Ni Surface Area Research Articles

Oxygen reduction from flammable off-gas for solid oxide fuel cell so as to avoid anode deterioration

In the present study, chemical equilibrium FactSage computations with an actual flammable off-gas have been firstly done for designing a prototype O2 reducing apparatus to convert the off-gas into safe SOFC fuel and determining a thermal pretreating temperature range. O2 reducing experiments from simulated flammable off-gases as thermal pretreatments before feeding to the SOFC anode side have been carried out.O2 concentration can be reduced in proportion to the Ni surface area, reaching the minimum concentration of about 0.16 vol% from its initial value of 10.2 vol% with the Ni surface areas of 562 m2/m3 at 1073 K. H2 and CO concentrations of the objective SOFC fuel constituents are close to their respective initial concentrations, due to accelerated Boudouard reactions and reverse shift reaction. Concentration of H2 plus CO reached the maximum value at 537 m2/m3 of Ni surface area, concretely 92.8% of H2 plus CO is remaining in comparison with the initial simulated flammable off-gas.Some recommended future strategies of this thermal pretreating process to convert the flammable off-gas into safe SOFC fuel are also proposed in every part through this paper so as to supply complete solutions for any global-scale problems.

Fabrication of nanographene using nickel supported by a tungsten mesh

A method for the fabrication of nanographene films using pentacene and H2 gas was proposed. A tungsten (W) mesh, a W mesh coated with nickel (Ni) (Ni/W mesh), and a W mesh supporting Ni (WNi mesh) were used as catalysts to synthesize the nanographene films. The decomposition temperature of the pentacene molecule using the Ni/W mesh was lower than that for the W mesh. The nanocarbon films prepared using the Ni/W and the WNi meshes had different film properties compared with those made using the W mesh. These nanocarbon films had an absorption peak similar to that of graphene around 270 nm. In addition, on the WNi mesh, which had a Ni surface area ratio of 3%, pentacene molecules coexisted with 6,13-dihydropentacene molecules. It is found that the pentacene multimer yield and the polymerization reaction rate were enhanced using the WNi mesh. The WNi mesh is useful as a catalyst for the rapid formation (0.03 nm/s) of nanocarbon films consisting of nanographene at temperatures below 250 °C.

Ni/La2O3 Catalysts for Dry Reforming of Methane: Insights into the Factors Improving the Catalytic Performance

AbstractTo understand the structure‐reactivity relationship of Ni/La2O3, and eventually get more applicable catalysts for DRM, glycine nitrate combustion (GNC), precipitation (PP) and thermal decomposition (TD) methods have been used to prepare La2O3 supports. Although all the supports possess a hexagonal La2O3 phase, their bulk and surface properties are significantly changed. By using them as supports, the interactions between NiO/Ni and La2O3 are varied, thus achieving Ni/La2O3 catalysts with different activity, stability and anti‐coking ability, which follow the order of 5Ni/La2O3‐GNC>5Ni/La2O3‐PP>5Ni/La2O3‐TD. On La2O3 having a higher surface area, a catalyst with a higher active metallic Ni surface area can be achieved. Therefore, the interfaces between Ni and La2O2CO3 can be enlarged, which effectively facilitates the reaction between carbon deposits and the La2O2CO3 formed during the DRM, thus preventing the accumulation of both and keeping the catalyst surface clean, active and stable. In addition, the amount of surface alkaline and active oxygen sites of the reduced catalysts obey the order of 5Ni/La2O3‐GNC>5Ni/La2O3‐PP>5Ni/La2O3‐TD, which is well consistent with the reaction performance. Therefore, these two factors are also believed to be critical to decide the reaction performance. It is concluded that Ni/La2O3 catalysts with high activity, stability and potent anti‐coking ability for DRM can be achieved by preparing catalysts with high Ni dispersion.

