accomplishments concerning the use of photocatalysts for the transformation and valorization of free carbohydrates. It discusses the approaches leading to the selective oxidation of free sugars, their degradation into organic chemicals, or their use for hydrogen production. Full article
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25 pages, 13043 KiB  
Review
Hydrogen Transfer Reactions of Carbonyls, Alkynes, and Alkenes with Noble Metals in the Presence of Alcohols/Ethers and Amines as Hydrogen Donors
by Eszter Baráth
Catalysts 2018, 8(12), 671; https://doi.org/10.3390/catal8120671 - 19 Dec 2018
Cited by 69 | Viewed by 19615
Abstract
Hydrogen transfer reactions have exceptional importance, due to their applicability in numerous synthetic pathways, with academic as well as industrial relevance. The most important transformations are, e.g., reduction, ring-closing, stereoselective reactions, and the synthesis of heterocycles. The present review provides insights into the [...] Read more.
Hydrogen transfer reactions have exceptional importance, due to their applicability in numerous synthetic pathways, with academic as well as industrial relevance. The most important transformations are, e.g., reduction, ring-closing, stereoselective reactions, and the synthesis of heterocycles. The present review provides insights into the hydrogen transfer reactions in the condensed phase in the presence of noble metals (Rh, Ru, Pd) as catalysts. Since the H-donor molecules (such as alcohols/ethers and amines (1°, 2°, 3°)) and the acceptor molecules (alkenes (C=C), alkynes (C≡C), and carbonyl (C=O) compounds) play a crucial role from mechanistic viewpoints, the present summary points out the key mechanistic differences with the interpretation of current contributions and the corresponding historical achievements as well. Full article
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11 pages, 2607 KiB  
Article
Synthesis of Soluble Star-Shaped Polymers via In and Out Approach by Ring-Opening Metathesis Polymerization (ROMP) of Norbornene: Factors Affecting the Synthesis
by Zelin Sun, Kazuya Morishita and Kotohiro Nomura
Catalysts 2018, 8(12), 670; https://doi.org/10.3390/catal8120670 - 19 Dec 2018
Cited by 8 | Viewed by 3471
Abstract
The methods for one-pot synthesis of ‘soluble’ star-shaped polymers by sequential living ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and cross-linking (CL) reagent using Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 have been explored. The method [...] Read more.
The methods for one-pot synthesis of ‘soluble’ star-shaped polymers by sequential living ring-opening metathesis polymerization (ROMP) of norbornene (NBE) and cross-linking (CL) reagent using Mo(CHCMe2Ph)(N-2,6-iPr2C6H3)(OtBu)2 have been explored. The method (called the “in and out” or core-first approach) basically consists of (i) the living ROMP of NBE (formation of arm), (ii) reaction with CL (formation of core), (iii) additional living ROMP of NBE (propagating arms from the core, formation of star), (iv) end-modification via Wittig-type cleavage of metal–carbon double bonds containing polymer chain with aldehyde. Two different approaches in the core formation step (reaction with CL mixed with/without NBE) for synthesis of the high molecular weight star-shaped ROMP polymers with more branching, unimodal molecular weight distributions have been explored in detail. The method (reacting CL with NBE in the core formation step) under highly diluted conditions afforded the high molecular weight polymers with unimodal molecular weight distributions. Full article
(This article belongs to the Section Catalytic Materials)
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10 pages, 2710 KiB  
Article
AuPt Nanoparticles Clusters on MWCNTs with Enhanced Electrocatalytic Activity for Methanol Oxidation
by Changzheng Wang, Fengnan Yang, Li Gao, Shoufang Xu, Louzhen Fan, Tao Guo, Yongfeng Liu, Lian Zhou and Yang Zhang
Catalysts 2018, 8(12), 669; https://doi.org/10.3390/catal8120669 - 19 Dec 2018
Cited by 7 | Viewed by 3114
Abstract
AuPt nanoparticles clusters (NPCs) were electrodeposited on multiwalled carbon nanotubes (MWCNTs). The as-prepared AuPt NPCs@MWCNTs nanocomposites exhibited considerably enhanced electrocatalytic activity than Pt NPs@MWCNTs for methanol oxidation in acid medium. In comparison with Pt NPs@MWCNTs, a remarkable resistance to CO poisoning and a [...] Read more.
AuPt nanoparticles clusters (NPCs) were electrodeposited on multiwalled carbon nanotubes (MWCNTs). The as-prepared AuPt NPCs@MWCNTs nanocomposites exhibited considerably enhanced electrocatalytic activity than Pt NPs@MWCNTs for methanol oxidation in acid medium. In comparison with Pt NPs@MWCNTs, a remarkable resistance to CO poisoning and a higher If/Ib value (the ratio of the forward scan oxidation peak current (If) and reverse scan oxidation peak current (Ib)) was achieved by AuPt NPCs@MWCNTs electrocatalyst, which is attributable to the unique NPCs nanostructure with enlarged electrochemical active surface areas. These results demonstrated the potential of AuPt NPCs@MWCNTs, which can be considered as an efficient electrocatalyst for methanol oxidation in direct methanol fuel cells. Full article
(This article belongs to the Section Electrocatalysis)
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12 pages, 2884 KiB  
Article
Comparing the Efficiency of N-Doped TiO2 and N-Doped Bi2MoO6 Photo Catalysts for MB and Lignin Photodegradation
by Ricardo Rangel, Verónica Janneth Cedeño, Jaime Espino, Pascual Bartolo-Pérez, Geonel Rodríguez-Gattorno and Juan José Alvarado-Gil
Catalysts 2018, 8(12), 668; https://doi.org/10.3390/catal8120668 - 19 Dec 2018
Cited by 24 | Viewed by 5448
Abstract
In this study, we tested the efficiency of nitrogen-doped titanium dioxide (N-TiO2) and nitrogen-doped bismuth molybdate (N-Bi2MoO6) compounds as photocatalysts capable of degrading methylene blue and lignin molecules under irradiation with ultraviolet (UV) and visible light (VIS). [...] Read more.
