Ni/Al2O3 catalysts for CO2 methanation: Effect of silica and nickel loading

Samples containing from 1 to 33 wt.% of NiO on silica and alumina doped with silica (1 and 20 wt.% silica in the support) have been prepared and characterized by BET, XRD, FT-IR, UV–vis–NIR, FE-SEM, EDXS, and TPR techniques. Catalysts have been pre-reduced in situ before catalytic experiments and data have been compared with Ni/Al₂O₃ reference sample. Characterization results showed that SiO₂ support has a low Ni dispersion ability mainly producing segregated NiO particles and a small amount of dispersed Ni²⁺ in exchange sites. Instead, for the Si-doped alumina a “surface spinel monolayer phase” is formed by increasing Ni loading and, only when the support surface is completely covered by this layer, NiO is formed. Moreover, H₂-TPR results indicated that NiO particles are more easily reduced compared to Ni species. Low loading Ni/SiO₂ catalysts show high selectivity and moderate activity for RWGS (reverse Water Gas Shift) reaction, likely mainly due to nickel species dispersed in silica exchange sites, as evidenced by visible spectroscopy. High loading Ni/SiO₂ catalysts show both methanation and RWGS but evident short-term deactivation for methanation, attributed to large, segregated Ni metal particles, covered by a carbon veil. Ni on alumina -rich carriers, where nickel disperses forming a surface spinel phase, show high activity and selectivity for methanation, and short-term catalyst stability as well. This activity is attributed to small nickel clusters or metal particles interacting with alumina, formed upon reaction. The addition of SiO₂ in Al₂O₃ support decreases the activity of Ni catalysts in CO₂ methanation, because it reduces the ability of the support to disperse nickel in form of the surface spinel phase, thus reducing the amount of Ni clusters in the reduced catalysts.     

Enhanced low-temperature catalytic performance in CO2 hydrogenation over Mn-promoted NiMgAl catalysts derived from quaternary hydrotalcite-like compounds

Mn-promoted NiMgAl mixed-oxide (NiMnx-LDO, x = 0, 5, 10, 15) catalysts derived from hydrotalcite were synthesized using co-precipitation for CO₂ hydrogenation to synthetic natural gas. By regulating Mn contents, NiMn5-LDO delivered the most excellent catalytic performance, being about 2 times higher than that of undoped NiMn0-LDO catalyst (TOF of NiMn5-LDO and NiMn0-LDO: 0.61 s⁻¹ vs 0.31 s⁻¹ @ 240 °C). Through extensive characterization, it was found that Mn dopants promoted the reduction of bulk NiO through tuning the interaction between Ni and Mg(Mn)AlOx support. A high surface ratio of Ni⁰/Ni²⁺ was achieved over NiMn5-LDO. Furthermore, the surface basicity strength was tailored by Mn dopants. With 5 wt% of Mn, NiMn5-LDO catalyst showed a stronger medium-strength basicity and higher capacity of CO₂ adsorption than others. Particularly, TOF indicates a good correlation with medium-strength basicity over NiMnx-LDO catalysts. The strong metal-support interaction originated from the hydrotalcite structure kept nickel uniformly dispersed, endowing to the improved catalytic performance.     

Hydrogen production through autothermal reforming of CH4: Efficiency and action mode of noble (M = Pt,Pd) and non-noble (M = Re,Mo, Sn) metal additives in the composition of Ni-M/Ce0.5Zr0.5O2/Al2O3 catalysts

