NiO Catalysts Research Articles

Effect of metal oxides concentration over supported cordierite monoliths on the partial oxidation of ethanol

The effect of metal oxide concentration supported over monoliths was studied on the partial oxidation of ethanol. Nano-structured Co3O4, NiO and CuO oxide catalysts were prepared by means of polymerization–combustion technique using citric acid as chelating agent and washcoated over cordierite monoliths, which after combustion process were calcined and tested under isothermal conditions. X-ray diffraction (XRD) and high resolution transmission electronic microscopy (TEM) showed nanostructure and stable crystallite materials. These metal oxides were tested in the partial oxidation reaction, showing that metal oxide concentration influences the product distribution and selectivity. The maximum concentration for all samples was 12% of corresponding metal oxide (MeO), resulting in high conversions and H2 selectivity. Diffuse reflectance infrared Fourier transform spectroscopy of adsorbed ethanol (DRIFTS-EtOH) and TPD desorption of ethanol showed the formation of intermediate ethoxy-species and preferential dehydrogenation reaction.

Ambient pressure thermal desorption spectroscopy (AP-TDS) of NiO/SiO2 catalysts

The Sabatier reaction is a key process in the “power-to-gas” application which is considered to contribute to future chemical energy storage systems. In this contribution we focus on the catalytic active sites of a NiO catalyst supported on SiO2 (NiO/SiO2) which is commonly used in the Sabatier reaction. A novel technique for the characterization of the active sites is presented and discussed using thermal desorption spectroscopy at ambient pressure. This analytical tool is operated under reaction conditions and allows element specific measurements during the catalytic process of CO2 reforming towards methane. Beside the desorption experiments, XPS and XAS measurements of pristine and catalytically used samples are performed to determine the influence of the Sabatier reaction conditions on the surface structure of the catalyst.

Toluene combustion over NiO nanoparticles on mesoporous SiO2 prepared by atomic layer deposition

NiO nanoparticles were deposited on mesoporous SiO2 by atomic layer deposition (ALD) consisting of sequential exposures to Ni(Cp)2 and H2O. NiO/SiO2 catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), inductively coupled plasma-optical emission spectroscopy (ICP-OES) and X-ray photoelectron spectroscopy (XPS). The catalytic activity of NiO/SiO2 catalysts for toluene combustion was measured in terms of toluene removal efficiency and conversion to CO2 and compared with that of commercial NiO nanoparticle catalysts. In order to investigate dependence of reaction temperature on toluene combustion, the toluene combustion experiments over NiO catalysts were carried out as various temperatures. We show that NiO catalysts can be efficient catalysts for toluene combustion below as well as above 200°C. The catalytic activity per Ni atom of NiO/SiO2 catalyst was higher than that of unsupported NiO nanoparticles. This high activity of NiO/SiO2 catalysts is attributed to large surface area of mesoporous SiO2 substrates, which is able to adsorb a large amount of toluene molecules and expedite oxidation of toluene by spill-over.

NiO and ZrO2-based catalysts in the reaction of complete methane oxidation

The reaction of complete methane oxidation over deposited catalysts (NiO/ZrO2 and NiO/YSZ) and binary oxides NiO_ZrO2 produced by co-precipitation, by the sol gel method, and using a bio-template (NiO content in the samples, 10.1 mol %) is investigated. It is shown that binary oxides cause methane oxidation at lower temperatures than their deposited analogue: the temperature of methane half-transformation is 470, 500, and 520°C for binary oxides, while T 50 = 570°C for NiO/ZrO2. Major factors affecting the activity of binary oxides in the methane oxidation reaction are determined: the dispersion of the active phase (NiO) and the availability of the second component with high mobility of the lattice oxygen.

Decomposition of Toluene in a Plasma Catalysis System with NiO, MnO2, CeO2, Fe2O3, and CuO Catalysts

The performance of NiO, MnO2, CeO2, Fe2O3, and CuO catalysts on alumina in removing toluene from a gas stream was studied in a plasma catalysis system. The NiO catalyst performed better than the other catalysts, generating more toluene-destroying oxygen species by decomposing ozone. The optimum nickel loading in the NiO/γ-Al2O3 catalyst was approximately 5 wt%, close to the monolayer dispersion threshold of NiO on γ-Al2O3. The presence of water vapor had a negative effect on catalytic performance due to its quenching of high speed electrons and its competition with toluene for adsorption sites. Water vapor also reduced the outlet ozone concentration by inhibiting the production of key intermediate in the ozone formation process.

