Editorial

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Open AccessEditorial

Reflections on Catalytic Selective Oxidation: Opportunities and Challenges

by Stuart H. Taylor

Catalysts 2017, 7(1), 34; https://doi.org/10.3390/catal7010034 - 20 Jan 2017

Cited by 3 | Viewed by 3892

Currently, and looking forward, there is an ever increasing demand to perform chemical transformations with optimized atom and energy efficiency [...] Full article

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

Research

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1344 KiB

Open AccessArticle

Selective Aerobic Oxidation of Benzyl Alcohol Driven by Visible Light on Gold Nanoparticles Supported on Hydrotalcite Modified by Nickel Ion

by Dapeng Guo, Yan Wang, Peng Zhao, Meifen Bai, Hui Xin, Zhi Guo and Jingyi Li

Catalysts 2016, 6(5), 64; https://doi.org/10.3390/catal6050064 - 27 Apr 2016

Cited by 16 | Viewed by 5642

Abstract

A series of hydrotalcite (HT) and hydrotalcite modified by the transition metal ion Ni(II) was prepared with a modified coprecipitation method before being loaded with gold nanoparticles. The gold supported on Ni₃Al hydrotalcite with a Ni²⁺/Al³⁺ molar ratio [...] Read more.

A series of hydrotalcite (HT) and hydrotalcite modified by the transition metal ion Ni(II) was prepared with a modified coprecipitation method before being loaded with gold nanoparticles. The gold supported on Ni₃Al hydrotalcite with a Ni²⁺/Al³⁺ molar ratio of 3:1 was investigated. Different techniques such as X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and UV-vis diffuse reflection spectrum (UV-vis DRS) were applied to characterize the catalysts. A single-phase catalyst with high crystallinity, a layered structure and good composition was successfully fabricated. Good conversions and superior selectivities in the oxidation of benzyl alcohol and its derivatives were obtained with visible light due to the effect of localized surface plasmon resonance (LSPR) of gold nanoparticles and the synergy of the transition metal ion Ni(II). This reaction was proven to be photocatalytic by varying the intensity and wavelength of the visible light. The catalyst can be recycled three times. A corresponding photocatalytic mechanism of the oxidation reaction of benzyl alcohol was proposed. Full article

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

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3336 KiB

Open AccessArticle

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

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

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

Cited by 23 | Viewed by 8117

Abstract

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

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

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

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1589 KiB

Open AccessArticle

Solvent-Free Selective Oxidation of Toluene with O₂ Catalyzed by Metal Cation Modified LDHs and Mixed Oxides

by Xiaoli Wang, Gongde Wu, Hao Liu and Qibo Lin

Catalysts 2016, 6(1), 14; https://doi.org/10.3390/catal6010014 - 15 Jan 2016

Cited by 17 | Viewed by 10453

Abstract

A series of metal cation modified layered-double hydroxides (LDHs) and mixed oxides were prepared and used to be the selective oxidation of toluene with O₂. The results revealed that the modified LDHs exhibited much higher catalytic performance than their parent LDH [...] Read more.

A series of metal cation modified layered-double hydroxides (LDHs) and mixed oxides were prepared and used to be the selective oxidation of toluene with O₂. The results revealed that the modified LDHs exhibited much higher catalytic performance than their parent LDH and the modified mixed oxides. Moreover, the metal cations were also found to play important roles in the catalytic performance and stabilities of modified catalysts. Under the optimal reaction conditions, the highest toluene conversion reached 8.7% with 97.5% of the selectivity to benzyldehyde; moreover, the catalytic performance remained after nine catalytic runs. In addition, the reaction probably involved a free-radical mechanism. Full article

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

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Catalytic Performance of Lanthanum Vanadate Catalysts in Ammoxidation of 2-Methylpyrazine

by Venkata N. Kalevaru, Naresh Dhachapally and Andreas Martin

Catalysts 2016, 6(1), 10; https://doi.org/10.3390/catal6010010 - 12 Jan 2016

Cited by 14 | Viewed by 4942

Abstract

The influence of reaction conditions on the catalytic performance of lanthanum vanadate (La_0.1V_0.9O_x) catalyst in the ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyarazine (CP) has been investigated. This novel catalytic material exhibited remarkably good performance with very high [...] Read more.

