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Catalysts, Volume 9, Issue 9 (September 2019)

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Open AccessArticle
Screening NOx Storage Performance—Demonstrating a High Throughput Approach for Evaluating Emission Control Catalysts under Transient Conditions
Catalysts 2019, 9(9), 776; https://doi.org/10.3390/catal9090776 (registering DOI) - 16 Sep 2019
Abstract
At hte the high throughput (HT) approach is applied in the field of environmental catalysis on a routine basis. Research programs for automotive applications require validated screening protocols for conditions relevant to engine exhaust as well as experimental measures to ensure quality control [...] Read more.
At hte the high throughput (HT) approach is applied in the field of environmental catalysis on a routine basis. Research programs for automotive applications require validated screening protocols for conditions relevant to engine exhaust as well as experimental measures to ensure quality control using statistical design of experiment. To illustrate the HT approach for a test protocol with dynamic feed switches in a 48-fold reactor, 15 model catalysts for lean NOx traps (LNT) were prepared and screened fresh and after 800 °C hydrothermal aging. In the fresh state, highest NOx efficiency was found at 350–450 °C. A ranking of BaO > SrO > CaO was found as the most active NOx storage components when used as dopants on alumina. 800 °C aging results in a severe performance loss. Using XRD and BET analysis, Pt sintering is identified as most likely cause. These findings agree well with results from conventional tests reported in the literature. Full article
(This article belongs to the Section Environmental Catalysis)
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Open AccessEditorial
Asymmetric Catalysis in Organic Synthesis
Catalysts 2019, 9(9), 775; https://doi.org/10.3390/catal9090775 - 15 Sep 2019
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(This article belongs to the Special Issue Asymmetric Catalysis in Organic Synthesis)
Open AccessCommunication
One-Pot Solvent-Free Synthesis of N,N-Bis(2-Hydroxyethyl) Alkylamide from Triglycerides Using Zinc-Doped Calcium Oxide Nanospheroids as a Heterogeneous Catalyst
Catalysts 2019, 9(9), 774; https://doi.org/10.3390/catal9090774 - 14 Sep 2019
Viewed by 165
Abstract
N,N-Bis(2-hydroxyethyl) alkylamide or fatty acid diethanolamides (FADs) were prepared from a variety of triglycerides using diethanolamine in the presence of different transition metal-doped CaO nanocrystalline heterogeneous catalysts. The Zn-doped Cao nanospheroids were found to be the most efficient heterogeneous catalyst, with complete [...] Read more.
N,N-Bis(2-hydroxyethyl) alkylamide or fatty acid diethanolamides (FADs) were prepared from a variety of triglycerides using diethanolamine in the presence of different transition metal-doped CaO nanocrystalline heterogeneous catalysts. The Zn-doped Cao nanospheroids were found to be the most efficient heterogeneous catalyst, with complete conversion of natural triglycerides to fatty acid diethanolamide in 30 min at 90 °C. The Zn/CaO nanoparticles were recyclable for up to six reaction cycles and showed complete conversion even at room temperature. The amidation reaction of natural triglycerides was found to follow the pseudo-first-order kinetic model, and the first-order rate constant was calculated as 0.171 min–1 for jatropha oil aminolysis. The activation energy (Ea) and pre-exponential factor (A) for the same reaction were found to be 47.8 kJ mol–1 and 4.75 X 108 min-1, respectively. Full article
(This article belongs to the Special Issue Biomass Derived Heterogeneous and Homogeneous Catalysts)
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Open AccessArticle
Reverse Water-Gas Shift Iron Catalyst Derived from Magnetite
Catalysts 2019, 9(9), 773; https://doi.org/10.3390/catal9090773 - 14 Sep 2019
Viewed by 114
Abstract
The catalytic properties of unsupported iron oxides, specifically magnetite (Fe3O4), were investigated for the reverse water-gas shift (RWGS) reaction at temperatures between 723 K and 773 K and atmospheric pressure. This catalyst exhibited a fast catalytic CO formation rate [...] Read more.
The catalytic properties of unsupported iron oxides, specifically magnetite (Fe3O4), were investigated for the reverse water-gas shift (RWGS) reaction at temperatures between 723 K and 773 K and atmospheric pressure. This catalyst exhibited a fast catalytic CO formation rate (35.1 mmol h−1 gcat.−1), high turnover frequency (0.180 s−1), high CO selectivity (> 99%), and high stability (753 K, 45000 cm3h−1gcat.−1) under a 1:1 H2 to CO2 ratio. Reaction rates over the Fe3O4 catalyst displayed a strong dependence on H2 partial pressure (reaction order of ~0.8) and a weaker dependence on CO2 partial pressure (reaction order of 0.33) under an equimolar flow of both reactants. X-ray powder diffraction patterns and XPS spectra reveal that the bulk composition and structure of the post-reaction catalyst was formed mostly of metallic Fe and Fe3C, while the surface contained Fe2+, Fe3+, metallic Fe and Fe3C. Catalyst tests on pure Fe3C (iron carbide) suggest that Fe3C is not an effective catalyst for this reaction at the conditions investigated. Gas-switching experiments (CO2 or H2) indicated that a redox mechanism is the predominant reaction pathway. Full article
(This article belongs to the Special Issue Iron and Cobalt Catalysts)
Open AccessArticle
Recent Advances in Industrial Sulfur Tolerant Water Gas Shift Catalysts for Syngas Hydrogen Enrichment: Application of Lean (Low) Steam/Gas Ratio
Catalysts 2019, 9(9), 772; https://doi.org/10.3390/catal9090772 - 14 Sep 2019
Viewed by 172
Abstract
A novel sulfur tolerant water gas shift (SWGS) catalyst has been developed for the applications under lean (low) steam/gas ratio conditions, which has been extensively used for H2/CO adjustment of syngas and H2 enrichment in the world since 2000s with [...] Read more.
