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Plastic pollution in natural waters and the continuous breakdown of plastic debris under environmental conditions has resulted in increased numbers of micro- and nano-sized plastic particles in the aquatic environment. Moreso, plastics are persistent in nature and could stay in the environment for thousands of years without completely degrading. Hence, researchers believe that the smaller sized particles will continue to break down to even smaller nano-sized plastics (i.e., nanoplastics). While many of the previous studies have focused on their short-time impacts, the long-term impacts of nanoplastics is not yet well understood. This study investigated the sublethal effects of dialyzed 20 nm and 200 nm carboxylated polystyrene nanoplastics to Daphnia magna. The study followed the OECD 211 protocol for 21-day chronic exposures. Separate groups of D. magna were exposed to 50 mg/L of both particle sizes and 0.1 mg/L of the 20 nm particles. Comparison of the results between the 50 mg/L for both particle sizes allows the use of particle mass concentration as a dose metric. Also, the particle numbers in the 50 mg/L 200 nm and 0.1 mg/L 20 nm treatments were comparable. Hence, comparison of their results allows the use of particle number as a dose metric. Overall, chronic exposure to both sizes of polystyrene nanoplastics showed sublethal effects such as growth, molting and reproduction of Daphnia magna, including at the 0.1 mg/L concentration of the 20 nm nanoplastics. The results of the comparison showed similar trends in most of the measured endpoints regardless of whether the results were compared using the mass concentration or particle counts as dose metrics. Also, the change in mass concentration did not cause any significant change in the observed toxicity impacts for the 20 nm nanoplastics. Also see: https://micro2022.sciencesconf.org/427138/document, In MICRO 2022, Online Atlas Edition: Plastic Pollution from MACRO to nano

Single-use face masks can release microfibres upon exposure to environmental conditions. This study investigates the number of microfibres released in the presence and absence of UV irradiation and mechanical friction and the removal of the released microfibres in a simulated conventional wastewater treatment process. UV exposure results in a four-fold increase in the number of microfibres released from new masks and used masks resulting in ~2400 microfibres/mask and ~1100 microfibres/mask, respectively. Application of mechanical friction to the UV-exposed new and used masks further increases the number of released microfibres per mask. In a simulated coagulation/flocculation process, the removals of microfibers originating from new masks and used masks are 79% and 91%, respectively. XPS analysis reveals that the silica content of the used masks is 240% higher than that of new masks, which could explain the higher removal efficiency of microfibers from used masks. FTIR analysis of the masks after UV exposure shows carbonyl indices of 0.73 ± 0.70 and 0.27 ± 0.10 for the microfibres from used and new masks, respectively. Based on available data, we estimate that 4-47 million polypropylene microfibres can be released into natural waters per day after wastewater treatment in an urban environment (for a population of 4300 persons/km

The wet air oxidation of benzene in the presence of phenol has been studied in an autoclave with a working volume of 1.24 L in the operating temperature range of 160–220 °C at 1.72 MPa oxygen parti...

Micro- and nanoplastics derived from environmental degradation of larger plastic debris can be ingested and accumulate in aquatic organisms, raising growing global ecological concerns. Toxicology s...

Graphene/TiO2 photocatalysts are gaining increasing attention for its application in the decomposition of aqueous organic compounds. In this perspective, we have synthesized molybdenum doped graphene/TiO2 (Mox-GT) hybrids via simple sol-gel method. The physico-chemical properties of the samples were characterized by various analytical and spectroscopic techniques. X-ray diffraction studies indicate that pure TiO2 and graphene/TiO2 were composed of anatase with minor brookite phase while Mo doped graphene/TiO2 powders were composed of only anatase phase. Scanning and transmission electron microscopy results showed particles spherical morphology and uniform distribution of particles on graphene nanoflakes. X-ray photoelectron microscopy revealed the presence of surface defects (Ti3+ centers and oxygen vacancies), dopants electronic states (Mo6+/Mo5+), surface hydroxyl groups and the chemical linkage of graphene with TiO2. UV-diffuse reflectance spectroscopy analysis showed that addition of Mo dopant to graphene/TiO2 greatly extends the absorption band edge to the visible region. In UV and visible light photocatalytic tests Mox-GT composites showed enhanced activities, specifically the Mo0.8-GT powder outperformed the rest of the prepared photocatalysts in the decomposition of synthetic textile dye, methylene blue. This highest photocatalytic performance is ascribed to the enhanced photo absorption and electron-hole separation, high surface area and pore size and surface defects. Moreover, the obtained encouraging results portrays that the performed work could provide new insights into the fabrication of metal doped graphene/TiO2 nano-hybrid materials as high performance photocatalyst and facilitates their applications in areas such as; environmental remediation’s, hydrogen productions, solar and fuel cells.

A batch process is developed to generate sulphur functionalized graphene nanoflakes (S-GNFs), corresponding to nanoparticles of stacked graphene. The growth and functionalization of the catalysts are done in a single thermal plasma reactor. The GNFs are first grown through the decomposition of methane in the thermal plasma volume followed by homogeneous nucleation of the nanoparticles in the well-controlled recombining plasma stream allowing the 2-dimensional evolution of the nanoparticle morphology. The precursor feeding conditions are then changed to liquid carbon disulphide in order to generate sulphur-based functional groups on the nanoparticles. The plasma conditions and carbon disulphide injection are varied, and samples with tuneable amount of sulphur between 4 and 28 at% are obtained. The functional groups generated include polythiophene polymer partly covering the GNFs, sulphur functionalities implemented directly on the graphitic structure, and traces of orthorhombic sulphur. The S-GNFs exhibit higher electrocatalytic activity toward the oxygen reduction reaction in alkaline medium for the samples containing the highest amounts of sulphur.

A cost effective alternative catalyst to platinum for the oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells is iron nanoparticles deposited into nitrogen-rich stacked graphene sheets. In this work graphene nanoflakes with high levels of nitrogen (HN-GNFs) are grown from the plasma phase and iron functionalities are added by a wet-chemical method. The amount of iron is varied to study the structural and electrochemical effects on the catalyst. The amount of iron in the sample and on the surface is measured and proven to have no effect on the qualitative surface conditions of HN-GNFs, as the iron is imbedded into the HN-GNFs. Electrochemical studies with a rotating disk electrode reveal that the addition of iron is beneficial in acid and neutral environments, with improvements of over 0.3 V to the onset potential and 1.85 mA cm −2 to the current density at 0 V versus a reversible hydrogen electrode when the iron catalysts are compared to untreated HN-GNFs. The iron did not improve the catalytic performance in alkaline environments, with untreated HN-GNFs already showing good activity towards the ORR.