The influence of reaction conditions on the catalytic performance of lanthanum vanadate (La_0.1V_0.9O_x) catalyst in the ammoxidation of 2-methylpyrazine (MP) to 2-cyanopyarazine (CP) has been investigated. This novel catalytic material exhibited remarkably good performance with very high space-time-yields (STY) of CP. The reaction parameters such as the effect of temperature, gas hourly space velocity (GHSV) and all other reaction variables (e.g., NH₃, air, and MP feed rates) on the catalytic performance were explored and optimized. For example, an increase in MP feed rate from 2 to >16 mmol/h led to decreased conversion of MP but increased the STY of CP significantly. Optimal performance was achieved when the reaction temperature was 420 °C and the molar ratio of 2-MP, ammonia, air, H₂O and N₂ in the feed gas was set to 1:7:26:13:22. Under these optimal reaction conditions, the catalyst showed a MP conversion of ~100%, CP selectivity of 86%, and STY of >500 g_CP/(kg_cat∙h). On the other hand, the formation of pyrazine (Py) as a by-product was found to be high when the NH₃:MP ratio was lower at increased contact time. This suggests possible differences in the reaction mechanism pathways with respect to feed composition over La_0.1V_0.9O_x catalysts. Full article

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

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312 KiB

Open AccessArticle

Selective Oxidation of Glycerol with 3% H₂O₂ Catalyzed by LDH-Hosted Cr(III) Complex

by Gongde Wu, Xiaoli Wang, Taineng Jiang and Qibo Lin

Catalysts 2015, 5(4), 2039-2051; https://doi.org/10.3390/catal5042039 - 27 Nov 2015

Cited by 11 | Viewed by 6999

Abstract

A series of layered double hydroxides (LDHs) –hosted sulphonato-salen Cr(III) complexes were prepared and characterized by various physico-chemical measurements, such as Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), powder X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) and elemental [...] Read more.

A series of layered double hydroxides (LDHs) –hosted sulphonato-salen Cr(III) complexes were prepared and characterized by various physico-chemical measurements, such as Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible spectroscopy (UV-Vis), powder X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) and elemental analysis. Additionally, their catalytic performances were investigated in the selective oxidation of glycerol (GLY) using 3% H₂O₂ as an oxidant. It was found that all the LDH-hosted Cr(III) complexes exhibited significantly enhanced catalytic performance compared to the homogeneous Cr(III) complex. Additionally, it was worth mentioning that the metal composition of LDH plates played an important role in the catalytic performances of LDH-hosted Cr(III) complex catalysts. Under the optimal reaction conditions, the highest GLY conversion reached 85.5% with 59.3% of the selectivity to 1,3-dihydroxyacetone (DHA). In addition, the catalytic activity remained after being recycled five times. Full article

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

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Review

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Open AccessFeature PaperReview

Catalysts for the Selective Oxidation of Methanol

by Catherine Brookes, Michael Bowker and Peter P. Wells

Catalysts 2016, 6(7), 92; https://doi.org/10.3390/catal6070092 - 23 Jun 2016

Cited by 42 | Viewed by 10541

Abstract

In industry, one of the main catalysts typically employed for the selective oxidation of methanol to formaldehyde is a multi-component oxide containing both bulk Fe₂(MoO₄)₃ and excess MoO₃. It is thought that the excess MoO₃ [...] Read more.

In industry, one of the main catalysts typically employed for the selective oxidation of methanol to formaldehyde is a multi-component oxide containing both bulk Fe₂(MoO₄)₃ and excess MoO₃. It is thought that the excess MoO₃ primarily acts to replace any molybdenum lost through sublimation at elevated temperatures, therefore preventing the formation of an unselective Fe₂O₃ phase. With both oxide phases present however, debate has arisen regarding the active component of the catalyst. Work here highlights how catalyst surfaces are significantly different from bulk structures, a difference crucial for catalyst performance. Specifically, Mo has been isolated at the surface as the active surface species. This leaves the role of the Fe in the catalyst enigmatic, with many theories postulated for its requirement. It has been suggested that the supporting Fe molybdate phase enables lattice oxygen transfer to the surface, to help prevent the selectivity loss which would occur in the resulting oxygen deficit environment. To assess this phenomenon in further detail, anaerobic reaction with methanol has been adopted to evaluate the performance of the catalyst under reducing conditions. Full article