A novel sulfur tolerant water gas shift (SWGS) catalyst has been developed for the applications under lean (low) steam/gas ratio conditions, which has been extensively used for H2/CO adjustment of syngas and H2 enrichment in the world since 2000s with safer operation and lower steam consumption. Technology design and catalyst performances under different lean steam/gas conditions were comprehensively reported. Industrial data were collected from several large scale running plants with a variety of served catalysts characterized and precisely re-examined in the laboratory. It is shown that the developed Mo–Co/alkali/Al2O3 SWGS catalyst can operate very steadily even with the steam/gas ratio as low as 0.2–0.3, and the main deactivation factors are accidental caking, sintering, as well as poisoning impurities, such as As or Cl. The adoption of lean steam/gas SWGS catalyst can significantly improve the plant efficiency & safety and remarkably reduce the actual steam consumption for H2 production, which can decrease CO2 emission correspondingly. The work helps to evaluate how specially designed SWGS catalysts performed under applied lean steam/gas conditions, providing important references for researchers and industry. Full article
(This article belongs to the Special Issue Catalysts for Syngas Production)
Open AccessReview
A Critical Review of Recent Progress and Perspective in Practical Denitration Application
Catalysts 2019, 9(9), 771; https://doi.org/10.3390/catal9090771 - 13 Sep 2019
Viewed by 161
Abstract
Nitrogen oxides (NOx) represent one of the main sources of haze and pollution of the atmosphere as well as the causes of photochemical smog and acid rain. Furthermore, it poses a serious threat to human health. With the increasing emission of [...] Read more.
Nitrogen oxides (NOx) represent one of the main sources of haze and pollution of the atmosphere as well as the causes of photochemical smog and acid rain. Furthermore, it poses a serious threat to human health. With the increasing emission of NOx, it is urgent to control NOx. According to the different mechanisms of NOx removal methods, this paper elaborated on the adsorption method represented by activated carbon adsorption, analyzed the oxidation method represented by Fenton oxidation, discussed the reduction method represented by selective catalytic reduction, and summarized the plasma method represented by plasma-modified catalyst to remove NOx. At the same time, the current research status and existing problems of different NOx removal technologies were revealed and the future development prospects were forecasted. Full article
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Open AccessArticle
Efficient Production of Medium-Chain Structured Phospholipids over Mesoporous Organosulfonic Acid-Functionalized SBA-15 Catalysts
Catalysts 2019, 9(9), 770; https://doi.org/10.3390/catal9090770 - 13 Sep 2019
Viewed by 135
Abstract
It is highly desirable that efficient recoverable heterogeneous catalysts should be developed to replace the costly biocatalysts used in producing structured phospholipids (SPLs) with medium-chain fatty acids (MCFAs). Thus, mesoporous propyl and phenyl sulfonic acid-functionalized SBA-15 materials synthesized via surface modification methods were [...] Read more.
It is highly desirable that efficient recoverable heterogeneous catalysts should be developed to replace the costly biocatalysts used in producing structured phospholipids (SPLs) with medium-chain fatty acids (MCFAs). Thus, mesoporous propyl and phenyl sulfonic acid-functionalized SBA-15 materials synthesized via surface modification methods were investigated for the soybean lecithin interesterification with methyl caprate or caprylate. The physicochemical properties of the synthesized solid acids were deeply studied by small-angle X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared and pyridine adsorption, etc. to build the possible structure–performance relationships. The results revealed that amounts of organosulfonic acid groups were successfully grafted onto the SBA-15 support, and most of the surface acid sites contained in the as-prepared organic–inorganic hybrid samples were assigned as strong Brӧnsted acid sites. Notably, the functionalized SBA-15 materials exhibited promising catalytic behaviors in producing MCFA-enriched SPLs under mild conditions (40 °C, 6 h) when compared with commercial Amberlyst-15 and typical phospholipases or lipases, mostly due to their high surface area, ordered structure and adequate Brӧnsted acid sites. Besides, the as-prepared materials could be easily recycled five times without obvious deactivation. This work might shed light on alternative catalysts for SPL production instead of the costly enzymes. Full article
(This article belongs to the Special Issue Catalysis by Silica and Related Materials)
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Open AccessArticle
Novel Submerged Photocatalytic Membrane Reactor for Treatment of Olive Mill Wastewaters
Catalysts 2019, 9(9), 769; https://doi.org/10.3390/catal9090769 - 13 Sep 2019
Viewed by 114
Abstract
A new hybrid photocatalytic membrane reactor that can easily be scaled-up was designed, assembled and used to test photocatalytic membranes developed using the sol–gel technique. Extremely high removals of total suspended solids, chemical oxygen demand, total organic carbon, phenolic and volatile compounds were [...] Read more.
A new hybrid photocatalytic membrane reactor that can easily be scaled-up was designed, assembled and used to test photocatalytic membranes developed using the sol–gel technique. Extremely high removals of total suspended solids, chemical oxygen demand, total organic carbon, phenolic and volatile compounds were obtained when the hybrid photocatalytic membrane reactor was used to treat olive mill wastewaters. The submerged photocatalytic membrane reactor proposed and the modified membranes represent a step forward towards the development of new advanced treatment technology able to cope with several water and wastewater contaminants. Full article
(This article belongs to the Special Issue Photocatalytic Membrane Reactors)
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Open AccessArticle
Effect of Zirconia Polymorph on Vapor-Phase Ketonization of Propionic Acid
Catalysts 2019, 9(9), 768; https://doi.org/10.3390/catal9090768 - 13 Sep 2019
Viewed by 126
Abstract
Vapor-phase ketonization of propionic acid derived from biomass was studied at 300–375 °C over ZrO2 with different zirconia polymorph. The tetragonal ZrO2 (t-ZrO2) are more active than monoclinic ZrO2 (m-ZrO2). The results of characterizations from X-ray [...] Read more.
