Methane reforming reaction with carbon dioxide over SBA-15 supported Ni-Mo bimetallic catalysts

A series of mesoporous molecular sieves SBA-15 supported Ni-Mo bimetallic catalysts (xMo1Ni, Ni = 12 wt.%, Mo/Ni atomic ratio = x, x = 0, 0.3, 0.5, 0.7) were prepared using co-impregnation method for carbon dioxide reforming of methane. The catalytic performance of these catalysts was investigated at 800 °C, atmospheric pressure, GHSV of 4000 ml·g_cat^− 1·h^− 1 and a V(CH₄)/(CO₂) ratio of 1 without dilute gas. The result indicated that the Ni-Mo bimetallic catalysts had a little lower initial activity compared with Ni monometallic catalyst, but it kept very stable performance under the reaction conditions. In addition, the Ni-Mo bimetallic catalyst with Mo/Ni atomic ratio of 0.5 showed high activity, superior stability and the lowest carbon deposition rate (0.00073g_c·g_cat^− 1·h^− 1) in 600-h time on stream. The catalysts were characterized by power X-ray diffraction, N₂-physisorption, H₂-TPR, CO₂-TPD, TG and TEM. The results indicate that the Ni-Mo bimetallic catalysts have smaller metal particle, higher metal dispersion, stronger basicity, metal-support interaction and Mo₂C species. It is concluded that Mo species in the Ni-Mo bimetallic catalysts play important roles in reducing effectively the amount of carbon deposition, especially the amount of shell-like carbon deposition.     

Catalytic decomposition of methane for the simultaneous co-production of CO2-free hydrogen and carbon nanofibre based polymers

Through the catalytic decomposition of methane (CDM) it is possible to obtain in a single step both CO₂-free hydrogen and carbon nanostructures with a wide range of applications such as nanocomposite reinforcements. In this work, a Ni-based catalyst has been used to carry out the catalytic decomposition, obtaining an hydrogen concentration up to 47% (vol.) in the flue gas and carbon nanofibres (CNF). These structures have been inserted into two epoxy resins with different viscosity in order to study the influence of the CNF load in the electrical resistivity of the new materials prepared. As a result, the resistivity of these materials decreases up to 10⁶ Ω cm, values which avoid the electrostatic discharge and allow the electrostatic painting.     

Steam carbon gasification of a nickel based oxygen carrier

Ni-based oxygen carriers are promising candidates for Chemical Looping applications due to a combination of excellent methane conversion performance, mechanical stability, oxygen transfer capacity. However, experiments conducted on NiO/NiAl₂O₄ in a micro-fluidized bed reactor show that methane forms coke on active nickel sites. In subsequent tests, water vapour was fed to the coked Ni oxygen carrier producing a highly concentrated stream of CO/H₂ (1/1). In the absence of water vapour, production of hydrogen dropped with time while a methane/argon mixture was fed to the reactor. Co-feeding water together with methane improves stability - both H₂ production and carbon deposition were constant for over 1 h. Despite the tremendous lay down of carbon, catalytic activity remained stable at levels as low as 3 vol.% water vapour (and 10% methane). Water vapour is an effective oxidant for Ni(0) but is insufficient to entirely re-oxidize the oxygen carrier from Ni to NiO.     

Catalytic test of supported Ni catalysts with core/shell structure for dry reforming of methane

Supported nickel catalysts with core/shell structures of Ni/Al₂O₃ and Ni/MgO-Al₂O₃ were synthesized under multi-bubble sonoluminescence (MBSL) conditions and tested for dry reforming of methane (DRM) to produce hydrogen and carbon monoxide. A supported Ni catalyst made of 10% Ni loading on Al₂O₃ and MgO-Al₂O₃, which performed best in the steam reforming of methane (97% methane conversion at 750 °C) and in the partial oxidation of methane (96% methane conversion at 800 °C), showed also good performance in DRM and excellent thermal stability for the first 150 h. The supported Ni catalysts Ni/Al₂O₃ and Ni/MgO-Al₂O₃ yielded methane conversions of 92% and 92.5%, respectively and CO₂ conversions of 95.0% and 91.8%, respectively, at a reaction temperature of 800 °C with a molar ratio of CH₄/CO₂ = 1. Those were near thermodynamic equilibrium values.     