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

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2566 KiB

Open AccessReview

An Overview of Recent Advances of the Catalytic Selective Oxidation of Ethane to Oxygenates

by Robert D. Armstrong, Graham J. Hutchings and Stuart H. Taylor

Catalysts 2016, 6(5), 71; https://doi.org/10.3390/catal6050071 - 16 May 2016

Cited by 25 | Viewed by 10233

Abstract

The selective partial oxidation of short chain alkanes is a key challenge within catalysis research. Direct ethane oxidation to oxygenates is a difficult aim, but potentially rewarding, and it could lead to a paradigm shift in the supply chain of several bulk chemicals. [...] Read more.

The selective partial oxidation of short chain alkanes is a key challenge within catalysis research. Direct ethane oxidation to oxygenates is a difficult aim, but potentially rewarding, and it could lead to a paradigm shift in the supply chain of several bulk chemicals. Unfortunately, low C–H bond reactivity and kinetically labile products are just some reasons affecting the development and commercialisation of such processes. Research into direct ethane oxidation is therefore disparate, with approaches ranging from oxidation in the gas phase at high temperatures to enzyme catalysed hydroxylation under ambient conditions. Furthermore, in overcoming the barrier posed by the chemically inert C–H bond a range of oxidants have been utilised. Despite years of research, this remains an intriguing topic from both academic and commercial perspectives. Herein we describe some recent developments within the field of catalytic ethane oxidation focusing on the formation of oxygenated products, whilst addressing the key challenges which are still to be overcome. Full article

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

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2955 KiB

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Heterogeneous Partial (amm)Oxidation and Oxidative Dehydrogenation Catalysis on Mixed Metal Oxides

by Jacques C. Védrine

Catalysts 2016, 6(2), 22; https://doi.org/10.3390/catal6020022 - 29 Jan 2016

Cited by 43 | Viewed by 10847

Abstract

This paper presents an overview of heterogeneous partial (amm)oxidation and oxidative dehydrogenation (ODH) of hydrocarbons. The review has been voluntarily restricted to metal oxide-type catalysts, as the partial oxidation field is very broad and the number of catalysts is quite high. The main [...] Read more.

This paper presents an overview of heterogeneous partial (amm)oxidation and oxidative dehydrogenation (ODH) of hydrocarbons. The review has been voluntarily restricted to metal oxide-type catalysts, as the partial oxidation field is very broad and the number of catalysts is quite high. The main factors of solid catalysts for such reactions, designated by Grasselli as the “seven pillars”, and playing a determining role in catalytic properties, are considered to be, namely: isolation of active sites (known to be composed of ensembles of atoms), Me–O bond strength, crystalline structure, redox features, phase cooperation, multi-functionality and the nature of the surface oxygen species. Other important features and physical and chemical properties of solid catalysts, more or less related to the seven pillars, are also emphasized, including reaction sensitivity to metal oxide structure, epitaxial contact between an active phase and a second phase or its support, synergy effect between several phases, acid-base aspects, electron transfer ability, catalyst preparation and activation and reaction atmospheres, etc. Some examples are presented to illustrate the importance of these key factors. They include light alkanes (C₁–C₄) oxidation, ethane oxidation to ethylene and acetic acid on MoVTe(Sb)Nb-O and Nb doped NiO, propene oxidation to acrolein on BiMoCoFe-O systems, propane (amm)oxidation to (acrylonitrile) acrylic acid on MoVTe(Sb)Nb-O mixed oxides, butane oxidation to maleic anhydride on VPO: (VO)₂P₂O₇-based catalyst, and isobutyric acid ODH to methacrylic acid on Fe hydroxyl phosphates. It is shown that active sites are composed of ensembles of atoms whose size and chemical composition depend on the reactants to be transformed (their chemical and size features) and the reaction mechanism, often of Mars and van Krevelen type. An important aspect is the fact that surface composition and surface crystalline structure vary with reaction on stream until reaching steady state, which makes characterisation of active and selective surface sites quite difficult. The use of oxidants other than O₂, such as H₂O₂, N₂O or CO₂, is also briefly discussed. Based on such analysis and recent discoveries and process developments, our perspective is given. Full article

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

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