Vapor-phase ketonization of propionic acid derived from biomass was studied at 300–375 °C over ZrO2 with different zirconia polymorph. The tetragonal ZrO2 (t-ZrO2) are more active than monoclinic ZrO2 (m-ZrO2). The results of characterizations from X-ray diffraction (XRD) and Raman suggest m-ZrO2 and t-ZrO2 are synthesized by the solvothermal method. NH3 and CO2 temperature-programmed desorption (NH3-TPD and CO2-TPD) measurements show that there were more medium-strength Lewis acid base sites with lower coordination exposed on m-ZrO2 relative to t-ZrO2, increasing the adsorption strength of propionic acid. The in situ DRIFTS (Diffuse reflectance infrared Fourier transform spectroscopy) of adsorbed propionic acid under ketonization reaction reveal that as the most abundant surface intermediates, the monodentate propionates are more active than bidentate propionates. In comparison with m-ZrO2, the t-ZrO2 surface favors monodentate adsorption over bidentate adsorption. Additionally, the adsorption strength of monodentate propionate is weaker on t-ZrO2. These differences in adsorption configuration and adsorption strength of propionic acid are affected by the zirconia structure. The higher surface concentration and weaker adsorption strength of monodentate propionates contribute to the higher ketonization rate in the steady state. Full article
(This article belongs to the Section Biomass Catalysis)
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Open AccessArticle
Hierarchical PtIn/Mg(Al)O Derived from Reconstructed PtIn-hydrotalcite-like Compounds for Highly Efficient Propane Dehydrogenation
Catalysts 2019, 9(9), 767; https://doi.org/10.3390/catal9090767 - 12 Sep 2019
Viewed by 185
Abstract
The challenges facing propane dehydrogenation are to solve the Pt sintering and carbon deposition. This paper provides a new way to disperse and stabilize Pt species and resist carbon deposition. Highly dispersed Pt species were topologically transformed from reconstructed PtIn-hydrotalcite-like precursors in a [...] Read more.
The challenges facing propane dehydrogenation are to solve the Pt sintering and carbon deposition. This paper provides a new way to disperse and stabilize Pt species and resist carbon deposition. Highly dispersed Pt species were topologically transformed from reconstructed PtIn-hydrotalcite-like precursors in a flower-like hierarchical microstructure. The lattice confinement of reconstructed hydrotalcite-like precursor is in favor of stabilizing the highly dispersed Pt species, and the hierarchical microstructure is an important factor to prolong its lifetime by enhancing tolerance to carbon deposition. In propane dehydrogenation, the propene selectivity decreases in the sequences of catalyst in flower-like > single-plate > block mass with small, flakeys. A propene selectivity of >97% with a conversion of 48% at 600 °C has been achieved over a flower-like PtIn/Mg(Al)O catalyst. Additionally, no visible Pt sintering can even be observed on this catalyst after a reaction time of 190 h. This strategy provides an effective and feasible alternative for the facile preparation of highly dispersed metal catalysts. Full article
(This article belongs to the Special Issue Catalytic Applications of Clay Minerals and Hydrotalcites)
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Open AccessArticle
Designing a Mesoporous Zeolite Catalyst for Products Optimizing in n-Decane Hydrocraking
Catalysts 2019, 9(9), 766; https://doi.org/10.3390/catal9090766 - 12 Sep 2019
Viewed by 137
Abstract
Mesoporous ZSM-5 zeolite is developed to enhance the catalytic performance in a hydrocracking reaction. The generated mesopores and mesoporous channels in the new catalyst supply more opportunities for reactant accessing the active sites according to the better mass transfer and diffusion. Meanwhile, the [...] Read more.
Mesoporous ZSM-5 zeolite is developed to enhance the catalytic performance in a hydrocracking reaction. The generated mesopores and mesoporous channels in the new catalyst supply more opportunities for reactant accessing the active sites according to the better mass transfer and diffusion. Meanwhile, the acidity of the mesoporous catalyst is also weakened because of the removal of Si and Al species from its MFI structure, which makes the products distribution drift to more valued chemicals such as olefins. In the modified mesoporous ZSM-5 zeolites via different metallic promoters, the olefins’ selectivity increases as the alkalinity of the catalyst increases. The reason for this is that the formed olefins will be further hydrogenated into corresponding alkanes immediately over the extremely acidic zeolite catalyst. Hence, the moderate alkalinity will limit this process, while at the same time the remaining olefins products will too. Furthermore, the Pd-based mesoporous ZSM-5 zeolite shows an excellent n-decane conversion and high propane selectivity due to the occurrence of hydrogen spillover via the Pd promoter. The phenomenon of hydrogen spillover supplies more chemisorbed sites of hydrogen atoms for hydrocracking and hydrogenating in this reaction. In short, this study explores the important effect factors in n-decane hydrocracking reaction activity and products distribution. It also shows a potential for the further industrial application of petroleum-derived fuel hydrocracking according to the optimized products distribution under metallic promoted mesoporous zeolite. Full article
(This article belongs to the Section Catalytic Materials)
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Open AccessEditorial
Catalytic, Photocatalytic, and Electrocatalytic Processes for the Valorization of CO2
Catalysts 2019, 9(9), 765; https://doi.org/10.3390/catal9090765 - 12 Sep 2019
Viewed by 126
Abstract
Worldwide yearly CO2 emissions reached 36 Gt in 2014, whereas they amounted to ca [...] Full article
Open AccessArticle
Novel Composite Electrode of the Reduced Graphene Oxide Nanosheets with Gold Nanoparticles Modified by Glucose Oxidase for Electrochemical Reactions
Catalysts 2019, 9(9), 764; https://doi.org/10.3390/catal9090764 - 11 Sep 2019
Viewed by 211
Abstract
Graphene-based composites have been widely explored for electrode and electrocatalyst materials for electrochemical energy systems. In this paper, a novel composite material of the reduced graphene oxide nanosheets (rGON) with gold nanoparticles (NPs) (rGON-AuNP) is synthesized, and its morphology, structure, and composition are [...] Read more.
