Catalysts

8601 KiB

Open AccessArticle

Sacrificial Template-Based Synthesis of Unified Hollow Porous Palladium Nanospheres for Formic Acid Electro-Oxidation

by Xiaoyu Qiu, Hanyue Zhang, Yuxuan Dai, Fengqi Zhang, Peishan Wu, Pin Wu and Yawen Tang

Catalysts 2015, 5(2), 992-1002; https://doi.org/10.3390/catal5020992 - 23 Jun 2015

Cited by 18 | Viewed by 6694

Large scale syntheses of uniform metal nanoparticles with hollow porous structure have attracted much attention owning to their high surface area, abundant active sites and relatively efficient catalytic activity. Herein, we report a general method to synthesize hollow porous Pd nanospheres (Pd HPNSs) [...] Read more.

Large scale syntheses of uniform metal nanoparticles with hollow porous structure have attracted much attention owning to their high surface area, abundant active sites and relatively efficient catalytic activity. Herein, we report a general method to synthesize hollow porous Pd nanospheres (Pd HPNSs) by templating sacrificial SiO₂ nanoparticles with the assistance of polyallylamine hydrochloride (PAH) through layer-by-layer self-assembly. The chemically inert PAH is acting as an efficient stabilizer and complex agent to control the synthesis of Pd HPNSs, probably accounting for its long aliphatic alkyl chains, excellent coordination capability and good hydrophilic property. The physicochemical properties of Pd HPNSs are thoroughly characterized by various techniques, such as transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy. The growth mechanism of Pd HPNSs is studied based on the analysis of diverse experimental observations. The as-prepared Pd HPNSs exhibit clearly enhanced electrocatalytic activity and durability for the formic oxidation reaction (FAOR) in acid medium compared with commercial Pd black. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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628 KiB

Open AccessArticle

Phosphorus and Nitrogen Dual Doped and Simultaneously Reduced Graphene Oxide with High Surface Area as Efficient Metal-Free Electrocatalyst for Oxygen Reduction

by Xiaochang Qiao, Shijun Liao, Chenghang You and Rong Chen

Catalysts 2015, 5(2), 981-991; https://doi.org/10.3390/catal5020981 - 23 Jun 2015

Cited by 121 | Viewed by 13922

Abstract

A P, N dual doped reduced graphene oxide (PN-rGO) catalyst with high surface area (376.20 m²·g⁻¹), relatively high P-doping level (1.02 at. %) and a trace amount of N (0.35 at. %) was successfully prepared using a one-step method [...] Read more.

A P, N dual doped reduced graphene oxide (PN-rGO) catalyst with high surface area (376.20 m²·g⁻¹), relatively high P-doping level (1.02 at. %) and a trace amount of N (0.35 at. %) was successfully prepared using a one-step method by directly pyrolyzing a homogenous mixture of graphite oxide (GO) and diammonium hydrogen phosphate ((NH₄)₂HPO₄) in an argon atmosphere, during which the thermal expansion, deoxidization of GO and P, N co-doping were realized simultaneously. The catalyst exhibited enhanced catalytic performances for oxygen reduction reaction (ORR) via a dominated four-electron reduction pathway, as well as superior long-term stability, better tolerance to methanol crossover than that of commercial Pt/C catalyst in an alkaline solution. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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733 KiB

Open AccessArticle

Oxygen Reduction Reaction Activity and Durability of Pt Catalysts Supported on Titanium Carbide

by Morio Chiwata, Katsuyoshi Kakinuma, Mitsuru Wakisaka, Makoto Uchida, Shigehito Deki, Masahiro Watanabe and Hiroyuki Uchida

Catalysts 2015, 5(2), 966-980; https://doi.org/10.3390/catal5020966 - 23 Jun 2015

Cited by 46 | Viewed by 8268

Abstract

We have prepared Pt nanoparticles supported on titanium carbide (TiC) (Pt/TiC) as an alternative cathode catalyst with high durability at high potentials for polymer electrolyte fuel cells. The Pt/TiC catalysts with and without heat treatment were characterized by X-ray diffraction (XRD), X-ray photoelectron [...] Read more.

We have prepared Pt nanoparticles supported on titanium carbide (TiC) (Pt/TiC) as an alternative cathode catalyst with high durability at high potentials for polymer electrolyte fuel cells. The Pt/TiC catalysts with and without heat treatment were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM). Hemispherical Pt nanocrystals were found to be dispersed uniformly on the TiC support after heat treatment at 600 °C in 1% H₂/N₂ (Pt/TiC-600 °C). The electrochemical properties (cyclic voltammetry, electrochemically active area (ECA), and oxygen reduction reaction (ORR) activity) of Pt/TiC-600 °C and a commercial Pt/carbon black (c-Pt/CB) were evaluated by the rotating disk electrode (RDE) technique in 0.1 M HClO₄ solution at 25 °C. It was found that the kinetically controlled mass activity for the ORR on Pt/TiC-600 °C at 0.85 V (507 A g⁻¹) was comparable to that of c-Pt/CB (527 A g⁻¹). Moreover, the durability of Pt/TiC-600 °C examined by a standard potential step protocol (E = 0.9 V↔1.3 V vs. RHE, holding 30 s at each E) was much higher than that for c-Pt/CB. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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3813 KiB

Open AccessArticle

Highly Active Non-PGM Catalysts Prepared from Metal Organic Frameworks

by Heather M. Barkholtz, Lina Chong, Zachary B. Kaiser, Tao Xu and Di-Jia Liu

Catalysts 2015, 5(2), 955-965; https://doi.org/10.3390/catal5020955 - 11 Jun 2015

Cited by 34 | Viewed by 7586

Abstract

Finding inexpensive alternatives to platinum group metals (PGMs) is essential for reducing the cost of proton exchange membrane fuel cells (PEMFCs). Numerous materials have been investigated as potential replacements of Pt, of which the transition metal and nitrogen-doped carbon composites (TM/N_x/C) [...] Read more.

