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Sökning: L773:2073 4344

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1.
  • Ajakaiye Jensen, Lucy Idowu, et al. (författare)
  • Effect of pd and ir as promoters in the activity of Ni/CeZrO2 catalyst for the reverse water-gas shift reaction
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:9
  • Tidskriftsartikel (refereegranskat)abstract
    • Catalytic conversion of CO2 to CO using reverse water gas shift (RWGS) reaction is a key intermediate step for many CO2 utilization processes. RWGS followed by well-known synthesis gas conversion may emerge as a potential approach to convert CO2 to valuable chemicals and fuels. Nickel (Ni) based catalysts with ceria-zirconia (Ce-Zr) support can be used to tune the metal-support interactions, resulting in a potentially enhanced CO2 hydrogenation rate and elongation of the catalyst lifespan. The thermodynamics of RWGS reaction is favored at high temperature for CO2 conversion. In this paper the effect of Palladium (Pd) and Iridium (Ir) as promoters in the activity of 10 wt%Ni 2 wt%Pd 0.1wt%Ir/CeZrO2 catalyst for the reverse water gas shift reaction was investigated. RWGS was studied for different feed (CO2:H2) ratios. The new active interface between Ni, Pd and Ir particles is proposed to be an important factor in enhancing catalytic activity. 10 wt%Ni 2 wt%Pd 0.1 wt%Ir/CeZrO2 catalyst showed a better activity with CO2 conversion of 52.4% and a CO selectivity of 98% for H2:CO2 (1:1) compared to the activity of 10%Ni/CeZrO2 with CO2 conversion of 49.9% and a CO selectivity of 93%. The catalytic activity for different feed ratios using 10 wt%Ni 2 wt%Pd 0.1 wt%Ir/CeZrO2 were also studied. The use of palladium and iridium boosts the stability and life span of the Ni-based catalysts. This indicates that the catalyst could be used potentially to design RWGS reactors for CO2 utilization units.
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2.
  • Al Soubaihi, Rola Mohammad, et al. (författare)
  • CO Oxidation Efficiency and Hysteresis Behavior over Mesoporous Pd/SiO2 Catalyst
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Carbon monoxide (CO) oxidation is considered an important reaction in heterogeneous industrial catalysis and has been extensively studied. Pd supported on SiO2 aerogel catalysts exhibit good catalytic activity toward this reaction owing to their CO bond activation capability and thermal stability. Pd/SiO2 catalysts were investigated using carbon monoxide (CO) oxidation as a model reaction. The catalyst becomes active, and the conversion increases after the temperature reaches the ignition temperature (T-ig). A normal hysteresis in carbon monoxide (CO) oxidation has been observed, where the catalysts continue to exhibit high catalytic activity (CO conversion remains at 100%) during the extinction even at temperatures lower than T-ig. The catalyst was characterized using BET, TEM, XPS, TGA-DSC, and FTIR. In this work, the influence of pretreatment conditions and stability of the active sites on the catalytic activity and hysteresis is presented. The CO oxidation on the Pd/SiO2 catalyst has been attributed to the dissociative adsorption of molecular oxygen and the activation of the C-O bond, followed by diffusion of adsorbates at T-ig to form CO2. Whereas, the hysteresis has been explained by the enhanced stability of the active site caused by thermal effects, pretreatment conditions, Pd-SiO2 support interaction, and PdO formation and decomposition.
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3.
  • Al Soubaihi, Rola Mohammad, et al. (författare)
  • Critical Review of Low-Temperature CO Oxidation and Hysteresis Phenomenon on Heterogeneous Catalysts
  • 2018
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 8:12
  • Forskningsöversikt (refereegranskat)abstract
    • There is a growing demand for new heterogeneous catalysts for cost-effective catalysis. Currently, the hysteresis phenomenon during low-temperature CO oxidation is an important topic in heterogeneous catalysis. Hysteresis provides important information about fluctuating reaction conditions that affect the regeneration of active sites and indicate the restoration of catalyst activity. Understanding its dynamic behavior, such as hysteresis and self-sustained kinetic oscillations, during CO oxidation, is crucial for the development of cost-effective, stable and long-lasting catalysts. Hysteresis during CO oxidation has a direct influence on many industrial processes and its understanding can be beneficial to a broad range of applications, including long-life CO2 lasers, gas masks, catalytic converters, sensors, indoor air quality, etc. This review considers the most recent reported advancements in the field of hysteresis behavior during CO oxidation which shed light on the origin of this phenomenon and the parameters that influence the type, shape, and width of the conversion of the hysteresis curves.
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4.
  • Alsharaeh, E. H., et al. (författare)
  • Sol-Gel-Assisted Microwave-Derived Synthesis of Anatase Ag/TiO2/GO Nanohybrids toward Efficient Visible Light Phenol Degradation
  • 2017
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 7:5
  • Tidskriftsartikel (refereegranskat)abstract
    • A simple microwave-assisted (MWI) wet chemical route to synthesize pure anatase phase titanium dioxide (TiO2) nanoparticles (NPs) is reported here using titanium tetrachloride (TiCl4) as starting material. The as-prepared TiO2 NPs were characterized by electron microscopy, X-ray diffraction, UV/visible absorption spectroscopy, and infrared and Raman spectroscopic techniques. Further modification of the anatase TiO2 NPs was carried out by incorporating plasmonic silver (Ag) NPs and graphene oxide (GO) in order to enhance the visible light absorption. The photocatalytic activities of the anatase TiO2, Ag/TiO2, and Ag/TiO2/GO nanocomposites were evaluated under both ultraviolet (UV) and visible light irradiation using phenol as a model contaminant. The presence of Ag NPs was found to play a significant role to define the photocatalytic activity of the Ag/TiO2/GO nanocomposite. It was found that the Ag performed like a sink under UV excitation and stored photo-generated electrons from TiO2, whereas, under visible light excitation, the Ag acted as a photosensitizer enhancing the photocatalytic activity of the nanocomposite. The detailed mechanism was studied based on photocatalytic activities of Ag/TiO2/GO nanocomposites. Therefore, the as-prepared Ag/TiO2/GO nanocomposite was used as photocatalytic materials under both UV and visible light irradiation toward degradation of organic molecules.
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5.
  • Amaro-Gahete, Juan, et al. (författare)
  • Hydroxyl-Decorated Diiron Complex as a [FeFe]-Hydrogenase Active Site Model Complex : Light-Driven Photocatalytic Activity and Heterogenization on Ethylene-Bridged Periodic Mesoporous Organosilica
  • 2022
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 12:3
  • Tidskriftsartikel (refereegranskat)abstract
    • A biomimetic model complex of the [FeFe]-hydrogenase active site (FeFeOH) with an ethylene bridge and a pendant hydroxyl group has been synthesized, characterized and evaluated as catalyst for the light-driven hydrogen production. The interaction of the hydroxyl group present in the complex with 3-isocyanopropyltriethoxysilane provided a carbamate triethoxysilane bearing a diiron dithiolate complex (NCOFeFe), thus becoming a potentially promising candidate for anchoring on heterogeneous supports. As a proof of concept, the NCOFeFe precursor was anchored by a grafting procedure into a periodic mesoporous organosilica with ethane bridges (EthanePMO@NCOFeFe). Both molecular and heterogenized complexes were tested as catalysts for light-driven hydrogen generation in aqueous solutions. The photocatalytic conditions were optimized for the homogenous complex by varying the reaction time, pH, amount of the catalyst or photosensitizer, photon flux, and the type of light source (light-emitting diode (LED) and Xe lamp). It was shown that the molecular FeFeOH diiron complex achieved a decent turnover number (TON) of 70 after 6 h, while NCOFeFe and EthanePMO@NCOFeFe had slightly lower activities showing TONs of 37 and 5 at 6 h, respectively.
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6.
