Feasibility of Na-based thermochemical cycles for the capture of CO2 from air—Thermodynamic and thermogravimetric analyses

Three Na-based thermochemical cycles for capturing CO₂ from air are considered: (1) a NaOH/NaHCO₃/Na₂CO₃/Na₂O cycle with 4 reaction steps, (2) a NaOH/NaHCO₃/Na₂CO₃ cycle with 3 reactions steps, and (3) a Na₂CO₃/NaHCO₃ cycle with 2 reaction steps. Depending on the choice of CO₂ sorbent – NaOH or Na₂CO₃ – the cycles are closed by either NaHCO₃ or Na₂CO₃ decomposition, followed by hydrolysis of Na₂CO₃ or Na₂O, respectively. The temperature requirements, energy inputs, and expected products of the reaction steps were determined by thermodynamic equilibrium and energy balance computations. The total thermal energy requirement for Cycles 1, 2, and 3 are 481, 213, and 390 kJ/mol of CO₂ captured, respectively, when heat exchangers are employed to recover the sensible heat of hot streams. Isothermal and dynamic thermogravimetric runs were carried out on the pertinent carbonation, decomposition, and hydrolysis reactions. The extent of the NaOH carbonation with 500 ppm CO₂ in air at 25 °C – applied in Cycles 1 and 2 – reached 9% after 4 h, while that for the Na₂CO₃ carbonation with water-saturated air – applied in Cycle 3 – was 3.5% after 2 h. Thermal decomposition of NaHCO₃ – applied in all three cycles – reached completion after 3 min in the 90–200 °C range, while that of Na₂CO₃ – applied in Cycle 1 – reached completion after 15 min in the 1000–1400 °C range. The significantly slow reaction rates for the carbonation steps and, consequently, the relatively large mass flow rates required, introduce process complications in the scale-up of the reactor technology and impede the application of Na-based sorbents for capturing CO₂ from air.     

Pressureless sintering and mechanical properties of SiO2–Al2O3–MgO–K2O–TiO2–F (CaO–Na2O) machinable glass–ceramics

To develop a high strength machinable glass–ceramic through pressureless sintering, the glassy compositions were obtained by mixing a mica-based frit and a frit in the SiO₂–CaO–Na₂O system. According to XRD results, the glass compositions mainly crystallized into phlogopite and diopside after sintering. The optimum sintered glass–ceramic with desirable mechanical properties, machinability and sinterability was achieved by addition of 30 wt.% SiO₂–CaO–Na₂O glass powder to 70 wt.% mica glass composition. SEM results confirmed presence of needle-like diopside crystals which played a reinforcement role to the platelet phlogopite and glassy matrix combination. The measurements showed bending strength and fracture toughness enhanced up to 144.6 ± 17.6 MPa and 1.7 ± 0.2 MPa m^1/2, respectively.     

Chemical aspects of uranium recovery from seawater by amidoximated electron-beam-grafted polypropylene membranes

The amidoximated macroporous membranes (AO membranes) were prepared by post irradiation grafting of acrylonitrile (AN) onto thermally bonded non-woven matrix of poly(propylene) sheet using electron beams. These precursor membranes were reacted with hydroxylamine to convert AN to AO groups, and conditioned by treating them with 2.5% KOH at 80°C for 1 h. The water uptake capacity in seawater, Na⁺-exchange capacity, and uranium loading capacity from seawater of AO membranes were found to be 200±10 wt.%, (3.1±0.2)×10⁻⁴ mol/g, and (1.60±0.18)×10⁻³ mol/g, respectively. The expected functional group density based on the degree of AN grafting (125 wt.%) and its subsequent conversion to AO groups (80%) was found to be 7.8×10⁻³ mol/g. The comparison of the expected functional group density and uranium uptake capacity seems to suggest that UO₂²⁺ forms a complex with AO groups in 1:4 proportion. The uranium could be quantitatively desorbed (>90%) from the AO membrane in Na₂CO₃ and mineral acids like HCl in the equilibration times of 60 min and 40 min, respectively. Alkaline conditioning was found to be necessary for reuse of the membrane equilibrated with acid. However, AO membranes equilibrated with Na₂CO₃ could be reused without any conditioning for uranium sorption.     