Finding inexpensive alternatives to platinum group metals (PGMs) is essential for reducing the cost of proton exchange membrane fuel cells (PEMFCs). Numerous materials have been investigated as potential replacements of Pt, of which the transition metal and nitrogen-doped carbon composites (TM/N_x/C) prepared from iron doped zeolitic imidazolate frameworks (ZIFs) are among the most active ones in catalyzing the oxygen reduction reaction based on recent studies. In this report, we demonstrate that the catalytic activity of ZIF-based TM/N_x/C composites can be substantially improved through optimization of synthesis and post-treatment processing conditions. Ultimately, oxygen reduction reaction (ORR) electrocatalytic activity must be demonstrated in membrane-electrode assemblies (MEAs) of fuel cells. The process of preparing MEAs using ZIF-based non-PGM electrocatalysts involves many additional factors which may influence the overall catalytic activity at the fuel cell level. Evaluation of parameters such as catalyst loading and perfluorosulfonic acid ionomer to catalyst ratio were optimized. Our overall efforts to optimize both the catalyst and MEA construction process have yielded impressive ORR activity when tested in a fuel cell system. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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224 KiB

Open AccessEditorial

Advances in Catalyst Deactivation and Regeneration

by Calvin H. Bartholomew and Morris D. Argyle

Catalysts 2015, 5(2), 949-954; https://doi.org/10.3390/catal5020949 - 11 Jun 2015

Cited by 30 | Viewed by 6809

Abstract

Catalyst deactivation, the loss over time of catalytic activity and/or selectivity, is a problem of great and continuing concern in the practice of industrial catalytic processes. Costs to industry for catalyst replacement and process shutdown total tens of billions of dollars per [...] Read more.

Catalyst deactivation, the loss over time of catalytic activity and/or selectivity, is a problem of great and continuing concern in the practice of industrial catalytic processes. Costs to industry for catalyst replacement and process shutdown total tens of billions of dollars per year. [...] Full article

(This article belongs to the Special Issue Advances in Catalyst Deactivation)

6779 KiB

Open AccessArticle

Effect of Particle Size and Operating Conditions on Pt₃Co PEMFC Cathode Catalyst Durability

by Mallika Gummalla, Sarah C. Ball, David A. Condit, Somaye Rasouli, Kang Yu, Paulo J. Ferreira, Deborah J. Myers and Zhiwei Yang

Catalysts 2015, 5(2), 926-948; https://doi.org/10.3390/catal5020926 - 29 May 2015

Cited by 57 | Viewed by 9338

Abstract

The initial performance and decay trends of polymer electrolyte membrane fuel cells (PEMFC) cathodes with Pt₃Co catalysts of three mean particle sizes (4.9 nm, 8.1 nm, and 14.8 nm) with identical Pt loadings are compared. Even though the cathode based on [...] Read more.

The initial performance and decay trends of polymer electrolyte membrane fuel cells (PEMFC) cathodes with Pt₃Co catalysts of three mean particle sizes (4.9 nm, 8.1 nm, and 14.8 nm) with identical Pt loadings are compared. Even though the cathode based on 4.9 nm catalyst exhibited the highest initial electrochemical surface area (ECA) and mass activity, the cathode based on 8.1 nm catalyst showed better initial performance at high currents. Owing to the low mass activity of the large particles, the initial performance of the 14.8 nm Pt₃Co-based electrode was the lowest. The performance decay rate of the electrodes with the smallest Pt₃Co particle size was the highest and that of the largest Pt₃Co particle size was lowest. Interestingly, with increasing number of decay cycles (0.6 to 1.0 V, 50 mV/s), the relative improvement in performance of the cathode based on 8.1 nm Pt₃Co over the 4.9 nm Pt₃Co increased, owing to better stability of the 8.1 nm catalyst. The electron microprobe analysis (EMPA) of the decayed membrane-electrode assembly (MEA) showed that the amount of Co in the membrane was lower for the larger particles, and the platinum loss into the membrane also decreased with increasing particle size. This suggests that the higher initial performance at high currents with 8.1 nm Pt₃Co could be due to lower contamination of the ionomer in the electrode. Furthermore, lower loss of Co from the catalyst with increased particle size could be one of the factors contributing to the stability of ECA and mass activity of electrodes with larger cathode catalyst particles. To delineate the impact of particle size and alloy effects, these results are compared with prior work from our research group on size effects of pure platinum catalysts. The impact of PEMFC operating conditions, including upper potential, relative humidity, and temperature on the alloy catalyst decay trends, along with the EMPA analysis of the decayed MEAs, are reported. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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3002 KiB

Open AccessArticle

Oxygen Storage Capacity and Oxygen Mobility of Co-Mn-Mg-Al Mixed Oxides and Their Relation in the VOC Oxidation Reaction

by María Haidy Castaño, Rafael Molina and Sonia Moreno

Catalysts 2015, 5(2), 905-925; https://doi.org/10.3390/catal5020905 - 29 May 2015

Cited by 17 | Viewed by 7251

Abstract

Co-Mn-Mg-Al oxides were synthesized using auto-combustion and co-precipitation techniques. Constant ratios were maintained with (Co + Mn + Mg)/Al equal to 3.0, (Co + Mn)/Mg equal to 1.0 and Co/Mn equal to 0.5. The chemical and structural composition, redox properties, oxygen storage capacity [...] Read more.

Co-Mn-Mg-Al oxides were synthesized using auto-combustion and co-precipitation techniques. Constant ratios were maintained with (Co + Mn + Mg)/Al equal to 3.0, (Co + Mn)/Mg equal to 1.0 and Co/Mn equal to 0.5. The chemical and structural composition, redox properties, oxygen storage capacity and oxygen mobility were analyzed using X-ray fluorescence (XRF), X-ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), temperature-programmed reduction of hydrogen (H₂-TPR), oxygen storage capacity (OSC), oxygen storage complete capacity (OSCC) and isotopic exchange, respectively. The catalytic behavior of the oxides was evaluated in the total oxidation of a mixture of 250 ppm toluene and 250 ppm 2-propanol. The synthesis methodology affected the crystallite size, redox properties, OSC and oxide oxygen mobility, which determined the catalytic behavior. The co-precipitation method got the most active oxide in the oxidation of the volatile organic compound (VOC) mixture because of the improved mobility of oxygen and ability to favor redox processes in the material structure. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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11752 KiB

Open AccessArticle

Surface Reaction Kinetics of Steam- and CO₂-Reforming as Well as Oxidation of Methane over Nickel-Based Catalysts

by Karla Herrera Delgado, Lubow Maier, Steffen Tischer, Alexander Zellner, Henning Stotz and Olaf Deutschmann

Catalysts 2015, 5(2), 871-904; https://doi.org/10.3390/catal5020871 - 29 May 2015

Cited by 131 | Viewed by 19830

Abstract

An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions [...] Read more.

