Nickel Oxide Silica Research Articles

Nickel oxide-silica core-shell catalyst for acetylene hydroxycarbonylation

Acrylic acid and its ester derivatives are important chemicals utilized to synthesize numerous end products. Acrylic acid is industrially produced via propylene oxidation. We report in this study a nickel oxide-silica core-shell catalyst (NiO@SiO2) for acetylene hydroxycarbonylation as an alternative way to synthesize acrylic acid. NiO@SiO2 catalyst provided the higher turnover frequency and yield than commercial nickel oxide catalyst on acetylene hydroxycarbonylation. The carbon monoxide/acetylene ratio influenced more significantly to initial reaction rate than final acrylic acid yield. The silica shell protected the nickel oxide from sintering during reaction, however, the catalyst was deactivated by coke formation, attributed to acetylene decomposition.

Reducing the exergy destruction in the cryogenic heat exchangers of hydrogen liquefaction processes

A present key barrier for implementing large-scale hydrogen liquefaction plants is their high power consumption. The cryogenic heat exchangers are responsible for a significant part of the exergy destruction in these plants and we evaluate in this work strategies to increase their efficiency. A detailed model of a plate-fin heat exchanger is presented that incorporates the geometry of the heat exchanger, nonequilibrium ortho-para conversion and correlations to account for the pressure drop and heat transfer coefficients due to possible boiling/condensation of the refrigerant at the lowest temperatures. Based on available experimental data, a correlation for the ortho-para conversion kinetics is developed, which reproduces available experimental data with an average deviation of 2.2%. In a plate-fin heat exchanger that is used to cool the hydrogen from 47.8 K to 29.3 K with hydrogen as refrigerant, we find that the two main sources of exergy destruction are thermal gradients and ortho-para hydrogen conversion, being responsible for 69% and 29% of the exergy destruction respectively. A route to reduce the exergy destruction from the ortho-para hydrogen conversion is to use a more efficient catalyst, where we find that a doubling of the catalytic activity in comparison to ferric-oxide, as demonstrated by nickel oxide-silica catalyst, reduces the exergy destruction by 9%. A possible route to reduce the exergy destruction from thermal gradients is to employ an evaporating mixture of helium and neon at the cold-side of the heat exchanger, which reduces the exergy destruction by 7%. We find that a combination of hydrogen and helium-neon as refrigerants at high and low temperatures respectively, enables a reduction of the exergy destruction by 35%. A combination of both improved catalyst and the use of hydrogen and helium-neon as refrigerants gives the possibility to reduce the exergy destruction in the cryogenic heat exchangers by 43%. The limited efficiency of the ortho-para catalyst represents a barrier for further improvement of the efficiency.

Interlayer free – nickel doped silica membranes for desalination

This work shows for the first time the potential of nickel oxide silica membranes for desalination applications. Nickel oxide silica xerogels were synthesised via a sol–gel method including TEOS, nickel nitrate with and without addition of hydrogen peroxide. The effects of nickel addition (5% - 50 mol %) on the structure–property relationship of the silica materials were systematically studied. The membrane performance were tested as a function of feed salt concentration (0.3–3.5 wt% NaCl) and temperature (27–60 °C). The membranes which were prepared using equal sol–gel conditions to the xerogel samples showed the raised feed temperatures resulted in increased water fluxes, whilst increasing the salt concentration resulted in decreased water fluxes. The membranes with addition of hydrogen peroxide exhibited better performances than their H2O2 absence counterpart. The salt rejection was in excess of 90% and the maximum flux observed was 7.3 kg m-2 h-1 at 60°C for a 0.3 wt% NaCl feed concentration.

Preparation and magnetic characteristics of mesoporous nickel oxide–silica composites

Mesoporous NiO–SiO2 (MCM-41) silica-matrix composites with various nickel oxide concentrations (NiO : SiO2 = 0.025 : 1 to 0.2 : 1) have been produced by oxide cocondensation under hydrothermal synthesis conditions in the presence of cetyltrimethylammonium bromide as a template and (2-cyanoethyl) triethoxysilane as an organosubstituted trialkoxysilane additive. X-ray diffraction data have been used to evaluate the maximum nickel(II) oxide concentration (NiO : SiO2 = 0.1 : 1) that allows the ordered mesopore structure of MCM-41 to persist in the silica-matrix composites. We have studied the magnetic properties of this material as functions of temperature and magnetic field. The results demonstrate that the magnetic properties of the nanocomposite with NiO : SiO2 = 0.1 : 1 at low temperatures (T < 20 K) are determined by incomplete spin compensation in the matrix and on the surface of the NiO nanoparticles.

