CH4 O2 Research Articles

Thermal Evolution of the Structure and Activity of Rh Overlayer Catalysts Prepared by Pulsed Arc-Plasma Deposition

Nanometric Rh overlayers were formed on Fe–Cr–Al stainless steel (SUS) foils by pulsed cathodic arc-plasma (AP) technique to investigate the thermal evolution of the structure and catalytic activity for stoichiometric NO–CO–C3H6–O2 reaction. As-prepared Rh overlayer catalysts (Rh/SUS) with 2000–8000 AP pulsing showed steep light-off of NO, CO and C3H6 at around 250 °C and their conversions soon reached to almost 100%. After thermal aging at 900 °C in H2O/air, however, the catalytic activity was decreased to the different extent depending on the number of AP pulsing. The most significant deactivation was observed for the smallest numbers of AP pulsing (2000), because Al in the foil was oxidized during the aging to form a passivation layer of α-Al2O3, which covered the surface of the foil and decreased the surface concentration of Rh. To overcome this deactivation, the Rh overlayer was formed by AP after preheating the foil at 1000 °C in air. This modified preparation process enables the deposition of Rh overlayer on the highly crystalline α-Al2O3 layer at the surface of the foil, which is found to be much more stable against thermal deactivation.

Characteristic Chemical Time Scale Analysis of a Partial Oxidation Flame in Hot Syngas Coflow

Characteristic chemical time scale analysis plays a key role in the understanding of turbulence–chemistry interaction in turbulent combustion research and is also an important basis for the selection or development of combustion models in turbulent combustion modeling. A new method named main direction identification (MDID) was developed based on the modification of the CTS-ID (chemical time scale identification) method to achieve the function of identifying the characteristic time scale. Direction weight factor combined with mole fraction limit were used as a criterion in MDID to determine the characteristic time scale. MDID was applied to study characteristic chemical time scales of a CH4–O2 inverse diffusion flame in hot syngas coflow, which is a model flame developed before to study the combustion process in partial oxidation reformers. Results show that the chemical time scale given by the MDID method is about 10–5 s in the combustion area and 10–2 s in the reforming area. The main reaction pathway w...

3D-Hierarchical porous nickel sculptured by a simple redox process and its application in high-performance supercapacitors

3D-Hierarchical micron porous nickel foam was created using a simple redox process in a CH4–O2 gas mixture at high temperatures. This process is simple and cost effective, avoiding the use of sacrificial materials or templates.

An attempt to stabilize supported Ru catalysts against oxidative volatilization

Ru/Al2O3 is an active catalyst for the stoichiometric NO–CO–C3H6–O2 reaction, whereas >90% of the loaded Ru was volatized during thermal ageing in airflow at 1000°C for 100h, resulting in considerable catalyst deactivation. Using α-Fe2O3 as support, the Ru volatilization was suppressed to a significant extent, because Ru oxide was stabilized by dissolving into Fe2O3 to form a solid solution. Nevertheless, this metal-support interaction decreased the Ru concentration on the catalyst surface, thus leading to another catalyst deactivation route. The catalytic activity can be regenerated by applying H2-reduction treatment to the aged Ru/Fe2O3 catalyst.

PRODUKSI GAS METANA DARI PENGOLAHAN SAMPAH PERKOTAAN DENGAN SISTEM SEL

Waste to energy now become one of the technology solution that is in many developed countries, in an effort to reduce greenhouse gas emissions from waste. Urban organic waste is a potential source of greenhouse gases. Methane gas is an energy source that can be used as fuel. It is difficult to find land for Landfill alocation in the major cities and often becomes a difficult social problem. Structured Landfill Cell is used to treat the waste at the landfill, with the aim to use land more scalable, easier waste management and control, better sanitation, better water control leachate and gas produced can bemanaged optimally and compost can be utilized with the production and quality control.This new system was first used in Indonesia by PT Navigats Organics Energy Indonesia in landfill Suwung, Denpasar, Bali. There are 5 cells already built in Suwung and two of cells have been filled with garbage. Each cell contains 12,000 m3 soliswaste. Observations carried out on gas productivity of two cells that have been filled, with a dry treatment on cell 1 (dry cell) and a wet treatment in cell 2 (wet cell). The observed gas is CH4, CO2,and O2 as the main parameters, with the addition parameters are CO and H2S. The instrument used is the GA 2000 Plus. Observations of two cells made for 4 months, with the content of CH4 around 40 to 50% in the first month and gradually decreased to reach 18 to 25% in the fourth month. Carbondioxyde going up and down following condition of CH4 and its value ranges between 16 and 28%. Oxygen consentration around 2 to 14%.For keeping engine performance the consentration of methane should more than 28%and O2 content lower than 6%. Cell with watering will temporarily reduce CH4 and CO2 and O2 increase, but it is slowly rising again. Carbonmonoside values tend to increase with age garbage (10 sd 350 ppm), whereas irregular H2S values ranging 0 up to 24 ppm, allegedly associated with the low protein content in the trash. Sewage treatment system is proven to increase CH4 gas, yet still needed modifications of structure and the gas collector pipe system so that productivity can be improved.Key Words : Solidwaste, Metana, Cell System