In this study, we tested the efficiency of nitrogen-doped titanium dioxide (N-TiO2) and nitrogen-doped bismuth molybdate (N-Bi2MoO6) compounds as photocatalysts capable of degrading methylene blue and lignin molecules under irradiation with ultraviolet (UV) and visible light (VIS). Moreover, we compared TiO2 and Bi2MoO6 catalysts with N-TiO2 and N-Bi2MoO6 compounds using chemical coprecipitation. The catalysts were prepared starting from Ti(OCH2CH2CH3)4, Bi(NO3)3·5H2O, and (NH4)6Mo7O24 reagents. N-doping was achieved in a continuous reflux system, using ethylene diamine as a nitrogen source. The resulting materials were characterized using Scanning Electron Microscopy (SEM), X-Ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Additionally, we observed the decrease in particle size after processing the compounds in the reflux system. The results regarding photocatalytic degradation tests show a remarkable effect for nitrogen doped samples, achieving 90% of lignin degradation. Full article
(This article belongs to the Special Issue Emerging Trends in TiO2 Photocatalysis and Applications)
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11 pages, 3619 KiB  
Article
Alkali-Free Zn–Al Layered Double Hydroxide Catalysts for Triglyceride Transesterification
by Nazrizawati A. Tajuddin, Jinesh C. Manayil, Mark A. Isaacs, Christopher M.A. Parlett, Adam F. Lee and Karen Wilson
Catalysts 2018, 8(12), 667; https://doi.org/10.3390/catal8120667 - 18 Dec 2018
Cited by 15 | Viewed by 5108
Abstract
Zn–Al layered double hydroxides (LDHs) of general formula [Zn2+(1−x)Al3+x(OH)2]x+(CO32−)x/2·yH2O are promising solid base catalysts for the transesterification of lipids to biofuels. However, conventional synthetic routes [...] Read more.
Zn–Al layered double hydroxides (LDHs) of general formula [Zn2+(1−x)Al3+x(OH)2]x+(CO32−)x/2·yH2O are promising solid base catalysts for the transesterification of lipids to biofuels. However, conventional synthetic routes employ alkali hydroxide/carbonate precipitants which may contaminate the final LDH catalyst and biofuel. The use of (NH3)2CO3 and NH3OH as precipitants affords alkali-free Zn–Al-LDHs spanning a wide composition range. The hydrothermal reconstruction of calcined Zn–Al-LDHs offers superior solid basicity and catalytic activity for the transesterification of C4–C18 triglycerides with methanol, compared with cold liquid phase or vapour phase reconstruction. Hydrothermally activated Zn3.3–Al-LDH was stable towards leaching during transesterification. Full article
(This article belongs to the Special Issue Catalytic Conversion of Biomass-Derived Molecules to Chemicals and Fuels)
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20 pages, 5273 KiB  
Article
AuPd/3DOM TiO2 Catalysts: Good Activity and Stability for the Oxidation of Trichloroethylene
by Xing Zhang, Yuxi Liu, Jiguang Deng, Kunfeng Zhang, Jun Yang, Zhuo Han and Hongxing Dai
Catalysts 2018, 8(12), 666; https://doi.org/10.3390/catal8120666 - 18 Dec 2018
Cited by 17 | Viewed by 4354
Abstract
Three-dimensionally ordered macroporous (3DOM) TiO2-supported AuPd alloy (xAuyPd/3DOM TiO2 (x = 0.87–0.91 wt%; y = 0.51–1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials [...] Read more.
Three-dimensionally ordered macroporous (3DOM) TiO2-supported AuPd alloy (xAuyPd/3DOM TiO2 (x = 0.87–0.91 wt%; y = 0.51–1.86)) catalysts for trichloroethylene (TCE) oxidation were prepared using the polymethyl methacrylate-templating and polyvinyl alcohol-protected reduction methods. The as-prepared materials possessed a good-quality 3DOM structure and a surface area of 49–53 m2/g. The noble metal nanoparticles (NPs) with a size of 3–4 nm were uniformly dispersed on the surface of 3DOM TiO2. The 0.91Au0.51Pd/3DOM TiO2 sample showed the highest catalytic activity with the temperature at a TCE conversion of 90% being 400 °C at a space velocity of 20,000 mL/(g h). Furthermore, the 0.91Au0.51Pd/3DOM TiO2 sample possessed better catalytic stability and moisture-resistant ability than the supported Au or Pd sample. The partial deactivation induced by H2O introduction of 0.91Au0.51Pd/3DOM TiO2 was reversible, while that induced by CO2 addition was irreversible. No significant influence on TCE conversion was observed after introduction of 100 ppm HCl to the reaction system over 0.91Au0.51Pd/3DOM TiO2. The lowest apparent activation energy (51.7 kJ/mol) was obtained over the 0.91Au0.51Pd/3DOM TiO2 sample. The doping of Au to Pd changed the TCE oxidation pathway, thus reducing formation of perchloroethylene. It is concluded that the high adsorbed oxygen species concentration, good low-temperature reducibility, and strong interaction between AuPd NPs and 3DOM TiO2 as well as more amount of strong acid sites were responsible for the good catalytic activity, stability, and water- and HCl-resistant ability of 0.91Au0.51Pd/3DOM TiO2. We believe that 0.91Au0.51Pd/3DOM TiO2 may be a promising catalyst for the oxidative elimination of chlorine-containing volatile organics. Full article
(This article belongs to the Special Issue Catalysis for the Removal of Gas-Phase Pollutants)
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14 pages, 2127 KiB  
Article
Structural and Electrocatalytic Properties of Platinum and Platinum-Carbon Layers Obtained by Magnetron-Ion Sputtering
by Olga K. Alekseeva, Artem I. Mikhalev, Elena K. Lutikova, Vladimir I. Porembsky, Mikhail Yu. Presnyakov, Vladimir N. Fateev, Boris L. Shapir and Sergey A. Grigoriev
Catalysts 2018, 8(12), 665; https://doi.org/10.3390/catal8120665 - 18 Dec 2018
Cited by 14 | Viewed by 4137
Abstract
This article is devoted to further development of magnetron sputtering technology for catalysts and catalysts layer production for fuel cells and other electrochemical devices. Platinum-carbon films with Pt content up to 95–97 wt % were deposited using different sputtering regimes—DC (direct current) sputtering [...] Read more.
