Oxidation Of Light Hydrocarbons Research Articles

Automated Generation of Microkinetics for Heterogeneously Catalyzed Reactions Considering Correlated Uncertainties.

The study presents an ab-initio based framework for the automated construction of microkinetic mechanisms considering correlated uncertainties in all energetic parameters and estimation routines. 2000 unique microkinetic models were generated within the uncertainty space of the BEEF-vdW functional for the oxidation reactions of representative exhaust gas emissions from stoichiometric combustion engines over Pt(111) and compared to experiments through multiscale modeling. The ensemble of simulations stresses the importance of considering uncertainties. Within this set of first-principles-based models, it is possible to identify a microkinetic mechanism that agrees with experimental data. This mechanism can be traced back to a single exchange-correlation functional, and it suggests that Pt(111) could be the active site for the oxidation of light hydrocarbons. The study provides a universal framework for the automated construction of reaction mechanisms with correlated uncertainty quantification, enabling a DFT-constrained microkinetic model optimization for other heterogeneously catalyzed systems.

Automatisierte Generierung von Mikrokinetiken für heterogen katalysierte Reaktionen unter Berücksichtigung korrelierter Unsicherheiten**

AbstractDie Studie stellt eine ab initio basierte Methode für die automatische Konstruktion von detaillierten Mikrokinetiken vor, welche korrelierte Unsicherheiten in allen energetischen Parametern und Schätzroutinen berücksichtigt. Hierfür wurden innerhalb des Unsicherheitsraums des BEEF‐vdW Funktionals 2000 Mikrokinetiken für die Oxidationsreaktionen repräsentativer Abgasemissionen von stöchiometrischen Verbrennungsmotoren auf Pt(111) generiert und durch Multiskalenmodellierung mit Experimenten verglichen. Das Ensemble der Simulationsergebnisse unterstreicht die Bedeutung der Berücksichtigung von Unsicherheiten. Innerhalb dieses Ensembles ist es möglich, eine Mikrokinetik zu identifizieren, welche mit den experimentellen Daten übereinstimmt. Diese Mikrokinetik lässt sich auf ein einziges Austausch‐Korrelations‐Funktional zurückführen und legt nahe, dass Pt(111) das aktive Zentrum für die Oxidation leichter Kohlenwasserstoffe sein könnte. Die Studie bietet einen universellen Rahmen für die automatisierte Konstruktion von Reaktionsmechanismen unter Berücksichtigung korrelierter Unsicherheiten und ermöglicht eine DFT‐basierte Optimierung der Mikrokinetik auch für andere heterogen katalysierte Systeme.

A Thermal Study on Peat Oxidation Behavior in the Presence of an Iron-Based Catalyst

Peat is a resource used for heat and energy, particularly in countries where peat is abundant and conventional fuels are not available. Some countries have made extensive use of peat resources to produce electricity and heat in addition to light hydrocarbons. By doing so, they were able to reduce the cost of importing fossil fuels. To the best of our knowledge, there is a lack of a detailed description of the peat oxidation process in the presence of other substances. Herein, the process of peat oxidation was studied in-depth by means of thermal analysis in the presence of iron tallate acting as a catalytic agent. Differential scanning calorimetry and thermogravimetric analysis demonstrated an oil-like oxidation behavior during the combustion of the used peat. The process of peat oxidation includes two main regions: low-temperature oxidation (LTO), which occurs during the oxidation of light hydrocarbons, followed by the so-called high-temperature oxidation (HTO), which includes the oxidation of the obtained coke-like product. Moreover, the application of non-isothermal kinetics experiments based on the isoconversional and model approach principle have confirmed the role of 2% iron tallate in peat mass by improving the oxidation rate at low- and high-temperature oxidation (HTO) regions. The results obtained from this study have proven that the added catalyst improves efficiency with regards to the energy activation in the process by leading to its significant decrease from 110.8 ± 7.8 kJ/mol to 81.8 ± 7.5 kJ/mol for LTO and from 157.8 ± 19.1 kJ/mol to 137.6 ± 9.3 kJ/mol for HTO. These findings clearly confirm the improvement in the rate of the process by shifting the LTO and HTO peaks to lower regions in the presence of the catalyst. These results further emphasize the possible impact which could be generated by the application of thermally enhanced oil recovery methods on peat development and exploitation.

