Hydrogen formation from a real biogas using electrochemical cell with gadolinium-doped ceria porous electrolyte

The electrochemical cell consisting of a gadolinium-doped ceria (GDC, Ce_0.9Gd_0.1O_1.95) porous electrolyte, Ni–GDC cathode and Ru–GDC anode was applied for the dry-reforming (CH₄+CO₂→2H₂+2CO) of a real biogas (CH₄ 60.0%, CO₂ 37.5%, N₂ 2.5%) produced from waste sweet potato. The composition of the supplied gas was adjusted to CH₄/CO₂=1/1 volume ratio. The supplied gas changed continuously into a H₂–CO mixed fuel with H₂/CO=1/0.949–1/1.312 vol ratios at 800 °C for 24 h under the applied voltage of 1–2 V. The yield of the mixed fuel was higher than 80%. This dry-reforming reaction was thermodynamically controlled at 800 °C. The application of external voltage assisted the reduction of NiO and the elimination of solid carbon deposited slightly in the cathode. The decrease of heating temperature to 700 °C reduced gradually the fraction of the H₂–CO fuel (61.3–18.6%) within 24 h. Because the Gibbs free energy change was calculated to be negative values at 700–600 °C, the above result at 700–600 °C originated from the gradual deposition of carbon over Ni catalyst through the competitive parallel reactions (CH₄→C+2H₂, 2CO→C+CO₂). The application of external voltage decreased the formation temperature of carbon by the disproportionation of CO gas. At 600 °C, the H₂–CO fuel based on the Faraday's law was produced continuously by the electrochemical reforming of the biogas.     

Pyrolysis of tire powder: influence of operation variables on the composition and yields of gaseous product

The pyrolysis of tire powder was studied experimentally using a specially designed pyrolyzer with high heating rates. The composition and yield of the derived gases and distribution of the pyrolyzed product were determined at temperatures between 500 and 1000 °C under different gas phase residence times. It is found that the gas yield goes up while the char and tar yield decrease with increasing temperature. The gaseous product mainly consists of H₂, CO, CO₂, H₂S and hydrocarbons such as CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈, C₄H₈ and C₄H₆ with a little other hydrocarbon gases. Its heating value is in the range of 20 to 37 MJ/Nm³. Maximum heating value is achieved at a temperature between 700 and 800 °C. The product distribution ratio of gas, tar and char is about 21:44:35 at 800 °C. The gas yield increases with increasing gas residence time when temperature of the residence zone is higher than 700 °C. The gas heating value shows the opposite trend when the temperature is higher than 800 °C. Calcined dolomite and limestone were used to explore their effect on pyrolyzed product distribution and composition of the gaseous product. It is found that both of them affect the product distribution, but the effect on tar cracking is not obvious when the temperature is lower than 900 °C. It is also found that H₂S can be absorbed effectively by using either of them. About 57% sulfur is retained in the char and 6% in the gas phase. The results indicated that high-energy recovery could not be achieved if fuel gas is the only target product. In view of this, multi-use of the pyrolyzed product is highly recommended.     

Steam gasification of apricot stones with olivine and dolomite as downstream catalysts

Apricot stone steam gasification with olivine and dolomite as downstream catalysts had been carried out for the production of hydrogen-rich gas at atmospheric pressure in a fixed-bed reactor. Reaction temperature, S/B (steam/biomass) ratio, particle size of the catalysts, and calcination of the catalyst, etc., have been studied. The results show that the catalytic activities of calcined olivine and dolomite are higher than the natural ones. With calcined dolomite, a H₂ potential yield of 130.9 gH₂/kg biomass (daf.), which is 86.1% of the stoichiometric yield (152 g H₂/kg biomass (daf.)), is obtained at 850 °C and S/B ratio 0.8, and that with calcined olivine at 800 °C and S/B ratio 0.8 is 67.7 g H₂/kg biomass (daf.), 44.5% of the stoichiometric yield. Calcination of catalysts causes the disappearance of (Mg,Fe)SiO₃ phase and the formation of Fe₂O₃ for olivine and eliminates CO₂ and forms CaO–MgO for dolomite, which may be the reason for the difference in the activity. The calcined dolomite becomes very friable and the calcined olivine keeps its good mechanical intensity after calcination and reaction.     

