Bulk Of Catalyst Research Articles

Borane-Catalyzed Enantioselective α-Alkylation of Unactivated 2-Alkylbenzoxazoles with Electron-Deficient Olefins.

Chiral borane-catalyzed reactions have recently emerged as a powerful tool for the enantioselective production of chiral scaffolds. In this study, we demonstrated for the first time that a chiral bisborane catalyst can be used for the α-functionalization of 2-alkylazaarenes; specifically, we accomplished unprecedented highly enantioselective α-alkylation of unactivated 2-alkylbenzoxazoles with electron-deficient olefins. The strong Lewis acidity and the steric bulk of the bisborane catalyst were essential to the observed reactivity and selectivity.

Nanochannel-Induced Efficient Water Splitting at the Superhydrophobic Interface.

Constructing a favorable reaction configuration at the water/catalyst interface is crucial for high-efficiency semiconductor-based water splitting. For a long time, a hydrophilic surface of semiconductor catalysts has been considered necessary for efficient mass transfer and adequate contact with water. In this work, by constructing a superhydrophobic PDMS-Ti3+/TiO2 interface (denoted P-TTO) with nanochannels arranged by nonpolar silane chains, we observe overall water splitting efficiencies improved by an order of magnitude under both the white light and simulated AM1.5G solar irradiation compared to the hydrophilic Ti3+/TiO2 interface. The electrochemical overall water splitting potential on the P-TTO electrode also decreased from 1.62 to 1.27 V, which is close to the thermodynamic limit of 1.23 V. Through the in situ diffuse reflection infrared Fourier transform spectroscopy, a nanochannel-induced water configuration transition is directly detected. The density functional theory calculation further verifies the lower reaction energy of water decomposition at the water/PDMS-TiO2 interface. Our work achieves efficient overall water splitting through nanochannel-induced water configurations without changing the bulk of semiconductor catalyst, which reveals the significant role of water status at the interface in the efficiency of the water splitting reaction over the properties of catalyst materials.

Selective Reduction of Carboxylic Acids to Alcohols in the Presence of Alcohols by a Dual Bulky Transition-Metal Complex/Lewis Acid Catalyst

Here, we report a molecular method for the generally applicable reduction of mono- and dicarboxylic acids that selectively furnishes a diverse variety of alcohols, including mono- and diols. One of the inherent drawbacks of the direct hydrogenation of carboxylic acids to alcohols is the in situ formation of the corresponding esters via condensation of the carboxylic acids with the produced alcohols. Especially, the hydrogenation of polycarboxylic acids frequently suffers from the formation of a complex mixture of oligomeric esters. This issue was successfully overcome by the combined use of a dual catalyst that consists of a bulky (PNNP)iridium complex and a Lewis acid. Owing to the steric bulk and robustness of the iridium catalyst, the main role of the Lewis acid is to independently catalyze the esterification, albeit the cooperative activation of (a resting state of) the iridium catalyst by the Lewis acid also seems to be implied.

An Investigation into the Bulk and Surface Phase Transformations of Bimetallic Pd-In/Al2O3 Catalyst during Reductive and Oxidative Treatments In Situ

A series of oxidative treatments of PdIn-supported intermetallic nanoparticles at different temperatures were performed. The bulk and surface structure of catalyst during phase transformation was investigated by bulk- and surface-sensitive techniques (in situ XAFS, DRIFTS of adsorbed CO). It was found that comparison of palladium and indium fractions in bulk and on the surface suggests the formation of a «core-shell» structure. According to obtained results, the core consists of In-depleted intermetallic compound or inhomogeneous bimetallic phase with the inner core of metallic Pd, when a mixture of indium oxide, metallic palladium and small part of PdIn is present on the surface.