  • Auvray, Xavier, 1986, et al. (författare)
  • Deactivation of Cu/SSZ-13 NH3-SCR catalyst by exposure to CO, H2, and C3H6
  • 2019
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 9:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Lean nitric oxide (NOx)-trap (LNT) and selective catalytic reduction (SCR) are efficient systems for the abatement of NOx. The combination of LNT and SCR catalysts improves overall NOx removal, but there is a risk that the SCR catalyst will be exposed to high temperatures and rich exhaust during the LNTs sulfur regeneration. Therefore, the effect of exposure to various rich conditions and temperatures on the subsequent SCR activity of a Cu-exchanged chabazite catalyst was studied. CO, H2, C3H6, and the combination of CO + H2 were used to simulate rich conditions. Aging was performed at 800 °C, 700 °C, and, in the case of CO, 600 °C, in a plug-flow reactor. Investigation of the nature of Cu sites was performed with NH3-temperature-programed desorption (TPD) and diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) of probe molecules (NH3 and NO). The combination of CO and H2 was especially detrimental to SCR activity and to NH3 oxidation. Rich aging with low reductant concentrations resulted in a significantly larger deactivation compared to lean conditions. Aging in CO at 800 °C caused SCR deactivation but promoted high-temperature NH3 oxidation. Rich conditions greatly enhanced the loss of Brønsted and Lewis acid sites at 800 °C, indicating dealumination and Cu migration. However, at 700 °C, mainly Brønsted sites disappeared during aging. DRIFT spectroscopy analysis revealed that CO aging modified the Cu2+/CuOH+ ratio in favor of the monovalent CuOH+ species, as opposed to lean aging. To summarize, we propose that the reason for the increased deactivation observed for mild rich conditions is the transformation of the Cu species from Z2Cu to ZCuOH, possibly in combination with the formation of Cu clusters. © 2019, MDPI AG. All rights reserved.
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7.
  • Auvray, Xavier, 1986, et al. (författare)
  • Effect of microwave drying, calcination and aging of Pt/Al2O3 on platinum dispersion
  • 2018
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:9
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of heating method employed for drying and calcination during the synthesis of 1 wt% Pt/Al2O3catalyst was investigated. Conventional heating (CH) in resistive oven and microwave heating (MW) in single mode were applied, and the Pt dispersion and Brunauer-Emmett-Teller (BET) surface area were measured to characterize the samples. It was evidenced that the fast and homogeneous heating offered by the microwave heating led to higher Pt dispersion. However, this benefit was only achieved when the subsequent calcination was performed in a conventional oven. The aging in microwave oven of conventionally prepared—as well as MW-prepared—catalysts demonstrated the great ability of microwave irradiation to accelerate platinum sintering. After 1 h at 800°C under microwave, catalysts showed a dispersion of 5%. Therefore, microwave treatment should be considered for accelerated catalyst aging but should be avoided as a calcination technique for the synthesis of highly dispersed Pt/Al2O3.
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8.
  • Axelsson, Anton, 1991, et al. (författare)
  • Ionic Liquids as Carbene Catalyst Precursors in the One-Pot Four-Component Assembly of Oxo Triphenylhexanoates (OTHOs)
  • 2015
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 5:4, s. 2052-2067
  • Tidskriftsartikel (refereegranskat)abstract
    • Ionic liquids (ILs) are a convenient and inexpensive source of N-heterocyclic carbenes (NHCs). In this study, dialkyl imidazolium-based ILs are used as carbene precursors in a four-component synthesis of oxo triphenylhexanoates (OTHOs), where it was found that IL outperformed commonly used NHC precatalysts in terms of reaction efficiency. The reaction is highly stereoselective, delivering the anti-diastereomer (20:1 dr), and the OTHOs can be obtained in high-to-excellent yields. By virtue of the four-component reaction-setup, facile construction of the OTHO scaffold with a diverse set of functional groups (21 examples) can be achieved. In the context of sustainability, the IL can be recovered and reused several times without affecting selectivity or yield. Moreover, most compounds can be isolated by precipitation and filtration, mitigating the use of solvent-demanding chromatography
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9.
  • Berdugo Vilches, Teresa, 1985, et al. (författare)
  • Mapping the effects of potassium on fuel conversion in industrial-scale fluidized bed gasifiers and combustors
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Potassium (K) is a notorious villain among the ash components found in the biomass, being the cause of bed agglomeration and contributing to fouling and corrosion. At the same time, K is known to have catalytic properties towards fuel conversion in combustion and gasification environments. Olivine (MgFe silicate) used as gasifier bed material has a higher propensity to form catalytically active K species than traditional silica sand beds, which tend to react with K to form stable and inactive silicates. In a dual fluidized bed (DFB) gasifier, many of those catalytic effects are expected to be relevant, given that the bed material becomes naturally enriched with ash elements from the fuel. However, a comprehensive overview of how enrichment of the bed with alkali affects fuel conversion in both parts of the DFB system is lacking. In this work, the effects of ash-enriched olivine on fuel conversion in the gasification and combustion parts of the process are mapped. The work is based on a dedicated experimental campaign in a Chalmers DFB gasifier, wherein enrichment of the bed material with K is promoted by the addition of a reaction partner, i.e., sulfur, which ensures K retention in the bed in forms other than inactive silicates. The choice of sulfur is based on its affinity for K under combustion conditions. The addition of sulfur proved to be an efficient strategy for capturing catalytic K in olivine particles. In the gasification part, K-loaded olivine enhanced the char gasification rate, decreased the tar concentration, and promoted the WGS equilibrium. In the combustion part, K prevented full oxidation of CO, which could be mitigated by the addition of sulfur to the cyclone outlet.
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10.
  • Bergman, Jenny, et al. (författare)
  • Co-detection of dopamine and glucose with high temporal resolution
  • 2018
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Neuronal activity and brain glucose metabolism are tightly coupled, where triggered neurotransmission leads to a higher demand for glucose. To better understand the regulation of neuronal activity and its relation to high-speed metabolism, development of analytical tools that can temporally resolve the transients of vesicular neurotransmitter release and fluctuations of metabolites such as glucose in the local vicinity of the activated neurons is needed. Here we present an amperometric biosensor design for rapid co-detection of glucose and the neurotransmitter dopamine. The sensor is based on the immobilization of an ultra-thin layer of glucose oxidase on to a gold-nanoparticle-covered carbon fiber microelectrode. Our electrode, by altering the potential applied at the sensor surface, allows for the high-speed recording of both glucose and dopamine. We demonstrate that, even though glucose is electrochemically detected indirectly through the enzymatic product and the electroactive dopamine is sensed directly, when exposing the sensor surface to a mixture of the two analytes, fluctuations in glucose and dopamine concentrations can be visualized with similar speed and at a millisecond time scale. Hence, by minimizing the enzyme coating thickness at the sensor surface, dual detection of glucose and dopamine can be realized at the same sensor surface and at time scales necessary for monitoring fast metabolic alterations during neurotransmission. © 2018 by the authors. Licensee MDPI, Basel, Switzerland.
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11.
  • Berwanger, Mailing, et al. (författare)
  • HfS2 and TiS2 Monolayers with Adsorbed C, N, P Atoms : A First Principles Study
  • 2020
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 10:1
  • Tidskriftsartikel (refereegranskat)abstract
    • First principles density functional theory was used to study the energetic, structural, and electronic properties of HfS2 and TiS2 materials in their bulk, pristine monolayer, as well as in the monolayer structure with the adsorbed C, N, and P atoms. It is shown that the HfS2 monolayer remains a semiconductor while TiS2 changes from semiconductor to metallic behavior after the atomic adsorption. The interaction with the external atoms introduces localized levels inside the band gap of the pristine monolayers, significantly altering their electronic properties, with important consequences on the practical use of these materials in real devices. These results emphasize the importance of considering the interaction of these 2D materials with common external atomic or molecular species.
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12.
  • Cao, Zhejian, 1991-, et al. (författare)
  • Rapid Ammonia Carriers for SCR Systems Using MOFs [M2(adc)2(dabco)] (M = Co, Ni, Cu, Zn)
  • 2020
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 10:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Ammonia is one of the most common reductants for the automotive selective catalytic reduction (SCR) system owing to its high NO2 reduction (deNOx) efficiency. However, ammonia carriers for the SCR system have sluggishly evolved to achieve rapid ammonia dosing. In this study, the MOFs [M2(adc)2(dabco)] (M = Co, Ni, Cu, Zn) were synthesized and characterized as ammonia carriers. Among the four obtained MOFs, Ni2(adc)2(dabco) possessed the highest surface area, 772 m2/g, highest ammonia uptake capacity, 12.1 mmol/g, and stable cyclic adsorption-desorption performance. All the obtained MOFs demonstrated physisorption of ammonia and rapid kinetics of ammonia adsorption and desorption. Compared with halide ammonia carrier MgCl2, the obtained MOFs showed four times faster adsorption kinetics to reach 90% of the ammonia uptake capacity. For the ammonia desorption, the Ni2(adc)2(dabco) provided 6 mmol/g ammonia dosing when temperature reached 125 °C in the first 10 min, which was six times of the ammonia dosing from Mg(NH3)6Cl2. The results offer a solution to shorten the buffering time for ammonia dosing in the SCR system.