Modulation of selective sites by introduction of N2O,CO2 and H2 as gaseous promoters into the feed during oxidation reactions

Results obtained by adding gaseous promoters (CO₂, N₂O and H₂) into the reaction feed are presented for two different reactions: (i) oxidative dehydrogenation of propane (ODP), and (ii) catalytic combustion of methane (CCM). The ODP is performed on a mixture of NiMoO₄ and CeO₂, by adding 3 vol.% CO₂ into the feed, and on a NiMoO₄/[Si,V]-MCM-41 mesoporous catalyst, in the presence of 1 or 5 vol.% N₂O in the feed. The CCM is carried out (i) on Pd(2 wt.%)/Ce_xZr_1−xO₂ and Pd(2 wt.%)/γ-Al₂O₃ catalysts, on pure CeO₂ and on a mixture of Pd(2 wt.%)/γ-Al₂O₃ and CeO₂ powders, by adding 3 vol.% CO₂ into the feed, and (ii) on a Pd(2 wt.%)/γ-Al₂O₃ catalyst, in the presence of various amounts of H₂ in the feed. It is shown, through all these various examples, that the activity and/or the selectivity of catalysts can be improved by tuning, in a very controlled manner, the oxidation state of active sites via the use of these gaseous promoters.     

Recent progress in Japan on hot gas cleanup of hydrogen chloride, hydrogen sulfide and ammonia in coal-derived fuel gas

The present review paper highlights on the recent progress in Japan on the hot gas cleanup of HCl, H₂S and NH₃ in raw fuel gas for coal-based, combined cycle power generation technologies. It has been shown that NaAlO₂, prepared by mixing Na₂CO₃ solution with Al₂O₃ sol, can reduce HCl in an air-blown gasification gas from the initial 200 ppm to < 1 ppm at 400 °C, and it is tolerable for 200 ppm H₂S. With regard to the removal of H₂S, studies on the stability and durability of ZnFe₂O₄ sorbent in a simulated fuel gas have indicated the presence of an optimal operation temperature from the viewpoint of the suppression of both vaporization of metallic Zn and carbon formation from CO. High-performance TiO₂-supported ZnFe₂O₄, which can decrease 1000 ppm H₂S to < 1 ppm at 450 °C and 1 MPa, has been developed by the homogeneous precipitation method using a mixture of SiO₂ sol and an aqueous solution of Zn and Fe nitrates, followed by mixing with TiO₂. Although this sorbent is regenerable and durable, the sorption ability should be improved in a syngas-rich fuel gas from an O₂-blown gasifier. A novel method to prepare carbon-supported ZnFe₂O₄ and CaFe₂O₄ by impregnating the corresponding nitrate solution with brown coal has been proposed, and the large desulfurization capacity of almost 100% has been achieved in the removal of 4000 ppm H₂S around 450 °C. The present authors have demonstrated that an Australian limonite rich in α-FeOOH is practically feasible as the catalyst material for the decomposition of 2000 ppm NH₃ in a syngas-rich gas of 25 vol.% H₂/50 vol.% CO at 750 °C, because small amounts of H₂O and CO₂ added to the gas can work efficiently for inhibiting carbon deposition from the CO.     

Sinterability,microstructures and electrical properties of Ni/Sm-doped ceria cermet processed with nanometer-sized particles

Ni/Sm-doped ceria (SDC) cermet was prepared from two types of NiO/SDC mixed powders: Type A—Mechanical mixing of NiO and SDC powders of micrometer-sized porous secondary particles containing loosely packed nanometer-sized primary particles. The starting powders were synthesized by calcining the oxalate precursor formed by adding the mixed nitrate solution of Ce and Sm or Ni nitrate solution into oxalic acid solution. Type B—Infiltration of Ni(NO₃)₂ solution into the SDC porous secondary particles subsequently freeze-dried. Type B powder gave denser NiO/SDC secondary particles with higher specific surface area than Type A powder. The above two types powders were sintered in air at 1100–1300 °C and annealed in the H₂/Ar or H₂/H₂O atmosphere at 400–700 °C. Increased NiO content reduced the sinterability of Type A powder but the bulk density of Type B powder compact showed a maximum at 34 vol.% NiO (25 vol.% Ni). Type B cermet was superior to Type A cermet in achieving fine-grained microstructure and a homogeneous distribution of Ni and SDC grains. The electrical resistance of the produced cermet decreased drastically at 15 vol.% Ni for Type B and at 20 vol.% Ni for Type A.     