Effect of preparation parameters on the catalytic performance of mesoporous NiO for the oxidative dehydrogenation of propane to propylene

Mesoporous NiO was prepared by the template synthesis method, using polyethylene glycol as a template, Ni(NO3)2·6H2O and Ni(CH3COO)2·4H2O as a nickel source. The major factors that influenced the formation of mesoporous NiO, such as nickel source, calcining temperature and molecular size of PEG, were estimated. As a result, the nickel source and calcination process could determine the crystallizability and organization of mesostructured NiO particles. The molecular size of PEG surfactant is not only relevant to the pore size of mesoporous NiO, but also of effect on the selectivity to propylene. The fine mesoporous NiO could be formed by using Ni(CH3COO)2·4H2O as nickel source and PEG400 as template, and then being calcined at 400–600 °C. The mesoporous NiO catalysts exhibit significant catalytic activities for the oxidative dehydrogenation of propane. The propylene yield of 14 % was obtained at propane conversion of 27 % at 350 °C. Furthermore, the selectivity to propylene can be maintained around 50 % even at 600 °C, indicating the high catalytic stabilities of mesoporous NiO catalysts in the present work. We proposed that a non-stoichiometric oxygen species on the surface is the catalytic active site and the mesoporous structure is the key factor for the high catalytic stabilities in the light of the characteristic results of mesoporous NiO catalysts.

Carbon dioxide reforming of methane over mesoporous Ni/SiO2

Mesoporous SiO2-supported Ni catalyst was fabricated by atomic layer deposition (ALD), and the catalytic activity and stability were investigated in carbon dioxide reforming of methane (CRM) reaction at 800°C. The Ni/SiO2 catalysts showed high initial activity and catalytic stability in the CRM reaction as a result of confinement of Ni particles with a mean size of ∼10nm within the pores of SiO2. The Ni particles in pores of mesoporous silica were not only resistant towards sintering but also coke formation during the reaction. In contrast, bare NiO nanoparticles were easily aggregated into larger particles and coke could form under the same reaction conditions, and therefore, much lower reactivity for CRM was found using bare NiO catalysts. It is suggested that Ni particles with very low loading on mesoporous SiO2 could be promising candidate as catalysts of CRM reaction.

CO2 reduction to syngas and carbon nanofibres by plasma-assisted in situ decomposition of water

Simultaneous activation of CO2 and H2O was carried out in a non thermal plasma dielectric barrier discharge reactor operated under ambient conditions. The plasma reactor packed with partially reduced NiO/Al2O3 catalyst showed better CO2 conversion than both the unreduced NiO/Al2O3 and with plasma (no catalyst), whereas, highest syngas selectivity was observed with unreduced NiO/Al2O3. An interesting observation is the formation of carbon nanofibres (CNFs) along with syngas with a reduced NiO catalyst integrated to the plasma, whereas, pure NiO only led to the formation of methane. The reduction of CO2 by in situ formation of hydrogen from water splitting may produce CH4 and plasma-assisted chemical vapour decomposition of CH4 may lead to the formation of CNFs.

Effect of the added amount of organically-modified montmorillonite on the catalytic carbonization of polypropylene into cup-stacked carbon nanotubes