Influence of Different Birnessite Interlayer Alkali Cations on Catalytic Oxidation of Soot and Light Hydrocarbons

A series of layered birnessite (AMn4O8) catalysts containing different alkali cations (A = H+, Li+, Na+, K+, Rb+, or Cs+) was synthesized. The materials were thoroughly characterized using X-ray diffraction, X-ray fluorescence, X-ray photoelectron spectroscopy, Raman spectroscopy, specific surface area analysis, work function, thermogravimetry/differential scanning calorimetry, and transmission electron microscopy. The catalytic activity in soot combustion in different reaction modes was investigated (tight contact, loose contact, loose contact with NO addition). The activity in the oxidation of light hydrocarbons was evaluated by tests with methane and propane. The obtained results revealed that alkali-promoted manganese oxides are highly catalytically active in oxidative reactions. In soot combustion, the reaction temperature window was shifted by 195 °C, 205 °C, and 90 °C in tight, loose + NO, and loose contact conditions against uncatalyzed oxidation, respectively. The catalysts were similarly active in hydrocarbon combustion, achieving a 40% methane conversion at 600 °C and a total propane conversion at ~450 °C. It was illustrated that the difference in activity between tight and loose contacts can be successfully bridged in the presence of NO due to its facile transformation into NO2 over birnessite. The particular activity of birnessite with H+ cations paves the road for the further development of the active phase, aiming at alternative catalytic systems for efficient soot, light hydrocarbons, and volatile organic compounds removal in the conditions present in combustion engine exhaust gases.

Thermodynamic analysis of in-situ hydrogen from hot compressed water for heavy oil upgrading

Due to many benefits of heavy oil upgrading in the green medium of hot compressed water (HCW), the present study considers the thermodynamic analysis of in-situ hydrogen created by partial oxidation of light hydrocarbons (HC) in HCW. The aim is seeking the upgrading condition where light hydrocarbons create hydrogen (H2) and carbon monoxide (CO) assisted by partial oxidation of light hydrocarbons. The formed CO collaborates in in-situ active hydrogen through water gas shift reaction (CO+H2O↔H2+CO2) which is more effective than external hydrogen for hydrogenation of heavy oil in HCW. Applying the powerful capability of Aspen Plus®, i.e., sensitivity analysis, the effect of significant parameters, such as temperature, pressure (water density), water to oil ratio, and oxygen (O2) to oil ratio are studied comprehensively in order to maximize the amount of active hydrogen. The results indicate that higher temperatures and the amount of water (H2O/heavy oil) are two favorable factors to increase the contribution of active hydrogen, while the pressure is not a determinant factor at supercritical condition (P ≥ 25 MPa). The formation of methane is also decreased at high temperature which is desired for upgrading system. The higher amount of water implies more quantity of O2 since partial oxidation affords the enthalpy of auto-thermal reforming of HO. Hence there should be a compromise in the selected ratios of H2O/HC and O2/HC in HCW upgrading system. A set of experiments are conducted in order to compare the simulation and experimental results. Although the experimental results are established on kinetic data which also reflect the physical effect of HCW during HO upgrading, however, the thermodynamic study provides valued information, in agreement with experiments, that improves our understanding of HO upgrading in HCW with less coke.

Status of CO<sub>2</sub>-stable dual-phase mixed conductor oxygen permeable membrane materials

