Heterogeneous Reaction Systems Research Articles

Recent Progress in the Preparation of Organoboron Reagents via Direct Borylations

Recent progress in the preparation of organoboron reagents for cross-coupling reactions is described. Organoboron reagents are versatile synthons in Suzuki-Miyaura coupling. A common method for the synthesis of organoboron reagents is the borylation of aryl or vinyl magnesium (or lithium) intermediates that are produced from aryl or vinyl halides. In addition to these traditional methods, the direct borylation of aromatic and heteroaromatic compounds has also been recently reported as a more atom-economical method. We describe our new homogeneous and heterogeneous catalysts for aromatic C-H borylation. Regarding the heterogeneous catalyst, the recovered catalyst could be reused without a loss of activity. We developed this heterogeneous batch reaction system into a continuous-flow reaction system using a column field with our heterogeneous catalyst.

10.2478/s11814-009-0218-3

Rubidium carbonate was used as an adsorbent to capture carbon dioxide from gaseous stream of carbon dioxide, nitrogen, and moisture in a fixed-bed to obtain the breakthrough data of CO2. Experiments were carried out at flow rates of carbon dioxide and nitrogen (5×10−6–35×10−6 m3/min), moisture (0.5×10−6–3.0×10−6 m3/h), amount of adsorbent (0.5×10−3–1.8×10−3 kg), mole fraction of carbon dioxide (0.03–0.22), and different sorption temperatures (323–353 K) at atmospheric pressure. The deactivation model in the non-catalytic heterogeneous reaction systems was used to analyze the sorption kinetics among carbon dioxide, carbonate, and moisture, employing the experimental breakthrough data that fit the deactivation model better than the adsorption isotherm models in the literature.

Elementary Reaction Kinetics of the CO ∕ CO2 ∕ Ni ∕ YSZ Electrode

Results of combined experimental and theoretical investigations of elementary chemical reaction processes of gas mixtures at nickel/yttria-stabilized zirconia (Ni/YSZ) solid oxide fuel cell (SOFC) model anode systems are presented. Temperature-programmed desorption and reaction measurements were performed in order to determine adsorption/desorption kinetic data as well as thermodynamic parameters for the and /yttria-stabilized zirconia (YSZ) heterogeneous reaction systems. From these data, an elementary kinetic reaction mechanism of the electrochemical CO oxidation at Ni/YSZ anodes was developed. Numerical simulations were performed for three different spillover mechanisms. Steady-state polarization curves and electrochemical impedance spectra were calculated, allowing for a direct comparison with experiments performed by Lauvstad et al. [ J. Electrochem. Soc. , 149 , E506 (2002) ]. Best agreement with the experimental data was obtained when assuming two consecutive charge-transfer steps from via to Ni–O, the second step being accompanied by oxygen spillover over the three-phase boundary.

Use of ionic liquids for improvement of cellulosic ethanol production

Cellulosic ethanol production has drawn much attention in recent years. However, there remain significant technical challenges before such production can be considered as economically feasible at an industrial scale. Among them, the efficient conversion of carbohydrates in lignocellulosic biomass into fermentable sugars is one of the most challenging technical difficulties in cellulosic ethanol production. Use of ionic liquids has opened new avenues to solve this problem by two different pathways. One is pretreatment of lignocellulosic biomass using ionic liquids to increase its enzymatic hydrolysis efficiency. The other is to transform the hydrolysis process of lignocellulosic biomass from a heterogeneous reaction system to a homogeneous one by dissolving it into ionic liquids, thus improving its hydrolysis efficiency.

H 2O chemisorption and H 2 oxidation on yttria-stabilized zirconia: Density functional theory and temperature-programmed desorption studies