Structural evolution of nickel oxide silica sol-gel for the preparation of interlayer-free membranes

This work investigates a modified sol-gel method for the preparation of interlayer-free nickel oxide silica membranes for desalination applications. The sol–gels were synthesized using TEOS, nickel nitrate hexahydrate, ethanol as solvent and water with and without peroxide (H2O2). The effect of the nickel embedded in the silica matrix as Ni/Si molar ratio was varied from 5 to 50mol% and systematically studied. The sols prepared with H2O2 resulted in microporous structures and lower pore volume, contrary to the mesoporous structures derived from sols without H2O2. The modified sol-gel method proved to be robust enough for coating directly on α-alumina substrates, as opposed to conventional methods which required substrates with interlayers. All interlayer-free nickel oxide silica membranes delivered high salt rejection ranging from 91.5 to 99.9%, and reaching water flux as high as 7.3kgm−2h−1. The membranes prepared using sols with H2O2 gave lower water flux and slightly higher salt rejection, attributed to lower pore volume and smaller pore size, respectively. The membranes prepared with Ni/Si molar ratio of 25% achieved the highest water flux, though salt rejection slightly decreased with the increase of feed salt concentration from brackish (NaCl 0.3wt%) to sea water (NaCl 3.5wt%).

Preparation of nickel oxide– and nickel–silica nanocomposites by spray pyrolysis

Nickel oxide–silica and nickel–silica nanocomposites were prepared by spray pyrolysis of aqueous sols of silica nanoparticles containing nickel nitrate hexahydrate, without and with ethanol, respectively. During pyrolysis, the silica nanoparticles were restructured, losing their identities, while the nickel oxide or nickel particles in the composites grew by coalescence and sintering. Compactness of the composites, higher in nickel–silica composites than their counterpart nickel oxide, increased with the temperature of preparation and the concentration of nickel nitrate. Nickel always formed larger crystallites than its counterpart nickel oxide, due to its higher sintering rate. At 500 °C, the crystallite growths of nickel oxide and nickel were inhibited by the low sintering rate and the formation of nickel intermediates, respectively, while at 1000 °C their phase-pure crystallites continuously grew with the increase in the nitrate concentration.

Preparation and desalination performance of multiwall carbon nanotubes

Multiwall carbon nanotubes (MWCNTs) were prepared by catalytic decomposition of methane at 680–700 °C, using nickel oxide-silica binary aerogels as the catalyst. The morphological structure of MWCNTs was investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and Raman spectroscopy. The results revealed that MWCNTs had a diameter of 40–60 nm, with high quality and high length/diameter ratio, and some metal catalyst particles were encapsulated at the tip of nanotubes. Using MWCNTs as the electrodes of flow-through capacitor (FTC), desalination performance was investigated. The results showed that modification methods had great effect on desalination performance of MWCNTs. The removal amount of NaCl was generally dependent on the surface area and pore volume of MWCNTs. After modification in diluted HNO 3 solution with ultrasonic and then ball milling, the metal catalyst particles at the tip of nanotubes disappeared, the nanotube length became short, the cap at the tip of nanotubes was opened, the internal surface area could be effectively used, leading to increasing the specific surface area and pore volume for MWCNTs, and thus, the desalination performance thereof was the best of all.

Preparation and modification of carbon nanotubes

Carbon nanotubes (CNTs) were prepared by the catalytic decomposition of methane at 680 °C for 120 min, using nickel oxide–silica binary aerogels as the catalyst. The morphological structure of CNTs was investigated by transmission electron microscopy (TEM), X-ray Diffraction (XRD) and Raman spectroscopy. The results revealed that CNTs with diameter 40–60 nm showed high quality, uniform diameter and high length/diameter ratio, the wall structure of CNTs was similar with that of highly oriented pyrolytic graphite (HOPG), and some metal catalyst particles were encapsulated at the tip of CNTs. Different methods were compared to modify CNTs. Investigated by TEM, XRD, Raman spectroscopy and nitrogen adsorption/desorption for modified CNTs, it was confirmed that after modification treatment by immersion in diluted HNO3 solution with ultrasonic and then milling by ball at a high velocity, the metal catalyst particles at the tip of CNTs disappeared, the unique cylinder wall structure remained, the CNT length became short, the cap at the tip of nanotube was opened, and thus the internal surface area could be effectively used, leading to the increase of the specific surface area and pore volume. This technique is relatively simple and effective for modifying CNTs which can be scaled up for industrial applications.