An experimental and kinetic modeling study on the Ni-catalyzed conversion of methane under oxidative and reforming conditions is presented. The numerical model is based on a surface reaction mechanism consisting of 52 elementary-step like reactions with 14 surface and six gas-phase species. Reactions for the conversion of methane with oxygen, steam, and CO₂ as well as methanation, water-gas shift reaction and carbon formation via Boudouard reaction are included. The mechanism is implemented in a one-dimensional flow field description of a fixed bed reactor. The model is evaluated by comparison of numerical simulations with data derived from isothermal experiments in a flow reactor over a powdered nickel-based catalyst using varying inlet gas compositions and operating temperatures. Furthermore, the influence of hydrogen and water as co-feed on methane dry reforming with CO₂ is also investigated. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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175 KiB

Open AccessEditorial

Metal Catalysts Recycling and Heterogeneous/Homogeneous Catalysis

by Masahiko Arai and Fengyu Zhao

Catalysts 2015, 5(2), 868-870; https://doi.org/10.3390/catal5020868 - 27 May 2015

Cited by 29 | Viewed by 6293

Abstract

Heterogeneous metal catalysts rather than homogeneous ones are recommended for industrial applications after considering their performance in activity, separation, and recycling [1]. The recycling of metal catalysts is important from economic and environmental points of view. When supported and bulk metal catalysts are [...] Read more.

Heterogeneous metal catalysts rather than homogeneous ones are recommended for industrial applications after considering their performance in activity, separation, and recycling [1]. The recycling of metal catalysts is important from economic and environmental points of view. When supported and bulk metal catalysts are used in liquid-phase organic reactions, there is a possibility that active metal species are leaching away into the liquid phases [2,3]. The metal leaching would make it difficult for the catalysts to maintain their desired initial performance for repeated batch reactions and during continuous ones. The metal leaching would also cause some undesired contamination of products by the metal species dissolved in the reaction mixture, and the separation of the metal contaminants would be required to purify the products. Therefore, various novel methods have been proposed so far to immobilize/stabilize the active metal species and to separate/collect/reuse the dissolved metal species [4]. In addition, knowledge on the heterogeneous and homogeneous natures of organic reactions using heterogeneous catalysts is important to discuss their reaction mechanisms and catalytically working active species. [...] Full article

(This article belongs to the Special Issue Metal Catalysts Recycling and Heterogeneous/Homogeneous Catalysis)

3794 KiB

Open AccessArticle

Co-Al Mixed Oxides Prepared via LDH Route Using Microwaves or Ultrasound: Application for Catalytic Toluene Total Oxidation

by Eric Genty, Julien Brunet, Christophe Poupin, Sandra Casale, Sylvie Capelle, Pascale Massiani, Stéphane Siffert and Renaud Cousin

Catalysts 2015, 5(2), 851-867; https://doi.org/10.3390/catal5020851 - 15 May 2015

Cited by 56 | Viewed by 6941

Abstract

Co₆Al₂HT hydrotalcite-like compounds were synthesized by three different methods: co-precipitation, microwaves-assisted and ultrasound-assisted methods. The mixed oxides obtained after calcination were studied by several techniques: XRD, TEM, H₂-TPR and XPS. They were also tested as catalysts in [...] Read more.

Co₆Al₂HT hydrotalcite-like compounds were synthesized by three different methods: co-precipitation, microwaves-assisted and ultrasound-assisted methods. The mixed oxides obtained after calcination were studied by several techniques: XRD, TEM, H₂-TPR and XPS. They were also tested as catalysts in the reaction of total oxidation of toluene. The physico-chemical studies revealed a modification of the structural characteristics (surface area, morphology) as well as of the reducibility of the formed mixed oxides. The solid prepared by microwaves-assisted synthesis was the most active. Furthermore, a relationship between the ratio of Co²⁺ on the surface, the reducibility of the Co-Al mixed oxide and the T₅₀ in toluene oxidation was demonstrated. This suggests a Mars Van Krevelen mechanism for toluene total oxidation on these catalysts. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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3855 KiB

Open AccessArticle

The Role of Ozone in the Reaction Mechanism of a Bare Zeolite-Plasma Hybrid System

by Yoshiyuki Teramoto, Hyun-Ha Kim, Nobuaki Negishi and Atsushi Ogata

Catalysts 2015, 5(2), 838-850; https://doi.org/10.3390/catal5020838 - 11 May 2015

Cited by 16 | Viewed by 5905

Abstract

We investigated the reaction mechanism of a metal-unloaded zeolite-plasma hybrid system for decomposition of toluene at room temperature. Short-lived radicals and fast electrons did not contribute substantially to the reaction mechanism of toluene decomposition in the zeolite-plasma hybrid system. The main factor enhancing [...] Read more.

We investigated the reaction mechanism of a metal-unloaded zeolite-plasma hybrid system for decomposition of toluene at room temperature. Short-lived radicals and fast electrons did not contribute substantially to the reaction mechanism of toluene decomposition in the zeolite-plasma hybrid system. The main factor enhancing the reaction mechanism was gas-phase O₃ directly reacting with toluene adsorbed onto the zeolite (the Eley-Rideal mechanism). CO₂ selectivity was not improved by using H-Y zeolite due to its low ability to retain the active oxygen species formed by O₃. The gas-phase O₃ reacted with adsorbed toluene to form a ring cleavage intermediate that was slowly converted into formic acid. The decomposition rate of formic acid was much lower than that of toluene on the H-Y surface. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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2667 KiB

Open AccessArticle

Electrochemical Oxidation of the Carbon Support to Synthesize Pt(Cu) and Pt-Ru(Cu) Core-Shell Electrocatalysts for Low-Temperature Fuel Cells

by Griselda Caballero-Manrique, Enric Brillas, Francesc Centellas, José Antonio Garrido, Rosa María Rodríguez and Pere-Lluís Cabot

Catalysts 2015, 5(2), 815-837; https://doi.org/10.3390/catal5020815 - 30 Apr 2015

Cited by 17 | Viewed by 8458

Abstract

The synthesis of core-shell Pt(Cu) and Pt-Ru(Cu) electrocatalysts allows for a reduction in the amount of precious metal and, as was previously shown, a better CO oxidation performance can be achieved when compared to the nanoparticulated Pt and Pt-Ru ones. In this paper, [...] Read more.