In-situ growth of nitrogen-doped mesoporous carbon nanostructure supported nickel metal nanoparticles for oxygen evolution reaction in an alkaline electrolyte

Rational three-dimensional nitrogen doped mesoporous carbon nanostructured surfaced Nickel metal (Ni) nanoparticles (nps), NCNP composites have been developed using nickel organic complex and utilized as an electrocatalyst for oxygen evolution reaction. The NCNP composites of tunable physio-chemical characteristics, such as Ni nps size (∼18–∼42 nm), surface area (∼18–∼43 m2 g−1), pore size (3.23–3.84 nm) and nitrogen doping amount (1.20–3.87 wt%) have been achieved via controlled carbonization temperature. An optimized NCNP composite of favorable physio-chemical properties has delivered good oxygen evolution kinetics such as a lower overpotential value (370 mV) at 10 mA cm−2, a minimum Tafel slope value (55 mV dec−1), and relatively a higher electrochemical surface area (0.6325 cm−2) than the other NCNP composites. Moreover, the best NCNP electrocatalyst has shown a comparable overpotential value with the benchmarking catalyst at 10 mA cm−2, equivalent to ∼10% solar photoelectrical conversion efficiency. In addition, the best NCNP electrocatalyst has exhibited excellent accelerated degradation test for 24 h at a constant current density of 10 mA cm−2 with an increase overpotential value of 0.029 V.

Effect of Pt Promotion on the Ni-Catalyzed Deoxygenation of Tristearin to Fuel-Like Hydrocarbons

Pt represents an effective promoter of supported Ni catalysts in the transformation of tristearin to green diesel via decarbonylation/decarboxylation (deCOx), conversion increasing from 2% over 20% Ni/Al2O3 to 100% over 20% Ni-0.5% Pt/Al2O3 at 260 °C. Catalyst characterization reveals that the superior activity of Ni-Pt relative to Ni-only catalysts is not a result of Ni particle size effects or surface area differences, but rather stems from several other phenomena, including the improved reducibility of NiO when Pt is present. Indeed, the addition of a small amount of Pt to the supported Ni catalyst dramatically increases the amount of reduced surface metal sites, which are believed to be the active sites for deCOx reactions. Further, Pt addition curbs the adsorption of CO on the catalyst surface, which decreases catalyst poisoning by any CO evolved via decarbonylation, making additional active sites available for deoxygenation reactions and/or preventing catalyst coking. Specifically, Pt addition weakens the Ni-CO bond, lowering the binding strength of CO on surface Ni sites. Finally, analysis of the spent catalysts recovered from deCOx experiments confirms that the beneficial effect of Pt on catalyst performance can be partially explained by decreased coking and fouling.

Is the CO2 methanation on highly loaded Ni-Al2O3 catalysts really structure-sensitive?

Highly loaded Ni-Al2O3 catalysts (14–88 wt.-% Ni) were prepared by dry impregnation, wet impregnation, deposition precipitation and coprecipitation and tested in the CO2 methanation. By means of ICP-OES, XRD, TPR, H2 chemisorption, N2 physisorption and thermogravimetry, different Ni species were identified, and their dependence on the synthesis method and the Ni loading was investigated. The catalysts prepared had Ni particle sizes of 5–91 nm and Ni surface areas of 5–51 m2 g−1. It could be shown that the turnover frequency (TOF) does not depend on metal-support interactions, the metal-support interface or the particle size. Hence, the CO2 methanation on Ni-Al2O3 catalysts is clearly a structure-insensitive reaction. There is a linear correlation between the conversion and the Ni surface area at constant modified residence time. Hence, catalysts with the highest Ni surfaces, i.e., the samples prepared by deposition precipitation and coprecipitation, reached the highest weight time yields. The prerequisites for high Ni surface areas at high Ni loadings could be elucidated: During the synthesis, Ni has to be able to completely penetrate the mesopores of the support. Furthermore, a linear correlation between the selectivity to CO and the weight percentage of the impurity Na could be revealed. The stability of the supported catalysts was highly dependent on the spatial distribution of Ni and the stability of the support: A high dispersion or the presence of unsupported Ni reduced the stability. Furthermore, the stability of the supported catalysts was smaller than the one of the coprecipitated catalysts, where the stability decreased with increasing nNi/nAl.