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13.
  • Charisteidis, Ioannis, et al. (författare)
  • Catalytic Fast Pyrolysis of Lignin Isolated by Hybrid Organosolv—Steam Explosion Pretreatment of Hardwood and Softwood Biomass for the Production of Phenolics and Aromatics
  • 2019
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:11
  • Tidskriftsartikel (refereegranskat)abstract
    • Lignin, one of the three main structural biopolymers of lignocellulosic biomass, is the most abundant natural source of aromatics with a great valorization potential towards the production of fuels, chemicals, and polymers. Although kraft lignin and lignosulphonates, as byproducts of the pulp/paper industry, are available in vast amounts, other types of lignins, such as the organosolv or the hydrolysis lignin, are becoming increasingly important, as they are side-streams of new biorefinery processes aiming at the (bio)catalytic valorization of biomass sugars. Within this context, in this work, we studied the thermal (non-catalytic) and catalytic fast pyrolysis of softwood (spruce) and hardwood (birch) lignins, isolated by a hybrid organosolv–steam explosion biomass pretreatment method in order to investigate the effect of lignin origin/composition on product yields and lignin bio-oil composition. The catalysts studied were conventional microporous ZSM-5 (Zeolite Socony Mobil–5) zeolites and hierarchical ZSM-5 zeolites with intracrystal mesopores (i.e., 9 and 45 nm) or nano-sized ZSM-5 with a high external surface. All ZSM-5 zeolites were active in converting the initially produced via thermal pyrolysis alkoxy-phenols (i.e., of guaiacyl and syringyl/guaiacyl type for spruce and birch lignin, respectively) towards BTX (benzene, toluene, xylene) aromatics, alkyl-phenols and polycyclic aromatic hydrocarbons (PAHs, mainly naphthalenes), with the mesoporous ZSM-5 exhibiting higher dealkoxylation reactivity and being significantly more selective towards mono-aromatics compared to the conventional ZSM-5, for both spruce and birch lignin.
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14.
  • Creci, Simone, 1992, et al. (författare)
  • Acidity as Descriptor for Methanol Desorption in B-, Ga- and Ti-MFI Zeotypes
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:1, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • The isomorphous substitution of Si with metals other than Al in zeotype frameworks allows for tuning the acidity of the zeotype and, therefore, to tailor the catalyst's properties as a function of the desired catalytic reaction. In this study, B, Ga, and Ti are incorporated in the MFI framework of silicalite samples and the following series of increasing acidity is observed: Ti-silicalite < B-silicalite < Ga-silicalite. It is also observed that the lower the acidity of the sample, the easier the methanol desorption from the zeotype surface. In the target reaction, namely the direct conversion of methane to methanol, methanol extraction is affected by the zeotype acidity. Therefore, the results shown in this study contribute to a more enriched knowledge of this reaction.
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15.
  • Damas, Giane B., et al. (författare)
  • On the Mechanism of Carbon Dioxide Reduction on Sn-Based Electrodes : Insights into the Role of Oxide Surfaces
  • 2019
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:8
  • Tidskriftsartikel (refereegranskat)abstract
    • The electrochemical reduction of carbon dioxide into carbon monoxide, hydrocarbons and formic acid has offered an interesting alternative for a sustainable energy scenario. In this context, Sn-based electrodes have attracted a great deal of attention because they present low price and toxicity, as well as high faradaic efficiency (FE) for formic acid (or formate) production at relatively low overpotentials. In this work, we investigate the role of tin oxide surfaces on Sn-based electrodes for carbon dioxide reduction into formate by means of experimental and theoretical methods. Cyclic voltammetry measurements of Sn-based electrodes, with different initial degree of oxidation, result in similar onset potentials for the CO2 reduction to formate, ca. −0.8 to −0.9 V vs. reversible hydrogen electrode (RHE), with faradaic efficiencies of about 90–92% at −1.25 V (vs. RHE). These results indicate that under in-situ conditions, the electrode surfaces might converge to very similar structures, with partially reduced or metastable Sn oxides, which serve as active sites for the CO2 reduction. The high faradaic efficiencies of the Sn electrodes brought by the etching/air exposition procedure is ascribed to the formation of a Sn oxide layer with optimized thickness, which is persistent under in situ conditions. Such oxide layer enables the CO2 “activation”, also favoring the electron transfer during the CO2 reduction reaction due to its better electric conductivity. In order to elucidate the reaction mechanism, we have performed density functional theory calculations on different slab models starting from the bulk SnO and Sn6O4(OH)4 compounds with focus on the formation of -OH groups at the water-oxide interface. We have found that the insertion of CO2 into the Sn-OH bond is thermodynamically favorable, leading to the stabilization of the tin-carbonate species, which is subsequently reduced to produce formic acid through a proton-coupled electron transfer process. The calculated potential for CO2 reduction (E = −1.09 V vs. RHE) displays good agreement with the experimental findings and, therefore, support the CO2 insertion onto Sn-oxide as a plausible mechanism for the CO2 reduction in the potential domain where metastable oxides are still present on the Sn surface. These results not only rationalize a number of literature divergent reports but also provide a guideline for the design of efficient CO2 reduction electrocatalysts.
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16.
  • De Abreu Goes, Jesus, 1989, et al. (författare)
  • Sulfur Poisoning Effects on Modern Lean NOx Trap Catalysts Components
  • 2019
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 9:6
  • Tidskriftsartikel (refereegranskat)abstract
    • In the present work, a series of different materials was investigated in order to enhance the understanding of the role of modern lean NOx trap (LNT) components on the sulfur poisoning and regeneration characteristics. Nine different types of model catalysts were prepared, which mainly consisted of three compounds: (i) Al2O3, (ii) Mg/Al2O3, and (iii) Mg/Ce/Al2O3 mixed with Pt, Pd, and Pt-Pd. A micro flow reactor and a diffuse reflectance infrared Fourier transform spectrometer (DRIFTS) were employed in order to investigate the evolution and stability of the species formed during SO2 poisoning. The results showed that the addition of palladium and magnesium into the LNT formulation can be beneficial for the catalyst desulfation due mainly to the ability to release the sulfur trapped at relatively low temperatures. This was especially evident for Pd/Mg/Al2O3 model catalyst, which demonstrated an efficient LNT desulfation with low H-2 consumption. In contrast, the addition of ceria was found to increase the formation of bulk sulfate species during SO2 poisoning, which requires higher temperatures for the sulfur removal. The noble metal nature was also observed to play an important role on the SOx storage and release properties. Monometallic Pd-based catalysts exhibited the formation of surface palladium sulfate species during SO2 exposure, whereas Pt-Pd bimetallic formulations presented higher stability of the sulfur species formed compared to the corresponding Pt- and Pd-monometallic samples.
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17.
  • Di Carlo, Gabriella, et al. (författare)
  • Design of Cobalt Nanoparticles with Tailored Structural and Morphological Properties via O/W and W/O Microemulsions and Their Deposition onto Silica
  • 2015
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 5:1, s. 442-459
  • Tidskriftsartikel (refereegranskat)abstract
    • Cobalt nanostructures with different size and morphology, i.e., spherical nanoparticles, nanorods, and particles arranged into elongated structures, were prepared using micelles and microemulsions as confined reaction media. The syntheses were carried out using three types of systems: aqueous surfactant solutions, oil-in water (O/W), and water-in-oil (W/O) microemulsions. The influence of the surfactant and the precipitating agent used for synthesis was also investigated. For this purpose, cobalt nanostructures were prepared using different non-ionic surfactants, namely Synperonic((R)) 10/6, Pluronic((R)) P123 and a mixture of SPAN 20-TWEEN 80. Three different precipitating agents were used: sodium borohydride, sodium hydroxide, and oxalic acid. Our findings revealed that by changing the type of reaction media as well as the precipitating agent it is possible to modify the shape and size of the cobalt nanostructures. Moreover, the use of O/W microemulsion generates better results in terms of colloidal stability and uniformity of particle size with respect to W/O microemulsion. The different cobalt nanostructures were supported on commercial and mesoporous silica; transmission electron microscopy (TEM) images showed that after deposition the Co nanocrystals remain well dispersed on the silica supports. This behavior suggests their great potential in catalytic applications.