Mixed and autothermal reforming of methane with supported Ni catalysts with a core/shell structure

Supported nickel catalysts with a core/shell structure of Ni/Al₂O₃ and Ni/MgO-Al₂O₃ synthesized under multi-bubble sonoluminescence (MBSL) conditions were tested for mixed steam and dry (CO₂) reforming and autothermal reforming of methane. In the previous tests, the supported Ni catalysts made of 10% Ni loading on Al₂O₃ or MgO-Al₂O₃ had shown good performances in the steam reforming of methane (methane conversion of 97% at 750 °C), in the partial oxidation of methane (methane conversion of 96% at 800 °C) and in dry reforming of methane (methane conversion of 96% at 850 °C) and showed high thermal stability for the first 50-150 h. In this study, the supported Ni catalysts showed good performance in the mixed and autothermal reforming of methane with their excellent thermal stability for the first 50 h. In addition, very interestingly, there was no appreciable carbon deposition on the surface of the tested catalysts after the reforming reaction.     

Oxygen reduction by Fe-based catalysts in PEM fuel cell conditions: Activity and selectivity of the catalysts obtained with two Fe precursors and various carbon supports

Fe-based catalysts for the oxygen reduction reaction (ORR) in polymer electrolyte membrane (PEM) fuel cell conditions have been prepared by adsorbing two Fe precursors on various commercial and developmental carbon supports. The resulting materials have been pyrolyzed at 900 °C in an atmosphere rich in NH₃. The Fe precursors were: iron acetate (FeAc) and iron tetramethoxy phenylporphyrin chloride (ClFeTMPP). The nominal Fe content was 2000 ppm (0.2 wt.%). The carbon supports were HS300, Printex XE-2, Norit SX-Ultra, Ketjenblack, EC-600JD, Acetylene Black, Vulcan XC-72R, Black Pearls 2000, and two developmental carbon black powders, RC1 and RC2 from Sid Richardson Carbon Corporation. The catalyst activity for ORR has been analyzed in fuel cell tests at 80 °C as well as by cyclic voltammetry in O₂ saturated H₂SO₄ at pH 1 and 25 °C, while their selectivity was determined by rotating ring-disk electrode in the same electrolyte. A large effect of the carbon support was found on the activity and on the selectivity of the catalysts made with both Fe precursors. The most important parameter in both cases is the nitrogen content of the catalyst surface. High nitrogen content improves both activity towards ORR and selectivity towards the reduction of oxygen to water (4e⁻ reaction). A possible interpretation of the activity and selectivity results is to explain them in terms of two Fe-based catalytic sites: FeN₂/C and FeN₄/C. Increasing the relative amount of FeN₂/C improves both activity and selectivity of the catalysts towards the 4e⁻ reaction, while most of the peroxide formation may be attributed to FeN₄/C. When FeAc is used as Fe precursor, iron oxide and/or hydroxide are also formed. The latter materials have low catalytic activity for ORR and reduce O₂ mainly to H₂O₂.     

Catalytic filamentous carbon: Structural and textural properties

Catalytic filamentous carbon (CFC) synthesized by the decomposition of methane over iron subgroup metal catalysts (Ni, Co, Fe or their alloys) is a new family of mesoporous carbon materials possessing the unique structural and textural properties. Microstructural properties of CFC (arrangement of the graphite planes in filaments) are shown to depend on the nature of catalyst for methane decomposition. These properties widely vary for different catalysts: the angle between graphite planes and the filament axis can be 0° (Fe-Co-Al₂O₃), 15° (Co-Al₂O₃), 45° (Ni-Al₂O₃), 90° (Ni-Cu-Al₂O₃). The textural properties of CFC depend both on the catalyst nature and the conditions of methane decomposition (T, °C). The micropore volume in CFC is very low, 0.001-0.022 cm³ g⁻¹ at the total pore volume of 0.26-0.59 cm³ g⁻¹. Nevertheless, the BET surface area may reach 318 m² g⁻¹. Results of the TEM (HRTEM), XRD, Raman spectroscopic, SEM and adsorption studies of the structural and textural properties of CFC are discussed.     