Lewis Pair Polymerization of Renewable Indenone to Erythro-Ditactic High-Tg Polymers with an Upcycling Avenue

Preparation and storage of biorenewable, monomeric indenone, much less the polymerization to a well-defined, high-molecular-weight polymer, is challenging because of antiaromaticity-driven radical autopolymerization. Herein, we report the successful preparation and subsequent Lewis pair polymerization (LPP) of indenone without autopolymerization side reactions using Lewis pairs consisting of sterically encumbered Lewis acid (LA) catalysts, such as B(C6F5)3 and bis(2,6-tert-butyl-4-methylphenoxy)methylaluminum and Lewis base initiators such as silyl ketene acetal and N-heterocyclic olefin nucleophiles. Thus, for the first time, the LPP enabled the synthesis of polyindenone (Pin) with high number-average molecular weight (Mn = 1.72 × 105 g mol–1) and low dispersity (D = 1.13). Observed correlations between the steric bulk of the LA catalyst and diastereoselectivity (57–75%) created the opportunity to model and investigate the relationships between β-substituted monomer motifs, catalyst steric accessibility...

Effect of the Specific Adsorption of Sulfonate Group in Ionomer and Adsorbed Oxide Species on the Oxygen Reduction Reaction Activity of PEFC Catalyst

Introduction For wide spread of Polymer Electrolyte Fuel Cell (PEFC), It is necessary to improve the oxygen reduction reaction (ORR) activity of cathode catalyst. While the Ionomer (e.g., Nafion®) have been used in commercial PFEC to improve the triple-phase boundary [1]and the effect of side-chain in perfluoro-sulfonic acid ionomers adsorbing on the surface of Pt has been discussed. [2,3] For the terminal sulfonate group is adsorbed on Pt by one or two oxygen atom(s) and the oxygen atom of ether group also interaction with the Pt, it’s shown that the existence of ionomer will block the oxygen reduction reaction. [4]In this study, the weight ratio of Ionomer and carbon which was used in the catalyst (I/C) has been changed to control the degree of specific adsorption in order to analysis the effect of specific activity and construct a model of specific adsorption on the surface of Pt. Experiment Core-shell catalyst (Pd@Pt@Vulcan) is used to eliminate the signal from bulk of Pt catalyst while XAFS measurement. Catalyst ink is made by mixture Catalyst powder(6.446mg) with ultrapure water (7.6ml), isopropanol (2.4ml) and 5wt% Nafion®solution (quantity is changed with I/C) then bath sonicated in ice bath for 20 mins to obtain well-dispersed ink. Thin-film Rotating Disk Electrode (TF-RDE) technique is used to get a homogeneous catalyst layer. Finally, 10μl aliquots of the ink were subsequently pipetted on to the GC disk and get a catalyst layer with ~12μgcatalyst/cm2. For ORR activity measurements, the limiting current is calculated from the raw currents at 0.90V and analyzed to determine the specific activity. Results and Discussion In compare with tiny changes of ECSA, the ORR activity shows evident decrease along with I/C increasing, the more Nafion®is mixed in the ink, the more catalyst will be covered by ionomer which lead to more specific adsorption. For the specific adsorption is only happening at the interface of ionomer and the catalyst, ORR activity of catalyst will not be decreasing continuously with the degree of ionomer increasing. When the amount of Nafion®reaches a certain level the ORR activity is expected to be constant. In this research the I/C increase over about 1.0, there was not any changes have been shown about ORR activity. Reference [1] Kazuma Shinozaki, Yu Morimoto, Bryan S. Pivovar , Shyam S. Kocha, Journal of Power Sources. 325,745(2016) [2]Kazuma Shinozaki, Jason W. Zack,Svitlana Pylypenko, Bryan S. Pivovar,Shyam S. Kocha, Journal of The Electrochemical Society, 162(12) F1384-F1396 (2015) [3]Ram Subbaraman, Dusan Strmcnik, Vojislav Stamenkovic, Nenad M Markovic, J. Phys. Chem. C .114, 8414–8422 (2010) [4] Kensaku Kodama,Kenta Motobayashi, Akihiro Shinohara, Naoki Hasegawa, Kenji Kudo, Ryosuke Jinnouchi, Masatoshi Osawa, Yu Morimoto, ACS Catal. 8, 694(2018) Acknowledgments This research is based on results obtained from a project commissioned by the New Energy and Industrial Technology Development Organization (NEDO)

