Increasing Catalyst Loading Research Articles

Etherification of Glycerol with Ethanol over Solid Acid Catalysts: Kinetic Study Using Cation Exchange Resin

The etherification of glycerol with ethanol is a novel process to utilise low-value by-product (glycerol) of the biodiesel industry to produce ethers of glycerol suitable for use as fuel additive or solvent. The etherification of glycerol with ethanol was investigated under the liquid phase in a high pressure batch reactor using two different types of commercial solid acid catalyst (zeolites and strongly acidic cation exchange resin (CER)). The CER showed superior catalytic activity over H-beta zeolite. The diethyl ether was observed as major product at high ethanol-to-glycerol mole ratio. The product selectivity diverted towards ethers of glycerol with decreasing ethanol-to-glycerol mole ratio. Among ethers of glycerol, glycerol monoethyl ether was the major product of the reaction. The reaction mechanism for etherification of glycerol with ethanol was delineated based on experimental observations. The reaction rate increased with increasing catalyst loading and temperature without affecting selectivity to the products significantly. The apparent activation energy of glycerol and ethanol was 25.1 and 26.6 kcal/mol, respectively. An empirical kinetic model was developed to correlate experimental data at different temperatures. The conversion of the reactants calculated from the kinetic model matched reasonably with experimental data.

Removal of free fatty acid in Palm Fatty Acid Distillate using sulfonated carbon catalyst derived from biomass wastefor biodiesel production

In this research, the esterification of PFAD using the sulfonatedcoconut shell biochar catalyst was studied. Carbon solid catalysts were prepared by a sulfonation of carbonized coconut shells. The performances of the catalysts were evaluated in terms of the reaction temperatures, the molar ratios of methanol to PFAD, the catalyst loading and the reaction times. The reusability of the solid acid carbon catalysts was also studied in this work. The results indicated that the FFA conversion was significantly increased with increasing catalyst loading and reaction times. It can be concluded that the optimal conditions were an PFAD to methanol molar ratio of 1:12, the amount of catalyst of 10%w, and reaction temperature of 60oC.At this optimum condition, the conversion to biodieselreached 88%.

Catalytic wet air oxidation of phenol over ultrasound-assisted synthesized Ni/CeO2–ZrO2 nanocatalyst used in wastewater treatment

Non-noble metal Ni with different loadings was coated on precipitated CeO2–ZrO2 support by the sonochemistry method and examined for catalytic wet air oxidation of phenol. The structure of the nanocatalysts was determined by BET, FESEM, XRD, and FTIR analyses. The results showed non-uniform morphology of the nanocatalyst at lower Ni contents changed to homogenous morphology with spherical nano particles at higher Ni contents. While the size of NiO crystals remained constant with rising Ni content, the crystallinity of NiO significantly increased. If the crystallinity of NiO was 100% in 20%wt Ni/CeO2–ZrO2, the crystallinity of NiO in 5%wt Ni was found to be 41.13%. The average particle size in Ni(15%)/CeO2–ZrO2 was 77nm in which 85.71% of particle diameters were less than 100nm. Catalytic wet air oxidation of phenol with different Ni loadings indicated improvement of phenol destruction at higher amounts of active phase. Removal of phenol increased with increasing catalyst loading from 4 to 9.0g/l but further increase to 10g/l declined the catalyst reactivity.

A low-temperature partial-oxidation-methanol micro reformer with high fuel conversion rate and hydrogen production yield

A partial oxidation methanol micro reformer (POM-μReformer) with finger-shaped channels for low operating temperature and high conversing efficiency is proposed in this study. The micro reformer employs POM reaction for low temperature operation (less than 200°C), exothermic reaction, and quick start-up, as well as air feeding capability; and the finger type reaction chambers for increasing catalyst loading as well as reaction area for performance enhancement. In this study, centrifugal technique was introduced to assist on the catalyst loading with high amount and uniform distribution. The solid content (S), binder’s ratio (B), and channel design (the ratio between channel’s length and width, R) were investigated in detail to optimize the design parameters. Scanning electron microscopy (SEM), gas chromatography (GC), and inductively coupled plasma-mass spectrometer (ICP-MS) were employed to analyze the performance of the POM-μReformer. The result depicted that the catalyst content and reactive area could be much improved at the optimized condition, and the conversion rate and hydrogen selectivity approached 97.9% and 97.4%, respectively, at a very low operating temperature of 180°C with scarce or no binder in catalyst. The POM-μReformer can supply hydrogen to fuel cells by generating 2.23J/min for 80% H2 utilization and 60% fuel cell efficiency at 2ml/min of supplied reactant gas, including methanol, oxygen and argon at a mixing ratio of 12.2%, 6.1% and 81.7%, respectively.