Hydrogen production through autothermal reforming of methane (ATR of CH₄) over promoted Ni catalysts was studied. The control of the ability to self-activation and activity of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was achieved by tuning their reducibility through the application of different types (M = Pt, Pd, Re, Mo or Sn) and content (molar ratio M/Ni = 0.003, 0.01 or 0.03) of additive. The comparison of the efficiency and action mode of noble (M = Pt, Pd) and non-noble (M = Re, Mo, Sn) metal additives in the composition of Ni-M/Ce_0.5Zr_0.5O₂/Al₂O₃ catalysts was performed using X-ray fluorescence analysis, N₂ adsorption, X-ray diffraction, high-resolution transmission electron microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, temperature-programmed reduction with hydrogen, and thermal analysis. The composition-characteristics-activity correlations were determined. It was shown that the introduction of a promoter does not affect the textural and structural properties of catalysts but influences their reducibility and performance in ATR of CH₄. At the similar dispersion of NiO active component (11 ± 2 nm), the Ni²⁺ reduction is intensified in the following order of additives: Mo < Sn < Re ≤ Pd < Pt. It was found that for the activation of Ni and Ni–Sn catalysts before ATR of CH₄ tests, the pre-reduction is required. On the contrary, the introduction of Pt, Pd and Re additives leads to the self-activation of catalysts under the reaction conditions and an increase of the H₂ yield due to the enhanced reducibility of Ni²⁺. The efficient and stable catalyst for hydrogen production has been developed: in ATR of CH₄ at 850 °C over an optimum 10Ni-0.9Re/Ce_0.5Zr_0.5O₂/Al₂O₃ catalyst the H₂ yield of 70% is attained. The designed catalyst has enhanced stability against oxidation and sintering of Ni active component as well as high resistance to coking.     

Effect of MgO/Al2O3 ratio in the support of mesoporous Ni/MgO–Al2O3 catalysts for CO2 utilization via reverse water gas shift reaction

2 and 5 wt.% nickel was supported on different MgO to Al₂O₃ (M/A) ratios (0.5, 1 and 1.5) and evaluated in reverse water gas shift (RWGS) reaction. The catalysts were prepared by impregnation method and the nanocrystalline supports were synthesized by simple surfactant (CTAB) assisted precipitation technique. The following catalytic activity was observed for 2% & 5% Ni supported on different M/A ratios; M/A = 1 > M/A = 1.5 > M/A = 0.5. The perceived order was related to difference in the structural properties of supports and catalysts. The BET results revealed decrease of specific surface area with increase in M/A ratio, mesoporous structure for M/A = 0.5 and 1 and meso-macroporous structure for M/A = 1.5. The effect of nickel loading on the support with M/A = 1 was also investigated. 1.5% Ni showed high CO₂ conversion of 39.2% at 700 °C and CO selectivity higher than 90% at all temperatures. Increase of nickel loading higher than 1.5% was in favor of CH₄ formation. The TEM images of 1.5% Ni on M/A = 1 revealed uniform distribution of Ni particles with average size of 4.9 nm. The H₂-TPR analysis displayed shifting of maximum temperature of the main peak (γ) to higher temperatures with increase of M/A ratio in the support, indicating harder reducibility of catalysts with higher MgO content. The 1.5% Ni supported on M/A = 1 (MgAl₂O₄) showed great catalytic stability and CO selectivity (>98%) after 15 h on stream.     

Bi-reforming of methane for hydrogen production using LaNiO3/CexZr1-xO2 as precursor material

In this work, the performance of Ni-based catalysts derived from LaNiO₃/Ce_xZr_1-xO₂ (x = 1, 0.75 and 0.50) for the bi-reforming of methane from biogas was studied. Furthermore, the catalysts were characterized by several techniques including in situ X-ray diffraction (in-situ XRD) and X-ray absorption near edge structure spectroscopy XANES at Ce L_III-edge and at Ni K-edge. It was shown that (i) all catalysts were reduced at temperatures below 700 °C and (ii) the addition of zirconium into cerium lattice improved the reducibility of the supports. Additionally, the catalytic test results showed that all supported catalysts initially exhibited a decrease in CH₄ and CO₂ conversions, which could be associated with possible oxidation of nickel particles. It has been proved that the precursor LaNiO₃/Ce_0.75Zr_0.25O₂ had the best performance since it presented the highest catalytic activity and good selectivity for hydrogen during the bi-reforming of methane at 800 °C.     

Investigation of Ni2+-doped ceria nanorods as the anode catalysts for reduced-temperature solid oxide fuel cells

