Heterogeneous Phase Reactions Research Articles

High-Temperature and Short-Contact-Time Oxidative Dehydrogenation of Ethane in the Presence of Pt/Al2O3 and BaMnAl11O19 Catalysts

The oxidative dehydrogenation of ethane over a Pt/γ-Al2O3 catalyst in adiabatic conditions (that is at T=800–1000°C and few milliseconds contact time) resulted in the production of ethylene with 50% yield. In order to better elucidate the single roles that gas-phase reactions and heterogeneous phase reactions might play in the high-temperature activation of ethane, a detailed experimental and theoretical investigation was addressed. The results suggested that the performance of the adiabatic reactor relied on a cooperation between catalytic reactions (responsible for deep and partial oxidation of ethane to COx, H2O, and H2) and homogeneous reactions (responsible for the formation of olefins). In autothermal conditions, thus, the main function of the Pt-catalyst appeared to be that of accelerating ignition of the radical process, through the initial combustion of ethane which can occur at temperatures as low as 200°C. It was demonstrated that the same function can be equally well accomplished by a Pt-free oxidation catalyst like the BaMnAl11O19 which is active in the deep oxidation of ethane. Even in the presence of the hexa-aluminate material, which has no activity in the selective oxidation of ethane to ethylene, yields to ethylene higher than 50% were observed in the autothermal reactor by preheating the ethane/air feed stream at a proper temperature.

Direct voltammetric investigation of the electrochemical properties of human hemoglobin: relevance to physiological redox chemistry.

Voltammetric measurements on solutions of human hemoglobin using gold electrodes modified with omega-hydroxyalkanethiols have yielded the first direct measure of the reorganization energy of the protein. The value obtained based on extrapolation of the experimentally measured currents, 0.76 eV, is independent of pH (i.e., over the physiologically relevant rage, pH 6.8-7.4) and is remarkably similar to values obtained for myoglobin. This result is perhaps surprising given the marked dependence of the measured reduction potential of hemoglobin on pH (i.e., the redox Bohr effect). Electron transfer rates from the electrode to hemoglobin were also measured. Using similarly measured heterogeneous electron-transfer rates for cytochrome b(5), it is possible to predict the magnitude of the homogeneous electron-transfer rate from cytochrome b(5) to methemoglobin using a formalism developed by Marcus. These predicted rates are in reasonable agreement with reported rates of this physiological reaction based on stopped-flow kinetics experiments. These results suggest that the intrinsic electroreactivity of these heme proteins is sufficient to account for physiologically observed rates. Residual differences between homogeneous phase kinetics and those predicted by heterogeneous phase reactions are suggested to be due to small reductions in the outer-sphere reorganization energy of both component proteins which arise due to solvent exclusion at the interface between the two proteins in complex.

The past, present and future of nitrogenous compounds in the atmosphere, and their interactions with plants

