Catalysts

2591 KiB

Open AccessReview

Deactivation Pattern of a “Model” Ni/MgO Catalyst in the Pre-Reforming of n-Hexane

by Giuseppe Trunfio and Francesco Arena

Catalysts 2014, 4(2), 196-214; https://doi.org/10.3390/catal4020196 - 19 Jun 2014

Cited by 8 | Viewed by 6733

The deactivation pattern of a “model” Ni/MgO catalyst in the pre-reforming of n-hexane with steam (T, 450 °C; P, 5–15 bar) is reviewed. The influence of the steam-to-carbon ratio (S/C, 1.5–3.5) on the rate of catalyst fouling by coking [...] Read more.

The deactivation pattern of a “model” Ni/MgO catalyst in the pre-reforming of n-hexane with steam (T, 450 °C; P, 5–15 bar) is reviewed. The influence of the steam-to-carbon ratio (S/C, 1.5–3.5) on the rate of catalyst fouling by coking is ascertained. Catalyst fouling leads to an exponential decay in activity, denoting 1^st-order dependence of the coking process on active sites availability. Hydrogen hinders the coking process, though slight activity decay is due to sintering of the active Ni phase. Deactivation by thiophene causes a sharp, almost linear, drop to nearly zero activity within only 6 h; this deactivation is likely due to dissociative adsorption of thiophene with subsequent strong, irreversible chemical adsorption of S-atoms on active Ni sites, i.e., irreversible poisoning. Modeling of activity decay curves (α, a_t/a₀) by proper kinetic equations allows assessing the effects of temperature, pressure, S/C, H₂ and thiophene feed on the deactivation pattern of the model Ni/MgO catalyst by coking, sintering, and poisoning phenomena. Full article

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

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1651 KiB

Open AccessArticle

Baker’s Yeast Mediated Reduction of 2-Acetyl-3-methyl Sulfolane

by Rebecca E. Deasy, Noreen O'Riordan and Anita R. Maguire

Catalysts 2014, 4(2), 186-195; https://doi.org/10.3390/catal4020186 - 18 Jun 2014

Cited by 5 | Viewed by 13143

Abstract

The baker’s yeast mediated reduction of 2-acetyl-3-methyl sulfolane 1 to provide the corresponding alcohol 2 is described. Excellent efficiency and enantioselectivity (>98% ee) has been achieved under these mild environmentally benign reaction conditions. In direct contrast, the chemical reduction of 1 proceeds [...] Read more.

The baker’s yeast mediated reduction of 2-acetyl-3-methyl sulfolane 1 to provide the corresponding alcohol 2 is described. Excellent efficiency and enantioselectivity (>98% ee) has been achieved under these mild environmentally benign reaction conditions. In direct contrast, the chemical reduction of 1 proceeds with poor yield (≤25%) and diastereocontrol. Full article

(This article belongs to the Special Issue Enzymes in Organic Synthesis)

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2000 KiB

Open AccessCommunication

Kinetic Isotope Effect of Prostaglandin H Synthase Exhibits Inverted Temperature Dependence

by Gang Wu, Richard J. Kulmacz and Ah-Lim Tsai

Catalysts 2014, 4(2), 174-185; https://doi.org/10.3390/catal4020174 - 11 Jun 2014

Cited by 3 | Viewed by 5648

Abstract

Conversion of arachidonic acid to prostaglandin G₂/H₂ catalyzed by prostaglandin H synthase (PGHS) is proposed to involve initial transfer of the C13 pro-(S) hydrogen atom from arachidonate to the Tyr385 radical in PGHS, followed by insertion of two [...] Read more.