Dense ceramic mixed ionic-electronic conducting membranes (MIECMs) are renowned for their rich and varied properties as admirable candidates in energy industries, such as oxygen separation from air, cathode materials for solid fuel oxide cells (SOFCs) or membrane reactors for partial oxidation of light hydrocarbons. Especially, the MIECMs integrated oxy-fuel combustion is considered to be a promising cost-effective and efficient method for CO2 capture and sequestration. During the oxy-fuel process, high purity oxygen production has been put forward to use OTMs technology instead of the conventional cryogenic technique, which can benefit from low costs and energy consumption and high efficiency. According to the phase numbers, the OTMs can be classified into single phase and composite OTMs. Extensive research activities have been directed towards the single phase perovskite-type oxides due to their high oxygen permeability. However, their industrial practical application was limited since they suffer from deactivation in the presence of CO2 due to alkaline earth carbonates forming on their surfaces. In order to overcome these issues, focus has shifted to the development of dual-phase membranes consisting of an oxygen ion conducting phase and an electron ion conducting phase, which benefit from the contribution of each phase and overcome the limitations of perovskite materials. Dual-phase OTM typically composed of an oxygen conducting phase (OCP) and an electronic conducting phase (ECP), which displays a better structural and mechanical stability comparing with the single phase OTM under reducing atmosphere due to the incorporation of fluorite phase. The first generation dual-phase OTMs are usually made from the fluorite oxides and noble metals, where fluorite oxides are used as the OCP and noble metals are adopted as the ECP. However, the noble metal-containing dual-phase OTM is too expensive. In order to lower the costs, researchers have developd the second generation dual-phase OTMs, which are consisted of fluorite oxides and perovskite oxides. Although the costs have been reduced, reactions between two phases were usually observed in the second generation dual-phase OTMs. Based on the previous findings and driven by the demands for oxy-fuel combustion for CO2 capture, research put forwards to the new CO2-stable dual-phase OTMs without noble metals and alkaline earth elements. Until now, already a large number of CO2-stable dual-phase membrane materials have been explored. However, their CO2 stabilities have been enhanced, but most of their oxygen permeabilities are too low for practical applications. Therefore, continues research efforts have to be made since most of available OTMs materials can′t satisfy the practical applications. In order to enhance the oxygen permeability and/or improve material thermochemical stability of dual-phase OTMs, the large majority of studies focused on tuning the composition through doping, synthesized temperatures, modified the membrane surfaces with coating or development of new synthesis methods. Meanwhile, considerable theoretical efforts have been put into the dual-phase OTMs, a number of models for permeation process such as Bouwmeester model, Xu-Thomson model, and Zhu model et al. are proposed. Up to now, countless publications has been produced in this field. In order to give the guidelines for the development of the dual-phase OTM materials and promote the process of industrialization of the OTMs technology in the oxy-fuel process, we summarize the status of CO2-stable dual-phase mixed conductor oxygen permeable membrane materials. In this review, the oxygen permeability mechanism and research progress of the dual-phase OTM materials are briefly introduced firstly. Subsequently, the influence of the preparation methods, sintering temperatures, ratios of two phases and the composition of the two phases on the oxygen permeability and stability are analyzed systematically. Next, the applications of dual phase MIECM reactor in partial oxidation of methane to syngas (POM), coupling reactions, water decomposition and oxy-fuel combustion are introduced and analyzed. Finally, the existing scientific problems and the possible research directions have been pointed out.

Aerobic Electrochemical Oxygenation of Light Hydrocarbons Catalyzed by an Iron–Tungsten Oxide Molecular Capsule

The selective oxidation of light hydrocarbons and their valorization with only dioxygen (O2) are important transformations toward development of efficient chemical processes. Monooxygenase enzymes can catalyze selective aerobic reactions under reducing and protic conditions. The translation of such enzymatic pathways to the practical electrocatalytic oxidation of light, gaseous hydrocarbons, using O2 as sole oxidant is now reported. An iron–tungsten oxide inorganic molecular catalyst with a capsular structure {Fe30W72} stabilized inside by sulfate/bisulfate anions provides a protic environment where three iron atoms are located at each of the pores of the capsule leading to a unique and potent active site for the oxidation reactions. Under mild electrochemical conditions, 1.8 V, in water at room temperature, using O2 from air, we demonstrate the low-pressure (1–2 bar) hydroxylation of alkanes, notably ethane to acetic acid, and the ozone like cleavage of the carbon–carbon double bonds of alkenes. Typical ...

Production of olefins by the conjugated oxidation of light hydrocarbons

A number of possibilities to increase the yield of propylene in the processing of light gaseous hydrocarbons are considered, including the oxidative pyrolysis of propane, conjugated oxidation of propane and ethylene, conjugated oxidation of ethylene and methane, and introduction of methane into the products of a rich methane flame. The principal possibility of production of olefins in non-catalytic gas-phase processes from light gaseous hydrocarbons, including methane, is demonstrated.