Tailoring the surface chemistry of oxides has been widely used to adjust their catalytic behavior in the energy conversion and storage devices. Herein, nanorods of Ni²⁺-doped ceria (Ce_1-xNi_xO_2-δ, x = 0, 0.05, 0.1, 0.15) are synthesized via a modified hydrothermal method, and evaluated as the anode catalysts for reduced-temperature solid oxide fuel cells (SOFCs). X-Ray diffraction patterns of as-synthesized powders in air imply successful incorporation of Ni²⁺ into the fluorite lattice of ceria for x = 0.05 and 0.1, with a secondary phase of NiO observed for x = 0.15. Transmission electron microscopy (TEM) examination confirms a rod-like morphology with a diameter of 10–13 nm and a length of 55–105 nm. Exposure of these powders in H₂ at 600°C results in exsolution of some spherical Ni particles of 11 nm in diameter. Electrochemical measurements on both symmetrical anode fuel cells and functioning cathode-supported fuel cells show an order of the catalytic activity toward hydrogen oxidation - CeO_2-δ < Ce_0·95Ni_0·05O_2-δ < Ce_0·9Ni_0·1O_2-δ. The anode polarization resistances in 97% H₂ – 3% H₂O are 0.24, 0.31 and 0.37 Ω?cm² for Ce_0·9Ni_0·1O_2-δ, Ce_0·95Ni_0·05O_2-δ and CeO_2-δ at 600°C, respectively. Thin (La_0·9Sr_0.1) (Ga_0.8Mg_0.2)O_3-δ-electrolyte fuel cells with nanostructured SmBa_0.5Sr_0·5Co₂O_5+δ cathodes and Ce_0·9Ni_0·1O_2-δ anodes yield the highest power densities among the investigated series of anodes, e.g., 820 mW?cm^?2 in 97% H₂ – 3% H₂O and 598 mW?cm^?2 in 68% CH₃OH - 32% N₂. XPS analyses of reduced nanorods indicate that the highest catalytic activities of Ce_0·9Ni_0·1O_2-δ toward fuel oxidation reactions should be correlated to the presence of highly active Ni nanoparticles and increased surface active oxygen, as confirmed by substantially facilitated extraction of the lattice oxygen on the surface by H₂ in temperature-programmed reduction (TPR) measurements.     

Cu,Mg and Co effect on nickel-ceria supported catalysts for ethanol steam reforming reaction

Ethanol steam reforming is a promising reaction which produces hydrogen from bio and synthetic ethanol. In this study, the nano-structured Ni-based bimetallic supported catalysts containing Cu, Co and Mg were synthesized through impregnation method and characterized by XRD, BET, SEM, TPR and TPD analysis. The prepared catalysts were tested in steam reforming of ethanol in the S/C = 6, GHSV of 20,000 mL/(g_cat h) at the temperature range of 450–600 °C. Among the xNi/CeO₂ (x = 10, 13, 15 wt%) catalyst, the sample containing 13 wt% Ni with surface area of 64 m²/g showed the best performance with 89% ethanol conversion and 71% H₂ selectivity as well as low CO selectivity of 8% at 600 °C and The addition of Cu, Mg, and Co to catalyst structure were evaluated and it was found that the nature of second metal has a strong influence on the catalyst selectivity for H₂ production. Considering to results of TPR analysis, the 13Ni–4Cu/CeO₂ catalyst showed proper reduction which caused in better activity. On the other side based on TPD analysis, the more basic property of 13Ni–4Mg/CeO₂ bimetallic catalyst provided a better condition to methane steam reforming, leading to lower CH₄ selectivity and consequently more H₂ production. The 13Ni–4Cu/CeO₂ exhibited the highest activity and lowest selectivity towards ethanol conversion and CO production about 99% and 4%, while the 13Ni–4Mg/CeO₂ catalyst possessed the highest H₂ selectivity and lowest CH₄ selectivity about 74% and 1% respectively at 600 °C. The Ni–Cu and Ni–Mg bimetallic catalysts shows good stability with time on stream.     

Enhanced coke suppression by using phosphate-zirconia supported nickel catalysts under dry methane reforming conditions

Ni based phosphate zirconium catalysts were prepared by impregnation technique and used under CH₄ dry reforming conditions. Catalysts (x%Ni/8%PO₄–Zr, where x = 5, 10, 15 or 20) were characterized by nitrogen physical adsorption-desorption, X-ray diffraction, temperature programmed reduction, CO₂ and NH₃ temperature programmed desorption, thermal gravimetric analysis and transmission electron microscopy (TEM-EDAX). Catalysts displayed a typical mesoporous structure and different reducibility grade as a function of Ni loading, diagnostic of a different extent of metal-support interaction. Activity and stability strongly depend upon Ni loading while the best performance was observed for catalyst characterized by a Ni loading of 10 wt%. The CO₂-TPD profiles of spent catalysts indicated that such catalyst had more tendency to gasify coke formed over the catalyst surface. TGA analysis of used catalysts quantitatively showed that catalysts at higher Ni loading deactivated as result of huge graphitic carbon formation on catalyst surface. On the contrary, system 10%Ni8%PO₄/ZrO₂ turns out to be an excellent candidate to conduct the methane reforming reaction with CO₂ without coke formation at high CH₄ and CO₂ conversions. Phosphate play a fundamental role in promoting Ni–ZrO₂ interaction which reflects in the stabilization of catalytic system against metal sintering and coke formation.     

