Active Ni Species Research Articles

Enhanced selectivity of syngas in partial oxidation of methane: A new route for promising Ni‐alumina catalysts derived from Ni/ γ‐AlOOH with modified Ni dispersion

Partial oxidation of methane was studied over new Ni nanocatalysts prepared from Ni-impregnated γ-AlOOH, which were compared with their counterparts derived from impregnated γ-Al2O3 and α-Al2O3. The prepared catalysts were characterized by powder X-ray diffraction (XRD), N2-sorption, H2-temperatue programmed reduction, scanning electron microscopy, transmission electron microscopy, thermal gravimetric analysis, CO2- and NH3-temperature-programmed desorption, Raman spectroscopy, CO chemisorption, and diffuse reflectance infrared Fourier transform spectroscopy of adsorbed CO. Employing γ-AlOOH as the support precursor resulted in significantly improved textural properties and catalytic activity. The structure of the support precursor and its surface properties showed a strong influence on the type of Ni active species and their interactions with the support. γ-AlOOH-derived catalysts showed NiO as the dominant Ni species when calcined at 500°C to 650°C, while NiAl2O4 became the sole phase at higher temperatures. On the other hand, mixtures of NiO and NiAl2O4 formed over γ-Al2O3, calcined before impregnation, regardless of the precalcination temperature. All γ-AlOOH-derived catalysts showed higher specific surface areas compared to their counterparts derived from impregnated γ-Al2O3. Upon calcination at moderate temperatures, γ-AlOOH-derived catalysts also showed modified textural and morphological properties of the Ni active particles, including higher Ni dispersion, larger metal surface area, and smaller Ni crystallites. The support precursor and the pretreatment conditions showed a strong influence on the catalytic performance, which was referred to their significant effect on the type of the Ni species and interactions with the support. All catalysts showed higher catalytic activity than the α-Al2O3-derived catalyst, with CH4 conversion between 86% and 88.5% at 700°C. While γ-AlOOH- and γ-Al2O3-derived catalysts calcined at 650°C showed a stable CH4 conversion around 88%, and higher syngas selectivity than the other catalysts, Ni/γ-AlOOH-650 showed the highest selectivity to syngas, with a H2/CO ratio very close to 2.0. The improved Ni dispersion and the enhanced syngas selectivity obtained in the preset work demonstrate that using γ-AlOOH as a support precursor holds a great promise for the development of a new route for more efficient Ni catalysts compared with the widely studied γ-Al2O3 and α-Al2O3 support precursors.

Influence of calcination temperature of Ni/Attapulgite on hydrogen production by steam reforming ethanol

Abstract Sustainable hydrogen production can be realized by steam reforming ethanol (SRE) derived from renewable biomass, but develop high-efficiency and sixpenny catalyst is a major challenge. Attapulgite-supported nickel catalyst (Ni/ATP) exhibits promising potential for SRE for hydrogen production. The influence of calcination temperature (CT) on the microscopic morphology and physicochemical properties of Ni/ATP was investigated by various technologies. The results revealed that increasing CT could improve metal-support interaction (MSI) and surface Ni active species content. However, extortionate CT (>700 °C) significantly led to catalyst structure collapse and crystal phase transfer accompanied with the formation of new species, which enhanced the MSI and reduced the surface Nio species content. The outcomes of SRE experiments demonstrated that Ni/ATP-C600 presented maximal activity and H2 yield due to its higher surface contents of the Nio active component and Ni/ATP-C900 exhibited unique stability owing to its stronger MSI. Hence, the coordination between active species distribution and MSI in Ni/ATP can be adjusted by CT. Additionally coke deposits on spent Ni/ATP-C300 were identified with quite aromatic species, which strongly attract to the surface of catalyst and encapsulate active site, while that on used Ni/ATP-C900 had higher degrees of graphitization, but did not affect the stability.

How the reflux treatment stabilizes the metastable structure of ZrO2 and improves the performance of Ni/ZrO2 catalyst for dry reforming of methane?