The synthesis of core-shell Pt(Cu) and Pt-Ru(Cu) electrocatalysts allows for a reduction in the amount of precious metal and, as was previously shown, a better CO oxidation performance can be achieved when compared to the nanoparticulated Pt and Pt-Ru ones. In this paper, the carbon black used as the support was previously submitted to electrochemical oxidation and characterized by XPS. The new catalysts thus prepared were characterized by HRTEM, FFT, EDX, and electrochemical techniques. Cu nanoparticles were generated by electrodeposition and were further transformed into Pt(Cu) and Pt-Ru(Cu) core-shell nanoparticles by successive galvanic exchange with Pt and spontaneous deposition of Ru species, the smallest ones being 3.3 nm in mean size. The onset potential for CO oxidation was as good as that obtained for the untreated carbon, with CO stripping peak potentials about 0.1 and 0.2 V more negative than those corresponding to Pt/C and Ru-decorated Pt/C, respectively. Carbon oxidation yielded an additional improvement in the catalyst performance, because the ECSA values for hydrogen adsorption/desorption were much higher than those obtained for the non-oxidized carbon. This suggested a higher accessibility of the Pt sites in spite of having the same nanoparticle structure and mean size. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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1541 KiB

Open AccessArticle

Non-Thermal Plasma Combined with Cordierite-Supported Mn and Fe Based Catalysts for the Decomposition of Diethylether

by Quang Hung Trinh and Young Sun Mok

Catalysts 2015, 5(2), 800-814; https://doi.org/10.3390/catal5020800 - 29 Apr 2015

Cited by 33 | Viewed by 6036

Abstract

The removal of dilute diethylether (DEE, concentration: 150 ppm) from an air stream (flow rate: 1.0 L min⁻¹) using non-thermal plasma combined with different cordierite-supported catalysts, including Mn, Fe, and mixed Mn-Fe oxides, was investigated. The experimental results showed that the [...] Read more.

The removal of dilute diethylether (DEE, concentration: 150 ppm) from an air stream (flow rate: 1.0 L min⁻¹) using non-thermal plasma combined with different cordierite-supported catalysts, including Mn, Fe, and mixed Mn-Fe oxides, was investigated. The experimental results showed that the decomposition of DEE occurred in a one-stage reactor without the positive synergy of plasma and supported catalysts, by which ca. 96% of DEE was removed at a specific input energy (SIE) of ca. 600 J L⁻¹, except when the mixed Mn-Fe/cordierite was used. Among the catalysts that were examined, Mn-Fe/cordierite, the catalyst that was the most efficient at decomposing ozone was found to negatively affect the decomposition of DEE in the one-stage reactor. However, when it was utilized as a catalyst in the post-plasma stage of a two-part hybrid reactor, in which Mn/cordierite was directly exposed to the plasma, the reactor performance in terms of DEE decomposition efficiency was improved by more than 10% at low values of SIE compared to the efficiency that was achieved without Mn-Fe/cordierite. The ozone that was formed during the plasma stage and its subsequent catalytic dissociation during the post-plasma stage to produce atomic oxygen therefore played important roles in the removal of DEE. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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2242 KiB

Open AccessReview

Coupling Noble Metals and Carbon Supports in the Development of Combustion Catalysts for the Abatement of BTX Compounds in Air Streams

by Sergio Morales-Torres, Francisco Carrasco-Marín, Agustín F. Pérez-Cadenas and Francisco José Maldonado-Hódar

Catalysts 2015, 5(2), 774-799; https://doi.org/10.3390/catal5020774 - 27 Apr 2015

Cited by 30 | Viewed by 7451

Abstract

The catalytic combustion of volatile organic compounds (VOCs) is one of the most important techniques to remove these pollutants from the air stream, but it should be carried out at the lowest possible temperature, saving energy and avoiding the simultaneous formation of nitrogen [...] Read more.

The catalytic combustion of volatile organic compounds (VOCs) is one of the most important techniques to remove these pollutants from the air stream, but it should be carried out at the lowest possible temperature, saving energy and avoiding the simultaneous formation of nitrogen oxides (NO_x). Under these experimental conditions, the chemisorption of water generated from VOCs combustion may inhibit hydrophilic catalysts. Nowadays, a wide variety of carbon materials is available to be used in catalysis. The behavior of these hydrophobic materials in the development of highly active and selective combustion catalysts is analyzed in this manuscript. The support characteristics (porosity, hydrophobicity, structure, surface chemistry, etc.) and the active phase nature (noble metals: Pt, Pd) and dispersion were analyzed by several techniques and the results correlated with the dual adsorptive and/or catalytic performance of the corresponding catalysts. The coupling of highly active phases and carbon materials (activated carbons, honeycomb coated monoliths, carbon aerogels, etc.) with tuneable physicochemical properties leads to the complete abatement of benzene, toluene and xylenes (BTX) from dilute air streams, being selectively oxidized to CO₂ at low temperatures. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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917 KiB

Open AccessArticle

Effect of Phosphine Doping and the Surface Metal State of Ni on the Catalytic Performance of Ni/Al₂O₃ Catalyst

by Xiaoru Li, Haiyang Cheng, Guanfeng Liang, Limin He, Weiwei Lin, Yancun Yu and Fengyu Zhao

Catalysts 2015, 5(2), 759-773; https://doi.org/10.3390/catal5020759 - 23 Apr 2015

Cited by 25 | Viewed by 7671

Abstract

Ni-based catalysts as replacement for noble metal catalysts are of particular interest in the catalytic conversion of biomass due to their cheap and satisfactory catalytic activity. The Ni/SiO₂ catalyst has been studied for the hydrogenolysis of glycerol, and doping with phosphorus (P) [...] Read more.