Conversion of arachidonic acid to prostaglandin G₂/H₂ catalyzed by prostaglandin H synthase (PGHS) is proposed to involve initial transfer of the C13 pro-(S) hydrogen atom from arachidonate to the Tyr385 radical in PGHS, followed by insertion of two oxygen molecules and several chemical bond rearrangements. The initial hydrogen-transfer was recently concluded to be a rate-limiting step in cyclooxygenase catalysis based on the observed intrinsic deuterium kinetic isotope effect values (^Dk_cat). In the present study, we have found that ^Dk_cat values of both PGHS-1 and -2 show an unusual increase with temperatures in the range of 288–310 K, exhibiting an inverted temperature dependence. The value of ln^Dk_cat, however, decreased linearly with 1/T, consistent with a typical Arrhenius relationship. Full article

(This article belongs to the Special Issue Enzymes in Organic Synthesis)

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2611 KiB

Open AccessArticle

Neighboring Hetero-Atom Assistance of Sacrificial Amines to Hydrogen Evolution Using Pt-Loaded TiO₂-Photocatalyst

by Masahide Yasuda, Takayuki Tomo, Shoichi Hirata, Tsutomu Shiragami and Tomoko Matsumoto

Catalysts 2014, 4(2), 162-173; https://doi.org/10.3390/catal4020162 - 26 May 2014

Cited by 9 | Viewed by 5587

Abstract

Photocatalytic H₂ evolution was examined using Pt-loaded TiO₂-photocatalyst in the presence of amines as sacrificial agents. In the case of amines with all of the carbon attached to the hetero-atom such as 2-aminoethanol, 1,2-diamonoethane, 2-amino-1,3-propanediol, and 3-amino-1,2-propanediol, they were completely [...] Read more.

Photocatalytic H₂ evolution was examined using Pt-loaded TiO₂-photocatalyst in the presence of amines as sacrificial agents. In the case of amines with all of the carbon attached to the hetero-atom such as 2-aminoethanol, 1,2-diamonoethane, 2-amino-1,3-propanediol, and 3-amino-1,2-propanediol, they were completely decomposed into CO₂ and water to quantitatively evolve H₂. On the other hand, the amines with both hetero-atoms and one methyl group at the β-positions (neighboring carbons) of amino group such as 2-amino-1-propanol and 1,2-diaminopropane were partially decomposed. Also, the photocatalytic H₂ evolution using amines without the hetero-atoms at the β-positions such as ethylamine, propylamine, 1-butylamine, 1,3-diaminopropane, 2-propylamine, and 2-butylamine was inefficient. Thus, it was found that the neighboring hetero-atom strongly assisted the degradation of sacrificial amines. Moreover, rate constants for H₂ evolution were compared among amines. In conclusion, the neighboring hetero-atom did not affect the rate constants but enhanced the yield of hydrogen evolution. Full article

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5475 KiB

Open AccessArticle

La_0.6Sr_0.4Co_0.2Fe_0.8O₃ Perovskite: A Stable Anode Catalyst for Direct Methane Solid Oxide Fuel Cells

by Jelvehnaz Mirzababaei and Steven S. C. Chuang

Catalysts 2014, 4(2), 146-161; https://doi.org/10.3390/catal4020146 - 09 May 2014

Cited by 41 | Viewed by 11565

Abstract

Direct methane solid oxide fuel cells, operated by supplying methane to a Ni/YSZ anode, suffer from degradation via accumulation of carbon deposits on the Ni surface. Coating a 40 µm thin film of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ [...] Read more.

Direct methane solid oxide fuel cells, operated by supplying methane to a Ni/YSZ anode, suffer from degradation via accumulation of carbon deposits on the Ni surface. Coating a 40 µm thin film of La_0.6Sr_0.4Co_0.2Fe_0.8O₃ (LSCF) perovskite on the Ni/YSZ anode surface decreased the amount of carbon deposits, slowing down the degradation rate. The improvement in anode durability could be related to the oxidation activity of LSCF which facilitates oxidation of CH₄ and carbon deposits. Analysis of the crystalline structure of LSCF revealed that LSCF was stable in the reducing anode environment under H₂ and CH₄ flow at 750 °C and retained its perovskite structure throughout the 475 h long-term stability test. Full article

