Coal Catalysts Research Articles

Ga-doped spinel-typed Co-Al catalysts for CO2-assisted ethane dehydrogenation

A series of Ga-doped spinel-typed Co-Al catalysts were prepared via one-step evaporation-induced self-assembly (EISA) method. These catalysts present promising catalytic performance for CO2-assisted ethane dehydrogenation, which can be ascribed to the conjunction effect of cobalt and gallium species. The incorporation of Ga into the structure of Co-Al spinel has been recognized for enhancing CO2 conversion via reverse water-gas shift reaction, leading to a favorable equilibrium shift towards ethylene, along with an improved catalyst stability as a result of coexisting Boudouard reaction. Through X-ray photoelectron spectroscopy (XPS), X-ray absorption fine structure (XAFS), NH3 and CO2 temperature-programmed desorption (TPD) characterizations, coordinatively unsaturated Co2+ and Ga3+ cations were identified as collaborative catalytic active sites, with gallium species taking the prominent role. These sites were closely associated with the formation of acid-base pairs on the catalyst surface, which were crucial for the adsorption and activation of the reactants.

Nitrogen species from Spirulina platensis derived bio-oil enhance catalytic activity of cobalt catalysts for hydrogenation

High nitrogen content in Spirulina platensis-derived bio-oil is a highly undesirable feature in upgrading of bio-oil to biofuel via hydrodeoxygenation. However, the nitrogen species could be potentially used as dopant for tailoring the catalytic behaviors of metallic sites in heterogeneous catalysts. In this study, the nitrogen species in the bio-oil from hydrothermal carbonization (HTC) of Spirulina platensis was used to modify Co-based catalyst for enhancing their catalytic activity for hydrogenation of o-chloronitrobenzene (o-CNB). The results showed that the introduction of N species not only promoted dispersion of Co particles via formation of Co–N sites, but also generated extra pores and significantly increased H2 uptake. The abundant Co–N sites, high dispersion of Co and higher surface area of N-doped catalyst (CoFeAl–N) jointly contributed to the enhanced catalytic activity for hydrogenation of o-CNB, achieving the yield of 90.3% for o-chloroaniline (o-CA) and lowering the activation energy from 63.0 kJ mol−1 (with N-free CoFeAl catalyst) to 55.1 kJ mol−1. The effectiveness of introducing nitrogen for enhancing catalytic activity for hydrogenation of o-CNB was also confirmed in the experiments for doping Co/Al2O3 (prepared via impregnation) and CoAl (prepared via co-precipitation) catalysts with the Spirulina platensis derived bio-oil.

Cobalt aluminate spinel-derived catalysts for glycerol steam reforming

Steam reforming of glycerol presents a promising possibility for the production of clean hydrogen. The steam reforming of glycerol (10 wt%) utilizing catalysts derived from cobalt aluminate spinel was examined at 550 °C, while the space–time covered 3.76–37.60 g·h/mol. Among the characterization techniques, glycerol desorption tests (glycerol-TPD) were conducted to assess the feasibility of the catalytic system for dehydration/dehydrogenation activity. The 0.625CoAl catalyst displayed the highest conversion of carbon to gas and selectivity to H2, which corresponds to the higher H2 desorption at lower temperature levels observed in the glycerol-TPD experiments. The catalyst's deactivation and regeneration were studied on 0.25CoAl catalyst under severe operation conditions and resulted in cobalt leaching detection. Raman spectroscopy and temperature programmed oxidation (TPO) revealed the formation of predominantly amorphous carbon on the surface of the catalyst.

Metal-Free Coal Catalyst for Hydrogen Production: Synthesis and Performance Assessment

In this study, a coal-based catalyst produced by protonating phosphoric acid was used as a metal-free catalyst for hydrogen production from sodium borohydride (NaBH4) methanolysis. Experiments were conducted with various acid concentrations, impregnation times, and carbonization temperatures and times in order to produce a metal-free coal catalyst with enhanced catalytic activity. The catalyst impregnated with 3M H3PO4 for 12 h and subsequently carbonized at 600°C for 90 min exhibited the highest catalytic activity. The hydrogen production at 60 °C methanolysis with 0.25 g of NaBH4 catalyzed by a metal-free coal catalyst was found to be 11,854 mL min−1g.cat−1. Additionally, the activation energy of the catalyst was determined to be 22.5 kJ mol-1.