Graphene-based composites have been widely explored for electrode and electrocatalyst materials for electrochemical energy systems. In this paper, a novel composite material of the reduced graphene oxide nanosheets (rGON) with gold nanoparticles (NPs) (rGON-AuNP) is synthesized, and its morphology, structure, and composition are characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopic (FTIR), Raman, and UV-Vis techniques. To confirm this material’s electrochemical activity, a glucose oxidase (GOD) is chosen as the target reagent to modify the rGON-AuNP layer to form GOD/rGON-AuNP/glassy carbon (GC) electrode. Two pairs of distinguishable redox peaks, corresponding to the redox processes of two different conformational GOD on AuNP, are observed on the cyclic voltammograms of GOD/rGON-AuNP/GC electrode. Both cyclic voltammetry and electrochemical impedance spectroscopy are employed to study the mechanism of direct electron transfer from GOD to GC electrode on the rGON-AuNP layer. In addition, this GOD/rGON-AuNP/GC electrode shows catalytic activity toward glucose oxidation reaction. Full article
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Open AccessFeature PaperEditorial
Enzyme-Mediated Stereoselective Synthesis
Catalysts 2019, 9(9), 763; https://doi.org/10.3390/catal9090763 - 11 Sep 2019
Viewed by 192
Abstract
All of us know very well the importance of the catalysis in organic synthesis [...] Full article
(This article belongs to the Special Issue Enzyme-Mediated Stereoselective Synthesis)
Open AccessReview
Bimetallic Iron–Cobalt Catalysts and Their Applications in Energy-Related Electrochemical Reactions
Catalysts 2019, 9(9), 762; https://doi.org/10.3390/catal9090762 - 11 Sep 2019
Viewed by 170
Abstract
Since the persistently increasing trend of energy consumption, technologies for renewable energy production and conversion have drawn great attention worldwide. The performance and the cost of electrocatalysts play two crucial roles in the globalization of advanced energy conversion devices. Among the developed technics [...] Read more.
Since the persistently increasing trend of energy consumption, technologies for renewable energy production and conversion have drawn great attention worldwide. The performance and the cost of electrocatalysts play two crucial roles in the globalization of advanced energy conversion devices. Among the developed technics involving metal catalysts, transition-metal catalysts (TMC) are recognized as the most promising materials due to the excellent properties and stability. Particularly, the iron–cobalt bimetal catalysts exhibit exciting electrochemical properties because of the interior cooperative effects. Herein, we summarize recent advances in iron–cobalt bimetal catalysts for electrochemical applications, especially hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). Moreover, the components and synergetic effects of the composites and catalytic mechanism during reaction processes are highlighted. On the basis of extant catalysts and mechanism, the current issues and prospective outlook of the field are also discussed. Full article
(This article belongs to the Special Issue Iron and Cobalt Catalysts)
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Open AccessArticle
New Evidence of the Enhanced Elimination of a Persistent Drug Used as a Lipid Absorption Inhibitor by Advanced Oxidation with UV-A and Nanosized Catalysts
Catalysts 2019, 9(9), 761; https://doi.org/10.3390/catal9090761 - 11 Sep 2019
Viewed by 146
Abstract
This work demonstrates new evidence of the efficient destruction and mineralization of an emergent organic pollutant using UV-A and titanium nanosized catalysts. The target compound considered in this work is the primary metabolite of a lipid regulator drug, clofibrate, identified in many studies [...] Read more.
This work demonstrates new evidence of the efficient destruction and mineralization of an emergent organic pollutant using UV-A and titanium nanosized catalysts. The target compound considered in this work is the primary metabolite of a lipid regulator drug, clofibrate, identified in many studies as refractory during conventional wastewater treatment. The photocatalytic performance study was carried out in batch mode at laboratory scale, in aqueous suspension. Kinetic data showed that titanium dioxide P25 Aeroxide® exhibits the highest photocatalytic efficiency compared to the other investigated catalysts. Pollutant degradation and mineralization efficiencies strongly increased when decreasing the initial substrate concentration. Target molecules oxidized faster when the catalyst load increased, and the mineralization was enhanced under acidic conditions: 92% of mineralization was achieved at pH 4 after 190 min of reaction. Radical quenching assays confirmed that HO and ( h vb + ) were the reactive oxygen species involved in the photocatalytic oxidation of the considered pollutant. In addition, further results revealed that the removal efficiency decreased in real water matrices. Finally, data collected through a series of phytotoxicity tests demonstrated that the photocatalytic process considerably reduces the toxicity of the treated solutions, confirming the process’s effectiveness in the removal of persistent and biorefractory emergent organic water pollutants. Full article
(This article belongs to the Special Issue Photocatalysis Science and Engineering in Europe)
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Open AccessReview
Molecular Catalysis for Utilizing CO2 in Fuel Electro-Generation and in Chemical Feedstock
Catalysts 2019, 9(9), 760; https://doi.org/10.3390/catal9090760 - 10 Sep 2019
Viewed by 207
Abstract
Processes for the conversion of CO2 to valuable chemicals are highly desired as a result of the increasing CO2 levels in the atmosphere and the subsequent elevating global temperature. However, CO2 is thermodynamically and kinetically inert to transformation and, therefore, [...] Read more.