Surface titration of supported Ni catalysts by O2-pulse thermal analysis

A new method for determining the Ni0 metal surface area of MgO supported catalysts is proposed. Different series of MgO supported Ni catalysts were prepared and titrated by chemical adsorption of oxygen inside an STA-MS setup. Simultaneous recording of the mass gain upon oxidation, the enthalpy of formation of the oxide and the evolved gas allowed a precise quantification of the metallic Ni surface area. In addition, any uncertainties linked with the complex Ni oxide stoichiometry could be ruled out. A comparison of the newly developed oxygen pulse method with already established techniques using H2 or N2O confirmed the applicability of the method and further revealed its surface sensitivity and accuracy with respect to MgO supported Ni catalysts.

Enhanced metal-support interaction on NiSi-P catalyst for improved COx methanation performance

NiSi-I and NiSi-P catalysts were synthesized by impregnation method and ammonia-evaporated method, respectively. They were investigated for COx methanation reaction in the fixed-bed reactor at atmospheric pressure. A series of characterization results demonstrated that the NiSi-P catalyst with phyllosilicates structure achieved superior catalytic performance to the conventional NiSi-I catalyst for COx methanation. Meanwhile, the stability test indicated that CH4 yield on the NiSi-P catalyst decreased slightly from 88.2% to 77.5% at 400 °C after thermal shock at 650 °C for 24 h. However, CH4 yield on the NiSi-I catalyst decreased greatly from 72.5% to 26.7% at the same reaction condition after thermal shock, suggesting that the stability of the NiSi-P catalyst was much better than that of NiSi-I. The superior performance of the NiSi-P catalyst was attributed to several factors including the small nickel particle size, the high Ni surface area, and the enhanced metal-support interaction. These properties contributed to the higher reactivity and better stability of NiSi-P than those of NiSi-I catalyst.

Methane dry reforming over Ni/Mg-Al-O: On the significant promotional effects of rare earth Ce and Nd metal oxides

In this study, with the purpose to obtain more efficient catalysts for methane dry reforming, an Mg-Al-O support having excess MgO and higher alkalinity than pure MgAl2O4 spinel support have been designed and used to prepare Ni/Mg-Al-O catalysts. XRD has demonstrated that this support consists of both MgO and MgAl2O4 spinel phases. As a result, Ni/Mg-Al-O displays better reaction performance than Ni/MgAl2O4 and Ni/Al2O3 catalysts. With the promotion by Ce and Nd oxides, the Ni dispersion and the surface active oxygen amount can be significantly improved, which results in more active and stable catalysts with also significantly improved coking resistance. It is revealed that the active metallic Ni surface area, surface alkalinity and active oxygen abundance are the major factors deciding the reaction performance of the Ni/Mg-Al-O catalysts. Because of the optimal concerted action of these factors, Ni-Ce/Mg-Al-O, the sample promoted by ceria, displays the best reaction performance among all the catalysts.

Reduced Temperature Ammonia Decomposition Using Ni/Zr-Doped Al2O3 Catalyst

The development of Ni/Zr-doped Al2O3 was achieved to reduce the reaction temperatures in ammonia decomposition by doping Zr into Al2O3 framework. The Ni/Zr-doped Al2O3 exhibits higher H2 yield and NH3 conversion than Ni/γ-Al2O3 in a continuous operation. Partial doping of Zr in Al2O3 framework can increase Ni dispersion, Ni surface area and basic sites of the Ni catalyst. These effects can promote in both dehydrogenation of NH3 and recombination of nitrogen adsorbates in an NH3 decomposition mechanism. The comparison between roles of Zr as a dopant and a promoter for Ni catalyst was also discussed.