Graphene nanoflakes (GNFs), a stack of 5–20 layers of graphene sheets, are generated here using methane decomposition in a thermal plasma followed by homogeneous nucleation of the 2-dimensional structures in the gas stream. The GNFs are functionalized with nitrogen and iron to improve their electrocatalytic activity. The iron functionalization step is carried out as a post-processing step within the same thermal plasma reactor used to grow the nanoparticles. Two different iron precursors are tested in the reactor, iron powder and iron (II) acetate solution. The iron source carried by a nitrogen flow is injected in the argon plasma, and parameters such as the plasma power, pressure, and the exposure time during functionalization are optimized for enhanced catalyst activity. Structure and composition of the resulting catalysts are characterized, and their electrocatalytic performances in terms of onset potential, half wave potential and current density show an increase compared to the non-functionalized GNFs. This study proves the ability to entirely produce a pure and highly crystalline graphene-based non-noble metal catalyst using a thermal plasma single batch process with simple precursors such as methane and nitrogen gas, and an iron powder or iron acetate solution.

In the present work, graphene nanoflakes (GNFs) were grown at both low and high levels of nitrogen functionalization and subsequently put through a wet-chemical method to add iron functionalities to the surface and create active catalyst centers. No mechanical treatments are used in order to minimize the formation of defects on the GNFs and evaluate if iron-nitrogen-GNF edges or surface sites can generate catalytic activity rather than the macropore structures holding these functionalities on porous carbon black. The catalysts produced under various synthesis routes were characterized and screened for their performance as an oxygen reduction reaction (ORR) catalyst. Characterization included an electrochemical study, an examination of the carbon and nitrogen content and bonding structure, in addition to Raman analysis and the calculation of the BET surface areas. It was found that samples that were both treated with iron acetate and put through pyrolysis produced the most active samples. These samples were composed of graphitic carbon and contained a large amount of pyridinic nitrogen. Additionally, when working with GNFs generated with high levels of nitrogen, no extra nitrogen source was needed during the iron incorporation step. This study further develops the GNF-based catalyst already seen to be a suitable ORR catalyst for the polymer electrolyte membrane fuel cell.

Graphene nanoflakes (GNFs) are a stack of 5–20 layers of highly crystalline graphene sheets having a planar size of approximately 100 by 100 nm and low defect concentration. They are produced here through homogeneous nucleation following the plasma decomposition of a carbon source in an inductively coupled thermal plasma reactor. Following synthesis within the plasma reactor, the GNFs are functionalized downstream in the plasma recombination zone with the addition of oxygen to the main plasma stream. Tunable oxygen functionalization is obtained and values up to 14.2 atomic percent are reached on the surface of the particles. While the non-functionalized GNFs are hydrophobic, the oxygen-functionalized GNFs (O-GNFs) show full stability of all the produced powders when directly dispersed in water or ethanol without any surfactant. The O-GNFs keep their structural integrity even after the implementation of the hydrophilic groups on the surface of the nanoparticles, and maintain their dispersion stability in water and ethanol over a long period of time.

In order to enhance the visible photocatalytic activity of titanium dioxide (TiO2), selenium (Se) doped TiO2 was prepared by sol–gel method using oxalic acid as a chelating agent. To characterize and describe the effect of Se+4 ions on the structural, optical and photocatalytic properties of TiO2, the powders were characterized by XRD, FTIR, UV-DRS, HR-TEM, PL, Raman, XPS and BET measurements. XRD analysis showed that doped powders consist of anatase phase, while undoped TiO2 is a composite mixture of anatase and rutile at a calcination temperature of 550 °C. Williamson–Hill plot results indicated the presence of tensile strain on the addition of 0.02, 0.04 and 0.06 mol% Se content, while compressive strain was specified on the addition of 0.08, 0.1 and 0.2 mol% Se content in TiO2 lattice. FTIR analysis revealed the chelating behaviour of oxalic acid with titanium ions in forming titanium oxalate stretches. Diffuse reflectance measurements showed that visible light absorption is induced by dopant localized/intermediate electronic states, probably originating from Se 4s and 4p states within the band gap of TiO2. Raman peak broadening and the small frequency shifting for the peaks (1-Eg and B1g) were attributed to oxygen vacancies and crystal lattice distortions. Photoluminescence (PL) analysis showed that electron hole recombination was decreased with the incorporation of Se+4 ions in TiO2, which act as trapping sites for the photogenerated electrons. Moreover, PL analysis demonstrated that Se doping produces Ti+3 centers, oxygen defects and localized electronic states in TiO2 band gap, which become responsible for the TiO2 response towards the visible light. The activity of the prepared photocatalysts powder were tested by investigating the kinectics of the photocatalytic decoloration of methylene blue (MB) under UV irradiations and decomposition of 4-chlorophenol (4-CP) under visible light irradiation. It was observed that the TSe0.08 powder with Bronsted acid sites, calcined at 550 °C showed highest photocatalytic activity under both UV and visible light irradiations for the selected pollutants. In the decoloration of MB, TSe0.08 powder attain a rate constant (kapp) value of 0.045 min−1 which is higher than Degussa P25 (0.033 min−1) as well two times higher than undoped TiO2 (0.021 min−1). Based on the obtained results, a UV/vis light irradiated photocatalytic mechanism has been proposed for the Se+4 doped anatase TiO2.

Modified glassy carbon RDE method is introduced in this work for the determination of heterogeneous reaction rate constant of H2O2 decomposition. This method is based on the analysis of RDE voltammograms of H2O2 reduction on a glassy carbon electrode covered with a catalyst layer. As a case study, the rate constant of H2O2 decomposition on nitrogen doped graphene is determined by using both glassy carbon and gold RDE methods. A good agreement is observed between the results of these two methods indicating the reliability of the glassy carbon method. Moreover, advantages and limitations of the glassy carbon method are discussed.

Fe–N-doped graphene containing 0.3 at% of Fe and 1.9 of N with an active specific surface area of 77.5 ± 4 m2 g−1 is synthesized in two steps: first N-doped graphene is produced by thermal dissociation of methane in an inductively coupled thermal plasma (ICP) reactor and subsequently the product is converted to Fe–N-doped graphene by a wet chemical method. The catalytic activity of this catalyst toward H2O2 reduction reaction (HPRR) is studied by rotating disk electrode for fuel cell applications. Although the mechanism of HPRR on Fe–N-doped graphene, N-doped graphene and graphene is similar, Fe–N-doped graphene shows the highest catalytic activity toward HPRR. The exchange current density based on the active surface area (j0A) of Fe–N-doped graphene in Na2SO4 solution is (4.4 ± 0.2) × 10−8 A cm−2, which is 5 times greater than j0A of the N-doped graphene. Direct reduction of H2O2, H2O2 decomposition, O2 reduction, and O2 desorption are predicted as the reactions involved in the HPRR while O2 reduction and O2 desorption are negligible at low and high overpotentials, respectively. Investigation of the effect of the electrolyte and catalyst loading reveals that HPRR on Fe–N-doped graphene suffers from kinetic limitations especially at low catalyst lodgings, fast rotation rates, and strong acidic and basic solutions.