Ammonia was necessary for the origin of life. However, NH3 would not have been a significant component of the neutral or mildly reducing (N2, CO2, H2O) atmosphere which characterized the Hadean earth (>3·8 Gyr ago), especially in view of the u.v. lability of NH3, the greater u.v. output of the young sun than pertains today, and the absence of an atmospheric u.v. screen. Heterogeneous phase reactions, following atmospheric chemistry, have been proposed as a prebiotic NH3 source. Lightning, or bolides (meteorites and comets), generated NOx., and Fe2+ in the sea could have reduced NO2− resulting from the NOx. to NH4+; this disequilibrium NH4+ level could have supported the production of the nitrogenous organic building blocks of life. NOx. and NHy thus could both have had important roles in the origin and evolution of life. Burgeoning biota could soon have depleted abiotically generated NH4+, and biological N2 fixation could have evolved in its present Fe‐demanding, O2‐sensitive forms in the Archaean O2‐free, Fe2+‐rich environment. Organic matter could have driven biological denitrification reactions based on NO2− and NO3− generated abiologically using some redox components which evolved in earlier chemolithotrophs and photolithotrophs, regenerating atmospheric NOx. and producing N2O. Any atmospheric NH3 leaking from oceanic biology would have been subject to u.v. breakdown and rain‐out. Although O2‐evolving photosynthesis probably began in the Archean some 3·5 Gyr ago, any O2 accumulation was local until 2·0 Gyr ago (Proterozoic) due to consumption by oxidation of Fe2+ and S2−. However, localized O2 accumulation before 2·0 Gyr ago could account for the observed early evolution of cytochrome oxidase and the possibility of O2‐consuming chemolithotrophic and chemoorganotrophic nitrification, with further possibilities of NOx. production. Oxygen accumulation globally from 2·0 Gyr onwards coincided approximately with the evolution of eukaryotes, which contributed phagotrophy to the reactions of the N cycle as well as the nutrification‐like aerobic production of NO. by nitric oxide synthetase, while lightning and bolides could now generate NO. from N2 and O2.Evidence for terrestrial ecosystems is found from 1·0 Gyr onwards; NOx. and NH3 generated by terrestrial biota stands a greater chance of escaping to the atmosphere than do these compounds generated in the sea where recycling within the water body is likely. As CO2 levels fell and O2 levels rose, NH3 cycling in the photorespiratory carbon oxidation cycle might have been evident as early as 1 Gyr ago, although this does not seem to be a major contributor to atmospheric NH3 today. Embryophyte evolution on land 450 Myr ago, together with symbionts and biophages, increased primary productivity and N cycling on land, with greater quantitative possibilities for NOx. and NH3 escape to the atmosphere. The evolution of lignin (and related phenylpropanoids) at least 400 Myr ago, with associated NH3 recycling in vascular land plant, does not seem (on present evidence) to increase NH3 loss to the atmosphere significantly. Biomass burning occurred at least 350 Myr ago with lightning as the likely ignition source; such burning yielded NO., NH3, N2O and N2 from organic N. As in earlier times, the existence of terrestrial embryophyte vegetation has been punctuated by major bolide impacts, with the Cretaceous‐Tertiary boundary impact generating perhaps 104 as much NO. as a year's thunderstorms do today, although the toxicity of NOx.per se to vegetation might not have been the major effect of the NOx. on biota. Terrestrial plants suffered fewer extinctions at this time than did many other major taxa. Despite such very significant generators of atmospheric combined N as major bolide impacts, the mean levels of NHy, NOx. and N2O (and O3) in the atmosphere during the 450 Myr existence of embryophyte vegetation was lower than the current, globally averaged, anthropogenically influenced values. Current globally averaged levels of atmospheric combined N are thus not without precedent in the history of life, globally for NOx., and locally for NHy, so vegetation has had evolutionary experience of high atmospheric combined N. However, this should not make us complacent about the impact of current wide‐spread and continuing anthropogenic inputs of combined N, in view of the rate and extent of the inputs, and their combination with other aspects of local anthropogenic influence (e.g. SO2 from burning of high‐S coal), stratospheric O3 depletion, and global environmental change (increasing CO2, temperature and sea‐level).

Synthesis and characterization of a new platinum supported catalyst based on poly-{acrylamide-co-[3-(acryloylamino)propyltrimethylammoniumchloride]} as carrier

In the following the synthesis of a new platinum supported catalyst founded upon the title copolymer is described. Adsorption of hexachloroplatinic acid through an ion exchange process followed by reduction in hydrogen leads to a catalyst which is useful in various heterogeneous gas phase reactions. Using several copolymers in different monomer proportions, it is demonstrated that a polymer carrier of composition 90% acrylamide and 10% quaternary compound is the most active one. On the basis of results obtained by use of X-ray photoelectron spectroscopy the presence of Pt 0 and Pt 2+ species on the surface of the carrier is proved. It is shown that both species are influenced by amide and quaternary groups of the support. Taking the catalytic activity of samples which differ in the Pt 0 and Pt 2+ content into consideration, it is demonstrated that platinum in the zerovalent state is active in the reactions.