Spin Coating technique for obtaining nanometric thin films in the system La0.7Sr0.3MnO3

Manganite in the La0.7Sr0.3MnO3 system is of great interest due to its potential application in fuel cells, information storage, magnetic field sensors, non-volatile memories, oxygen sensors, and catalysts in the oxidation of light hydrocarbons. Given the scientific relevance of this material, this study describes the procedure to synthesize and characterize thin films of La0.7Sr0.3MnO3. Manganites were synthesized by means of the Pechini method, and deposited on strontium titanate substrates using spin-coating. Both the crystallinity of the films and their phases were studied with X-ray diffraction (XRD), finding that the films are polycrystalline and have a simple cubic structure with a lattice constant a=3.8653 ± 0.066 Ǻ. Scanning electron microscopy (SEM) showed a uniform surface with good morphological features, and the spectrum resulted from the Energy Dispersive X-Ray Spectroscopy (EDS) analysis over the same film was consistent with the molar ratio of the perovskite. Samples of 2, 4, and 6 layers were synthesized, obtaining thicknesses of 75.10 ± 0.01, 75.02 ± 0.01 and 74.07 ± 0.08 nm per monolayer. The results indicate that this method is useful to synthesize films of high crystalline quality and nanometric size.

Authigenic mineral formation in fluid permeability zones in the West Siberia Permafrost

Basic chemical and mineralogical anomalies in permafrost caused by hydrocarbon migration are considered. Direct evidence for bacterial oxidation of light hydrocarbons, primarily methane, were first obtained in fluid permeability zones in the permafrost as a stepwise formation of authigenic minerals such as iron sulfides and oxides, carbonates, silicates, and gypsum.

Evolution of self-sustained kinetic oscillations in the catalytic oxidation of propane over a nickel foil

The evolution of self-sustained reaction-rate oscillations in the catalytic oxidation of propane over a nickel foil has been studied in situ using X-ray photoelectron spectroscopy coupled with online mass spectrometry and gas chromatography. Changes in the effective surface area and in the catalyst morphology under reaction conditions have been examined by scanning electron microscopy and a krypton adsorption technique. It is shown that the regular kinetic oscillations arise under oxygen-lean conditions. CO, CO2, H2, H2O, and propylene are detected as products. The conversion of propane oscillates in a range from 1% to 23%. During the half-periods with high activity, the main reaction pathway is the partial oxidation of propane: selectivity toward CO achieves 98%. In contrast, during the half-periods with low activity, the reaction proceeds through three competitive pathways: the partial oxidation of propane, the total oxidation of propane, and the dehydrogenation of propane to propylene. The driving force for the self-sustained kinetic oscillations is the periodic reoxidation of nickel. According to the Ni2p and O1s core-level spectra measured in situ, the high-active catalyst surface is represented by metallic nickel, whereas during the inactive half-periods the catalyst surface is covered with a thick layer of NiO. The intensity of O1s spectra follows the oscillations of O2 in the gas phase during the oxidation of propane. It is found that during the induction period before the regular oscillations appear, a rough and porous structure develops because of strong reconstruction of the catalyst surface. The thickness of the reconstructed layer is approximately 10–20μm. This process is accompanied with at least an 80-fold increase in the effective surface area compared with a clean, non-treated nickel foil, which undoubtedly leads to a drastic increase in the number of active sites. We believe that it is the main reason for the induction period always being observed before the appearance of self-sustained oscillations in the catalytic oxidation of light hydrocarbons over catalysts with a low specific surface area (single crystals, foils, or wires). Moreover, without such reconstruction, the oscillations cannot arise due to low activity of such catalysts.

