NiO Crystallite Size Research Articles

Glycerol dry reforming over Ni supported on fibrous ZSM5 and ZY: Correlation of structural properties on H2 production

This study investigates fibrous ZSM5 (FZSM5) and Zeolite Y (FZY) as supports for producing hydrogen via glycerol dry reforming. The fibrous ZSM5 and ZY were synthesized hydrothermally with microemulsion and impregnated with 10 wt% Ni via a sonication method. The catalytic test was conducted via a vertical stainless steel fixed-bed rig, at 800°C with a glycerol/CO2 ratio of 1. XRD and N2 sorption revealed the reduced surface area and crystallinity in Ni/FZSM5 compared to Ni/FZY. Ni/FZY catalyst displayed a larger surface area (264 m2/g) and aperture width (6.70 nm) in comparison to Ni/FZSM5, which had a surface area of 238 m2/g and an aperture width of 3.90 nm. Ni/FZY also had a smaller NiO crystallite size (8.73 nm) than Ni/FZSM5 (9.79 nm), suggesting well-dispersed Ni species on the wrinkle fiber of FZY’s surface. Ni/FZY outperformed Ni/FZSM5 with 52.49 % glycerol conversion, 44.87 % H2 yield, 71.31 % CO yield, and only 14.4 % carbon formation, attributed to robust Ni-O-Si contact and larger pore diameter. The discovery highlights the catalytic efficiency of the Ni-loaded fibrous zeolite in GDR, offering versatility for application in energy storage and catalysis.

NiO/vermiculite composites prepared for photocatalytic degradation of methanol-water solution and hydrogen generation

A novel eco-friendly NiO/Vm clay based photocatalysts were synthesized from two vermiculites (Vm1 and Vm2) and nickel(II) nitrate hexahydrate (Ni(NO3)2·6H2O salt precursor by the chemical precipitation without and with the sodium hydroxide (NaOH) or ammonium hydroxide (NH4OH, 28% NH3 in H2O) as precipitation agents (Synthesis A) in comparison with the solid-state thermal decomposition (Synthesis B) at 600 °C. Structural properties of all specimens were characterized by X-ray fluorescence, scanning electron microscopy, X-ray diffraction, infrared (IR) and Raman spectroscopy. The photocatalytic performance of NiO/Vm composites was evaluated under UV radiation (λ = 254 nm) for decomposition of methanol-water to hydrogen over 4-h and the stable yield of hydrogen over the 24-h periods. The NaOH and NH4OH affected the NiO crystallite size and therefore the photocatalytic activity during 4 h. Different 2:1 layer charge of Vm1 (0.82 e−) and Vm2 (0.40 e−) and the specific surface area of Vm1 (about 43 m2/g) and Vm2 (about 34 m2/g) supported H2 yield of 628.2 μmol/gcat. and 596.8 μmol/gcat., close to 657.0 μmol/gcat. produced in the presence of commercial photocatalyst TiO2 Evonik P25. Crystalline NiO precipitated and anchored in NiO/Vm composites contained smaller crystallites than those in free NiO. Vermiculite silica surface supports coverage of NiO by hydrogen bonding to Si-OH groups influencing the geometry of the NiO crystal structure (disorder NiO(X)). The heterojunction with Si-O-Ni bonding, at which electrons transfer from Vm to NiO cause enriching electron density in NiO and favoring its photocatalytic activity. Photocatalytic hydrogen generation from methanol–water mixture at the presence of all specimens indicated the main product H2 and minimum by-products CH4 and CO. The stable hydrogen production for 24 h was confirmed only in the presence NiO/Vm1–24 while maintaining the NiO(X) in small crystallites. The thermal solid-state procedure provided the gradual dehydration of vermiculites and Ni(NO3)2·6H2O to the same amount and crystallinity of NiO in NiO/Vm1 and NiO/Vm2 composites. The results of this work confirm that vermiculites mixed layer structures with different negative layer charge play a dominant role as semiconductors for anchored NiO. The photocatalytic activity of NiO/vermiculite composites can be harnessed to treat wastewater containing organic contaminants.