Copolymers of poly-{acrylamide-co-[3- (acryloylamino)propyltrimethylammoniumchloride]} as carriers for platinum species and their use as catalysts in heterogeneous gas phase reactions

In the following, the binding of PtCl62− to quarternary ammonium groups of the copolymers followed by reduction of platinum to a zerovalent state is described. At temperatures between 60 and 180°C the supported catalysts were effective in isomerization and hydrogenation of hexene(1). The dependence of catalytic activity and selectivity on copolymer composition and the average molecular weight (Mw) of the polymer have been analyzed. Copolymers of the composition 90% acrylamide/10% quarternary compound and average molecular weights of about one million were found to be the most active ones. Thermal and chemical stability of the catalysts were studied by differential thermal analyses, thermal gravimetric analyses, and elemental analyses. Morphology and structure were analyzed by raster electron microscopy, x-ray photon spectroscopy, far infrared spectroscopy, and Fourier transform infrared spectroscopy. Several particle properties of the new catalysts, such as pore volume and surface area, were also investigated. © 1996 John Wiley & Sons, Inc.

Copolymers of poly‐{acrylamide‐co‐[3‐ (acryloylamino)propyltrimethylammoniumchloride]} as carriers for platinum species and their use as catalysts in heterogeneous gas phase reactions

Copolymers of poly‐{acrylamide‐co‐[3‐ (acryloylamino)propyltrimethylammoniumchloride]} as carriers for platinum species and their use as catalysts in heterogeneous gas phase reactions

Reactions of Neopentyl 2,2,2,‐Trifluoroethanesulfonate (Tresylate) with Nucleophiles: A Model Study for the Coupling of Nucleophiles with Tresyl Agarose

Is it prudent to compare homogeneous and heterogeneous phase reactions? One side of this discussion on the reactivity of certain tresylates to nucleophiles such as butylamine and butanethiol says “Yes”, but the other says “Not always”.

Reactions of Neopentyl 2,2,2,‐Trifluoroethanesulfonate (Tresylate) with Nucleophiles: A Model Study for the Coupling of Nucleophiles with Tresyl Agarose

Is it prudent to compare homogeneous and heterogeneous phase reactions? One side of this discussion on the reactivity of certain tresylates to nucleophiles such as butylamine and butanethiol says “Yes”, but the other says “Not always”.

Sn-promoting mechanism for ketone hydrogenation over [formula omitted

Hydrogenation of acetophenone, 2-butanone, styrene and 1-hexene over RhSn SiO 2 in heterogeneous liquid phase reaction systems was studied by in situ EXAFS, FT-IR, TEM, analytical TEM, CO and H 2 adsorption measurements. The catalytic activity of Rh SiO 2 for hydrogenation of acetophenone and 2-butanone increased by a factor of 5–500 by Sn addition, showing a maximum activity at surface composition Sn s Rh s = 1.5 , whereas hydrogenation of styrene and 1-hexene decreased monotonously and drastically by Sn addition. In situ Sn K-edge EXAFS of the well characterized CVD-RhSn SiO 2 catalyst prepared by using Sn(CH 3) 4 vapor suggested that oxygen of CO group makes a bond with Sn atom upon acetophenone adsorption.

Silylated Cellulose Materials in Design of Supramolecular Structures of Ultrathin Cellulose Films

Abstract To use the structure-forming potential and the biodegradability of cellulose and nonionic cellulose ethers, we developed synthesis pathways for soluble and regenerable silyl celluloses suitable for the design of advanced materials. A 6-0-silylation of cellulose takes place in a heterogeneous phase reaction in the presence of ammonia-saturated polar aprotic solvents at −15°C with thexyldimethylchlorosilane. After 2,3-di-O-methylation, this type of regioselectively-substituted cellulose derivatives yields sensor matrices for the detection of halohydrocarbons in air. On the other hand, thexyldimethylsilyl celluloses and trimethylsilyl celluloses with degrees of substitution in the 2.6 to 3.0 range form mono-and multilayered supramolecular structures by applying the Langmuir–Blodgett technique and, after desilylation, oriented ultrathin cellulose films.