Ni/ZrO2 catalyst has been widely investigated for dry reforming of methane (DRM), but it suffers from rapid deactivation due to nickel aggregation and carbon deposition under the harsh conditions. Herein, we introduce the post-treatment of reflux in Ni/ZrO2 catalyst prepared by the conventional co-precipitation method. The detailed characterization results demonstrate that the catalysts after reflux exhibit the metastable structure with enlarged specific surface area and abundant porosity, thereby highly dispersing the active Ni species. The residue of Si and K is inevitable during the reflux process under the basic solution and the residual amount increases with the extended reflux time and the raised solution pH value. The residual Si is undesirable to improve the acidity while the residual K is expected to enhance the desirable basicity. Therefore, the stabilized metastable structure and mediated properties should be considered comprehensively in practically designing the highly active and stable DRM catalyst. The evaluation at 700 °C with gas hourly space velocity of 50000 mL·g−1·h−1 (volume ratio: CH4/CO2 = 1/1) and time on stream of 600 min demonstrates that the treatment of reflux remarkably improves the activity and stability of Ni/ZrO2 catalyst. Especially, the catalyst with 5-day reflux displays the robust activity (CH4 conversion: ~72%, CO2 conversion: ~80%) and carbon-resistant ability (0.01 mg/mg cat.). However, although the metastable structure is somewhat stabilized by the treatment of reflux and the residual ions, eventually it is easily destroyed when suffering from long-life (6000 min) or high-temperature (beyond 800 °C) run, behaving as the sintering of Ni particles and carbon deposition.

Influence of Urea on the Synthesis of NiCo2O4 Nanostructure: Morphological and Electrochemical Studies

The widespread use of miniature electronic devices calls for energy-dense storage strategies. The supercapacitor-based energy storage devices with high areal capacitance are desired energy storage alternative. It is still a challenge to fabricate supercapacitor-based energy devices with consistent performance. The porous metal oxides with large areal capacitance are desired materials for electrode, but there exists a limited understanding of the influence of synthesis parameters on microstructural properties, which largely govern their electrochemical performance. In the present work, hierarchal spinel nickel cobaltite (NiCo₂O₄) nanostructures were synthesized in the presence of the varying amount of hydrolyzing agent via a simple hydrothermal method coupled with a simple post-annealing process. This work focuses on understanding the influence of hydrolyzing agent in controlling the microstructure and hence ensuing electrochemical properties of the NiCo₂O₄ based electrode. Based on the urea hydrolyzing content, the as synthesized NiCo₂O₄ nanostructure varied from the rod, plate to nanoflower. The mesoporous nanostructures, with urea content 1.49 gm, exhibit a sizeable BJH surface area (79.2 m² g-1) and high mesopore volume (0.140 cm³ g-1). Remarkably, the NiCo₂O₄ nanoflower shows high specific capacitance of 3143.451 F/g at 2 mV/s scan rate, 1264.5 F/g at 1 A/g current density, energy density of 56 Wh/kg and power density of 8,400 W/kg in 3 M KOH electrolyte. The capacitance loss after 5000 cycles is 48% at the current density of 10 A/g, indicating their excellent cycling stability. The impressive electrocatalytic activity is largely ascribed to the high intrinsic electronic conductivity, superior mesoporous nanostructures and rich surface Ni active species of the NiCo₂O₄ materials, which can largely boost the interfacial electroactive sites and charge transfer rates indicating promising applications as electrodes in future supercapacitors.

Undoped SnO2 as a Support for Ni Species to Boost Oxygen Generation through Alkaline Water Electrolysis.

In this study, the synergistic behavior of Ni species and bimodal mesoporous undoped SnO2 is investigated in oxygen evolution reactions (OERs) under alkaline conditions without any other modification of the compositional phases or using noble metals. An efficient and environmentally friendly hydrothermal method to prepare bimodal mesoporous undoped SnO2 with a very high surface area (>130 m2 g-1) and a general deposition-precipitation method for the synthesis of well-dispersed Ni species on undoped SnO2 are reported. The powders were characterized by adsorption-desorption isotherms, TG-DTA, XRD, SEM, TEM, Raman, TPR-H2, and XPS. The best NiSn composite generates, under certain experimental conditions, a very high TOF value of 1.14 s-1 and a mass activity higher than 370 A g-1, which are remarkable results considering the low amount of Ni deposited on the electrode (3.78 ng). Moreover, in 1 M NaOH electrolyte, this material produces more than 24 mA cm-2 at an overpotential value of approximately +0.33 V, with only 5 wt % Ni species. This performance stems from the dual role of undoped SnO2, on the one hand, as a support for active and well-dispersed Ni species and on the other hand as an active player through the oxygen vacancies generated upon Ni deposition.