Hydrogen balance for catalytic pyrolysis of atmospheric residue

The catalytic pyrolysis of atmospheric residue over the commercial catalytic pyrolysis process catalyst (Al₂O₃/Fe₂O₃/Na₂O (46.3, 0.27 and 0.04 wt.%, respectively)) was investigated in a confined fluidized bed reactor. The yield of light olefins was above 37 wt.% at reaction temperature above 600 °C and it reached a maximum of 47 wt.% at 660 °C. The main components in light olefins were ethylene and propylene, and those in liquid samples were aromatics. The main components in light alkanes were propane and i-butane at low reaction temperature (600 °C), and those were methane and ethane at high reaction temperature (700 °C). The hydrogen content of light olefins was about 14.27 wt.%, that of light alkanes was above 18.5 wt.%, that of gasoline was below 12.5 wt.%, and that of diesel was below 7.8 wt.%. The percentage of the hydrogen in light alkanes to total hydrogen was above 29% and that in light olefins was above 40%. The effective utilization ratio of hydrogen decreased from 66.60% at 600 °C to 61.44% at 700 °C.     

Selective methanation of CO over supported Ru catalysts

The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO₂ has been investigated with respect to the loading (0.5–5.0 wt.%) and mean crystallite size (1.3–13.6 nm) of the metallic phase as well as with respect to the nature of the support (Al₂O₃, TiO₂, YSZ, CeO₂ and SiO₂). Experiments were conducted in the temperature range of 170–470 °C using a feed composition consisting of 1%CO, 50% H₂ 15% CO₂ and 0–30% H₂O (balance He). It has been found that, for all catalysts investigated, conversion of CO₂ is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO₂ methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO₂ hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO₂ catalysts, TOFs of both CO (at 215 °C) and CO₂ (at 330 °C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5 nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al₂O₃. Experiments conducted with the use of Ru catalyst of the same metal loading (5 wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO₂, compared to YSZ or SiO₂, whereas CeO₂- and Al₂O₃-supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO₂ catalyst, which is able to completely and selectively convert CO at temperatures around 230 °C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO₂ conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO₂ catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications.     

Liquefaction of rice straw in sub- and supercritical 1,4-dioxane–water mixture

The critical liquefaction of rice straw in sub- and supercritical 1,4-dioxane–water mixture was investigated in a 500 mL autoclave at temperature of 260–340 °C, resistance time of 0–20 min, and volume ratios 0–100 vol.% (1,4-dioxane:mixture). The yields of oil and PA + A (preasphaltene and asphaltene) were in the range of 29.64–57.30 wt.% and 6.42–22.68 wt.%, depending on the temperature, resistance time and volume ratio. The synergistic capability of 1,4-dioxane–water mixture could allow the great decomposition of the tubular structure of lignocelluloses. It was shown by the results that the “oxygen-transfer” reaction, deoxygenation and decarboxylation may occur in the liquefaction of rice straw with 1,4-dioxane–water mixture, while deoxygenation and decarboxylation may be the main reaction. The oil and PA + A fractions obtained at different volume ratios were analyzed by FTIR and GC–MS to investigate the effect of the ratios on the type of the compounds in the liquid products. It is shown that the nucleophilic and hydrolytic functions of water might be weaken at the higher ratio of 1,4-dioxane runs, resulting the lower amount of phenolic, acidic, hydrocarbon and ester derivatives in the oil and PA + A fractions.     

Catalytic treating of gas pollutants over cobalt catalyst supported on porous carbons derived from rice husk and carbon nanotube

Porous carbons were prepared from rice husks, commercial coconut-shell-derived carbon, and carbon nanotube (CNT) by activation with CO₂, KOH, and ZnCl₂. Cobalt catalysts were supported on the six different porous carbons by excess-solution impregnation, and were used to carry out reactions with different constituents such as NO + CO, toluene, NO + toluene, and NO + CO + toluene in the presence of 6% O₂ at 250 °C to evaluate the activity of porous catalysts. The properties of the catalysts were analyzed by X-ray powder diffractometer (XRD), a field-emission scanning electron microscope (FESEM), transmission electron microscope (TEM), and an X-ray energy dispersive spectrometer (EDS). The cobalt catalysts supported on rice-husk-based carbon activated by CO₂ and those on commercial-activated-carbon re-treated by KOH showed 100% conversion on toluene oxidation. CNT-cobalt catalyst showed 63% NO conversion with CO and 46% with toluene at 250 °C. Among the six porous supported catalysts, the cobalt catalysts prepared with CNT and rice-husk-derived carbon by using CO₂ showed the best catalytic activity and thermal stability when compared to the others.     