The mechanism of H 2O dissociation as well as the adsorption and oxidation reaction of H 2 on yttria-stabilized zirconia (YSZ), commonly used as part of solid oxide fuel cell (SOFC) anodes, was investigated employing temperature-programmed desorption (TPD) spectroscopy and density functional theory (DFT). In agreement with theory the experimental results show that interaction of gaseous H 2O with YSZ results in dissociative adsorption leading to strongly bound OH surface species. In the interaction of gaseous H 2 with an oxygen-enriched YSZ surface (YSZ + O) similar OH surface species are formed as reaction intermediates in the H 2 oxidation. Our experiments showed that in both the H 2O/YSZ and the H 2/YSZ + O heterogeneous reaction systems noticeable amounts of H 2O are “dissolved” in the bulk as interstitial hydrogen and hydroxyl species. The experimental H 2O desorption data is used to access the accuracy of the H 2/H 2O/YSZ adsorption/desorption and surface reaction kinetics data, employed in previous modeling studies of the electrochemical H 2 oxidation on Ni-pattern/YSZ model anodes by Vogler et al. [J. Electrochem. Soc., 156 (2009) B663] and Goodwin et al. [J. Electrochem. Soc., 156 (2009) B1004]. Finally a refined experimentally validated H 2/H 2O/YSZ adsorption/desorption and surface reaction kinetics data set is presented.

ChemInform Abstract: Catalysts for Heterogeneous Reaction Systems. Possibilities for the Application of Open Cross-Channel Structures

ChemInform Abstract: Catalysts for Heterogeneous Reaction Systems. Possibilities for the Application of Open Cross-Channel Structures

Novel Chemical Kinetics for a Single Enzyme Reaction: Relationship between Substrate Concentration and the Second Moment of Enzyme Reaction Time

We report a robust quadratic relation between the inverse substrate concentration and the second moment, <t(2)>, of the catalytic turnover time distribution for enzyme reactions. The results hold irrespective of the mechanism and dynamics of the enzyme reaction and suggest a novel single molecule experimental analysis that provides information about reaction processes of the enzyme-substrate complex and ergodicity of the enzyme reaction system, which is beyond the reach of the conventional analysis for the mean reaction time, <t>. It turns out that <t(2)> - 2<t>(2) is linear in inverse substrate concentration for an ergodic homogeneous enzyme system given that the enzyme substrate encounter is a simple rate process, and its value at the high substrate concentration limit provides direct information about if any non-Poisson reaction process of the enzyme-substrate complex. For a nonergodic heterogeneous reaction system, the corresponding quantity becomes a quadratic function of the inverse substrate concentration. This leads us to suggest an ergodicity measure for single enzyme reaction systems. We obtain a simple analytic expression of the randomness parameter for the single catalytic turnover time, which could provide a quantitative explanation about the previously reported randomness data of the beta-galactosidase enzyme. In obtaining the results, we introduce novel chemical kinetics applicable to a non-Poisson reaction network with arbitrary connectivity, as a generalization of the conventional chemical kinetics.

Coupling aerosol surface and bulk chemistry with a kinetic double layer model (K2-SUB): oxidation of oleic acid by ozone

Abstract. We present a kinetic double layer model coupling aerosol surface and bulk chemistry (K2-SUB) based on the PRA framework of gas-particle interactions (Pöschl-Rudich-Ammann, 2007). K2-SUB is applied to a popular model system of atmospheric heterogeneous chemistry: the interaction of ozone with oleic acid. We show that our modelling approach allows de-convoluting surface and bulk processes, which has been a controversial topic and remains an important challenge for the understanding and description of atmospheric aerosol transformation. In particular, we demonstrate how a detailed treatment of adsorption and reaction at the surface can be coupled to a description of bulk reaction and transport that is consistent with traditional resistor model formulations. From literature data we have derived a consistent set of kinetic parameters that characterise mass transport and chemical reaction of ozone at the surface and in the bulk of oleic acid droplets. Due to the wide range of rate coefficients reported from different experimental studies, the exact proportions between surface and bulk reaction rates remain uncertain. Nevertheless, the model results suggest an important role of chemical reaction in the bulk and an approximate upper limit of ~10−11 cm2 s−1 for the surface reaction rate coefficient. Sensitivity studies show that the surface accommodation coefficient of the gas-phase reactant has a strong non-linear influence on both surface and bulk chemical reactions. We suggest that K2-SUB may be used to design, interpret and analyse future experiments for better discrimination between surface and bulk processes in the oleic acid-ozone system as well as in other heterogeneous reaction systems of atmospheric relevance.