Enhanced hydrogen production through methane dry reforming: Evaluating the effects of promoter-induced variations in reducibility, basicity, and crystallinity on Ni/ZSM-5 catalyst performance

The pursuit of sustainable hydrogen production through the conversion of methane (CH4) and carbon dioxide (CO2), two prevalent greenhouse gases, is advanced by utilizing cost-effective Ni-supported catalysts within the framework of methane dry reforming. Utilizing crystalline porous zeolite, specifically ZSM-5, enhances the dispersion of nickel (Ni) across the catalyst surface and within its pore channels, hence increasing catalytic efficiency. Herein, we investigate the impact of incorporating various promoters (Ce, Cs, Cu, Fe, Sr) into the 5Ni/ZSM-5 catalyst, systematically examining how these modifications influence the reducibility, basicity, and crystallinity of the catalyst’s active sites, thereby affecting its hydrogen yield potential.Our findings reveal that the inferior activity of Cu-promoted catalysts is due to the depletion of basic sites and larger NiO crystallite size (than rest-promoted catalysts). The introduction of Fe results in a highly dispersed Ni with a stable NiFe phase, but dilution of active sites results in low hydrogen yield. Conversely, Sr promotion enhances the basicity and accessibility of NiO active sites both on the surface and within the pore channels of the zeolite, leading to a notable hydrogen yield of 28 % at 700℃ after 300 min. Furthermore, the addition of 2 wt% ceria significantly optimizes Ni dispersion within the pore channels and surges the maximum population of basic sites (including the presence of very strong basic sites), achieving 35 % hydrogen yield at 700 °C and ∼ 70 % at 800℃. This investigation underscores the critical role of promoter-induced modifications in enhancing catalyst performance for hydrogen production, contributing to the development of more efficient and sustainable energy conversion technologies.

Effect of molar concentration on optoelectronic properties of NiO nanoparticles for p-n junction diode application

In this work, fine nickel oxide nanoparticles (NiO NPs) were successfully made utilizing a straightforward co-precipitation approach at low temperature. The effects of precursor concentration on the structural, optical, and electrical characteristics of NiO nanoparticles were investigated. All indexed diffraction peaks in XRD demonstrate the production of NiO with cubic structure. An increase in NiO crystallite size above 16.8 nm was observed when the precursor concentration exceeds 2 M, suggesting the presence of nanostructure in the final product. In FT-Raman spectra, the band centered at ∼ 500 cm–1 is due to Ni-O stretching (LO) mode, and two-magnon (2 M) scattering mode causes the band at 1514 cm–1. The synthesized product is composed of almost rod-shaped particles with a size range of 10–20 nm, according to FESEM pictures. The UV absorption studies showed a high absorption at the fundamental absorption edges originating at 332 nm, which gradually shifted to a lower energy region up to 400 nm with increasing precursor concentration, which means a reduction in bandgap values. The effect of precursor concentration associated with the electrical characteristics of the produced NiO nanoparticles has been investigated for the temperature range 30 to 130 °C. The I-V characterization was used to compute the different photo-diode parameters including n, ФB, Io, PS, R, QE, and D* . The remarkable high photosensitivity of 1100% and specific detectivity of 4.324 × 10−10 Jones for the diode evaluated at 120 mW/cm2 was observed in a 2 M fabricated diode. These findings imply that all the fabricated diodes are exceptionally light-sensitive and are well-suited for upcoming UV photodetector applications.

Green synthesis of nickel oxide nanoparticles using Acacia nilotica leaf extracts and investigation of their electrochemical and biological properties

Green synthesis of nanoparticles (NPs) has attracted the researcher's attention due to its rapid, cost-effective, sustainable and eco-friendly nature. Current studies were carried out to perform and investigate the green synthesis of NiO NPs with aqueous (NiO(aqueous)) and ethanolic extracts (NiO(ethanolic)) of Acacia nilotica leaves, respectively. The NPs were characterized by spectroscopic, microscopic and thermometric techniques including FTIR, Raman, XRD, SEM, TGA and DSC. The electrochemical properties, antibacterial potential and haemolytic activities of the synthesized NPs were also examined. XRD patterns revealed the face-centred cubic structures of NiO NPs and a high degree of crystallinity. The average crystallite size of NiO(aqueous) NPs was significantly smaller (16 nm) than that of NiO(ethanolic) NPs (28 nm). SEM images show that NiO NPs are spherical. The synthesized NiO NPs demonstrate good electrochemical stability at an operating potential of −0.5-0.5 V. The inhibition effect of NiO NPs(ethanol) against B. subtilis, was comparable to the ciprofloxacin.

