Au/Mg(OH)2 catalysts with two different sizes (4 and 14 nm) of Au nanoparticles (NPs) have been prepared by depositing pre-fabricated Au NPs onto Mg(OH)2 nanosheets (NSs). It was found that 14 nm Au NPs supported on Mg(OH)2 exhibited unexpected activity for CO oxidation at ambient temperature that could be comparable with those of Au NPs of 4 nm. The Mg(OH)2 support was suggested to be responsible for the observed catalytic activity of larger gold supported catalysts. 相似文献
A series of Ga-containing hydrotalcite-like materials (GaHTs), [Mg1-xGax(OH)2](CO3)x/2 ·mH2O wherex = 0.072 0.35 (Mg/Ga = 12.9 1.8), was synthesized by a coprecipitation method. The resulting solids were characterized by means of X-ray diffraction, thermal gravimetric and infrared analyses. All GaHTs showed diffraction patterns typical of Mg-Al hydrotalcites. Small amounts of brucite, Mg(OH)2, were detected only in the GaHT with Mg/Ga = 12.9. Attempts to obtain Ga-richer hydrotalcites, Mg/Ga < 1.8, resulted in solids with an invariably constant Mg/Ga = 1.8 ratio, which appears to be the maximum Ga content limit. Judging from the TGA pattern of a GaHT (Mg/Ga = 7.7), the layered structure is stable up to ca. 573 K, and at 873 K the resulting solid shows a MgO-like diffraction pattern, suggesting that Ga3+ may be replacing some Mg2+ ions in MgO. Once their layered structure collapses (i.e., at 873 K), GaHT can be easily converted back into the original layered material by treating in a carbonate-containing aqueous solution, i.e., they show the memory effect typical of Mg-Al hydrotalcites. 相似文献
Summary: Different styrene‐ and acrylate‐based organic‐inorganic polymer composites incorporating magnesium hydroxide were successfully synthesized using MPTMS as a coupling agent and MgCl2 as an inorganic precursor. The polymer composites were prepared by free‐radical emulsion polymerization following different procedures. The samples were investigated by means of FT‐IR spectroscopy, XRD, TGA, DSC, and rheometry. It is shown that the preparation method does only affect the ratio of organic to inorganic component, but not the chemical structure of the composites. The obtained polymer composites consist of Mg(OH)2 particles which are linked covalently via MPTMS groups to the polymer backbone.
Scheme of Mg(OH)2 crosslinked with MPTMS units as proposed for the emulsion polymer composite. 相似文献
The effect of Ca(OH)2 or Ca(H2PO4)2 2H2O (MCP) on potassium (K) or magnesium (Mg) leaching through and out of columns of soil with predominantly variable charge was studied. Calcium hydroxide was mixed with soil from the A and B horizon to raise the pH to about 6 or 7, and MCP, equivalent to 952 mg P, was mixed with the A horizon of each soil. Various concentrations of KCl or MgCl2 were applied as a pulse to the soil surface and leached with five pore volumes of deionised water.Calcium hydroxide or MCP addition increased leaching losses of K and Mg initially present in the soil.Liming to about pH 6 reduced leaching of applied K and Mg in all soils. This was attributed to the increase in the cation exchange capacity (CEC). Applied K leached to a greater extent at pH 7 than at pH 6 in the A horizon of each soil despite a two-fold increase in CEC. However, when Mg was applied to all soils and K applied to soil from B horizons, leaching decreased as the pH increased from 6 to about 7.The addition of MCP increased the CEC of all soils, but this had little effect on the leaching of applied K compared with the untreated soils.A proportion of applied K or Mg was displaced from the soil column for all Ca(OH)2 or MCP treatments. In many columns, no increase in exchangeable K or Mg in the lower segments of the soil column was found. Where this occurred the activity ratio in the leachate was the same as the equilibrium activity ratio. 相似文献
The influence of Mg2+ and Al3+ ions on a.c. deposition of copper nanowires into aluminium anodic oxide film (AOF) nanotubes has been studied using cyclic voltammetry and d.c. plasma emission spectrometry. From the analysis of copper quantities deposited into the Al AOF nanotubes (mCu), 0.02 M MgSO4 concentration was found to be optimal for Cu(II) solutions. Moreover, it was shown that Mg2+ and Al3+ ions not only prevent the breakdown of the barrier layer of AOF, but change the rate of copper deposition and modify the shape of the mCu against pH plots depending on the a.c. voltage applied. From the analysis of the quantities of magnesium (mMg) incorporated into the Al AOF nanotubes, presumably in the form of Mg(OH)2, the mMg against pH dependences were determined in MgSO4 and MgSO4 + CuSO4 solutions. An increase in mMg from 30 g dm–2 to 1 mg dm–2 at pH 1.5 and from 6 g dm–2 to 16 g dm–2 at pH 7.0 was found under the same a.c. treatment conditions from MgSO4 solutions without and with Cu2+ ions, respectively, indicating the incorporation of Mg(OH)2 into the Al AOF nanotubes to be lower up to about one hundred times in the case of Cu deposition. Based on the experimental results, it was suggested that incorporation of the Mg(OH)2 particles into the Al AOF nanotubes occurred simultaneously with growing copper nanowires under a.c. bias is insignificant, if the pH of the CuSO4 + MgSO4 solution is 2.5. 相似文献