Selective Production of Carbon Monoxide via Methane Oxychlorination over Vanadyl Pyrophosphate

AbstractA catalytic process is demonstrated for the selective conversion of methane into carbon monoxide via oxychlorination chemistry. The process involves addition of HCl to a CH4–O2 feed to facilitate C−H bond activation under mild conditions, leading to the formation of chloromethanes, CH3Cl and CH2Cl2. The latter are oxidized in situ over the same catalyst, yielding CO and recycling HCl. A material exhibiting chlorine evolution by HCl oxidation, high activity to oxidize chloromethanes into CO, and no ability to oxidize CO, is therefore essential to accomplish this target. Following these design criteria, vanadyl pyrophosphate (VPO) was identified as an outstanding catalyst, exhibiting a CO yield up to approximately 35 % at 96 % selectivity and stable behavior. These findings constitute a basis for the development of a process enabling the on‐site valorization of stranded natural‐gas reserves using CO as a highly versatile platform molecule.

An experimental study of [formula omitted] dilution effects on [formula omitted]–[formula omitted] flame stabilization characteristics in a two-section porous medium

N2 dilution effects on CH4–O2 flame stabilization in a two-section porous medium burner were experimentally investigated for its potential application to the destruction of highly N2-diluted CF4. The burner was made up of two axially-stacked silicon carbide foams having different pore sizes. Various flame behaviors, such as stable flame, flashback, blowout, extinction and transient flames, were observed and, for the stable flame, temperature distributions and exhaust gas emissions were measured. Results showed that the flame was only stable in a belt-like region on the domain of fuel flow rate and oxygen concentration. The region boundaries, termed as O2-enriched and O2-deficient limits, were determined for various equivalence ratios. It was found that our burner configuration was able to sustain the submerged combustion even under the N2 dilution amounting to at least 10.4 times of CH4 flow rate. In addition, temperature measurements showed that the stable flames could have their peak temperatures higher than 1600°C, which is known to be a thermal destruction temperature of CF4. These results may indicate that porous media burners can practically applied in destructing highly N2-diluted CF4 with a reduced fuel consumption.

Effect of Rare Earth Additives on the Catalytic Performance of Rh/ZrO2 Three-Way Catalyst

The catalytic activity of Rh/ZrO2 for NO–CO–C3H6–O2 reaction under stoichiometric conditions was significantly improved by addition of rare earth. Among the catalysts tested here, Y-doped Rh/ZrO2 (Rh/Y/ZrO2) showed the highest three-way catalytic performance. The catalytic activity of rare earth-doped Rh/ZrO2 was strongly related to the Rh dispersion, which was improved by using rare earth-doped ZrO2 with large amount of surface basic sites. The role of rare earth additive was considered to control the surface basicity of ZrO2 and stabilize the Rh species in high dispersion state. Y-stabilized ZrO2 was found to be effective support for Rh catalyst in NO–CO–C3H6–O2 reaction. The site geometry and the surface electric state of Rh can be altered by interacting with Y2O3, leading us to consideration that the presence of suitable Rh–Y2O3 interaction is responsible for high NO reduction activity of Rh/Y–ZrO2.