Effects of Electron-Beam Radiation on the Dielectric Properties of PVA/xNiO Nanocomposite for Energy Storage Applications

For energy storage applications, a material that has high dielectric permittivity, low loss factor, strong thermal resistance, easy processability, and low cost is highly desirable. In the present study, PVA/xNiO nanocomposite films with different NiO contents of (0, 10, and 50) wt% were prepared by casting technique. The PVA/xNiO of 50 wt% NiO has been irradiated with 3 MeV electron beam at a dose of 50 kGy at room temperature in order to investigate the modifications induced in its dielectric properties. The results show that the NiO nanoparticles are well incorporated inside the PVA matrix and the crystallite size of NiO has been decreased upon doping by 50 wt% NiO from 15.45 to 11.44 nm. Also, PVA/(50%)NiO nanocomposite shows indirect allowed optical transition (3.43 eV) with relatively high dielectric constant (7.60 to 9.55) and low loss factor (<0.1) at high frequency (1 MHz) and the entire indicated range of temperature which proposes to use this material in energy storage applications. The electron beam radiation has increased the dielectric constant (10.52 to 13.94) which is preferable. However, a slight increase is observed in the loss factor (<0.109).

Influence of Various Concentrations of Cetyltrimethylammonium Bromide on the Properties of Nickel Oxide Nanoparticles for Supercapacitor Application

In this paper, the impact of the crystallite sizes of nickel oxide nanoparticles (NiO NPs) on their efficiency for electrochemical capacitors (EC) has been investigated. NiO NPs were prepared without and with low and high concentrations (0.02[Formula: see text]M and 0.1[Formula: see text]M) of cetyltrimethylammonium bromide (CTAB) using the hydrothermal process that represent NiO, NiO-1, NiO-2, respectively. The crystallite size of NiO, NiO-1, NiO-2 NPs was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) analysis. The thermogravimetry/differential thermal analysis (TG/DTA) was used to investigate the thermal observation of as-prepared precursor to transform as NiO NPs. HRTEM revealed spherical seed-like morphologies, which consist of aggregated NiO-1 NPs with an average particle size of 9[Formula: see text]nm. The NiO-1 shows the large specific capacitance value of 168[Formula: see text]Fg[Formula: see text] at a current density of 0.5[Formula: see text]Ag[Formula: see text] compared with other NiO and NiO-2 NPs. The study suggests that the low concentration of surfactant CTAB of NiO NPs plays an important role in supercapacitor applications because of the smaller crystallite sizes of the materials as well as a large number of active sites for faradic reaction.

Solar light irradiated photocatalytic activity of ZnO–NiO/rGO nanocatalyst

The current study is based on the synthesis and characterization of ZnO–NiO/rGO nanohybrid for photocatalytic degradation of organic pollutants. The physicochemical properties of synthesized products were estimated by X-ray diffraction technique (XRD), Fourier transform infrared spectroscopy (FTIR), field emission-scanning electron microscopy (FESEM), and Ultraviolet–Visible spectroscopy. The diffraction data showed the formation of binary metal oxide nanocomposite, containing ZnO in hexagonal whereas NiO in the cubic crystalline phase. XRD results revealed that the calculated crystallite size of NiO and ZnO in the ZnO–NiO nanocomposite was <20 nm. The spectroscopic results were found to be in close agreement with XRD data. The morphological analysis exposed the nano-island morphology of the product. The solar light assisted photocatalytic degradation outcome showed 89% degradation of methylene blue and 51% degradation of benzimidazole under similar conditions using ZnO–NiO/rGO nanohybrid. Moreover, the experiment showed that hydroxyl radicals, electrons, and holes were the main active species during the degradation mechanism. In contrast to the ZnO–NiO nanocomposite, the ZnO–NiO/rGO nanohybrid exhibited greater degradation efficiency. This superb photocatalytic performance of ZnO–NiO/rGO nanohybrid proved to be a durable candidate in the field of catalysis.