Direct synthesis of DME over nanostructured CuO–ZnO–Al2O3/HZSM-5 catalyst washcoated on high pressure microreactor: Effect of catalyst loading and process condition on reactor performance

Direct conversion of syngas to DME (STD) has been successfully implemented over CuO–ZnO–Al2O3/HZSM-5 catalyst coated over a micro-channel reactor. Effect of catalyst loading (0.02, 0.025 and 0.03g) coated over the microchannels has been investigated and physiochemical properties of the coatings were examined by FESEM, EDX Dot-mapping, EDX Line-mapping and adherence sonication test. Although higher amounts of catalyst loading resulted in enhancement of active phase numbers but due to the thicker layer of catalyst, distance of diffusion was longer. Higher loadings of catalyst led to high coverage of top surface by copper and zinc but to weaker adherence of catalyst layer to the micro-channel plate. With increasing catalyst loading from 0.02 to 0.025g, the CO conversion and DME yield significantly enhanced but with increasing catalyst loading from 0.025 to 0.03g, the improvement in CO conversion and DME yield was not noticeable. The CO conversion and DME yield significantly decreased at high feed flow rates in the case of high loadings of catalyst.

Hydrogen production by catalytic gasification of coal in supercritical water with alkaline catalysts: Explore the way to complete gasification of coal

Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by catalytic gasification of coal in supercritical water (SCW) was carried out in a micro batch reactor with various alkaline catalysts: Na2CO3, K2CO3, Ca(OH)2, NaOH and KOH. H2 yield in relation to the alkaline catalyst was in the following order: K2CO3 ≈ KOH ≈ NaOH > Na2CO3 > Ca(OH)2. Then, hydrogen production by catalytic gasification of coal with K2CO3 was systematically investigated in supercritical water. The influences of the main operating parameters including feed concentration, catalyst loading and reaction temperature on the gasification characteristics of coal were investigated. The experimental results showed that carbon gasification efficiency (CE, mass of carbon in gaseous product/mass of carbon in coal × 100%) and H2 yield increased with increasing catalyst loading, increasing temperature, and decreasing coal concentration. In particular, coal was completely gasified at 700 °C when the weight ratio of K2CO3 to coal was 1, and it was encouraging that raw coal was converted into white residual. At last, a reaction mechanism based on oxygen transfer and intermediate hybrid mechanism was proposed to understand coal gasification in supercritical water.

Evaluation of MEA manufacturing parameters using EIS for SO2 electrolysis

Membrane electrode assembly (MEA) manufacturing parameters such as hot pressing pressure and pressing time were investigated for the use in a SO2 electrolyser. The SO2 electrolysis was optimised in terms of cell temperature, membrane thickness and catalyst loading. The electrolysis efficiency was evaluated using polarisation curves while electrochemical impedance spectroscopy (EIS) was used to determine the membrane resistance, activation energy and mass transport limitations. An electrical circuit, which included inductance, ohmic resistance, charge transfer, constant phase and Warburg elements, was used to fit the experimental data. The optimum hot pressing conditions were 50 kg cm−2 for 5 min at 120 °C. Increased cell temperature (80 °C) resulted in a reduction of mass transport, while thicker membranes resulted in an increased mass transport due to lower water transport through the membrane. Increased catalyst loading (from 0.3 to 1 mgPtC.cm−2) improved the cell performance due to improved kinetics confirmed by the EIS data.

