Showing papers in "Journal of Molecular Catalysis A-chemical in 2010"
TL;DR: In this paper, the photocatalytic degradation of organic dyes containing different functionalities using TiO2 nanomaterials in aqueous solution is discussed and the influence of different substitutes such as alkyl side chains, methyl, nitrate, hydroxyl and carboxylic groups as well as the presence of chloro atom have been discussed in detail.
Abstract: Synthetic dyes are a major part of our life as they are found in the various products ranging from clothes to leather accessories to furniture. These carcinogenic compounds are the major constituents of the industrial effluents. Various approaches have been developed to remove organic dyes from the natural environment. Over the past few years, there has been an enormous amount of research with advanced oxidation processes (AOPs) as an effective method of wastewater treatment. Among AOPs, heterogeneous photocatalytic process using TiO2 nanomaterials appears as the most emerging destructive technology due to its cost effectiveness and the catalyst inert nature and photostability. This review deals with the photocatalytic degradation of organic dyes containing different functionalities using TiO2 nanomaterials in aqueous solution. It first discusses the photocatalytic properties of nanostructured TiO2. The photocatalytic degradation rate strongly depends on the basic structure of the molecule and the nature of auxiliary groups attached to the aromatic nuclei of the dyes. So, this review then explains the influence of structure of dyes on their photocatalytic degradation rates. The influences of different substitutes such as alkyl side chains, methyl, nitrate, hydroxyl and carboxylic groups as well as the presence of chloro atom have been discussed in detail.
572 citations
TL;DR: In this paper, a novel Bi 2 O 2 CO 3 photocatalyst was first put forward by virtue of structural understanding, and the results confirmed that the higher efficiency of the photocatalytic activity should be contributed synergistically by the higher BET surface area and the special exposed surface.
Abstract: In this work a novel Bi 2 O 2 CO 3 photocatalyst was first put forward by virtue of structural understanding. In particular, the flower-like Bi 2 O 2 CO 3 hierarchitecture with the controlled special {0 0 1} plane exposed was first synthesized via a mild route, showing the excellent photocatalytic activity due to the large distortion of Bi–O on the exposed surface. The Bi 2 O 2 CO 3 nanostructures have proved to be not only a new photocatalyst under solar light irradiation, but also a possible example for investigating the key factors of which may impact on the photocatalytic ability. The results confirmed that the higher efficiency of the photocatalytic activity should be contributed synergistically by the higher BET surface area and the special exposed surface.
240 citations
TL;DR: In this article, a review of the synthesis of DMC is presented, dealing with the catalysts, the mechanisms as well as the industrial processes and the reactions for producing DMC, within the policy of developing clean and eco-friendly processes.
Abstract: This review reports on the synthesis of dimethylcarbonate (DMC) and deals with the catalysts, the mechanisms as well as the industrial processes and the reactions for producing DMC, within the policy of developing clean and eco-friendly processes. DMC is considered as an environmentally benign chemical due to a negligible ecotoxicity, a low bioaccumulation and a low persistence, so that the production and chemical use of DMC have attracted much attention in the view of the so-called ‘sustainable society’ and ‘green chemistry’, mainly for replacing dimethylsulfate and methylhalides in methylation reactions and for replacing the harmful phosgene in polycarbonate and isocyanate syntheses. Special focus is made on the vapour phase oxycarbonylation of methanol by carbon monoxide in substitution to the old phosgenation process abandoned with years, and as an alternative process to both liquid phase methanol oxycarbonylation and methylnitrite carbonylation processes. The catalytic materials consist in high surface area active carbon supported copper chloride-based catalysts and chloride-free zeolite catalysts, both investigated in terms of catalyst preparation, active phase nature, performances and catalytic mechanisms.
201 citations
TL;DR: In this article, the Fischer-Tropsch synthesis of unpromoted and nano-sized iron oxide supported on δ-Al2O3 was investigated using a fixed-bed reactor.
Abstract: The Fischer–Tropsch synthesis of unpromoted and nano-sized iron oxide supported on δ-Al2O3 was investigated using a fixed-bed reactor. The catalysts prepared from pre-synthesized iron oxide with varying particle size (2–12 nm) showed much higher catalytic activities than the one prepared by using conventional impregnation method. The best results for CO conversion were obtained when the catalyst had Fe particle size of 6.1 nm. With an increase in particle size, the reduction degree and C5+ selectivity was increased, whereas CH4 selectivity and the uptake of adsorbed CO were decreased. Turnover frequency (TOF) at 300 °C was increased from 0.02 to 0.16 s−1 when d(Fe0) was increased from 2.4 to 6.2 nm, and then it remains almost constant up to a particle size of 11.5 nm. Particle sizes of prepared iron oxide were analyzed by XRD and TEM, and the reduction behaviors of Fe/Al2O3 catalysts were studied by H2-TPR. The effective iron size, metal dispersion and reduction degree of Fe/Al2O3 catalysts were measured by CO chemisorption and O2 titration.