Dry Reforming of Methane over Ni–Al2O3 and Ni–SiO2 Catalysts: Role of Preparation Methods

The production of synthesis gas via the conversion of the two greenhouse gases CO2 and CH4 is an efficient process due to its dual industrial and environmental interest. The catalysts based on Ni–SiO2 and Ni–Al2O3 are typical and suitable for this reaction due to their mechanical strength, their good chemical and thermal stability in addition to their low cost and good availability. In this work, we have compared the catalytic performances of these two types of catalysts prepared by two different synthesis methods in dry reforming of methane (DRM).The results indicate that the catalytic performances are much more dependent on the support properties and that they are deeply influenced by the catalyst synthesis method. The textural properties as shown by N2-physisorption analysis are strongly dependent on the support nature in the case of the catalysts prepared by the microemulsion (ME) method and the alumina-based Ni catalyst has a higher specific surface area and a higher pore volume compared to the SiO2 based one. The XRD, H2-TPR and XPS results indicate that the preparation method has a significant influence on the state of NiO species. A Ni particle in the two Ni–SiO2–ME and Ni–Al2O3–ME catalysts prepared by microemulsion is much smaller. The strong metal support interaction promotes the formation of NiAl2O4 and Ni2SiO4 species respectively during the catalyst preparation process and makes the reduction of corresponding catalysts very difficult which may lead to a decrease in the content of active Ni species and give the Ni–Al2O3–ME catalyst a relatively low catalytic activity in DRM, especially when it is reduced under unfavorable conditions as is the case in this work. However, the strong metal support interaction between Ni and the support is also of beneficial to the formation and stabilization of small Ni particles well dispersed on the support after reduction of the Ni–SiO2–ME catalyst. In this system, the sintering and the carbon deposition are inhibited and the catalyst presents both better activity and stability. The Ni/Al2O3 catalyst exhibits a synergistic effect between the various phases NiO and NiAl2O4 formed during the synthesis process due to the different interactions strength between metal and support, which are in favor of the dispersion and stabilization of NiO species. As a result, Ni/Al2O3 provided with both proper textural properties and this synergistic effect, exhibits superior catalytic performances in term of activity, selectivity and stability in DRM. Despite the formation of carbon over this catalyst, it maintains its stability during a long-term test of more than 66 hours. This is due to the formation of active type of carbon and the delocalization of the Ni active sites on the latter to maintain their activity.

FeOOH-enhanced bifunctionality in Ni3N nanotube arrays for water splitting

Here we report the functional FeOOH as a cocatalyst to enhance excellent bifunctionality of the Ni3N catalyst, which demonstrate remarkable electrocatalytic activity for hydrogen evolution reaction (HER) and oxygen evolution reduction (OER) compared to the pristine Ni3N sample. Experimental data and theoretical calcinations demonstrate that the FeOOH facilitates surface adsorption and cleavage of OH−/H2O species and decrease the d-band center of active Ni species for optimizing the Gibbs free energy of intermediates. Furthermore, relatively vertical Ni3N nanotubes can promote the mass transport and electrons transfer as a main catalyst. The unusual synergistic effect in hybrid system with high density of heterointerface is contributed to the improvement of HER/OER catalytic performance. Specifically, the obtained FeOOH/Ni3N hybrid catalysts display excellent OER/HER performance with an overpotential of 244 mV/67 mV at 10 mA cm−2 in 1.0 M KOH, along with an applied potential of 1.58 V to boost overall water splitting at 10 mA cm−2. This simple and effective strategy may provide a new path to design the bifunctional catalysts and improve the catalytic performance for water splitting.

Bis(dialkylphosphino)ferrocene-Ligated Nickel(II) Precatalysts for Suzuki-Miyaura Reactions of Aryl Carbonates.