Ethylene Epoxidation Catalyzed by a Cu38 Nanoparticle: A Computational Study

The reaction mechanisms of ethylene epoxidation on a Cu38 nanoparticle have been investigated by the first-principles calculations. The adsorption of C2H4 and O2 as well as the coadsorption of O2–C2H4 were also examined. Our results show that C2H4 and O2 are likely to adsorb on the top (T) and hollow (H) sites with adsorption energies of −0.51 and −2.19 eV, respectively. The climbing image nudged elastic band method was carried out to illustrate the potential energy profile of the ethylene oxidation reaction. Both epoxide and acetaldehyde are formed by the Langmuir–Hinshelwood mechanism. The overall reaction for the formation of epoxide is predicted to be exothermic by 3.20–3.56 eV whereas it is exothermic by 3.83–4.31 eV for the formation of acetaldehyde. The Cu38 nanoparticle exhibits higher catalytic properties and selectivity for the epoxide formation than the Au38 nanoparticle.

Ni(Co)–Gd0.1Ti0.1Zr0.1Ce0.7O2 mesoporous materials in partial oxidation and dry reforming of methane into synthesis gas

Mesoporous Ni(Co)–Gd0.1Ti0.1Zr0.1Ce0.7O2 catalysts were synthesized by a simple co-precipitation method with sonication. It was shown that Ni-, Co- and Ni–Co- (Ni/Co=1/1mol.) containing catalysts demonstrate high activity and selectivity in synthesis gas production by CH4–O2 and CH4–CO2 reforming at 850–900°C. To trace the compositional and structural evolution of the catalysts XRD, SEM, TEM, BET–BJH methods were used. It was established that initial mesoporous structure of catalysts undergoes transformation after partial oxidation and dry reforming of methane, but these systems demonstrate stable conversion and selectivity during catalytic test. It was revealed that Co- and Ni–Co-containing system unexpectedly were more active in partial oxidation of methane than Ni-containing sample, whereas Ni-containing system was more active in dry reforming of methane. These results may be connected to specific influence of ceria-based support on results of methane reforming.

Influences of cation and anion substitutions on oxidative coupling of methane over hydroxyapatite catalysts

Lead substituted hydroxyapatite (Pb-HAP) has been an active catalyst for oxidative coupling of methane (OCM) reactions. CO32− substituted HAP (HAP-CO3) has showed enhanced oxide ion conductivity than bare HAP in high temperature solid oxide fuel cells. Substitutions for both cations and anions in HAP structure (Pb-HAP-CO3) are promising to integrate the catalytic property of Pb-HAP and oxide ion conductive property of HAP-CO3 into one apatite-based ceramic material that can be manufactured into membrane reactors for possessing CH4 activation and O2 permeation capabilities for efficient OCM reactions. In this work, the effects of substitutions for both cation (Pb2+) and anion (CO32−) in HAP structure on OCM reactions were studied. The composition and physicochemical properties of HAP catalysts were changed by the cation and anion substitutions, respectively, and as consequences, they influenced the catalytic performances of HAP structure in OCM reactions. The selectivity to C2 (ethylene and ethane) products increased in the order of HAP-CO3<HAP<Pb-HAP-CO3<Pb-HAP, while Pb-HAP-CO3 showed the best stability and comparable C2 yield (under optimized reaction conditions) to Pb-HAP catalyst. Under different reaction temperature and/or CH4/O2 ratio in the OCM reactions, the CH4 conversion and C2 or COx (CO and CO2) selectivity showed a strong dependence on the composition of HAP-based catalysts. The present study forms a basis for understanding of the correlations between the composition, structure, and catalytic performance of HAP and other apatite structured catalysts, which are potential membrane materials for OCM reactions in membrane reactors.

Characterization of initiator dynamics in a rotating detonation combustor

The performance of a tangentially-injecting initiator tube of a rotating detonation combustor (RDC) is assessed for a range of initiator conditions. Two initiator fuels are evaluated for a range of RDC channel pressures, and channel widths to determine the effect on the blast wave generated by the initiator tube. Blast wave trajectories exhibit asymmetric bias in the initiator injection (forward) direction. The energy content is estimated by fitting the blast wave trajectory to a theoretical model for blast propagation. Maximum energy deposition is achieved for a rich H2–O2 initiator mixture (ϕ>2), which provides twice the energy deposition of the highest performing C2H4–O2 mixture. The highest recorded initiator energy deposition is an order of magnitude smaller than the critical value to directly initiate detonation in a stoichiometric H2–air mixture, precluding direct initiation for this configuration. RDC initiation behavior is assessed for a near-stoichiometric H2–air mixture using the highest-performing initiator tube setting, and verifies the absence of direct initiation. A complex, transitory period follows the subcritical initiation event and culminates in stable detonation rotation within several milliseconds.