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18.
  • Dobrota, Ana S., et al. (författare)
  • What Is the Real State of Single-Atom Catalysts under Electrochemical Conditions-From Adsorption to Surface Pourbaix Plots?
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:10
  • Tidskriftsartikel (refereegranskat)abstract
    • The interest in single-atom catalysts (SACs) is increasing, as these materials have the ultimate level of catalyst utilization, while novel reactions where SACs are used are constantly being discovered. However, to properly understand SACs and to further improve these materials, it is necessary to consider the nature of active sites under operating conditions. This is particularly important when SACs are used as electrocatalysts due to harsh experimental conditions, including extreme pH values or high anodic and cathodic potential. In this contribution, density functional theory-based thermodynamic modelling is used to address the nature of metal centers in SACs formed by embedding single metal atoms (Ru, Rh, Ir, Ni, Pd, Pt, Cu, Ag, and Au) into graphene monovacancy. Our results suggest that none of these SAC metal centers are clean at any potential or pH in the water thermodynamic stability region. Instead, metal centers are covered with H-ads, OHads, or O-ads, and in some cases, we observed the restructuring of the metal sites due to oxygen incorporation. Based on these findings, it is suggested that setting up theoretical models for SAC modelling and the interpretation of ex situ characterization results using ultra-high vacuum (UHV) techniques requires special care, as the nature of SAC active sites under operating conditions can significantly diverge from the basic models or the pictures set by the UHV measurements.
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19.
  • Engedahl, Unni, 1990, et al. (författare)
  • Reaction mechanism for methane-to-methanol in CU-SSZ-13: First-principles study of the Z 2 [Cu 2 O] and Z 2 [Cu 2 oh] motifs
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:1, s. 1-12
  • Tidskriftsartikel (refereegranskat)abstract
    • As transportation continues to increase world-wide, there is a need for more efficient utilization of fossil fuel. One possibility is direct conversion of the solution gas bi-product CH4 into an energy-rich, easily usable liquid fuel such as CH3OH. However, new catalytic materials to facilitate the methane-to-methanol reaction are needed. Using density functional calculations, the partial oxidation of methane is investigated over the small-pore copper-exchanged zeolite SSZ-13. The reaction pathway is identified and the energy landscape elucidated over the proposed motifs Z2 [Cu2O] and Z2 [Cu2OH]. It is shown that the Z2[Cu2O] motif has an exergonic reaction path, provided water is added as a solvent for the desorption step. However, a micro-kinetic model shows that neither Z2 [Cu2O] nor Z2 [Cu2OH] has any notable activity under the reaction conditions. These findings highlight the importance of the detailed structure of the active site and that the most stable motif is not necessarily the most active.
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20.
  • Englund, Johanna, 1988, et al. (författare)
  • Deactivation of a Pd/Pt Bimetallic Oxidation Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation
  • 2019
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:12
  • Tidskriftsartikel (refereegranskat)abstract
    • The reduction of anthropogenic greenhouse gas emissions is crucial to avoid further warming of the planet. We investigated how effluent gases from a biogas powered Euro VI heavy-duty engine impact the performance of a bimetallic (palladium and platinum) oxidation catalyst. Using synthetic gas mixtures, the oxidation of NO, CO, and CH4 before and after exposure to biogas exhaust for 900 h was studied. The catalyst lost most of its activity for methane oxidation, and the activity loss was most severe for the inlet part of the aged catalyst. Here, a clear sintering of Pt and Pd was observed, and higher concentrations of catalyst poisons such as sulfur and phosphorus were detected. The sintering and poisoning resulted in less available active sites and hence lower activity for methane oxidation.
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21.
  • Englund, Johanna, 1988, et al. (författare)
  • Deactivation of a Vanadium-Based SCR Catalyst Used in a Biogas-Powered Euro VI Heavy-Duty Engine Installation
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:5
  • Tidskriftsartikel (refereegranskat)abstract
    • We have investigated how the exhaust gases from a heavy-duty Euro VI engine, powered with biogas impact a vanadium-based selective catalytic reduction (SCR) catalyst in terms of performance. A full Euro VI emission control system was used and the accumulation of catalyst poisons from the combustion was investigated for the up-stream particulate filter as well as the SCR catalyst. The NO(x)reduction performance in terms of standard, fast and NO2-rich SCR was evaluated before and after exposure to exhaust from a biogas-powered engine for 900 h. The SCR catalyst retains a significant part of its activity towards NO(x)reduction after exposure to biogas exhaust, likely due to capture of catalyst poisons on the up-stream components where the deactivation of the oxidation catalyst is especially profound. At lower temperatures some deactivation of the first part of the SCR catalyst was observed which could be explained by a considerably higher surface V4+/V(5+)ratio for this sample compared to the other samples. The higher value indicates that the reoxidation of V(4+)to V(5+)is partially hindered, blocking the redox cycle for parts of the active sites.
  •  
22.
  • Friberg, Ida, 1990, et al. (författare)
  • Hydrothermal Aging of Pd/LTA Monolithic Catalyst for Complete CH4 Oxidation
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Palladium-based catalysts are known to provide high CH4 oxidation activity. One drawback for these materials is that they often lose activity in the presence of water vapor due to the formation of surface hydroxyls. It is however possible to improve the water vapor tolerance by using zeolites as support material. In this study, we have investigated Pd supported on thermally stable LTA zeolite with high framework Si/Al ratio (Si/Al = ~44) for CH4 oxidation and the effect of hydrothermal aging at temperatures up to 900◦C. High and stable CH4 oxidation activity in the presence of water vapor was observed for Pd/LTA after hydrothermal aging at temperatures ≤ 700◦C. However, aging at temperatures of 800–900◦C resulted in catalyst deactivation. This deactivation was not a result of structural collapse of the LTA zeolite as the LTA zeolite only showed minor changes in surface area, pore volume, and X-ray diffraction pattern after 900◦C aging. We suggest that the deactivation was caused by extensive formation of ion-exchanged Pd2+ together with Pd sintering. These two types of Pd species appear to have lower CH4 oxidation activity and to be more sensitive to water deactivation compared to the well dispersed Pd particles observed on the LTA support prior to the hydrothermal aging. By contrast, Pd/Al2O3 was generally sensitive to water vapor no matter of the aging temperature. Although the aging caused extensive Pd sintering in Pd/Al2O3, only minor deterioration of the CH4 oxidation activity was seen. The results herein presented show that Pd/LTA is a promising CH4 oxidation catalyst, however Pd rearrangement at high temperatures (≥800◦C) is one remaining challenge.
  •  
23.
  • Fuoco, Tiziana, et al. (författare)
  • Aluminum Alkyl Complexes Bearing Salicylaldiminato Ligands : Versatile Initiators in the Ring-Opening Polymerization of Cyclic Esters
  • 2017
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 7:2
  • Forskningsöversikt (refereegranskat)abstract
    • Linear aliphatic polyesters are degradable thermoplastic polymers, which can be obtained by ring-opening polymerization (ROP) of cyclic esters through a coordination-insertion mechanism. Aluminum based organometallic complexes have a leading position as efficient catalysts for this polymerization process. Aluminumalkyl complexes bearing salicylaldiminato ligands, although less explored, have been shown to be efficient and versatile catalysts for the ROP of various cyclic esters. These species have the potential to function as active catalysts in the ROP because of their less coordinatively saturated nature with respect to analogous SALEN-type complexes. They have been used as efficient catalysts in the ROP of commercially available cyclic esters, such as epsilon-caprolactone, L-lactide, rac-lactide, and glycolide. Moreover, they resulted in efficient catalysts for the ROP of cyclic esters with large ring-size and for the ROP of functionalized lactide. Furthermore, they have been used in the co- and ter-polymerization of various cyclic esters affording well controlled polymerization and a plethora of microstructural architectures, ranging from random to block to multiblock.
  •  
24.