Aryl carbonates, a common protecting group in synthetic organic chemistry, are potentially valuable electrophiles in cross-coupling reactions. Here, after performing a thorough evaluation of different precatalysts, we demonstrate that (dcypf)Ni(2-ethylphenyl)(Br) (dcypf = 1,1-bis-(dicyclohexylphosphino)ferrocene) is an efficient precatalyst for Suzuki-Miyaura reactions using a variety of aryl carbonates as substrates. Mechanistic studies indicate that (dcypf)Ni(2-ethylphenyl)(Br), which contains a bidentate phosphine that binds in a trans geometry, is an effective precatalyst for these reactions for two reasons: (i) it rapidly forms the Ni(O) active species and (ii) it minimizes comproportionation reactions between the Ni(O) active species and both the unactivated Ni(II) precatalyst and on-cycle Ni(II) complexes to form catalytically inactive Ni(I) species. In contrast, the state of the art precatalyst (dppf)Ni(o-tolyl)(Cl) (dppf = 1,1-bis(diphenylphosphino)ferrocene), which contains a bidentate phosphine that binds in a cis geometry, forms Ni(I) species during activation and is essentially inactive for aryl carbonate couplings. Although the exact reasons on a molecular level why the dcypf system is more active than the dppf system are unclear, our results indicate that in general Ni catalysts supported by the dcypf ligand will give better performance for catalytic reactions involving substrates which undergo relatively slow oxidative addition, such as aryl carbonates.

In situ fabrication of nickel-based layered double hydroxides catalysts with carboxymethyl chitosan as biomass template for hydrogenation

Herein, we have facilely fabricated a series of novel nickel-based layered double hydroxides catalysts with carboxymethyl chitosan as sacrificial template using an in situ method. A Ni1Mg4Al2-CMC-in situ catalyst shows excellent catalytic performance in benzophenone selective hydrogenation. The addition and elimination of CMC was confirmed to play an important role in increasing the BET specific surface area and improving the dispersion of the active Ni species. Furthermore, the strong interaction between the active species and support was also enhanced, simultaneously. These behaviors are believed to promote the catalytic efficiency and suppress the unexpected Ni aggregation. Considering its good catalytic performance and low cost, it has vast potential significance in the fabrication of nickel-based layered double hydroxides catalysts for catalytic reactions.

Activity and stability of NiCe@SiO2 multi–yolk–shell nanotube catalyst for tri-reforming of methane

Tri-reforming of methane (TRM) produces syngas by directly utilizing flue gas from a fossil fuel-fired power plant without requiring post-combustion CO2 separation. In this work, different yolk sizes of a NiCe@SiO2 multi–yolk–shell nanotube catalyst were prepared and their catalytic properties were evaluated at different oxidizer (CO2 + H2O + O2) to methane (O/M) feed ratios for TRM. The NiCe@SiO2 multi–yolk–shell nanotube catalyst can exhibit longer stability than the conventional NiCe/SiO2Imp catalyst synthesized by impregnation method due to its controlled morphology and synergetic interactions of Ni–Ce and Ni–Si species. At a low O/M feed ratio of 1.0, NiCe@SiO2 with smaller yolks (< 20 nm) shows higher resistance to carbon deposition than NiCe@SiO2 with larger yolks due to the facile oxidation of carbon. On the other hand, NiCe@SiO2 with larger yolks (> 30 nm) presents stable TRM activity at a high O/M feed ratio of 1.1, whereas NiCe@SiO2 consisting of smaller yolks deactivates. Deactivation of NiCe@SiO2 with smaller yolks can be explained by the re-oxidation of active Ni species, in which carbon formation and oxidation rates, and Ce3+/Ce4+ redox properties play a crucial role. Our results indicate that the NiCe@SiO2 multi–yolk–shell nanotube structures can provide high TRM activity, yet their structure should be tuned for stable performance by considering the yolk sizes and interaction of Ni–Ce species.

3D printed Ni/Al2O3 based catalysts for CO2 methanation - a comparative and operando XRD-CT study

Ni-alumina-based catalysts were directly 3D printed into highly adaptable monolithic/multi-channel systems and evaluated for CO2 methanation. By employing emerging 3D printing technologies for catalytic reactor design such as 3D fibre deposition (also referred to as direct write or microextrusion), we developed optimised techniques for tailoring both the support’s macro- and microstructure, as well as its active particle precursor distribution. A comparison was made between 3D printed commercial catalysts, Ni-alumina based catalysts and their conventional counterpart, packed beds of beads and pellet. Excellent CO2 conversions and selectivity to methane were achieved for the 3D printed commercial catalyst (95.75% and 95.63% respectively) with stability of over 100 h. The structure-activity relationship of both the commercial and in-house 3D printed catalysts was explored under typical conditions for CO2 hydrogenation to CH4, using operando ‘chemical imaging’, namely X-Ray Diffraction Computed Tomography (XRD-CT). The 3D printed commercial catalyst showed a more homogenous distribution of the active Ni species compared to the in-house prepared catalyst. For the first time, the results from these comparative characterisation studies gave detailed insight into the fidelity of the direct printing method, revealing the spatial variation in physico-chemical properties (such as phase and size) under operating conditions.