Magnetic homogeneity in Fe-Mn co-doped NiO nanoparticles

The effect of Fe and Mn co-doping on the magnetic properties of the antiferromagnetic (AFM) NiO nanoparticles which offer large potential for different magnetic applications have been studied. The Rietveld refinement fitting of powder x-ray diffractometry (XRD) patterns confirmed the phase formation of face-centred cubic crystal structure of NiO and average crystallite size lies in the short range of 32–38 nm. The cavity and broadband ferromagnetic resonance (FMR) measurements taken at room temperature demonstrate the smaller local magnetic inhomogeneity for 4%Mn-4%Fe co-doped NiO nanoparticles as compared to undoped, single doped and co-doped with different concentration NiO nanoparticles. The M-H loops revealed the room temperature ferromagnetism-like behaviour for higher Fe doping concentration and lower Mn doping concentration. This can be attributed to the double exchange interaction. The zero field cooled (ZFC) and field cooled (FC) dc magnetization curves showed a small surface freezing peak (at at low temperatures and a blocking peak (at at higher temperatures. For samples with 4%Mn-4%Fe and 2%Mn-6%Fe, the blocking peak was found at a relatively high temperature in comparison to other samples. This can be attributed to the presence of magnetic exchange interactions which block the magnetic spins against a thermal increase. The ZFC AC-susceptibility showed three peaks; a surface freezing peak at Tf, a blocking peak at TB peak and an anomalous peak at Tx in between and , which was found to be most prominent for the 4%Mn-4%Fe co-doped nanoparticles. The neutron diffraction pattern confirmed the AFM order of the core of the 4%Mn-4%Fe co-doped nanoparticles, which indicates an AFM coupling between the Fe2+ and Mn2+ ions and the Ni2+ ions through super-exchange interaction. Therefore, the origin of TX peak can be attributed to the ferromagnetic coupling between the Fe2+ and Mn2+ ions which has a maximum strength at equal concentration. Thus, small and equal doping concentration of Fe and Mn in NiO nanoparticles increase the magnetic homogeneity which makes them attractive for magnetic applications.

Influence of Ni/Al ratio on the fast pyrolysis of myristic acid when adsorbed on unsupported mixed oxides derived from layered double hydroxides

Residual lipids with high fatty acid content represent an important source of raw material for renewable biofuels. They are not suitable for the production of biodiesel via alkaline transesterification but can be converted to biodiesel via esterification. For these feedstocks, hydrodeoxygenation is suitable for producing hydrocarbons. However to limit hydrogen consumption, thermal processes are also object of studies. In these thermal processes nickel has been used in the form of supported catalysts but has not been well studied in the form of mixed oxides. This work aims at studying the Ni/Al ratio influence on the properties of unsupported mixed oxides prepared from layered double hydroxides (LDH) precursors, to evaluate their performance in the fast pyrolysis of myristic acid (MA) as a model compound of residual acidic lipids. Prepared materials had molar ratios Ni/Al = 0.3, 1 and 3. The catalysts were obtained through calcination of the precursors, and were characterized by XRD, TGA, FTIR, N2 adsorption isotherms, TPD of NH3 and EDX analysis. Myristic acid pyrolysis, with catalyst:MA mass ratio of 5:1, was carried out in a micropyrolyzer at 550 °C, and the products were analyzed through online GC/MS. Results show that the obtained catalysts presented a rather high surface area, important mesoporosity and NiO and NiAl2O4 crystalline phases. The catalysts with the highest Al content favored cracking with the production of hydrocarbons in the gasoline range, while the sample with highest Ni content favored the production of hydrocarbons in the kerosene range. The catalyst obtained with the combination of Ni/Al = 1 presented the highest surface area and acidity and the lowest NiO crystallite size, resulting in the best MA conversion (∼84 %) and deoxygenation degree. It also produced the highest yield in aromatic compounds due to the higher acidity and hydrogen transfer, compared to other catalysts. The present results confirm that catalytic reaction under pyrolysis conditions is able to identify some intrinsic properties of catalysts using model molecules as starting feed.