195 citations
TL;DR: In this article, the photocatalytic activities of divalent transition metal catalysts were evaluated in the degradation of Aniline Blue (AB) under UV/solar light, which is attributed to the synergistic effect in the bicrystalline framework of anatase and rutile.
Abstract: Anatase TiO2 was doped with divalent transition metal ions like Mn2+, Ni2+ and Zn2+ and characterized by various analytical techniques. Powder X-ray diffraction revealed stabilization of anatase phase for Ni2+ and Zn2+ doped samples, while phase transformation from anatase to rutile was promoted due to Mn2+ inclusion. The rutile fraction increased with Mn2+ concentration due to the creation of surface oxygen vacancies. All the doped catalysts showed red shift in the band gap absorption to the visible region. The photocatalytic activities of these catalysts were evaluated in the degradation of Aniline Blue (AB) under UV/solar light. Among the photocatalysts, Mn2+ (0.06 at.%)–TiO2 showed enhanced activity, which is attributed to the synergistic effect in the bicrystalline framework of anatase and rutile. Further the unique half filled electronic structure of Mn2+ serves as a shallow trap for the charge carriers to enhance the photocatalytic activity. An insight to the mechanism of interfacial charge transfer in the mixed phase of anatase and rutile is explored, taking into consideration the theories of previous models.
195 citations
TL;DR: The application of artificial neural networks for modeling of water and wastewater treatment using various homogeneous and heterogeneous nanocatalytic processes is described.
Abstract: Artificial neural networks (ANNs) are computer based systems that are designed to simulate the learning process of neurons in the human brain. ANNs have been attracting great interest during the last decade as predictive models and pattern recognition. Artificial neural networks possess the ability to “learn” from a set of experimental data (e.g. processing conditions and corresponding responses) without actual knowledge of the physical and chemical laws that govern the system. Therefore, ANNs application in data treatment is especially important where systems present nonlinearities and complex behavior. In recent years “advanced oxidation processes” (AOPs), including homogeneous and heterogeneous nanocatalytic processes, have been proposed to oxidize quickly and non-selectively a broad range of water pollutants. Due to the complexity of reactions in AOPs, the effect of different operational parameters involved are very difficult to determine, leading to uncertainties in the design and scale-up of chemical reactors of industrial interest. It is evident that this problem can not be solved by simple linear multivariate correlation. Artificial neural networks are a promising alternative modeling technique. This paper briefly describes the application of artificial neural networks for modeling of water and wastewater treatment using various homogeneous and heterogeneous nanocatalytic processes. Examples of early applications of ANNs in modeling and simulation of photocatalytic, photooxidative and electrochemical treatment processes are reviewed.
167 citations
TL;DR: In this paper, a novel BiFeO 3 photocatalyst in the shape of uniform microspheres has been synthesized by solvothermal process assisted with chelating effect of citric acid.
Abstract: A novel BiFeO 3 photocatalyst in the shape of uniform microspheres has been synthesized by solvothermal process assisted with chelating effect of citric acid. The higher photoactivity of this catalyst than that of BiFeO 3 via solid-state reaction for methylene blue (MB) degradation under visible-light irradiation is owing to the high crystallization of perovskite-type BiFeO 3 , high surface area with hollow structure, narrow band gap energy of 2.1 eV, and the promotion of separation of photo-induced electrons and holes. Additionally, no decrease of activity after being reused repetitively for five times is indicative of the high hydrothermal stability of BiFeO 3 particles without crystal phase transformation.
162 citations
TL;DR: In this paper, the photooxidation of oxalic acid, catalyzed by nanosized TiO2 or WO3 and composite photocatalysts, was studied under irradiation with UV, visible and combined UV-visible light.