Calculations of the geometry and binding energy of the van der Waals complex of ethylene with oxygen C2H4–O2

Quantum chemistry methods are used to analyze in detail the structure of the van der Waals complex of ethylene with oxygen C2H4–O2, and binding energies for stable configurations of the complex are calculated. The calculations are carried out by the MP2 method using the 6-311++G(2d,2p) and aug-cc-pVnZ (n = 2, 3, 4) basis sets. It is demonstrated that the most stable structure of the van der Waals complex of ethylene with oxygen is a structure with C2v symmetry, where the oxygen and ethylene molecules are located parallel and lie in the same plane. The calculation of the binding energy for this structure using the aug-cc-pVnZ (n = 2, 3, 4) basis sets with the extrapolation of results to the infinite basis set limit (n→∞) gives a value of 206 cm–1.

Rh Supported on LaPO4/SiO2 Nanocomposites as Thermally Stable Catalysts for TWC Applications

Hydrothermally synthesized LaPO4/SiO2 nanocomposites were investigated as thermally stable support materials for Rh catalysts. The nanocomposites were composed of macroporous SiO2 and highly dispersed columnar LaPO4 crystallites of approximately 20 nm in thickness and 100 nm in length, the surface of which anchored Rh nanoparticles via Rh–O–P interfacial bonding. The microstructure was useful to prevent agglomeration and sintering of LaPO4 during high-temperature thermal aging under both oxidizing and reducing atmospheres. The Rh catalyst supported on the LaPO4/SiO2 composite exhibited higher catalytic activities for simulated NO–CO–C3H6–O2 reactions over a wide Rh loading range (0.01–0.4 wt%), compared to those of Rh catalysts supported on the individual components (LaPO4 and SiO2), and on ZrO2, which is widely used as a support for Rh in commercial three-way catalysts. Enhanced catalytic activities for elementary CO–O2, CO–H2O, and CO–NO reactions were achieved while maintaining the activity toward C3H6 as an advanced feature of phosphate supports.

Surface Properties of Rh/AlPO4 Catalyst Providing High Resistance to Sulfur and Phosphorus Poisoning

A rhodium catalyst supported on AlPO4 exhibited a much higher resistance to sulfur and phosphorus poisoning compared with a reference catalyst (Rh/Al2O3). The acidic surface of AlPO4 was effective in preventing the adsorption of sulfur oxides (SO2), whereas Lewis acid/base sites on Al2O3 favored SO2 adsorption followed by the formation of sulfite, leading to deterioration of the activity of Rh/Al2O3 for the model NO–CO–C3H6–O2 reaction. Similarly, the AlPO4 support suppressed the extent of phosphorus poisoning caused by dimethylphosphite (DMP) (CH3O)2POH, which was used as a model phosphorus source. A greater amount of inactive phosphate overlayers were deposited from the gas feed containing DMP and O2 on Rh/Al2O3 than Rh/AlPO4 because of the reaction between P2O5 vapors and Al2O3. Consequently, the active Rh surface was covered to a greater extent for Rh/Al2O3 than Rh/AlPO4.

GdxZryTizCe1–x–y–zO2 mesoporous catalysts for oxidation reactions

GdxZryTizCe1–x–y–zO2 solid solutions with a crystallite size of 5–10nm have been prepared by the sonochemical method from inorganic salts. Ceria-based materials exhibited a mesoporous structure with diameter of 2–10nm. The activity of the solid solution in the oxidation of carbon monoxide is determined by the flow method within a temperature range of 20–500°C at atmospheric pressure for the following gas mixture composition, vol.%: CO – 4.2; O2 – 9.6; N2 – balance or CO – 1.8; CH4 – 1.6; O2 – 9.6; N2 – balance. It was shown that the temperature of full conversion of CO was 250–270°C for CO–O2–N2 mixture and 380–420°C for CO–CH4–O2–N2 mixture without methane oxidation.

