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1.
A solid ternary mixture consisting of NaF, silicon and one of the metal oxides such as Al2O3, MgO, CaO, SrO, BaO was prepared and used as a defluorinated reagent for CF4 decomposition. The results show that the initial conversion of CF4 reached 100% over NaF-Si-MgO and NaF-Si-CaO at 850°C, and the reagent with NaF/Si/MgO molar ratio of 33/34/33 exhibited a high reactivity with a full conversion of CF4 lasting for 57 min. The plausible paths of CF4 decomposition over NaF-Si-Al2O3, NaF-Si-MgO, NaF-Si-CaO, NaF-Si-SrO and NaF-Si-BaO are proposed. 相似文献
2.
NF3 decomposition in the absence of water over Al2O3, Fe2O3, Co3O4 and NiO, and transition metal oxides (Fe2O3, Co3O4 and NiO) coated Al2O3 reagents was investigated. The results show that Al2O3 is an active reagent for NF3 decomposition with 100% conversion lasting for 8.5 h at 400 ℃. Fe2O3, Co3O4 and NiO coated Al2O3 reagents are superior to bare Al2O3, and 5%Co3O4/Al2O3 has a high reactivity with NF3 full conversion maintaining for 10.5 h. It is suggested that the presence of transition metal oxide is beneficial to the reactivity of Al2O3, and results in a significant enhancement in the fluorination of Al2O3. 相似文献
3.
NF 3 plasma etching is used for dry cleaning of reactors after plasma-enhanced chemical vapor deposition of hydrogenated amorphous silicon from SiH 4. The NF 3 plasma chemistry, in a closed isothermal plasma box with silicon coated walls, is analyzed by mass spectrometry of gases. Silicon is etched as SiF 4 by F atoms produced in the NF 3 dissociation into F+NF 2, or 2F+NF. The NF radicals recombine as N 2 +2F whereas the long-lived NF 2 radicals do not react with Si, but recombine as N 2F 4 This is the main limitation (or fluorine conversion into SiF 4. The pressure increase at the end point of etching is attributed to the sudden increase of F atom concentration in the gas phase and the consequent recombination q( F atoms as F 2. 相似文献
4.
The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present
review mainly focuses on CDR to produce synthesis gas over Ni/MO x/Al 2O 3 (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La 2O 3, MgO, and CaO have been found. The addition of promoters to Al 2O 3-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent
on the loading amount of promoters. For example, the highest CH 4 and CO 2 conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La 2O 3/Al 2O 3 catalyst, the highest CH 4 conversion (96%) and CO 2 conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al 2O 3 catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH 4 conversion (91%) and CO 2 conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al 2O 3 catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH 4 conversion (89%) and CO 2 conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al
for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic
performance of Al 2O 3-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization
of metal oxide on Al 2O 3 and the basic property of metal oxide to prevent carbon formation. 相似文献
5.
The review is devoted to the use of high-level quantum-chemical calculations by the density functional method for the simulation
of heterogeneous catalytic systems based on transition metals. The following problems are considered: (1) the development
of methods for simulating metal particles supported on the surfaces of ionic and covalent oxides; (2) the calculation of the
properties of individual transition metal atoms and small clusters adsorbed on the surfaces of MgO, α-Al 2O 3, γ-Al 2O 3, and various modifications of SiO 2 and in the pores of zeolites; (3) the mechanisms of hydrogen activation and acrolein hydrogenation on the metallic and partially
oxidized surface of silver; and (4) the mechanism of formation of carbon residues upon the decomposition of methanol on nanosized
Pd particles. 相似文献
6.
Ammonia synthesis from H 2-N 2 mixed gas was studied at room temperature in a glow-discharge plasma in the presence of metals or metal oxides. Magnesia (MgO) and calcia (CaO), which are oxides with solid basicity, revealed catalytic activity in the plasma synthesis of ammonia, although they are catalytically inactive in industrial ammonia synthesis. The acidic oxides (Al 2O 3, WO 3, and SiO 2-Al 2O 3) lead to the consumption of the reactant, i.e., the H 2-N 2 mixed gas. No ammonia was isolated. Metal catalysts showed higher activity than the above basic oxides. They have, however, different activities. The reaction was faster over the active materials than over sodium chloride (NaCl) or glass wool or in a blank reactor without any catalyst. 相似文献
7.