Flame and radiation characteristics of gas-fired O2/CO2 combustion

This paper presents an experimental study on the flame properties of O₂/CO₂ combustion (oxy-fuel combustion) with focus on the radiation characteristics and the burn-out behaviour. The experiments were carried out in a 100 kWth test unit which facilitates O₂/CO₂ combustion with real flue gas recycle. The tests comprise a reference test in air and two O₂/CO₂ test cases with different recycled feed gas mixture concentrations of O₂ (OF 21 @ 21 vol.% O₂, 79 vol.% CO₂ and OF 27 @ 27 vol.% O₂, 73 vol.% CO₂). In-furnace gas concentration, temperature and total radiation (uni-directional) profiles are presented and discussed. The results show that the fuel burn-out is delayed for the OF 21 case compared to air-fired conditions as a consequence of reduced temperature levels. Instead, the OF 27 case results in more similar combustion behaviour compared to the reference conditions in terms of in-flame temperature and gas concentration levels, but with significantly increased flame radiation intensity. The information obtained from the radiation and temperature profiles show that the flame emissivity for the OF 21 and OF 27 cases both differ from air-fired conditions. The total emissivity and the gas emissivity of the OF 27 and the air-fired environment are discussed by means of an available model. The gas emissivity model shows that the increase in radiation intensity (up to 30%) of the OF 27 flame compared to the air flame can partly, but not solely, be explained by an increased gas emissivity. Hence, the results show that the OF 27 flame yields a higher radiative contribution from in-flame soot compared to the air-fired flame in addition to the known contribution from the elevated CO₂ partial pressure.     

Low Temperature Growth of In2O3 and InN Nanocrystals on Si(111) via Chemical Vapour Deposition Based on the Sublimation of NH4Cl in In

Indium oxide (In₂O₃) nanocrystals (NCs) have been obtained via atmospheric pressure, chemical vapour deposition (APCVD) on Si(111) via the direct oxidation of In with Ar:10% O₂ at 1000 °C but also at temperatures as low as 500 °C by the sublimation of ammonium chloride (NH₄Cl) which is incorporated into the In under a gas flow of nitrogen (N₂). Similarly InN NCs have also been obtained using sublimation of NH₄Cl in a gas flow of NH₃. During oxidation of In under a flow of O₂ the transfer of In into the gas stream is inhibited by the formation of In₂O₃ around the In powder which breaks up only at high temperatures, i.e. T > 900 °C, thereby releasing In into the gas stream which can then react with O₂ leading to a high yield formation of isolated 500 nm In₂O₃ octahedrons but also chains of these nanostructures. No such NCs were obtained by direct oxidation for T _G < 900 °C. The incorporation of NH₄Cl in the In leads to the sublimation of NH₄Cl into NH₃ and HCl at around 338 °C which in turn produces an efficient dispersion and transfer of the whole In into the gas stream of N₂ where it reacts with HCl forming primarily InCl. The latter adsorbs onto the Si(111) where it reacts with H₂O and O₂ leading to the formation of In₂O₃ nanopyramids on Si(111). The rest of the InCl is carried downstream, where it solidifies at lower temperatures, and rapidly breaks down into metallic In upon exposure to H₂O in the air. Upon carrying out the reaction of In with NH₄Cl at 600 °C under NH₃ as opposed to N₂, we obtain InN nanoparticles on Si(111) with an average diameter of 300 nm.     