Tailoring Structure of Fe/N/C Catalysts By Brief Calcination of Hemin for Efficient Oxygen Reduction Reaction

Introduction Polymer electrolyte membrane fuel cells (PEMFCs) are one of the promising candidates for next generation clean power sources. As a low-cost alternative to the Pt based catalysts used in PEMFCs for oxygen reduction reaction (ORR), metal/nitrogen/carbon (M/N/C) catalysts have been paid much attention. Recently, highly active M/N/C catalysts have been reported [1-6].Carbon-supported Fe/N/C catalysts synthesized from Hemin have recently shown high fuel cell performances [3]. Hemin, an iron-containing porphyrin, contains catalytically active structure, the iron coordinated to nitrogen, for the ORR. The Fe/N/C catalysts were synthesized by the calcination of Hemin at 600ºC for 2-3 hours [3, 4]. The heat treatment process is usually applied for Fe/N/C catalysts because the pyrolysis and graphitization of organic carbons as the source of iron and nitrogen are considered necessary for the activity and stability of catalysts [5]. At the same time, however, the high temperature calcination in a long period of time accompanies with the aggregation of iron nanoparticles as a result of desorption of Fe/N/C catalytic centers, which would cause the decrease of ORR activity [5, 6]. On the other hand, Kamiya et al. reported Fe/N/C catalyst produced by instantaneous calcination (45s) of pentaethylenehexamine coordinated with iron (Fe-PEHA) and graphenoxide [6]. They found that the instantaneous calcination would preferentially form atomic iron coordinated to nitrogen without producing aggregated iron nanoparticles.Here, we investigated the effect of brief calcination on ORR activity with different precursors, Hemin and Fe-PEHA. If it is possible to selectively place iron atoms into catalytically active sites, which is an advantage of the method [6], it would be useful to maximize the performance of Fe/N/C catalysts. Experimental Hemin and Fe-PEHA were mixed with carbon black (CB) in dimethylformamide and ethanol, respectively. After ultrasonicating the solution, dried mixture was obtained by a rotary evaporator, and then heated at 900 ºC for 100s and 70s for Hemin and Fe-PEHA, respectively. ORR activity of the catalysts was evaluated in 0.5M H2SO4(aq) by rotating disk electrode(RDE) experiments. Single cell tests were performed using a 36cm2MEA which used the Fe/N/C catalyst and Pt catalyst as cathode and anode, respectively. Current-voltage (I-V) curves were obtained at a cell temperature of 65 ºC by feeding fully humidified hydrogen and air or pure oxygen. The gases were supplied with a restricted stoichiometry which resembles the realistic operating conditions. Under these conditions, one can reasonably evaluate a performance difference between the Fe/N/C and Pt catalysts. Results and Discussion Fig. 1 shows the result of RDE for the synthesized Fe/N/C catalysts. Our Hemin based catalyst (red curve) showed the onset potential of about 0.91V vs. RHE. The onset potential was defined as the potential realizing a current density of 50µA in this study. This onset potential is comparable to those of other Hemin-based catalysts supported on graphene nanoplatelets or CB by long calcination of 2-3hours [3,4]. It is difficult to precisely compare ORR activity of these catalysts at this point because they may be mounted on RDE in a different manner. However, it is still interesting that the two different time scales of calcination, a couple of hours and 100s, can realize the comparable onset potential. The detailed analysis for comparing the structure and ORR mechanism in the two types of catalysts is in progress. We also note that our TEM and XPS analysis showed the coordination of iron to nitrogen without any sign of aggregated iron nanoparticles.The purple line in Fig. 1 shows the result for the Fe/N/C catalyst by 70s-calcination of Fe-PEHA. Although the Hemin- and Fe-PEHA based catalysts seem to possess similar Fe-N-modified graphite structure, the latter showed lower onset potential (about 0.8 V vs. RHE). Since it is not clear what critically causes the difference in ORR activity between them, we are unable to conclude the superiority of Hemin as the precursor over Fe-PEHA. However, it seems worth investigating how the structures of Fe/N/C active centers are modulated by choosing different precursors.We also obtained I-V curves for the Hemin-based Fe/N/C catalysts with different loadings of 0.2-4mg/cm2 by single cell tests. It was found that the cell performance improves with increasing catalyst loading. For the case of 4mg/cm2, OCV was 0.86V and a cell voltage of 0.4V was obtained at a current density of 0.5A/cm2. Further analysis will be discussed in the session.