Nucleation and growth kinetics of multi-layered graphene on copper substrate

The nucleation and growth kinetics of multilayered graphene on Cu substrates in low pressure chemical vapor deposition is investigated. Uniform millimeter-sized single crystalline graphene grains are formed under high temperature and high hydrogen to methane ratio conditions. Moreover, beneath each first layered grain, we found numerous multi-layered adlayer grains with wide size distribution. Through Raman spectroscopy, atomic force microscopy, and image processing, we quantitatively characterize the graphene growth. We show evidence for non-equilibrium growth kinetics in the adlayer, in contrast to the equilibrium growth kinetics of the first layer. The out-diffused carbon sources from the bulk of catalyst plays important role in the multi-layered graphene growth through generation of new nucleation sites underneath the first layer during the whole growth process. Balance between the role of hydrogen as catalysis and etchant, and the capping area of first layer, are shown to be important factors in determining the eventual multilayer characteristics.

Correlating the properties of hydrogenated titania to reaction kinetics and mechanism for the photocatalytic degradation of bisphenol A under solar irradiation

Hydrogenation of a commercially available TiO2 anatase catalyst was carried out at several annealing temperatures in the range 400–800°C to improve its photocatalytic activity for the degradation of endocrine disruptor bisphenol A (BPA) under simulated solar irradiation. The prepared hydrogenated catalysts, as well as their counterparts calcined in air were characterized with respect to their morphological, optical and electronic properties by means of BET, XRD, XPS, DRS and UPS analyses. Thermal treatment under flowing hydrogen resulted in increased absorption at wavelengths below 400nm, as well as in the appearance of a broad and almost uniform absorption band in the visible region, the intensity of which increased with increase of annealing temperature. The latter was attributed to the creation of gap states in the hydrogenated samples, which was not observed for the samples calcined in air. Interestingly, sodium inherently present in the bulk of the pristine catalyst was found to diffuse at the surface and this was more pronounced for the hydrogenated samples prepared at temperatures above 700°C.The relative catalytic activity was tested to degrade 240μg/L BPA in pure water and it was found that the hydrogenated catalysts were more active than those calcined in air at the same temperatures. The maximum rate (0.0647min−1) was observed for the catalyst hydrogenated at 600°C, i.e. three times greater than the respective calcined catalyst. Higher annealing temperatures had a detrimental effect on photocatalytic activity and this may be associated with a collapse of the specific surface area. Other than the annealing temperature, the rate was also strongly dependent on the water matrix (slower for more complex matrices), BPA and catalyst concentration and the presence of electron acceptors.LC–MS/TOF analysis was employed to identify transformation by-products (TBPs) and elucidate reaction pathways. BPA degradation by hydrogenated catalysts seems to occur mainly through consecutive hydroxylation/oxidation reactions, as evidenced by the various oxygenated TBPs formed; conversely, scission of BPA through the isopropylidene group and further oxidation, yielding different para-substituted phenolic intermediates seems to be the main degradation route in the presence of calcined catalysts.

Optimal Synthesis of Sal (Shorea robusta) Oil Biodiesel Using Recycled Bentonite Nanoclay at High Temperature

Fresh and recycled bentonite nanoclay was used as a basic catalyst for the optimal synthesis of sal oil methyl ester biodiesel at high temperature. Bulk and surface properties of fresh and recycled catalyst were determined to check the recyclability. A catalyst concentration dependent lumped-parameter kinetic model was proposed for the transesterification of sal oil, and a simple genetic algorithm was used to determine the rate constants. Proposed rate constants were able to predict the experimental conversion of sal oil accurately under varying catalyst and methanol concentrations. A multiobjective optimization problem involving conflicting objectives (i.e., minimization of transesterification time, and minimization of undesirable intermediates) was formulated and solved using a nondominated sorting genetic algorithm. The temperature trajectory over the entire transesterification period was considered as a decision variable to obtain the fixed conversion of sal oil. A set of nondominated optimal Pareto solutions was obtained for the problem studied. For optimal synthesis, a higher isothermal temperature trajectory (≥503 K) was preferred for a short transesterification time (i.e., ≤35 min), whereas a nonisothermal temperature trajectory with lower reaction temperature (446.7–470.7 K) was required to keep undesirable intermediates at a minimum level (i.e., ≤0.0825 mol L–1) for 96.5% conversion of sal oil.