Nanoreactors for Polymerizations and Organic Reactions

The aim of this Perspective is to use the knowledge of the underpinning kinetic and thermodynamic precepts that govern free-radical and “living” radical water-based heterogeneous polymerizations and apply this to small molecule organic reactions in nanoreactors. The difficulty in applying “living” radical polymerization to water-based heterogeneous systems has led to such an understanding, including partitioning of agents between the phases, nucleation of particles, and other phenomena including superswelling. This knowledge has allowed us to prepare polymers in heterogeneous systems with well-defined molecular weight distributions and particle size distributions. However, to overcome the physical chemistry constraints, researchers had to develop complex nanoreactor systems. For the field of small molecule organic reactions in heterogeneous systems to be industrially relevant and to grow rapidly, such physical chemistry precepts should be more greatly developed.

Macro-/microporous MOF composite beads

We have prepared a series of metal–organic framework (MOF) composite materials by depositing crystalline MOFs into mm-sized macroporous polyacrylamide (PAM), oxide or oxide–PAM beads using solvothermal methods or immersion in mother solutions. The facile nature of the composite preparation is in part due to the inherent hydrophilicity and processability of the PAM, which bears suitable functionality to interact with the MOF. The resulting composites display hierarchical porosity across the macro- and microporous length scales; the MOF loading level, and hence degree of microporosity in the composites, can be tuned by modulating the concentration of the reactants in the MOF synthesis. The MOF@PAM beads display enhanced mechanical stability and handling over bulk MOF phases in heterogeneous reaction systems, clearly indicating that such materials can improve recovery and recyclability of crystalline MOFs. This is an important step for future applications.

Búsqueda de Catalizadores Sólidos Básicos para la Producción de Biodiesel

This work aimed to find active and stable solid base catalysts for clean biodiesel production using heterogeneous reaction systems. Three types of catalysts were synthesized and evaluated in the transesterification of triacetin: CaO, γ-Al2O3 modified with Na and K, and MgO modified with Na, Li, Rb and Cs. The influence of the textural proprieties, the type and amount of alkali metal impregnated and the activation with N2 on the basicity and the catalytic behavior were analyzed. Stability of catalysts was analyzed using atomic absorption measurements and reuse reactions. Results showed that metal impregnation does not lead to the formation of stable solids, because they present lixiviation in the reaction system. The CaO maintained a high catalytic activity during five reaction cycles showing its high potential of its use in an industrial process.

Enhanced Catalytic Activity of Gold Nanoparticles Doped in a Mesoporous Organic Gel Based on Polymeric Phloroglucinol Carboxylic Acid−Formaldehyde

Gold nanoparticles were supported by a phloroglucinolcarboxylic acid-formaldehyde (PF) gel, a new organic gel with a 30 nm spheroid-like structure. The surface area of the PF gel with gold nanoparticles was 550 m(2)/g. Gold nanoparticles supported on a PF gel exhibited catalytic activity in the reduction of 4-nitrophenol with a reaction rate constant of 7.4 x 10(-3) s(-1), which is high in the reported heterogeneous reaction system. The adsorption behavior of 4-nitrophenol into the gel support was observed by ultraviolet-visible absorption spectroscopy. Gold nanoparticles in the PF network were characterized by scanning electron microscopy, atomic force microscopy, and transmission electron microscopy observation. The high reduction rate would be attributed to the extraction and diffusion of the reactant through the pores of a PF gel support to encounter the highly dispersed gold nanoparticles on the surface and inside the material.

Sorption kinetics of carbon dioxide onto rubidium carbonate

Rubidium carbonate was used as an adsorbent to capture carbon dioxide from gaseous stream of carbon dioxide, nitrogen, and moisture in a fixed-bed to obtain the breakthrough data of CO2. Experiments were carried out at flow rates of carbon dioxide and nitrogen (5×10−6–35×10−6 m3/min), moisture (0.5×10−6–3.0×10−6 m3/h), amount of adsorbent (0.5×10−3–1.8×10−3 kg), mole fraction of carbon dioxide (0.03–0.22), and different sorption temperatures (323–353 K) at atmospheric pressure. The deactivation model in the non-catalytic heterogeneous reaction systems was used to analyze the sorption kinetics among carbon dioxide, carbonate, and moisture, employing the experimental breakthrough data that fit the deactivation model better than the adsorption isotherm models in the literature.