Nano-iron carbide synthesized by plasma as catalyst for Fischer–Tropsch synthesis in slurry reactors: The role of iron loading and K, Cu promoters

Nano-iron carbides (NFeC), generated by a plasma spray technique, were used as-produced and promoted with potassium (K) and copper (Cu) in Fischer–Tropsch synthesis (FTS) in a 3-φ continuously stirred tank slurry reactor. NFeC particles were initially encapsulated in a carbon matrix to protect them from air-borne oxidation. This matrix was partially removed under reductive conditions as a pre-treatment of subsequent FTS reactions. Cu and K promoters were added to the catalyst by mixing Cu metallic powder and/or K2CO3 powder with iron–oil suspension fed to the plasma. The reactants simulated the composition of synthesis gas produced by urban biomass gasification.At-line gas chromatography of the more volatile products and global liquid product analyses by micro-distillation provided the necessary data for mass balance, conversion and selectivity estimations. Also, an appropriate algorithm successfully estimated the ratio of FTS over water–gas shift (WGS) reactions extents.The results disclosed that this nano-powder, characterized by very low internal porosity, generated a liquid fuel that was lighter than other commercial catalysts under similar reaction severities but at a significantly lower catalyst load (9% of the mass of liquid). Increased catalyst loading in the slurry above a critical limit led to higher product water hold-up and, consequently, higher rates of catalyst deactivation. Conversion, selectivity and the Anderson–Schulz–Flory distribution probability of chain growth “α” were compiled and reported.Tests with Cu- and K-promoted catalysts showed a highly significant decrease of the catalyst deactivation rate, with CO and H2 conversion increasing respectively to 82% and 44% from 35% and 30% obtained with no-doped catalyst. Moreover, CH4 yield was reduced to 4.7% from 12%, and the WGS rate tripled.Finally, the absence of internal porosity in the catalyst facilitated the definition of process-operating conditions in which surface reaction kinetics was the controlling step.

Sonophotocatalytic Degradation of Poly (Vinyl Pyrrolidone) in the Presence of Fe (III)/H2O2

The degradation of poly (vinyl pyrrolidone) (PVP) by means of ultrasound irradiation and its combination with homogeneous photocatalysis (photo-Fenton) was investigated. Emphasis was given on the effect of additive on degradation rate constants. 24 kHz of ultrasound irradiation was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. To increase the efficiency of degradation process, degradation system was combined with Fe (III) (2.510-4mol/L) and H2O2 (0.020 - 0.118 mol/L) in the presence of UV irradiation and the rate of degradation process change from 4.07x10-5 to 8.24x10-5 mol15 l-1.5 min-1. Photo-Fenton process led to complete PVP degradation in 150 min with the rate increasing with increasing catalyst loading. Sonophotocatalysis in the presence of Fe (III)/H2O2 was always faster than the respective individual processes. A negative order for the dependence of the reaction rate on total molar concentration of PVP solution within the degradation process was suggested. Results of this study indicate that the presence of catalyst in the reaction medium can be utilized to reduce molecular weight of PVP while maintaining the power of irradiated ultrasound.

The Reactivity and H2 Production Characteristics of Petroleum Coke-steam Gasification Catalyzed by Potassium Salts

Potassium salts-catalyzed steam gasification of petroleum coke for H2 production was performed using a laboratory fixed-bed reaction system with an on-line quadruple mass spectrometer. The gasification reactivity and H2 production characteristics of petroleum coke-steam gasification catalyzed by potassium salts were investigated mainly. The potassium salt catalysts could not only enhance effectively the gasification reactivity of petroleum coke, but also promote greatly the H2 production. The catalytic action of various potassium salts was ordered as K2CO3 > KAc > KNO3 > K2SO4 > KCl. The increasing catalyst loading could promote the H2 production of petroleum coke gasification. However, different potassium salts almost had no effect on the distribution of product gases. It was feasible to produce syngases with high H2 (up to 60%) and no virtual CH4 (below 0.1%) through the catalytic steam gasification of petroleum coke at relatively low temperatures.