CO2 methanation over Fe- and Mn-promoted co-precipitated Ni-Al catalysts: Synthesis, characterization and catalysis study

The methanation reaction of CO2 is in discussion to be a sustainable pathway to address future questions arising from limited primary energy feedstock and the accumulation of CO2 in the atmosphere. Therefore, the development of highly active and thermostable catalysts for this reaction is an indispensable matter of research. For this reason, an equimolar NiAlOx benchmark catalyst (44 wt.% Ni loading) was synthesized and modified by doping with Fe or Mn up to 10 wt.% of promoter by co-precipitation at constant pH 9. Their activity and stability performances in the CO2 methanation reaction were evaluated by comparing the conversion versus temperature characteristics before and after an aging period of 32 h at 500 °C. Material characterization studies comprising BET, XRD, in situ IR spectroscopy, XPS, H2 and CO2 chemisorption, and EPR/FMR contributed to derive structure-activity relationships and to obtain a deeper understanding of the catalytic behavior. Promotion with Mn led to a significant enhancement of the catalytic activity. This is assumed to be caused by a higher density of medium basic sites and an enhanced CO2 adsorption capacity on the activated catalyst related to interactions between Mn oxide species and the mixed oxide phase, in combination with a stabilization of the Ni surface area at moderate Mn loadings. Promotion with Fe increased the thermal stability of the catalyst, which is attributed to the formation of a Ni-Fe alloy during catalyst activation. For both phenomena, the optimum molar Ni to promoter ratio for co-precipitated catalysts was found to be around 5.

Effects of ZnO on Characteristics and Selectivity of Coprecipitated Ni/ZnO/Al2O3Catalysts for Partial Hydrogenation of Sunflower Oil

Ni/ZnO/Al2O3 catalysts at different molar ratios were synthesized and characterized, and the catalytic performances were assessed by partial hydrogenation of sunflower oil. Ni:Zn at various molar ratios have resulted in varying degrees of Ni and Zn migration from the bulk to the catalyst surface, which led to different pore characteristics. Catalysts with equimolar Ni:Zn have shown wider pores and higher pore volumes and achieved 23% higher hydrogenation activity than Ni/Al2O3. The presence of ZnO also led to higher Ni surface area and dispersion, and TEM images have indicated that this could be attributed to ZnO that acts as a spacer for the Ni crystallites. However, the Ni surface area diminishes as the ZnO content becomes higher. The presence of ZnO in Ni/ZnO/Al2O3 catalysts is also shown to lower trans-fats formation when wide pores are available.

BASF opens new chemical catalysts production plant in China

CO2 methanation using nickel-based catalysts has attracted large interest as a promising power-to-gas route. Ni nanoparticles supported on nitrogen-doped CNTs with Ni loadings in the range from 10 wt% to 50 wt% were synthesized by impregnation, calcination and reduction and characterized by elemental analysis, X-ray powder diffraction, H2 temperature-programmed reduction, CO pulse chemisorption and transmission electron microscopy. The Ni/NCNT catalysts were highly active in CO2 methanation at atmospheric pressure, reaching over 50% CO2 conversion and over 95% CH4 selectivity at 340 °C and a GHSV of 50,000 mL g−1 h−1 under kinetically controlled conditions. The small Ni particle sizes below 10 nm despite the high Ni loading is ascribed to the efficient anchoring on the N-doped CNTs. The optimum loading of 30 wt%–40 wt% Ni was found to result in the highest Ni surface area, the highest degree of conversion and the highest selectivity to methane. A constant TOF of 0.3 s−1 was obtained indicating similar catalytic properties of the Ni nanoparticles in the range from 10 wt% to 50 wt% Ni loading. Long-term experiments showed that the Ni/NCNT catalyst with 30 wt% Ni was highly stable for 100 h time on stream.

Ni- and Sb-Doped SnO2 Electrocatalysts with High Current Efficiency for Ozone Production via Electrodeposited Nanostructures

Ozone is a powerful disinfectant in water treatment, and electrochemical ozone production (EOP) is desirable because it can be safer than current production methods. The greatest challenge for electrochemical ozone production is the lack of catalysts with high selectivity for ozone evolution. Nickel- and antimony- doped tin oxide electrodes synthesized from sol-gels and nanoparticles have been reported to reach ozone current efficiencies up to 50% for electrochemical ozone production. In this study, we present a novel electrodeposition synthesis method that results in current efficiencies up to 63%. The optimal temperature of the post-deposition oxidation treatment is determined by the tradeoff between catalyst stability and crystallinity. Analysis via microscopy and X-ray diffraction suggests that electrodeposited films provide sufficient Ni concentration, surface area, and morphology to support a solution-mediated ozone production reaction.