Hydrogen production via gasification of meat and bone meal in two-stage fixed bed reactor system

Gasification of meat and bone meal followed by thermal cracking of tar was carried out at atmospheric pressure using a two-stage fixed bed reaction system in series. The first stage was used for the gasification and the second stage was used for thermal cracking of tar. In this work, the effects of temperature (650-850 °C) of both stages, equivalence ratio (actual O₂ supply/stoichiometric O₂ required for complete combustion) (0.15-0.3) and the second stage packed bed height (40-100 mm) on the product (char, tar and gas) yield and gas (H₂, CO, CO₂, CH₄, C₂H₄, C₂H₆, C₃H₆, C₃H₈) composition were studied. It was observed that the two-stage process increased hydrogen production from 7.3 to 22.3 vol.% (N₂ free basis) and gas yield from 30.8 to 54.6 wt.% compared to single stage. Temperature and equivalence ratio had significant effects on the hydrogen production and product distribution. It was observed that higher gasification (850 °C) and cracking (850 °C) reaction temperatures were favorable for higher gas yield of 52.2 wt.% at packed bed height of 60 mm and equivalence ratio of 0.2. The residence time of tar and product gases was varied by varying the packed bed height of second stage. The tar yield decreased from 18.6 wt.% to 14.2 wt.% and that of gas increased from 50.6 wt.% to 54.6 wt.% by changing the packed bed height of second stage from 40 to 100 mm while the gross heating value (GHV) of the product gas remained almost constant (16.2-16.5 MJ/m³).     

Characteristics of hemicellulose,cellulose and lignin pyrolysis

The pyrolysis characteristics of three main components (hemicellulose, cellulose and lignin) of biomass were investigated using, respectively, a thermogravimetric analyzer (TGA) with differential scanning calorimetry (DSC) detector and a pack bed. The releasing of main gas products from biomass pyrolysis in TGA was on-line measured using Fourier transform infrared (FTIR) spectroscopy. In thermal analysis, the pyrolysis of hemicellulose and cellulose occurred quickly, with the weight loss of hemicellulose mainly happened at 220–315 °C and that of cellulose at 315–400 °C. However, lignin was more difficult to decompose, as its weight loss happened in a wide temperature range (from 160 to 900 °C) and the generated solid residue was very high (∼40 wt.%). From the viewpoint of energy consumption in the course of pyrolysis, cellulose behaved differently from hemicellulose and lignin; the pyrolysis of the former was endothermic while that of the latter was exothermic. The main gas products from pyrolyzing the three components were similar, including CO₂, CO, CH₄ and some organics. The releasing behaviors of H₂ and the total gas yield were measured using Micro-GC when pyrolyzing the three components in a packed bed. It was observed that hemicellulose had higher CO₂ yield, cellulose generated higher CO yield, and lignin owned higher H₂ and CH₄ yield. A better understanding to the gas products releasing from biomass pyrolysis could be achieved based on this in-depth investigation on three main biomass components.     

Hydrothermal synthesis,crystal structure and magnetic properties of a novel nickel carboxylate–phosphonate with a layered structure

Hydrothermal reactions of N-(phosphonomethyl)proline (H₃L) with nickel sulfate hexahydrate resulted in a novel nickel carboxylate–phosphonate: |H₂O|[Ni₃(O₃PCH₂–NC₄H₇–CO₂)₂(H₂O)₄] (complex 1). Single-crystal X-ray diffraction analysis revealed that complex 1 crystallizes in the triclinic space group P-1 (No. 2), with lattice parameters of a = 10.0167(5) Å, b = 10.3882(5) Å, c = 11.9528(5) Å, α = 90.132(3)°, β = 107.246(3)°, γ = 111.158(3)°, V = 1099.39(9) Å³, and Z = 2. Complex 1 features a 2D layered structure. The structure contains alternating Ni-centered octahedra (Ni(1)O₆, Ni(2)O₅N and Ni(3)O₅N) and O₃PC tetrahedra linked to construct a layer with rhombohedral 12-MRs holes. The cyclopentylamine moieties of H₃L were grafted onto the layer through coordination of CPO₃, CO₂ and (CH₂)₂NCH₂ with central nickel atoms. These layers are stacked in an AA sequence, which results in a one-dimensional channel in the [001] direction. Water molecules are located in these channels. Magnetic studies showed that complex 1 exhibits predominantly paramagnetic behavior.     