This article is devoted to further development of magnetron sputtering technology for catalysts and catalysts layer production for fuel cells and other electrochemical devices. Platinum-carbon films with Pt content up to 95–97 wt % were deposited using different sputtering regimes—DC (direct current) sputtering with and without application of a pulse negative bias voltage to the titanium substrate and also bipolar pulse sputtering with frequency of 10 kHz and 100 kHz. Composite platinum carbon targets were used for sputtering. Characteristics of platinum-carbon films were compared with those of platinum films deposited using the same regimes. The main methods of investigation were scanning transmission electron microscopy (STEM) with energy dispersive X-ray spectroscopy; potentiostatic and potentiodynamic methods. The catalytic activity of platinum-carbon films increased with platinum content and at a platinum concentration of 95–97 wt % became higher than that of platinum films sputtered in the same regimes. It was proposed that carbon atoms deposited on the substrate limited the mobility of the deposited platinum species and inhibited Pt cluster growth. Platinum-carbon films produced by pulsed DC magnetron sputtering with pulsed frequency 100 kHz consisted of narrow Pt columns with dome nanotops forming a well-developed surface. The porosity and specific surface of these columnar nanopillar films were higher compared with those of pure platinum films deposited under the same conditions. Moreover, the platinum-carbon films deposited using a bipolar pulse regime with a frequency of 100 kHz had the highest specific surface, porosity (30%) and catalytic activity in hydrogen and oxygen evolution due to a high ion current density and reduced pulse duration which inhibited the growth of large platinum globules. Full article
(This article belongs to the Section Electrocatalysis)
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14 pages, 3458 KiB  
Article
Properties of Carbon-supported Precious Metals Catalysts under Reductive Treatment and Their Influence in the Hydrodechlorination of Dichloromethane
by Alejandra Arevalo-Bastante, Maria Martin-Martinez, M. Ariadna Álvarez-Montero, Juan J. Rodriguez and Luisa M. Gómez-Sainero
Catalysts 2018, 8(12), 664; https://doi.org/10.3390/catal8120664 - 18 Dec 2018
Cited by 11 | Viewed by 3244
Abstract
This study analyzes the effect of the reduction temperature on the properties of Rh, Pt and Pd catalysts supported on activated carbon and their performance in the hydrodechlorination (HDC) of dichloromethane (DCM). The reduction temperature plays an important role in the oxidation state, [...] Read more.
This study analyzes the effect of the reduction temperature on the properties of Rh, Pt and Pd catalysts supported on activated carbon and their performance in the hydrodechlorination (HDC) of dichloromethane (DCM). The reduction temperature plays an important role in the oxidation state, size and dispersion of the metallic phase. Pd is more prone to sintering, followed by Pt, while Rh is more resistant. The ratio of zero-valent to electro-deficient metal increases with the reduction temperature, with that effect being more remarkable for Pd and Pt. The higher resistance to sintering of Rh and the higher stability of electro-deficient species under thermal reductive treatment can be attributed to a stronger interaction with surface oxygen functionalities. Dechlorination activity and a TOF increase with reduction temperature (250–450 °C) occurred in the case of Pt/C catalyst, while a great decrease of both was observed for Pd/C, and no significant effect was found for Rh/C. Pt0 represents the main active species for HDC reaction in Pt/C. Therefore, increasing the relative amount of these species increased the TOF value, compensating for the loss of dispersion. In contrast, Pdn+ appears as the main active species in Pd/C and their relatively decreasing occurrence together with the significant decrease of metallic area reduces the HDC activity. Rh/C catalyst suffered only small changes in dispersion and metal oxidation state with the reduction temperature and thus this variable barely affected its HDC activity. Full article
(This article belongs to the Special Issue Catalysis by Precious Metals, Past and Future)
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9 pages, 2889 KiB  
Article
Network Structured CuWO4/BiVO4/Co-Pi Nanocomposite for Solar Water Splitting
by Ben Peng, Mengyang Xia, Chao Li, Changshen Yue and Peng Diao
Catalysts 2018, 8(12), 663; https://doi.org/10.3390/catal8120663 - 17 Dec 2018
Cited by 16 | Viewed by 6060
Abstract
A network structured CuWO4/BiVO4 nanocomposite with a high specific surface area was prepared from CuWO4 nanoflake (NF) arrays via a method that combined drop-casting and thermal annealing. The obtained CuWO4/BiVO4 exhibited high catalytic activity toward photoelectrochemical [...] Read more.
A network structured CuWO4/BiVO4 nanocomposite with a high specific surface area was prepared from CuWO4 nanoflake (NF) arrays via a method that combined drop-casting and thermal annealing. The obtained CuWO4/BiVO4 exhibited high catalytic activity toward photoelectrochemical (PEC) water oxidation. When cobalt phosphate (Co-Pi) was coupled with CuWO4/BiVO4, the activity of the resulting CuWO4/BiVO4/Co-Pi composite for the oxygen evolution reaction (OER) was further improved. The photocurrent density (Jph) for OER on CuWO4/BiVO4/Co-Pi is among the highest reported on a CuWO4-based photoanode in a neutral solution. The high activity for the PEC OER was attributed to the high specific surface area of the composite, the formation of a CuWO4/BiVO4 heterojunction that accelerated electron–hole separation, and the coupling of the Co-Pi co-catalyst with CuWO4/BiVO4, which improved the charge transfer rate across composite/solution interface. Full article
(This article belongs to the Special Issue Photocatalytic Nanocomposite Materials)
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17 pages, 746 KiB  
Review
Detoxification of Olive Mill Wastewaters by Fenton’s Process
by Eva Domingues, João Gomes, Margarida J. Quina, Rosa M. Quinta-Ferreira and Rui C. Martins
Catalysts 2018, 8(12), 662; https://doi.org/10.3390/catal8120662 - 17 Dec 2018
Cited by 46 | Viewed by 4250
Abstract
Olive mill wastewaters (OMW) constitute an environmental problem affecting mainly Mediterranean Sea area countries where the olive mill industry is a very important economic sector. The strong impact and management issues of these effluents are mainly due to their seasonality, localized production, and [...] Read more.
Olive mill wastewaters (OMW) constitute an environmental problem affecting mainly Mediterranean Sea area countries where the olive mill industry is a very important economic sector. The strong impact and management issues of these effluents are mainly due to their seasonality, localized production, and high organic load with high toxic features and low biodegradability. As the olive oil industry is highly water demanding, the search for suitable water recovery strategies requires the development and optimization of advanced treatment technologies. The classical Fenton’s process is an interesting alternative, as it operates at room conditions of pressure and temperature. However, it shows some drawbacks, such as the generation of iron sludges, which require further management. Nevertheless, because of its features that make it industrially desirable, overcoming these limitations has been the focus of researchers in the last years. Bearing this in mind, this paper focuses on the recent research regarding OMW treatment using Fenton’s process. The use of Fenton’s peroxidation treatment at homogenous, heterogeneous, and photo-aided conditions is analysed. The use of solid catalysts may be an interesting way to avoid sludge formation. Light-driven Fenton can also reduce the amount of iron needed for effective degradation. Moreover, Fenton’s process integration in combined treatment schemes is discussed. Finally, remarks regarding its application at full scale are given. Full article
(This article belongs to the Section Environmental Catalysis)
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0 pages, 5013 KiB  
Article
RETRACTED: The Influence of Texture on Co/SBA–15 Catalyst Performance for Fischer–Tropsch Synthesis
by Jun Han, Zijiang Xiong, Zelin Zhang, Hongjie Zhang, Peng Zhou and Fei Yu
Catalysts 2018, 8(12), 661; https://doi.org/10.3390/catal8120661 - 16 Dec 2018
Cited by 9 | Viewed by 3868 | Retraction
Abstract
The influence of the Co/SBA–15 catalyst texture, such as pore size and pore length on Fischer–Tropsch (FT) Synthesis, was investigated in this paper. The morphology, structure, and microstructures of Co/SBA–15 catalysts were characterized by SEM, Brunauer–Emmett–Teller (BET), TPR, HRTEM, and XRD. The experimental [...] Read more.