Prediction of Nickel Morphological Evolution in Composite Solid Oxide Fuel Cell Anode Using Modified Phase Field Model

The morphological change in nickel (Ni) caused by coarsening during a high temperature operation has been considered one of the main reasons for the performance degradation of conventional composite Ni-yttria stabilized zirconia (Ni-YSZ) solid oxide fuel cell (SOFC) anodes. An improved phase field model is proposed to simulate the Ni coarsening in a Ni-YSZ anode with both the Ni volumetric morphology and multiple crystallographic orientations evolved. Using a three-dimensional (3D) reconstruction of the initial anode microstructure obtained based on focused ion beam-scanning electron microscopy (FIB-SEM), the time dependent evolutions of triple phase boundary (TPB) density, specific Ni surface and Ni-YSZ interface areas, the volume fraction of isolated Ni, and the other factors can be quantitatively analyzed. To validate the model, it was tested based on different initial microstructures from the same anode. Multiple factors that may influence the anode durability during a long-term operation were quantitatively investigated based on the model.

Nonmetal—Metal transition in carbon films embedded by Ni nanoparticles: The temperature coefficient of resistivity (TCR), Raman spectra and surface morphology

In this paper, carbon films embedded by Ni nanoparticles were deposited on glass substrates. Films using four mosaic targets made of carbon and nickel with Ni surface areas 1.78, 3.21, 3.92 and 4.64% are made. With increasing Ni content in these films a nonmetal–metal transition especially above room temperature region is observed. This transition is explainable by electrical measurements in temperature range 15–500K. With increasing Ni surface areas from 1.87 to 4.64%, Ni content of films increases from59.68 to 92.89%. The electrical conductivity of dielectric films was explained by tunneling effect. Activation tunneling energy that was obtained from temperature dependence of electrical resistivity correlates both with G and D peaks of Raman spectra and depend on Ni content of films. With increasing Ni surface areas from1.78 to 3.92% due to increasing graphen like carbon, a nonmetal–metal and from 3.92 to 4.64% due to increasing amorphous carbon interconnections of Ni nanoparticles, a peculiar effect of metallic to nonmetallic state occurs. The RMS roughness of films in 3.92% has minimum value about 0.54nm.

Effects of reduction on the catalytic performance of limonite ore

The catalytic performance of Ni-containing limonite ore in the dry reforming reaction of methane (CH4 + CO2 → 2H2 + 2CO) was determined before and after hydrogen reduction, and under a flow of hydrogen. After hydrogen reduction, the limonite ore exhibited higher catalytic performance, because of the formation of Fe–Ni. However, the Fe in Fe–Ni was readily oxidized by the input CO2 gas, resulting in a rapid decrease in the catalytic performance of limonite ore. The performance decrease was due to a decrease in the Ni surface area; Ni could not dissolve in iron oxides and this caused segregation in the iron oxides. When the reaction was conducted under a hydrogen flow, the Fe–Ni was formed and maintained. Ni was highly dispersed in the Fe–Ni phase, resulting in greater surface area of Ni and higher conversion rate of CH4 and CO2. The catalytic performance of the limonite ore was inferior to the Ni/Al2O3 catalyst because the effect of catalyst support was small, however, the limonite ore was more stable during catalytic use and much cheaper than the Ni/Al2O3.