Preparation and characterizations of Ni-alumina,Ni-ceria and Ni-alumina/ceria catalysts and their performance in biomass pyrolysis

The catalytic activity of Ni/Al₂O₃, Ni/CeO₂, and Ni/Al₂O₃-CeO₂ catalysts of different compositions were investigated over biomass pyrolysis process. Catalysts were prepared using co-precipitation method with various compositions of nickel and support materials. Surface characterizations of the materials were evaluated using XRD, SEM, and BET surface area analysis with N₂ adsorption isotherm. XRD analysis reveals the presence of Al₂O₃, CeO₂, NiO, and NiAl₂O₄ phases in the catalysts. Paper samples used for daily writing purposes were chosen as biomass source in pyrolysis. TGA experiment was performed on biomass with and without presence of catalysts, which resulted in the decrease of initial degradation temperature of paper biomass with the influence of catalysts. In a fixed-bed reactor, untreated and catalyst mixed biomasses were pyrolyzed up to 800 °C, with a residence time of 15 min. The non-condensable gases were collected through gas bags every after 100 °C and also at 5, 10, and 15 min residence time at 800 °C, which were analyzed using TCD-GC equipment. Comparative distributions of solid, liquid and gaseous components were made. Results indicated diminished amount of tar production in presence of catalysts. 30 wt% Ni/CeO₂ catalyst yielded least amount of tar product. The least amount of CO was produced over the same catalyst. According to gas analysis result, 30 wt% Ni doped alumina sample produced maximum amount of H₂ production with 43.5 vol% at 800 °C (15 min residence time).     

Development of Ni-Pd bimetallic catalysts for the utilization of carbon dioxide and methane by dry reforming

The present research deals with catalyst development for the utilization of CO₂ in dry reforming of methane with the aim of reaching highest yield of the main product synthesis gas (CO, H₂) at lowest possible temperatures. Therefore, Ni-Pd bimetallic supported catalysts were prepared by simple impregnation method using various carriers. The catalytic performance of the catalysts was investigated at 500, 600 and 700 °C under atmospheric pressure and a CH₄ to CO₂ feed ratio of 1. Fresh, spent and regenerated catalysts were characterized by N₂ adsorption for BET surface area determination, XRD, ICP, XPS and TEM. The catalytic activity of the studied Ni-Pd catalysts depends strongly on the support used and decreases in the following ranking: ZrO₂-La₂O₃, La₂O₃ > ZrO₂ > SiO₂ > Al₂O₃ > TiO₂. The bimetallic catalysts were more active than catalysts containing Ni or Pd alone. A Ni to Pd ratio = 4 at a metal loading of 7.5 wt% revealed the best results. Higher loading lead to increased formation of coke; partly in shape of carbon nanotubes (CNT) as identified by TEM. Furthermore, the effect of different calcination temperatures was studied; 600 °C was found to be most favorable. No effect on the catalytic activity was observed if a fresh catalyst was pre-reduced in H₂ prior to use or spent samples were regenerated by air treatment. Ni and Pd metal species are the active components under reaction conditions. Best conversions of CO₂ of 78% and CH₄ of 73% were obtained using a 7.5 wt% NiPd (80:20) ZrO₂-La₂O₃ supported catalyst at a reaction temperature of 700 °C. CO and H₂ yields of 57% and 59%, respectively, were obtained.     

The use of NiO as an oxygen carrier in chemical-looping combustion

The feasibility of using NiO as an oxygen carrier during chemical-looping combustion has been investigated. A thermodynamic analysis with CH₄ as fuel showed that the yield of CH₄ to CO₂ and H₂O was between 97.7 and 99.8% in the temperature range 700–1200 °C, with the yield decreasing as the temperature increases. Carbon deposition is not expected as long as sufficient metal oxide is supplied to the fuel reactor. Hydrogen sulfide, H₂S, in the fuel gas will be converted partially to SO₂ in the gas phase, with the degree of conversion increasing with temperature, but decreasing as a function of pressure. There is the possibility of sulfide formation as Ni₃S₂ at higher partial pressures of H₂S+SO₂ in the reactor. The reactivity of freeze granulated particles of NiO with NiAl₂O_4, MgAl₂O₄, TiO₂ and ZrO₂ sintered at different temperatures was investigated in a small fluidized bed reactor by exposing them cyclically to 50% CH₄/50% H₂O and 5% O₂ at 950 °C. During the reducing period, the NiO initially reacted with the CH₄ to form CO₂ and H₂O. However, there were always minor amounts of CO from the outlet of the reactor even at high concentrations of CO₂, which was due to the thermodynamic limitations. Here, the ratio CO/(CO₂+CO+CH₄) was between 1.5 and 2.5% at 950 °C for the oxygen carriers with alumina based inert. A small amount of CH₄ was released from the reactor at high degrees of oxidation of the NiAl₂O₄ and MgAl₂O₄-based carriers. As the time under reducing conditions increased, steam reforming of CH₄ to CO and H₂ became considerable, with Ni catalyzing this reaction. Whereas the ZrO₂ particles showed similar behavior as the alumina-based carriers, the TiO₂-based particles showed a markedly different reaction behavior, likely due to the complex interaction between NiO and TiO₂.     