Robust Ni/Dendritic fibrous SBA-15 (Ni/DFSBA-15) for methane dry reforming: Effect of Ni loadings

A series of spherical mesoporous Ni/Dendritic Fibrous SBA-15 (Ni/DFSBA-15) catalysts with different Ni loadings (3–15 wt.%) were successfully synthesized and catalytically investigated by methane dry reforming. The XRD and Raman analyses indicated the structural stability of DFSBA-15 regardless of the Ni loading quantity, and the NiO nanocrystalline size increased with increasing Ni loading. The BET analysis showed the surface area of the catalysts decreased upon increment in Ni loading. Meanwhile, the TEM images revealed the distribution of Ni particles over the spherical shape DFSBA-15, with the most homogeneous dispersion was shown by 10Ni/DFSBA15, while Ni agglomeration was observed for 15Ni/DFSBA-15. The optimal catalytic performance and stability was achieved by 10Ni/DFSBA-15 (XCO2 = 93.11%, XCH4 = 91.76%, YH2 = 91.77%, YCO = 96.35%, SCO = 48.89%, SH2 = 46.57% and H2/CO = 0.95) with no sign of deactivation was observed for 30 h time-on-stream, in agreement with the XRD, XPS, and TGA analyses of spent catalysts. The superior catalytic performance by 10Ni/DFSBA-15 could be credited to its strong Si-O-Ni interaction, moderate NiO crystallite size, and homogeneous active metal dispersion. The favorable properties of 10Ni/DFSBA-15 led to a strong synergistic effect between Ni active metal sites and the DFSBA-15 support and thus enhanced the reactivity between two gaseous reactants, CH4 and CO2. The 10 wt.% Ni loading was certified as optimal Ni content to sufficiently suppress the coke deposition on the DFSBA-15 and thus enhance the catalytic activity and stability.

Evolution of NiO phase at the expense of metallic nickel: Structure, magnetic and electronic properties

The role of oxidation on the structural, magnetic and electronic properties of a Ni-NiO compound is reported. XRD results indicate that NiO is formed at the expense of metallic Ni and complete NiO phase formation was observed at 1000 °C. The average crystallite size of NiO is found to increase from 12 to 35 nm upon calcination. Using transmission electron microscopy (TEM) the average particle size for the samples calcined at 1000 °C was found to be approximately 126 nm. Hence, comparing it to the crystallite sizes estimated from the XRD, it is clear that the powder samples are polycrystalline in nature, consisting of smaller crystallites clustered together. Both the ferromagnetic and AFM contributions from Ni and NiO, respectively, were observed in the magnetization data. The saturation magnetization and coercivity were found to decrease with increasing calcination temperature with a shifting of hysteresis loop towards the negative axis. The optical band-gap of the powders was found to be unchanged upon calcination (3.3 eV or 3.4 eV). The density of electrons near the Fermi level was found to be higher in the non-calcined and dried sample, resulting in a higher magnetic moment compared to the other samples.

Syngas production via CO2 reforming of CH4 over Ni-based SBA-15: Promotional effect of promoters (Ce, Mg, and Zr)

The promotional effect of different types of metals (Ce, Mg, and Zr) over Ni/SBA-15 which synthesized using ultrasonic co-impregnation technique were scientifically evaluated via CO2 reforming of CH4 (CRM). Characterizations including XRD, BET, FTIR, CO2-TPD were done to examine their physical attributes, metal-support interactions, and basicity properties. XRD results suggested that NiO particles were not distributed homogeneously within the confined framework of SBA-15 for Ni-Ce/SBA-15. Nevertheless, Mg and Zr promoters could effectively improve Ni dispersion over the SBA-15's siliceous framework and controlled the NiO crystallize sizes. The smallest NiO crystallite size of 9.3 nm was obtained by Ni-Zr/SBA-15. BET results verified the alteration of pore structure without changing the ordered structure of SBA-15 upon promoter addition. FTIR results suggested the partial transformation of Si–OH groups to the Si–O–X bond (X = Ce, Mg and Zr), whereas, CO2-TPD results confirmed the moderate basic sites present in Ni-Zr/SBA-15. H2-TPR evidenced the strongest metal-support interaction in Ni-Zr/SBA-15 owing to its high temperature reduction behaviour. At operating condition of P = 1.0 bar and WHSV = 15,000 mLg−1h−1, catalytic performance and stability ascended the trend of un-promoted < Ce-promoted < Mg-promoted < Zr-promoted Ni/SBA-15, in which Zr-promoted Ni/SBA-15 manifested the best catalytic activity (CO2 conversion = 93.8%; CH4 conversion = 88.3%; H2/CO ratio = 0.82). The ascendency catalytic activity and stability of Ni-Zr/SBA-15 catalyst were attributed to its favourable properties such as strong Si–O–Zr bond formation, smallest NiO crystallite size and a moderate amount of basic sites, which crucial for sintering restriction of NiO particles and carbon deposition, thus facilitated CRM reaction.