Processes for the conversion of CO2 to valuable chemicals are highly desired as a result of the increasing CO2 levels in the atmosphere and the subsequent elevating global temperature. However, CO2 is thermodynamically and kinetically inert to transformation and, therefore, many efforts were made in the last few decades. Reformation/hydrogenation of CO2 is widely used as a means to access valuable products such as acetic acids, CH4, CH3OH, and CO. The electrochemical reduction of CO2 using hetero- and homogeneous catalysts recently attracted much attention. In particular, molecular CO2 reduction catalysts were widely studied using transition-metal complexes modified with various ligands to understand the relationship between various catalytic properties and the coordination spheres above the metal centers. Concurrently, the coupling of CO2 with various electrophiles under homogeneous conditions is also considered an important approach for recycling CO2 as a renewable C-1 substrate in the chemical industry. This review summarizes some recent advances in the conversion of CO2 into valuable chemicals with particular focus on the metal-catalyzed reductive conversion and functionalization of CO2. Full article
(This article belongs to the Special Issue Catalysis and Catalytic Processes for CO2 Conversion)
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Open AccessArticle
A Facile Synthesis of ZrOx-MnCO3/Graphene Oxide (GRO) Nanocomposites for the Oxidation of Alcohols using Molecular Oxygen under Base Free Conditions
Catalysts 2019, 9(9), 759; https://doi.org/10.3390/catal9090759 - 10 Sep 2019
Viewed by 227
Abstract
Graphene and its nanocomposites are showing excellent potential in improving the catalytic performances of different materials. However, the synthetic protocol and its form, such as graphene oxide (GRO) or highly reduced graphene oxide (HRG), influence the catalytic efficiencies. Here, we present, a facile [...] Read more.
Graphene and its nanocomposites are showing excellent potential in improving the catalytic performances of different materials. However, the synthetic protocol and its form, such as graphene oxide (GRO) or highly reduced graphene oxide (HRG), influence the catalytic efficiencies. Here, we present, a facile synthesis of graphene oxide (GRO) and ZrOx-MnCO3-based nanocomposites [(1%)ZrOx–MnCO3/(x%)GRO] and their outcome as an oxidation catalyst for alcohol oxidation under mild conditions using O2 as a clean oxidant. The ZrOx–MnCO3/GRO catalyst prepared by incorporating GRO to pre-calcined ZrOx-MnCO3 using ball milling showed remarkable enhancement in the catalytic activities as compared to pristine ZrOx–MnCO3, ZrOx–MnCO3 supported on HRG or ZrOx–MnCO3/GRO prepared by in-situ growth of ZrOx–MnCO3 onto GRO followed by calcination. The catalyst with composition (1%)ZrOx–MnCO3/(1%)GRO exhibited superior specific activity (57.1 mmol/g·h) with complete conversion and >99% selectivity of the product within a short period of time (7 min) and at a relatively lower temperature (100 °C). The catalyst could be recycled at least five times with a negligible decrease in efficiency and selectivity. The catalytic study was extended to different aromatic as well as aliphatic alcohols under optimized conditions, which confirmed the efficiency and selectivity of the catalyst. Full article
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Open AccessReview
Zeolite-Based Catalysts: A Valuable Approach toward Ester Bond Formation
Catalysts 2019, 9(9), 758; https://doi.org/10.3390/catal9090758 - 09 Sep 2019
Viewed by 243
Abstract
Zeolite-based catalysts are versatile catalytic systems for a wide range of laboratory studies and industrial scale processes. The chemical composition, ion exchange, and pore size structure attributes of zeolites are responsible for their extensive catalytic applications. Esterification is one of the most important [...] Read more.
Zeolite-based catalysts are versatile catalytic systems for a wide range of laboratory studies and industrial scale processes. The chemical composition, ion exchange, and pore size structure attributes of zeolites are responsible for their extensive catalytic applications. Esterification is one of the most important and routinely processes in diverse fields of organic synthesis. It has a long history in both industrial processes and laboratory work due to its versatility. This review intends to give a detailed insight into the significance of zeolite-based catalysts for ester bond formation Full article
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Open AccessArticle
Adsorption Characteristics of Gas Molecules (H2O, CO2, CO, CH4, and H2) on CaO-Based Catalysts during Biomass Thermal Conversion with in Situ CO2 Capture
Catalysts 2019, 9(9), 757; https://doi.org/10.3390/catal9090757 - 09 Sep 2019
Viewed by 207
Abstract
Biomass thermochemical conversion with in situ CO2 capture is a promising technology in the production of high-quality gas. The adsorption competition mechanism of gas molecules (H2O, CO2, CO, CH4, and H2) on CaO-based catalyst [...] Read more.
Biomass thermochemical conversion with in situ CO2 capture is a promising technology in the production of high-quality gas. The adsorption competition mechanism of gas molecules (H2O, CO2, CO, CH4, and H2) on CaO-based catalyst surfaces was studied using density functional theory (DFT) and experimental methods. The adsorption characteristics of CO2 on CaO and 10 wt % Ni/CaO (100) surfaces were investigated in a temperature range of 550–700 °C. The adsorption energies were increased and then weakened, reaching their maximum at 650 °C. The simulation results were verified by CO2 temperature-programmed desorption (CO2-TPD) experiments. By the density of states and Mulliken population analysis, CaO doped with Ni caused a change in the electronic structure of the Osurf atom and decreased the C–O bond stability. The molecular competition mechanism on the CaO-based catalyst surface was identified by DFT simulation. As a result, the adsorption energies decreased in the following order: H2O > CO2 > CO > CH4 > H2. The increase of CO2 adsorption energy on the 10 wt % Ni/CaO surface, compared with the CaO surface, was the largest among those of the studied molecules, and its value increased from 1.45 eV to 1.81 eV. Therefore, the 10 wt % Ni/CaO catalyst is conducive to in situ CO2 capture in biomass pyrolysis. Full article
(This article belongs to the Special Issue Catalysts for Production and Conversion of Syngas)
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Open AccessArticle
Surfactant-Free Synthesis of Reduced Graphene Oxide Supported Well-Defined Polyhedral Pd-Pt Nanocrystals for Oxygen Reduction Reaction
Catalysts 2019, 9(9), 756; https://doi.org/10.3390/catal9090756 - 09 Sep 2019
Viewed by 185
Abstract
Well-defined polyhedral Pd-Pt nanocrystals anchored on the reduced graphene oxide (rGO) are successfully synthesized via a facile and efficient surfactant-free solvothermal route. The formation mechanism is carefully illustrated via tuning the surface state of rGO substrate and the Pd/Pt ratio in Pd-Pt nanocrystals. [...] Read more.