Experimental and Modeling Studies of the Degradation of Estrogen Hormones in Aqueous TiO2 Suspensions under Simulated Solar Radiation

The efficiency of TiO2 photocatalysis to degrade three estrogen hormones, that is, 17α-ethynylestradiol (EE2), estrone (E1), and 17β-estradiol (E2), in environmentally relevant samples was investigated. Radiation at a photon flux of 1.7 × 10–7 einstein/s was provided by a solar simulator and experiments were conducted at various TiO2 loadings (25–1500 mg/L), estrogen concentrations (85–300 μg/L in individual solutions and 400 μg/L in mixture), and water matrices (ultrapure water, drinking water, and secondary treated wastewater). Changes in estrogen concentration were followed by high performance liquid chromatography and estrogenicity by the yeast estrogen screening assay. Aeroxide P25, a commercially available mixture of 75:25 anatase/rutile, was considerably more active than carbon-doped and undoped anatase titania, with degradation increasing with increasing catalyst loading and treatment time. The organic and inorganic constituents typically found in wastewater and drinking water impeded degradation presumably due to the scavenging of oxidizing species. For example, the time needed for complete 100 μg/L EE2 degradation in pure water was an order of magnitude lower than that in wastewater. The three estrogens exhibited comparable reactivity, with E1 being slightly more reactive than the rest. Degradation in multicomponent mixtures was slower than in individual solutions, thus implying estrogen competition for oxidizing species. Although the mixture of three in wastewater could be degraded fully after 120 min, overall estrogenicity was reduced by just about 30%, highlighting the role of the complex water matrix. Several oxidation products of EE2 were identified by means of LC–MS/MS and a reaction network for the photocatalytic degradation of EE2 is suggested. An artificial neural network comprising five input variables (reaction time, TiO2 and EE2 concentration, organic content, and conductivity of the water matrix), eight neurons and an output variable (conversion) was optimized, tested, and validated for EE2 degradation. The network, based on tangent sigmoid and linear transfer functions for the hidden and input/output layers, respectively, and the Levenberg–Marquardt back-propagation training algorithm, can successfully predict EE2 degradation.

Enhanced photocatalytic activity of fish scale loaded TiO2 composites under solar light irradiation

Fish scale (FS) loaded TiO2 composites were investigated as photocatalysts in degradation of Methyl Orange under solar light irradiation. Composites were prepared through sol-gel method by varying mass ratio of TiO2/FS at 90:10, 70:30 and 50:50, respectively. The catalysts prepared in this study were characterized by using XRD, SEM, FT-IR and nitrogen sorption. The effects of solar irradiation, mass ratio of TiO2/FS composites, irradiation time and catalyst loadings were studied. Synergistic effect was found in TiO2/FS of 90:10 composite which performed higher photocatalytic degradation than synthesized TiO2 under solar light irradiation. However, further increasing fish scale content in the composites reduced the photocatalytic activity drastically. Under solar light irradiation, all the catalysts in this study exhibited photocatalytic activity, except TiO2/FS of 50:50 composite that only acted as a weak biosorbent without performing any photocatalytic property. Photocatalytic degradation increased with increasing catalyst loading and irradiation time but decreased with increased of initial dye concentration.

Photocatalytic (UV-A/TiO2) degradation of 17α-ethynylestradiol in environmental matrices: Experimental studies and artificial neural network modeling

Abstract The efficiency of heterogeneous photocatalysis to degrade 17α-ethynylestradiol (EE2), a synthetic estrogen hormone, in environmentally relevant samples was investigated. In most cases, UV-A radiation at a photon flux of 2.81 × 10 −4 einstein/min was provided by a 9 W lamp and experiments were conducted at various concentrations of Aeroxide P25 TiO 2 (50–1000 mg/L), EE2 concentrations (50–900 μg/L) and water matrices (from ultrapure water to secondary treated wastewater). Some runs were performed at photon fluxes between 6.4 × 10 −7 and 3.7 × 10 −4 einstein/min to study the effect of intensity on degradation. Changes in estrogen concentration were followed by high performance liquid chromatography. EE2 degradation, which follows first order kinetics, increases with (i) increasing catalyst loading up to a threshold value beyond which it remains unaffected; (ii) increasing photon flux and (iii) decreasing matrix complexity, i.e. the organic and inorganic constituents of wastewater retard degradation. This may be overcome coupling photocatalysis with ultrasound radiation at 80 kHz and 41 W/L power density; the combined sonophotocatalytic process acts synergistically toward EE2 degradation. Several transformation products were identified by means of UPLC–MS/MS and a reaction network for the photocatalytic degradation of EE2 is suggested. An artificial neural network comprising five input variables (reaction time, TiO 2 and EE2 concentration, organic content and conductivity of the water matrix), thirteen neurons and an output variable (EE2 conversion) was optimized, tested and validated for EE2 degradation. The network, based on tangent sigmoid and linear transfer functions for the hidden and input/output layers, respectively, and the Levenberg–Marquardt back propagation training algorithm, can successfully predict EE2 degradation.