For the first time, cup-stacked carbon nanotubes (CS-CNTs) with high quality were efficiently synthesized by a one-pot approach through the carbonization of polypropylene (PP) under the combined catalysis of organically-modified montmorillonite (OMMT)/NiO. The effects of the added amount of OMMT on the yield, morphology, microstructure, phase structure and thermal stability of carbon nanomaterials (including CS-CNTs and carbon nanofibers (CNFs)) were fully investigated by scanning electron microscope, transmission electron microscope (TEM), high-resolution TEM (HRTEM), X-ray diffraction, Raman spectroscopy and thermal gravimetric analysis. Furthermore, the effects of OMMT on the degradation products of PP and the coalescence and reconstruction of NiO nanoparticles before the growth of CS-CNTs and CNFs were analyzed by gas chromatography, gas chromatography–mass spectrometry and HRTEM. It was found that after adding a low amount of OMMT, a relatively large amount of light hydrocarbons and a small amount of aromatics were produced during the degradation of PP, which promoted the coalescence and reconstruction of NiO nanoparticles into rhombic shape. Subsequently, the reshaped NiO catalysts catalyzed the light hydrocarbons and aromatics into long, straight and smooth-surface CS-CNTs with narrow length and diameter distributions. This approach offers a new potential way to largely transform waste polymer materials into valuable CS-CNTs.

Effects of catalyst characters on the photocatalytic activity and process of NiO nanoparticles in the degradation of methylene blue

By a hydrothermal method combining a subsequent calcination process, series of nano-scale NiO samples with different morphologies and sizes were synthesized and characterized. The effects of synthesis conditions including using different alkali reactants and being calcined at different temperatures on the characters of NiO samples have been investigated. In these characters the integrality of crystal structure and the crystallinity of NiO were found to become the determinative factors which affect the photocatalytic activity and process of NiO catalyst in the degradation of methylene blue (MB). The NiO sample which has a good crystallinity and small particle size (≤100nm) possesses more shallowly trapped holes to react with chemisorbed oxhydryl OH− or H2O to generate OH radicals, exhibiting a high photocatalytic activity, furthermore, in this UV/NiO suspension the photocatalytic oxidation process of MB occurrs via the attack by OH radicals. The NiO sample which has a higher crystallinity and bigger particle size (>200nm) possesses more deeply trapped holes (hvb+) to react directly with physisorbed organism, exhibiting a low photocatalytic activity, therefore, in this system the MB is oxidized by direct reacting with holes (hvb+).

High-performance solid catalysts for H2 generation from ammonia borane: progress through synergetic Cu–Ni interactions

Chemical hydrogen storage materials, in particular B–N compounds such as ammonia-borane (AB), with a potential storage capacity of 19.6 wt% H2 and 0.145 kg H2 l−1 have been regarded as potential solutions for addressing H2 storage issues. In this work, we report the exceedingly high catalytic performance of easily prepared bi-component CuO–NiO catalysts for the H2 evolution from ammonia-borane in aqueous solution. These non-noble metal catalysts could be synthesized either by simple thermal treatment of a physical mixture of the metal precursors or through an improved hard templating method. This work clearly shows that metal precursors, composition, and heat treatment conditions have a profound influence on the synergetic interaction existing between Cu species and NiO, which is decisive in accelerating the hydrogen evolution of AB. Therefore, the present finding demonstrates that combinations of non-noble metals can provide viable approaches for the development of practical catalysts.

201 単分散型NiO触媒の調製および熱分解ガス変換への応用(安定化・無害化、循環型廃棄物処理技術)

201 単分散型NiO触媒の調製および熱分解ガス変換への応用(安定化・無害化、循環型廃棄物処理技術)

Preparation and characterization of porous Nb2O5 photocatalysts with CuO, NiO and Pt cocatalyst for hydrogen production by light-induced water splitting

In this study, porous Nb2O5 photocatalyst materials are prepared through thermal oxidation. According to X-ray photoelectron spectroscopy (XPS), at a temperature of 500 °C, an optimum porous Nb2O5 photocatalyst is obtained with an O/Nb ratio close to the theoretical value of 2.5. The X-ray powder diffractometer (XRD) result shows that at the main diffraction angles of 22.63° and 28.33°, crystalline diffraction signals of Nb2O5 appear with corresponding diffraction planes of (001) and (180). When CuO, NiO and Pt catalysts are added to Nb2O5 as the cocatalyst for comparison, the maximum hydrogen production efficiency for a CuO/Nb2O5 photocatalyst is achieved (1405 μmol h−1 g−1). However, when NiO and Pt are added as cocatalysts, the hydrogen production efficiencies are decreased to 800 μmol h−1 g−1 and 510 μmol h−1 g−1, respectively. Through the photoelectrochemical analysis, it finds that the CO signal peak with incomplete oxidation significantly increases as the reaction time increases, thus causing CO to adsorb on the catalyst surface (such as NiO or Pt) leading to catalyst poisoning. This results in reduced catalyst performance and hydrogen production rates.