Nanometer MgO samples with high surface area, small crystal size and mesoporous texture were synthesized by thermal decomposition
of MgC 2O 4 · 2H 2O prepared from solid-state chemical reaction between H 2C 2O 4 · 2H 2O and Mg (CH 3COO) 2 · 4H 2O. Steam produced during the decomposition process accelerated the sintering of MgO, and MgO with surface area as high as
412 m 2 · g −1 was obtained through calcining its precursor in flowing dry nitrogen at 520°C for 4 h. The samples were characterized by
X-ray diffraction, N 2 adsorption, transmission electron microscopy, thermogravimetry, and differential thermal analysis. The as-prepared MgO was
composed of nanocrystals with a size of about 4–5 nm and formed a wormhole-like porous structure. The MgO also had good thermal
stability, and its surface areas remained at 357 and 153 m 2·g −1 after calcination at 600 and 800°C for 2 h, respectively. Compared with the MgO sample prepared by the precipitation method,
MgO prepared by solid-state chemical reaction has uniform pore size distribution, surface area, and crystal size. The solid-state
chemical method has the advantages of low cost, low pollution, and high yield, therefore it appears to be a promising method
in the industrial manufacture of nanometer MgO.
Translated from Chinese Journal of Catalysis, 2006, 27(9): 793–798 (in Chinese) 相似文献
8.
Highly selective conversion of methane (CH 4) to methanol (CH 3OH) is an emerging attractive but challenging process for future development of hydrogen economy, which requires efficient catalysts. Herein, we systematically explore the catalytic properties of Pt(111) overlayer on transition metal oxides (TMOs) for CH 4 conversion by first principles calculations. The Pt(111) monolayer supported by Ce-terminated CeO 2(111) substrate exhibits high activity and selectivity for CH 4 conversion to CH 3OH, with the kinetic barrier of rate-limiting step of 1.05 eV. Intriguingly, the surface activity of Pt overlayer is governed by its d-band center relative to the energy of bonding states of adsorbed molecules, which in turn depends on the number of charge transfer between Pt(111) monolayer and underlying TMOs substrates. These results provide useful insights in the design of metal overlayers as catalysts with high-ultra performance and atomic utilization. 相似文献
9.
The results obtained showed that the addition of small amounts of LiNO 3 to the reacting mixed solids, consisting of equimolar proportion of Fe 2O 3 and basic MgCO 3 much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO 3 (6 mol% Li 2O) decreased the decomposition temperature of MgCO 3 from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe 2O 4. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the
completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li 2O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe 2O 4 phase at temperatures starting from 700°C. The addition of 6 mol% Li 2O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides
into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR
transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe 2O 4 structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility
of the various reacting cations. The activation energy of formation (Δ E) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61
kJ mol −1 for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li 2O, respectively.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
10.
The solid-solid interactions between manganese and magnesium oxides in absence and in presence of small amounts of Li 2O have been investigated. The molar ratios between manganese and magnesium oxides in the form of Mn 2O 3 and MgO were varied between 0.05:1 to 0.5:1. The mixed solids were calcined in air at 400-1000°C. The techniques employed were DTA, XRD and H 2O 2 decomposition at 20-40°C.The results obtained revealed that solid-solid interactions took place between the reacting solids at 600-1000°C yielding magnesium manganates (Mg 2MnO 4, Mg 6MnO 8, MgMnO 4 besides unreacted portions of MgO, Mn 2O 3 and Mn 3O 4). Li 2O-doping (0.75-6 mol%) of the investigated system followed by calcination at 600 and 800°C decreased progressively the intensity of the diffraction lines of Mn 2O 3 (Bixbyite) with subsequent increase in the lattice parameter ' a' of MgO to an extent proportional to the amount of Li 2O added. This finding might suggest that the doping process enhanced the dissolution of Mn 2O 3 in MgO forming solid solution. This treatment led also to the formation of Li 2MnO 3. Furthermore, the doping with 3 and 6 mol% Li 2O conducted at 800°C resulted in the conversion of Mn 2O 3 into Mn 3O 4, a process that took place at 1000°C in absence of Li 2O. The produced Li 2MnO 3 phase remained stable by heating at up to 1000°C. Furthermore, Li 2O doping of the investigated system at 400-1000°C resulted in a progressive measurable increase in the particle size of MgO.The catalytic activity measurements showed that the increase in the molar ratio of Mn 2O 3 in the samples precalcined at 400-800°C was accompanied by a significant increase in the catalytic activity of the treated solids. The maximum increase in the catalytic activity expressed as reaction rate constant measured at 20°C ( k
20°C) attained 3.14, 2.67 and 3.25-fold for the solids precalcined at 400, 600 and 800°C, respectively. Li 2O-doping of the samples having the formula 0.1 Mn 2O 3/MgO conducted at 400-600°C brought a progressive significant increase in its catalytic activity. The maximum increase in the value of k
20°C due to Li 2O attained 1.93 and 2.75-fold for the samples preheated at 400 and 600°C, respectively and opposite effect was found for the doped samples preheated at 800°C.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
11.