Catalytic activities of nickel-containing catalysts for ethylene dimerization and butene isomerization and their relationship to acidic properties

Nickel oxide-silica catalysts were prepared by precipitation from an acidic solution of a nickel salt–sodium silicate mixture. Two types of nickel hydrosilicate, montmorillonite and antigorite are formed in the catalysts. Catalytic activities of nickel silicates for ethylene dimerization and butene isomerization run parallel when the catalysts are activated by evacuation at elevated temperatures, giving two maxima in activities. The variations in catalytic activities are closely correlated to the acidity of catalysts. The acid site responsible for the catalytic activity is protonic on montmorillonite, while non-protonic on antigorite, as evidenced by the effect of water content and the IR spectra of adsorbed pyridine. Catalytic activities of NiO-TiO 2 catalysts modified with H 2SO 4, H 3PO 4, H 3BO 3 and H 2SeO 4 for ethylene dimerization and butene isomerization were examined. The order of catalytic activities for both reactions was found to be NiO-TiO2/SO 4 2−⪢NiO-TiO 2/PO 4 3−>NiO-TiO 2/BO 3 3−>NiO-TiO 2/SeO 4 2−>NiO-TiO 2, showing clear dependence of catalytic activity upon acid strength. Catalytic activity of nickel sulfate supported on γ-Al 2O 3 (NiSO 4/γ-Al 2O 3) for ethylene dimerization is also closely correlated to the acidity of catalysts, showing that the active sites consist of a low-valent nickel (Ni +) and an acid.

Nickel oxide–silica and nickel–silica aerogel and xerogel nanocomposite materials

The sol-gel method was used to prepare nickel oxide–silica and nickel–silica nanocomposite materials and the corresponding silica matrices. Different drying conditions were used to obtain aerogel and xerogel materials. The samples were characterized by thermal analysis, x-ray diffraction, N2–physisorption, transmission electron microscopy techniques, and infrared spectroscopy. Aerogel samples had a much higher surface area than the xerogel samples; moreover, different supercritical drying conditions gave rise to a different porous structure, which influenced the size and distribution of the nanoparticles in the matrix.

Preparation of Aerogel and Xerogel Nanocomposite Materials

ABSTRACTSol-gel method was used to prepare nickel oxide-silica and iron oxide-silica nanocomposites materials in form of aerogels and xerogels. The samples were characterized by thermal analysis, X-ray diffraction, N2 physisorption and transmission electron microscopy techniques. The variation of the supercritical solvent extraction conditions gives rise to differences in the morphological characteristics of the aerogels. These differences influence the size of the nickel oxide nanoparticles in nickel containing aerogels. On the other hand they do not affect the structure and size of the iron oxide nanoparticles in iron containing aerogels. The differences between the xerogel and aerogel nanocomposites are discussed.

Effect of acid strength on the catalytic activity of NiOTiO 2 modified with acids

Nickel oxide-silica is known to be effective for the dimerization of ethylene at room temperature. The catalyst is also active for the isomerization of n-butane, the mechanism of which has been proved to be of a proton donor-acceptor type. It has been suggested that the active site for dimerization is formed by an interaction of a low valent nickel ion with an acid site. In the previous papers from this laboratory, it has been shown that the NiO-TiO{sub 2} and NiO-ZrO{sub 2} modified with sulfate ion is very active for ethylene dimerization. High catalytic activities in the reactions were attributed to the enhanced acidic properties of the modified catalysts, which originated from the inductive effect of S{double bond}O bonds of the complex formed by the interaction of oxides with sulfate ion. The dependency of the catlaytic activity on the acid strength was reported by numerous investigators. The acid strength of a solid is the ability of the surface to convert an adsorbed neutral base into its conjugate acid as described by Walling. The present paper is concerned with the preparation of NiO-TiO{sub 2} modified with various acids, H{sub 2}SO{sub 4}, H{sub 3}PO{sub 4}, H{sub 3}BO{sub 3}, and H{sub 2}SeO{sub 4},more » and the dependence of catalytic activity on acid strength. For this purpose, 1-butene isomerization and ethylene dimerization, which is known to be catalyzed by acid catalysts, were chosen as test reactions.« less