Research on de-NO by low-temperature SCR based on MnOx-CeO2/PPSN

Polyphenylene sulfide (PPS) filter was treated by nitric acid to form PPSN filter. 40% manganese molar fraction of MnOx-CeO2 was loaded on PPSN filter using ultrasonic method, and calcined at 400°C to form MnOx-CeO2/PPSN. The activity of MnOx-CeO2/PPSN was tested in the presence of NH3 as reducing agent for selective catalytic reduction of NO. The influences of catalyst temperature, volume fraction of NH3 and O2, and catalyst loadings on the de-NO efficiency were studied. It was found that MnOx-CeO2/PPSN filter with catalyst loading of 296 g/m2 showed higher de-NO efficiency under temperature of 130–160°C, NH3/NO ratio of 1, and O2 concentration of 5%. When the catalyst temperature and volume fraction of NH3 and O2 were constant, de-NO efficiency of MnOx-CeO2/PPSN was higher with increasing catalyst loading.

Photo-Assisted Sondegradation of Hydrogels in the Presence of TiO2Nanoparticles

The degradation of one of the commercially important hydrogel based on acrylic acid and acryl amide, (acrylic acid-co-acryl amide) hydrogels, by means of ultrasound irradiation and its combination with heterogeneous (<TEX>$TiO_2$</TEX>) was investigated. 24 kHz of ultrasound irradiation was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. The extent of sonolytic degradation increased with increasing ultrasound power (in the range 30-80 W). <TEX>$TiO_2$</TEX> sonophotocatalysis led to complete (acrylic acid-co-acryl amide) hydrogels degradation with increasing catalyst loading, while, the presence of <TEX>$TiO_2$</TEX> in the dark generally had little effect on degradation. Therefore, emphasis was totally on the sonolytic and sonophotocatalytic degradation of hydrogels and a synergy effect was calculated for combined degradation procedures (Ultrasound and Ultraviolet) in the presence of <TEX>$TiO_2$</TEX> nanoparticles. <TEX>$TiO_2$</TEX> sonophotocatalysis was always faster than the respective individual processes due to the enhanced formation of reactive radicals as well as the possible ultrasound-induced increase of the active surface area of the catalyst. A kinetics model based on viscosity data was used for estimation of degradation rate constants at different conditions and a negative order for the dependence of the reaction rate on total molar concentration of (acrylic acid-co-acryl amide) hydrogels solution within the degradation process was suggested.

Sonophotocatalytic Degradation of Chitosan in the Presence of Fe(III)/H2O2 System

The degradation of chitosan by means of ultrasound irradiation and its combination with homogeneous photocatalysis (photo-Fenton) was investigated. Emphasis was given on the effect of additive on degradation rate constants. 24 kHz of ultrasound irradiation was provided by a sonicator, while an ultraviolet source of 16 W was used for UV irradiation. To increase the efficiency of degradation process, degradation system was combined with Fe(III) (2.5 × 10−4mol/L) and H2O2 (0.020–0.118 mol/L) in the presence of UV irradiation and the rate of degradation process change from 1.873 × 10−9−6.083 × 10−9 mol1.7 L s−1. Photo-Fenton process led to complete chitosan degradation in 60 min with the rate increasing with increasing catalyst loading. Sonophotocatalysis in the presence of Fe(III)/H2O2 was always faster than the respective individual processes. A synergistic effect between ultrasound and ultraviolet irradiation in the presence of Fenton reagent was calculated. The degraded chitosans were characterized by X-ray diffraction (XRD), gel permeation chromatography (GPC) and Fourier transform infrared (FT-IR) spectroscopy and average molecular weight of ultrasonicated chitosan was determined by measurements of intrinsic viscosity of samples. The results show that the total degree of deacetylation (DD) of chitosan change, partially after degradation and the decrease of molecular weight led to transformation of crystal structure. A negative order for the dependence of the reaction rate on total molar concentration of chitosan solution within the degradation process was suggested. Results of this study indicate that the presence of catalyst in the reaction medium can be utilized to reduce molecular weight of chitosan while maintaining the power of irradiated ultrasound and degree of deacetylation.