  • Goszewska, Ilona, et al. (författare)
  • Boosting the Performance of Nano-Ni Catalysts by Palladium Doping in Flow Hydrogenation of Sulcatone
  • 2020
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 10:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of Pd doping on nano-Ni catalyst hydrogenation aptitude in sulcatone (6-methyl-5-hepten-2-one) hydrogenation was investigated. Obtained results demonstrated that the addition of non-catalytic amounts of Pd to the surface of parent Ni catalyst improves the activity to the extent that it surpassed the activity of 2.16 wt% Pd catalyst (model catalyst) at optimal reaction conditions in the flow hydrogenation of an unsaturated ketone. Pd doping improves hydrogen activation on the catalyst, which was found to be a rate-limiting step using kinetic isotopic measurements and theoretical calculations.
  •  
25.
  • Granestrand, Jonas, et al. (författare)
  • Assessment of the Impact of Trace Elements in FAME Biodiesel on Diesel Oxidation Catalyst Activity after Full Lifetime of Operation in A Heavy-Duty Truck
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Fatty acid methyl ester (FAME) biodiesel contains some trace amounts of Na, K, P, Ca, and Mg. Our objective was to investigate whether the presence of such elements can poison a diesel oxidation catalyst that has been used for an entire regulatory lifetime in a heavy-duty truck fueled by FAME biodiesel. The investigated vehicle-aged catalyst contained high loadings of S, P, and Na, as well as a visible layer of soot. Activity in the NO oxidation reaction was severely decreased compared to a fresh catalyst of the same type, while the CO and C3H6 oxidation reactions were less affected. Subsequent selective trace element removal procedures, followed by activity tests, were used to decouple the effect of different poisons. Sintering was observed to be the main cause of catalyst deactivation. Of the trace elements present on the catalyst, P had the greatest effect on catalyst activity, while the other trace elements had little effect.
  •  
26.
  • Guo, Shaoxia, et al. (författare)
  • K-Modulated Co Nanoparticles Trapped in La-Ga-O as Superior Catalysts for Higher Alcohols Synthesis from Syngas
  • 2019
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:3
  • Tidskriftsartikel (refereegranskat)abstract
    • Owing to the outstanding catalytic performance for higher alcohol synthesis, Ga-Co catalysts have attracted much attention. In view of their unsatisfactory stability and alcohol selectivity, herein, K-modulated Co nanoparticles trapped in La-Ga-O catalysts were prepared by the reduction of La1-xKxCo0.65Ga0.35O3 perovskite precursor. Benefiting from the atomic dispersion of all the elements in the precursor, during the reduction of La1-xKxCo0.65Ga0.35O3, Co nanoparticles could be confined into the K-modified La-Ga-O composite oxides, and the confinement of La-Ga-O could improve the anti-sintering performance of Co nanoparticles. In addition, the addition of K modulated parts of La-Ga-O into La2O3, which ameliorated the anti-carbon deposition performance. Finally, the addition of K increased the dispersion of cobalt and provided more electron donors to metallic Co, resulting in a high activity and superior selectivity to higher alcohols. Benefiting from the above characteristics, the catalyst possesses excellent activity, good selectivity, and superior stability.
  •  
27.
  • Gutic, Sanjin J., et al. (författare)
  • Hydrogen Evolution Reaction-From Single Crystal to Single Atom Catalysts
  • 2020
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 10:3
  • Forskningsöversikt (refereegranskat)abstract
    • Hydrogen evolution reaction (HER) is one of the most important reactions in electrochemistry. This is not only because it is the simplest way to produce high purity hydrogen and the fact that it is the side reaction in many other technologies. HER actually shaped current electrochemistry because it was in focus of active research for so many years (and it still is). The number of catalysts investigated for HER is immense, and it is not possible to overview them all. In fact, it seems that the complexity of the field overcomes the complexity of HER. The aim of this review is to point out some of the latest developments in HER catalysis, current directions and some of the missing links between a single crystal, nanosized supported catalysts and recently emerging, single-atom catalysts for HER.
  •  
28.
  • Hemmingsson, Felix, 1992, et al. (författare)
  • CO2 Methanation over Rh/CeO2 Studied with Infrared Modulation Excitation Spectroscopy and Phase Sensitive Detection
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:6
  • Tidskriftsartikel (refereegranskat)abstract
    • Methane is a well-established fuel molecule whose production from CO2 through methanation garners increasing interest as an energy storage solution. While often produced with Ni based catalysts, other metals are of interest thanks to higher robustness and activity-selectivity numbers. The Rh/CeO2 catalyst has shown appreciable properties for CO2 methanation and its structural dynamics has been studied in situ. However, the reaction pathway is unknown. Here, we present infrared modulation excitation spectroscopy measurements with phase sensitive detection of a Rh/CeO2 catalyst adsorbate composition during H2 pulsing (0–2 vol.%) to a constant CO2 (0.5 vol.%) feed. Various carbonyl (CO) and carbonate (b-CO3 /p-CO3 ) ad-species clearly respond to the hydrogen stimulus, making them potential reaction intermediates. The different CO ad-species are likely intermediates for product CO and CH4 but their individual contributions to the respective formations are not unambiguously ascertained. As for the carbonate dynamics, it might be linked to the reduction/oxidation of the CeO2 surface upon H2 pulsing. Formate (HCOO) ad-species are clearly visible but appear to be, if not spectators, linked to slow side reactions possibly also affected by CeO2 redox processes.
  •  
29.
  • Hulteberg, Christian, et al. (författare)
  • Scaling up a Gas-Phase Process for Converting Glycerol to Propane
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:9
  • Tidskriftsartikel (refereegranskat)abstract
    • It is of interest to study not only the fundamental behavior of catalysts and reactors but also to ensure that they can be scaled up in size. This paper investigates the scale-up of a glycerol-to-propane process starting from fundamental laboratory data from micro-reactor testing to the kilogram scale. The process is described in detail and consist of the use of design documents and computer simulations for determining the sizes of the unit operations involved. The final design included a vaporizer section for a glycerol/water mixture, four reactors in tandem with subsequent dehydration and hydrogenation reactions, a flash vessel to separate the excess hydrogen used, and a compressor for recycling the excess hydrogen with additional light components. The system was commissioned in a linear fashion, which is described, and operated for more than 3000 h and more than 1000 h in the final operating mode including recycle. The major results were that no catalyst deactivation was apparent aside from the slow build-up of carbonaceous material in the first dehydration reactor. That the system design calculations proved to be quite close to the results achieved and that the data generated is believed to be sufficient for up-scaling the process into the 1000 to 10,000 tonnes-per-annum range.
  •  
30.
  • Jonsson, Rasmus, 1989, et al. (författare)
  • Gas-phase phosphorous poisoning of a Pt/Ba/Al2O3 NOx storage catalyst
  • 2018
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:4
  • Tidskriftsartikel (refereegranskat)abstract
    • The effect of phosphorous exposure on the NO x storage capacity of a Pt/Ba/Al 2 O 3 catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H 2 O and O 2 . The NOx storage capacity was measured before and after the phosphorus exposure and a significant loss of the NO x storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N 2 -physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P 4 O 10 . However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO 3 – ). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample
  •  
31.
  • Jonsson, Rasmus, 1989, et al. (författare)
  • The Impact of Lanthanum and Zeolite Structure on Hydrocarbon Storage
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:5
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrocarbon traps can be used to bridge the temperature gap from the cold start of a vehicle until the exhaust after-treatment catalyst has reached its operating temperature. In this work, we investigate the effect of zeolite structure (ZSM-5, BEA, SSZ-13) and the effect of La addition to H-BEA and H-ZSM-5 on the hydrocarbon storage capacity by temperature-programmed desorption and DRIFT spectroscopy. The results show that the presence of La has a significant effect on the adsorption characteristics of toluene on the BEA-supported La materials. A low loading of La onto zeolite BEA (2% La-BEA) improves not only the toluene adsorption capacity but also the retention of toluene. However, a higher loading of La results in a decrease in the adsorbed amount of toluene, which likely is due to partial blocking of the pore of the support. High loadings of La in BEA result in a contraction of the unit cell of the zeolite as evidenced by XRD. A synergetic effect of having simultaneously different types of hydrocarbons (toluene, propene, and propane) in the feed is found for samples containing ZSM-5, where the desorption temperature of propane increases, and the quantity that desorbed increases by a factor of four. This is found to be due to the interaction between toluene and propane inside the structure of the zeolite.