The catalytic activity of LaNiO 3 toward H 2 O 2 reduction reaction (HPRR), with a potential application in the cathode side of fuel cells, is studied in alkaline, neutral and acidic solutions by rotating disk electrode. The LaNiO 3 particles synthesised by citrate-based sol–gel method have sizes between 30 and 70 nm with an active specific surface area of 1.26 ± 0.05 m 2 g −1 . LaNiO 3 shows high catalytic activity toward HPRR in 0.1 M KOH solution with an exchange current density based on the active surface area ( j 0 A ) of (7.4 ± 1) × 10 −6 A cm −2 which is noticeably higher than the j 0 A of N-doped graphene. The analysis of kinetic parameters suggests that the direct reduction of H 2 O 2 , H 2 O 2 decomposition, O 2 reduction and O 2 desorption occur through HPRR on this catalyst. In order to control and minimize oxygen evolution from the electrode surface, the effects of catalyst loading, bulk concentration of H 2 O 2 , and using a mixture of LaNiO 3 and N-doped graphene are studied. Although the mechanism of HPRR is independent of the aforementioned operating conditions, gas evolution decreases by increasing the catalyst loading, decreasing the bulk concentration of H 2 O 2 , and addition of N-doped graphene to LaNiO 3 .

Undoped, mono and codoped TiO 2 nanoparticles were prepared with Mo +6 and V +5 dopants using ultrasonic-assisted sol–gel method. XRD diffraction revealed that photocatalyst powders calcined at 550 °C are composed of anatase with minor brookite and rutile phases. Codoped powders showed largest red shift in the band gap and the decrease in photoluminescence intensity demonstrated that electrons holes recombination has decreased. Mo +6 and V +5 have been detected by XPS analysis indicating that the dopants Mo +6 and V +5 substitute for titanium (Ti +4 ) in the lattice of TiO 2 . The activity tests reveal that codoped (TMo 0.125 V 0.125 ) powder has the best photocatalytic performance in the degradation of methylene blue (MB) dye and antibiotic sulfamethoxazole (SMX) under UV and visible light irradiations. Briefly, the enhanced activity of codoped TiO 2 is due to the synergistic effect of TiO 2 polymorphs, the Mo +6 and V +5 energy levels and their d-d transition with TiO 2 conduction band electrons, high specific surface area via small crystallite size, surface acidity, Ti +3 surface states and oxygen defects. The mechanistic study illustrates that the complex band structure of the codoped powders does not only improve visible light absorption and promote the separation of photoinduced electron hole pairs, but it also facilitates the enhanced formation of hydroxyl radicals (OH ) and superoxide anions (O 2 − ). Degradation of methylene blue (MB) and sulfamethoxazole (SMX) showed pseudo first order kinetics. With MB experiments under UV irradiation a rate constant ( k app ) of 0.064 min −1 was obtained with TMo 0.125 V 0.125 powder, which is higher than that of commercially available Degussa P25 (0.05 min −1 ) and twice as high than the undoped TiO 2 (0.031 min −1 ).

H2O2 reduction reaction (HPRR) is studied on both graphene (GNF) and nitrogen doped graphene nanoflakes in 0.1 M Na2SO4 solution by rotating disk electrode. The XPS results indicate that N-doped graphene nanoflakes with high nitrogen content, 32 at%N (N-GNF32), are synthesised successfully by an inductively-coupled thermal plasma (ICP) reactor. Pyridinic, pyrrolic and graphitic N species contribute up to 67% of the total nitrogen. Kinetic parameters such as Tafel slope and stoichiometric number suggest that HPRR occurs by the same mechanism on both GNF and N-GNF32. Although nitrogen does not change the mechanism of HPRR, the results indicate that the reaction rate of H2O2 reduction is enhanced on N-GNF32. The exchange current density of H2O2 reduction based on the active surface area of N-GNF32 is (8.3 ± 0.3) × 10−9 A cm−2, which is 6 times higher than the value determined for GNF. The apparent number of electrons involved in the process suggests that H2O2 decomposition competes with H2O2 reduction on both catalysts. Evaluation of the apparent heterogeneous reaction rate constant and the Tafel slope indicate that simultaneous reduction of O2 and H2O2 is negligible on the N-GNF32. On the other hand, the reduction of O2 and H2O2 occurs simultaneously on the GNF surface.

In the current study, it was found that the physiochemical properties of TiO2 are effected with formic acid as a chelating agent in a sol–gel process. From XRD studies it was revealed that due to the chelation of formate group with titanium precursor, anatase/brookite mixture of 86:14 is obtained while the control sample which has been prepared without formic acid showed pure anatase at 400 °C. FTIR studies indicated that, the formate group favored a monodentate mode of coordination with titanium precursor under the effect of addition of increasing amount of formic acid, while under the effect of increasing titanium precursor content the formate group is chelated with titanium atoms in a bidentate bridging mode. In addition, from the FTIR study it was demonstrated that increasing the amount of water in the hydrolysis step, a reduction in the intensity of the carboxylate (COO−) stretches was observed indicating that the titania formate bridging complex becomes weaker, resulting in a weakened titanium gel network structure which could readily collapse during calcination favoring early rutile formation. Raman spectroscopy showed that as a result of sample composite nature and presence of oxygen vacancies as demonstrated by PL analysis causes the broadening and frequency shifting of the Raman bands. Photocatalytic studies demonstrated that the formic acid modified sample composed of anatase/rutile mixture of 94:6 calcined at 600 °C show significantly higher catalytic activity compared to the control sample prepared under similar conditions. Kinetic analysis show first order kinetics for the decomposition of methylene blue, a rate constant (kapp) of 0.074 min−1 was obtained with anatase/rutile (94:6) mixture which is even higher than the Degussa P25 (0.067 min−1).