The influence of the Co/SBA–15 catalyst texture, such as pore size and pore length on Fischer–Tropsch (FT) Synthesis, was investigated in this paper. The morphology, structure, and microstructures of Co/SBA–15 catalysts were characterized by SEM, Brunauer–Emmett–Teller (BET), TPR, HRTEM, and XRD. The experimental results indicated that the increase of pore size could improve the activity of the Co/SBA–15 catalyst, and the further increase of pore size could not significantly promote the activity. Moreover, it was also found that the pore length of the Co/SBA–15 catalyst played a key role in the catalytic activity. CO2 and C4+ selectivity were 2.0% and 74% during the simulated syngas (64% H2: 32% CO: balanced N2) FT over the Co/SBA–15 catalysts, and CO conversion rate and CH4 selectivity were 10.8% and 15.7% after 100 h time on stream. Full article
(This article belongs to the Special Issue Catalytic Transformation of Renewables (Olefin, Bio-sourced, et. al))
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19 pages, 3484 KiB  
Review
Critical Review of Low-Temperature CO Oxidation and Hysteresis Phenomenon on Heterogeneous Catalysts
by Rola Mohammad Al Soubaihi, Khaled Mohammad Saoud and Joydeep Dutta
Catalysts 2018, 8(12), 660; https://doi.org/10.3390/catal8120660 - 14 Dec 2018
Cited by 81 | Viewed by 12992
Abstract
There is a growing demand for new heterogeneous catalysts for cost-effective catalysis. Currently, the hysteresis phenomenon during low-temperature CO oxidation is an important topic in heterogeneous catalysis. Hysteresis provides important information about fluctuating reaction conditions that affect the regeneration of active sites and [...] Read more.
There is a growing demand for new heterogeneous catalysts for cost-effective catalysis. Currently, the hysteresis phenomenon during low-temperature CO oxidation is an important topic in heterogeneous catalysis. Hysteresis provides important information about fluctuating reaction conditions that affect the regeneration of active sites and indicate the restoration of catalyst activity. Understanding its dynamic behavior, such as hysteresis and self-sustained kinetic oscillations, during CO oxidation, is crucial for the development of cost-effective, stable and long-lasting catalysts. Hysteresis during CO oxidation has a direct influence on many industrial processes and its understanding can be beneficial to a broad range of applications, including long-life CO2 lasers, gas masks, catalytic converters, sensors, indoor air quality, etc. This review considers the most recent reported advancements in the field of hysteresis behavior during CO oxidation which shed light on the origin of this phenomenon and the parameters that influence the type, shape, and width of the conversion of the hysteresis curves. Full article
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45 pages, 1823 KiB  
Review
Catalytic Pyrolysis of Biomass and Polymer Wastes
by Laibao Zhang, Zhenghong Bao, Shunxiang Xia, Qiang Lu and Keisha B. Walters
Catalysts 2018, 8(12), 659; https://doi.org/10.3390/catal8120659 - 13 Dec 2018
Cited by 124 | Viewed by 14840
Abstract
Oil produced by the pyrolysis of biomass and co-pyrolysis of biomass with waste synthetic polymers has significant potential as a substitute for fossil fuels. However, the relatively poor properties found in pyrolysis oil—such as high oxygen content, low caloric value, and physicochemical instability—hampers [...] Read more.
Oil produced by the pyrolysis of biomass and co-pyrolysis of biomass with waste synthetic polymers has significant potential as a substitute for fossil fuels. However, the relatively poor properties found in pyrolysis oil—such as high oxygen content, low caloric value, and physicochemical instability—hampers its practical utilization as a commercial petroleum fuel replacement or additive. This review focuses on pyrolysis catalyst design, impact of using real waste feedstocks, catalyst deactivation and regeneration, and optimization of product distributions to support the production of high value-added products. Co-pyrolysis of two or more feedstock materials is shown to increase oil yield, caloric value, and aromatic hydrocarbon content. In addition, the co-pyrolysis of biomass and polymer waste can contribute to a reduction in production costs, expand waste disposal options, and reduce environmental impacts. Several promising options for catalytic pyrolysis to become industrially viable are also discussed. Full article
(This article belongs to the Special Issue Catalytic Pyrolysis)
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11 pages, 3500 KiB  
Article
Combining Carbon Fibers with Ni/γ–Al2O3 Used for Syngas Production: Part A: Preparation and Evaluation of Complex Carrier Catalysts
by Lei Yu, Min Song, Yuexing Wei and Jun Xiao
Catalysts 2018, 8(12), 658; https://doi.org/10.3390/catal8120658 - 13 Dec 2018
Cited by 13 | Viewed by 4903
Abstract
To promote the adsorption and activation of carbon dioxide in the dry reforming of methane (DRM), Ni and Al2O3 were coprecipitated on activated carbon fibers (ACF). Various characterization methods were adopted in order to investigate the surface characteristics of different [...] Read more.
To promote the adsorption and activation of carbon dioxide in the dry reforming of methane (DRM), Ni and Al2O3 were coprecipitated on activated carbon fibers (ACF). Various characterization methods were adopted in order to investigate the surface characteristics of different catalysts. Chemisorption characterization results, such as H2-temperature programmed reduction (H2-TPR), H2-temperature programmed desorption (H2-TPD), and CO2-temperature programmed desorption (CO2-TPD) illustrated that ACF in a nickel-based catalyst could enhance the basic sites and improve the metal dispersion on a catalyst surface, which is beneficial for the adsorption and activation of feed gas. The coprecipitated coating on ACF proved by scanning electron microscope (SEM) can prevent the carbon of ACF from participating in the reaction, while retain good surface properties of carbon fibers. X-ray diffraction (XRD) patterns illustrated that the ACF in a nickel-based catalyst could decrease the crystallite size of the spinel NiAl2O4, which is beneficial for methane reforming. In addition, the Fourier transform infrared spectroscopy (FTIR) of different catalysts revealed that the added ACF could provide abundant functional groups on the surface, which could be the intermediate product of DRM, and effectively promote the reaction. Different to the catalyst supported on single alumina, the performance evaluation and stability test proved that the catalyst added with ACF exhibited a better catalytic performance especially for CO2 conversion. Moreover, based on the characterization results as well as some related literature, the dry reforming mechanism over optimum catalyst was derived. Full article
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41 pages, 10858 KiB  
Review
Earth-Abundant Electrocatalysts in Proton Exchange Membrane Electrolyzers
by Xinwei Sun, Kaiqi Xu, Christian Fleischer, Xin Liu, Mathieu Grandcolas, Ragnar Strandbakke, Tor S. Bjørheim, Truls Norby and Athanasios Chatzitakis
Catalysts 2018, 8(12), 657; https://doi.org/10.3390/catal8120657 - 13 Dec 2018
Cited by 66 | Viewed by 10005
Abstract
In order to adopt water electrolyzers as a main hydrogen production system, it is critical to develop inexpensive and earth-abundant catalysts. Currently, both half-reactions in water splitting depend heavily on noble metal catalysts. This review discusses the proton exchange membrane (PEM) water electrolysis [...] Read more.