Well-defined polyhedral Pd-Pt nanocrystals anchored on the reduced graphene oxide (rGO) are successfully synthesized via a facile and efficient surfactant-free solvothermal route. The formation mechanism is carefully illustrated via tuning the surface state of rGO substrate and the Pd/Pt ratio in Pd-Pt nanocrystals. rGO substrates with continuous smooth surface, which can offer continuous 2D larger π electrons, play important roles in the formation of the well-defined polyhedral Pd-Pt nanocrystals. Suitable Pd/Pt ratio, which determines the affinity between the rGO substrate and polyhedral Pd-Pt nanocrystals, is another important factor for the formation of polyhedral Pd-Pt nanocrystals. Due to the well-defined surface of Pd-Pt nanocrystals, rich corners and edges from polyhedral structure, as well as more exposed (111) facets, the low-Pt polyhedral Pd-Pt nanocrystals anchored on rGO, used as electrocatalysts, exhibit high electrocatalytic activity for oxygen reduction reaction with excellent methanol tolerance. Full article
(This article belongs to the Section Electrocatalysis)
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Open AccessFeature PaperArticle
Catalyst Stability Assessment in a Lab-Scale Liquid-Solid (LS)² Plug-Flow Reactor
Catalysts 2019, 9(9), 755; https://doi.org/10.3390/catal9090755 - 08 Sep 2019
Viewed by 278
Abstract
A packed-bed plug-flow reactor, denoted as the lab-scale liquid-solid (LS)² reactor, has been developed for the assessment of heterogeneous catalyst deactivation in liquid-phase reactions. The possibility to measure intrinsic kinetics was first verified with the model transesterification of ethyl acetate with methanol, catalyzed [...] Read more.
A packed-bed plug-flow reactor, denoted as the lab-scale liquid-solid (LS)² reactor, has been developed for the assessment of heterogeneous catalyst deactivation in liquid-phase reactions. The possibility to measure intrinsic kinetics was first verified with the model transesterification of ethyl acetate with methanol, catalyzed by the stable commercial resin Lewatit K2629, for which a turnover frequency (TOF) of 6.2 ± 0.4 × 10−3 s−1 was obtained. The absence of temperature and concentration gradients was verified with correlations and experimental tests. The potential for assessing the deactivation of a catalyst was demonstrated by a second intrinsic kinetics evaluation where a methylaminopropyl (MAP)-functionalized mesoporous silica catalyst was used for the aldol reaction of acetone with 4-nitrobenzaldehyde in different solvents. The cooperative MAP catalyst deactivated as a function of time on stream when using hexane as solvent. Yet, the monofunctional MAP catalyst exhibited stable activity for at least 4 h on stream, which resulted in a TOF of 1.2 ± 0.1 × 10−3 s−1. It did, however, deactivate with dry acetone or DMSO as solvent due to the formation of site-blocking species. This deactivation was mitigated by co-feeding 2 wt % of water to DMSO, resulting in stable catalyst activity. Full article
(This article belongs to the Special Issue Reactors and Models in Catalysis)
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Open AccessCommunication
Enhanced Selective Production of Carbonyl Products for Aerobic Oxidation of Benzylic Alcohols over Mesoporous Fe2O3 Supported Gold Nanoparticles
Catalysts 2019, 9(9), 754; https://doi.org/10.3390/catal9090754 - 08 Sep 2019
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Abstract
Ordered mesoporous Fe2O3 supported gold nanoparticles with a desired specific surface area and porous structure (Au/meso-Fe2O3) was successfully fabricated with a hard templating method by using KIT-6 as the template. The morphology and physico-chemical properties of [...] Read more.
Ordered mesoporous Fe2O3 supported gold nanoparticles with a desired specific surface area and porous structure (Au/meso-Fe2O3) was successfully fabricated with a hard templating method by using KIT-6 as the template. The morphology and physico-chemical properties of Au/meso-Fe2O3 were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM), etc. The gold nanoparticles are highly dispersed on the surface of the mesoporous Fe2O3. The catalytic performance of the synthesized catalyst was studied for the aerobic oxidation of benzylic alcohols in β–O–4 linked lignin model dimers to the corresponding carbonyl products under atmosphere pressure. Au/meso-Fe2O3 shows an enhanced activity for the aerobic oxidation of 1-phenylethanol in comparison with that of Au/bulk-Fe2O3. The promoted catalytic activity is related to the confined porous structure of mesoporous Fe2O3 and more boundaries contact between gold and meso-Fe2O3, which shows that the porous structure of the support has a significant influence on the activity of gold catalysts. Full article
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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Open AccessArticle
Microwave-Assisted One-Step Conversion of Wood Wastes into Levulinic Acid
Catalysts 2019, 9(9), 753; https://doi.org/10.3390/catal9090753 - 07 Sep 2019
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Abstract
This study aimed to evaluate the use of softwood and hardwood waste for the production of levulinic acid by one-stage conversion using microwave radiation combined with acid catalysis. The analysis demonstrated that the type and concentration of the acid used, the concentration of [...] Read more.