The control of nanoparticle synthesis using thermal plasmas is difficult and often leads to problems of chemical and structural purity, and poor process robustness in terms of consistency of product from run to run. Good reactor design allowed to overcome these issues and to develop a new material based on graphene with a flake-like structure (labeled graphene nanoflakes, GNF) supporting nitrogen for catalytic applications, for example as platinum replacement in fuel cells. These structures showed not only to be active, but also stable in polymer electrolyte fuel cell operation. Characterization of these structures, in situ fuel cell studies and modeling analysis all indicate that achievement of stability relates on the crystalline two-dimensional graphene structure. This paper first reviews the basic aspects behind the structural objectives, describes the synthesis process design leading to this crystalline structure, and provides a two-dimensional analysis on the graphitic growth based on fundamental theory and CFD calculations. These calculations indicate that an independent control of the graphene structure thickness (number of atomic planes) and sheet lengths is possible in a thermal plasma reactor.

This work presents a methodology to analyze hydrogen peroxide reduction reaction (HPRR) studied by rotating disk electrode (RDE). Generally the Koutecky–Levich equation is used to determine the kinetic parameters of an electrochemical reaction. This equation is not applicable to electrochemical reactions with a complex reaction mechanism. The HPRR is an example of these complex reactions because the H2O2 reduction, H2O2 decomposition and O2 reduction may take place simultaneously on the electrode surface. In the current work the mass transport equations of H2O2 in the electrolyte and the reaction equations on the electrode surface are solved simultaneously under the steady state conditions to derive a specific equation for HPRR. The new equation shows the same linear relationship between the inverse of the current density (j−1) and the inverse square root of the rotation frequency (ω−1/2), but the slopes and the intercepts of the lines are shown to be functions of the reaction rate constants involved in the HPRR. One of the most important results of the work is the possibility to determine the hydrogen peroxide decomposition rate constant directly from RDE data. Prediction of simultaneous reduction of H2O2 and O2 on the electrode and suggestion a mechanism for HPRR are other advantages of the derived equation when compared with Koutecky–Levich equation.

In this work, we use an inorganic titanium precursor (titanium oxysulfate, TiOSO4) for the preparation of doped TiO2 by the sol–gel method. Molybdenum (Mo), iron (Fe) and vanadium (V) in the concentration range of 0.0312–2.0 mol% are added as dopants. The prepared samples were characterized by XRD, FTIR, N2 isotherms, SEM–EDX, TEM, UV–Vis DRS and PL techniques. X-ray diffraction revealed that an increase in the concentration of Mo causes the transformation of brookite into anatase phase. In contrast, Fe and V favor the formation of brookite phase. A decrease in crystallite size was observed on the addition of dopant ions compared to that of pure TiO2 (7 nm), for 0.0312 mol% concentration of dopant in TiO2, a crystallite size of 6.3 nm (Mo), 6.2 nm (Fe) and 6.4 nm (V) was calculated. A noticeable change in anatase lattice parameter along the “c” direction was observed with increasing dopant concentration, this is evidence that the dopant ions have entered the TiO2 crystal lattice by substitutional doping, which induces local distortion of the crystal structure and variation in interatomic distances. An increase in BET surface area and a decrease in pore size were observed with increasing dopant concentration, this may be due to their substitutional doping in crystal lattice and or their presence in the grain boundaries hindering the crystal growth. Diffuse reflectance studies indicate that doped TiO2 showed visible light absorption compared to that of pure TiO2 (3.1 eV). For 0.25 mol% concentration of dopant in TiO2, energy values of 2.6 eV (Mo), 2.95 eV (Fe) and 2.92 eV (V) were obtained. PL analysis clearly shows that the dopant ions have the capability to alter the oxygen vacancies and to produce Ti+3 surface species which trap the photogenerated electron and transfer the electron to surface absorbed oxygen and results in the decrease of electron hole pair recombination rate. Visible light photoactivity tests for the discoloration of methylene blue demonstrated that the doped samples showed enhanced photoactivity compared to undoped TiO2 and commercially available Degussa P25, because of composite nature, surface hydroxyl groups, narrowed band gap and decreased recombination rate of photogenerated electron–hole pairs. The highest photocatalytic activity was observed with 0.25 mol% dopant concentration, the calculated reaction rate constant (kobs) was 0.97 min−1 (Mo), 1.18 min−1 (Fe) and 1.17 min−1 (V) compared to 0.18 min−1 (undoped TiO2) and 0.17 min−1 (Degussa P25).

Vanadium doped titanium dioxide (V–TiO2) photocatalyst was synthesized by the sol–gel method using ammonium vanadate as vanadium source. The prepared samples were characterized by XRD, N2 adsorption–desorption method, UV–Vis DRS, Fourier transform infrared (FTIR), scanning electron microscope–energy dispersive X-ray and photoluminescence (PL) analysis. The results show that V5+ ions were successfully incorporated into the crystal lattice of TiO2 as a consequence, not only an obvious decrease in the band gap and a red shift of the absorption threshold into the visible light region was recorded for the V modified TiO2, but, also a decrease in photogenerated electrons and holes recombination rate was observed as demonstrated by PL analysis. FTIR study indicated that in undoped TiO2 sample the acetate group favored a bidentate bridging mode of binding with titanium atoms, whereas a bidentate chelating mode of linkage was observed in V–TiO2 powders. The crystallite size of the samples calcined at 300 and 500 °C were decreased beyond the molar ratio of 200:1 (V:Ti), this may be due to dopant presence in the grain boundaries hindering the crystal growth. The photocatalytic activities for both pure and vanadium doped TiO2 powders were tested in the discoloration of a reactive dyestuff, methylene blue, under visible light. The 100:1 (V:Ti) doped photocatalyst, calcined at 300 °C showed enhanced photocatalytic activity under visible light with a rate constant (kobs) of 5.024 × 10−3 min−1 which is nearly five times higher than that of pure TiO2, as result of low band gap value, high specific surface area and a decrease in recombination rate.

Two of the major challenges for the commercialization of automotive fuel cells are cost and durability. Cost estimations indicate that at a large production rate, the majority of the stack component cost comes from the catalyst ink. Decreasing this cost depends on finding a durable cost-effective platinum-free electrocatalyst. In this work, pure graphene nano-flake (GNFs) powders are produced by plasma decomposition. The GNFs are composed of 5–20 layers of stacked graphene sheets, a structure that appears to be closely associated to catalyst stability and durability. Additionally, the large number of attachment sites for nitrogen and atomic iron functionalization provide an avenue for improving activity. The GNFs were nitrogen functionalized and then used to support atomic iron to create the active sites for a non-noble catalyst. Iron was successfully incorporated at a value of 0.28 at% on the surface of the catalyst structure. The catalyst was used on the cathode side of a polymer electrolyte membrane fuel cell (PEMFC) and showed stability over 100 h. The performance of the catalyst demonstrates, to our knowledge, the first proof of a stable strictly iron-based fuel cell catalyst.