  •  
32.
  • Jonsson, Rasmus, 1989, et al. (författare)
  • Zeolite beta doped with La, Fe, and Pd as a hydrocarbon trap
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Hydrocarbon trapping is a technique of great relevance, since a substantial part of hydrocarbon emissions from engines are released from engines before the catalyst has reached the temperature for efficient conversion of the hydrocarbons. In this work, the influence of doping zeolite beta (BEA) with Fe, Pd, and La on the storage and release of propene and toluene is studied. Five monolith samples were prepared; Fe/BEA, La/BEA, Pd/BEA, Pd/Fe/BEA, and Pd/La/BEA using incipient wetness impregnation, and the corresponding powder samples were used for catalyst characterization by Inductively coupled plasma sector field mass spectrometry (ICP-SFMS), Temperature-programmed oxidation (TPO), X-ray photoelectron spectroscopy (XPS) and Scanning transmission electron microscopy with Energy dispersive X-ray analysis (STEM-EDX). The hydrocarbon trapping ability of the samples was quantified using Temperature-programmed desorption (TPD) of propene and toluene, and in situ Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). The results from the TPD experiments show that the addition of Pd and La to the zeolite affected the release patterns of the stored hydrocarbons on the trapping material in a positive way. The in situ DRIFTS results indicate that these elements provide H-BEA with additional sites for the storage of hydrocarbons. Furthermore, EDX-mapping showed that the La and Pd are located in close connection.
  •  
33.
  • Kanerva, Tomi, et al. (författare)
  • Microstructural characteristics of vehicle-aged heavy-duty diesel oxidation catalyst and natural gas three-way catalyst
  • 2019
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 9:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Techniques to control vehicle engine emissions have been under increasing need for development during the last few years in the more and more strictly regulated society. In this study, vehicle-aged heavy-duty catalysts from diesel and natural gas engines were analyzed using a cross-sectional electron microscopy method with both a scanning electron microscope and a transmission electron microscope. Also, additional supporting characterization methods including X-ray diffractometry, X-ray photoelectron spectroscopy, Fourier-transform infrared spectroscopy and catalytic performance analyses were used to reveal the ageing effects. Structural and elemental investigations were performed on these samples, and the effect of real-life ageing of the catalyst was studied in comparison with fresh catalyst samples. In the real-life use of two different catalysts, the poison penetration varied greatly depending on the engine and fuel at hand: the diesel oxidation catalyst appeared to suffer more thorough changes than the natural gas catalyst, which was affected only in the inlet part of the catalyst. The most common poison, sulphur, in the diesel oxidation catalyst was connected to cerium-rich areas. On the other hand, the severities of the ageing effects were more pronounced in the natural gas catalyst, with heavy structural changes in the washcoat and high concentrations of poisons, mainly zinc, phosphorus and silicon, on the surface of the inlet part.
  •  
34.
  • Karnaouri, Anthi C., et al. (författare)
  • Tailoring Celluclast (R) Cocktail's Performance towards the Production of Prebiotic Cello-Oligosaccharides from Waste Forest Biomass
  • 2019
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:11
  • Tidskriftsartikel (refereegranskat)abstract
    • The main objective of this study focused on the sustainable production of cellobiose and other cellulose-derived oligosaccharides from non-edible sources, more specifically, from forest residues. For this purpose, a fine-tuning of the performance of the commercially available enzyme mixture Celluclast® was conducted towards the optimization of cellobiose production. By enzyme reaction engineering (pH, multi-stage hydrolysis with buffer exchange, addition of β-glucosidase inhibitor), a cellobiose-rich product with a high cellobiose to glucose ratio (37.4) was achieved by utilizing organosolv-pretreated birch biomass. In this way, controlled enzymatic hydrolysis combined with efficient downstream processing, including product recovery and purification through ultrafiltration and nanofiltration, can potentially support the sustainable production of food-grade oligosaccharides from forest biomass. The potential of the hydrolysis product to support the growth of two Lactobacilli probiotic strains as a sole carbon source was also demonstrated
  •  
35.
  • Kaufhold, Simon, et al. (författare)
  • Design and synthesis of photoactive iron n-heterocyclic carbene complexes
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:1
  • Forskningsöversikt (refereegranskat)abstract
    • The use of iron in photoactive metal complexes has been investigated for decades. In this respect, the charge transfer (CT) states are of particular interest, since they are usually responsible for the photofunctionality of such compounds. However, only recently breakthroughs have been made in extending CT excited state lifetimes that are notoriously short-lived in classical polypyridine iron coordination compounds. This success is in large parts owed to the use of strongly σ-donating N-heterocyclic carbene (NHC) ligands that help manipulating the photophysical and photochemical properties of iron complexes. In this review we aim to map out the basic design principles for the generation of photofunctional iron NHC complexes, summarize the progress made so far and recapitulate on the synthetic methods used. Further, we want to highlight the challenges still existing and give inspiration for future generations of photoactive iron complexes.
  •  
36.
  • Kawde, Anurag, et al. (författare)
  • Photoelectrochemical oxidation in ambient conditions using earth-abundant hematite anode : A green route for the synthesis of biobased polymer building blocks
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:8
  • Tidskriftsartikel (refereegranskat)abstract
    • This study demonstrates the use of a photoelectrochemical device comprising earth-abundant hematite photoanode for the oxidation of 5-hydroxymethylfurfural (5-HMF), a versatile bio-based platform chemical, under ambient conditions in the presence of an electron mediator. The results obtained in this study showed that the hematite photoanode, upon doping with fluorine, can oxidize water even at lower pH (4.5 and 9.0). For 5-HMF oxidation, three different pH conditions were investigated, and complete oxidation to 2,5-furandicarboxylic acid (FDCA) via 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) was achieved at pH above 12. At lower pH, the oxidation followed another route via 2,5-diformylfuran (DFF), yielding 5-formyl-2-furancarboxylic acid (FFCA) as the main product. Using the oxidized intermediates as substrates showed DFF to be most efficiently oxidized to FDCA. We also show that, at pH 4.5, the addition of the laccase enzyme promoted the oxidation of 5-HMF to FFCA.
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37.
  • Khan, Farooq-Ahmad, et al. (författare)
  • Ruthenium Nanoparticles Intercalated in Montmorillonite (nano-Ru@MMT) Is Highly Efficient Catalyst for the Selective Hydrogenation of 2-Furaldehyde in Benign Aqueous Medium
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:1
  • Tidskriftsartikel (refereegranskat)abstract
    • Chemoselective hydrogenation of 2-furaldehyde to furfuryl alcohol using green solvents is an important research area to get eco-friendly fuels and fine chemicals. Herein, we report ruthenium nanoparticles (similar to 1.8 nm) intercalated in montmorillonite as an efficient catalytic system, which can selectively hydrogenate 2-furaldehyde in a benign aqueous medium. The complete conversion was observed at 40 degrees C with 1 MPa H-2, the selectivity of furfuryl alcohol being >99%, and turnover number 1165. After a catalytic run, the montmorillonite-supported ruthenium nanoparticles can be recycled and reused without losing their activity and selectivity.
  •  
38.
  • Kubiak, L., et al. (författare)
  • Mechanistic investigation of the reduction of NOx over Pt-and Rh-based LNT catalysts
  • 2016
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 6:3, s. Art. no. 46-
  • Tidskriftsartikel (refereegranskat)abstract
    • The influence of the noble metals (Pt vs. Rh) on the NOx storage reduction performances of lean NOx trap catalysts is here investigated by transient micro-reactor flow experiments. The study indicates a different behavior during the storage in that the Rh-based catalyst showed higher storage capacity at high temperature as compared to the Pt-containing sample, while the opposite is seen at low temperatures. It is suggested that the higher storage capacity of the Rh-containing sample at high temperature is related to the higher dispersion of Rh as compared to Pt, while the lower storage capacity of Rh-Ba/Al2O3 at low temperature is related to its poor oxidizing properties. The noble metals also affect the catalyst behavior upon reduction of the stored NOx, by decreasing the threshold temperature for the reduction of the stored NOx. The Pt-based catalyst promotes the reduction of the adsorbed NOx at lower temperatures if compared to the Rh-containing sample, due to its superior reducibility. However, Rh-based material shows higher reactivity in the NH3 decomposition significantly enhancing N2 selectivity. Moreover, formation of small amounts of N2O is observed on both Pt- and Rh-based catalyst samples only during the reduction of highly reactive NOx stored at 150 °C, where NOx is likely in the form of nitrites.