Ni-based catalysts as replacement for noble metal catalysts are of particular interest in the catalytic conversion of biomass due to their cheap and satisfactory catalytic activity. The Ni/SiO₂ catalyst has been studied for the hydrogenolysis of glycerol, and doping with phosphorus (P) found to improve the catalytic performance significantly because of the formation of Ni₂P alloys. However, in the present work we disclose a different catalytic phenomenon for the P-doped Ni/Al₂O₃ catalyst. We found that doping with P has a significant effect on the state of the active Ni species, and thus improves the selectivity to 1,2-propanediol (1,2-PDO) significantly in the hydrogenolysis of glycerol, although Ni-P alloys were not observed in our catalytic system. The structure and selectivity correlations were determined from the experimental data, combining the results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), hydrogen temperature-programmed reduction (H₂-TPR) and ammonia temperature-programmed desorption (NH₃-TPD). The presence of NiO species, formed from P-doped Ni/Al₂O₃ catalyst, was shown to benefit the formation of 1,2-PDO. This was supported by the results of the Ni/Al₂O₃ catalyst containing NiO species with incomplete reduction. Furthermore, the role the NiO species played in the reaction and the potential reaction mechanism over the P-doped Ni/Al₂O₃ catalyst is discussed. The new findings in the present work open a new vision for Ni catalysis and will benefit researchers in designing Ni-based catalysts. Full article

(This article belongs to the Special Issue Metal Catalysts Recycling and Heterogeneous/Homogeneous Catalysis)

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1231 KiB

Open AccessArticle

A Facile Synthesis of Hollow Palladium/Copper Alloy Nanocubes Supported on N-Doped Graphene for Ethanol Electrooxidation Catalyst

by Zhengyu Bai, Rumeng Huang, Lu Niu, Qing Zhang, Lin Yang and Jiujun Zhang

Catalysts 2015, 5(2), 747-758; https://doi.org/10.3390/catal5020747 - 23 Apr 2015

Cited by 25 | Viewed by 7271

Abstract

In this paper, a catalyst of hollow PdCu alloy nanocubes supported on nitrogen-doped graphene support (H-PdCu/ppy-NG) is successfully synthesized using a simple one-pot template-free method. Two other catalyst materials such as solid PdCu alloy particles supported on this same nitrogen-doped graphene support (PdCu/ppy-NG) [...] Read more.

In this paper, a catalyst of hollow PdCu alloy nanocubes supported on nitrogen-doped graphene support (H-PdCu/ppy-NG) is successfully synthesized using a simple one-pot template-free method. Two other catalyst materials such as solid PdCu alloy particles supported on this same nitrogen-doped graphene support (PdCu/ppy-NG) and hollow PdCu alloy nanocubes supported on the reduced graphene oxide support (H-PdCu/RGO) are also prepared using the similar synthesis conditions for comparison. It is found that, among these three catalyst materials, H-PdCu/ppy-NG gives the highest electrochemical active area and both the most uniformity and dispersibility of H-PdCu particles. Electrochemical tests show that the H-PdCu/ppy-NG catalyst can give the best electrocatalytic activity and stability towards the ethanol electrooxidation when compared to other two catalysts. Therefore, H-PdCu/ppy-NG should be a promising catalyst candidate for anodic ethanol oxidation in direct ethanol fuel cells. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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2473 KiB

Open AccessReview

Abatement of VOCs with Alternate Adsorption and Plasma-Assisted Regeneration: A Review

by Sharmin Sultana, Arne M. Vandenbroucke, Christophe Leys, Nathalie De Geyter and Rino Morent

Catalysts 2015, 5(2), 718-746; https://doi.org/10.3390/catal5020718 - 23 Apr 2015

Cited by 116 | Viewed by 12161

Abstract

Energy consumption is an important concern for the removal of volatile organic compounds (VOCs) from waste air with non-thermal plasma (NTP). Although the combination of NTP with heterogeneous catalysis has shown to reduce the formation of unwanted by-products and improve the energy efficiency [...] Read more.

Energy consumption is an important concern for the removal of volatile organic compounds (VOCs) from waste air with non-thermal plasma (NTP). Although the combination of NTP with heterogeneous catalysis has shown to reduce the formation of unwanted by-products and improve the energy efficiency of the process, further optimization of these hybrid systems is still necessary to evolve to a competitive air purification technology. A newly developed innovative technique, i.e., the cyclic operation of VOC adsorption and NTP-assisted regeneration has attracted growing interest of researchers due to the optimized energy consumption and cost-effectiveness. This paper reviews this new technique for the abatement of VOCs as well as for regeneration of adsorbents. In the first part, a comparison of the energy consumption between sequential and continuous treatment is given. Next, studies dealing with adsorption followed by NTP oxidation are reviewed. Particular attention is paid to the adsorption mechanisms and the regeneration of catalysts with in-plasma and post-plasma processes. Finally, the influence of critical process parameters on the adsorption and regeneration steps is summarized. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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8714 KiB

Open AccessArticle

Increasing Octane Value in Catalytic Cracking of n-Hexadecane with Addition of *BEA Type Zeolite

by Iori Shimada, Ryoichi Imai, Yoshinori Hayasaki, Hiroshi Fukunaga, Nobuhide Takahashi and Toru Takatsuka

Catalysts 2015, 5(2), 703-717; https://doi.org/10.3390/catal5020703 - 22 Apr 2015

Cited by 10 | Viewed by 7833

Abstract

In this study, multifunctional catalysts were developed by adding *BEA or MFI zeolite with high Si/Al ratio to a residual fluidized catalytic cracking (RFCC) catalyst and tested in the catalytic cracking of n-hexadecane, which is a heavy crude oil model compound, for [...] Read more.

In this study, multifunctional catalysts were developed by adding *BEA or MFI zeolite with high Si/Al ratio to a residual fluidized catalytic cracking (RFCC) catalyst and tested in the catalytic cracking of n-hexadecane, which is a heavy crude oil model compound, for the purpose of increasing the octane value of produced gasoline under the strong hydrogen transfer activity of the RFCC catalyst. Reaction products analysis revealed that the addition of *BEA zeolite to the RFCC catalyst increased the yields of olefins and multi-branched paraffins, which resulted in improvement of the octane value without sacrificing gasoline yield. On the contrary, the addition of MFI zeolite decreased the gasoline yield because it cracks the gasoline range olefins into LPG range olefins. In general, it is difficult to increase the yield of multi-branched molecules because the multi-branched molecule is more easily cracked than linear molecules. Our results suggest the possibility for the selective acceleration of isomerization reaction by the addition of less acidic *BEA zeolite to the RFCC catalyst. Full article

(This article belongs to the Special Issue Upgrading Tar Sands and Heavy Crude)

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2016 KiB

Open AccessArticle

Silica Supported Platinum Catalysts for Total Oxidation of the Polyaromatic Hydrocarbon Naphthalene: An Investigation of Metal Loading and Calcination Temperature

by David R. Sellick, David J. Morgan and Stuart H. Taylor

Catalysts 2015, 5(2), 690-702; https://doi.org/10.3390/catal5020690 - 22 Apr 2015

Cited by 10 | Viewed by 5563

Abstract

A range of catalysts comprising of platinum supported on silica, prepared by an impregnation method, have been studied for the total oxidation of naphthalene, which is a representative Polycyclic Aromatic Hydrocarbon. The influence of platinum loading and calcination temperature on oxidation activity was [...] Read more.