Graphene nanoflakes (GNF), a stack of 5 to 20 layers of graphene sheets with typically 100 nm side lengths, are the product of methane decomposition using an argon ICP thermal plasma. GNFs are good candidates to support non-noble catalytic sites for the oxygen reduction reaction. This material has a high crystallinity allowing the graphene to be acid resistant, together with a high electrical conductivity, these properties providing a good basis for a stable catalyst material in fuel cells. The GNFs are functionalized with nitrogen to support iron atoms and create catalytic sites dispersed at the atomic level on the nano-structured powders. The iron functionalization step is realized in situ as a post-processing step within the synthesis reactor through the vaporization of two different Fe precursors in the core of the plasma. The first consists of pure iron powders carried by a nitrogen flow; this method having the advantage of avoiding impurities during the functionalization step. The second precursor is an iron(II) acetate solution also carried by a nitrogen flow, with the iron already in atomic form once dissociated in the thermal plasma core. The effects of the type of precursor, the power of the plasma, and the reactor chamber pressure on the iron functionalization are studied in the present contribution. The structure, composition, and activity of the resulting catalyst are also fully characterized.

Removal of the fluoroquinolone antibiotic levofloxacin (LEVO) was studied in two oxidation processes: photocatalysis (UVC lamp (254 nm), TiO 2 ) and ozonation. LEVO ( C o = 20 mg/L) was no longer detected after an ozone dose of 20.5 mg/L and after 180 min of photocatalytic oxidation. COD removals of 59% and 70% were measured for 270 mg/L of transferred ozone dose and 300 min of photocatalytic oxidation, respectively. Extensive treatment with ozone did not result in further reduction in COD levels reaching a plateau at the above mentioned value, however increased irradiation time led to increased COD removal during photocatalytic treatment. Both treatment methods proved to be effective ways of removing antibacterial activity. From agar diffusion test with Escherichia coli , it was observed that a transferred ozone dose of at least 20.5 mg/L and 180 min of irradiation were enough to completely remove antibacterial activity. Both treatments methods were shown to efficiently remove LEVO and its antibacterial activity and show promising results as possible applications for removal of antibiotics in wastewater.

Attached growth biological treatment systems are a promising solution to ammonia removal in cold-temperature climates. Environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy in combination with fluorescent in situ hybridization (FISH) was used to investigate the effects of 4 months of exposure to 4 degrees C on nitrifying biofilm and biomass. These molecular and microscopic methods were modified to minimize loss of mass and distortion of in situ perspectives. Environmental scanning electron microscopy revealed that nitrifying biofilm did not exhibit significant changes in volume with exposure to 4 degrees C. Confocal laser scanning microscopy in combination with FISH showed that the number of ammonia-oxidizing bacteria (AOB) cells present in the biofilm was statistically consistent during exposure to 4 degrees C. The RNA content of AOB cells remained sufficient for FISH enumeration. The number of nitrite-oxidizing bacteria cells remained steady during exposure to 4 degrees C; however, the RNA content of the cells appeared to decrease with exposure to 4 degrees C, thereby preventing their enumeration using FISH.

Photolytic and photocatalytic removals of 17α-ethinylestradiol (EE2) and levonorgestrel (LNG) in pharmaceutical wastewater were investigated under UVC radiation. Wastewater collected from WYETH, St-Laurent, Canada contained high concentrations of EE2 and LNG in suspension and coloring agent tartrazine in solution. Aqueous phase removals of EE2 and LNG were studied as individual contaminants in water and in complex matrices including: co-contaminants in water, in simulated synthetic wastewater and in the wastewater. After 30 min of UVC photocatalysis of the individual contaminants, removal efficiencies of EE2 and LNG were 92% and 97%, respectively, while higher photolytic removal was observed for LNG (94%) compared to EE2 (60%). Hydroxyl radicals were shown to contribute significantly to the removal of both compounds in water. In contrast to EE2, photolytic removal of LNG was higher than its photocatalytic removal efficiencies in all complex matrices. Higher photolytic removal of LNG was attributed to the fact that it absorbs UVC radiation considerably more than EE2. Lower photocatalytic removals of LNG in complex matrices compared to its photocatalytic removal as an individual contaminant was due to the presence of EE2 at concentrations up to five times larger than LNG in water, thus leading to increased competition for hydroxyl radicals and retarding LNG removal. In the wastewater matrix photocatalytic removals for EE2 and LNG were similar at 48%, whereas the photolytic removal of LNG (76%) was higher than EE2 (29%). The applicability of UVC processes for reduction of hormone content in similar wastewaters was demonstrated.

Carbon black nanopowders were produced using two thermal plasma processes based on DC, respectively ICP plasma torches. Although the produced particles were in the nanometer size range, the values obtained for the surface area of the particles using a Brunauer Emmett Teller technique were very small. This indicated the presence of contaminants in the experimental powders, as confirmed by Raman spectroscopy and thermogravimetric Analysis. A thermal treatment process was developed in order to extract these volatile compounds, which were then identified using a Gas Chromatography–Mass Spectrometry method. The experimental powders were analyzed using scanning and transmission electron microscopy, X-ray diffraction and Raman spectroscopy before and after the thermal treatment in order to determine the effect of the heat treatment on the powder structural properties.

Carbon material was produced using an inductively coupled thermal plasma torch system of 35 kW and a conical shape reactor. The carbon nanopowders were obtained by plasma decomposition of methane at various flow rates and show a uniform microstructure throughout the reactor. The product has a crystalline graphitic structure, with a stacking of between 6 and 16 planes and a nano-flake morphology with particles dimensions of approximately 100 nm long, 50 nm wide and 5 nm thick. Nitrogen was also introduced in some synthesis experiments along with the methane precursor using flow rates of 0.1 and 0.2 slpm. The resulting product has the same structural properties and the nitrogen is incorporated into the graphitic structure through pyridinic type bonds.

In this study, photolytic and photocatalytic removal of the antibiotic sulfamethoxazole (SMX) under UVC radiation ( λ = 254 nm) was investigated. The light intensity distribution inside the batch photoreactor was characterized by azoxybenzene actinometry. The intensity of incident radiation was found to be a strong function of position inside the reactor. 12 mg L −1 of SMX was completely removed within 10 min of irradiation under UVC photolysis, compared to 30 min under TiO 2 photocatalysis. COD measurement was used as an indication of the mineralization efficiency of both processes and higher COD removal with photocatalysis was shown. After 6 h of reaction with photolysis and photocatalysis, 24% and 87% removal of COD was observed, respectively. Two of the intermediate photo-products were identified as sulfanilic acid and 3-amino-5-methylisoxazole by direct comparison of the HPLC chromatograms of standards to those of treated solutions. Ecotoxicity of treated and untreated solutions of SMX towards Daphnia magna was also investigated. It was found that a 3:1 ratio of sample to standard freshwater and a high initial concentration of 60 mg L −1 of SMX were used to obtain reliable and reproducible results. The photo-products formed during photocatalytic and photolytic processes were shown to be generally more toxic than the parent compound.