Abstract: The photooxidation of oxalic acid, catalyzed by nanosized TiO2 or WO3 and composite photocatalysts: Au/TiO2, Au/WO3, WO3/TiO2, Au/WO3/TiO2 was studied under irradiation with UV, visible and combined UV–visible light. The catalysts were characterized by the XRD, XPS, SEM and TEM methods. The photocatalytic mineralization of oxalic acid, catalyzed by WO3/TiO2 or Au/WO3/TiO2, proceeded at a significantly higher rate under UV-A irradiation than that under visible light. This is due to the lower specific surface area of the WO3 and its small amount in the composite catalyst. Doping of the semiconductor materials with gold nanoparticles more than doubles the rates of mineralization of oxalic acid, compared to the un-doped samples, and more significantly in the case of Au/WO3/TiO2. The higher rate constants of oxalic acid decomposition under UV, visible or UV–visible light irradiation with the WO3/TiO2 and Au/WO3/TiO2 catalysts, compared with those measured with the individual oxide photocatalysts, are due to the more efficient separation of the electron–hole charges generated upon irradiation. Especially efficient is the charge separation in the case of the Au/WO3/TiO2 photocatalyst under irradiation with UV or combined UV–visible light, when the rate constants of oxalic acid destruction are approximately 1.7 times higher than that of the process catalyzed by Au/TiO2 and 3 times higher than that catalyzed by pure TiO2.
143 citations
TL;DR: In this paper, the full catalytic cycle of the Suzuki-Miyaura coupling between PhBr and PhB(OH)3− with four different palladium monophosphine catalysts derived from Pd(PMe3)2, PdP(CF3)3), PdPh3, PhPh3 and PdpBu3 were explored and the differences between the ligands have been analyzed.
Abstract: DFT calculations have been used to explore the full catalytic cycle of the Suzuki–Miyaura coupling between PhBr and PhB(OH)3− with four different palladium monophosphine catalysts derived from Pd(PMe3)2, Pd(P(CF3)3)2, Pd(PPh3)2 and Pd(PtBu3)2. All the steps of the reaction have been studied and the differences between the ligands have been analyzed; special attention has been devoted to the ligand dissociation and catalyst regeneration processes, as well as the typical cross-coupling steps of oxidative addition, transmetallation and reductive elimination. Multiple linear regressions of the computationally derived energy barriers have been carried out in order to quantify the ligand effects of the different phosphines on the key steps of the reaction. These ligand effects, relevant to the catalytic activity, are described in terms of the phosphine donor/acceptor and steric features. The regression models show that oxidative addition is mainly governed by electronic effects whereas the transmetallation and the reductive elimination processes are controlled by a mixture of both ligand effects. For transmetallation, electron-withdrawing ligands lower the energy barrier.
133 citations
TL;DR: In this article, an overview of the evolution, advancements, and capabilities of the temporal analysis of products (TAP) reactor system as a unique catalyst characterization tool is presented, along with experimental designs and results coupling the TAP reactor to other experimental systems such as a time-of-flight mass spectrometer and atomic beam deposition system.
Abstract: This paper presents an overview of the evolution, advancements, and capabilities of the temporal analysis of products (TAP) reactor system as a unique catalyst characterization tool. The origination of the TAP reactor based on molecular beam scattering experiments is briefly mentioned. The advancement in TAP reactor design from the TAP-1 system to the TAP-3 system is introduced to highlight its relevance as a valuable tool for elucidating mechanistic and kinetic aspects of adsorption, diffusion, and reaction in gas–solid systems. Since the invention of the TAP reactor system, a series of TAP microreactor configurations has been introduced with different amounts of catalyst packing starting from the one-zone microreactor to the most recent introduction, the single particle microreactor in which a single Pt particle is packed among 100,000 inert quartz particles. An advantage to decreasing the catalyst zone inside the microreactor is to eliminate non-uniformity in the active zone while still achieving high conversions (95%). Experimental designs and results coupling the TAP reactor to other experimental systems such as a time-of-flight mass spectrometer and atomic beam deposition system is also presented. Key results from recent TAP experiments are presented to show how the TAP reactor is used to answer fundamental questions in catalysis such as bridging the pressure gap between industrial catalysis and surface science, understanding the surface lifetimes of reactive adspecies in TAP pump-probe experiments, finding kinetic rate constants related to changes in catalyst composition and its performance.
122 citations
TL;DR: Aldol condensation of acetaldehyde was investigated over silica supported magnesium and zirconium oxides in this paper, where the acid and basic properties of the catalysts were studied by TPD of NH 3 and CO 2.