Hydrogen production by catalysed pyrolysis of polymer blends

Differently composed mixtures of HDPE and PMMA were pyrolysed at 700 °C and 815 °C in pyrolysis reactor. It was directly coupled with gas chromatography/mass spectrometry (GC/MS). On line pyrolysis GC/MS was applied in analysis of hydrogen, methane and carbon monoxide yielding in polymer blends pyrolyzate with/without metal (Ni,Co) coated particles, tested as a methane to hydrogen conversion catalysts supporting additives. They were prepared by electrochemical deposition of Ni and Co on the small iron particles surface. Maximum hydrogen production was confirmed at the highest pyrolysis temperature (815 °C), and the highest HDPE contents in the blends mixture. Higher content of the PMMA in the mixture led to higher production of CO and lower hydrogen contents in pyrolyzate. Nickel and cobalt containing additives affected production of hydrogen and other components at both 700 °C and 815 °C pyrolysis temperatures. An effect of different heat distribution between metal particles and polyblends occurred and affected hydrogen production. Application of pyrolysis gas chromatography in hydrogen production from polyblends represents an important tool to model future technological outputs as well simultaneous hydrogen production and CO, CO₂ elimination. Moreover, catalysis assisted conversion of methane to hydrogen can improve final hydrogen content in pyrolyzate. Effectivity of pyrolysis hydrogen production was determined by its quantification based on analytical calibration.     

Intermetallic catalyst for carbon nanotubes (CNTs) growth by thermal chemical vapor deposition method

The methane conversion and carbon yield of the chemical vapor deposition (CVD) reaction suggests that the optimum reaction conditions of the formation of multi-wall carbon nanotubes (MWCNTs) can be obtained by using a 50 mg of nano-MgNi alloy under pyrolysis of the pure CH₄ gas with the flow rate about 100-120 cm³/min at 650 °C for 30 min. Raman results indicate the CNTs are in multi-wall structure, since no single-wall characteristic features appearing in the 200-400 cm⁻¹ region. This is consistent with those of the XRD and TGA findings. Under selected condition, the carbon yield and the CNTs purity can reach up to 1231% and 92% in the presence of hydrogen. It is presumable that the presence of hydrogen in the pyrolysis of CH₄ prevents the deactivation of catalysts and enhances the graphitization degree of CNTs. In addition, the presence of Mg metal in the alloy can prevent the aggregation of the Ni metal and forms the active Mg₂Ni phase to enhance the CH₄ pyrolysis to form CNTs. After the purification procedures with both air oxidation at 550 °C and HCl treatments, the final purified yield and purity of CNT reach to 73.2% and (98.04 ± 0.2)% respectively.     

Efficient production of hydrogen and multi-walled carbon nanotubes from ethanol over Fe/Al2O3 catalysts

Fe/Al₂O₃ catalysts with different Fe loadings (10-90 mol%) were prepared by hydrothermal method. Ethanol decomposition was studied over these Fe/Al₂O₃ catalysts at temperatures between 500 and 800 °C to produce hydrogen and multi-walled carbon nanotubes (MWCNTs) at the same time. The results showed that the catalytic activity and stability of Fe/Al₂O₃ depended strongly on the Fe loading and reaction temperature. The Fe(30 mol%)/Al₂O₃ and Fe(40 mol%)/Al₂O₃ were both the effective catalyst for ethanol decomposition into hydrogen and MWCNTs at 600 °C. Several reaction pathways were proposed to explain ethanol decomposition to produce hydrogen and carbon (including nanotube) at the same time.     