Incorporation of vapor permeation process to esterification reaction of propionic acid and isopropanol for performance improvement

A commercial tubular zeolite membrane (NaA) was employed in a vapor permeation system to dehydrate the reaction mixture during the esterification of propionic acid with isopropanol. The reaction was performed in a batch reactor, using Amberlyst 15 as a catalyst with different weight fractions relative to propionic acid. Experiments were conducted to investigate the effect of the alcohol-to-acid molar ratio on the performance of the hybrid process. The integration of the chemical reaction with the vapor permeation process significantly enhanced the conversion of the reversible esterification reaction. It was observed that contrary to the effect of increasing alcohol-to-acid molar ratio from 1: 1 to 1.5: 1, the acid conversion and the permeated water flux decreased when the reactants molar ratio increased from 1.5: 1 to 3: 1. This effect was due to the reducing effect of reaction mixture composition on the boiling point and reaction and evaporation rates during the hybrid process. Also, increasing catalyst loading had noticeable influence on the acid conversion and the permeated water flux.

Gold-Catalyzed Hydroamination-Hydroarylation Route to Fused Indoles

Reported is a gold-catalyzed 5-endo-dig hydroamination followed by a 6-endo-trig hydroarylation of aniline diynes, leading to the synthesis of fused indoles. Initially the reaction was effected in good yields using Ph3PAuCl/­AgOTf as catalyst system, but this approach gave only low yields of products for electron-rich systems. Since increasing catalyst loading did not ­improve yields, it was reasoned that bulky biaryl­phosphine ligands would promote the dissociation of the gold catalyst from the substrate, improving chances of alkyne activation for the hydroamination. The approach was successful, and these conditions were applied in the studies on substrate scope. For R³ = 2-NCC6H4, the reaction essentially fails (10% yield); otherwise, all the yields are above 70%. The scope was well studied and the reaction was extended to azepino- and oxepinoindoles. The synthesized indoles were evaluated for antifungal activity, which ranged from nonexistent to very potent.

The Role of Reactive Reaction Intermediates in Two‐Step Heterogeneous Electrocatalytic Reactions: A Model Study

AbstractThis paper summarises the result of previous experimental investigations of heterogeneous electrocatalytic reactions performed in flow cells which provide an environment with controlled parameters. Measurements of the oxygen reduction reaction in a flow cell with an electrode consisting of an array of Pt nanodisks on a glassy carbon substrate exhibited a decreasing fraction of the intermediate H2O2 in the overall reaction products with increasing density of the nanodisks. A similar result is true for the dependence on the catalyst loading in the case of a supported Pt/C catalyst thin‐film electrode, where the fraction of the intermediate decreases with increasing catalyst loading. Similar effects have been detected for the methanol oxidation.In order to give a possible explanation to the observed effect, we present a model of multistep heterogeneous electrocatalytic oxidation and reduction reactions based on an adsorption‐reaction‐desorption scheme using the Langmuir assumption and macroscopic transport equations. A continuum based model problem in a vertical cross‐section of a rectangular flow cell is proposed in order to explain basic principles of the experimental situation. It includes three model species A, B, C, which undergo adsorption and desorption at a catalyst surface, as well as adsorbate reactions from A to B to C. These surface reactions are coupled with diffusion and advection in the Hagen Poiseuille flow in the flow chamber of the cell. High velocity asymptotic theory and a finite volume numerical method are used to obtain approximate solutions to the model. Both approaches show a behaviour similar to the experimentally observed. Working in more general situations, the finite volume scheme was applied to a catalyst layer consisting of a number of small catalytically active areas corresponding to nanodisks. Good qualitative agreement with the experimental findings is established for this case as well.