Abstract: Aldol condensation of acetaldehyde was investigated over silica supported magnesium and zirconium oxides. The acidic and basic properties of the catalysts were studied by TPD of NH 3 and CO 2 and IR spectroscopy of adsorbed pyridine and CO 2 . MgO/SiO 2 catalyst was characterized by high content of both basic and acidic sites, while ZrO 2 /SiO 2 contained mainly Lewis acid sites. All materials studied were shown to catalyze the aldol condensation of acetaldehyde with selectivity to crotonaldehyde of ca. 85%. The activity of the catalysts was found to be in the following order: ZrO 2 /SiO 2 > MgO/SiO 2 ≫ SiO 2 . To assess the role of acidic and basic sites in condensation reaction, pyridine and carbon dioxide were used as probe molecules for poisoning of the corresponding active sites during catalytic runs. The results pointed to the key role of Lewis acid sites in acetaldehyde condensation. A concerted mechanism involving Lewis and Bronsted acid sites of the catalysts is proposed on the basis of in situ IR spectroscopic studies.
TL;DR: In this article, a comparison of photocatalytic degradation of an anionic dye (CI Acid Blue 92 (AB92) and a cationic dye(CI Basic Blue 3 (BB3) under UV light irradiation using supported TiO2 nanoparticles in a rectangular photoreactor was studied.
Abstract: In this work, comparative photocatalytic degradation of an anionic dye (CI Acid Blue 92 (AB92)) and a cationic dye (CI Basic Blue 3 (BB3)) under UV light irradiation using supported TiO2 nanoparticles in a rectangular photoreactor was studied The investigated TiO2 was Millennium PC-500 (crystallites mean size 8 nm and surface area of 32076 m2/g) immobilized on glass plates Response surface methodology (RSM) was employed to assess individual and interactive effects of the four main independent parameters (initial dye concentration, UV light intensity, flow rate and reaction time) on the decolorization efficiency Central composite design was used for optimization of UV/TiO2 process Predicted values of decolorization efficiency were found to be in good agreement with experimental values for AB92 and BB3 (R2 = 09435 and Adj-R2 = 08941, R2 = 09309 and Adj-R2 = 08704, respectively) Optimization results showed that maximum decolorization efficiency was achieved at the optimum conditions: initial dye concentration 10 mg/L, UV light intensity 472 W/m2, flow rate 100 mL/min and reaction time 200 min Photocatalytic mineralization of the dyes was monitored by total organic carbon (TOC) decrease The degradation pathway of AB92 was proposed based on the identified compounds by GC–Mass technique
TL;DR: In this article, a polystyrene (PS)-supported 1-(propyl-3-sulfonate) imidazolium hydrosulfate acidic ionic liquid (PS-CH 2 -[SO 3 H-pIM][HSO 4 ] catalyst was prepared by supporting the ionic fluid onto highly cross-linked chloromethylated poly styrene.
Abstract: Polystyrene (PS)-supported 1-(propyl-3-sulfonate) imidazolium hydrosulfate acidic ionic liquid (PS-CH 2 -[SO 3 H-pIM][HSO 4 ]) catalyst was prepared by supporting the ionic liquid onto highly cross-linked chloromethylated polystyrene (PS-CH 2 Cl). FT-IR, SEM and TG-DSC were employed to characterize the structure and property of the catalyst. Results suggested that acidic ionic liquid was supported onto the surface of PS-CH 2 Cl by covalent bond. The original rough surface of PS-CH 2 Cl was covered with acidic ionic liquid, forming a compact and thin surface layer, and its size had no obvious change. Moreover, the PS-CH 2 -[SO 3 H-pIM][HSO 4 ] catalyst showed a better thermal stability than that of PS-CH 2 Cl support. It also exhibited high catalytic activity for a series of esterifications. After the catalyst was reused for 13 times in the synthesis of n-butyl acetate, the yield only decreased 7.3%. A reaction mechanism of esterification over this new catalyst was proposed as well.
TL;DR: In this paper, the authors proposed a cathodic co-electrodeposition route from baths containing Zn(NO3)2 and Cu(CH3COO)2 for the first time, and the obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-Ray spectroscopy (EDS).