Supercritical CO2 extraction of essential oil from yarrow

Essential oil was extracted from yarrow flowers (Achillea millefolium) with supercritical CO₂ at pressure of 10 MPa and temperatures of 40–60 °C, and its composition and yield were compared with those of hydrodistillate. The yield of total extract, measured in dependence on extraction time, was affected by extraction temperature but not by particle size of ground flowers. CO₂-extraction of cuticular waxes was lowest at 60 °C. Major essential oil components were camphor (26.4% in extract, 38.4% in distillate), 1,8-cineole (9.6% in extract, 16.2% in distillate), bornyl acetate (16.7% in extract, 4.3% in distillate), γ-terpinene (9.0% in extract, 9.4% in distillate), and terpinolene (7.6% in extract, 3.9% in distillate). Compared to hydrodistillation, the yield of monoterpenes was lower due to their incomplete separation from gaseous CO₂ in trap but the yield of less volatile components like monoterpene acetates and sesquiterpenes was higher. Hydrolysis of γ-terpinene and terpinolene, occuring in hydrodistillation, was suppressed in supercritical extraction, particularly at extraction temperature of 40 °C.     

Ionic liquid as reaction medium for the synthesis and crystallization of a metal-organic framework: (BMIM)2[Cd3(BDC)3Br2] (BMIM = 1-butyl-3-methylimidazolium, BDC = 1,4-benzenedicarboxylate)

An ionic liquid, 1-butyl-3-methylimidazolium bromide, is used as reaction medium for the synthesis and crystallization of a coordination polymer, (BMIM)₂[Cd₃(BDC)₃Br ₂] (1) (BMIM = 1-butyl-3-methylimidazolium, BDC =  1,4-benzenedicarboxylate), which forms an anionic two-dimensional framework with the imidazolium cations located between the layers. This compound is thermally stable up to ca. 340 °C and exhibits blue emission in solid state at room temperature. Other characterizations by IR and UV–visible spectra are also described.     

Correlation of methane uptake with microporosity and surface area of chemically activated carbons

Two series of activated carbon discs have been prepared by chemical activation of olive stones with ZnCl₂ and H₃PO₄. Some of the carbons have been post-treated in order to modify their porous texture and/or surface chemical composition. All carbons have been characterized by adsorption of N₂ (−196 °C) and CO₂ (0 °C) and immersion calorimetry into dichloromethane. The volume of methane adsorbed at 25 °C and 3.5 MPa is proportional to the surface area deduced from immersion calorimetry into dichloromethane. Consequently, it is possible to estimate, using a single experiment, the possibility of using activated carbons for the storage of natural gas. On the other hand, the methane uptake can be also correlated to the volume of micropores, provided by the adsorption of N₂ at −196 °C and CO₂ at 0 °C, although the correlations is not as good. Only carbons slightly activated, with low surface area and microporosity below around 0.6 nm, do not adjust the above correlations because they adsorb more methane than the expected, the effect of chemical nature of the carbon surface being almost negligible.     

Selective steam reforming of methanol over silica-supported copper catalyst prepared by sol–gel method

Silica-supported copper prepared by a sol–gel method can selectively catalyze methanol steam reforming to hydrogen and carbon dioxide at 250 °C. The catalytic activity increases with the copper content up to 40 wt.%. The selectivity to carbon monoxide with the catalysts containing 20–40 wt.% of copper is significantly lower than that with a commercial Cu/ZnO/Al₂O₃ catalyst. Copper particles are highly dispersed in the catalyst whose Cu content is 20 wt.% or less. After the reaction at 250 °C the particles are present as Cu₂O with the mean crystallite size less than 4 nm. In the catalyst with the Cu content of 30–50 wt.%, the fine Cu₂O particles coexist with large metallic Cu particles whose mean crystallite size is 30–40 nm after the reaction. The large metallic particles are supposed to contribute to the reaction as well as the fine Cu₂O particles although the surface area is estimated to be significantly smaller than that of the latter.     

Porous Carbon Spheres Derived from Hemicelluloses for Supercapacitor Application

With the increasing demand for dissolving pulp, large quantities of hemicelluloses were generated and abandoned. These hemicelluloses are very promising biomass resources for preparing carbon spheres. However, the pore structures of the carbon spheres obtained from biomass are usually poor, which extensively limits their utilization. Herein, the carbon microspheres derived from hemicelluloses were prepared using hydrothermal carbonization and further activated with different activators (KOH, K₂CO₃, Na₂CO₃, and ZnCl₂) to improve their electrochemical performance as supercapacitors. After activation, the specific surface areas of these carbon spheres were improved significantly, which were in the order of ZnCl₂ > K₂CO₃ > KOH > Na₂CO₃. The carbon spheres with high surface area of 2025 m²/g and remarkable pore volume of 1.07 cm³/g were achieved, as the carbon spheres were activated by ZnCl₂. The supercapacitor electrode fabricated from the ZnCl₂-activated carbon spheres demonstrated high specific capacitance of 218 F/g at 0.2 A/g in 6 M KOH in a three-electrode system. A symmetric supercapacitor was assembled in 2 M Li₂SO₄ electrolyte, and the carbon spheres activated by ZnCl₂ showed excellent electrochemical performance with high specific capacitance (137 F/g at 0.5 A/g), energy densities (15.4 Wh/kg), and good cyclic stability (95% capacitance retention over 2000 cycles).     