Biotemplate-Assisted Synthesis of Layered Double Oxides Confining Ultrafine Ni Nanoparticles as a Stable Catalyst for Phenol Hydrogenation

A confined Ni(0) nanocatalyst derived from NiAl-layered double hydroxide (NiAl-LDH), with ultrafine Ni nanoparticles implanted in the NixAlyO support, was first fabricated by the urea coprecipitation method using pine pollen as a biotemplate, together with subsequent calcination/reduction process. This hollow biotemplate-assisted catalyst displayed high phenol-hydrogenation activity and stability, which can be ascribed to its higher surface area, better dispersibility, and ultrafine Ni particle size. The hollow morphology and confinement effect of lamellar NiAl-LDH can not only lead to better dispersion of the active Ni(0) species, but also strengthen the interaction between Ni(0) species and NixAlyO support. This protocol can overcome the shortcomings of conventional LDH-derived catalysts that lack specifically shaped morphology and hierarchical structure, inhibiting the aggregation of the Ni nanoparticles, hence resulting in its good activity and stability.

Nickel phosphate materials regulated by doping cobalt for urea and methanol electro-oxidation

Efficient catalytic electro-oxidation of methanol or urea is critical to the development of fuel cells, which have attracted considerable interest due to their high energy conversion efficiency, ease of operation and low pollutant emission. In this work, nickel cobalt phosphate (NiCoPO) with different Ni/Co ratio are successfully fabricated by co-precipitation method. The electronic states and texture properties of the active Ni(III) species can be regulated by the introduced Co phosphate. The cobalt introduction effectively reduced the onset potential and increased the oxidation current. Compared with nickel phosphate (NiPO), the onset potential of NiCoPO (4:6) and NiCoPO (6:4) decreased by 135 and 132 mV in urea and methanol electro-oxidation process, respectively. The amperometric i-t curves show that the current densities of NiCoPO electrodes are significantly higher than that of NiPO and CoPO. The NiCoPO (4: 6) and (5: 5) exhibits the highest current of urea and methanol oxidation, respectively. This work provides a research reference about the cobalt doping effect for nickel phosphate as catalysts in electro-oxidation reaction.

Ni-bearing nanoporous alumina loaded ultralow-concentrated Pd as robust dual catalyst toward hydrogenation and oxidation reactions

Rational combination of noble and non-noble active metals in heterogeneous catalysis especially emerged as a dual catalyst is intriguing on account of their certain promotive catalytic activity. Herein, we report Ni-Pd co-supported nanoporous alumina with ultralow-loading Pd and concentration-adjusted Ni as dual catalyst both affording robust hydrogenated and oxidized capacity. The active Pd species in the alumina emerged as the quasi single site state responsible for hydrogenation of phenylacetylene thanks to the introduction of Ni compared with the only Pd-bearing ones, while the Pd and Ni both acted as the catalytically active center specific to the oxidized activity of benzyl alcohol. Ulteriorly, it is demonstrated that the chemical state of quasi single site Pd species in alumina was obviously influenced in the presence/absence of nickel compared to aggregated Pd. The catalytic results further affirmed that the introduced nickel in the alumina is beneficial to the improvement of catalytic hydrogenated property, and the selectivity of products in the phenylacetylene hydrogenation was obviously tuned based on the varying concentrations of nickel-containing catalyst in the presence of low additive dosage of catalyst. Impressively, as the dual catalyst, the resulted catalyst also revealed the superior catalytic oxidative capacity(99% conversion, 97% selectivity) toward the oxidation of benzyl alcohol with molecular oxygen resulted from the synergetic effect of active Pd and Ni species.