In order to adopt water electrolyzers as a main hydrogen production system, it is critical to develop inexpensive and earth-abundant catalysts. Currently, both half-reactions in water splitting depend heavily on noble metal catalysts. This review discusses the proton exchange membrane (PEM) water electrolysis (WE) and the progress in replacing the noble-metal catalysts with earth-abundant ones. The efforts within this field for the discovery of efficient and stable earth-abundant catalysts (EACs) have increased exponentially the last few years. The development of EACs for the oxygen evolution reaction (OER) in acidic media is particularly important, as the only stable and efficient catalysts until now are noble-metal oxides, such as IrOx and RuOx. On the hydrogen evolution reaction (HER) side, there is significant progress on EACs under acidic conditions, but there are very few reports of these EACs employed in full PEM WE cells. These two main issues are reviewed, and we conclude with prospects for innovation in EACs for the OER in acidic environments, as well as with a critical assessment of the few full PEM WE cells assembled with EACs. Full article
(This article belongs to the Special Issue Catalysts for Polymer Membrane Fuel Cells)
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14 pages, 2460 KiB  
Article
Increased Aromatics Formation by the Use of High-Density Polyethylene on the Catalytic Pyrolysis of Mandarin Peel over HY and HZSM-5
by Young-Kwon Park, Muhammad Zain Siddiqui, Yejin Kang, Atsushi Watanabe, Hyung Won Lee, Sang Jae Jeong, Seungdo Kim and Young-Min Kim
Catalysts 2018, 8(12), 656; https://doi.org/10.3390/catal8120656 - 12 Dec 2018
Cited by 15 | Viewed by 4280
Abstract
High-density polyethylene (HDPE) was co-fed into the catalytic pyrolysis (CP) of mandarin peel (MP) over different microporous catalysts, HY and HZSM-5, with different pore and acid properties. Although the non-catalytic decomposition temperature of MP was not changed during catalytic thermogravimetric analysis over both [...] Read more.
High-density polyethylene (HDPE) was co-fed into the catalytic pyrolysis (CP) of mandarin peel (MP) over different microporous catalysts, HY and HZSM-5, with different pore and acid properties. Although the non-catalytic decomposition temperature of MP was not changed during catalytic thermogravimetric analysis over both catalysts, that of HDPE was reduced from 465 °C to 379 °C over HY and to 393 °C over HZSM-5 because of their catalytic effects. When HDPE was co-pyrolyzed with MP over the catalysts, the catalytic decomposition temperatures of HDPE were increased to 402 °C over HY and 408 °C over HZSM-5. The pyrolyzer-gas chromatography/mass spectrometry results showed that the main pyrolyzates of MP and HDPE, which comprised a large amount of oxygenates and aliphatic hydrocarbons with a wide carbon range, were converted efficiently to aromatics using HY and HZSM-5. Although HY can provide easier diffusion of the reactants to the catalyst pore and a larger amount of acid sites than HZSM-5, the CP of MP, HDPE, and their mixture over HZSM-5 revealed higher efficiency on aromatics formation than those over HY due to the strong acidity and more appropriate shape selectivity of HZSM-5. The production of aromatics from the catalytic co-pyrolysis of MP and HDPE was larger than the theoretical amounts, suggesting the synergistic effect of HDPE co-feeding for the increased formation of aromatics during the CP of MP. Full article
(This article belongs to the Special Issue Catalytic Fast Pyrolysis)
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19 pages, 5693 KiB  
Review
Photocatalytic Hydrogen Evolution via Water Splitting: A Short Review
by Yifan Zhang, Young-Jung Heo, Ji-Won Lee, Jong-Hoon Lee, Johny Bajgai, Kyu-Jae Lee and Soo-Jin Park
Catalysts 2018, 8(12), 655; https://doi.org/10.3390/catal8120655 - 12 Dec 2018
Cited by 51 | Viewed by 14421
Abstract
Photocatalytic H2 generation via water splitting is increasingly gaining attention as a viable alternative for improving the performance of H2 production for solar energy conversion. Many methods were developed to enhance photocatalyst efficiency, primarily by modifying its morphology, crystallization, and electrical [...] Read more.
Photocatalytic H2 generation via water splitting is increasingly gaining attention as a viable alternative for improving the performance of H2 production for solar energy conversion. Many methods were developed to enhance photocatalyst efficiency, primarily by modifying its morphology, crystallization, and electrical properties. Here, we summarize recent achievements in the synthesis and application of various photocatalysts. The rational design of novel photocatalysts was achieved using various strategies, and the applications of novel materials for H2 production are displayed herein. Meanwhile, the challenges and prospects for the future development of H2-producing photocatalysts are also summarized. Full article
(This article belongs to the Special Issue Photocatalytic Hydrogen Evolution)
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15 pages, 1847 KiB  
Article
Application of Uniform Design Method in the Optimization of Hydrothermal Synthesis for Nano MoS2 Catalyst with High HDS Activity
by Haiping Zhang, Hongfei Lin and Ying Zheng
Catalysts 2018, 8(12), 654; https://doi.org/10.3390/catal8120654 - 12 Dec 2018
Cited by 9 | Viewed by 3403
Abstract
The optimization of catalyst synthesis conditions using traditional single factor method involves extensive experimental time and costs. To overcome the drawbacks, a uniform design method was applied in the hydrothermal synthesis of nano MoS2 catalyst. An optimal synthesis condition is reached with [...] Read more.