Combined steam and CO2 reforming of methane for syngas production over carbon-resistant boron-promoted Ni/SBA-15 catalysts

The unpromoted and B-promoted 10%Ni/SBA-15 catalysts synthesized via sequential incipient wetness impregnation approach were assessed for combined steam and CO2 reforming of methane (CSCRM) at various reaction temperatures of 973–1073 K and stoichiometric feed composition. An expected and noteworthy drop in mean NiO crystallite size and BET surface area with boron promotion from 1% to 5%B loading could be due to the agglomeration of B2O3 particles and deboration reaction during calcination and hence blocking mesopores of SBA-15 support at elevated B composition. The complete NiO reduction to metallic Ni0 form was achieved during H2 activation and the reduction temperature of NiO phase was shifted towards higher temperature with B-addition owing to enhancing interaction between the acidic B2O3 and basic NiO phases. For all reaction temperature employed, 3%B appeared to be the optimal promoter loading in terms of reactant conversions and 3%B-10%Ni/SBA-15 catalyst revealed the greatest H2 yield (69.4%) at 1073 K. In addition, CH4 and CO2 conversions were enhanced about 23.2% and 32.4%, correspondingly with rising reaction temperature from 973 to 1073 K. Ratio of H2 to CO varied from 1.26 to 2.71 and the desired H2/CO ratio of about 2 favored for Fischer-Tropsch synthesis was achieved on 3%B-10%Ni/SBA-15 sample at 973 K. Boron promoter suppressed graphitic carbon formation and the amount of carbonaceous deposition was reduced about 4 times. Noticeably, 3%B-10%Ni/SBA-15 was also resilient to metallic Ni0 re-oxidation throughout CSCRM.

GROWTH OF RF SPUTTERED NiO FILMS ON DIFFERENT SUBSTRATES — A COMPARATIVE STUDY

This work explores the structural, surface and optical properties of NiO films grown on Si, GaAs, PET and glass substrates. The NiO films were deposited on these substrates under same conditions by using radiofrequency (RF) magnetron sputtering of NiO target at 100[Formula: see text]C. The structural study by X-ray diffraction (XRD) showed the existence of (200) and (220) oriented NiO peaks on all the substrates. The preferred orientation of NiO films on Si, GaAs and glass was along (200) plane whereas the film grown on PET was observed to be oriented along (220) plane. The crystallite size of NiO on GaAs was the largest among the other substrates. The RMS surface roughness on PET was higher as compared to the other substrates. The band gap of NiO films grown on glass and PET was estimated from UV–Vis transmittance spectroscopy whereas the UV–Vis reflection spectroscopy was carried out to find out the band gap of NiO grown on GaAs and Si substrates. The band gap of NiO on PET was higher than its band gap obtained on other substrates. The results obtained on properties of NiO films on different substrates were correlated with each other.

Influence of Lanthanide Promoters on Ni/SBA-15 Catalysts for Syngas Production by Methane Dry Reforming

The catalytic performance of Ce- and La-promoted Ni/SBA-15 catalysts for syngas production from CO2 reforming of methane has been investigated in a fixed-bed reactor at stoichiometric feed composition. Both promoted and unpromoted catalysts possessed high BET surface area of 303-445 m2 g-1. Additionally, SBA-15 support had a relatively uniform rod-like shape with a diameter of about 0.55μm and a reduction in the crystallite size of NiO phase from 27.0 to 19.1nm was observed with promoter addition reasonably due to the strong interaction between promoter and NiO particles. CeO2 and La2O3 dopants were finely dispersed on catalyst surface. Temperature-programmed oxidation of spent catalysts showed that coke-resistance was improved significantly with promoter modification and 3%La-10%Ni/SBA-15 catalyst was the most resistant to carbonaceous deposition rationally due to the least NiO crystallite size hindering the nucleation and growth of graphitic carbon. Hence, La-promoted catalyst appeared to be the optimum catalyst in terms of reactant conversion, H2 yield and stability whilst a gradual decline in both reactant conversion and H2 yield was experienced with unpromoted and Ce-doped catalysts. Regardless of catalyst types, the ratio of H2 to CO was always less than unity preferred for Fischer-Tropsch synthesis.