Structure of NiOSiO catalyst for ethylene dimerization as observed by infrared absorption

Nickel oxide-silica catalysts were prepared by precipitation from an acidic solution of a nickel salt-sodium silicate mixture, and the structure of prepared catalyst was examined by infrared absorption spectra. Two types of nickel-hydrosilicate, montmorillonite and antigorite, are formed in the catalysts, the relative abundance of which is indicated by ir bands at 710 and 665 cm−1. It is shown that the higher the final pH in precipitation, or the higher the Ni/SiO2 ratio in the starting mixture, the more the formation of antigorite. The NiO/SiO2 catalysts thus prepared are activated for ethylene dimerization by evacuation at elevated temperatures, giving two optimum temperatures, about 100 and 600°C. The first activation is ascribed to a montmorillonite-type site, while the second activation is ascribed to an antigorite-type site.

Catalytic Dehydration of Ethers on Nickel Oxide–Silica–Alumina

Abstract The dehydration of diethyl ether was studied on synthetic nickel oxide–silica–alumina catalysts in the temperature range of 340–400 °C and at pressures less than 50 Torr. It was found that ethylene, butenes, water, and small amounts of carbon monoxide and methane were formed on the catalysts of lower nickel content. The rate constant for the formation of butenes showd a maximum on the catalyst of 10 atom% nickel. The mechanism of the formation of the butenes was discussed by studying the catalytic dehydration of various ethers.

Dimerisation of propene catalysed by transition-metal compounds and complexes

Propene dimerisation has been studied using catalysts of the following types: (a) aluminium alkyl halides, (b) cobalt (or nickel) halide–aluminium alkyls, (c) cobalt chloride–aluminium chloride and related systems, (d) cobalt chloride–aluminium chloride–aluminium alkyls, and (e) nickel oxide–silica–alumina.

Tracer study of ethylene dimerization over nickel oxide-silica catalyst

The role of proton originally held by the catalyst NiOSiO 2 in the dimerization of ethylene was investigated by means of the deuterium tracer, taking the subsequent isomerization of butene into consideration. It was shown that the deuterium involved in the catalyst did appear in the product butene by way of the isomerization and not of the dimerization. Further study on the dimerization in the presence of C 3D 6 or C 2D 4 revealed that the reacting ethylene molecules rapidly exchange their hydrogen with each other prior to the dimerization. A few micromoles of carbon monoxide adsorbed completely prevented both the isotopic exchange and the dimerization. The mechanism of the dimerization is discussed on the basis of these results. It is suggested that the active site responsible for the dimerization consists of a low valent nickel and an acid.

Heat of Adsorption of Carbon Monoxide on Coprecipitated Nickel Oxide-Silica Catalyst

Heat of Adsorption of Carbon Monoxide on Coprecipitated Nickel Oxide-Silica Catalyst

The effective site on acid catalysts revealed in n-butene isomerization

1-Butene isomerization experiments were carried out at near room temperatures with deuterated acid catalysts such as silica-alumina, silica-magnesia, silica-zirconia, nickel oxide-silica, alumina, alumina-boria, and nickel sulfate-on-silica, as well as with nondeuterated catalysts in the presence of deuterated propylene or other hydrocarbons. Reaction mixtures were separated by gas chromatographic column and analyzed for deuterium distribution by mass spectrometry. The exchange behavior revealed in the experiments was remarkably dependent on the evacuation temperature of the deuterated catalysts. For the evacuation temperatures near 100 °C, most of the deuterated catalysts gave deuterated products, the deuterobutene concentrations found in product 2-butenes being much larger than in unreacted 1-butene. However the larger deuterobutene concentrations in 2-butenes decreased with a rise in the evacuation temperature of the deuterated catalysts, down to negligible concentration for the evacuation at 500 °C, whereas the conversions of reactant increased with rise in the evacuation temperature above 100 °C. On the other hand, with most of the nondeuterated catalysts evacuated at 500 °C, 1-butene isomerization in the presence of deuteropropylene revealed an essentially identical behavior of hydrogen exchange with that on the deuterated catalysts evacuated at 100 °C. These results suggest that n-butene isomerization on these catalysts proceeds at least partly through a proton donor-acceptor mechanism with either Bronsted acids on the surface or the carbonium ions formed by adsorption of olefins on Lewis acid sites serving as proton donors, although the conclusion is open to question in the case of alumina.