(This article belongs to the Special Issue Perovskite Catalysts)

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6831 KiB

Open AccessArticle

In Situ XANES/XPS Investigation of Doped Manganese Perovskite Catalysts

by Daniel Mierwaldt, Stephanie Mildner, Rosa Arrigo, Axel Knop-Gericke, Emanuel Franke, Andreas Blumenstein, Jörg Hoffmann and Christian Jooss

Catalysts 2014, 4(2), 129-145; https://doi.org/10.3390/catal4020129 - 23 Apr 2014

Cited by 68 | Viewed by 16583

Abstract

Studying catalysts in situ is of high interest for understanding their surface structure and electronic states in operation. Herein, we present a study of epitaxial manganite perovskite thin films (Pr_1−xCa_xMnO₃) active for the oxygen evolution reaction [...] Read more.

Studying catalysts in situ is of high interest for understanding their surface structure and electronic states in operation. Herein, we present a study of epitaxial manganite perovskite thin films (Pr_1−xCa_xMnO₃) active for the oxygen evolution reaction (OER) from electro-catalytic water splitting. X-ray absorption near-edge spectroscopy (XANES) at the Mn L- and O K-edges, as well as X-ray photoemission spectroscopy (XPS) of the O 1s and Ca 2p states have been performed in ultra-high vacuum and in water vapor under positive applied bias at room temperature. It is shown that under the oxidizing conditions of the OER a reduced Mn²⁺ species is generated at the catalyst surface. The Mn valence shift is accompanied by the formation of surface oxygen vacancies. Annealing of the catalysts in O₂ atmosphere at 120 °C restores the virgin surfaces. Full article

(This article belongs to the Special Issue Perovskite Catalysts)

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1174 KiB

Open AccessArticle

Selective Synthesis of Gasoline-Ranged Hydrocarbons from Syngas over Hybrid Catalyst Consisting of Metal-Loaded ZSM-5 Coupled with Copper-Zinc Oxide

by Ting Ma, Hiroyuki Imai, Manami Yamawaki, Kazusa Terasaka and Xiaohong Li

Catalysts 2014, 4(2), 116-128; https://doi.org/10.3390/catal4020116 - 23 Apr 2014

Cited by 25 | Viewed by 8570

Abstract

The conversion of syngas (CO + H₂) to gasoline-ranged hydrocarbons was carried out using a hybrid catalyst consisting of metal-loaded ZSM-5 coupled with Cu-ZnO in a near-critical n-hexane solvent. Methanol was synthesized from syngas over Cu-ZnO; subsequently, was converted to [...] Read more.

The conversion of syngas (CO + H₂) to gasoline-ranged hydrocarbons was carried out using a hybrid catalyst consisting of metal-loaded ZSM-5 coupled with Cu-ZnO in a near-critical n-hexane solvent. Methanol was synthesized from syngas over Cu-ZnO; subsequently, was converted to hydrocarbons through the formation of dimethyl ether (DME) over the metal-loaded ZSM-5. When 0.5 wt% Pd/ZSM-5 and 5 wt% Cu/ZSM-5 among the metal-loaded ZSM-5 catalysts with Pd, Co, Fe or Cu were employed as a portion of the hybrid catalyst, the gasoline-ranged hydrocarbons were selectively produced (the gasoline-ranged hydrocarbons in all hydrocarbons: 59% for the hybrid catalyst with Pd/ZSM-5 and 64% for that with Cu/ZSM-5) with a similar CO conversion during the reaction. An increase in the Cu loading on ZSM-5 resulted in increasing the yield of the gasoline-ranged hydrocarbons, and in decreasing the yield of DME. Furthermore, the hybrid catalyst with Cu/ZSM-5 exhibited no deactivation for 30 h of the reaction. It was revealed that a hybrid catalyst containing Cu/ZSM-5 was efficient in the selective synthesis of gasoline-ranged hydrocarbons from syngas via methanol in the near-critical n-hexane fluid. Full article