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.     

ZnBO-doped (Ba, Sr)TiO3 ceramics for the low-temperature sintering process

ZnBO-doped (Ba, Sr)TiO₃ ceramics were investigated for low-temperature co-fired ceramics (LTCCs) applications. Until now, B₂O₃ and Li₂CO₃ dopants have been commonly employed as the low-temperature sintering aids. In this paper, we suggest ZnBO as an alternative dopant to the B₂O₃ and Li₂CO₃. To reduce the sintering temperature of (Ba, Sr)TiO₃, we have added 1–5 wt.% of ZnBO to (Ba, Sr)TiO₃. ZnBO-doped (Ba, Sr)TiO₃ ceramics were respectively sintered from 750 to 1350 °C by 50 °C to confirm the sintering temperature with different dopant contents. By adding 5 wt.% of ZnBO to the (Ba, Sr)TiO₃ ceramics, the sintering temperature of (Ba, Sr)TiO₃ ceramics can be reduced to 1100 °C. From the XRD analysis, ZnBO-doped (Ba, Sr)TiO₃ has no pyro phase. By adding ZnBO dopants to (Ba, Sr)TiO₃ ceramics, both of relative dielectric permittivity and loss tangent were decreased. From the frequency dispersion of dielectric properties, the relative dielectric permittivity and loss tangent of 5 wt.% ZnBO-doped (Ba, Sr)TiO₃ were 1180 and 3.3 × 10⁻³, while those of BST were 1585 and 4.8 × 10⁻³, respectively.     

Optimization of removal of lead from bearing-lead anode slime

An optimization process is conducted by the Taguchi experimental design method for removal of lead from decopperized anode slime in aqueous Na₂CO₃/HNO₃ media. The effects of parameters such as reaction temperature, Na₂CO₃ concentration, solid–liquid ratio and reaction period on the conversion are studied. It is seen that the most important parameters affecting the conversion of lead sulphate to lead carbonate are solid–liquid ratio and reaction period. The optimum conversion conditions for process are found to be solid–liquid ratio of 0.05 g/mL, reaction period of 600 s, reaction temperature of 50 °C and Na₂CO₃ concentration of 2 M. Under optimal conditions, the experimental results put out that the conversion of lead sulphate at the 95% confidence level can be 97%, approximately.     

Mineralogical phase analysis of alkali and sulfate bearing belite rich laboratory clinkers

The activation of laboratory belite clinkers has been carried out by adding variable amounts of alkaline salts (K₂CO₃, Na₂CO₃), and/or SO₃ as gypsum in the raw materials but keeping almost constant the main elements ratios, Ca/Si/Al/Fe. Quantitative phase analyses by the Rietveld method using high resolution synchrotron and strictly monochromatic CuKα₁ laboratory X-ray powder diffraction data has been performed. Quantitative phase analysis results have been compared to validate the protocol using laboratory X-ray data. The agreement in the results is noteworthy, which indicates that good quantitative phase analyses can be obtained from laboratory X-ray powder data. Qualitative studies have confirmed that the addition of alkaline salts to raw mixtures promotes the stabilization, at room temperature, of the highest temperature polymorphs: α′_H-C₂S and α-C₂S. Quantitative studies gave the phase assemblage for ten different laboratory belite clinkers. As an example, an active belite clinker with 1.0 wt.% of K₂O and 1.0 wt.% of Na₂O (amounts added to the raw mixtures) contains 8.5(3) wt.% of β-C₂S, 21.2(3) wt.% of α'_H-C₂S, 24.1(2) wt.% of α-C₂S, 18.9(3) wt.% of total C₃S, 17.3(2) wt.% of C₃A and 10.0(2) wt.% of C₄AF. A belite clinker with 0.8 wt.% SO₃ (nominal loading) contains 60.7(1) wt.% of β-C₂S, 6.7(2) wt.% of α′_H-C₂S, 12.3(7) wt.% of C₃S, 9.1(2) wt.% of C₃A and 11.2(2) wt.% of C₄AF. Overall, quantitative phase analyses have shown that alkaline oxides stabilize α′_H-C₂S and α-C₂S, sulfur stabilizes β-C₂S, with a large unit cell volume, and the joint presence of alkaline oxides and sulfur promotes mainly the stabilization of the α′_H-C₂S polymorph.     