A range of catalysts comprising of platinum supported on silica, prepared by an impregnation method, have been studied for the total oxidation of naphthalene, which is a representative Polycyclic Aromatic Hydrocarbon. The influence of platinum loading and calcination temperature on oxidation activity was evaluated. Increasing the platinum loading up to 2.5 wt.% increased the catalyst activity, whilst a 5.0 wt.% catalyst was slightly less active. The catalyst containing the optimum 2.5 wt.% loading was most active after calcination in air at 550 °C. Characterisation by carbon monoxide chemisorption and X-ray photoelectron spectroscopy showed that low platinum dispersion to form large platinum particles, in combination with platinum in metallic and oxidised states was important for high catalyst activity. Catalyst performance improved after initial use in repeat cycles, whilst there was slight deactivation after prolonged time-on-stream. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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2200 KiB

Open AccessArticle

Catalytic Oxidation of Propene over Pd Catalysts Supported on CeO₂, TiO₂, Al₂O₃ and M/Al₂O₃ Oxides (M = Ce, Ti, Fe, Mn)

by Sonia Gil, Jesus Manuel Garcia-Vargas, Leonarda Francesca Liotta, Giuseppe Pantaleo, Mohamed Ousmane, Laurence Retailleau and Anne Giroir-Fendler

Catalysts 2015, 5(2), 671-689; https://doi.org/10.3390/catal5020671 - 22 Apr 2015

Cited by 73 | Viewed by 9209

Abstract

In the following work, the catalytic behavior of Pd catalysts prepared using different oxides as support (Al₂O₃, CeO₂ and TiO₂) in the catalytic combustion of propene, in low concentration in excess of oxygen, to mimic the [...] Read more.

In the following work, the catalytic behavior of Pd catalysts prepared using different oxides as support (Al₂O₃, CeO₂ and TiO₂) in the catalytic combustion of propene, in low concentration in excess of oxygen, to mimic the conditions of catalytic decomposition of a volatile organic compound of hydrocarbon-type is reported. In addition, the influence of different promoters (Ce, Ti, Fe and Mn) when added to a Pd/Al₂O₃ catalyst was analyzed. Catalysts were prepared by the impregnation method and were characterized by ICP-OES, N₂ adsorption, temperature-programmed reduction, temperature-programmed oxidation, X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy. Catalyst prepared using CeO₂ as the support was less easily reducible, due to the stabilization effect of CeO₂ over the palladium oxides. Small PdO particles and, therefore, high Pd dispersion were observed for all of the catalysts, as confirmed by XRD and TEM. The addition of Ce to the Pd/Al₂O₃ catalysts increased the metal-support interaction and the formation of highly-dispersed Pd species. The addition of Ce and Fe improved the catalytic behavior of the Pd/Al₂O₃ catalyst; however, the addition of Mn and Ti decreased the catalytic activity in the propene oxidation. Pd/TiO₂ showed the highest catalytic activity, probably due to the high capacity of this catalyst to reoxidize Pd into PdO, as has been found in the temperature-programmed oxidation (TPO) experiments. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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1423 KiB

Open AccessArticle

Non-Calorimetric Determination of the Adsorption Heat of Volatile Organic Compounds under Dynamic Conditions

by Abdelhamid Korrir, Achraf El Kasmi, Mhamed Assebban, Ahmed Souikny, Soukaina Haffane, Ouafae Achak and Tarik Chafik

Catalysts 2015, 5(2), 653-670; https://doi.org/10.3390/catal5020653 - 22 Apr 2015

Cited by 11 | Viewed by 5788

Abstract

Avoiding strong chemical bonding, as indicated by lower heat of adsorption value, is among the selection criteria for Volatile Organic Compounds adsorbents. In this work, we highlight a non-calorimetric approach to estimating the energy of adsorption and desorption based on measurement of involved [...] Read more.

Avoiding strong chemical bonding, as indicated by lower heat of adsorption value, is among the selection criteria for Volatile Organic Compounds adsorbents. In this work, we highlight a non-calorimetric approach to estimating the energy of adsorption and desorption based on measurement of involved amounts, under dynamic conditions, with gaseous Fourier Transform Infrared spectroscopy. The collected data were used for obtaining adsorption heat values through the application of three different methods, namely, isosteric, temperature programmed desorption (TPD), and temperature-programmed adsorption equilibrium (TPAE). The resulting values were compared and discussed with the scope of turning determination of the heat of adsorption with non-calorimetric methods into a relevant decision making tool for designing cost-effective and safe operating of adsorption facilities. Full article

(This article belongs to the Special Issue Catalytic Removal of Volatile Organic Compounds)

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1157 KiB

Open AccessReview

Solid-Liquid Phase C-Alkylation of Active Methylene Containing Compounds under Microwave Conditions

by Alajos Grün, Erika Bálint and György Keglevich

Catalysts 2015, 5(2), 634-652; https://doi.org/10.3390/catal5020634 - 21 Apr 2015

Cited by 14 | Viewed by 7537

Abstract

The solid–liquid phase C-alkylation of active methylene containing compounds with C=O or P=O functions under phase transfer catalysis or microwave conditions has been summarized in this minireview. The mono- and dialkylation of the methylene containing derivatives was investigated under microwave (MW) conditions. [...] Read more.