The optimization of catalyst synthesis conditions using traditional single factor method involves extensive experimental time and costs. To overcome the drawbacks, a uniform design method was applied in the hydrothermal synthesis of nano MoS2 catalyst. An optimal synthesis condition is reached with only a few trials. Catalyst synthesis temperature is reduced to 200 °C. The catalyst synthesized at the screened condition shows high hydrotreating activities. The results conclude that the catalyst has thread-like slabs with a lattice structure that is less mature than fully developed MoS2. The characterization results indicate that the appearance of such structure may be due to the weak links of successive MoS2 nuclei. The high catalytic activity is a result of the layered structure and a significantly large number of defects on the slabs. Full article
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21 pages, 6167 KiB  
Article
9,10-Phenanthrenedione as Visible-Light Photoredox Catalyst: A Green Methodology for the Functionalization of 3,4-Dihydro-1,4-Benzoxazin-2-Ones through a Friedel-Crafts Reaction
by Jaume Rostoll-Berenguer, Gonzalo Blay, José R. Pedro and Carlos Vila
Catalysts 2018, 8(12), 653; https://doi.org/10.3390/catal8120653 - 12 Dec 2018
Cited by 16 | Viewed by 5336
Abstract
A visible-light photoredox functionalization of 3,4-dihydro-1,4-benzoxazin-2-ones through a Friedel-Crafts reaction with indoles using an inexpensive organophotoredox catalyst is described. The reaction uses a dual catalytic system that is formed by a photocatalyst simple and cheap, 9,10-phenanthrenedione, and a Lewis acid, Zn(OTf)2. [...] Read more.
A visible-light photoredox functionalization of 3,4-dihydro-1,4-benzoxazin-2-ones through a Friedel-Crafts reaction with indoles using an inexpensive organophotoredox catalyst is described. The reaction uses a dual catalytic system that is formed by a photocatalyst simple and cheap, 9,10-phenanthrenedione, and a Lewis acid, Zn(OTf)2. 5W white LEDs are used as visible-light source and oxygen from air as a terminal oxidant, obtaining the corresponding products with good yields. The reaction can be extended to other electron-rich arenes. Our methodology represents one of the most valuable and sustainable approach for the functionalization of 3,4-dihydro-1,4-benzoxazin-2-ones, as compared to the reported procedures. Furthermore, several transformations were carried out, such as the synthesis of the natural product cephalandole A and a tryptophol derivative. Full article
(This article belongs to the Special Issue Photocatalytic Organic Synthesis)
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13 pages, 2694 KiB  
Article
Efficient Reduction of Bromate by Iodide-Assisted UV/Sulfite Process
by Tuqiao Zhang, Jiajie Wang, Dingyun Yan, Lili Wang and Xiaowei Liu
Catalysts 2018, 8(12), 652; https://doi.org/10.3390/catal8120652 - 11 Dec 2018
Cited by 18 | Viewed by 4779
Abstract
Bromate ( BrO 3 − ) residue in drinking water poses a great health risk. Ultra-fast reduction of BrO 3 − , under aerobic conditions, was realized using an ultraviolet (UV)/sulfite process in the presence of iodide (UV/sulfite/iodide). The UV/sulfite/iodide process produced [...] Read more.
Bromate ( BrO 3 − ) residue in drinking water poses a great health risk. Ultra-fast reduction of BrO 3 − , under aerobic conditions, was realized using an ultraviolet (UV)/sulfite process in the presence of iodide (UV/sulfite/iodide). The UV/sulfite/iodide process produced BrO 3 − removal efficiency of 100% at about 5 min with complete conversion to bromide, while UV/sulfite induced 13.1% BrO 3 − reduction under the same conditions. Hydrated electrons, generated from the photolysis of sulfite and iodide, was confirmed as the main contributor to BrO 3 − degradation (77.4% of the total contribution). As the concentration of iodide was kept constant, its presence remarkably enhancing the generation of hydrated electrons led to its consideration as a homogeneous catalyst in the UV/sulfite/iodide system. Sulfite played a role not only as a hydrated electron precursor, but also as a reactive iodine species shielding agent and a regenerant of iodide. Results surrounding the effects on common water quality parameters (pH, bicarbonate, nitrate, natural organic matter, and solution temperature) indicated that preferred degradation of BrO 3 − occurred in an environment of alkaline pH, low-content natural organic matter/bicarbonate/nitrate, and high natural temperature. Full article
(This article belongs to the Section Photocatalysis)
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36 pages, 4061 KiB  
Review
Catalytic Tuning of Sorption Kinetics of Lightweight Hydrides: A Review of the Materials and Mechanism
by Ankur Jain, Shivani Agarwal and Takayuki Ichikawa
Catalysts 2018, 8(12), 651; https://doi.org/10.3390/catal8120651 - 11 Dec 2018
Cited by 42 | Viewed by 5786
Abstract
Hydrogen storage materials have been a subject of intensive research during the last 4 decades. Several developments have been achieved in regard of finding suitable materials as per the US-DOE targets. While the lightweight metal hydrides and complex hydrides meet the targeted hydrogen [...] Read more.
Hydrogen storage materials have been a subject of intensive research during the last 4 decades. Several developments have been achieved in regard of finding suitable materials as per the US-DOE targets. While the lightweight metal hydrides and complex hydrides meet the targeted hydrogen capacity, these possess difficulties of hard thermodynamics and sluggish kinetics of hydrogen sorption. A number of methods have been explored to tune the thermodynamic and kinetic properties of these materials. The thermodynamic constraints could be resolved using an intermediate step of alloying or by making reactive composites with other hydrogen storage materials, whereas the sluggish kinetics could be improved using several approaches such as downsizing and the use of catalysts. The catalyst addition reduces the activation barrier and enhances the sorption rate of hydrogen absorption/desorption. In this review, the catalytic modifications of lightweight hydrogen storage materials are reported and the mechanism towards the improvement is discussed. Full article
(This article belongs to the Section Catalytic Materials)
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14 pages, 1058 KiB  
Review
Methanol-Tolerant M–N–C Catalysts for Oxygen Reduction Reactions in Acidic Media and Their Application in Direct Methanol Fuel Cells
by Carmelo Lo Vecchio, David Sebastián, María Jesús Lázaro, Antonino Salvatore Aricò and Vincenzo Baglio
Catalysts 2018, 8(12), 650; https://doi.org/10.3390/catal8120650 - 11 Dec 2018
Cited by 36 | Viewed by 5607
Abstract
Direct methanol fuel cells (DMFCs) are emerging technologies for the electrochemical conversion of the chemical energy of a fuel (methanol) directly into electrical energy, with a low environmental impact and high efficiency. Yet, before this technology can reach a large-scale diffusion, specific issues [...] Read more.