Tuning the CO2 hydrogenation path by moderately phosphating the Co-Al catalyst toward methanol synthesis

Regulating diversified reaction paths is one of the key challenges for commercial CO2 hydrogenation. Herein, a phosphating strategy is proposed to modify the surface structure of a layered double hydroxide-derived Co-Al catalyst for CO2 hydrogenation to CH3OH. It is shown that moderate phosphating can achieve a uniform incorporation of P without damaging the original layered morphology and crystal structure. Experiments and density functional theory calculations demonstrate that a significant electron transfer occurs in the surface oxygen vacancies after phosphating, which promotes the direct hydrogenation of key intermediate H3CO* to CH3OH by constraining the cleavage of the C-O bond in H3CO*. The CH3OH selectivity and space-time yield are, therefore, substantially boosted after moderate phosphating, far superior to those on conventional Cu-, In2O3- and noble metal-based catalysts. This work provides valuable insights into the manipulation of reaction paths through the design and rational modification of catalytic materials.

Co supported on Cex[Al2O3]0.5-x as an effective catalyst for low-temperature CO oxidation: Effect of calcination temperature

The low-temperature behavior of CO oxidation was investigated using 0.1 mol Ce doped Co supported on alumina catalysts prepared using co-precipitation followed by deposition precipitation method. The impact of calcination temperature on CO oxidation with kinetic aspects has been studied in detail and correlated to the characterizations. The Ce doped CoAl catalyst calcined at optimum temperature (550 ⁰C) shoed formation of more facile Co3+, Ce3+, and adsorbed species. The Co, Ce, and alumina interaction leads to the formation of optimum penta and hexa coordinated alumina. The physicochemical properties of the catalyst have been studied in detail using XRD, FTIR, Raman, TPR, XPS, and 27Al NMR and correlated to the catalytic activity.

Selective production of γ-valerolactone or 1,4-pentanediol from levulinic acid/esters over Co-based catalyst: Importance of the synergy of hydrogenation sites and acidic sites

γ-Valerolactone (GVL) or 1,4-pentanediol (1,4-PDO) are the value-added chemicals, selectivities of which from conversion of levulinic acid/ester depend on balanced distribution of metallic sites and other active sites of the catalysts. In this study, Co-based catalysts with various precursors of LDH structures were synthesized to investigate the roles of hydrogenation, acidic and basic sites in the formation of GVL and 1,4-PDO from ethyl levulinate (EL). The results indicated that Al in Co-Mg-Al or Co-Al created acidic sites and facilitated cobalt dispersion by developing porous structures and strong interaction with Co species. Kinetic study indicated that the conversion of GVL controlled the formation rate of 1,4-PDO from EL. The superior catalytic activity and recyclability were observed over Co-Mg-Al and Co-Al catalysts, with the selectivity of both of GVL and 1,4-PDO reaching 98%, which was equivalent or superior to noble-metal based catalysts. Brønsted acidic sites in catalyst could facilitate the lactonization of ethyl 4-hydroxyvalerate to GVL and the ring-opening of GVL to 1,4-PDO, by cooperating with hydrogenation sites. Lewis acidic sites improved the adsorption of substrates and reaction intermediates, accelerating the ring-opening of GVL. The synergy between acidic sites together with hydrogenation sites was the key for achieving the excellent catalytic performance.

Hydrogen-free hydrogenation of furfural to furfuryl alcohol and 2-methylfuran over Ni and Co-promoted Cu/γ-Al2O3 catalysts

Catalytic transformation of furfural to furfuryl alcohol and 2-methylfuran without H2 supply toward transfer hydrogenation process using 2-propanol as a H2 source was systematically investigated over the bimetallic NiCuAl and CoCuAl catalysts in comparison with the monometallic CuAl, NiAl, and CoAl catalysts. The XRD analysis confirmed the generation of Ni-Cu and Co-Cu alloys after the reduction in presence of H2. The interaction between Cu and Ni or Co resulted in a simplicity of the reduction behavior of Ni and Co species observed in H2-TPR experiments. It was evident from pyridine adsorption FTIR analysis that the formation of bimetallic Ni-Cu and Co-Cu alloys apparently improved the stronger Lewis acidic sites. The influences of reaction temperature and time were examined and optimized to maximize the yields of furfuryl alcohol and 2-methylfuran. The highest two major products yield and selectivity with lower by-products were obtained over the NiCuAl and CoCuAl catalysts compared with the CuAl and NiAl catalysts. The superior performance of the bimetallic catalysts was attributed to the stronger Lewis acidic centre on the catalyst surface. The CoCuAl catalyst was found to have lower catalyst deactivation and carbon deposition among the CuAl and NiCuAl catalysts under H2-free atmosphere.