Microwaves in Heterogeneous Gas‐Phase Catalysis: Experimental and Numerical Approaches

AbstractThis review paper focuses on the effects of microwave irradiation on heterogeneous gas phase catalytic reaction systems. Both experimental and modeling approaches are discussed. The currently available methods for temperature measurements in the microwave heating of solid particles are critically examined. The existence of microwave‐created temperature gradients in beds of solid particles is discussed. The not fully established mechanism of catalyst (nano)particle heating and imperfect temperature measurement techniques implicate that different effects are often observed and contradictory conclusions are drawn. For further progress here, the development of accurate and possibly non‐invasive techniques for local temperature measurements under microwave irradiation is needed.

Novel Relationship between Hydroxyl Radical Initiation and Surface Group of Ceramic Honeycomb Supported Metals for the Catalytic Ozonation of Nitrobenzene in Aqueous Solution

Comparative experiments have been performed to investigate the degradation efficiency of nitrobenzene and the removal efficiency of TOC in aqueous solution bythe processes of ceramic honeycomb supported different metals (Fe, Ni, and Zn) catalytic ozonation, indicating that the modification with metals can enhance the activity of ceramic honeycomb for the catalytic ozonation of nitrobenzene, and the loading percentage of metal and the metallicity respectively presents a positive influence on the degradation of nitrobenzene. The degradation efficiency of nitrobenzene is determined by the initiation of hydroxyl radical (*OH) according to a good linear correlation in all the processes of modified ceramic honeycomb catalytic ozonation at the different loading percentages of metals. The modification of ceramic honeycomb with metals results in the conversion of the pH at the point of zero charge (pHpzc) and the evolution of surface groups. Divergence from the conventional phenomenon, the enhancement mechanism of ozone decomposition on the modified ceramic honeycomb with metals is proposed due to the basic attractive forces of electrostatic forces or/and hydrogen bonding. Consequently, a novel relationship between the initiation of *OH and the surface-OH2+ group on the modified catalyst is established based on the synergetic effect between homogeneous and heterogeneous reaction systems.

Fabrication of microfluidic devices incorporating bead-based reaction and microarray-based detection system for enzymatic assay

In this study, we developed a novel microfluidic device for enzyme-based assays that incorporates heterogeneous reaction and microarray-based detection systems. The microfluidic device had two serial chambers connected through microchannels; one for the reaction between analytes and enzymes, and the other for the quantitative detection of analytes. The reaction chamber was filled with glass microbeads covalently bound to enzymes via aminopropyltriethoxysilane (APTES). Enzyme-immobilized microbeads 70 μm in diameter were retained within the reaction chamber using a microfilter composed of micropillars with 30 μm interspaces. In the detection chamber, a poly(ethylene glycol)-based hydrogel microarray was fabricated using photolithography, which could immobilize other protein molecules or fluorescent dyes for the optical analysis of enzyme-catalyzed reaction. Different concentrations of glucose were detected within the microfluidic system where the reaction chamber was filled with glucose oxidase (GOX)-immobilizing glass microbeads, and a horseradish peroxidase (POD)-entrapping hydrogel microarray was placed in the detection chamber. A sequential bienzymatic reaction resulted in the conversion of non-fluorescent Amplex Red into fluorescent resorufin within the hydrogel microarray and glucose concentrations ranging from 1 to 10 mM were successfully detected by measuring the change of emission intensity of resorufin inside the hydrogel microarray.

Sonochemical decomposition of organic acids in aqueous solution: Understanding of molecular behavior during cavitation by the analysis of a heterogeneous reaction kinetics model

The sonochemical decomposition of a low concentration of butyric acid was performed in an aqueous solution by use of 200 kHz ultrasound to discuss the reaction kinetics and molecular behavior during cavitation. Taking into account a Langmuir-type adsorption model, we propose a heterogeneous reaction kinetics model, which is based on the local reaction zone at the interface region of the cavitation bubbles, where the adsorption and desorption of butyric acid molecules from the bulk solution occur during bubble oscillation and then the existing molecules inside the local reaction zone are finally decomposed. To confirm our proposed kinetics model, the rates of decomposition were investigated as a function of the initial concentration of butyric acids in the different pH solutions. It was confirmed that our model could be reasonably applied to explain the obtained results and the pseudo rate constant ( k) and the equilibrium constant ( K) were able to be calculated: k is 8.0 μM min −1 (pH 2) and 3.5 μM min −1 (pH 10), and K is 5.7 × 10 −3 μM −1 (pH 2) and 8.0 × 10 −3 μM −1 (pH 10), respectively. By the analysis of the obtained K values, it was clear that the ionized organic acid molecules are relatively difficult to accumulate at the reaction zone, because of their lower hydrophobicity compared with that of the neutral ones. The results obtained in the sonochemical decomposition of benzoic acid were also able to be analyzed with the proposed kinetics model. In addition, we proposed an opinion toward the interpretation of a Langmuir-type adsorption model which has often been applied to explain heterogeneous reaction systems.