Ethanol steam reforming reactions over Al2O3 · SiO2-supported Ni-La catalysts

Nickel-based catalysts supported on Al₂O₃ · SiO₂ were prepared with modification of the second metal involving La, Co, Cu, Zr or Y, of which the catalytic behaviors were assessed in the ethanol steam reforming reaction. Activity test indicated that addition of La resulted in higher selectivity of hydrogen and lower selectivity of carbon monoxide, compared with Co-doped nickel catalyst. Influences of lanthanum amounts on catalytic performance were studied over 30NixLa/Al₂O₃ · SiO₂ (x = 5, 10, 15), and characterizations by XRD, TPR and XPS indicated that low amount of lanthanum additives (5%) was superior to inhibit the crystal growth of nickel as well as beneficial to the reduction of nickel oxide. Finally 100 h test for the optimal catalyst 30Ni5La/Al₂O₃ · SiO₂ indicated its good long-term stability to provide high hydrogen selectivity and low carbon monoxide formation, as well as good resistance to coke deposition at low temperature.     

Thermogravimetric studies of carbon nanofiber formation from methane at low temperature over Ni-based skeletal catalysts and the effect of substrate pre-carburization

Using thermogravimetry (TG) under conditions that minimize inhibition by the hydrogen produced, the intrinsic catalytic rates of skeletal Ni, pure and alloyed with solute metals Fe, Co, or Cu, were evaluated in methane decomposition to carbon nanofibers. In “standard” tests, i.e., after pre-reduction in H₂ and exposure to CH₄ directly at 450 °C, several catalysts reached stable activities exceeding 4 mg C/mg cat./h, comparable with literature values obtained at 500 °C or above. TG evidence is presented for partial bulk carburization of Ni in CH₄ below 350 °C, which leads to substantially increased coking rates. TEM evidence supports the view that carburization promotes catalyst particle disintegration, thereby inducing faster and more stable nanofiber growth. Irregularities in alloy response to carburization are interpreted in terms of the stability of the respective mixed-metal carbides. TEM also shows that alloying changes the metal nanocrystallite shape (habit), with consequences for the carbon nanofiber structure. Evidence for the easy dissociation of CH₄ is corroborated by direct catalyst activation in the absence of H₂. Reduction begins in pure hydrocarbon around 300 °C and leads to coking activities at 450 °C comparable to those for samples pre-reduced in H₂. Skeletal metal catalysts offer distinct advantages in low-temperature natural gas conversion.     

Evaluation of different oxygen carriers for biomass tar reforming (II): Carbon deposition in experiments with methane and other gases

This work is a continuation of a previous paper by the authors [1] which analyzed the suitability of the Chemical Looping technology in biomass tar reforming. Four different oxygen carriers were tested with toluene as tar model compound: 60% NiO/MgAl₂O₄ (Ni60), 40% NiO/NiAl₂O₄ (Ni40), 40% Mn₃O₄/Mg-ZrO₂ (Mn40) and FeTiO₃ (Fe) and their tendency to carbon deposition was analyzed in the temperature range 873-1073 K. In the present paper, the reactivity of these carriers to other compounds in the gasification gas is studied, also with special emphasis on the tendency to carbon deposition. Experiments were carried out in a TGA apparatus and a fixed bed reactor. Ni-based carriers showed a tendency to form carbon in the reaction with CH₄, especially Ni60. The addition of water in H₂O/CH₄ molar ratios of 0.4-2.3 could decrease the carbon deposited, but not in the case of Ni60. Mn-based sample reacted with CH₄ almost completely and with low tendency to carbon deposition, while the Fe-based sample showed low reactivity. Ni40 showed more reactivity to CO than Mn40, although in both cases carbon was deposited, especially at 873 K. When H₂ was present, it reacted rapidly with both carriers, decreasing the amount of carbon deposited. The presence of CO₂ could also decrease the carbon deposited on Ni40 at 1073 K. According to both these and the previous results [1], it can be concluded that Mn40 is the most adequate for minimization of carbon deposition in Chemical Looping Reforming (CLR).     