Niobia-Supported Nanoscaled Bulk-NiO Catalysts for the Ammoxidation of Ethane into Acetonitrile

Two series of supported nanoscaled NiO catalysts have been prepared using Nb2O5 supports with different surface areas. NiO nanoparticles interacting with Ni–O–Nb mixed phases are active and selective for ethane ammoxidation; both are required in order to have an active and selective catalyst. In this paper we report the dispersion of NiO nanoparticles on two Nb2O5 supports in order to generate an active phase for ethane ammoxidation. The use of a support stabilizes NiO nanoparticles, which otherwise would sinter. This work shows how the activity can be modulated by the size of the NiO nanoparticles and by the NiO/Ni–Nb–O ratio, which depends on the nickel coverage and support surface area. The catalysts obtained are very promising for ethane ammoxidation reaction.

Producing Hydrogen-Rich Gases by Steam Reforming of Syngas Tar over CaO/MgO/NiO Catalysts

The objective of this study was to develop nanosized CaO, MgO, and NiO catalysts for tar removal in biomass gasification, significantly enhancing the quality of the produced gases. Catalysts were tested in a fixed-bed reactor for biomass tar steam reforming. Toluene was chosen as a model syngas tar compound. For this purpose, pure Ca(OH)2, Mg(OH)2, and Ni(OH)2 precursors were successfully synthesized via a facile solvothermal method. Subsequent calcination of the metal hydroxide precursor at 450 °C resulted in nanosized CaO, MgO, and NiO. Different analytical techniques such as XRD, TEM, SEM, and BET were used to characterize the synthesized nanomaterials. Bulk NiO, CaO, and MgO nanomaterials and a physical mixture of CaO/MgO/NiO (equal NiO/CaO/MgO ratio) were used as catalysts for the steam gasification of toluene. Research showed higher toluene conversions, which resulted in increases in H2 yield as well as CO and CO2 selectivity. Mixed metal oxide CaO/MgO/NiO catalyst exhibited higher performance on toluene conversion, resulting in higher H2 yield and CO2 selectivity.

Catalytic performance of MnOx–NiO composite oxide in lean methane combustion at low temperature

A series of MnOx–NiO composite oxide catalysts were prepared by co-precipitation method and used in the catalytic combustion of lean methane at low temperature. Compared with the corresponding single NiO and MnOx oxides, the MnOx–NiO composite oxide with proper composition exhibits much higher catalytic performance in the lean methane oxidation. XRD and HRTEM results demonstrate that MnOx–NiO is in the form of a Ni–Mn–O solid solution. XAFS and XPS results indicate that the content of manganese in MnOx–NiO has a significant influence on the oxidation state of manganese and the crystal defect of nickel oxide. MnOx–NiO catalyst with an atomic Mn/(Mn+Ni) ratio of 0.13 is provided with abundant highly dispersed manganese species of higher valence (Mn4+) and higher coordination number as well as certain nickel vacancies, due to the strong interaction between Ni and Mn species. H2-TPR and O2-TPD results show that the MnOx–NiO composite oxide exhibits better reducibility and oxygen mobility than NiO. All these characterizations suggest a prominent synergism between NiO and MnOx in the MnOx–NiO composite oxide, which contributes to its high performance in the lean methane combustion.

Sites for the selective hydrogenation of ethyne to ethene on supported NiO/Au catalysts

Au, NiO, and NiO/Au clusters of 2.5–16 nm, supported on Al2O3, ZrO2, TiO2, and ZnO, were studied in the purification of ethene feedstock from ethyne by hydrogenation at 357 K. The Au, NiO, and NiO/Au catalysts possessed 100 % selectivity to ethene. As the size of NiO clusters decreased from 7 to 3 nm, the turnover frequency (TOF) decreased from 812–1,023 to 276 h−1. In contrast with NiO, Au activity increased with decreasing particle size. NiO/Au catalysts possessed higher stability and activity in comparison with Au and NiO catalysts. The synergistic gain on NiO/Au clusters (SG) calculated as TOFNiO/Au – TOFAu – TOFNiO was 1,466; 1,147; 563; and 569 h−1 for NiO/Au/Al2O3, NiO/Au/TiO2, NiO/Au/ZnO, and NiO/Au/ZrO2, respectively. The reasons of the observed catalytic trends and the origin of the most active and selective sites are discussed.