Probing the Diastereoselectivity of Staudinger Reactions Catalyzed by N-Heterocyclic Carbenes.

The reaction of ethylphenylketene with 1,3-dimesitylimidazol-2-ylidene (IMes) or 1,3-dimesitylimidazolin-2-ylidene (SIMes) afforded the corresponding azolium enolates in high yields. The two zwitterions were fully characterized by various analytical techniques. Their thermal stabilities were monitored by thermogravimetric analysis and the molecular structure of SIMes⋅EtPhCCO was determined by means of X-ray crystallography. A mechanism was proposed to account for the trans-diastereoselectivity observed in the [2+2] cycloaddition of ketenes and N-protected imines catalyzed by N-heterocyclic carbenes and an extensive catalytic screening was performed to test its validity. The steric bulk of the NHC catalyst markedly affected the cis/trans ratio of the model β-lactam product. The nature of the solvent used to carry out the Staudinger reaction also significantly influenced its diastereoselectivity. Conversely, the nature of the substituent on the N-sulfonated imine reagent and the reaction temperature were less critical parameters.

A combined "electrochemical-frustrated lewis pair" approach to hydrogen activation: surface catalytic effects at platinum electrodes.

Herein, we extend our “combined electrochemical–frustrated Lewis pair” approach to include Pt electrode surfaces for the first time. We found that the voltammetric response of an electrochemical–frustrated Lewis pair (FLP) system involving the B(C6F5)3/[HB(C6F5)3]− redox couple exhibits a strong surface electrocatalytic effect at Pt electrodes. Using a combination of kinetic competition studies in the presence of a H atom scavenger, 6-bromohexene, and by changing the steric bulk of the Lewis acid borane catalyst from B(C6F5)3 to B(C6Cl5)3, the mechanism of electrochemical–FLP reactions on Pt surfaces was shown to be dominated by hydrogen-atom transfer (HAT) between Pt, [Pt–H] adatoms and transient [HB(C6F5)3]⋅ electrooxidation intermediates. These findings provide further insight into this new area of combining electrochemical and FLP reactions, and proffers additional avenues for exploration beyond energy generation, such as in electrosynthesis.

Selective Hydrogenation of Acetylene over a MoP Catalyst

A MoP catalyst was prepared by high temperature hydrogen reduction. Its properties were investigated by X-ray diffraction and in-situ X-ray photoelectron spectroscopy. It was used for the selective catalytic hydrogenation of acetylene. The results indicated that MoP is formed by hydrogen reduction at 650 °C. The prepared MoP catalyst contained high valence molybdenum and phosphorus species. The catalyst is a bifunctional catalyst, which includes a hydrogenation center and an electron-deficient center. Ethylene selectivity can exceed 73% when the acetylene conversion is higher than 99%. ：通过高温还原法制得磷化钼 (MoP) 催化剂, 采用 X 射线衍射和原位 X 射线光电子能谱对其进行了表征, 并考察其催化乙炔选择性加氢性能. 结果表明, 在 650 ºC 经 H 2 还原制得的催化剂中形成了大量的低价态物种 MoP, 但仍含有大量的高价态 Mo 和 P 物种, 该催化剂具有加氢活性中心和缺电子中心双重功能, 在乙炔选择性加氢反应中, 乙炔转化率超过 99% 时, 乙烯选择性仍能保持在 73% 以上. H 2 molecules can be activated by a MoP catalyst to form active hydrogen species, which can obtain the supplement from the gas phase hydrogen by hydrides in the bulk of MoP catalyst. Ethylene selectivity can exceed 73% when the acetylene conversion is higher than 99%.