Some filler effects on cross‐linking of unsaturated polyesters

AbstractThe effect of five fillers on the cross‐linking macro‐and microcharacteristics of simple unsaturated polyester resins was investigated by differential scanning calorimetry (DSC), reactivity tests, and gel time tests. Glass beads and silica flour appeared to have little influence on the cross‐linking reaction of the resin itself, their effect being comparable to mere dilution of the resin. Kaolin presented some interaction with the resin due to its absorption characteristics and acid groups. Reground polyester/glass fiber powder and especially wood flour appeared to present clear chemical interactions with the curing behavior of the resin. Wood flour, in particular, was shown by DSC analysis to strongly co‐react with the resin during cross‐linking and altered markedly the resin enthalpy change and energy of activation during curing. The wood flour component causing the altered behavior of the resin appears to be lignin. DSC analysis of resins filled with three different types of isolated lignins indicated that this wood flour component reacts in a heterogeneous phase reaction with the resin during cross‐linking. It appears that it is the lignin unsaturated carbon–carbon double bonds at the polyester/wood flour and at the polyester/lignin interphases that are likely to co‐react by heterogeneous phase radical cross‐linking with the polyester resin and styrene unsaturation, markedly changing the resin curing behavior. © 1993 John Wiley & Sons, Inc.

Intercalation of MgCl 2 in graphite

Intercalation compounds of natural and commercial graphites with MgCl 2 have been synthesized by a high temperature heterogeneous phase reaction. The stoichiometry of the compounds was found by chemical analysis, and the structure has been examined by powder X-ray diffraction. The intercalation compounds were found to be stable up to 800°C which is contradictory to previously reported results.

New approach to low temperature deposition of high-quality thin films by electron cyclotron resonance microwave plasmas

An electron cyclotron resonance microwave plasma processing system consisting of a plasma chamber and a processing chamber as well as a new apparatus called the ‘‘species selector and energy controller (SSEC)’’ are described in detail. Silicon dioxide (SiO2) films fabricated using this system without and with the SSEC are used for various experiments to demonstrate that the SSEC can effectively suppress the damaging effects resulting from the bombardment on the substrates and the on-growing films by energetic particles and photons produced in the plasma during film deposition, as well as effectively reduce the upstream diffusion of the reactant gas from the processing chamber to the plasma chamber, thus suppressing the formation of microdust particles due to the heterogeneous gas phase reaction. The film growth for the films fabricated without the SSEC is due mainly to mass-limited reaction and that with the SSEC is due to surface rate-limited reaction. The electronic properties of the SiO2 films fabricated with the SSEC at temperatures higher than 250 °C approach those of high-quality thermally grown silicon oxides. The effects of the SSEC on the film properties and the film growth mechanism are also discussed.

Chlorine substitution reactions of polycyclic aromatic hydrocarbons on fly ash from coal-fired power plants

Naphthalene, anthracene, and biphenyl were individually adsorbed in fly ash from a coal-fired power plant and treated with HCl(g) in nitrogen at 150°C. Products from the reaction included mono- and poly-chlorinated cogeners of the parent PAH at total yields of ca. 9–15% for all products. Brominated aromatic products, observed in identical studies using municipal incinerator fly ash, were not detected in significant amounts. The results suggest that the absence of chlorinated compounds in coal combustion effluent can not be attributed to chemical properties of fly ash surfaces involved in heterogeneous gas-solid phase reactions. Alternate explanations should be sought in the low levels of HCl in the effluent stream or the chemistry of the combustion event.

Thermal decomposition of energetic materials: 20. A comparison of the structural properties and thermal reactivity of an acyclic and cyclic tetramethylenetetranitramine pair