Abstract: CuO/ZnO composite films with different atomic Cu/Zn ratios were for the first time fabricated on indium tin oxide (ITO)-coated glass substrates via a cathodic co-electrodeposition route from baths containing Zn(NO3)2 and Cu(CH3COO)2. The obtained composite films were characterized with X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). Hexavalent chromium (Cr(VI)) was used as a model pollutant to evaluate their photocatalytic activity. For a bath containing Zn(NO3)2 with a certain concentration, the concentration of Cu2+ ions added into this bath play an important role in fabrication of CuO/ZnO composite films. When the Cu2+ concentration in a bath is lower, the obtained composite is a Cu-doped ZnO film. The electrodeposited CuO/ZnO composite films show higher photocatalytic activity towards reduction of Cr(VI) compared to pure ZnO both under UV and under UV–vis light illumination. Furthermore, the photocatalytic activity of CuO/ZnO composite films is related to their atomic Cu/Zn ratios. The mechanism of CuO/ZnO composite films for improvement in photocatalytic activity was also discussed.
TL;DR: In this article, a chitosan-g -mTEG (methoxy triethylene glycol)-supported palladium (0) catalyst was used for the Suzuki cross-coupling reaction in water.
Abstract: A chitosan- g -mTEG (methoxy triethylene glycol)- or mPEG (methoxy polyethylene glycol)-supported palladium (0) catalyst was prepared for the Suzuki cross-coupling reaction in water. The catalyst showed excellent catalytic activity in the Suzuki cross-coupling reaction without additional phase transfer reagents due to the enhanced solubility of the organic substrate by PEG grafting. In addition, the catalyst could be reused up to five times with the catalytic activity being recovered easily after simple manipulations.
TL;DR: In this article, the iridium(III) catalyzed hydrogenation of carbon dioxide under basic conditions was studied with density functional theory, and it was found that the insertion of CO2 into an Ir-H bond proceeds via a two-step mechanism.
Abstract: The iridium(III) catalyzed hydrogenation of carbon dioxide under basic conditions was studied with density functional theory. It was found that the insertion of CO2 into an Ir-H bond proceeds via a two-step mechanism. The rate-limiting step was calculated to be the regeneration of the iridium(III) trihydride intermediate, and the overall barrier for the reaction was calculated to 26.1 kcal mol(-1). The formation of the iridium trihydride proceeds via formation of a cationic Ir(H)(2)(H-2) complex at which the base abstracts a proton from the dihydrogen ligand. (C) 2010 Elsevier B.V. All rights reserved.
TL;DR: In this paper, a series of task-specific acidic ionic liquids (TSILs), immiscible with oil, halogen-free and containing COOH group in the cations, were used for oxidative desulfurization as both the catalyst and extractant.
Abstract: A series of task-specific acidic ionic liquids (TSILs), immiscible with oil, halogen-free and containing –COOH group in the cations, were used for oxidative desulfurization as both the catalyst and extractant. The removal of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) from model diesel at 298 K could reach 96.7% and 95.1%, respectively. The TSIL could be recycled 5 times without any apparent loss of the catalytic activity. Meanwhile, the structures, acidities and interactions between the cation and the anion of TSILs have been investigated by density functional theory (DFT) method, and found that catalytic properties of TSILs are close related to the structures, acidities and extraction capabilities. Furthermore, an oxidative desulfurization mechanism has been proposed.
TL;DR: In this article, the surface atomic carbon, the oligomerized carbon species and the bulk iron carbide are more reactive to hydrogen, whereas the large-size amorphous carbons are relatively inert to hydrogen.
Abstract: H2, CO chemisorptions and the carbon hydrogenation on promoted iron Fischer–Tropsch synthesis (FTS) catalysts (Fe/SiO2 and FeK/SiO2) were investigated using temperature programmed surface reaction with X-ray photoelectron spectroscopy and laser Raman spectroscopy. It is found that potassium, used as promoter, does not lead to a distinct variation in the carbon species but changes the surface H/C ratio of carburized catalysts. Besides bulk iron carbide, several carbon species with different cluster sizes exist in the carburized catalysts, which have different reactivities towards hydrogen. The surface atomic carbon, the oligomerized carbon species and the bulk iron carbide are more reactive to hydrogen, whereas the large-size amorphous carbons are relatively inert to hydrogen. There is a good correlation between the chemisorption of H2 or CO and the corresponding feed gas conversion activity in FTS reaction. Meanwhile, the methane selectivity is correlated with the hydrogenation capability of catalysts, indicating that the surface H concentration has an important effect on the selectivity of hydrocarbons.
TL;DR: In this article, a co-precipitation method at 450°C was used to synthesize molybdate for the degradation of rhodamine B (rhB), indigo carmine (IC), and methyl orange (MO) under visible light irradiation.