The production of a homogeneous and well-attached layer of carbon nanofibers on metal foils

Carbon nanofibers (CNFs) were deposited on metal foils including nickel (Ni), iron (Fe), cobalt (Co), stainless steel (Fe:Ni; 70:11 wt.%) and mumetal (Ni:Fe; 77:14 wt.%) by the decomposition of C₂H₄ at 600 °C. The effect of pretreatment and the addition of H₂ on the rate of carbon formation, as well the morphology and attachment of the resulting carbon layer were explored. Ni and mumetal show higher carbon deposition rates than the other metals, with stainless steel and Fe the least active. Pretreatment including an oxidation step normally leads to higher deposition rates, especially for Ni and mumetal. Enhanced formation of small Ni particles by in situ reduction of NiO, compared to formation using a Ni carbide, is probably responsible for higher carbon deposition rates after oxidation pretreatment. The addition of H₂ during the CNF growth leads to higher carbon deposition rates, especially for oxidized Ni and mumetal, thus enhancing the effect of the reduction of NiO. The diameters of CNFs grown on metal alloys are generally larger compared to those grown on pure metals. Homogenously deposited and well-attached layers of nanotubes are formed when the carbon deposition rate is as low as 0.1-1 mg cm⁻² h⁻¹, as mainly occurs on stainless steel.     

Comparative study of CO and CO2 hydrogenation over supported Rh–Fe catalysts

The hydrogenation of CO, CO + CO₂, and CO₂ over titania-supported Rh, Rh–Fe, and Fe catalysts was carried out in a fixed-bed micro-reactor system nominally operating at 543 K, 20 atm, 20 cm³ min^− 1 gas flow (corresponding to a weight hourly space velocity (WHSV) of 8000 cm³ g_cat^− 1 h^− 1), with a H₂:(CO + CO₂) ratio of 1:1. A comparative study of CO and CO₂ hydrogenation shows that while Rh and Rh–Fe/TiO₂ catalysts exhibited appreciable selectivity to ethanol during CO hydrogenation, they functioned primarily as methanation catalysts during CO₂ hydrogenation. The Fe/TiO₂ sample was primarily a reverse water gas shift catalyst. Higher reaction temperatures favored methane formation over alcohol synthesis and reverse water gas shift. The effect of pressure was not significant over the range of 10 to 20 atm.     

Catalytic characteristics of carbon black for decomposition of ethane

The catalytic activities of rubber, color and conductive carbon black catalysts for decomposition of ethane were investigated in the temperature range from 973 to 1173 K. Significantly higher ethane conversion and lower ethylene selectivity were obtained in the presence of carbon black catalysts compared with non-catalytic decomposition, resulting in much higher hydrogen yields. This indicates that carbon black catalysts are effective catalysts for dehydrogenation of ethane to hydrogen and ethylene, as well as for the subsequent decomposition of ethylene to hydrogen and solid carbon. However, more methane was produced in the presence of carbon black catalysts than in non-catalytic decomposition. A reaction mechanism was proposed for the catalytic decomposition of ethane. The hydrogen yield increased with an increase in the specific surface area of the nonporous rubber and color carbon black catalysts with a surface area of up to approximately 100 m²/g. However, the hydrogen yield over the carbon black catalysts with higher surface areas, including the conductive carbon black catalysts with very high surface areas, did not increase significantly. The carbon black catalysts exhibited stable activity for ethane decomposition and hydrogen production for 36 h despite carbon deposition.     