Bridging exchange bias effect in NiO and Ni(core)@NiO(shell) nanoparticles

Among all bi-magnetic core(transition metal)@shell(transition metal oxide) nanoparticles (NPs), Ni@NiO ones show an onset temperature for the exchange bias (EB) effect far below the Néel temperature of bulk antiferromagnetic NiO. In this framework, the role played by the magnetism of NiO at the nanoscale is investigated by comparing the microstructure and magnetic properties of NiO and Ni@NiO NPs. With the aim of bridging the two systems, the diameter of the NiO NPs (~4nm) is chosen to be comparable to the shell thickness of Ni@NiO ones (~2nm). The EB effect in Ni@NiO NPs is attributed to the exchange coupling between the core and the shell, with an interfacial exchange energy of ΔE~0.06ergcm−2, thus comparable to previous reports on Ni/NiO interfaces both in thin film and NP morphologies. In contrast, the EB detected in NiO NPs is explained in a picture where uncompensated spins located on a magnetically disordered surface shell are exchange coupled to the antiferromagnetic core. In all the studied NPs, the variation of the EB field as a function of temperature is described according to a negative exponential law with a similar decay constant, yielding a vanishing EB effect around T~40–50K. In addition, the onset temperature for the EB effect in both NiO and Ni@NiO NPs seems to follow a universal dependence with the NiO crystallite size.

Influence of Ni catalyst support on the product distribution of cellulose fast pyrolysis vapors upgrading

In this work, an influence of Ni catalyst support on the product distribution in the upgrading of cellulose fast pyrolysis vapors was investigated. The catalysts containing 20% of Ni introduced by impregnation on Al2O3, SiO2, MgO, CeO2 and ZrO2 surface were prepared. In the case, of the zirconium oxide synthesis three different methods of support preparation were applied. The effects of surface acidity, type of the precursor and support preparation method, crystalline phase of the support, interactions between active phase and support, surface area of the catalyst and NiO crystallite size on the distribution of reaction products were studied. Moreover, an impact of CaO addition to the Ni/ZrO2 catalysts was evaluated. The composition of reaction products was identified using Py-GC/MS. The surface properties of the investigated catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and temperature-programmed reduction (TPR). Acidity and surface area of the catalysts were also determined. The obtained results, revealed that while surface acidity exerts a significant impact on the reaction yield, other factors can also considerably change the distribution of products in the upgrading of vapors from cellulose fast pyrolysis.

Microbial induced synthesis of hollow cylinder and helical NiO micro/nanostructure

Abstract

Diesel pre-reforming over highly dispersed nano-sized Ni catalysts supported on MgO–Al2O3 mixed oxides

Abstract A highly dispersed 50 wt% Ni/MgO–Al 2 O 3 catalyst was prepared by deposition–precipitation (DP) method for the diesel pre-reforming reaction. The pH of the precursor solution was controlled from pH 9.5 to 12.0 to examine the effects on NiO crystallite size and metal dispersion. The increase of pH of the precursor solution causes an increase of specific surface area and metal dispersion, and reduces NiO crystallite size. The pre-reforming reaction was carried out using n -tetradecane as surrogate compound of diesel. The coke formation of used catalysts was examined by TGA, TEM, SEM, and Raman analysis. The 50 wt% Ni/MgO–Al 2 O 3 catalyst prepared at pH 11.5 showed a high catalytic activity and excellent coke resistance due to high metal dispersion (8.71%), small NiO crystallite size (3.5 nm), and strong interaction between Ni and support. Furthermore, this catalyst showed a good stability in the pre-reforming reaction at S/C ratio of 3.5 and 450 °C for 88 h.