Synergistic effect of Ni-Co alloying on hydrodeoxygenation of guaiacol over Ni-Co/Al2O3 catalysts

The hydrodeoxygenation (HDO) of guaiacol was investigated in a batch reactor using Ni-Co/γ-Al2O3 catalysts prepared by co-impregnation method. The structural and physicochemical properties of the catalysts were investigated using BET, XRD, H2-TPR, FT-IR, and NH3-TPD. The characterization results revealed that the formation of various Ni-Co composite species strongly depend on the Ni/Co mole ratio, total metal loadings, and the calcination/reduction temperature. The 6.1Ni3.05CoAl (Ni/Co = 1:2) catalyst seeds the formation of NiCo2O4 spinel structure and subsequent formation of Ni-Co alloy, which represents as specific active site for direct demethoxylation/deoxygenation reaction. The synergistic interaction of Ni-Co enhances the selectivity of benzene. The benzene selectivity of 35.2 % and cyclohexane selectivity of 59.1 % with complete conversion of guaiacol (98.9 %) were achieved with the 3.05Ni6.1CoAl catalyst at 575 K. A tentative reaction pathway is proposed based on the product distribution accomplished during HDO reaction. The structural property was correlated with activity to explore the mechanistic insights.

Application of Co-Al Catalysts in Hydrogenation of Glycidol to 1,3-Propanediol

Application of Co-Al Catalysts in Hydrogenation of Glycidol to 1,3-Propanediol

Heterogeneous Fenton Catalytic Removal of Organic Pollutant in Aqueous Solution by using Coal Gangue as a Catalyst

Background: Coal gangue was used as a catalyst in heterogeneous Fenton process for the degradation of azo dye and phenol. The influencing factors, such as solution pH gangue concentration and hydrogen peroxide dosage were investigated, and the reaction mechanism between coal gangue and hydrogen peroxide was also discussed. Methods: Experimental results showed that coal gangue has the ability to activate hydrogen peroxide to degrade environmental pollutants in aqueous solution. Under optimal conditions, after 60 minutes of treatment, more than 90.57% of reactive red dye was removed, and the removal efficiency of Chemical Oxygen Demand (COD) up to 72.83%. Results: Both hydroxyl radical and superoxide radical anion participated in the degradation of organic pollutant but hydroxyl radical predominated. Stability tests for coal gangue were also carried out via the continuous degradation experiment and ion leakage analysis. After five times continuous degradation, dye removal rate decreased slightly and the leached Fe was still at very low level (2.24-3.02 mg L-1). The results of Scanning Electron Microscope (SEM), energy dispersive X-Ray Spectrometer (EDS) and X-Ray Powder Diffraction (XRD) indicated that coal gangue catalyst is stable after five times continuous reuse. Conclusion: The progress in this research suggested that coal gangue is a potential nature catalyst for the efficient degradation of organic pollutant in water and wastewater via the Fenton reaction.

Structural and Catalytic Properties of Co-doped Perovskite Oxide on Coal Combustion

In this paper, the structural and catalytic properties of co-doped perovskite oxide La0.8Ce0.2Mn1−xCoxO3 are investigated. First, coal combustion catalysts of mesoporous perovskite-type La0.8Ce0.2Mn1−xCoxO3 were prepared by using sol–gel method. The resulting powder was characterised by scanning electron microscopy (SEM), X-ray diffraction (XRD), Brunauer–Emmett–Teller’s test (BET), and thermogravimetric analysis (TGA). Then, the results showed that after partially substituting La with Ce and substituting Mn with Co in LaMnO3, Ce occupied parts of the La site and Co occupied parts of the Mn site. As the substitution rate of Co increased, the pore diameter significantly decreased, and the specific surface area increased first and then decreased. Thirdly, thermogravimetric measurements and coal combustion constructed single-reaction model in the presence of the La0.8Ce0.2Mn1−xCoxO3 catalysis indicated that the presence of catalysts reduced the reaction initiation temperature (Teo), the maximum mass loss velocity temperature (Tmax), and the completion temperature of the main pyrolysis (Tf). The addition of 5 % La0.8Ce0.2Mn0.9Co0.1O3 to coal caused the reaction initiation temperature (Teo) to decrease by 34 °C compared with coal alone. Lastly, a distributed activation energy model of 5 % La0.8Ce0.2Mn0.9Co0.1O3 obtained an activation energy distribution curve. Results indicated that the activation energy of samples at the primary pyrolysis stage did not present a single peak value but mainly accumulated at 140–160 kJ, which could replace the mean activation energy of pyrolysis reaction. At the same time, frequency factor was not constant but presented a certain degree of linear correlation with activation energy, thereby indicating the presence of more than a single-reaction pyrolysis mechanism.