  •  
39.
  • Kulik, Tetiana, et al. (författare)
  • Catalytic Pyrolysis of Aliphatic Carboxylic Acids into Symmetric Ketones over Ceria-Based Catalysts : Kinetics, Isotope Effect and Mechanism
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Ketonization is a promising way for upgrading bio-derived carboxylic acids from pyrolysis bio-oils, waste oils, and fats to produce high value-added chemicals and biofuels. Therefore, an understanding of its mechanism can help to carry out the catalytic pyrolysis of biomass more efficiently. Here we show that temperature-programmed desorption mass spectrometry (TPD-MS) together with linear free energy relationships (LFERs) can be used to identify catalytic pyrolysis mechanisms. We report the kinetics of the catalytic pyrolysis of deuterated acetic acid and a reaction series of linear and branched fatty acids into symmetric ketones on the surfaces of ceria-based oxides. A structure-reactivity correlation between Taft's steric substituent constants Es* and activation energies of ketonization indicates that this reaction is the sterically controlled reaction. Surface D3-n-acetates transform into deuterated acetone isotopomers with different yield, rate, E-not equal and deuterium kinetic isotope effect (DKIE). The obtained values of inverse DKIE together with the structure-reactivity correlation support a concerted mechanism over ceria-based catalysts. These results demonstrate that analysis of Taft's correlations and using simple equation for estimation of DKIE from TPD-MS data are promising approaches for the study of catalytic pyrolysis mechanisms on a semi-quantitative level.
  •  
40.
  • Kulik, Tetiana, et al. (författare)
  • Catalytic Pyrolysis of Lignin Model Compound (Ferulic Acid) over Alumina : Surface Complexes, Kinetics, and Mechanisms
  • 2021
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:12
  • Tidskriftsartikel (refereegranskat)abstract
    • Studies of the thermochemical properties of the important model compound of lignin-ferulic acid (FA) and its surface complexes are substantial for developing technologies for catalytic pyrolysis of renewable biomass into biofuels and lignin-derived chemicals as well as for bio-oil upgrading. In this work, the catalytic pyrolysis of ferulic acid over alumina was studied by temperature-programmed desorption mass spectrometry (TPD MS), in situ FT-IR spectroscopy, thermogravimetric analysis, and DFT calculations. We established that both the carboxyl group and the active groups (HO and CH3O) of the aromatic ring interact with the alumina surface. We calculated the kinetic parameters of formation of the main products of catalytic pyrolysis: 4-vinylguaiacol, guaiacol, hydroxybenzene, benzene, toluene, cresol, naphthalene, and PACs. Possible methods of their forming from the related surface complexes of FA are suggested.
  •  
41.
  • Kürten, Charlotte, et al. (författare)
  • Mechanism-Guided Discovery of an Esterase Scaffold with Promiscuous Amidase Activity
  • 2016
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 6:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The discovery and generation of biocatalysts with extended catalytic versatilities are of immense relevance in both chemistry and biotechnology. An enhanced atomistic understanding of enzyme promiscuity, a mechanism through which living systems acquire novel catalytic functions and specificities by evolution, would thus be of central interest. Using esterase-catalyzed amide bond hydrolysis as a model system, we pursued a simplistic in silico discovery program aiming for the identification of enzymes with an internal backbone hydrogen bond acceptor that could act as a reaction specificity shifter in hydrolytic enzymes. Focusing on stabilization of the rate limiting transition state of nitrogen inversion, our mechanism-guided approach predicted that the acyl hydrolase patatin of the alpha/beta phospholipase fold would display reaction promiscuity. Experimental analysis confirmed previously unknown high amidase over esterase activity displayed by the first described esterase machinery with a protein backbone hydrogen bond acceptor to the reacting NH-group of amides. The present work highlights the importance of a fundamental understanding of enzymatic reactions and its potential for predicting enzyme scaffolds displaying alternative chemistries amenable to further evolution by enzyme engineering.
  •  
42.
  • Lage, Sandra, et al. (författare)
  • Microalgae Cultivation for the Biotransformation of Birch Wood Hydrolysate and Dairy Effluent
  • 2019
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:2
  • Tidskriftsartikel (refereegranskat)abstract
    • In order to investigate environmentally sustainable sources of organic carbon and nutrients, four Nordic green microalgal strains, Chlorella sorokiniana, Chlorella saccharophila, Chlorella vulgaris, and Coelastrella sp., were grown on a wood (Silver birch, Betula pendula) hydrolysate and dairy effluent mixture. The biomass and lipid production were analysed under mixotrophic, as well as two-stage mixotrophic/heterotrophic regimes. Of all of the species, Coelastrella sp. produced the most total lipids per dry weight (~40%) in the mixture of birch hydrolysate and dairy effluent without requiring nutrient (nitrogen, phosphorus, and potassium-NPK) supplementation. Overall, in the absence of NPK, the two-stage mixotrophic/heterotrophic cultivation enhanced the lipid concentration, but reduced the amount of biomass. Culturing microalgae in integrated waste streams under mixotrophic growth regimes is a promising approach for sustainable biofuel production, especially in regions with large seasonal variation in daylight, like northern Sweden. To the best of our knowledge, this is the first report of using a mixture of wood hydrolysate and dairy effluent for the growth and lipid production of microalgae in the literature.
  •  
43.
  • Larsson, Ragnar (författare)
  • A SET approach to the interplay of catalysts and reactants
  • 2018
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 8:3
  • Forskningsöversikt (refereegranskat)abstract
    • Research within the area of selective energy transfer (SET) on how resonance develops between a specific vibration within a catalyst system and a corresponding vibration within a reacting system that resonates with it is discussed here. The catalyst system is assumed to donate one or more vibrational quanta to the reacting system. The term ‘specific vibration’ refers to vibration of a type involving bending or stretching that, when transferred resonantly to the reacting system, serves to drive the reactant molecules involved to assume the basic structure of the molecules of the catalyst system. Regardless of whether the catalyst is a pure metal surface or a complex polymolecular system (an enzyme), its role is seen to be that of transferring energy to corresponding vibrations of the reactant system. Examples are here presented of vibrators of various types that can act as catalysts.
  •  
44.
  • Liao, Haidong, et al. (författare)
  • Generation of Free OHaq radicals by Black Light Illumination of Degussa P25 TiO2 Aqueous Suspensions
  • 2013
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 3:2, s. 418-443
  • Tidskriftsartikel (refereegranskat)abstract
    • This work demonstrates how formation of strongly chemiluminescent 3-hydroxyphthalic hydrazide by hydroxylation of non-chemiluminescent phthalic hydrazide can be applied as a selective reaction probe to obtain information on authentic hydroxyl radical, i.e., (OHaq)-O-center dot, formation, in black light illuminated Degussa P25 TiO2 aerated suspensions in the pH range from 3 to 11. The (OHaq)-O-center dot formation was found to be strongly pH dependent. At alkaline pH, the apparent quantum efficiency of (OHaq)-O-center dot formation was estimated to be at the similar to 10(-2) level whereas at acidic pH it was near zero. Addition of phosphate and fluoride ions substantially enhanced the (OHaq)-O-center dot production in the acidic pH range. It is suggested that (OHaq)-O-center dot-radical formation in TiO2 photocatalysis can occur by oxidation of hydroxyl ions in the water layer adsorbed on TiO2 surfaces.
  •  
45.
  • Lidskog, Anna, et al. (författare)
  • Asymmetric ring-opening of epoxides catalyzed by metal–salen complexes
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:6
  • Tidskriftsartikel (refereegranskat)abstract
    • The asymmetric ring-opening of epoxides is an important reaction in organic synthesis, since it allows for the enantioselective installation of two vicinal functional groups with specific stereochemistry within one step from a highly available starting material. An effective class of catalysts for the asymmetric ring-opening of epoxides is metal–salen complexes. This review summarizes the development of metal–salen catalyzed enantioselective desymmetrization of meso-epoxides and kinetic resolution of epoxides with various nucleophiles, including the design and application of both homogeneous- and heterogeneous epoxide-opening catalysts as well as multi-metallic covalent and supramolecular catalytic systems.