Recent results on the surface modification of petroleum cokes and their electrochemical properties as anodes of secondary lithium batteries are summarized. The surface of petroleum coke and those heat-treated at 1860-2800 °C were fluorinated by elemental fluorine (F 2), chlorine trifluoride (ClF 3) and nitrogen trifluoride (NF 3). No surface fluorine was found except only one sample when ClF 3 and NF 3 were used as fluorinating agents while surface region of petroleum coke was fluorinated when F 2 was used. Transmission electron microscopic (TEM) observation revealed that closed edge of graphitized petroleum coke was destroyed and opened by surface fluorination. Raman spectra showed that surface fluorination increased the surface disorder of petroleum cokes. Main effect of surface fluorination with F 2 is the increase in the first coulombic efficiencies of petroleum cokes graphitized at 2300-2800 °C by 12.1-18.2% at 60 mA/g and by 13.3-25.8% at 150 mA/g in 1 mol/dm 3 LiClO 4-ethylene carbonate (EC)/diethyl carbonate (DEC) (1:1, v/v). On the other hand, main effect of the fluorination with ClF 3 and NF 3 is the increase in the first discharge capacities of graphitized petroleum cokes by ∼63 mAh/g (∼29.5%) at 150 mA/g in 1 mol/dm 3 LiClO 4-EC/DEC. 相似文献
12.
A serial of protonated and layered transition metal oxides, including layered HTa WO_6, HNbMoO_6 as well as HNb WO_6, were synthesized by solid-state reaction and ion-exchange. The layered HTa WO_6 has been systematically studied as a solid acid to realize the dehydration of fructose to 5-hydroxymethylfurfural(HMF). The transition metal oxide samples were characterized with ICP-OES, EDS, XRD, XPS, SEM, TGA,FT-IR, N2adsorption–desorption and NH3-TPD. The influential factors such as reaction temperature, reaction time, solvent, catalyst amount and substrate concentration were deeply investigated. The optimized fructose conversion rate of 99% with HMF yield of 67% were achieved after 30 min at 140 °C in dimethylsulfoxide. 相似文献
13.
Paramagnetic complexes of 9, 10-anthraquinone and 9-fluorenone adsorbed on the surface of calcium, magnesium, zinc, zirconium,
and aluminum oxides and modified Al 2O 3 as well as on mixed oxides were studied by ESR and electron-nuclear double resonance. Radical anions that do not interact
with Lewis acid sites are generated on the surfaces of oxides with electrondonating properties (CaO, MgO). Paramagnetic complexes
of the anthraquinone or fluorenone radical anion with Lewis acid sites (coordinatively unsaturated metal cations) are formed
in other cases. Several types of similar complexes can be formed. Mechanisms of interaction of the probe molecules with the
metal oxide surface were proposed. 相似文献
14.
Summary The effect of La 2O 3 and TiO 2 on product selectivity, methane conversion and coke formation over NiO/MgO/ α -Al 2O 3 catalyst were studied in a simultaneous steam and CO 2 reforming of methane to syngas. La 2O 3 and TiO 2 were added to the catalyst via incipient wetness impregnation and bulk precipitation techniques and catalyst activity was tested in a fixed bed quartz reactor. Results reveal that although the addition of these oxides has no effect on the product selectivity and methane conversion, but can reduce coke formation on the surface of the catalysts as it can enhance the mobility of lattice oxygen anions. The results further show that the catalysts prepared by bulk precipitation technique decrease the coke formation more effectively. 相似文献
15.
Degradation of organic contaminants in water by high-voltage pulse discharges was investigated. The effects of gas flow rate and liquid conductivity on the degradation of 4-chlorophenol were studied. With the increase of time, the liquid conductivity increases, which have an important effect on discharge. Meanwhile, with the increase of time, the concentration of H 2O 2 increases. Addition of 200 mg/L H 2O 2, the conversion of 4-chlorophenol was greatly enhanced. This may be due to the synergistic effect of high-voltage pulsed discharge and H 2O 2. Also, it was found that the influence of quantity of TiO 2or CuO on degradation of acetophenone is not apparent, maybe the presence of metal oxides hinders the formation of plasma channel due to increase of collusions between metal oxides and oxygen. 相似文献
16.
Photoredox catalysis provides opportunities in harnessing clean and green resources such as sunlight and O 2, while the acid and base surface sites of metal oxides are critical for industrial catalysis such as oil cracking. The contribution of metal oxide surfaces towards photocatalytic aerobic reactions was elucidated, as demonstrated through the hydroxylation of boronic acids to alcohols. The strength and proximity of the surface base sites appeared to be two key factors in driving the reaction; basic and amphoteric oxides such as MgO, TiO 2, ZnO, and Al 2O 3 enabled high alcohol yields, while acidic oxides such as SiO 2 and B 2O 3 gave only low yields. The reaction is tunable to different irradiation sources by merely selecting photosensitizers of compatible excitation wavelengths. Such surface complexation mechanisms between reactants and earth abundant materials can be effectively utilized to achieve a wider range of photoredox reactions. 相似文献
17.