Carbon black (CB) nanopowders were obtained by plasma decomposition of methane at various flow rates using inductively coupled thermal plasma torch system of 35 kW. Nitrogen was also introduced in some experiments along with the methane. Using a cylindrical shape reactor the obtained powders were composed mainly of spherical particles, non-uniform in terms of particles size with diameters between 30 and 150 nm. The shape and size of this reactor resulted in the presence of recirculation areas enabling the formation of large CB particles and other secondary volatile compounds. Changing the reactor to a conical geometry resulted in the production of CB powders showing a crystalline and flake-like morphology made of sheets having 6–16 graphitic planes. The conical shape avoids the presence of recirculation areas and promotes the formation of a uniform powder morphology throughout the reactor.

The rate of nitrification within a laboratory-scale Biological Aerated Filtration treatment system at 4 degrees C was investigated during an exposure time of approximately four months (acclimatized experiments). In addition, shock experiments from 20 degrees C to 4 degrees C and from 4 degrees C to 20 degrees C were performed. The acclimatized experiments demonstrated that the exposure time the system remained at low temperature strongly affects the rates of nitrification. Nevertheless, the experiments showed that significant nitrification rates are maintained for up to 115 days at 4 degrees C. The rate of ammonia removal after an exposure time of 115 days at 4 degrees C was shown to be as high as 16% of the rate of removal observed at 20 degrees C. The 20 degrees C to 4 degrees C shock experiment demonstrated a 56% decrease in the rate of ammonia removal. On the other hand, the 4 degrees C to 20 degrees C shock experiment demonstrated an increase in the relative rates of ammonia removal of up to 300% when compared to rates of removal measured after 115 days at 4 degrees C. Thus, although the rates of nitrification have been shown to decrease significantly as a function of exposure time at 4 degrees C, the process has demonstrated important rates of ammonia removal at 4 degrees C for the approximate span of the North American winter.

Methods for characterizing nitrifying bacteria within biofilms are of key importance to understand and optimize the nitrification kinetics of attached growth treatment facilities. In this work, we propose an analytical protocol based upon environmental scanning electron microscopy (ESEM) and confocal laser scanning microscopy (CSLM) in combination with fluorescent in situ hybridization (FISH) to characterize the structure of nitrifying biofilm as it remains attached to the original reactor substratum. This protocol minimizes the loss of mass and distortion of in situ perspective commonly associated with traditionally applied microscopic techniques and thereby enables a more accurate estimation of the nitrifying biomass within biofilm attached to the substratum. The use of ESEM eliminates the destructive preparatory procedures associated with traditional scanning electron microscopy and thus the loss of mass and shrinking of the samples. ESEM is used in this study to evaluate the percent coverage of the substratum with biofilm and the biofilm thickness. CLSM–FISH is used to determine cell counts in the biofilm and to characterize the undisturbed substratum/biofilm interface. By hybridizing and analyzing the nitrifying biofilm using CLSM as it remains attached to the substratum, the loss of material and distortion of in situ perspective associated with the biofilm detachment process is minimized. Moreover, by conducting the CLSM analysis directly on the nitrifying biofilm as it remains attached to the substratum it is shown that cell counts at the substratum/biofilm interface differ significantly from that located above the interface.

A convenient way to synthesize aluminum nanoparticles is to evaporate the metal, direct this vapor into a tubular reactor and quench it with a radial flow of cold gas. The supersaturated vapors nucleate and grow into the desired nanoparticles. For small-scale operations, because of the high temperatures and relatively low flow rates involved, the conditions of operation are usually laminar. As the units are scaled up to higher production rates, the flows become transitional or even fully turbulent. This work reports on the use of a Low Reynolds Number (LRN) turbulent model to simulate this system and its scale up for the synthesis of pure aluminum powders. Coagulation was identified as the dominating mechanism in particle growth for the conditions and scales studied. Scale up with dynamic similitude results in increased residence time which significantly changes the particle properties during scale-up. In scale-up with constant residence time, the flow field regime changes from laminar to turbulent. These...

The wet air oxidation of benzene has been studied in a 1.24 L stainless steel autoclave at a temperature in the range of 190−260 °C. The oxygen partial pressure was varied from 0.69 to 1.72 MPa. The initial C6H6 concentration was 5.63 mmol/L. The influence of the pH was studied, and the main reaction intermediates were determined. It was found that the temperature has a great influence on the wet air oxidation of benzene. The effect of the oxygen partial pressure was significant only at the beginning of the reaction. Decrease of the initial pH of the reaction results in a considerable increase in the benzene degradation rate, especially at the lower temperature. The main intermediates were found to be acetic acid and formic acid.

Silver powders can be produced by the reduction of a silver salt in an aqueous solution. The manipulation of the rates of the reaction allows the control of the properties such as size and size distribution of the produced particles. In the present work, we studied the addition of ethylenediamine tetraacetic acid (EDTA) as a complexation agent to moderate the rate of the reduction of silver cations with hydrazine as the reducing agent. The experiments were carried out in a batch reactor at different concentrations of the reactants. In the absence of EDTA, the reaction between hydrazine and the silver cations is extremely fast. It was found that, in the absence of seeds, the reaction starts by the precipitation of the free silver ions followed by a period where any reduced elemental silver forms sub-micrometer particles by nucleation. The addition of seeds promotes the growth of particles and suppresses nucleation. When the concentration seeds are greater than 5.4 x 10 -1 mM, no nucleation is apparent. This allows the determination of the reaction rate between hydrazine and silver cations. At 20 °C, the empirical rate law for the reduction of silver was r Ag = 9.35 [Ag] 1.3 [N 2 H 4 ] 0.7 [EDTA] -1.1 in mmol of Ag/L-min.

A two-dimensional axi-symmetric turbulent model of a particle generator with radial injection of a quenching gas was developed to gain a better understanding of the particle forming process. The model uses the Jones–Launder Low Reynolds Number (LRN) Turbulence model to calculate the fluid flow field. The evolution of the particle size distribution is calculated using the method of moments (MOM) assuming a lognormal particle size distribution and no coagulation when the gas temperature is lower than the melting point of Aluminium. The model provides information on distributions of flow, temperature and concentration fields and particle generation within the reactor as well as mixing cup data as a function of reactor length. The effect of the injection flow rate on the characteristics of the final product was studied. The model can be used to study laminar, turbulent and systems where both regimes are present.