Preparation of Stable Exfoliated Pt−Clay Nanocatalyst

In this paper, we report a novel experimental protocol for the preparation of stable and exfoliated nano-Pt catalysts supported on layered silicate clay surfaces. Uniformly dispersed highly crystalline Pt nanoparticles with diameters between 2 and 5 nm were chemically adsorbed on to the layered silicate surfaces using a chemical vapor deposition (CVD) method employing organoclay as the initial support. The as-prepared catalysts were found to be extremely stable against both intensive mechanical agitation and high temperature treatment. No Pt loading or morphology changes were observed after ultrasonication under a sonication power density of 6 MW/m(3) for up to 72 h at room temperature or annealing at 700 degrees C for 1 h under Ar flow. On the other hand, Pt catalysts prepared using the inorganic clay as the initial support were found to be highly unstable against both mechanical agitation and high temperature treatment. Significant leaching and catalyst restructuring or sintering was observed. Exfoliation of catalysts and the nature of Pt adsorption were elucidated by systematic analysis using wide-angle X-ray diffraction (WAXD) analysis, Brunauer-Emmett-Teller (BET) surface area analysis, and time-of-flight secondary ion mass spectroscopy (ToF-SIMS) analysis. No low angle diffraction peak was observed in the WAXD pattern, and a 700% increase in BET surface area was observed after Pt deposition on clay surfaces. Depth profiling ToF-SIMS on Pt deposited on SiO(2) wafer surfaces showed the presence of PtSiO ion at the Pt and SiO(2) interface. This ion group was also detected in the bulk of Pt-OrC catalyst, confirming chemisorption of Pt on layered silicate clays. A much lower concentration of PtSiO ion was observed in the Pt-NaC with a similar Pt loading. In addition, X-ray photoelectron spectroscopy (XPS) shows that the binding energy of Pt4f(7/2) in Pt-OrC is much higher than that in the Pt-NaC. The protocol reported in this paper can also be applicable to other clay supported stable metallic catalysts.

Transient isotopic kinetics study to investigate reaction mechanisms

This overview includes discussion of the principles, experimental and theoretical features of the isotopic transient kinetics for the study of reaction mechanism and evaluation of kinetic parameters. The results of the mechanistic study of ethylene epoxidation over silver, selective NO reduction with methane over Co-ZSM-5 and fiberglass based catalysts are presented. Investigation of 18O isotope transfer dynamics allowed to reveal the reaction pathways towards ethylene oxide and CO 2 formation as well as to estimate the concentrations of active oxygen species and reaction rate coefficients of key steps. It was found that both ethylene epoxidation and deep oxidation proceed very fast in the microsecond range. A detailed SSITKA study of the NO reduction with methane using 15N, 13C and 18O labels showed that reaction occurred via two parallel pathways involving in nitrite–nitrate and NO 2 δ+ species, the last ones being 20 times more reactive. For the first time a transient isotopic kinetic study was used for evaluation of mass transfer parameters by an example of NO and water diffusion into the bulk of Pt-containing fiberglass catalyst.

Problem of catalyst ageing during the hot-wire chemical vapour deposition of thin silicon films

The filament in a hot-wire chemical vapour deposition (HWCVD) reactor is an important component. When tantalum (Ta) filaments are used for the deposition of thin silicon films, strong degradation takes place: there is a large amount of silicon not only at the surface but also in the bulk of the tantalum catalyst. Ta–Si phases form on the filament surface and in the bulk, which can lead to a porous structure of the catalyst filament. Filament contamination (silicide formation and thick silicon deposits (TSDs)) is the reason for the changes in filament resistance. It also reduces filament lifetime, which is a serious concern for HWCVD deposition technology. A cleaning procedure for the filament at high-temperatures in a vacuum (about 2000 °C) can neither remove the thick silicon deposits nor fully restore the filament surface properties. In order to decrease the silicon content in the tantalum catalyst and suppress TSD formations on the filament surface, we use radio-frequency alternating current (RF, 13.5 MHz) instead of direct current (DC) to heat the filament. The skin effect of the RF current reduces the formation of TSDs on the surface and silicon diffusion into the filament. We show that it is possible to clean the filament surface of TSDs by means of a high-frequency current. Combined RF + DC filament heating allows us to increase the lifetime of the catalyst (almost twofold) and to improve HWCVD process reproducibility without any deterioration in the quality of the deposited film.