Abstract: γ-Bi 2 MoO 6 was prepared by the co-precipitation method at 450 °C. The molybdate was characterized by X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), simultaneous thermogravimetric and differential thermal analysis (TGA/DTA), diffuse reflectance spectroscopy (DRS), and surface analysis (BET). The synthesized material was tested as photocatalyst for the degradation of rhodamine B (rhB), indigo carmine (IC), and methyl orange (MO) under visible light irradiation. The γ-Bi 2 MoO 6 photocatalyst showed the capacity to bleach the dye solution in the following sequence: indigo carmine (IC) > rhodamine B (rhB) > methyl orange (MO). The degradation of rhB by γ-Bi 2 MoO 6 seems to happen predominantly through the photosensitization of the organic dye by the action of visible light irradiation. On the other hand, the IC degradation simultaneously happens by photosensitization and true photocatalytic processes. The activity of γ-Bi 2 MoO 6 for the degradation of MO was negligible. The reached mineralization degrees after 100 h of irradiation were 86% for rhB and 80% for IC.
TL;DR: In this paper, the authors investigated the catalytic performance of Fe-based Fischer-Tropsch synthesis (FTS) catalysts and found that the FTS reaction behaviors of the catalysts were measured at 1.5MPa, 260°C and syngas with H 2 /CO ratio of 2.0.
Abstract: The promotional effects of transition metals of Zn, Mn and Cr on the textural properties, reduction behavior, surface basicity, structural changes during reduction and reaction, and the catalytic performances of Fe-based Fischer–Tropsch synthesis (FTS) catalysts were investigated by N 2 physisorption, X-ray diffraction (XRD), Mossbauer spectroscopy (MES), extended X-ray absorption fine structure (EXAFS), X-ray photoelectron spectroscopy (XPS), CO temperature-programmed reduction (CO-TPR), H 2 -differential thermogravimetric analysis (H 2 -DTG) and CO 2 temperature-programmed desorption (CO 2 -TPD). The FTS reaction behaviors of the catalysts were measured at 1.5 MPa, 260 °C and syngas with H 2 /CO ratio of 2.0. The results show that there are two distinct forms of bimetallic interactions for the promoted catalysts, namely (1) ZnFe 2 O 4 compound formed for Zn-promoted iron catalyst and (2) solid solutions observed for those promoted by either Cr or Mn promoters. The presence of ZnFe 2 O 4 compound in the Zn-promoted catalyst leads to the phase separations between Zn and Fe oxides, and therefore very similar catalytic behavior to that of unpromoted catalyst. The stability of activity was improved due to the increased dispersion of active site through the formation of ZnFe 2 O 4 compound. In contrast, for the Mn- and Cr-promoted catalysts, the solid solutions in FeMn and FeCr systems strongly inhibit the reduction of the catalysts, and enhance the stability of catalytic activity. The FTS tests show that Mn and Cr promoters enhance the olefin and C 5+ hydrocarbon selectivity and restrain the methane selectivity due to their more strong basic sites. Besides the surface basicity the selectivities of Mn-promoted catalyst are also correlated with the enrichment of Mn on the catalyst surface.
TL;DR: In this article, a mesoporous cage-like material SBA-16 was modified by adsorption of Pd(OAc) 2 and reduction with NaBH 4, leading to a new solid catalyst for the aerobic oxidation of alcohols.
Abstract: Via modification of mesoporous cage-like material SBA-16 followed by adsorption of Pd(OAc) 2 and reduction with NaBH 4 , Pd nanoparticles with a uniform size distribution were successfully confined in the nanocages of SBA-16, leading to a new solid catalyst for the aerobic oxidation of alcohols. The solid catalyst was characterized with N 2 sorption, XRD, TEM, FT-IR and XPS. Such a catalyst showed a high activity for the oxidation of benzylic alcohols, 1-phenylethanol and allylic alcohols without the presence of bases under air or O 2 atmosphere in water even at room temperature. The selectivities for the corresponding aldehydes and ketones were more than 99% in all the cases investigated. The developed catalyst could be facilely recovered and reused twelve times without significant decreases in activity and selectivity. Its recyclability was much better than that of the catalyst derived from amorphous silica under the same conditions.
TL;DR: In this paper, the authors showed that the difference between the conduction band edges of the two phases may produce charge transfer from one phase to the other, which results in effectively the photo-generated charge separation and thus facilitates the redox reaction involving these charges.