Characterization of nickel catalysts with transient methods

The Ni surface area is a key factor in catalytic performance of supported Ni catalysts employed in heterogeneously catalyzed reactions. For its characterization, transient measurement techniques are powerful but need a proper experimental design and a high level of accuracy. In this study, several transient methods, namely temperature programmed desorption of H2 (H2-TPD), pulsed H2 chemisorption and N2O chemisorption, were applied and evaluated for the characterization of Ni catalysts. Results were compared with those from static H2 chemisorption. Ni powder, as well as NiAlOx and Ni/γ-Al2O3 with varying Ni loadings, synthesized via precipitation and incipient wetness impregnation, respectively, were used as model catalysts. H2-TPD within the temperature range from 84 to 753K is able to completely describe the interaction of H2 with supported Ni. However, a quantitative analysis of the specific Ni surface area based on H2-TPD is difficult whereas pulsed H2 chemisorption leads to comparable results as obtained from static measurements. Adsorption and pre-treatment conditions have a strong impact on the desorption spectra. Reversible morphologic changes of the Ni surface were revealed by H2-TPD when changing the gas atmosphere during pre‐treatment. N2O chemisorption occurs in three steps including fast oxygen uptake, growth of the oxide layer and subsequent layer thickening due to subsurface and bulk oxidation. A separation of surface and subsurface/bulk oxidation of NiAlOx and Ni/γ-Al2O3, both of which are readily oxidized even under mild conditions, is only achievable at temperatures between 190 and 195K. In this temperature range, the ratio of adsorbed oxygen atoms, O, and the number of Ni surface atoms, NiS, (O/NiS) is 0.38±0.07, which can be applied for specific Ni surface area determination. The experimental mode of N2O chemisorption (flow or titration mode) does not influence the extent of subsurface oxidation. The separation of surface and subsurface/bulk oxidation is more feasible in the case of Ni powder. Here, a suitable temperature for Ni surface area determination lies within 265 and 285K with an O/NiS ratio of 0.96±0.05.

Reversible H2/H2O electrochemical conversion mechanisms on the patterned nickel electrodes

The patterned nickel (Ni) electrode enables to quantify the triple-phase boundary (TPB) length and Ni surface area as well as exclude the interference of bulk gas diffusion. In this study, the patterned Ni electrodes are investigated in both the solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) modes at the atmosphere of H2O/H2. The experimental test shows the patterned Ni electrode keeps stable and intact only at the specific operating condition due to instability of Ni at the H2O-containing atmosphere. The effects of the temperature, partial pressure of H2O and H2 on the electrochemical performance are measured. The electrochemical performance has a positive correlation with the temperature, partial pressure of H2 and H2O. Further, the experimental results are compared with the mechanism containing two-step charge-transfer reaction used in the existing literature. An analytical calculation is performed to indicate the rate-limiting steps may be different for SOFC and SOEC modes. In SOFC mode, H2 electrochemical oxidation could be dominated by both charge transfer reaction at low polarization voltage and by the charge-transfer reaction H(Ni) + O2−(YSZ) → OH−(YSZ) + (Ni) + e− at high polarization voltage, however in SOEC mode, H2O electrochemical reduction is considered to be dominated by H2O(YSZ) + (Ni) + e− → OH−(YSZ) + H(Ni).

Hydrogen generation from hydrous hydrazine over Ni/CeO2 catalysts prepared by solution combustion synthesis

Hydrous hydrazine is a promising hydrogen carrier for fuel cell vehicles owing to its high hydrogen content (8.0wt% for N2H4·H2O), low cost and stable liquid state at ambient temperature. The development of cost effective catalysts with high activity and 100% selectivity for hydrogen generation under mild conditions, however, is a significant challenge for its practical use. In this work, a series of Ni/CeO2 catalysts were prepared by solution combustion synthesis (SCS), varying the SCS parameters in terms of ratio of precursor oxidizers (nickel nitrate and ammonium cerium nitrate), fuel-to-oxidizer ratio (0.5–3) and fuel type (hydrous hydrazine and glycine). These parameters influence the combustion behavior and, in turn, the physicochemical properties of catalysts such as crystallinity, Ni particle size, surface area and pore size as well as formation of NiOCe solid solution. The reaction mechanism for the SCS process is discussed. The tailored 6wt% Ni/CeO2 catalyst synthesized with fuel-to-oxidizer ratio 2 and hydrous hydrazine fuel, exhibited 100% selectivity for hydrogen generation and good activity with a TOF value 34.0h−1 at 50°C, which is the highest catalytic performance among all prior reported catalysts containing Ni alone.