The effect of water vapour on kinetics of ethyl- tert-butyl ether (ETBE) and tert-butyl alcohol (TBA) synthesis in the gas phase on Wells–Dawson catalyst

The effect of water vapour in the feed on the synthesis of ethyl- tert-butyl ether (ETBE) produced from isobutene and ethanol was investigated. The kinetics of gas phase etherification and accompanying formation of tert-butyl alcohol (TBA) by Wells–Dawson acid heteropolyacid H 6P 2W 18O 62 as catalyst was determined at 40 °C. Rate expression in the form of a power equation was developed to correlate the experimental data over a wide range of reactants pressures. Water presence in the catalytic reactor inhibited the formation of ETBE and was introduced into the kinetic equation as an independent additional factor. The experimental evidence of ethanol and water sorption into the bulk of catalyst was confirmed by independent gas phase sorption experiments. The results of catalytic experiments were interpreted qualitatively on the basis of the model of catalytic system containing solid heteropolyacid in which tertiary ethers are synthesized.

Effect of oxygen mobility in solid catalyst on transient regimes of catalytic reaction of methane partial oxidation at short contact times

Mathematical modeling of the effect of the oxygen mobility in a solid oxide catalyst on the dynamics of transients of fast catalytic reactions has been carried out. The analysis was based upon the redox mechanistic scheme with a due regard for diffusion of oxygen from the bulk of catalyst to its surface. Parameters of kinetic and mathematical models were selected via fitting of the experimental data for methane selective oxidation into syngas on 1.4%Pt/Gd0.2Ce0.4Zr0.4O x catalyst. The range of the Thiele parameter (φ) where the oxygen bulk diffusion affects the most strongly reaction transients corresponds to φe [0.3 ÷ 7]. For high-surface-area oxide catalysts, the bulk oxygen diffusion coefficients corresponding to this range of the Thiele parameter are in the range of 10–18 ÷ 10–13cm2/s.

Kinetics of gas phase synthesis of ethyl- tert-butyl ether (ETBE) on Wells–Dawson catalyst

Mechanism and kinetics of gas phase synthesis of ethyl- tert-butyl ether (ETBE) over Wells–Dawson heteropolyacid H 6P 2W 18O 62 in an anhydrous system have been discussed. The rates of ETBE synthesis were measured in a differential reactor for ethanol–isobutene system, far from the limitation by chemical equilibrium. In the pressure range studied, kinetic measurements show that isobutene has an enhancing effect on the reaction while ethanol has an inhibitory one. Catalytic and sorption experiments allowed to formulate the mechanism of ETBE synthesis which assumed isobutene adsorption and oligomerization at the surface of heteropolyacid crystallites and the formation of carbocation using protons supplied from the bulk of catalyst. Kinetic equations were deduced indicating that it is the concentration of protons forming inter-anionic bonds between heteropolyacid anions which determines the catalytic activity of heteropolyacid.

Investigation of the tantalum catalyst during the hot wire chemical vapor deposition of thin silicon films

After extensive utilization of tantalum (Ta) catalyst filaments for hot wire (HW) CVD of silicon films we found a high amount of silicon not only at the surface but also in the bulk of the tantalum catalyst (up to 8%). The amount of silicon accumulation in the bulk depends on the concentration of silane in the process gas. SIMS investigation indicates a silicide/silicon formation on the surface and significant diffusion of silicon into the bulk of the catalyst. This silicon contamination changes the filament resistance and seems to be the reason for rather short lifetime of the filament, which is a serious concern for the HWCVD deposition technology. Annealing of the filament by direct current (DC) at high temperature in vacuum enables to drastically reduce the silicon content (silicides) in a surface region of about 2–3 μm. However, it cannot remove the thick silicon deposits (> 10 μm) from the filament surface. In order to decrease the silicon content in the tantalum catalyst and the silicon formation on the filament surface we used alternating current (AC) (13.5 MHz) to heat the filament. Due to the “skin” effect of the radio frequency (RF) current the silicon indiffusion and the formation of silicon deposits on the surface are suppressed.

The Role of Bulk Oxide Ion in the Catalytic Oxidation Reaction over Metal Oxide Catalyst

AbstractFor Abstract see ChemInform Abstract in Full Text.