Modification of silica supported nickel catalysts with lanthanum for stability improvement in methane reforming with CO2

Dry reforming of methane (DRM) with excessive methane composition at CH₄/CO₂ = 1.2:1 was studied over lanthanum modified silica supported nickel catalysts (Ni-xLa-SiO₂, x: 1, 2, 4, and 6% in the target weight percent of La). The catalysts were prepared by ammonia evaporation method. Nickel phyllosilicate and La₂O₃ were the main phases in calcined catalysts. The modification of La enhanced the formation of 1:1 and Tran-2:1 nickel-phyllosilicate. There existed an optimum content of La loading at 1.50 wt% in Ni–2La–SiO₂ which resulted in its highest reduction degree (95.3%). The catalysts with appropriate amounts of La exhibited higher amount of CO₂ adsorption and created more medium and strong base centers. The sufficient number of exposed metallic nickel sites to catalyze the reforming reaction, as well as enough medium and strong basic sites in Ni–La–SiO₂ interface to accomplish the carbon removal were two important factors to attenuate catalyst deactivation. The catalyst stability evaluated at 750 °C for 10 h followed the order: Ni–2La–SiO₂ > Ni–4La–SiO₂ > Ni–1La–SiO₂ ≈ Ni–6La–SiO₂ > Ni–SiO₂. Ni–2La–SiO₂ catalyst possessed the lowest deactivation behavior, whose CH₄ conversion dropped from 60.2 to 55.9% after 30 h operation at 750 °C, indicating its high resistance against carbon deposition and sintering.     

Catalytic CO2 reforming of CH4 over Cr-promoted Ni/char for H2 production

The objective of the study is to investigate the catalytic performance of Cr-promoted Ni/char in CO₂ reforming of CH₄ at 850 °C. The char obtained from the pyrolysis of a long-flame coal at 1000 °C was used as the support. The catalysts were prepared by incipient wetness impregnation methods with different metal precursor doping sequence. The characterization of the composite catalysts was evaluated by XRD, XPS, SEM-EDS, TEM, H₂-TPR, CO₂-TPD, CH₄-TPSR, and CO₂-TPO. The results indicate that the catalyst prepared by co-impregnation of Ni and Cr possess higher activity than those by sequential impregnation. The optimal loading of Cr on 5 wt% Ni/char is 7.8 wt‰. Moreover, the molar feed ratio of CH₄/CO₂ has a considerable effect on both the stability and the activity of Cr–Ni/char. The main effect of Cr is the great enhance of the adsorption to CO₂. It is interesting that the conversions of CH₄ and CO₂ over Cr-promoted Ni/char and Ni/char decrease initially, following by a steady rise as the reaction proceeds with time-on-stream (TOS). In addition, cyclic tests were conducted and no distinct deterioration in the catalytic performance of the catalysts was observed. On the basis of the obtained results, nickel carbide was speculated to be the active species which was formed during the CO₂ reforming of CH₄ reaction.     

Preparation and characterization of Ni based catalysts for the catalytic partial oxidation of methane: Effect of support basicity on H2/CO ratio and carbon deposition

The catalytic partial oxidation of methane (CPOM) was studied on Ni based catalysts. Catalysts were prepared by wet impregnation method and characterized by using AAS, BET, XRD, HRTEM, TPR, TPO, Raman Spectroscopy and TPSR techniques. The prepared catalysts showed nearly 95% CH₄ conversion and nearly 96% H₂ selectivity under the flow of 157,500 (L kg⁻¹ h⁻¹) with the ratio of CH₄/O₂ = 2 by using air as an oxidant at 1 atm and 800 °C. Support basicity greatly influenced the H₂/CO ratio and carbon deposition. It was found that the lowest carbon deposition occurred on Ni impregnated MgO catalyst. Considering the results, it was found that Ni/MgO catalyst with 10% Ni content would be the best catalyst amongst Ni/Al₂O₃, Ni/MgO/Al₂O₃, Ni/MgAl₂O₄ and Ni/Sorbacid for the CPOM only under more reductive conditions. Under optimum conditions, Ni/MgO showed poor performance and therefore Ni/Sorbacid would be the ideal catalyst because of its greater carbon resistance than the other catalysts.     