Synergetic effect of Pd addition on catalytic behavior of monolithic platinum–manganese–alumina catalysts for diesel vehicle emission control

The advanced diesel emission control catalyst Pt–Pd–MnOx–Al2O3 has been developed on the basis of the synergetic effect of Pt with Pd and manganese oxides observed in hydrocarbon and carbon monoxide oxidation reactions. This effect allows a decrease in the total loadings of Pt and Pd down to 0.52g/L in the monolithic catalyst, providing high activity in low temperature oxidation of light hydrocarbons and high thermal stability.The catalytic activity of Pt–Pd–MnOx–Al2O3 monolithic catalysts in butane oxidation and DIESEL tests depends on the Pt and Pd precursors, their individual loadings and their ratio (Pt/Pd). For a selected Pt precursor at its content 0.17g/L, the catalytic performance of Pt–Pd–MnOx–Al2O3 catalyst improves with an increase in Pd loading from 0 to 0.35g/L and is nearly constant at a higher Pd loading (0.70g/L). The most active monolithic Pt–Pd–MnOx–Al2O3 catalyst is prepared by using platinum-dinitrodiamine and palladium nitrate solutions as noble metal precursors.The catalytic activity in light hydrocarbon oxidation is shown to correlate with the RedOx properties of PdPt–MnOx–Al2O3 catalysts and the Pt–Pd particle size. The non-additive increase in the catalytic activity of bimetallic catalyst is suggested to connect with a formation of nanoscale PdO–PtOx particles on the surface of Mn3O4 and a modification of alumina structure by Mn3+ and PtPd clusters.

Geochemical evidences of trace metal anomalies for finding hydrocarbon microseepage in the petroliferous regions of the Tatipaka and Pasarlapudi areas of Krishna Godavari Basin, India

The long-term seepage of hydrocarbons, either as macroseepage or microseepage, can set up near-surface oxidation reduction zones that favor the development of a diverse array of chemical and mineralogical changes. The bacterial oxidation of light hydrocarbons can directly or indirectly bring about significant changes in the values of pH and Eh of the surrounding environment, thereby also changing the stability fields of the different mineral species present in that environment. The paper reports the role of hydrocarbon microseepage in surface alterations of trace metal concentrations. In this study trace metal alterations were mapped that appear to be associated with hydrocarbon microseepages in the oil/gas fields. A total of 50 soil samples were collected near oil and gas fields of the Tatipaka and Pasarlapudi areas of the Krishna Godavari Basin, Andhra Pradesh. The soil samples were collected from a depth of 2–2.5 m. The paper reports the chemical alterations associated with trace metals in soils that are related to hydrocarbon microseepages above some of the major oil and gas fields of this petroliferous region. Trace metals, such as scandium (Sc), vanadium (V), chromium (Cr), cobalt (Co), nickel (Ni), copper (Cu), zinc (Zn), barium (Ba) and strontium (Sr), in soil samples were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). The concentrations of Sc (8 to 40 mg/kg), V (197 to 489 mg/kg), Cr (106 to 287 mg/kg), Co (31 to 52 mg/kg), Ni (65 to 110 mg/kg), Cu (88 to 131 mg/kg), Zn (88 to 471 mg/kg), Ba (263 to 3,091 mg/kg) and Sr (119 to 218 mg/kg) were obtained. It was observed that the concentrations of trace elements were tremendously increased when they were compared with their normal concentrations in soils. The analysis of adsorbed soil gas showed the presence of high concentrations of ΣC2+ (C2H6, C3H8 and n-C4H10) ranging from 7 to 222 μg/kg respectively. Integrated studies of trace elements over adsorbed light gaseous hydrocarbons (ΣC2+) anomalies showed good correlation with the existing oil and gas wells. The carbon isotopic composition of δ13C1 of the samples ranges between −36.6‰ to −22.7‰ (Pee Dee Belemnite) values indicate thermogenic origin, which presents convincing evidence that the adsorbed soil gases collected from these sediments are of catagenetic origin. The increase in the concentrations of trace metals near oil/gas producing areas, suggests a soil chemical change to a reducing environment, presumably due to the influence of hydrocarbon microseepage, which could be applied with other geoscientific data to identify areas of future hydrocarbon exploration in frontier areas.