Abstract: Fibril photocatalyst of mixed TiO2(B) and anatase phases, pure TiO2(B) and pure anatase are obtained by calcining titanate nanofibers prepared via hydrothermal reaction at different temperatures between 300 and 700 °C. They are used to verify the theory that the difference between the conduction band edges of the two phases may produce charge transfer from one phase to the other, which results in effectively the photo-generated charge separation and thus facilitates the redox reaction involving these charges. Indeed, the mixed-phase nanofibers exhibit higher photocatalytic activity for degradation of sulforhodamine B (SRB) under UV light than the nanofibers of either pure phase alone, or the mechanical mixtures of the two pure phase nanofibers with a similar phase composition. The interfaces between the two phases have a function of preventing charge recombination and enhancing the activity for photocatalytic oxidation. These interfaces are not random contacts between the crystals of the two phases, but form from well-matched lattice planes of the two phases. For instance, (2 0 2) planes in anatase and (2 0 2) planes of TiO2(B) are similar in d-spaces ∼0.18 nm, and they join together to form a stable interface. Such an interface structure is advanced for charge transfer crossing the interfaces, which reduces the recombination between the photo-generated electrons and holes. The knowledge acquired in this study is important not only for design of efficient TiO2 photocatalysts but also for understanding the photocatalysis process.
TL;DR: In this paper, the synthesis of bimetallic CoMo compounds from ammonium heptamolybdate, citric acid and cobalt acetate for the preparation of catalysts for the ultra-deep hydrodesulfurization (HDS) of diesel fuel is reported.
Abstract: The synthesis of bimetallic Co–Mo compounds from ammonium heptamolybdate, citric acid and cobalt acetate for the preparation of catalysts for the ultra-deep hydrodesulfurization (HDS) of diesel fuel is reported. The structure of the Co–Mo compounds formed in solution and on alumina surfaces was studied by 95 Mo, 17 O, 13 C, and 27 Al NMR, FTIR, Raman and XAS spectroscopy. It was found that the oxidic precursor of the catalyst consists of tetrameric molybdenum (VI) citrate anions with Co 2+ cations coordinated to the carboxyl groups and terminal oxygen atoms. After sulfidation, the prepared catalyst was tested in the HDS of straight run gas oil, demonstrating high activity in the production of ultra-clean diesel fuel.
TL;DR: In this article, the authors studied the catalytic performance of calcined and reduced Pt-Pd/γ-Al2O3 catalysts in the presence and absence of SO2 in the CH4-O2 reaction feed.
Abstract: The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al2O3 catalysts, in the presence and the absence of SO2 in the CH4–O2 reaction feed. The effect of sulfation (SO2 + O2 for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al2O3 catalysts resulted in a strong deactivation for the CH4–O2 reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al2O3 catalyst for CH4–O2 reaction remained rather unaffected in the presence and in the absence of SO2 in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al2O3 catalysts, the presence of Pt(0) metallic surface species on which SO2 interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO2 and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al2O3 catalysts for CH4–O2 reactions remained rather unaffected despite the presence of SO2 in the reaction feed.
TL;DR: In this article, a microkinetic model of steam and dry methane reforming on Ni-catalyst is proposed and proved based on new own and known published experimental data, and the model eliminates drawbacks of the known previous models.
Abstract: A critical analysis of known kinetic models of methane reforming on Ni-catalyst is performed. Based on new own and known published experimental data a microkinetic model of steam and dry methane reforming on Ni-catalyst is proposed and proved. The model eliminates drawbacks of the known previous models. The kinetic equations are derived. Kinetic parameters of the model are adjusted by means of mathematical modeling with the use of own and published data. Pore-diffusion resistance was taken into account during calculations. The obtained values of kinetic parameters agree with the estimated ones obtained according to the transition state theory.
TL;DR: Chitosan was modified through the hydrogel synthesis route and its catalytic activity was evaluated for the synthesis of jasminaldehyde by the condensation of 1-heptanal with benzaldehyde under solvent-free conditions as mentioned in this paper.
Abstract: Chitosan was modified through the hydrogel synthesis route and its catalytic activity was evaluated for the synthesis of jasminaldehyde by the condensation of 1-heptanal with benzaldehyde under solvent-free conditions. Chitosan being natural product and also the solvent-free synthesis procedure of jasminaldehyde have the advantage of green catalysis. Maximum conversion of >99% and 88% selectivity to jasminaldehyde were obtained at 160 °C. The effect of reaction parameters such as the amount of the catalyst, temperature and the benzaldehyde to 1-heptanal molar ratio on the conversion and selectivity was studied. The catalyst was recycled up to six times without significant loss in its activity and selectivity.
TL;DR: In this paper, the adsorption energies, favored binding sites and geometric parameters of the adaption configurations of all the carbonaceous species were determined and compared with published experimental data to evaluate the reliability of the calculation method.