Cobalt aluminate spinel-derived catalysts for glycerol aqueous phase reforming

Catalytic activity at mild (235 °C/3.5 MPa) and severe (260 °C/5.0 MPa) APR conditions was investigated over catalysts based on cobalt aluminate spinel synthetized by coprecipitation. Co/Al ratio was varied and physicochemical characteristics were assessed by N2 adsorption, H2 chemisorption, XRD, H2-TPR, DRS-UV, FTIR, CO2-TPD, NH3-TPD and XPS. Formation of cobalt aluminate produced strong Co-O-Al interaction in the catalyst precursor leading to improved Co dispersion upon activation. Co/Al ratio could be used to tune catalyst characteristics, thus selectivity towards the desired reaction pathway. Overall, Co/Al above the stoichiometric value produced smaller and more stable metallic Co, which allowed best APR performance. For instance, at 235 °C/3.5 MPa glycerol conversion and conversion to gas of 0.625CoAl (88% and 22%) were notably higher than those of bare Co3O4 (23% and 5%). At severe conditions, 0.625CoAl catalyst produced 231 μmolH2/gcat min (60% H2). Statistical analysis of data collected from long-term run was used to investigate reaction mechanism. Long-term run revealed that sintering and oxidation were main mechanisms for catalyst deactivation whereas some leaching of Co nanoparticles, and carbonaceous deposition was also detected.

Hydrogen and syngas production from catalytic steam gasification of char derived from ion-exchangeable Na- and Ca-loaded coal

Catalytic steam gasification of char derived from low-rank coal possesses substantial potential as a source of hydrogen energy and syngas feedstocks, and its performances are largely associated with the employed catalysts. Therein, ion-exchangeable Na or Ca species are always regarded as excellent in-situ catalysts in low-rank coal. In this paper, gasification of Na-Char, Ca-Char and a Na/Ca-Char mixture with different partial pressures of steam was performed within a temperature range of 700–900 °C using a micro fluidized bed reaction analyzer. The results indicate that Na and Ca species could accelerate the gas release rate during gasification and even significantly increase H2 production, in sharp contrast to non-catalytic gasification. Variations in the product gases during Na-Char and Ca-Char gasification were completely different, which associated with the different deactivation pathways and catalytic reaction mechanisms of Na and Ca catalysts. With an increasing gasification temperature, the decreasing trend of H2 production for Na-Char gasification was mainly due to the loss of Na during gasification. Conversely, the enhancement of Ca activity promoted the H2 production. The H2/CO ratio of Ca-Char gasification at 700 °C approximately ranged from 1.0 to 2.0 as a function of the partial pressure of steam, which suggested catalytic gasification can be suitable for hydrogen-rich production and subsequent synthesis reactions. In addition, gasification of Na/Ca-Char mixture produced a higher hydrogen content in the product gases than that of Na-Char or Ca-Char gasification alone, particularly for the 30%Na/70%Ca-Char mixture. It implies that the high H2 production of 70%Ca30%Na-Char mixture was attributed to the cooperative effects of the Na and Ca species on the catalytic activity. This study provides comprehensive information regarding the effects of ion-exchangeable Na, Ca and a Na/Ca mixture on the hydrogen production and syngas composition during steam gasification, which provides new insight into the utilization of low-rank coal.

Transition metal oxide supported on alumina catalysts: a comparative study for the hydrogenation of octanal

Monometallic (10 wt.%) Co, Ni and Cu nanoparticles supported on alumina catalysts were prepared using an ultrasonic impregnation- cavitation method and characterized using ICP, XRD, physisorption, chemisorption and temperature programmed techniques. The copper catalyst showed higher metal dispersion and greater hydrogen and CO chemisorption capacity when compared to the nickel and cobalt catalysts. Hydrogenation of octanal carried out in a continuous flow high pressure fixed bed reactor showed that the rate of reaction and turnover number of octanol depended on the amount of hydrogen chemisorbed. The copper catalyst showed the lowest activation energy, as well as best catalytic activity. The Cu-Al catalyst which showed higher metal dispersion and low acidity, showed the highest selectivity towards octanol with no C24 acetal formation, when compared to the Ni-Al and Co-Al catalysts. Keywords: Octanal hydrogenation, octanol, copper, nickel, cobalt

Enhanced stability of Co catalysts supported on phosphorus-modified Al2O3 for dry reforming of CH4