The interaction of mineral oxides (α-Al 2O 3, MgO, Fe 2O 3, and SiO 2) with hydrogen peroxide was investigated using the Knudsen cell reactor. The initial reactive uptake coefficients for the commercially available powders are measured as (1.00±0.11)×10 -4 for α-Al 2O 3, (1.66±0.23)×10 -4 for MgO, (9.70±1.95)×10 -5 for Fe 2O 3, and (5.22±0.9)×10 -5 for SiO 2. These metal oxide powders exhibit some catalytic behavior toward the decomposition of hydrogen peroxide excluding SiO 2. H 2O 2 can be destroyed on Fe 2O 3 surface and O 2 is formed. The experimental results suggest that the heterogeneous loss on mineral surface can represent an important sink of hydrogen peroxide. 相似文献
18.
The effects of -Fe 2O 3 and -Al 2O 3 additives on the thermal decomposition of perchlorates, oxalates and hydroxides were investigated by means of DTA, TG and X-ray techniques. It was found that the oxide additives catalytically promoted the decomposition of perchlorates (NaClO 4, KClO 4 and Mg(ClO 4) 2) and resulted in a lowering of the initial decomposition temperature ( Ti). On the other hand, the oxides showed no significant effect on the decomposition of oxalates (FeC 2O 4 and CuC 2O 4) and hydroxides (Mg(OH) 2 and Al(OH) 3). The thermal decomposition of KClO4 was chosen to compare the catalytic effect of twelve metal oxides. The results indicated that the transition metal oxides such as Cr2O3, -Fe2O3 and CuO markedly accelerated the decomposition; these oxides resulted in a solid-phase decomposition before fusion of KClO4, and the initial decomposition temperature (Ti) of KClO4 with oxides was about 100–200°C lower than that without catalyst. The oxides such as -Al2O3 and MgO resulted in a slight lowering of the temperature of the fusion and promoted the molten-phase decomposition of KClO4, but their effects were not so remarkable as those of the transition metal oxides. The modified catalytic mechanisms of transition metal oxides were proposed by considering the electron transfer and the oxygen-abstraction models. 相似文献
19.
结合行星式球磨机,采用低温固相法制备Ni-Al_2O_3催化剂,考察了球磨时间对Ni-Al_2O_3催化剂晶相结构(XRD)、还原特征(H2-TPR)、孔道结构(BET)、粒径分布(PSD)、表面形貌(SEM)和浆态床CO甲烷化性能的影响.结果表明,球磨时间为60 min,催化剂(CT-60)平均粒径最小,为141 nm;比表面积最大,为329 m2/g.随球磨时间延长,Ni-Al_2O_3催化剂的甲烷化性能(CO转化率、CH_4选择性和CH_4收率)均先增加后减少.其中,球磨时间为60 min制备的催化剂(CT-60)甲烷化性能最佳,其CO转化率、CH_4选择性和CH_4收率分别达87.9%、8 6.8%和74.3%.结合催化剂表征可知,CT-60优异的性能与其具有较小的颗粒尺寸(141 nm)和较大的比表面积(329 m2·g-1)有很大的关联.即,催化剂颗粒尺寸越小,比表面积越大,其性能越好. 相似文献
20.
Various metal oxides with 0.1 wt% Ag loaded as a cocatalyst were prepared by an impregnation method and examined their photocatalytic activity for CO 2 reduction with water. Among all the prepared Ag-loaded metal oxides, Ga 2O 3, ZrO 2, Y 2O 3, MgO, and La 2O 3 showed activities for CO and H 2 productions under ultraviolet light irradiation. Thus, metal oxides involving metal cations with closed shell electronic structures such as d 0, d 10, and s 0 had the potential for CO 2 reduction with water. In situ Fourier transform infrared measurement revealed that the photocatalytic activity and selectivity for CO production are controlled by the amount and chemical states of CO 2 adsorbed on the catalyst surface and by the surface basicity, as summarized as follows: Ag/ZrO 2 enhanced H 2 production rather than CO production due to very little CO 2 adsorption. Ag/Ga 2O 3 exhibited the highest activity for CO production, because adsorbed monodentate bicarbonate was effectively converted to bidentate formate being the reaction intermediates for CO production owing to its weak surface basicity. Ag/La 2O 3, Ag/Y 2O 3, and Ag/MgO having both weak and strong basic sites adsorbed larger amount of carbonate species including their ions and suppressed H 2 production. However, the adsorbed carbonate species were hardly converted to the bidentate formate. 相似文献
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