Effect of rare earth element (Ln = La, Pr, Sm, and Y) on physicochemical properties of the Ni/Ln2Ti2O7 catalysts for the steam reforming of methane

Ln2Ti2O7 (Ln = La, Pr, Sm, and Y) and Ni/Ln2Ti2O7 catalysts were prepared using the co-precipitation and incipient wetness impregnation methods, respectively. XRD and Raman results reveal that with the decrease in rA/rB ratio of A2B2O7 (A = La, Pr, Sm, and Y; B = Ti), the crystal structure transformed from the monoclinic layered perovskite (La2Ti2O7 and Pr2Ti2O7) to the ordered pyrochlore (Sm2Ti2O7 and Y2Ti2O7). H2-TPR results demonstrate that the active Ni species had a stronger interaction with Sm2Ti2O7 or Y2Ti2O7 than with La2Ti2O7 or Pr2Ti2O7. Therefore, smaller Ni crystallites with larger active metallic surface areas could be formed in the Ni/Sm2Ti2O7 and Ni/Y2Ti2O7 catalysts. XPS results indicate that the oxygen vacancies and oxygen mobility were also gradually enhanced with the decrease in rA/rB ratio. As a consequence, the Ni/Y2Ti2O7 sample exhibited the highest catalytic activity and the best coke-resistant ability in the steam reforming of methane for hydrogen production among all of the catalysts. It is concluded that the change in A-site element influenced the structures of Ln2Ti2O7 significantly, which ultimately affected catalytic performance of Ni/Ln2Ti2O7 for the steam reforming of methane.

A comparison of Al2O3 and SiO2 supported Ni-based catalysts in their performance for the dry reforming of methane

Dry reforming of methane (DRM) with CO2 is of great significance in the environmental protection and the utilization of natural gas. SiO2 and Al2O3 are two typical catalyst supports used in DRM. To elucidate the effect of these two supports on the catalytic performance, in this work, Ni/SiO2 and Ni/Al2O3 catalysts are prepared by the incipient wetness method and characterized by BET, TEM, H2-TPR, XRD, TG and Raman technologies. The results indicate that the performance of Ni-based catalyst is closely related to the properties of support and the Ni/SiO2 and Ni/Al2O3 catalysts are rather different in their DRM performance. Ni/SiO2 catalyst exhibits higher initial activity but poor stability; its catalytic activity decreases rapidly in 15 h for DRM at 800°C. Because of the weak metal-support interaction, Ni species on the Ni/SiO2 catalyst is present as large Ni particles, which may promote the formation of coke precursors, viz., the multi-carbon Cn species, leading to the fast carbonaceous deposition and catalyst deactivation. In contrast, the Ni/Al2O3 catalyst displays a lower activity but a much higher stability; its activity in DRM keeps stable in 50 h. Although Ni particles in the Ni/Al2O3 catalyst is much smaller, the strong metal-support interaction promotes the formation of NiAlxOy species during the catalyst preparation process, which may lead to a decrease in the content of active Ni species and give the Ni/Al2O3 catalyst a relatively low catalytic activity in DRM; however, the strong metal-support interaction between Ni and Al2O3 is also of benefit to the formation and stabilization of small Ni particles, which can alleviate the carbanceous deposition and afford the Ni/Al2O3 catalyst a better stability.

Catalytic behavior of nickel loaded on acid-activated and pillared clay in total gas-phase oxidation of ethanol

Layered and acid-activated clays, used as catalytic support, were synthesized from natural Algerian montmorillonite. All supports were prepared by (1) pillaring with aquo/hydroxo/oxo Al clusters, in particular Al13 that contains only octahedral Al-species, (2) an acidic H2SO4 treatment, and (3) combined pillaring + acid treatment. Five and 10 wt% of active Ni species are deposited by impregnation. The obtained catalysts are characterized by XRD, SAXS (structure), N2 sorption, SEM (texture), XRF (chemical composition), FTIR (to evidence Al13 clusters), and H2-TPR (to distinguish NiO and other Ni-containing species). The activity is measured for the gas-phase total oxidation of ethanol, which is a highly reactive volatile organic molecule. The acid activation pretreatment affects the clay (montmorillonite sheets) because of its delamination (exfoliation) associated with a decreased number of superposed sheets seen in XRD, SEM, and a decreased Si/Al ratio observed by XRF. The d001 spacing in XRD increases from 11.70 (before pillaring) to 18.24 A (after pillaring) evidencing the inclusion of hydroxylaluminic cations and water in the inter-sheets space. d001 = 17.50 A has already been reported with less dealuminated pillared clays. The 10% Ni-loaded pillared clay is the best catalyst (giving up to 100% of conversion) for ethanol total oxidation at relatively low temperatures (T ≤ 250 °C) and ambient pressure. Thus, pillaring, acidic treatments, and Ni amount are the main factors governing on the changing of textural, structural, and catalytic properties of montmorillonite for ethanol oxidative reaction.