Phosphorous-modified γ-Al2O3 support is used to prepare cobalt-based catalysts (CoP(x)Al, x=0–4wt%) for dry reforming of methane (DRM). From the studied catalysts, CoAl displays the highest conversions of CH4 and CO2 at the initial stage due to good cobalt dispersion. However, both conversions decrease significantly after 20h on stream due to the formation of inactive CoAl2O4 phase through the reaction of oxidized CoOx with the alumina surface. For the CoP(x)Al catalysts, although the initial CH4 and CO2 conversions decrease gradually as the phosphorus loadings increased, all catalysts show more stable catalytic activity than the CoAl catalyst. Formation of aluminum phosphate (AlPO4) on the alumina surface can be achieved by the addition of phosphorus. The AlPO4 phase has the capacity to suppress the formation of CoAl2O4 phase. Phosphorous loadings on alumina surface of up to 1–2wt% exerted positive effect on catalyst stability, whereas loadings above this threshold exerted opposite effect.

35 バイオマスタールモデル物質を用いた褐炭担持Ni触媒の炭素析出劣化に対する検討(ガス化・燃焼(4))

35 バイオマスタールモデル物質を用いた褐炭担持Ni触媒の炭素析出劣化に対する検討(ガス化・燃焼(4))

Hydrogen production by methane decomposition over Co-Al mixed oxides derived from hydrotalcites: Effect of the catalyst activation with H2 or CH4

This study examines the influence of catalyst activation for methane decomposition over Co-Al mixed oxides derived from hydrotalcites. Samples were prepared by coprecipitation and characterized by surface area measurements and temperature-programmed reduction. Spent catalysts and carbon produced in the reaction were characterized by X-ray diffractometry, temperature-programmed oxidation and scanning electron microscopy. Activity runs using previously reduced samples with H2 or activated under CH4 flow were carried out in a fixed-bed reactor between 500 and 750 °C using in-line gas chromatography analysis. The specific surface area decreases as the Co/Al ratio increases, which is related to the increased Co3O4 phase rather than Co-Al mixed oxides. The TPR results indicate the reduction of four types of Co species: Co3+ and Co2+ species from Co3O4, and Co from inverse spinel (Co2AlO4) and normal spinel (CoAl2O4). Reduction with hydrogen at 750 °C was very severe. Samples reduced with H2 showed large Co° crystallites, which increased with the Co/Al ratio. Co-Al catalyst activation under methane flow leads to lower crystallite size and higher thermal stability for hydrogen production by methane decomposition.

Vapor phase hydrogenation of furfural over nickel mixed metal oxide catalysts derived from layered double hydroxides

The hydrogenation of furfural is investigated over various reduced nickel mixed metal oxides derived from layered double hydroxides (LDHs) containing Ni-Mg-Al and Ni-Co-Al. Upon reduction, relatively large Ni(0) domains develop in the Ni-Mg-Al catalysts, whereas in the Ni-Co-Al catalysts smaller metal particles of Ni(0) and Co(0), potentially as alloys, are formed, as evidenced by XAS, XPS, STEM and EELS. All the reduced Ni catalysts display similar selectivities towards major hydrogenation products (furfuryl alcohol and tetrahydrofurfuryl alcohol), though the side products varied with the catalyst composition. The 1.1Ni-0.8Co-Al catalyst showed the greatest activity per titrated site when compared to the other catalysts, with promising activity compared to related catalysts in the literature. The use of base metal catalysts for hydrogenation of furanic compounds may be a promising alternative to the well-studied precious metal catalysts for making biomass-derived chemicals if catalyst selectivity can be improved in future work by alloying or tuning metal-oxide support interactions

Effect of Three Different Catalysts (KCl, CaO, and Fe2O3) on the Reactivity and Mechanism of Low-Rank Coal Pyrolysis

The pyrolysis behavior of Huangling coal (HL) was investigated using KCl, CaO, and Fe2O3 as the catalysts. The catalytic pyrolysis characteristics of coal were studied by thermogravimetry, as well as from the yield of the pyrolysis products and gas and tar composition. The catalytic mechanism was discussed in terms of the changes in gas composition and kinetic analysis. The Doyle integral method was employed for investigating the reaction kinetics of the coal catalyst mixture. The general effect of the additive on the reactivity of coal pyrolysis was evaluated using the pyrolysis characteristic index P. The results show that KCl, CaO, and Fe2O3 exhibit a catalytic effect on the pyrolysis of HL. The char and gas yield increased with the addition of catalysts, and the tar yield first increased and then decreased. With the addition of 1.5% of KCl or Fe2O3 catalyst or 0.5% CaO, the best catalytic effect was observed for the pyrolysis of coal. Coal pyrolysis can be divided into two regions: 472–655 °C and 655–...