Ni–Fe/Mg(Al)O alloy catalyst for carbon dioxide reforming of methane: Influence of reduction temperature and Ni–Fe alloying on coking

Various Ni–Fe/Mg(Al)O alloy catalysts were obtained by calcination of Ni–Fe–Mg–Al hydrotalcite-like compounds, followed by reduction at different temperatures (973–1173 K). The characterizations of XRD and STEM-EDX suggest that the resulting Ni–Fe alloy particles are composition-uniform and size-controllable. The alloy composition is little affected by the reduction temperature, whereas the particle size (5.8–8.2 nm) increases with the increase of reduction temperature. This property is ascribed to the homogeneous distribution of nickel and iron species during the catalyst preparation. All of the Ni–Fe/Mg(Al)O alloy catalysts show relatively high and stable activity for CH₄–CO₂ reforming during 25 h of investigation at 773–1073 K. Particularly, the 973 K-reduced catalyst exhibits higher coke-resistance due to its smaller particle size. E_a-CH₄ and CH₄-TPSR measurements indicate that Ni–Fe alloying inhibits CH₄ dissociation. It is considered that during DRM CH₄ is dissociated at the Ni sites and CO₂ may be activated at the metal-support interface as well as the Fe sites. Ni–Fe alloying may inhibit CH₄ dissociation and/or promote CO₂ activation, thus contributing to the suppression of coke deposition.     

Steam reforming of CH4 at low temperature on Ni/ZrO2 catalyst: Effect of H2O/CH4 ratio on carbon deposition

In present work, the H₂O/CH₄ on carbon deposition in SRM reaction over Ni/ZrO₂ was studied. Prepared by impregnation, the catalysts were characterized by TEM, XPS, H₂-TPR, TG-DSC-MS, Raman, and XRD. The results showed that when H₂O/CH₄ = 2 with GHSV of 14460 h⁻¹, the highest CH₄ conversion (46.8%) was achieved on the Ni/ZrO₂ catalyst at 550 °C. This was due to the relatively high surface content of Ni⁰ (27%) species and the formation of easy removal polymer carbon (C₁). When the H₂O/CH₄ was 1, a large amount of difficult to remove fiber carbon (C₂) formed and polymer carbon would wrap around the catalyst to reduce its activity. However, excess water might promote surface reconstruction by converting Ni⁰ to Ni(OH)₂, which reduced the surface Ni⁰ content and then inhibited the catalytic activity, while the amount of carbon deposited, especially C₂, reduced significantly.     

Characterization and catalytic behavior of hydrotalcite-derived Ni–Al catalysts for methane decomposition

A series of Ni catalysts were prepared from Ni–Al hydrotalcite-like compounds (HTlcs) by varying the Ni/Al molar ratio (1–4) and calcination temperature (773–1173 K) of HTlcs. The catalysts were reduced with H₂ at 1073 K and tested for CH₄ decomposition at 773–923 K on a thermal gravimeter. Various techniques including N₂ physical adsorption, XRD, H₂-TPR, XPS, HAADF-STEM, TEM, and Raman were applied to characterize the catalysts and the as-produced carbon. The characterizations show that calcination of Ni–Al HTlcs leads to Ni(Al)O solid solution and minor NiO and/or NiAl₂O₄ spinel may be formed depending on the Ni/Al ratio and calcination temperature; upon reduction at 1073 K, most nickel species are reduced to metallic Ni. In CH₄ decomposition, carbon yield shows a volcano-type dependence on the Ni content with the optimum Ni/Al ratio equal to 3. On the other hand, carbon yield is affected by the calcination temperature of the Ni₃Al HTlcs to a small extent. Carbon yield is also significantly affected by the reaction temperature, which decreases remarkably with a rise of temperature to 923 K. TEM and Raman indicate that fish-bone carbon nanofibers are formed at 773–823 K, whereas multi-walled carbon nanotubes are formed at 873–923 K.     