Studies on the dehydrogenative polymerizations (DHPs) of monolignol β-glycosides: Part 4. Horseradish peroxidase-catalyzed copolymerization of isoconiferin and isosyringin

Abstract Horseradish peroxidase (HRP)-catalyzed dehydrogenative copolymerization of guaiacyl (G)-type monolignol glycoside (isoconiferin, coniferyl alcohol γ-O-β-d-glucopyranoside, iso-G) and syringyl (S)-type monolignol glycoside (isosyringin, sinapyl alcohol γ-O-β-d-glucopyranoside, iso-S) were performed in continuous dehydrogenation mode (end-wise polymerization) to result in the formation of water-soluble lignin-like copolymers (iso-G/S-DHPs) in a homogeneous phase. The yield of iso-G/S-DHP increased with increasing iso-G content in the mixture of monomers from 23% (iso-G/iso-S 0:100) to 81% (iso-G/iso-S 50:50). The degree of polymerization (DP) of the resulting iso-G/S-DHP also increased proportionally from 7 (iso-G/iso-S 0:100) to 27 (iso-G/iso-S 50:50) as the iso-G content increased. It is obvious that iso-G plays an important role in the polymerization of iso-S. A similar tendency was also observed in conventional copolymerization of coniferyl alcohol (G-alc) and sinapyl alcohol (S-alc). The highest DP for DHP obtained in the conventional system was only ∼10 due to the heterogeneous reaction system. As the HRP-catalyzed monomer consumption rate of iso-S was greatly enhanced by addition of iso-G as a co-monomer, radical transfer from iso-G to iso-S seems to be plausible. Conventional copolymerization of G-alc and S-alc also supports this view. Spectroscopic studies and alkaline nitrobenzene oxidation analyses indicated that iso-G/S-DHPs had typical lignin structures composed of both G and S units. It was confirmed that the copolymerization behavior of the glycosides iso-G and iso-S in a homogeneous phase are well reflected by that of the monolignols G-alc and S-alc in a heterogeneous phase. Results also indicated that the presence of G-type co-monomers sensitively affects the polymerization of S-type monomers.

Medical biofilms.

For more than two decades, Biotechnology and Bioengineering has documented research focused on natural and engineered microbial biofilms within aquatic and subterranean ecosystems, wastewater and waste-gas treatment systems, marine vessels and structures, and industrial bioprocesses. Compared to suspended culture systems, intentionally engineered biofilms are heterogeneous reaction systems that can increase reactor productivity, system stability, and provide inherent cell:product separation. Unwanted biofilms can create enormous increases in fluid frictional resistances, unacceptable reductions in heat transfer efficiency, product contamination, enhanced material deterioration, and accelerated corrosion. Missing from B&B has been an equivalent research dialogue regarding the basic molecular microbiology, immunology, and biotechnological aspects of medical biofilms. Presented here are the current problems related to medical biofilms; current concepts of biofilm formation, persistence, and interactions with the host immune system; and emerging technologies for controlling medical biofilms.

A Novel Adsorption/Saturation Approach to Ultrasonic Degradation of Phenol

AbstractThe study describes development and application of a kinetic model based on the local concentration of solutes and hydroxyl radicals to predict the rate of ultrasonically induced oxidative degradation of phenol at 300 kHz. The results reveal that the degradation follows saturation kinetics. The rate is slow at low concentrations of the solute, increases with concentration and reaches a maximum at what we defined as “the critical concentration”. At higher concentrations (than the “critical”) the rate slows down and stabilizes at a plateau as it becomes concentration-independent. Owing to the similarity of sonochemical reactions in water to chemical reactions in heterogeneous systems, a kinetic model based on Langmuir adsorption isotherm is developed to predict the rate of reaction in terms of the initial concentration of the solute. The similarity of the model to models describing catalytic and adsorptive reaction kinetics is explained by reduced mass transfer limitations under ultrasonic irradiation, and localization of the solute at the bubble-liquid interface as a function of concentration.