The linear secondary nitramine, 1,7-dimethyl-1,3,5,7-tetranitrotrimethylenetetramine CH 3[N(NO 2)CH 2] 3N(NO 2)CH 3 (OHMX) and its cyclic analog, octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, (CH 2NNO 2) 4 (HMX) are compared. By IR spectroscopy and DTA, OHMX is found to exist in five polymorphs between 273 K and its melting point at 490 K. The IR spectra suggest that the structural differences involve mostly the NO 2 and CH 3 groups and changes in lattice symmetry without a significant alteration in the conformation of the backbone. The kinetic parameters for the OHMX(III → IV) phase transition are first order ( E a = 50.8 kcal mol −1) and are comparable to those of HMX. The nucleation process is probably being measured. The values of Δ H for the phase transitions of OHMX (0.8–2.1 kcal mol −1) are also similar to those of HMX. The molecular structure of OHMX(II) was determined: monoclinic, P2 1/ c, a = 20.952(7), b = 9.477(2), c = 6.521(2) Å, β = 96.29(3)°, Z = 4, D calc = 1.598 g cm −3, R F = 3.84, R wF = 4.68%. It consists of a helical chain of CH 2NNO 2 units staggered at approximately 120° intervals. A pseudo-C 2 axis is present. OHMX is slightly less thermally stable than HMX. High-rate thermolysis (d T /d t =110 K s −1) of OHMX liberates products that are the same, with a few exceptions, as for HMX. Competitive N-N and C-N bonds fission occurs as predicted by the IR data and molecular structure. The pressure dependence of the decomposition process indicates that the heterogeneous gas-condensed phase reactions occur to a greater extent as the pressure increases.

Mecanisme de transfert mono electronique dans la reaction de Cannizzaro en phase heterogene solide-liquide,en conditions sonochimiques

The Cannizzaro reaction in heterogeneous phase(solid -liquid), catalyzed by baryum hydroxide catalyst under ultrasonic conditions is reported.The process takes place by single electron transfer by means of reducing sites of the solid. It is proved by selective poisoning experiments.

Particulate sulfur and chlorine in Arctic aerosols, spring 1983

In each of 10 flights of the AGASP Arctic program, particulate sulfur and chlorine were determined by PIXE analysis of eight cascade impactor fractions from <0.25 to > 16 μm aerodynamic diameter (μmad). S occurred mainly in fine aerosol sizes of <2 μmad whereas Cl was mainly in coarser sizes. Two fine S modes could be identified, one being ultrafine (‘nuclei mode’) <0.25 fimad and the other being fine (‘accumulation mode’) centered around the 0.5–1.0 μmad range, with relative abundances of the two modes apparently depending on flight location. This suggests that both homogeneous gas phase and heterogeneous liquid phase reactions led to sulfuric acid formation in the haze. Qualitative comparisons of aerosol S and Cl distributions with particle size suggest that aerosol Cl concentrations are controlled by a sea surface source, particle coagulation and surface deposition, and volatility after reaction with acidic trace gases. Stratospheric aerosols sampled at 500 mb within a tropopause fold structure contained S concentrations greater than those in the Arctic haze and contained an appreciable Cl component.

Diffusion control of the binding of carcinoembryonic antigen (CEA) with insoluble anti-CEA antibody.

Analysis of the kinetics of CEA binding to rabbit anti-CEA antibody insolubilized on filter paper discs provided six lines of evidence indicating diffusion control of this reaction: 1) The observed forward rate constant, k1obs, decreased when solvent viscosity was increased with sucrose or Ficoll. 2) k1obs per receptor site increased from 1.2 x 10(4) M-1 sec-1 to 2.6 x 10(4) M-1 sec-1 as receptor site density on immunosorbent discs decreased from 5.2 x 10(-13) to 2.1 x 10(-13) moles/disc. 3) Stirring the reacting mixture of CEA and insoluble anti-CEA increased k1obs from 1.2 x 10(4) M-1 sec-1 to 3.4 x 10(4) M-1 sec-1. 4) The activation energy for CEA-insoluble anti-CEA binding was indistinguishable (p greater than 0.1 by t-test) from 4.1 Kcal/mole expected for diffusion controlled reactions. 5) Bimolecular reaction theory predicted a diffusion limited forward rate constant, k1max, for CEA binding to insoluble anti-CEA, which was consistent with our observed k1 of 1.2 x 10(4) M-1 sec-1. 6) k1obs for CEA binding to soluble rabbit anti-CEA antibody was 6.4 x 10(4) M-1 sec-1, 5 times faster than the k1obs of the heterogeneous phase reaction for receptor site density of 5.2 x 10(-13) moles/disc. Diffusion control of ligand binding to insoluble receptors, as exemplified by the CEA-insoluble anti-CEA model system, may be a very general biologic phenomenon.