Anode-supported single-chamber solid oxide fuel cell based on cobalt-free composite cathode of Nd0.5Sr0.5Fe0.8Cu0.2O3−δ–Sm0.2Ce0.8O1.9 at intermediate temperatures

As a candidate of cathode material of single-chamber solid oxide fuel cell (SC-SOFC), cobalt-free mixed ionic electronic conductor (MIEC) Nd0.5Sr0.5Fe0.8Cu0.2O3−δ (NSFCu) is synthesized by sol–gel method with ethylene diamine tetraacetic acid and citric acid as co-complexing agents. The XRD shows NSFCu is stable after CO2 treatment and chemical compatible with SDC at high temperatures. CO2-TPD (CO2-temperature programmed desorption) demonstrates both CO2 adsorption and desorption phenomenon on NSFCu surface. However, the polarization resistances (Rp) of NSFCu and SDC (10:4 in weight) composite electrodes showed no decay in 5% CO2. Single cell using N2–O2–CH4 mixed gas (CH4 to O2 ratio = 1.5) as fuel shows maximum power density of 635 mW cm−2 at 700 °C. These results suggest that NSFCu-SDC is a promising composite cathode material for application in single-chamber solid oxide fuel cell.

Deformable wall effects on the detonation of combustible gas mixture in a thin-walled tube

We present a multi-material numerical investigation on the propagation of combustible gas mixture detonation in thin-walled metal tubes. We use experimentally tuned one step Arrhenius chemical reaction and an ideal gas equation of state (EOS) to describe the stoichiometric H2–O2 and C2H4–O2 detonations. Purely plastic deformations of copper and stainless steel tubes are modeled by the Mie–Gruneisen EOS and the Johnson–Cook strength model. To precisely track the interface motion between the detonating gas and the deforming wall, we use the hybrid particle level-sets within the ghost fluid framework. The calculated results are compared with the theory and validated against the experimental data. The results on thin-walled tube response explain the process of generation and subsequent interaction of the expansion waves along the tube wall that may further complicate the detonative loading conditions within the tube.

Windrow composting mitigated CH4 emissions: characterization of methanogenic and methanotrophic communities in manure management.

With increasing livestock breeding, methane (CH4 ) emissions from manure management will increasingly contribute more to atmospheric CH4 concentration. The dynamics of methanogens and methanotrophs have not yet been studied in the manure environment. The current study combines surface CH4 emissions with methanogenic and methanotrophic community analyses from two management practices, windrow composting (WCOM) and solid storage (SSTO). Our results showed that there was an c. 50% reduction of CH4 emissions with WCOM compared with SSTO over a 50-day period. A sharp decrease in the quantities of both methanogens and methanotrophs in WCOM suggested that CH4 mitigation was mainly due to decreased CH4 production rather than increased CH4 oxidation. Pyrosequencing analysis demonstrated that aeration caused a clear shift of dominant methanogens in the manure, with specifically a significant decrease in Methanosarcina and increase in Methanobrevibacter. The composition of methanogenic community was influenced by manure management and regulated CH4 production. A sharp increase in the quantity of methanotrophs in SSTO suggested that microbial CH4 oxidation is an important sink for the CH4 produced. The increased abundance of Methylococcaceae in SSTO suggested that Type I methanotrophs have an advantage in CH4 oxidation in occupying niches under low CH4 and high O2 conditions.

Influence of steam dilution on the ignition of hydrogen, syngas and natural gas blends at elevated pressures

This paper presents the influence of steam dilution on the autoignition behaviour of hydrogen, carbon monoxide, syngas, methane, and natural gas mixtures under gas turbine-relevant conditions. Rapid compression machine experiments were performed for fuel/air mixtures at equivalence ratios of 0.5, 1.0, and 2.0, in the temperature range 895–1140K for the H2 and CO mixtures and 730–1060K for the natural gas mixtures and at pressures of 10 and 30bar. Shock-tube experiments were performed for CH4–O2–Argon mixtures with and without H2O addition, highly diluted in argon (98% by vol.). The parameters were varied using an L9 Taguchi matrix for equivalence ratios of 0.5, 1.0, and 2.0; pressures of 1.6, 11, and 30atm; and water contents of 0%, 10%, and 30% of the fuel by volume. It was found that significant changes in the thermal properties of the mixtures affect the reactivity, whereas no chemical effect of the steam addition was observed for the majority of the mixtures investigated. Only mixtures of pure carbon monoxide were strongly influenced by water addition. In this case, the presence of water in the mixture allows the formation of relatively reactive ȮH radicals which enhances the possible oxidation chemistry of carbon monoxide leading to a greater observed reactivity of CO in the presence of water.