High-surface-area Ce0.8Zr0.2O2 solid solutions supported Ni catalysts for ammonia decomposition to hydrogen

Three kinds of Ce_0.8Zr_0.2O₂ solid solutions synthesized via surfactant-assisted route, co-precipitation, and sol–gel method were used as supports of Ni-based catalysts by impregnation. Their catalytic activities in ammonia decomposition to hydrogen were tested, and the structural effect of support and the influence of nickel content on catalytic activity were evaluated. Mesoporous/high-surface-area Ce_0.8Zr_0.2O₂ support synthesized by surfactant-assisted method exhibited better promoting effect than other supports when the same content of Ni was loaded. The interactions between Ni species and Ce_0.8Zr_0.2O₂ supports were found to greatly affect the chemical properties of catalysts, including redox, H₂ adsorption, and catalysis. The promoting effects of Ce in catalysts, plentiful vacancies in the solid solutions due to the doping of Zr⁴⁺, and high surface areas of the supports were discussed on the ammonia decomposition activities of the resultant catalysts, as well as the influence of hydrogen spillover. The ammonia conversion of 95.7% with the H₂ producing rate of 89.3 mL/min·g_cat was achieved at 550 °C over the Ni catalysts supported on the mesoporous/high-surface-area Ce_0.8Zr_0.2O₂.     

Carbon dioxide methanation over Ni catalysts prepared by reduction of NixMg3‒xAl hydrotalcite-like compounds: Influence of Ni:Mg molar ratio

A series of supported Ni catalysts have been prepared from Ni_xMg_3?xAl hydrotalcite-like compounds (HTlcs) and the influence of Ni:Mg molar ratio on the structural property and catalytic activity for CO₂ methanation is investigated. The catalysts were characterized by N₂ physical adsorption, X-ray powder diffraction (XRD), temperature-programmed reduction (H₂-TPR), temperature-programmed desorption (CO₂-TPD), H₂ chemisorption, scanning electronic microscopy (SEM), scanning transmission electronic microscopy (STEM), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). By reducing HTlcs at 800 °C, well dispersed Ni particles with average size of 5–10 nm are formed. The Ni crystal size decreases with the decrease of Ni:Mg ratio, attributable to the strong interaction between nickel and magnesium oxides. Among the catalysts, Ni₂Mg₁Al-HT shows the highest activity, giving ～93% CO₂ conversion and >99% CH₄ selectivity at 275 °C and SV = 5000 mL g^?1 h^?1. Meanwhile, this catalyst exhibits good stability without obvious sintering and coking. The high activity is related to the large amount of surface Ni⁰ species and medium basic sites. From CO₂-TPD and DRIFTS, it is inferred that CO₂ adsorbs on the medium basic sites, i.e., Ni–Mg(Al)O interface, forming monodentate carbonate. In situ DRIFTS reveals that monodentate carbonate, monodentate formate, and adsorbed CO are the main intermediate species, suggesting that the reaction may proceed via the formate formation route.     

Various nickel doping in commercial Ni–Mo/Al2O3 as catalysts for natural gas decomposition to COx-free hydrogen production

Non-oxidative decomposition of natural gas to CO_x-free hydrogen production over commercial nickel-molybdate hydrotreating catalysts with different Ni loading from 5 to 40wt% were studied at 700 °C. The catalysts were characterized by XRD, BET, TEM, Raman spectroscopy and TG-DTA analysis. The catalytic decomposition activities showed that a tremendous hydrogen production (∼90%) was obtained over 20–40wt%Ni/Mo–Al₂O₃ catalysts. Moreover, all catalysts exhibited excellent durability up to 9 h with stable catalytic activity toward H₂ production. Although the increase of Ni content reduces the catalyst surface area, the H₂ productivity and longevity increases with increased Ni content, i.e., the catalytic decomposition activity primarily depends on the active Ni sites which overcompensates the surface deficiencies. TEM, TGA and XRD data of used catalysts indicated that a higher thermal stability and graphitization degree of multi-walled carbon nanotubes were obtained on all Ni containing catalysts. Higher metal loading produced carbon nanofibers beside CNTs due to increment of particle size and long reaction time.     