This study aimed to evaluate the use of softwood and hardwood waste for the production of levulinic acid by one-stage conversion using microwave radiation combined with acid catalysis. The analysis demonstrated that the type and concentration of the acid used, the concentration of biomass in the reaction mixture and pressure value had the greatest impact on the yield of levulinic acid. The highest efficiency of carbohydrate conversion to levulinic acid, regardless of the type of raw material, was achieved using a pressure of 225 PSI and sulfuric acid as a catalyst. Maximum yield from biomass, ca. 16.5% for cherry wood chips and ca. 25% for pine chips, was obtained using sulfuric acid at a concentration of 1% v/v and 2% v/v, respectively, for the following process parameters: Exposure time 20 min, biomass concentration 3.3%, and the pressure of 225 PSI. The ratio of actual yield to theoretical yield was high: 64.7% ± 4.5% for pine chips and 43.4% ± 1.0% for cherry wood chips. High efficiency of the presented method of biomass conversion to levulinic acid indicates the possibility of its use for waste management in the wood processing industry. High concentration of levulinic acid in the post-reaction mixture allows for cost-effective extraction and purification of the compound. Full article
(This article belongs to the Section Biomass Catalysis)
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Open AccessArticle
Effect of Preparation Method on ZrO2-Based Catalysts Performance for Isobutanol Synthesis from Syngas
Catalysts 2019, 9(9), 752; https://doi.org/10.3390/catal9090752 - 06 Sep 2019
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Abstract
Two types of amorphous ZrO2 (am-ZrO2) catalysts were prepared by different co-precipitation/reflux digestion methods (with ethylenediamine and ammonia as the precipitant respectively). Then, copper and potassium were introduced for modifying ZrO2 via an impregnation method to enhance the catalytic [...] Read more.
Two types of amorphous ZrO2 (am-ZrO2) catalysts were prepared by different co-precipitation/reflux digestion methods (with ethylenediamine and ammonia as the precipitant respectively). Then, copper and potassium were introduced for modifying ZrO2 via an impregnation method to enhance the catalytic performance. The obtained catalysts were further characterized by means of Brunauer-Emmett-Teller surface areas (BET), X-ray diffraction (XRD), H2-temperature-programmed reduction (H2-TPR), and In situ diffuse reflectance infrared spectroscopy (in situ DRIFTS). CO hydrogenation experiments were performed in a fixed-bed reactor for isobutanol synthesis. Great differences were observed on the distribution of alcohols over the two types of ZrO2 catalysts, which were promoted with the same content of Cu and K. The selectivity of isobutanol on K-CuZrO2 (ammonia as precipitant, A-KCZ) was three times higher than that on K-CuZrO2 (ethylenediamine as precipitant, E-KCZ). The characterization results indicated that the A-KCZ catalyst supplied more active hydroxyls (isolated hydroxyls) for anchoring and dispersing Cu. More importantly, it was found that bicarbonate species were formed, which were ascribed as important C1 species for isobutanol formation on the A-KCZ catalyst surface. These C1 intermediates had relatively stronger adsorption strength than those adsorbed on the E-KCZ catalyst, indicating that the bicarbonate species on the A-KCZ catalyst had a longer residence time for further carbon chain growth. Therefore, the selectivity of isobutanol was greatly enhanced. These findings would extend the horizontal of direct alcohols synthesis from syngas. Full article
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Open AccessArticle
In Situ Preparation of Pr1-xCaxMnO3 and La1-xSrxMnO3 Catalysts Surface for High-Resolution Environmental Transmission Electron Microscopy
Catalysts 2019, 9(9), 751; https://doi.org/10.3390/catal9090751 - 06 Sep 2019
Viewed by 218
Abstract
The study of changes in the atomic structure of a catalyst under chemical reaction conditions is extremely important for understanding the mechanism of their operation. For in situ environmental transmission electron microscopy (ETEM) studies, this requires preparation of electron transparent ultrathin TEM lamella [...] Read more.
The study of changes in the atomic structure of a catalyst under chemical reaction conditions is extremely important for understanding the mechanism of their operation. For in situ environmental transmission electron microscopy (ETEM) studies, this requires preparation of electron transparent ultrathin TEM lamella without surface damage. Here, thin films of Pr1-xCaxMnO3 (PCMO, x = 0.1, 0.33) and La1-xSrxMnO3 (LSMO, x = 0.4) perovskites are used to demonstrate a cross-section specimen preparation method, comprised of two steps. The first step is based on optimized focused ion beam cutting procedures using a photoresist protection layer, finally being removed by plasma-etching. The second step is applicable for materials susceptible to surface amorphization, where in situ recrystallization back to perovskite structure is achieved by using electron beam driven chemistry in gases. This requires reduction of residual water vapor in a TEM column. Depending on the gas environment, long crystalline facets having different atomic terminations and Mn-valence state, can be prepared. Full article
(This article belongs to the Section Electrocatalysis)
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Open AccessArticle
Characteristics of Water and Urea–Water Solution Sprays
Catalysts 2019, 9(9), 750; https://doi.org/10.3390/catal9090750 - 06 Sep 2019
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Abstract
In spray studies related to selective catalytic reduction (SCR) systems a common approach is to replace the urea–water solution (UWS) with pure water, even though there is very limited detailed information on the spray properties for these two liquids obtained under the same [...] Read more.