Mixtures of Ca(OH)2 and diatomite were hydrated at different conditions to produce reactive SO2 sorbents. Two different hydration techniques were used; namely, atmospheric and pressure hydration. The effect of the hydration temperature, time and diatomite/Ca(OH)2 weight ratio on the physical properties of the activated sorbents were investigated. In atmospheric hydration, it was found that increasing the temperature and hydration time caused an increase in the total surface area of the sorbents. However, surface area values of the sorbents prepared from mixtures which have different diatomite/Ca(OH)2 weight ratio were generally not changed significantly. In pressure hydration, the surface area of the activated sorbents was positively affected from the hydration temperature and pressure. Finally, Ca(OH)2 and two diatomite/Ca(OH)2 sorbents were sulphated at constant temperature using a synthetic gaseous mixture consisting of 5% O2, 10% CO2, and the balance of nitrogen with a 55% relative humidity. The sulphation reaction of these sorbents were investigated and modelled. The unreacted shrinking core model was chosen to describe this non-catalytic solid/gas (hydrated sorbent/SO2) reaction mechanism. The experimental results were found to be correlated successfully by this model. 相似文献
Tetradentate thioacetyl porphyrin ligand (1) was synthesized to protect gold nanoparticles. 1-protected gold nanoparticles were characterized by UV-vis spectroscopy and XPS. Analysis by XPS showed that all of four thioacetyl groups of 1 were dissociated and bound to the surface of gold nanoparticles in thiolate form. The size of 1-protected gold nanoparticles (GN:1) was controlled by thioacetyl group/HAuCl4 molar ratio and approached to 2 nm. Compared with a protecting ligand without porphyrin plane (2) or dodecanethiol, 1 can control the size of gold nanoparticles efficiently probably due to the tetradentate ligation effect. 相似文献
The oxidation of furfural in H2O2 and H2O2–Mg(OH)2 system were systematically investigated and a rational explanation for the reaction mechanism was proposed. 2-formyloxyfuran, from selective oxidation of HCO group in furfural, was a crucial intermediate. The addition of Mg(OH)2 suppressed the oxidation of furan ring of furfural and enhanced selectivities of 2(5H)-furanone (44.8%) and succinic acid (38.0%). FT-IR, Gaussian calculation and experimental results indicated that the process of furfural oxidation with H2O2 is homogeneous, and the synergy between dissolved Mg2 + cations and OH− ions facilitates the HOO− attacking the carbon atom of HCO other than the CC bound of furan ring. 相似文献
The chemical solution deposition of Mg(OH)2 thin films on glass substrates and their transformation to MgO by annealing in air is presented. The chemical solution deposition consists of a chemical reaction employing an aqueous solution composed of magnesium sulfate, triethanolamine, ammonium hydroxide, and ammonium chloride. The as-deposited films were annealed at different temperatures ranging from 325 to 500?°C to identify the Mg(OH)2-to-MgO transition temperature, which resulted to be around 375?°C. Annealing the as-deposited Mg(OH)2 films at 500?°C results in homogeneous MgO thin films. The properties of the Mg(OH)2 and MgO thin films were analyzed by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV–Vis spectroscopy, and by circular transmission line model. Results by X-ray diffraction show that the as-deposited thin films have a brucite structure (Mg(OH)2), that transforms into the periclase phase (MgO) after annealing at 500?°C. For the as-deposited Mg(OH)2 thin film, a nanowall surface morphology is found; this morphology is maintained after the annealing to obtain MgO, which occurred with the evident formation of pores on the nanowall surface. The assessed chemical composition from X-ray photoelectron spectroscopy yields Mg0.36O0.64 (O/Mg ratio of 1.8) for the as-deposited Mg(OH)2 film, where the expected stoichiometric composition is Mg0.33O0.67 (O/Mg ratio of 2.0); the same assessment yields Mg0.60O0.40 (O/Mg ratio of 0.7) for the annealed thin film, which indicates the obtainment of a MgO material with oxygen vacancies, given the deviation from the stoichiometric composition of Mg0.50O0.50 (O/Mg ratio of 1.0). These results confirm the deposition of Mg(OH)2 films and the obtainment of MgO after the heat-treatment. The energy band gap of the films is found to be 4.64 and 5.10?eV for the as-deposited and the film annealed at 500?°C, respectively. The resistivity of both Mg(OH)2 and MgO thin films lies around 108?Ω·cm. 相似文献