Dehydrogenation of ethylbenzene to styrene over Fe2O3/Al2O3 catalysts in the presence of carbon dioxide

Thermodynamic consideration of the dehydrogenation of ethylbenzene clearly indicates that the equilibrium yield of styrene for the dehydrogenation in the presence of CO₂ is much higher than that for the dehydrogenation in the presence of steam. A two-step pathway for the dehydrogenation in the presence of CO₂ appears to provide higher equilibrium yield of styrene at a given temperature. The amount of energy required for the new process using CO₂ is much lower than that for a typical present commercial process using steam. An Fe₂O₃(10 wt.%)/Al₂O₃(90 wt.%) catalyst prepared by a coprecipitation method was found to be effective for the dehydrogenation of ethylbenzene to produce styrene in the presence of CO₂.     

Hydrogenation of aromatic compounds during gas oil hydrodewaxing: I. Effect of ruthenium content and method of nickel catalyst preparation

Ni-based (8 wt.% NiO) dewaxing catalysts for the hydroconversion of the hydroraffinate of oil fraction (d_20 °C = 0.845 g/cm³; cloud point (CP) = −2 °C; aromatics = 25.8 wt.%; S = 25 ppm) were modified with Ru. The effect of Ru content (0.6, 0.75 and 0.9 wt.% of RuO₂) and the methods of Ni catalyst preparation were examined. The catalysts were characterised by N₂ sorption, TPR, ICP, XRD, SEM, XPS, H₂ chemisorption. Activity was tested in a continuous-flow system at 6 MPa (LHSV, 2.5 h⁻¹; H₂:CH, 350 N m³/m³). NiO and RuO₂ were found to exert a synergic effect on catalytic activity. The rise in RuO₂ content from 0.6 to 0.9 wt.% increased the HDA of HON from 23 to 65% at 240 °C and was parallelled by a drop in CP (by about 15 °C). The effect of Ru was found to depend on the method of Ni catalyst preparation.     

The enantioselective hydrolysis of racemic naproxen methyl ester in supercritical CO2 using Candida rugosa lipase

The enantioselective hydrolysis of racemic naproxen methyl ester by Candida rugosa lipase (CRL) was studied in aqueous buffer solution/isooctane reaction system in the presence of supercritical CO₂. The effects pressure (75–160 bar), temperature (32–42 °C) and reaction time (0.5–12 h) on the enantiomeric excesses of the product (ee_p) and the substrate (ee_s), enantiomeric ratio (E), conversion (x) and enzyme activity were investigated in a batch reactor system. The highest enantiomeric ratio achieved at 120 bar of pressure, 37 °C of temperature and 2 h of reaction time was E = 193 with x = 41.3%, ee_p = 97.9% and ee_s = 68.8%. CRL remained active at least for 12 h at 37 °C and 120 bar in supercritical CO₂ medium. Furthermore, enantiomeric ratio increased with increasing reaction time and reached the value of E = 236 with ee_p = 98.2%, ee_s = 70.0% and x = 41.6% after 12 h of hydrolysis.     

Integrated coal pyrolysis with CO2 reforming of methane over Ni/MgO catalyst for improving tar yield

A new process to integrate coal pyrolysis with CO₂ reforming of methane over Ni/MgO catalyst was put forward for improving tar yield. And several Chinese coals were used to confirm the validity of the process. The experiments were performed in an atmospheric fixed-bed reactor containing upper catalyst layer and lower coal layer to investigate the effect of pyrolysis temperature, coal properties, Ni loading and reduction temperature of Ni/MgO catalysts on tar, water and char yields and CH₄ conversion at fixed conditions of 400 ml/min CH₄ flow rate, 1:1 CH₄/CO₂ ratio, 30 min holding time. The results indicated that higher tar yield can be obtained in the pyrolysis of all four coals investigated when coal pyrolysis was integrated with CO₂ reforming of methane. For PS coal, the tar, water and char yield is 33.5, 25.8 and 69.5 wt.%, respectively and the CH₄ conversion is 16.8%, at the pyrolysis temperature of 750 °C over 10 wt.% Ni/MgO catalyst reduced at 850 °C. The tar yield is 1.6 and 1.8 times as that in coal pyrolysis under H₂ and N₂, respectively.