Ni-Mg/γ-Al2O3 catalyst for 4-methoxyphenol hydrogenation: effect of Mg modification for improving stability

A highly stable Mg-modified Ni/γ-Al2O3 catalyst was fabricated by a simple deposition-precipitation method and investigated in the hydrogenation of 4-methoxyphenol. The Mg-modified catalyst showed enhanced catalytic activity and stability, with no appreciable loss of its initial activity for up to 26 times of recycling, as compared to the unmodified Ni/γ-Al2O3 catalyst. This could be ascribed to the formation of strong metal-support interaction due to the addition of Mg. TEM observation indicated that the Mg addition could enhance the dispersion of the active Ni species and decreased its particle sizes, contributing to a high catalytic activity. TPR and XPS results proved the existence of strong interaction between Ni and the modified support as well as the formed MgAl2O4, thus effectively suppressing the loss and agglomeration of the active Ni species during the hydrogenation process and accounting for its outstanding stability.

Nickel-Catalyzed Aromatic Cross-Coupling Difluoromethylation of Grignard Reagents with Difluoroiodomethane.

The nickel-catalyzed cross-coupling difluoromethylation of the Grignard reagents with difluoroiodomethane is shown to provide the corresponding aromatic difluoromethyl products in excellent to moderate yields. The difluoromethylation proceeds smoothly within 1 h at room temperature with 1.5 equiv of the Grignard reagents in the presence of Ni(cod)2/TMEDA (2.5-0.5 mol %). Mechanistic studies clarify that the oxidative addition of the Ni(0) catalyst to difluoroiodomethane provides the TMEDA-Ni(II)(CF2H)I complex. This intermediate is transformed to TMEDA-Ni(II)(CF2H)Ph via transmetalation with PhMgBr. The reductive elimination takes place to give the aromatic cross-coupling difluoromethylation product along with regeneration of the TMEDA-Ni(0) catalyst. Electron paramagnetic resonance (EPR) and radical clock analyses of the nickel-catalyzed reaction provide no EPR active Ni(I) and Ni(III) species at around g = 2 and only a trace amount of the cyclization product.

Enhanced electrochemical property of graphite felt@Co2(OH)2CO3 via Ni−P electrodeposition for flexible supercapacitors

In this work, we propose a novel and delicate strategy to significantly boost the supercapacitive performance of graphite felt (GF)@Co2(OH)2CO3 hybrid via a facile Ni−P electrodeposition on the pre-hydrothermally generated GF@Co2(OH)2CO3 (denoted as GF@Co2(OH)2CO3@Ni−P). Electrochemical measurements show that the areal specific capacitances of the resulting GF@Ni−P, GF@Co2(OH)2CO3 and GF@Co2(OH)2CO3@Ni−P are 118, 1022 and 1360 mF cm−2 at a current density of 1 mA cm−2. Besides, 72.8% of specific capacitance can be maintained upon rising the current density from 1 to 20 mA cm−2 for GF@Co2(OH)2CO3@Ni−P, far higher than 47.0% for GF@Co2(OH)2CO3. More strikingly, the assembled all-solid-state flexible symmetric supercapacitor GF@Co2(OH)2CO3@Ni−P//KOH//GF@Co2(OH)2CO3@Ni−P delivers high energy densities of 46.8 Wh kg−1 at a power density of 0.5 kW kg−1, and 20.7 Wh kg−1 at elevated 5.0 kW kg−1, surpassing most of the reported analogues. Moreover, the device holds 92.9% capacitance retention after 2500 cycles at a current density of 10 mA cm−2. Such substantially enhanced electrochemical performance of GF@Co2(OH)2CO3@Ni−P owes to the improvement of the electronic conductivity by the Ni−P coating and the reinforced synergic effect contributing to the capacitance between the active Co2(OH)2CO3 and Ni species including Ni−P and Ni−OH species. To the best of our knowledge, this is the first report on the coating of Ni−P onto inorganic metal compounds for energy-storage/conversion systems.