Direct methanol fuel cells (DMFCs) are emerging technologies for the electrochemical conversion of the chemical energy of a fuel (methanol) directly into electrical energy, with a low environmental impact and high efficiency. Yet, before this technology can reach a large-scale diffusion, specific issues must be solved, in particular, the high cost of the cell components. In a direct methanol fuel cell system, high capital costs are mainly derived from the use of noble metal catalysts; therefore, the development of low-cost electro-catalysts, satisfying the target requirements of high performance and durability, represents an important challenge. The research is currently addressed to the development of metal–nitrogen–carbon (M–N–C) materials as cheap and sustainable catalysts for the oxygen reduction reaction (ORR) in an acid environment, for application in polymer electrolyte fuel cells fueled by hydrogen or alcohol. In particular, this mini-review summarizes the recent advancements achieved in DMFCs using M–N–C catalysts. The presented analysis is restricted to M–N–C catalysts mounted at the cathode of a DMFC or investigated in rotating disk electrode (RDE) configuration for the ORR in the presence of methanol in order to study alcohol tolerance. The main synthetic routes and characteristics of the catalysts are also presented. Full article
(This article belongs to the Special Issue Platinum-Free Electrocatalysts)
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8 pages, 3028 KiB  
Article
Electrochemical Oxidation of Amines Using a Nitroxyl Radical Catalyst and the Electroanalysis of Lidocaine
by Katsuhiko Sato, Tetsuya Ono, Yusuke Sasano, Fumiya Sato, Masayuki Kumano, Kentaro Yoshida, Takenori Dairaku, Yoshiharu Iwabuchi and Yoshitomo Kashiwagi
Catalysts 2018, 8(12), 649; https://doi.org/10.3390/catal8120649 - 10 Dec 2018
Cited by 19 | Viewed by 6186
Abstract
The nitroxyl radical of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) can electro-oxidize not only alcohols but also amines. However, TEMPO has low activity in a neutral aqueous solution due to the large steric hindrance around the nitroxyl radical, which is the active site. Therefore, nortropine N [...] Read more.
The nitroxyl radical of 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) can electro-oxidize not only alcohols but also amines. However, TEMPO has low activity in a neutral aqueous solution due to the large steric hindrance around the nitroxyl radical, which is the active site. Therefore, nortropine N-oxyl (NNO) was synthesized to improve the catalytic ability of TEMPO and to investigate the electrolytic oxidation effect on amines from anodic current changes. Ethylamine, diethylamine, triethylamine, tetraethylamine, isopropylamine, and tert-butylamine were investigated. The results indicated that TEMPO produced no response current for any of the amines under physiological conditions; however, NNO did function as an electrolytic oxidation catalyst for diethylamine, triethylamine, and isopropylamine. The anodic current depended on amine concentration, which suggests that NNO can be used as an electrochemical sensor for amine compounds. In addition, electrochemical detection of lidocaine, a local anesthetic containing a tertiary amine structure, was demonstrated using NNO with a calibration curve of 0.1–10 mM. Full article
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10 pages, 2290 KiB  
Article
Theoretical Study on the Mechanism of Hydrogen Donation and Transfer for Hydrogen-Donor Solvents during Direct Coal Liquefaction
by Haigang Hao, Tong Chang, Linxia Cui, Ruiqing Sun and Rui Gao
Catalysts 2018, 8(12), 648; https://doi.org/10.3390/catal8120648 - 10 Dec 2018
Cited by 25 | Viewed by 4625
Abstract
As a country that is poor in petroleum yet rich in coal, it is significant for China to develop direct coal liquefaction (DCL) technology to relieve the pressure from petroleum shortages to guarantee national energy security. To improve the efficiency of the direct [...] Read more.
As a country that is poor in petroleum yet rich in coal, it is significant for China to develop direct coal liquefaction (DCL) technology to relieve the pressure from petroleum shortages to guarantee national energy security. To improve the efficiency of the direct coal liquefaction process, scientists and researchers have made great contributions to studying and developing highly efficient hydrogen donor (H-donor) solvents. Nevertheless, the details of hydrogen donation and the transfer pathways of H-donor solvents are still unclear. The present work examined hydrogen donation and transfer pathways using a model H-donor solvent, tetralin, by density functional theory (DFT) calculation. The reaction condition and state of the solvent (gas or liquid) were considered, and the specific elementary reaction routes for hydrogen donation and transfer were calculated. In the DCL process, the dominant hydrogen donation mechanism was the concerted mechanism. The sequence of tetralin donating hydrogen atoms was α-H (C1–H) > δ-H (C4–H) > β-H (C2–H) > γ-H (C3–H). Compared to methyl, it was relatively hard for benzyl to obtain the first hydrogen atom from tetralin, while it was relatively easy to obtain the second and third hydrogen atoms from tetralin. Comparatively, it was easier for coal radicals to capture hydrogen atoms from the H-donor solvent than to obtain hydrogen atoms from hydrogen gas. Full article
(This article belongs to the Special Issue DFT and Catalysis)
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19 pages, 11119 KiB  
Article
Ag/Ag2O as a Co-Catalyst in TiO2 Photocatalysis: Effect of the Co-Catalyst/Photocatalyst Mass Ratio
by Soukaina Akel, Ralf Dillert, Narmina O. Balayeva, Redouan Boughaled, Julian Koch, Mohammed El Azzouzi and Detlef W. Bahnemann
Catalysts 2018, 8(12), 647; https://doi.org/10.3390/catal8120647 - 10 Dec 2018
Cited by 64 | Viewed by 7509
Abstract
Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites [...] Read more.
Mixtures and composites of Ag/Ag2O and TiO2 (P25) with varying mass ratios of Ag/Ag2O were prepared, employing two methods. Mechanical mixtures (TM) were obtained by the sonication of a suspension containing TiO2 and Ag/Ag2O. Composites (TC) were prepared by a precipitation method employing TiO2 and AgNO3. Powder X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) confirmed the presence of Ag(0) and Ag2O. The activity of the materials was determined employing methylene blue (MB) as the probe compound. Bleaching of MB was observed in the presence of all materials. The bleaching rate was found to increase with increasing amounts of TiO2 under UV/vis light. In contrast, the MB bleaching rate decreased with increasing TiO2 content upon visible light illumination. XRD and XPS data indicate that Ag2O acts as an electron acceptor in the light-induced reaction of MB and is transformed by reduction of Ag+, yielding Ag(0). As a second light-induced reaction, the evolution of molecular hydrogen from aqueous methanol was investigated. Significant H2 evolution rates were only determined in the presence of materials containing more than 50 mass% of TiO2. The experimental results suggest that Ag/Ag2O is not stable under the experimental conditions. Therefore, to address Ag/Ag2O as a (photo)catalytically active material does not seem appropriate. Full article
(This article belongs to the Special Issue New Trends in Photo(Electro)catalysis: From Wastewater Treatment to Energy Production)
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15 pages, 5521 KiB  
Article
Mn Modified Ni/Bentonite for CO2 Methanation
by Yuexiu Jiang, Tongxia Huang, Lihui Dong, Tongming Su, Bin Li, Xuan Luo, Xinling Xie, Zuzeng Qin, Cuixia Xu and Hongbing Ji
Catalysts 2018, 8(12), 646; https://doi.org/10.3390/catal8120646 - 10 Dec 2018
Cited by 30 | Viewed by 5471
Abstract
To enhance the low-temperature catalytic activity and stability of Ni/bentonite catalyst, Ni-Mn/bentonite catalyst was prepared by introducing Mn into Ni/bentonite catalyst and was used for CO2 methanation. The results indicated that the addition of Mn enhanced the interaction between the NiO and [...] Read more.