Pyrolysis of wood at high temperature: The influence of experimental parameters on gaseous products

The pyrolysis of wood was carried out in an Entrained Flow Reactor at high temperature (650 to 950 °C) and under rapid heating conditions (> 10³ K s^− 1). The influence of the diameter and initial moisture of the particle, reactor temperature, residence time and the nature of the gaseous atmosphere on the composition of the gaseous products has been characterised. Particle size, between 80-125 and 160-200 μm, did not show any impact. Pyrolysis and tar cracking essentially happen in very short time period: less than 0.6 s; the products yields are only slightly modified after 0.6 s in the short residence times (several seconds) of our experiments. Higher temperatures improve hydrogen yield in the gaseous product while CO yield decreases. Under nitrogen atmosphere, after 2 s at 950 °C, 76% (daf) of the mass of wood is recovered as gases: CO, CO₂, H₂, CH₄, C₂H₂, C₂H₄ and H₂O. Tests performed under steam partial pressure showed that hydrogen production is slightly enhanced.     

CO2 reforming of methane over Ni/Sm2O3–CaO catalyst prepared by a sol–gel technique

A sol–gel method was employed to prepare Ni/CaO, Ni/Sm₂O₃ and a series of Ni/Sm₂O₃–CaO catalysts dispersed uniformly. The catalytic performance in CO₂/CH₄ reforming and the physicochemical properties were investigated by means of GC, BET, XRD, TG/DTA and HRTEM techniques, respectively. Under the condition of an atmospheric pressure at 700 °C and a GHSV of 4.8 × 10⁴ ml/h/g_cat, the conversion of CH₄ and CO₂ over 10% Ni/Sm₂O₃–CaO (1:4) catalyst were 60% and 63%, respectively, the selectivity of H₂ and CO were 85% and 95%, significantly higher than those over Ni/CaO and Ni/Sm₂O₃ due to high dispersion of Ni nanometer particles and interfacial effect of support in 10% Ni/Sm₂O₃–CaO.     

Conversion of methane on catalysts obtained via self-propagating high-temperature synthesis

Monolith metalloceramic catalysts for the selective oxidation of methane are prepared via self-propagating high-temperature synthesis (SHS) from NiO, ZrO₂, MgO, Al, Ni and other powders. Catalytic tests of monolith samples are performed in a flow reactor at 800°C using a methane-air mixture (methane, 29.6 vol %). SHS catalysts are shown to attain the level of platinum and platinum/rhodium catalysts through the yield of syngas (CO + H₂) and to surpass them in the case of Ni 52.9 ZrO₂ 9.5 composition. The latter is used as a catalyst to develop a pilot autothermal syngas generator with a capacity of 30 m³/h. Syngas is generated via carbon dioxide methane conversion (CDMC) on SHS platinum-modified Ni₃Al powder catalysts. The samples are tested in a flow fixed-bed reactor at a catalyst volume of 1 cm³, a grain size of 600–1000 μm, temperatures of 600–900°C, and a volumetric flow rate of 100 cm³/min (CH₄ : CO₂ : He = 20 : 20 : 60 vol %). The catalysts developed for converting natural gas into syngas are shown to be highly active and stable in a high-temperature redox medium. This work is the first step in the synthesis of dimethyl ether, which could compete successfully with diesel fuel.     