High performance Ni exsolved and Cu added La0.8Ce0.2Mn0.6Ni0.4O3-based perovskites for ethanol steam reforming

La_0.8Ce_0.2Mn_0.6Ni_0.4O₃ with (LCMN@CuO) and without (LCMN) CuO addition are prepared by solution methods, followed by reduction in 5% H₂–N₂ stream at 650 °C to form Ni exsolved and CuO reduced catalysts, LCMN@Ni and LCMN@Ni/Cu, for ethanol (EtOH) steam reforming (ESR). The catalysts are characterized by X-ray diffraction (XRD), scanning and transmission electron microscopies (SEM and TEM), temperature programmed reduction (H₂-TPR), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy etc., and are evaluated for ESR with a steam/carbon ratio of 3 and a weight hourly space velocity (WHSV) of 4 h⁻¹ at temperatures between 500 and 700 °C. Ni exsolution and CuO reduction are confirmed on the substrates in LCMN@Ni and LCMN@Ni/Cu. Both the catalysts demonstrate a complete conversion of EtOH, forming mainly H₂, CO₂, CO and CH₄. And increasing temperature to 700 °C increases the yields of H₂ and CO to the levels about 90% and 40%, respectively, at the cost of CH₄; and such performance remains unchanged for 30 h. These results indicate that both LCMN@Ni and LCMN@Ni/Cu are promising catalysts for ESR, the main difference between them is that the latter is more chemically stable and more resistant to carbon deposition under ESR conditions.     

Ni/CeAl2O3 for optimum hydrogen production from biomass/tar model compounds: Role of support type and ceria modification on desorption kinetics

This communication presents the synergistic role of ceria and alumina support type, in the gasification of glucose/toluene as biomass/tar model compounds over Ni/CeAl₂O₃. Two catalysts having 20 wt% nickel on a mesoporous Ce(x)-mesoAl₂O₃ (x = 0 or 1) were prepared via successive incipient wetness impregnation method. Two similar catalysts (i.e. Ni(20)/Ce(x)-γAl₂O₃, x = 0 or 1), were also prepared using a commercial γ-Al₂O₃ support. The catalysts show excellent activities for glucose/toluene mix feed as a biomass/tar model species. Physicochemical characterizations indicate that this method produces Ni/CeAl₂O₃ catalysts of moderate acidity, desirable pore size for biomass/tar conversion to syngas. Activity test in a riser simulator revealed that all the four catalysts are highly active for biomass/tar reforming at moderate temperature (i.e. 700 °C). In particular, Ni(20)/Ce-meso-Al₂O₃ was the best in terms of hydrogen production at low gasification temperature (i.e. 500 °C). This is due to its unique properties resulting from the synergistic effect of ceria promoter and our methodology for synthesizing Ce-doped-mesoAl₂O₃. For a 15 wt% mixed glucose/toluene feed at 700 °C and 30 s reaction time, the product composition over the Ni(20)/Ce-meso-Al₂O₃ catalyst was 74.33 mol% H₂, 22.60 mol% COx and 3.06 mol% HC's (i.e. C₁, C_2, and C₂⁼) with no tar in the product.     

Impacts of nickel loading on properties,catalytic behaviors of Ni/γ–Al2O3 catalysts and the reaction intermediates formed in methanation of CO2

In this study, methanation of CO₂ over Ni/Al₂O₃ with varied nickel loading (from 0 to 50 wt%) was evaluated, striving to explore the effects of nickel loading on catalytic behaviors and the reaction intermediates formed. The results showed that agglomeration of nickel particles were closely related to interaction between nickel and alumina. Increasing nickel loading resulted in the increased proportion of nickel having medium strong interaction with alumina, the reduced reduction degree of NiO, the increase of medium to strong basic sites, the enhanced activity for methanation and the competition between reverse water gas shift (RWGS) reaction and methanation. Lower nickel loading promoted RWGS reaction while methanation of CO₂ dominated at higher nickel loading. The catalyst with a nickel loading around 25% achieved the best activity for methanation. The in–situ DRIFTS studies of methanation of CO₂ showed that CO₂ could be absorbed on surface of metallic Ni, NiO or alumina. More metallic nickel species on alumina suppressed formation of carbonate species while promoted further conversion of HCOO¹ species and ¹CH₃ species, achieving a higher catalytic efficiency. Moreover, more metallic nickel species was crucial for gasifying the carbonaceous intermediates, prevented aggregation of the intermediates to coke and achieving a higher catalytic stability.