EDTA forms a strong complex with a variety of metals. These metal−EDTA complexes are very stable and often inert to conventional biological or chemical treatment methods. Photocatalytic oxidation has shown promising results in oxidizing metal−EDTA complexes. Thus, the objective of this research was to investigate the photocatalytic oxidation of the Ni−EDTA complex. For this investigation, experiments were carried out in a semi-batch reactor equipped with up to four UV lamps (with light intensities varying from 1.6 × 10-6 to 6.4 × 10-6 einstein/min). Preliminary studies demonstrated that the photocatalytic degradation of Ni−EDTA could not take place in the absence of a source of light energy, TiO2, and oxygen. From degradation experiments, it was found that the light energy and catalyst concentration limit the production of the electron/hole pair and thus the degradation of Ni−EDTA. The effect of the initial Ni−EDTA concentration was also investigated. The results display Langmuir−Hinshelwood type kinetic ...

In industrial wet etching reactors, the fluid contacts the substrate surface as a spray of flowing stream, thus introducing mass-transfer resistances to the reaction rate. The etching of gallium arsenide in H2O2-NH4OH-H2O solutions was studied using an open-channel flow reactor to simulate the industrial conditions. The etch rate was always lower than that obtained under kinetic control, and the dependence of etch rate on H2O2 concentration shifted closer to first order. From the calculation of the ratio of rate constant to mass-transfer coefficient, the reaction-rate and mass-transfer resistances were both significant in this system. When the mass-transfer coefficient was calculated from equations for flow past a flat plate, the prediction of etch rate was good, particularly when the starting length for velocity boundary layer development ahead of concentration boundary layer development was taken into account. Another approach for the calculation of mass-transfer coefficient, based on the assumptions fo...

The nucleation and growth of an ammonium chloride aerosol starting from gaseous ammonia and hydrogen chloride was investigated experimentally and with the use of a mathematical model. The reactor was composed of 2 opposed jets perpendicular to a main stream and was operated under laminar/transition flow conditions. The reactants were segregated when they entered the reactor. The parameter observed was the particle size distribution of the aerosol described by its moments. Considerable scatter in the experimental results complicated their analysis, but some important trends could be identified. The model results were strongly affected by the fluid mechanics model, which influenced the predicted mixing inside the reactor. This work shows the importance of fluid mixing in controlling the aerosol size distribution.

The mixing of a tracer in a reactor composed of two opposed jets perpendicular to a main stream is studied both experimentally and theoretically. For the experimental conditions, the gas flow was in a transitional state between laminar and turbulent due to the interaction of the mixed streams. Both the measurements and the mathematical model focus on the fluid flow (gas velocity) and the dispersion of a nonreacting species (tracer concentration) injected through one of the reactor streams. Two models are tested against experimental data: a laminar flow model (giving a time-dependent solution) and a standard k-ϵ turbulent flow model. These two models give quite different results, both qualitatively and quantitatively. This study demonstrates the importance of the selection of an appropriate mathematical model and computational domain.

The residence time distribution (RTD) was obtained in a tubular reactor with mean residence times of the order of milliseconds by using an infrared laser absorption technique. The reactor was operated at room conditions with a nitrogen or helium gas flow, the tracer used was methane. The fast response of the measuring device allowed a qualitative analysis of the micromixing in the flow. An axial dispersion model was used to describe the RTD of the reactor. It was found that the values for the dispersion coefficient were strongly influenced by the radial velocity profile in the reactor.

GaAs, a compound semiconductor commonly used in optoelectronic devices, is often subjected to wet-etching techniques during microelectronic device manufacture. In this work we investigated the wet etching of GaAs by H2O2−NH4OH−H2O solutions using a batch stirred-tank reactor and determined the intrinsic kinetics of the dissolution reaction. Increasing the NH4OH content produced a constant rate above a minimum concentration. The reaction rate was found, in the presence of excess NH4OH, to fit a rate equation r = k[H2O2]0.75 at 15, 25, and 40 °C with an activation energy of 33.7 kJ/mol. Using NaOH instead of NH4OH resulted in greatly reduced reaction rates, and it was concluded that the presence of the ammonium ion increases the rate by forming soluble compounds with oxidized species of Ga and As. Analysis of the surface by X-ray photon spectroscopy confirmed that samples etched in solutions containing NH4OH had considerably less oxide content on the surface than that etched in H2O2−H2O only. NH4OH does not...

The reduction of sulfur dioxide by methane for the production of elemental sulfur using two hydrodesulfuriz-ation catalysts was studied. Oxides of cobalt-molybdenum and molybdenum alone supported on γ-alumina were employed. The reactions were carried out in a quartz reactor at 650°C and 750°C and at molar feed ratios (SO2/CH4 varying between 0.50 to 2.50. The physicochemical stale of the catalysts was examined by SEM, BET and X-ray diffraction. Molybdenum oxide was converted to sulphide after the chemical reaction. The cobalt molybdenum catalyst was found to be the more active of the two; however, the molybdenum catalyst exhibited higher elemental sulphur yield (99%). Side reactions resulted in the formation of H2S, COS, CO, and elemental carbon. The production of these is minimized by operating at molar feed ratios greater than 1 and low temperature. The production of H2S is favoured over COS below 700°C.

An experimental investigation of the effect of sulphidation method of supported molybdenum catalysts used in the reduction of SO2 with Ch4 was carried out. Two sulphidation methods, one using H2S and the other using a mixture of SO2/CH4, are compared. The methods are evalauted with respect to molybdenum retention, extent of molybdenum sulphidation, and catalytic activity. Mo/Al2O3 catalysts sulphided with H2S are superior to those sulphided under SO2 and CH4 reaction conditions. Although complete sulphidation is never achieved in either of the two cases, the higher activity found with H2S-sulphided catalysts is attributed to a higher degree of molybdenum sulphidation resulting in a higher MoS2 content. The 15% Mo/Al2O3 catalyst sulphided with H2S at 600°C showed the highest activity and had the highest MoS2 content. On a etudie de maniere experimentale l'effet de la methode de sulfuration sur des catalyseurs de molybdene supportes dans la reduction du SO2 avec du CH4. Deux methodes de sulfuration, l'une utilisant du H2S, l'autre un melange de SO2/CH4, sont comparees. Les methodes sont evaluees par rapport a la retention de molybdene, l'importance de la sulfuration de molybdene et l'activite catalytique. Les catalyseurs Mo/AlO3 sulfures par le H2S sont superieurs aux catalyseurs sulfures dans des conditions de reaction du SO2 et du CH4. Bien que la sulfuration complete ne soit jamais realisee dans aucun des cas, l'activite plus intense observee avec les catalyseurs sulfures par le H2S est attribuee a un degre plus eleve de sulfuration de molybdene qui donne une plus forte teneur en MoS2. Le catalyseur a 15% de Mo/Al2O3 sulfure par le H2S a 600°C montre la plus forte activite et affiche egalement la plus forte teneur en MoS2.