Preparation and application of water-soluble polymer-metal complexes

A series of water-soluble polymers and derivatives with chelating groups has been prepared and investigated for the complex formation with various metals. The complexation of basis polymers, such as poly(ethyleneiruine) , poly(vinylamine) , and poly(acrylic acid), as well as copolymers was carried out in homogeneous phase. Membrane filtration allowed continuous or discontinuous separation of the polymer chelates from metallic ions not bound to the polymer. The polymer complexes remained water-soluble independent of the chelated metal and the polymeric ligand. Studies on the dependency of the capacities of the polymers upon various parairters and methods for regenerating the polymeric ligands are described. The introduction of chelating groups, e.g. pyridine-2-aldimine, thiourea, iminodiacetic acid, 8-hydroxy quinoline, and hydroxyaniline, to the macromolecules by polymer-analogous reaction or by copolymerization improved significantly the selectivity for the metals cobalt, nickel, copper, cadmium, palladium, mercury, silver, gold, and platinum. By the use of membrane filtration in the preparation and application of water-soluble polymer—metal complexes it is possible to recover metal ions from solutions in a short time and in homogeneous phase. INTRODUCTION Water-soluble polymer complexes are. not only of theoretical importance but also of increasing practical interest, since they involve the potentiality of versatile applications in chemistry. Insoluble chelating resins, on the contrary, have considerable disadvantages, such as reaction in heterogeneous phase and long contact times. Up to present, many investigations have been carried out in this field, particularly on synthesis and properties of soluble polymer ligands and coordinating groups (Ref. 1-10). In general, there are three requirements with which polymers as chelating agents should comply: sufficient solubilizing power of the constitutional repeating unit which provides water-solubility of the polymer complexes, a great number of functional groups of the complexing agent for a high capacity, and a high molecular weight which allows an easy separation by usual methods from the metal not bound to the polymer. Preferable for these studies are molecular masses between 10 000 and 100 000. Molecular masses of polymers smaller than 10 000 are not suitable because of separation problems in membrane filtration. Therefore, all prepared macromolecular ligands consisted of molecular mass fractions greater than 10 000, which was verified by membrane filtration. Possibilities for the synthesis of polymer chelating agents are the following: 1) Preparation of polymers with chelating units, e.g. poly(vinylamine), poly (ethyleneimine). 2) Polymerization of monomers already bearing the complex forming group, e.g. acrylic acid, vinylmethyl ketone, vinylsulfonic acid. 3) Polymerization of monomers containing protected functional groups with following polymer-analogous deblocking reaction, e.g. poly(vinylalcohol) from poly(vinylacetate). 4) Conversion of side chains or functional units in order to form or to change complexing groups, e.g. hydrolysis of poly(1-vinyl-2-pyrrolidinone)

Kinetic and thermodynamic studies of antigen-antibody interactions in heterogeneous phase reaction systems—II.: Interaction of l-triiodothyronine ( l-t 3) with specific antibody immobilized on controlled-pore glass

The binding of triiodothyronine (T 3) to its specific antibody immobilized on a porous inorganic support (controlled-pore glass) was treated kinetically as a general heterogeneous reaction. The reactions follow apparent second order kinetics, where the rate is proportional to the amount of antibody and to the instantaneous concentration of available unbound T 3; this unbound T 3 is inversely related to the concentrations of those serum proteins which normally bind T 3. In the presence of these proteins T 3 diffusion is not the rate determining step of the reaction. For reaction times in hr the extent of the T 3 binding is inversely related to the protein concentration and the reaction rate does not change greatly with varying protein concentration. For reaction times of weeks the presence or absence of protein or deblocking agent has no effect on the amount of T 3 bound, but the reaction rates are inversely related to the protein concentration. The function of 8-anilinonaphthalene sulfonic acid (ANS) deblocking agent is to effectively displace the T 3 from the TBG fraction of the proteins, which has no effect on the equilibrium point but greatly accelerates the reaction rate. The rate determining step is believed to be the rate of desorption of T 3 from the protein, since the T 3 binding rate to antibody takes place rapidly. The measured enthalpy of the reaction (0–1.3 kcal/mol) indicates that the reaction is principally entropy driven.