The solid–liquid phase C-alkylation of active methylene containing compounds with C=O or P=O functions under phase transfer catalysis or microwave conditions has been summarized in this minireview. The mono- and dialkylation of the methylene containing derivatives was investigated under microwave (MW) conditions. It was found that in many cases, there was no need to use phase transfer catalyst under MW conditions. Moreover, most of the reactions were carried out without any solvent. These results mean a serious green chemical advantage. Full article

(This article belongs to the Special Issue Phase-Transfer Catalysts)

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8899 KiB

Open AccessArticle

Pt/MO_x/SiO₂, Pt/MO_x/TiO₂, and Pt/MO_x/Al₂O₃ Catalysts for CO Oxidation

by Hongmei Qin, Xiaoshuang Qian, Tao Meng, Yi Lin and Zhen Ma

Catalysts 2015, 5(2), 606-633; https://doi.org/10.3390/catal5020606 - 20 Apr 2015

Cited by 49 | Viewed by 13438

Abstract

Conventional supported Pt catalysts have often been prepared by loading Pt onto commercial supports, such as SiO₂, TiO₂, Al₂O₃, and carbon. These catalysts usually have simple metal-support (i.e., Pt-SiO₂) interfaces. To [...] Read more.

Conventional supported Pt catalysts have often been prepared by loading Pt onto commercial supports, such as SiO₂, TiO₂, Al₂O₃, and carbon. These catalysts usually have simple metal-support (i.e., Pt-SiO₂) interfaces. To tune the catalytic performance of supported Pt catalysts, it is desirable to modify the metal-support interfaces by incorporating an oxide additive into the catalyst formula. Here we prepared three series of metal oxide-modified Pt catalysts (i.e., Pt/MO_x/SiO₂, Pt/MO_x/TiO₂, and Pt/MO_x/Al₂O₃, where M = Al, Fe, Co, Cu, Zn, Ba, La) for CO oxidation. Among them, Pt/CoO_x/SiO₂, Pt/CoO_x/TiO₂, and Pt/CoO_x/Al₂O₃ showed the highest catalytic activities. Relevant samples were characterized by N₂ adsorption-desorption, X-ray diffraction (XRD), transmission electron microscopy (TEM), H₂ temperature-programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS), CO temperature-programmed desorption (CO-TPD), O₂ temperature-programmed desorption (O₂-TPD), and CO₂ temperature-programmed desorption (CO₂-TPD). Full article

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695 KiB

Open AccessArticle

Cyclopropanation of 5-(1-Bromo-2-phenyl-vinyl)-3-methyl-4-nitro-isoxazoles under Phase Transfer Catalysis (PTC) Conditions

by Linda Piras, Maria Moccia, Mauro Cortigiani and Mauro F. A. Adamo

Catalysts 2015, 5(2), 595-605; https://doi.org/10.3390/catal5020595 - 13 Apr 2015

Cited by 21 | Viewed by 5773

Abstract

Heavily substituted cyclopropane esters were prepared in high yields, complete diastereoselection and average (up to 58%) enantioselectivity. The reaction described herein entailed reacting 4-nitro-5-bromostyrylisoxazoles, a class of powerful Michael acceptors with malonate esters under the catalysis of 5 mol% of a chincona derived [...] Read more.

Heavily substituted cyclopropane esters were prepared in high yields, complete diastereoselection and average (up to 58%) enantioselectivity. The reaction described herein entailed reacting 4-nitro-5-bromostyrylisoxazoles, a class of powerful Michael acceptors with malonate esters under the catalysis of 5 mol% of a chincona derived phase-transfer catalyst. Full article

(This article belongs to the Special Issue Phase-Transfer Catalysts)

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4548 KiB

Open AccessReview

Deactivation of Pd Catalysts by Water during Low Temperature Methane Oxidation Relevant to Natural Gas Vehicle Converters

by Rahman Gholami, Mina Alyani and Kevin J. Smith

Catalysts 2015, 5(2), 561-594; https://doi.org/10.3390/catal5020561 - 31 Mar 2015

Cited by 176 | Viewed by 12314

Abstract

Effects of H₂O on the activity and deactivation of Pd catalysts used for the oxidation of unburned CH₄ present in the exhaust gas of natural-gas vehicles (NGVs) are reviewed. CH₄ oxidation in a catalytic converter is limited by low [...] Read more.

Effects of H₂O on the activity and deactivation of Pd catalysts used for the oxidation of unburned CH₄ present in the exhaust gas of natural-gas vehicles (NGVs) are reviewed. CH₄ oxidation in a catalytic converter is limited by low exhaust gas temperatures (500–550 °C) and low concentrations of CH₄ (400–1500 ppmv) that must be reacted in the presence of large quantities of H₂O (10–15%) and CO₂ (15%), under transient exhaust gas flows, temperatures, and compositions. Although Pd catalysts have the highest known activity for CH₄ oxidation, water-induced sintering and reaction inhibition by H₂O deactivate these catalysts. Recent studies have shown the reversible inhibition by H₂O adsorption causes a significant drop in catalyst activity at lower reaction temperatures (below 450 °C), but its effect decreases (water adsorption becomes more reversible) with increasing reaction temperature. Thus above 500 °C H₂O inhibition is negligible, while Pd sintering and occlusion by support species become more important. H₂O inhibition is postulated to occur by either formation of relatively stable Pd(OH)₂ and/or partial blocking by OH groups of the O exchange between the support and Pd active sites thereby suppressing catalytic activity. Evidence from FTIR and isotopic labeling favors the latter route. Pd catalyst design, including incorporation of a second noble metal (Rh or Pt) and supports high O mobility (e.g., CeO₂) are known to improve catalyst activity and stability. Kinetic studies of CH₄ oxidation at conditions relevant to natural gas vehicles have quantified the thermodynamics and kinetics of competitive H₂O adsorption and Pd(OH)₂ formation, but none have addressed effects of H₂O on O mobility. Full article

(This article belongs to the Special Issue Advances in Catalyst Deactivation)

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15014 KiB

Open AccessReview

Magnetically Separable and Sustainable Nanostructured Catalysts for Heterogeneous Reduction of Nitroaromatics

by Mohammadreza Shokouhimehr

Catalysts 2015, 5(2), 534-560; https://doi.org/10.3390/catal5020534 - 31 Mar 2015

Cited by 176 | Viewed by 15059

Abstract

This review is focused on the strategies and designs of magnetic nanostructured catalysts showing the enhanced and sustainable catalytic performances for the heterogeneous reduction of nitoaromatics. Magnetic catalysts have the benefits of easy recovery and reuse after the completion of the reactions and [...] Read more.