To enhance the low-temperature catalytic activity and stability of Ni/bentonite catalyst, Ni-Mn/bentonite catalyst was prepared by introducing Mn into Ni/bentonite catalyst and was used for CO2 methanation. The results indicated that the addition of Mn enhanced the interaction between the NiO and the bentonite carrier, increased the dispersion of the active component Ni and decreased the grain size of the active component Ni, increased the specific surface area and pore volume of the Ni/bentonite catalyst, and decreased the average pore size, which suppressed the aggregation of Ni particles grown during the CO2 methanation process. At the same time, the Mn addition increased the amount of oxygen vacancies on the Ni/bentonite catalyst surface, which promoted the activation of CO2 in the methanation reaction, increasing the low-temperature activity and stability of the Ni/bentonite catalyst. Under the reaction condition of atmospheric pressure, 270 °C, V(H2):V(CO2) = 4, and feed gas space velocity of 3600 mL·gcat−1·h−1, the CO2 conversion on the Ni-Mn/bentonite catalyst with 2wt% Mn was 85.2%, and the selectivity of CH4 was 99.8%. On the other hand, when Mn was not added, the CO2 conversion reached 84.7% and the reaction temperature only raised to 300 °C. During a 150-h stability test, the CO2 conversion of Ni-2wt%Mn/bentonite catalyst decreased by 2.2%, while the CO2 conversion of the Ni/bentonite catalyst decreased by 6.4%. Full article
(This article belongs to the Special Issue Supported Catalysts for Carbon Oxides Methanation)
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19 pages, 4848 KiB  
Article
Hydrotreatment Followed by Oxidative Desulfurization and Denitrogenation to Attain Low Sulphur and Nitrogen Bitumen Derived Gas Oils
by Sandeep Badoga, Prachee Misra, Girish Kamath, Ying Zheng and Ajay K. Dalai
Catalysts 2018, 8(12), 645; https://doi.org/10.3390/catal8120645 - 10 Dec 2018
Cited by 13 | Viewed by 6209
Abstract
To lower the sulphur content below 500 ppm and to increase the quality of bitumen derived heavy oil, a combination of hydrotreating followed by oxidative desulfurization (ODS) and oxidative denitrogenation (ODN) is proposed in this work. NiMo/γ-Al2O3 catalyst was synthesized [...] Read more.
To lower the sulphur content below 500 ppm and to increase the quality of bitumen derived heavy oil, a combination of hydrotreating followed by oxidative desulfurization (ODS) and oxidative denitrogenation (ODN) is proposed in this work. NiMo/γ-Al2O3 catalyst was synthesized and used to hydrotreat heavy gas oil (HGO) and light gas oil (LGO) at typical operating conditions of 370–390 °C, 9 MPa, 1–1.5 h−1 space velocity and 600:1 H2 to oil ratio. γ-Alumina and alumina-titania supported Mo, P, Mn and W catalysts were synthesized and characterized using X-ray diffractions, N2 adsorption-desorption using Brunauer–Emmett–Teller (BET) method, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR). All catalysts were tested for the oxidation of sulphur and nitrogen aromatic compounds present in LGO and HGO using tert-butyl hydroperoxide (TBHP) as oxidant. The oxidized sulphur and nitrogen compounds were extracted using adsorption on activated carbon and liquid-liquid extraction using methanol. The determination of oxidation states of each metal using XPS confirmed the structure of metal oxides in the catalyst. Thus, the catalytic activity determined in terms of sulphur and nitrogen removal is related to their physico-chemical properties. In agreement with literature, a simplistic mechanism for the oxidative desulfurization is also presented. Mo was found to be more active in comparison to W. Presence of Ti in the support has shown 8–12% increase in ODS and ODN. The MnPMo/γ-Al2O3-TiO2 catalyst showed the best activity for sulphur and nitrogen removal. The role of Mn and P as promoters to molybdenum was also discussed. Further three-stage ODS and ODN was performed to achieve less than 500 ppm in HGO and LGO. The combination of hydrotreatment, ODS and ODN has resulted in removal of 98.8 wt.% sulphur and 94.7 wt.% nitrogen from HGO and removal of 98.5 wt.% sulphur and 97.8 wt.% nitrogen from LGO. Full article
(This article belongs to the Special Issue Catalysis for the Production of Sustainable Fuels and Chemicals)
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14 pages, 1463 KiB  
Article
Effect of Additives on the Activity of Nickel–Tungsten Sulfide Hydroconversion Catalysts Prepared In Situ from Oil-Soluble Precursors
by Mariia Kniazeva and Anton Maximov
Catalysts 2018, 8(12), 644; https://doi.org/10.3390/catal8120644 - 10 Dec 2018
Cited by 17 | Viewed by 3742
Abstract
The nickel–tungsten sulfide catalysts for the hydroconversion of hydrocarbons were prepared from oil-soluble nickel and tungsten precursor compounds in situ with the use of silica, alumina, titania, zeolite Y, and amorphous aluminosilicate as additives in a vacuum gas oil medium. It was found [...] Read more.
The nickel–tungsten sulfide catalysts for the hydroconversion of hydrocarbons were prepared from oil-soluble nickel and tungsten precursor compounds in situ with the use of silica, alumina, titania, zeolite Y, and amorphous aluminosilicate as additives in a vacuum gas oil medium. It was found that the catalytic activity in hydrocracking depends on the concentration of acid sites in the resulting catalyst. With the use of oxide additives, the dispersion and the promoter ratio of the in situ formed sulfide particles increased in the order SiO2–Al2O3–TiO2. It was noted that the promoter ratio of sulfide particles obtained with the use of aluminosilicate additives depended on their porous structure peculiarities. The use of titanium dioxide as a catalytic system component made it possible to reach high activity in hydrocracking, hydrodearomatization, and hydrodesulfurization, which was comparable to that of a system based on zeolite Y, a highly acidic component. Full article
(This article belongs to the Section Nanostructured Catalysts)
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