  •  
46.
  • Lindh, Linnea, et al. (författare)
  • Photophysics and photochemistry of iron carbene complexes for solar energy conversion and photocatalysis
  • 2020
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 10:3
  • Forskningsöversikt (refereegranskat)abstract
    • Earth-abundant first row transition metal complexes are important for the development of large-scale photocatalytic and solar energy conversion applications. Coordination compounds based on iron are especially interesting, as iron is the most common transition metal element in the Earth’s crust. Unfortunately, iron-polypyridyl and related traditional iron-based complexes generally suffer from poor excited state properties, including short excited-state lifetimes, that make them unsuitable for most light-driven applications. Iron carbene complexes have emerged in the last decade as a new class of coordination compounds with significantly improved photophysical and photochemical properties, that make them attractive candidates for a range of light-driven applications. Specific aspects of the photophysics and photochemistry of these iron carbenes discussed here include long-lived excited state lifetimes of charge transfer excited states, capabilities to act as photosensitizers in solar energy conversion applications like dye-sensitized solar cells, as well as recent demonstrations of promising progress towards driving photoredox and photocatalytic processes. Complementary advances towards photofunctional systems with both Fe(II) complexes featuring metal-to-ligand charge transfer excited states, and Fe(III) complexes displaying ligand-to-metal charge transfer excited states are discussed. Finally, we outline emerging opportunities to utilize the improved photochemical properties of iron carbenes and related complexes for photovoltaic, photoelectrochemical and photocatalytic applications.
  •  
47.
  • Lopez Nina, Luis Gagarin, et al. (författare)
  • Synthesis of Ethanol from Syngas over Rh/MCM-41 Catalyst : Effect of Water on Product Selectivity
  • 2015
  • Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 5, s. 1737-1755
  • Tidskriftsartikel (refereegranskat)abstract
    • The thermochemical processing of biomass is an alternative route for the manufacture of fuel-grade ethanol, in which the catalytic conversion of syngas to ethanol is a key step. The search for novel catalyst formulations, active sites and types of support is of current interest. In this work, the catalytic performance of an Rh/MCM-41 catalyst has been evaluated and compared with a typical Rh/SiO2 catalyst. They have been compared at identical reaction conditions (280 degrees C and 20 bar), at low syngas conversion (2.8%) and at same metal dispersion (H/Rh = 22%). Under these conditions, the catalysts showed different product selectivities. The differences have been attributed to the concentration of water vapor in the pores of Rh/MCM-41. The concentration of water vapor could promote the water-gas-shift-reaction generating some extra carbon dioxide and hydrogen, which in turn can induce side reactions and change the product selectivity. The extra hydrogen generated could facilitate the hydrogenation of a C-2-oxygenated intermediate to ethanol, thus resulting in a higher ethanol selectivity over the Rh/MCM-41 catalyst as compared to the typical Rh/SiO2 catalyst; 24% and 8%, respectively. The catalysts have been characterized, before and after reaction, by N-2-physisorption, X-ray photoelectron spectroscopy, X-ray diffraction, H-2-chemisorption, transmission electron microscopy and temperature programmed reduction.
  •  
48.
  • Mandic, Mina, et al. (författare)
  • Identification and Characterization of New Laccase Biocatalysts from Pseudomonas Species Suitable for Degradation of Synthetic Textile Dyes
  • 2019
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 9:7
  • Tidskriftsartikel (refereegranskat)abstract
    • Laccases are multicopper-oxidases with variety of biotechnological applications. While predominantly used, fungal laccases have limitations such as narrow pH and temperature range and their production via heterologous protein expression is more complex due to posttranslational modifications. In comparison, bacterial enzymes, including laccases, usually possess higher thermal and pH stability, and are more suitable for expression and genetic manipulations in bacterial expression hosts. Therefore, the aim of this study was to identify, recombinantly express, and characterize novel laccases from Pseudomonas spp. A combination of approaches including DNA sequence analysis, N-terminal protein sequencing, and genome sequencing data analysis for laccase amplification, cloning, and overexpression have been used. Four active recombinant laccases were obtained, one each from P. putida KT2440 and P. putida CA-3, and two from P. putida F6. The new laccases exhibited broad temperature and pH range and high thermal stability, as well as the potential to degrade selection of synthetic textile dyes. The best performing laccase was CopA from P. putida F6 which degraded five out of seven tested dyes, including Amido Black 10B, Brom Cresol Purple, Evans Blue, Reactive Black 5, and Remazol Brilliant Blue. This work highlighted species of Pseudomonas genus as still being good sources of biocatalytically relevant enzymes.
  •  
49.
  • Manzoor, Numair, et al. (författare)
  • RETRACTED: Experimental Study of CO2 Conversion into Methanol by Synthesized Photocatalyst (ZnFe2O4/TiO2) Using Visible Light as an Energy Source
  • 2020
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 10:2
  • Tidskriftsartikel (refereegranskat)abstract
    • Ozone layer depletion is a serious threat due to the extensive release of greenhouse gases. The emission of carbon dioxide (CO2) from fossil fuel combustion is a major reason for global warming. Energy demands and climate change are coupled with each other. CO2is a major gas contributing to global warming; hence, the conversion of CO2 into useful products such as methanol, formic acid, formaldehyde, etc., under visible light is an attractive topic. Challenges associated with the current research include synthesizing a photocatalyst that is driven by visible light with a narrow band gap range between 2.5 and 3.0 eV, the separation of a mixed end product, and the two to three times faster recombination rate of an electron–hole pair compared with separation over yield. The purpose of the current research is to convert CO2 into useful fuel i.e., methanol; the current study focuses on the photocatalytic reduction of CO2into a useful product. This research is based on the profound analysis of published work, which allows the selection of appropriate methods and material for this research. In this study, zinc ferrite (ZnFe2O4) is synthesized via the modified sol–gel method and coupled with titanium dioxide (TiO2). Thereafter, the catalyst is characterized by Fourier transform infrared (FTIR), FE-SEM, UV–Vis, and XRD characterization techniques. UV–Vis illustrates that the synthesized catalyst has a low band gap and utilizes a major portion of visible light irradiation. The XRD pattern was confirmed by the formation of the desired catalyst. FE-SEM illustrated that the size of the catalyst ranges from 50 to 500 nm and BET analysis determined the surface area, which was 2.213 and 6.453 m2/g for ZnFe2O4 and ZnFe2O4/TiO2, respectively. The continuous gas flow photoreactor was used to study the activity of the synthesized catalyst, while titanium dioxide (TiO2) has been coupled with zinc ferrite (ZnFe2O4) under visible light in order to obtain the maximum yield of methanol as a single product and simultaneously avoid the conversion of CO2 into multiple products. The performance of ZnFe2O4/TiO2was mainly assessed through methanol yield with a variable amount of TiO2 over ZnFe2O4 (1:1, 1:2, 2:1, 1:3, and 3:1). The synthesized catalyst recycling ability has been tested up to five cycles. Finally, we concluded that the optimum conditions for maximum yield were found to be a calcination temperature of ZnFe2O4at 900 °C, and optimum yield was at a 1:1 w/w coupling ratio of ZnFe2O4/TiO2. It was observed that due to the enhancement in the electron–hole pair lifetime, the methanol yield at 141.22 μmol/gcat·h over ZnFe2O4/TiO2was found to be 7% higher than the earlier reported data.
  •  
50.
  • Margarita, Cristiana, et al. (författare)
  • Recent Advances in Asymmetric Catalytic Electrosynthesis
  • 2020
  • Ingår i: Catalysts. - : MDPI. - 2073-4344. ; 10:9
  • Forskningsöversikt (refereegranskat)abstract
    • The renewed interest in electrosynthesis demonstrated by organic chemists in the last years has allowed for rapid development of new methodologies. In this review, advances in enantioselective electrosynthesis that rely on catalytic amounts of organic or metal-based chiral mediators are highlighted with focus on the most recent developments up to July 2020. Examples of C-H functionalization, alkene functionalization, carboxylation and cross-electrophile couplings are discussed, along with their related mechanistic aspects.
  •  
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