This review is focused on the strategies and designs of magnetic nanostructured catalysts showing the enhanced and sustainable catalytic performances for the heterogeneous reduction of nitoaromatics. Magnetic catalysts have the benefits of easy recovery and reuse after the completion of the reactions and green chemical processes. Magnetic separation, among the various procedures for removing catalysts, not only obviates the requirement of catalyst filtration or centrifugation after the completion of reactions, but also provides a practical technique for recycling the magnetized nanostructured catalysts. Consequently, discussions will address the methodologies and exemplars for the reusable magnetic composite catalysts. Because the synthesis of ideal magnetic nanostructured catalysts is of primary importance in the development of high-quality sustainable processes, the designs, preparation methods and recyclability of various recoverable magnetic nanostructured catalysts are emphasized. The representative methods and strategies for the synthesis of durable and reusable magnetic nanostructured catalysts are highlighted. The advantages, disadvantages, recyclability and the efficiency of the introduced heterogeneous systems have been explored in the reduction of nitrobenzene derivatives. Full article

(This article belongs to the Special Issue Metal Catalysts Recycling and Heterogeneous/Homogeneous Catalysis)

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2174 KiB

Open AccessArticle

Real-Time Raman Monitoring during Photocatalytic Epoxidation of Cyclohexene over V-Ti/MCM-41 Catalysts

by Hsiang-Yu Chan, Van-Huy Nguyen, Jeffrey C.S. Wu, Vanesa Calvino-Casilda, Miguel A. Bañares and Hsunling Bai

Catalysts 2015, 5(2), 518-533; https://doi.org/10.3390/catal5020518 - 30 Mar 2015

Cited by 13 | Viewed by 9086

Abstract

A series of V- and/or Ti-loading MCM-41 catalysts are successfully synthesized with a hydrothermal method. The photocatalytic and thermal epoxidations of cyclohexene in the presence of tert-butyl hydroperoxide (t-BuOOH) were investigated with real-time monitored by NIR-Raman spectroscopy. It suggests that [...] Read more.

A series of V- and/or Ti-loading MCM-41 catalysts are successfully synthesized with a hydrothermal method. The photocatalytic and thermal epoxidations of cyclohexene in the presence of tert-butyl hydroperoxide (t-BuOOH) were investigated with real-time monitored by NIR-Raman spectroscopy. It suggests that both V- and Ti-loading can be responsible for the cyclohexene epoxidation. Moreover, the complementary behavior of V- and Ti-loading may be related to a similar role of activation. Interestingly, the progress of the photo-epoxidation on V_0.25Ti₂/MCM-41 photocatalyst was monitored by changes in intensity of the characteristic Raman bands without interference from the UV-light irradiation. The result, for the first time, reveals that cyclohexene was directly photo-epoxidized to 1,2-epoxycyclohexane by t-BuOOH during the reaction. A possible mechanism of cyclohexene photo-epoxidation is also proposed for this study. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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8635 KiB

Open AccessReview

Acyclic Diene Metathesis (ADMET) Polymerization for Precise Synthesis of Defect-Free Conjugated Polymers with Well-Defined Chain Ends

by Tahmina Haque and Kotohiro Nomura

Catalysts 2015, 5(2), 500-517; https://doi.org/10.3390/catal5020500 - 30 Mar 2015

Cited by 21 | Viewed by 9614

Abstract

This accounts introduces unique characteristics by adopting the acyclic diene metathesis (ADMET) polymerization for synthesis of conjugated polymers, poly(arylene vinylene)s, known as promising molecular electronics. The method is more suitable than the other methods in terms of atom efficiency affording defect-free, stereo-regular (exclusive [...] Read more.

This accounts introduces unique characteristics by adopting the acyclic diene metathesis (ADMET) polymerization for synthesis of conjugated polymers, poly(arylene vinylene)s, known as promising molecular electronics. The method is more suitable than the other methods in terms of atom efficiency affording defect-free, stereo-regular (exclusive trans) polymers with well-defined chain ends; the resultant polymers possess better property than those prepared by the conventional methods. The chain ends (vinyl group) in the resultant polymer prepared by ruthenium-carbene catalyst(s) can be modified by treating with molybdenum-alkylidene complex (olefin metathesis) followed by addition of various aldehyde (Wittig type cleavage), affording the end-functionalized polymers exclusively. An introduction of initiating fragment, the other conjugated segment, and one-pot synthesis of end-functionalized block copolymers, star shape polymers can be achieved by adopting this methodology. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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4697 KiB

Open AccessReview

Deactivation and Regeneration of Commercial Type Fischer-Tropsch Co-Catalysts—A Mini-Review

by Erling Rytter and Anders Holmen

Catalysts 2015, 5(2), 478-499; https://doi.org/10.3390/catal5020478 - 26 Mar 2015

Cited by 112 | Viewed by 13450

Abstract

Deactivation of commercially relevant cobalt catalysts for Low Temperature Fischer-Tropsch (LTFT) synthesis is discussed with a focus on the two main long-term deactivation mechanisms proposed: Carbon deposits covering the catalytic surface and re-oxidation of the cobalt metal. There is a great variety in [...] Read more.

Deactivation of commercially relevant cobalt catalysts for Low Temperature Fischer-Tropsch (LTFT) synthesis is discussed with a focus on the two main long-term deactivation mechanisms proposed: Carbon deposits covering the catalytic surface and re-oxidation of the cobalt metal. There is a great variety in commercial, demonstration or pilot LTFT operations in terms of reactor systems employed, catalyst formulations and process conditions. Lack of sufficient data makes it difficult to correlate the deactivation mechanism with the actual process and catalyst design. It is well known that long term catalyst deactivation is sensitive to the conditions the actual catalyst experiences in the reactor. Therefore, great care should be taken during start-up, shutdown and upsets to monitor and control process variables such as reactant concentrations, pressure and temperature which greatly affect deactivation mechanism and rate. Nevertheless, evidence so far shows that carbon deposition is the main long-term deactivation mechanism for most LTFT operations. It is intriguing that some reports indicate a low deactivation rate for multi-channel micro-reactors. In situ rejuvenation and regeneration of Co catalysts are economically necessary for extending their life to several years. The review covers information from open sources, but with a particular focus on patent literature. Full article

(This article belongs to the Special Issue Advances in Catalyst Deactivation)

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Catalysts, Volume 5, Issue 2 (June 2015) – 29 articles , Pages 478-1002

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