DFT-assisted structure determination of α1- and α2-VOPO4: new insights into the understanding of the catalytic performances of vanadium phosphates

Structural investigations on vanadium phosphates, which are extensively used as catalysts in industry, often resulted in important advances in the understanding of the mechanisms driving the catalytic oxidation of light hydrocarbons. Layer translations in the two lamellar vanadium phosphates α1- and α2-VOPO4 phases identified during the catalysis were investigated by the combination of first-principles calculations, synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and solid-state NMR. This analysis reveals an important feature: the α1-form is the only polymorph of VOPO4 to exhibit layer translations that prevent the formation of infinite VO6 chains. A detailed investigation of this structural characteristic in vanadium phosphates reveals the correlation between the presence of infinite VO6 chains and the catalytic performances of related phases.

Thermal Degradation of Polyethylene Bags and Millet Stalks: Influence of the Temperature and the Local Concentration of Oxygen on the Conversion Rate of Carbon

This paper concerns the influence of temperature and local concentration of oxygen on the conversion efficiency of carbon into CO, CO2, CH4, C3H8, C2H4, C2H2, C2H6, C6H6, during the thermal degradation of plastic bags and millet stalks. The experimental device used is the tubular kiln, coupled to an analyzer Fourier Transform Infrared (FTIR) and a Non Dispersive Infrared analyzer (NDIR). Temperatures are considered between 800 and 1000°C. Local concentrations of oxygen during thermal degradation are 0%, 10% and 21%. On the one hand results obtained on the influence of temperature show that for each type of thermal degradation and whatever the temperature of the combustion, the rate of conversion of carbon remains substantially the same. In the case of plastic bags, the rate of carbon converted during pyrolysis is about 90% of carbon converted during reductive combustion. On the other hand, with millet stalks, the carbon converted represents only 60% of the rate of carbon converted during combustion to 10% oxygen. 1 to 2% of carbon not analyzed is in the form of aromatic compounds that are found most often in the soot and/or tar from this combustion system. Moreover, whatever the temperature, the overall efficiency of carbon conversion increases linearly with the local concentration of oxygen. During the thermal degradation of plastic bags, we see that the reducer environment has fostered the conversion of 7% of carbon more while the presence of oxygen in double proportion promotes the conversion of 27% carbon. Regarding the influence of the local content of oxygen, it is clear that for plastic bags, the reactions of oxidation of CO into CO2 tend to be favored for the benefit of those of hydrocarbons into CO. The formation of CO and CO2 by oxidation of light hydrocarbons is primarily from gaseous compounds CH4 and C2H4. At 950°C, we have also acetylene (C2H2) which is involved in the production of carbon oxides. At 1000°C, benzene (C6H6) heavily involved in the formation of CO and CO2. However, with millet stalks, more the local content of oxygen increases, more combustion is better, that is to say that the oxidation reactions producing CO2 are faster than the oxidation reactions of hydrocarbons into CO. The rate of carbon converted into CO and CO2 is higher for millet stalks than for plastic bags, due to this oxygen levels higher in millet stalks than in plastic bags. Similarly, for the millet stalks, from pyrolysis to combustion (at 10 and 21% oxygen), there is practically no hydrocarbon emitted.

Recent developments and trends in the electrochemical promotion of catalysis (EPOC)

Electrochemical Promotion of Catalysis (EPOC or NEMCA effect) is one of the most exciting discoveries in Electrochemistry with great impact on many catalytic and electrocatalytic processes. According to the words of John O’M. Bockris, EPOC is a triumph, and the latest in a series of advances in electrochemistry which have come about in the last 30 years. It has been shown with more than 80 different catalytic systems that the catalytic activity and selectivity of conductive catalysts deposited on solid electrolytes can be altered in a very pronounced, reversible and, to some extent, predictable manner by applying electrical currents or potentials (typically up to ±2 V) between the catalyst and a second electronic conductor (counter electrode) also deposited on the solid electrolyte. The induced steady-state change in catalytic rate can be up to 135 × 103% higher than the normal (open-circuit) catalytic rate and up to 3 × 105 higher than the steady-state rate of ion supply. EPOC studies in the last 7 years mainly focus on the following four areas: Catalytic reactions with environmental impact (such as reduction of NOx and oxidation of light hydrocarbons), mechanistic studies on the origin of EPOC (using mainly oxygen ion conductors), scale-up pf EPOC reactors for potential commercialization via development of novel compact monolithic reactors and application of EPOC in high or low temperature fuel cells via introduction of the concept of triode fuel cell. The most recent EPOC studies in these areas are discussed in the present review and some of the future trends and aims of EPOC research are presented.