(This article belongs to the Special Issue Metal-Loaded Zeolite Catalysts)

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1490 KiB

Open AccessArticle

Inhibition of a Gold-Based Catalyst in Benzyl Alcohol Oxidation: Understanding and Remediation

by Emmanuel Skupien, Rob J. Berger, Vera P. Santos, Jorge Gascon, Michiel Makkee, Michiel T. Kreutzer, Patricia J. Kooyman, Jacob A. Moulijn and Freek Kapteijn

Catalysts 2014, 4(2), 89-115; https://doi.org/10.3390/catal4020089 - 15 Apr 2014

Cited by 41 | Viewed by 12990

Abstract

Benzyl alcohol oxidation was carried out in toluene as solvent, in the presence of the potentially inhibiting oxidation products benzaldehyde and benzoic acid. Benzoic acid, or a product of benzoic acid, is identified to be the inhibiting species. The presence of a basic [...] Read more.

Benzyl alcohol oxidation was carried out in toluene as solvent, in the presence of the potentially inhibiting oxidation products benzaldehyde and benzoic acid. Benzoic acid, or a product of benzoic acid, is identified to be the inhibiting species. The presence of a basic potassium salt (K₂CO₃ or KF) suppresses this inhibition, but promotes the formation of benzyl benzoate from the alcohol and aldehyde. When a small amount of water is added together with the potassium salt, an even greater beneficial effect is observed, due to a synergistic effect with the base. A kinetic model, based on the three main reactions and four major reaction components, is presented to describe the concentration-time profiles and inhibition. The inhibition, as well as the effect of the base, was captured in the kinetic model, by combining strong benzoic acid adsorption and competitive adsorption with benzyl alcohol. The effect of the potassium salt is accounted for in terms of neutralization of benzoic acid. Full article

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

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1884 KiB

Open AccessArticle

LaNi_0.3Co_0.7O_3-δ and SrFe_0.2Co_0.8O_3-δ Ceramic Materials: Structural and Catalytic Reactivity under CO Stream

by Andarair Gomes Dos Santos, Madjid Arab, Loic Patout and Carlson Periera De Souza

Catalysts 2014, 4(2), 77-88; https://doi.org/10.3390/catal4020077 - 31 Mar 2014

Cited by 10 | Viewed by 5652

Abstract

In this study, we presented the synthesis of LaNi_0.3Co_0.7O_3−δ (LNCO) and SrCo_0.8Fe_0.2O_3−δ (SFCO) perovskites and their catalytic reactivity under CO gas flow. The synthesis method is based on the complexation method combining ethylenediaminetetraacetic [...] Read more.

In this study, we presented the synthesis of LaNi_0.3Co_0.7O_3−δ (LNCO) and SrCo_0.8Fe_0.2O_3−δ (SFCO) perovskites and their catalytic reactivity under CO gas flow. The synthesis method is based on the complexation method combining ethylenediaminetetraacetic acid (EDTA)-citrate. The as-prepared materials were characterized using X-ray diffraction/Rietveld refinement and electron microscopy. The diffractograms and Rietveld refinement showed that the EDTA-citrate method allows us to obtain monophasic powders with submicronic size. The structural analyses revealed different morphologies linked to the crystallinity of LNCO and SFCO, and to the mean crystallite size. The catalytic performances of LNCO and SFCO were studied in situ by Fourier Transform InfraRed spectrometer as a function of time and temperature. The catalytic process gave rise to total oxidation with carbon dioxide and water production. LNCO and SFCO exhibit the same profile for catalytic activity with a conversion rate of twice as high for LNCO. Below 150 °C, the kinetic conversion is slow, but beyond this temperature they reach rapidly the complete transformation at 250 °C and 275 °C for LNCO and SFCO, respectively. Full article

(This article belongs to the Special Issue Perovskite Catalysts)

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Catalysts, Volume 4, Issue 2 (June 2014) – 9 articles , Pages 77-214

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