In spray studies related to selective catalytic reduction (SCR) systems a common approach is to replace the urea–water solution (UWS) with pure water, even though there is very limited detailed information on the spray properties for these two liquids obtained under the same conditions using the same experimental equipment. Neither is it known how the possible differences in spray properties influence computational fluid dynamics (CFD) simulations. In this study, besides the flow characteristics, we compare both global and local spray parameters measured for UWS and pure water in the same conditions. To our knowledge, this is the first study which examines the influence on the injection process of replacing UWS with water over such a wide range. Moreover, the influence of different spray properties on CFD simulations is also examined. The experimental studies showed differences in almost all considered spray parameters. Moreover, different spray behaviour was noticed in terms of primary break-up. One important finding is that water and UWS sprays do have a similar Sauter mean diameter, but at the same time the droplet size distribution is considerably different. The simulation results indicated noticeable differences in terms of wall film formation; nevertheless, the overall mixing performance was not significantly affected. Full article
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Open AccessArticle
New Insights into the Electrocatalytic Mechanism of Methanol Oxidation on Amorphous Ni-B-Co Nanoparticles in Alkaline Media
Catalysts 2019, 9(9), 749; https://doi.org/10.3390/catal9090749 - 05 Sep 2019
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Abstract
Despite an increased interest in sustainable energy conversion systems, there have been limited studies investigating the electrocatalytic reaction mechanism of methanol oxidation on Ni-based amorphous materials in alkaline media. A thorough understanding of such mechanisms would aid in the development of amorphous catalytic [...] Read more.
Despite an increased interest in sustainable energy conversion systems, there have been limited studies investigating the electrocatalytic reaction mechanism of methanol oxidation on Ni-based amorphous materials in alkaline media. A thorough understanding of such mechanisms would aid in the development of amorphous catalytic materials for methanol oxidation reactions. In the present work, amorphous Ni-B and Ni-B-Co nanoparticles were prepared by a simple chemical reduction, and their electrocatalytic properties were investigated by cyclic voltammetry measurements. The diffusion coefficients (D0) for Ni-B, Ni-B-Co0.02, Ni-B-Co0.05, and Ni-B-Co0.1 nanoparticles were calculated to be 1.28 × 10−9, 2.35 × 10−9, 4.48 × 10−9 and 2.67 × 10−9 cm2 s−1, respectively. The reaction order of methanol in the studied transformation was approximately 0.5 for all studied catalysts, whereas the reaction order of the hydroxide ion was nearly 1. The activation energy (Ea) values of the reaction were also calculated for the Ni-B and Ni-B-Co nanoparticle systems. Based on our kinetic studies, a mechanism for the methanol oxidation reaction was proposed which involved formation of an electrocatalytic layer on the surface of amorphous Ni–B and Ni-B-Co nanoparticles. And methanol and hydroxide ions could diffuse freely through this three-dimensional porous conductive layer. Full article
(This article belongs to the Section Electrocatalysis)
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Open AccessArticle
Rapid Microwave-Assisted Polyol Synthesis of TiO2-Supported Ruthenium Catalysts for Levulinic Acid Hydrogenation
Catalysts 2019, 9(9), 748; https://doi.org/10.3390/catal9090748 - 05 Sep 2019
Viewed by 241
Abstract
One wt% Ru/TiO2 catalysts prepared by a one-pot microwave-assisted polyol method have been shown to be highly active for Levulinic acid hydrogenation to γ-Valerolactone. Preparation temperature, microwave irradiation time and choice of Ru precursor were found to have a significant effect on [...] Read more.
One wt% Ru/TiO2 catalysts prepared by a one-pot microwave-assisted polyol method have been shown to be highly active for Levulinic acid hydrogenation to γ-Valerolactone. Preparation temperature, microwave irradiation time and choice of Ru precursor were found to have a significant effect on catalyst activity. In the case of Ru(acac)3-derived catalysts, increasing temperature and longer irradiation times increased catalyst activity to a maximum LA conversion of 69%. Conversely, for catalysts prepared using RuCl3, shorter preparation times and lower temperatures yielded more active catalysts, with a maximum LA conversion of 67%. Catalysts prepared using either precursor were found to contain highly dispersed nanoparticles <3 nm in diameter. XPS analysis of the most and least active catalysts shows that the catalyst surface is covered in a layer of insoluble carbon with surface concentrations exceeding 40% in some cases. This can be attributed to the formation of large condensation oligomers from the reaction between the solvent, ethylene glycol and its oxidation products, as evidenced by the presence of C-O and C = O functionality on the catalyst surface. Full article
(This article belongs to the Special Issue Microwave-Assisted Catalysis)
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Open AccessArticle
Oxidative Degradation of Trichloroethylene over Fe2O3-doped Mayenite: Chlorine Poisoning Mitigation and Improved Catalytic Performance
Catalysts 2019, 9(9), 747; https://doi.org/10.3390/catal9090747 - 05 Sep 2019
Viewed by 201
Abstract
Mayenite was recently successfully employed as an active catalyst for trichloroethylene (TCE) oxidation. It was effective in promoting the conversion of TCE in less harmful products (CO2 and HCl) with high activity and selectivity. However, there is a potential limitation to the [...] Read more.
Mayenite was recently successfully employed as an active catalyst for trichloroethylene (TCE) oxidation. It was effective in promoting the conversion of TCE in less harmful products (CO2 and HCl) with high activity and selectivity. However, there is a potential limitation to the use of mayenite in the industrial degradation of chlorinated compounds—its limited operating lifespan owing to chlorine poisoning of the catalyst. To overcome this problem, in this work, mayenite-based catalysts loaded with iron (Fe/mayenite) were prepared and tested for TCE oxidation in a gaseous phase. The catalysts were characterized using different physico-chemical techniques, including XRD, ICP, N2-sorption (BET), H2-TPR analysis, SEM-EDX, XPS FESEM-EDS, and Raman. Fe/mayenite was found to be more active and stable than the pure material for TCE oxidation, maintaining the same selectivity. This result was interpreted as the synergistic effect of the metal and the oxo-anionic species present in the mayenite framework, thus promoting TCE oxidation, while avoiding catalyst deactivation. Full article
(This article belongs to the Special Issue Sustainable and Environmental Catalysis)
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