Influence of the Anatase/Rutile Ratio on the TiO2 Photocatalytic Activity for the Photodegradation of Light Hydrocarbons

A set of TiO2 samples with different anatase/rutile ratios was prepared by calcinations at different temperatures from commercial photocatalyst Degussa P25. The effects of the two crystalline phases of titanium (IV) oxide on the photocatalytic activity in gaseous phase through oxidation of light hydrocarbons were studied. Crystalline phase transformation from anatase to rutile occurred at 700°C for P25. Results indicate that samples with higher anatase/rutile ratios presented higher intrinsic activities for the photodegradation of a propane/isobutane/butane (40/35/25 %V) mixture. However, the activity did not totally disappear after complete crystalline transformation from anatase to rutile, indicating that the pure rutile phase also presents photoactivity. During the photocatalytic reaction of TiO2 samples, a linear dependence was found between the inverse of the intrinsic reaction rate constant (k intrinsic) and the water adsorption capacity in the surface (WAPS) of the synthesized TiO2 catalyst. The thermal treatment used to induce the formation of rutile by calcination would presumably reduce water adsorption capacity and surface area, leading to a decrease in photocatalytic activity.

Re-evaluation of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ perovskite as oxygen semi-permeable membrane

Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF), a mixed oxygen ionic and electronic conducting ceramic derived from SrCo 0.8Fe 0.2O 3− δ (SCF), was re-evaluated for its possible application as an oxygen semi-permeable membrane and membrane reactor for partial oxidation of light hydrocarbons. The partial substitution of Sr 2+ with Ba 2+ in SCF led to an increase in the phase stability of the cubic perovskite structure. Both BSCF and SCF were found to have high oxygen nonstoichiometry. However, BSCF possessed a higher oxygen nonstoichiometry than SCF at room temperature, but a similar value at high temperatures. This resulted in the lower chemical expansion for BSCF than SCF. The doping of Ba 2+ in SCF led to the decrease of the electronic conductivity, but an increase in the oxygen ionic conductivity. The oxygen permeation study of the BSCF membrane demonstrated that the permeation rate was mainly rate-determined by the slow surface exchange kinetics at the oxygen lean side (or reaction side) membrane surface. The high ionic conductivity and the slow surface exchange kinetics resulted in the surface oxygen partial pressure at the reaction side membrane surface to be much higher than the surrounded atmosphere, therefore protecting the BSCF membrane from reduction.

The role of the catalysts with highly dispersed and isolated active sites in the selective oxidation of light hydrocarbons

Abstract This review summarizes the role of catalysts with highly dispersed and isolated actives sites (active sites: supported atoms f≤0.5%) in the selective oxidation of light hydrocarbons, such as methane, ethane and propane, into oxygenates and the epoxidation of olefins. The plausible structures of the highly dispersed and isolated active species, as well as their effects on the catalytic performances are discussed. The special physico-chemical properties and the functional mechanism of the catalysts with highly dispersed and isolated active sites, as well as the preparation, characterization of the catalysts with highly dispersed and isolated active sites and their applications in other types of reactions of lower hydrocarbons are summarized. ∗Supported by National Natural Science Foundation of china (Grant No. 20373043) and the Scientific Research Key Foundation for the Returned Overseas Chinese Scholars of Ministry of Education

Selective oxidation of hydrocarbons and the global warming problem

Based on recently published studies on the life cycle analysis of several chemicals, and the CO 2 emissions associated with their production, a new approach to the selective oxidation of light hydrocarbons is discussed. By nature, selective oxidations are also producing CO 2 as the end product, much preferred by the thermodynamics. New technologies such as the circulating fluid bed reactor in selective oxidation, could be considered to propose a solution to reduce the CO 2 emissions both with respect to the yield improvement, but also as a solution to recover CO 2 from a high partial pressure recycling loop.