Layered double hydroxides as catalysts for the efficient growth of high quality single-walled carbon nanotubes in a fluidized bed reactor

A family of layered double hydroxides (LDHs), such as Fe/Mg/Al, Co/Mg/Al, and Ni/Mg/Al LDHs, were used as catalysts for the efficient growth of single-walled carbon nanotubes (SWCNTs) in a fluidized bed reactor. The LDH flakes were agglomerated into clusters with sizes ranging from 50 to 200 μm, and they can be easily fluidized with a gas velocity ranging from 2.3 to 24 cm/s. After calcination and reduction, small metal catalyst particles formed and distributed uniformly on the flakes. At the reaction temperature, the introduction of methane realized the growth of SWCNTs with the diameter of 1-4 nm. The loose structure of LDH agglomerates afforded a yield as high as 0.95 g_CNT/(g_cat h) of SWCNTs with a surface area of 930 m²/g. Compared with Fe/Mg/Al LDH, Ni/Mg/Al and Co/Mg/Al LDHs showed a better selectivity to SWCNTs. The highest selectivity for metallic SWCNTs was obtained using Co/Mg/AI LDHs as the catalyst.     

Biomass to hydrogen via catalytic steam reforming of bio-oil over Ni-supported alumina catalysts

Production of hydrogen (H₂) from catalytic steam reforming of bio-oil was investigated in a fixed bed tubular flow reactor over nickel/alumina (Ni/Al₂O₃) supported catalysts at different conditions. The features of the steam reforming of bio-oil, including the effects of metal content, reaction temperature, W_bHSV (defined as the mass flow rate of bio-oil per mass of catalyst) and S/C ratio (the molar ratio of steam to carbon fed) on the hydrogen yield were investigated. Carbon conversion (moles of carbon in the outlet gases to moles of the carbon feed) was also studied, and the outlet gas distributions were obtained. It was revealed that the Al₂O₃ with 14.1% Ni content gave the highest yield of hydrogen (73%) among the catalysts tested, and the best carbon conversion was 79% under the steam reforming conditions of S/C = 5, W_bHSV = 13 1/h and temperature = 950 °C. The H₂ yield increased with increasing temperature and decreasing W_bHSV; whereas the effect of the S/C ratio was less pronounced. In the S/C ratio range of 1 to 2, the hydrogen yield was slightly increased, but when the S/C ratio was increased further, it did not have an effect on the H₂ production yield.     

Production of hydrocarbons in Fischer-Tropsch synthesis with Fe-based catalyst: Investigations of primary kerosene yield and carbon mass balance

The Fischer-Tropsch synthesis (FTS) of syngas was carried out using Fe-based catalysts in order to produce hydrocarbons (HCs) equivalent to kerosene, which is used as an alternative aviation fuel. The FTS was conducted in a downdraft continuous-flow-type fixed-bed reactor under a temperature of 533-573 K and a pressure of 3.0 MPa. The effects of reduction gases and time of the Fe-based catalyst, reaction temperature and the chemical species included in the Fe-based catalyst on the FTS were studied by focusing on primary kerosene yield and the carbon mass balance. The carbon mass balances in the study were almost 100%. In C6 + HCs, the selectivity of CO to the C11−C14 HCs equivalent to kerosene was found to be the second highest, the highest being its selectivity to C20 + HCs equivalent to wax. The amount of primary kerosene produced was maximum under the following conditions: the prepared Fe catalyst did not contain other chemical species, the feed ratio of the reduction gases H₂:CO:N₂ was 2:1:3, the catalyst reduction time was 8 h, and the FTS reaction temperature was 553 K.     

Characterization of active sites for methane decomposition on carbon black through acetylene chemisorption

The use of carbon black as a stable catalyst for methane decomposition for the production of hydrogen without CO_x emissions has recently been reported. In order to characterize the catalytically active sites on carbon black, acetylene adsorption was examined at 773 and 873 K by using a pulse technique. As the injection was repeated at 773 K, the adsorbed amount gradually decreased and eventually the adsorption ceased. At 873 K a constant amount of C₂H₂ was consumed repeatedly after several injections. Good relationships were obtained between the methane decomposition rate at 1123 or 1173 K and the cumulative acetylene adsorption at 773 K or the constant acetylene consumption at 873 K. Acetylene adsorption at 773 K can be used for quantitative determination of the number of active sites on the carbon black and the constant consumption at 873 K can be utilized as a probe reaction for comparison of activities of different carbon catalysts. Different physicochemical processes taking place at 773 and 873 K were discussed and a model for these adsorption processes was proposed.