A 1.9 wt% Ni/Mg(Al)O hydrotalcite-derived catalyst is studied for the dry reforming of propane to synthesis gas at 600 °C and 1 atm. The catalyst showed limited initial deactivation and then was exceptionally stable throughout a 34-day test. Catalyst characterisation indicates that the carrier material consists of a mixed Mg(Al)O phase before and after testing, and that carbonate forms on the support surface under dry reforming conditions. The Ni particles are in close contact with, and partially decorated by, the basic support. No carbon whisker formation is observed by transmission electron microscopy after catalytic testing.Alternating pulse experiments in a Temporary Analysis of Product-II (TAP-II) reactor system indicate that CO2 is associatively adsorbed on the basic Mg(Al)O carrier and acts as a permanent source of oxygen species for the Ni metal. Propane reacts rapidly with NiO species to form CO and H2O. Under TAP conditions, reduced Ni reacts gradually with carbonate from the support to give NiO species and CO. 相似文献
Substitution of 20 aluminium for nickel in the lattice of nickel hydroxide, prepared by coprecipitation, leads to a hydrotalcite-like compound of formula Ni0.8Al0.2(OH)2(CO3)0.1.0.66H2O. It has been found that the compound has prolonged stability in 6m KOH solution and can be used as the positive electrode material in rechargeable alkaline batteries. The structure, morphology and composition of the compound have been investigated by X-ray diffraction, scanning electron microscopy and infrared spectroscopy. The electrode comprising the aluminium-substituted nickel hydroxide has greater discharge capacity and higher utilization of active material than the -Ni(OH)2 electrode. Cyclic voltammetry suggest that the aluminium-substituted nickel hydroxide has better reversibility of the Ni(OH)2/NiOOH redox couple and higher oxygen evolution overpotential than -Ni(OH)2. The mechanism of the electrode reaction has also been discussed and the proton diffusion coefficient in the compound has been determined. 相似文献
Ca(OH)2/silica fume sorbents were prepared with various Ca(OH)2/silica fume weight ratios and slurrying times at 65°C and a water/solid ratio of 10/1. Dry sorbents prepared were characterized, and their reactivities toward SO2 were measured in a differential fixed-bed reactor at the conditions similar to those in the bag filters in the dry and semidry flue gas desulfurization (FGD) processes. The reaction between Ca(OH)2 and silica fume in the slurry was very fast. The formation of calcium silicate hydrates, which were mainly C-S-H(I), resulted in sorbent particles with a highly porous structure that seemed compressible under high pressures. The sorbents were mesoporous, and their specific surface areas and pore volumes were much larger than those of Ca(OH)2 alone. The utilization of Ca of sorbent increased with increasing silica fume content mainly due to the increase in the specific surface area of sorbent. The sorbent with Ca(OH)2 had the maximum SO2 capture. Sorbents with Ca(OH)2 contents less than and greater than would have a SO2 capture greater than that of Ca(OH)2 alone. Both the utilization of Ca and SO2 capture per unit specific surface area of sorbent decreased in general with increasing specific surface area. At the same Ca(OH)2 content, the utilization of Ca or SO2 capture of the Ca(OH)2/silica fume sorbent was greater than that of the Ca(OH)2/fly ash sorbent; however, the amount of SO2 captured per unit surface area of the former sorbent was smaller than that of the latter sorbent. The results of this study are useful to the preparation of silica-enhanced sorbents for use in the dry and semidry FGD processes. 相似文献