Selective oxidative dehydrogenation of ethane over SnO2-promoted NiO catalysts

NiSnO mixed oxides catalysts have been investigated for the oxidative dehydrogenation of ethane. The catalysts were prepared through the evaporation of aqueous solutions of nickel nitrate and tin oxalate and finally calcined in air at 500°C for 2h. These materials have been characterized by several techniques (N2-adsorption, X-ray diffraction, High-Resolution Electron Microscopy, temperature programmed reduction, X-Ray Photoelectron Spectroscopy, Fourier Transformed Infrared Spectroscopy of adsorbed CO and 18O/16O isotope exchange). The addition of just a tiny amount of tin highly increases the selectivity to ethylene (from ca. 40% to 80–90%). Thus, high selectivity to ethylene (near to 90%) is observed on samples with high Ni/Sn atomic ratios (3<Ni/Sn<50), in which no influence of ethane conversion on selectivity to ethylene is observed (suggesting high stability of ethylene on these catalysts). Additionally, for low Sn-loadings, an increase in the catalytic activity has also been observed. The enhanced catalytic properties have been explained in terms of changes in the nature of Ni species on the catalyst surface, which can be considered as the active sites. The nature of Ni species is related to changes in the crystal size of NiO particles (and surface area) of catalysts as well as to the presence of SnOx crystals. In addition, the role of the presence of acid sites on the catalyst surface on the selectivity to ethylene is also discussed.

Development of a support for a NiO catalyst for selective adsorption and post-adsorption catalytic steam gasification of thermally converted asphaltenes

Insight on the role of a new heterogeneous catalyst for catalytic steam gasification of adsorbed asphaltenes is reported. The catalyst was prepared by incorporating NiO nanoparticles into mesoporous–macroporous Ba-based meta kaolin intended both as catalyst support as well as adsorbent. Variations on the catalyst support were made in form of extrudates by adding a binder (Ba(CH3COO)2 and/or Ca(CH3COO)2) and sucrose as a porogenic substance, to kaolin and calcining in air typically at 650°C. Effect of the binder type and content, sucrose content and calcination temperature upon adsorption was determined by performing adsorption study of Quinoline-65 (Q-65) using UV–Vis spectrophotometry. The surface basicity of catalyst support was measured by CO2 temperature programmed desorption (TPD) experiments. Pore size distribution was determined by Nitrogen physisorption. The Q-65 uptake was correlated to the pore size distribution and the basicity of the adsorbents. The results suggest that solids having low surface basicity and with increased pore size distribution between 200 and 800Å showed better adsorption. Further, incorporation of NiO nanoparticles into these catalyst supports not only enhanced the adsorption of asphaltenes, but also promoted the steam gasification of the adsorbed asphaltenes, leading to CO2 and H2 as major products.

Production of hydrogen by steam reforming of methane over alumina supported nano-NiO/SiO2 catalyst

Steam reforming of methane (SRM) was carried out over alumina supported nano NiO catalyst in silica synthesized using sol–gel method. The crystallite size of NiO in NiO–SiO2 catalysts was found to vary with the calcination temperature and the extent of Ni loading in the catalyst. The NiO crystallite size was found to be 9–15nm in the Ni loading range of 5–15% and calcinations temperature range of 350–500°C studied. Catalyst containing 10% Ni was found to be the best one for steam reforming reaction in terms of methane conversion. The catalyst was found to be very active and stable in the temperature range of 500–700°C. The most favorable reaction condition was established at a temperature of 700°C, steam to methane molar ratio of 3.5 and a space–time of 11.31kgcath/kmol of inlet methane. At this optimum condition, the conversion of methane was 95.7% and the yield of hydrogen was about 3.8moles of hydrogen per mole of methane reacted.