Wet etching is commonly used to produce patterned copper films for printed circuit boards and semiconductor devices. The investigation of copper etching by FeCl 3 -HCl solutions in a batch stirred-tank reactor was undertaken to determine the intrinsic reaction kinetics. The variation of the etch rate with FeCl 3 concentration was linear at low concentrations and gave first-order rate constants of 0.2039, 0.3083, and 0.3362 mg Cu-kg H 2 O/cm 2 s.mol FeCl 3 at 30, 40, and 50 o C, respectively. At approximately 2 mol/kg the etch rate reached a maximum. Etch rates obtained with 0.85 and 2 mol/L HCI over the range of FeCl 3 concentration were similar. The etch rate was substantially reduced with the use of Fe(NO 3 ) 3 -HNO 3 solutions and increased uniformly as the chloride content of the solution was increased. Concentrations of the chloro complexes of the iron(III) ion were computed and showed that FeCl 2 + and FeCl 3 0 are the principal species present in the etchants studied. The etch rate was found to vary linearly with FeCl 2 + concentration at low (

Proton Exchange Membrane fuel cells (PEMFCs) have two major hurdles to overcome before they may be commercially viable: cost and operating life. Platinum (Pt) catalyst represents the bulk of the PEMFC cost and is in finite supply, but functionalized carbon nanomaterials have been identified as potential replacements for Pt cathode catalyst. This work's objective is to produce graphene nanoflakes (GNFs) and dope them with nitrogen in pyridinic sites through a second treatment step. An inductively-coupled thermal plasma (ICP) is used to dissociate methane at very high temperatures, with GNF nucleation commencing shortly after by way of rapid quenching. In a post-treatment, nitrogen doping occurs by manipulating plasma conditions and nitrogen precursor selection. Nitrogen doping up to 33.4 at.% has been demonstrated which, to our knowledge, more than doubles the largest reported amount.

Summary form only given. This project relates to the creation of a specific carbon structure for the replacement of Pt catalyst by a non-noble metal such as Fe functionalized on the carbon support1. Pt-nanoparticles are typically used as catalyst materials in a large series of applications, for example in the development of polymer electrolyte membrane fuel cells (PEM-FC) as electrical energy sources for the car industry. One main limiting factor in the demand scale up is the availability and increasing price of Pt. Iron atoms dispersed at the atomic level directly on carbon nanoparticles using nitrogen coordination mimicking the blood structure proved recently to have activities that can rival Pt-based catalyst; the stability of this complex however is lacking and high crystallinity of the support structure proved to strongly improve this parameter.

The continuous pyrolysis of CANMET coprocessing residue in argon/hydrogen plasma was studied for the temperature range 2700 to 3670 K using an induction plasma torch. Hydrogen was injected into the argon plasma tailflame at molar concentrations ranging from 0 to 23 %. The residue was continuously fed in liquid form to a laboratory-scale reactor specially built for the study. The residue flow rate ranged from 6 to 9 g/min. A maximum of 10% of the residue pyrolysed with up to 90 % conversion to gaseous hydrocarbons. The rate of residue pyrolysis and the rate of formation of the gaseous products were found to be strongly dependent on the rate of heat transfer at the residue surface. The only gaseous products detected were acetylene, ethylene and methane. Some soot was produced, but no liquid hydrocarbons were detected. On a etudie la pyrolyse continue du residu de cotraitement CANMET dans un plasma argon-hydrogenea des temperatures variant de 2700 a 3670 K a l'aide d'un chalumeau a plasma d'induction. L'hydrogene a ete inject6 dans la flamme du plasmades concentrations a molaires comprises entre 0 et 23 %. Le residu a ete ajoute en continu sous forme liquide au reacteur a l'echelle de laboratoire conp specialement pour cette etude. Le debit du residu varie de 6 a 9 g/min. Dix p. 100 au maximum de residu est pyrolyse, la conversion en hydrocarbures gazeux pouvant atteindre 90 %. On a trouve que la vitesse de pyrolyse de residu et la vitesse de formation des produits gazeux dependaient fortement de la cinetique du transfert de matiere a la surface du residu. Les seuls produits gazeux detectes sont I'acetyene, l'Cthylhe et le methane. De la suie est produite, mais aucun hydrocarbure liquide n'a ete detecte.

This paper reports on pitch-like vacuum-distilled residue from the CANMET coprocessing process that was treated in a stationary particle reactor with argon/hydrogen plasmas. The production of light, unsaturated hydrocarbons was optimized as a function of the average plasma temperature, composition, and residence time. The unconverted residue was characterized in terms of its elemental and mineralogical content. In pure argon plasma, the conversion to acetylene was about 14% and did not vary appreciably with temperature; other hydrocarbons were detected only in trace quantities. In argon/hydrogen plasmas the maximum conversion to acetylene and ethylene (25%) was attained between 2900 and 3400 K. Large quantities of soot were produced, but no liquid hydrocarbons were detected. Sulfur was fixed in the unconverted residue by the reduction of calcium sulfate to calcium sulfide.

This paper on an experimental investigation of the reduction of SO{sub 2} with CH{sub 4} using molybdenum sulfide supported on alumina as a catalyst that was carried out. Three molybdenum loadings of 5, 10, and 15% were used. In addition, a catalyst which contained cobalt (5% Co-15% Mo/Al{sub 2}O{sub 3}) was evaluated. The evaluations were based on the activity as well as the yields of sulfur and carbon dioxide. Experiments were carried out at temperatures ranging from 650 to 725{degrees}C and inlet molar feed ratios of SO{sub 2} to CH{sub 4} of 1.0 and 2.0. The 5 and 10% molybdenum loadings showed similar activities and yields to each other. The catalyst containing 15% molybdenum had the highest activity and yields. All catalysts tested were more effective than alumina itself. THe activity of the 15% Mo/Al{sub 2}O{sub 3} catalyst was 1.5-2 times that of alumina. This catalyst was stable under all reaction conditions. The addition of cobalt reduced the activity by 20%. In order to minimize the production of undesired by-products, the reaction temperature should be less than 700{degrees}C.