Hydrogen production through dry reforming of biogas using a porous electrochemical cell: Effects of a cobalt catalyst in the electrode and mixing of air with biogas

This paper reports the performance of porous Gd-doped ceria (GDC) electrochemical cells with Co metal in both electrodes (cell No. 1) and with Ni metal in the cathode and Co metal in the anode (cell No. 2) for CO₂ decomposition, CH₄ decomposition, and the dry reforming reaction of a biogas with CO₂ gas (CH₄ + CO₂ → 2H₂ + 2CO) or with O₂ gas in air (3CH₄ +?1.875CO₂ +?1.314O₂ → 6H₂ +?4.875CO +?0.7515O₂). GDC cell No. 1 produced H₂ gas at formation rates of 0.055 and 0.33?mL-H₂/(min?m²-electrode) per 1?mL-supplied gas/(min?m²-electrode) at 600?°C and 800?°C, respectively, by the reforming of the biogas with CO₂ gas. Similarly, cell No. 2 produced H₂ gas at formation rates of 0.40?mL-H₂/(min?m²) per 1?mL-supplied gas/(min?m²) at 800?°C from a mixture of biogas and CO₂ gas. The dry reforming of a real biogas with CO₂ or O₂ gas at 800?°C proceeded thermodynamically over the Co or Ni metal catalyst in the cathode of the porous GDC cell. Faraday's law controlled the dry reforming rate of the biogas at 600?°C in cell No. 2. This paper also clarifies the influence of carbon deposition, which originates from CH₄ pyrolysis (CH₄ → C + 2H₂) and disproportionation of CO gas (2CO → C + CO₂), on the cell performance during dry reforming. The dry reforming of a biogas with O₂ molecules from air exhibits high durability because of the oxidation of the deposited carbon by supplied air.     

Catalysis of gasification of coal-derived cokes and chars

Calcium is the most important in-situ catalyst for gasification of US coal chars in O₂, CO₂ and H₂O. It is a poor catalyst for gasification of chars by H₂. Potassium and sodium added to low-rank coals by ion exchange and high-rank coals by impregnation are excellent catalysts for char gasification in O₂, CO₂ and H₂O. Carbon monoxide inhibits catalysis of the CH₂O reaction by calcium, potassium and sodium; H₂ inhibits catalysis by calcium. Thus injection of synthesis gas into the gasifier will inhibit the CH₂O reaction. Iron is not an important catalyst for the gasification of chars in O₂, CO₂ and H₂O, because it is invariably in the oxidized state. Carbon monoxide disproportionates to deposit carbon from a dry synthesis gas mixture (3 vol H₂ + 1 vol CO) over potassium-, sodium- and iron-loaded lignite char and a raw bituminous coal char, high in pyrite, at 1123 K and 0.1 MPa pressure. The carbon is highly reactive, with the injection of 2.7 kPa H₂O to the synthesis gas resulting in net carbon gasification. The effect of traces of sulphur in the gas stream on catalysis of gasification or carbon-forming reactions by calcium, potassium, or sodium is not well understood at present. Traces of sulphur do, however, inhibit catalysis by iron.     

Visual and Raman spectroscopic observations of hot compressed water oxidation of guaiacol in fused silica capillary reactors

Using fused silica capillary reactors (FSCRs), we investigated the decomposition of guaiacol during hot compressed water oxidation (HCWO), with H₂O₂ added in stoichiometric ratios from 100 to 300%. Reactions were performed between 180 and 300 °C for durations from 2 to 10 min while the concurrent generation of CO₂ during the oxidation process was followed by Raman spectroscopy and the phase behavior of guaiacol in HCW, with or without H₂O₂, was observed visually under a polarized microscope configured with a heating/cooling stage. We found that complete conversion of guaiacol and 100% yield of CO₂ were achieved with a 150% stoichiometric ratio of oxidizer after 10 min at 200 and 300 °C, respectively. Based on the global reaction kinetics for the complete conversion of guaiacol to CO₂, the reaction is considered to be first order. The activation energy and pre-exponential factor for CO₂ formation are 18.62 kJ mol⁻¹ and 12.81 s⁻¹, respectively.