Theoretical studies on ethylene polymerization by single site homogeneous catalysts, as well as by Ziegler–Natta heterogeneous catalysts, have been reviewed. Studies on cation–anion interactions in ion-pair systems of the type [LLMR]+[A]– [L, L=Cp, NCR2, NPR3; M=Ti, Zr; A=MeB(C6F5)3–, MAOMe–, B(C6F5)4–] provided indications as to which ancillary ligands on the cation acted as good electron donors, and also revealed the importance of having a weakly coordinating anion to enable the ion-pair to separate more easily in solution. Subsequent calculations of barriers to ethylene insertion into the metal-methyl bond in ion-pair systems of the type LLMeM--B(C6F5)3[M=Ti, Zr] revealed that the ease of separation of the anion from the cation in solution was an important criterion in determining the activity of the catalysts. The barrier to insertion was found to be the rate determining step during the first insertion of ethylene into the metal–methyl bond, but second insertion studies conducted for two different ion-pair systems showed that the barrier to uptake of the monomer became the rate determining step during the second insertion of the ethylene monomer. Theoretical studies conducted on TiCl4/MgCl2 heterogeneous Ziegler–Natta catalysts provided insights into the nature of the binding of the titanium catalysts (with the Ti in different oxidation states) on to the MgCl2 support. The results indicated that the support worked best when a few Ti atoms replaced Mg atoms in the crystal lattice of the support. Ethylene polymerization studies, along with investigations on chain termination, led to the conclusion that the TiCl3-based edge site on MgCl2 would be the most promising model for the actual catalytic species. Studies on addition of tetrahydrofuran (THF) to the active sites showed that the presence of the base would lead to higher molecular weights of the polymers, as it acted to increase the barrier to termination (by chain transfer to monomer) more than the barrier to insertion. 相似文献
Nanostructured nickel hydroxide powder has been synthesized by a chemical precipitation method with the aid of ultrasound radiation, and the physical properties of the synthesized material were characterized by scanning electron microscopy, specific surface area, X-ray diffraction and differential scanning calorimetry. It was found that nanostructured nickel hydroxide was crystalline -Ni(OH)2 with a nanocrystalline and nanoporous surface structure. The crystallite sizes of nanostructured -Ni(OH)2 along the c- and a-axis were 2.5 and 2.3 nm, respectively, as calculated from (001) and (100) X-ray diffraction peaks. In comparison with spherical -Ni(OH)2 which has now been widely used as the active material for pasted nickel electrodes, nanostructured -Ni(OH)2 possessed a smaller crystallite size, more structural defects, a larger lattice parameter of c0, a higher specific surface area and lower thermal decomposition temperature. These physical characteristics were advantageous to the improvement of electrochemical activity of the nanostructured nickel hydroxide powder. Studies indicated that the filling property and flowability of nanostructured -Ni(OH)2, which were characterized by the measurements of tapping density and angle of repose, were inferior to those of spherical -Ni(OH)2. Pasted nickel electrodes with a porous nickel-foam substrate were prepared using a mixture of the nanostructured and spherical Ni(OH)2 powders as the active material. Charge/discharge tests showed that the addition of an appropriate amount of nanostructured Ni(OH)2 powder to spherical Ni(OH)2 powder could enhance the specific discharge capacity and high-rate capability of the pasted nickel electrodes. This enhancement could be attributed to a lowered electrochemical reaction impedance for the nickel electrode with the addition of nanostructured Ni(OH)2 relative to the electrode without nanostructured Ni(OH)2. 相似文献
The electrochemical response of the Pt/Ni(OH)2 interface subjected to potentiodynamic sweeps shows the contribution of the Ni (OH)2/Ni(OOH) redox couple immediately attached to the Pt(O) surface, when the substrate surface to Ni(OH)2 layer volume ratio is varied. A comparison with previously published results shows that the response of the innermost portion of the Ni(OH)2/NiOOH layer depends on the characteristic of the substrate, the temperature, the electrolyte concentration, the degree of hydration of the Ni(OH)2 film and the hydrophobicity of the substrate. The results indicate that the water content of the inner film is probably lower than that of the bulk, the Ni(III) species probably approaching the O-octahedral co-ordination corresponding to
1-NiOOH. 相似文献
The reactions of ethanol with CO/H2 or CH3OH to form 1-propanol proceed most efficiently over Cs/Cu/ZnO catalysts with selective oxygen retention from CO/H2 or CH3OH and removal of oxygen associated with the OH group of ethanol, in contrast to that predicted by the classic aldol condensation mechanism. Isotopic labeling experiments reveal a novel path12CH313CH2OH+12CO/H213CH312CH212CH2OH. 相似文献