Abstract: DFT–GGA calculations have been used to study the chemisorption of CH x ( x = 0–3), C 2 H y ( y = 3–5) and C 3 H z ( z = 3–8) on Pt(1 1 1) at the coverage of 1/9 ML. The adsorption energies, favored binding sites and geometric parameters of adsorption configurations are determined. All the carbonaceous species are found to be adsorbed on Pt(1 1 1) with C atoms sp 3 -hybridized. The geometries of adsorption configurations have been compared with published experimental data to evaluate the reliability of our calculation method. The calculated adsorption energies of C 1 species, ranked in descending order, are as follows, C > CH > CH 2 > CH 3 , and the similar trend has been observed with respect to the chemisorption of C 2 species. As for the C 3 species, propylene prefers binding to the surface in the di-σ mode and the adsorption energy is calculated to be −0.93 eV. The stepwise dehydrogenation of propane to propynyl (CCCH 3 ) is investigated by calculating the change of reaction heat, which suggests that propylidyne (CCH 2 CH 3 ) is the most stable species on Pt(1 1 1). Based on the adsorption energies and Bronsted–Evans–Polanyi (BEP) analysis, propyne is predicted to be the most likely starting point for the C–C scission.
TL;DR: In this article, the effect of impregnation medium on the activity of Co/CeO2 catalysts in ethanol steam reforming was investigated using various characterization techniques including temperature programmed calcination, temperature programmed reduction, X-ray diffraction, laser Raman spectroscopy, and diffuse reflectance infrared fourier transform analyzer.
Abstract: The effect of impregnation medium on the activity of Co/CeO2 catalysts in ethanol steam reforming was investigated using various characterization techniques including temperature programmed calcination, temperature programmed reduction, X-ray diffraction, laser Raman spectroscopy, X-ray photoelectron spectroscopy, and diffuse reflectance infrared fourier transform spectroscopy. The steady-state reaction experiments showed that catalysts that were prepared in an organic medium (e.g., ethanol) during impregnation gave higher H2 yields than those prepared in aqueous media. Characterization results showed the presence of oxygenated carbonaceous species left on the surface from the impregnation step. These species, which were stable through oxidation and reduction pre-treatment steps, may possibly contribute to the activity, selectivity and stability of the catalysts by keeping the Co particles segregated and by blocking the sites for side reactions.
TL;DR: In this article, 3-(2-Hydroxy-4-nitrophenylhydrazo)pentane-2,4-dione (H2L, 1) was synthesized by azocoupling of diazonium salts of 2-hydroxy 4-nitroaniline with pentane 2,4dione and shown to exist in the hydrazone tautomeric form in the free state.
Abstract: 3-(2-Hydroxy-4-nitrophenylhydrazo)pentane-2,4-dione (H2L, 1) was synthesized by azocoupling of diazonium salts of 2-hydroxy-4-nitroaniline with pentane-2,4-dione and shown to exist in the hydrazone tautomeric form in the free state and in its new dicopper(II) complex [Cu2(H2O)2(μ-L)2] (2) whose X-ray crystal structure was determined. Complex 2 acts as a catalyst, under mild conditions, for the peroxidative oxidation (with H2O2) of cyclohexane to cyclohexanol, cyclohexanone and cyclohexyl hydroperoxide, in MeCN/H2O, and for the aerobic TEMPO-mediated selective oxidation of benzylic alcohols to the corresponding aldehydes, thus showing that azoderivatives of β-diketones can be the suitable ligands for such types of reactions.
TL;DR: Compared with its homogeneous counterparts, the immobilised gel catalyst exhibited significantly improved catalytic activity under mild conditions as shown in Suzuki–Miyaura C–C coupling, and could be reused for several times.
Abstract: A metal–organic gel (MOG) route to immobilised catalysts has been developed based on the reversibility of coordination bond formation in a Fe3+–carboxylate MOG. The ferric gel was rationally designed based on a bifunctional ligand, 5-1H-benzo[d]imidazole-1,3-dicarboxylic acid (L1), in which the imidazole N atom may further bind to a soft ion like Pd2+ more strongly due to the HSAB matching. Palladium(II) was successfully loaded in the gel to yield a supported coordination catalyst. Compared with its homogeneous counterparts, the immobilised gel catalyst exhibited significantly improved catalytic activity under mild conditions as shown in Suzuki–Miyaura C–C coupling, and could be reused for several times.