首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
A novel and high performance silver loaded hydroxyapatite (HAp) catalyst for the selective catalytic reduction (SCR) of NOx by propene is reported for the first time. The catalysts with variable silver contents have been prepared and characterized extensively by different techniques such as XRD, XPS, BET-surface area, TPR, TPD and ICP analyses. The DeNOx activities of these catalysts are measured at reaction temperature ranged from 250 to 500 °C. The 1.5 wt.% Ag/HAp is found to be best among all the catalysts studied showing about 70% conversion and 60% selectivity towards N2 formation at 375 °C in oxygen rich atmosphere.  相似文献   

2.
Lean reduction of NO x with DME occurs with high selectivity to N2 over Al2O3 between 300 °C and 550 °C with a maximum of 47% at 380 °C, and with lower selectivity over Ag/Al2O3 between 250 °C and 400 °C due to the catalysts’ sensitivity to gas phase radical reactions and activity for NO x reduction with methanol.  相似文献   

3.
Silver salt preparation was obtained by neutralizing solution of H6P2W18O62 in water with solid Ag2CO3. In the introductory experiments the conditions of silver salt reduction with ethanol vapours were studied at 170–290 °C. At 250 °C and 2.5 h complete reduction to silver and free heteropolyacid was observed. During reduction with ethanol the initially not active salt became catalyst on which typical for free acid alcohol dehydration to ethylene occurred. In a series of experiments carried out within temperature range 210–290 °C ethanol conversion was studied on the catalyst previously reduced at 250 °C. When air was used as the carrier gas the bi-functional behavior of the catalyst was distinct, besides ethylene, diethyl ether and water, typical products of acid–base type catalytic reaction also comparable amount of acetaldehyde, the product of redox type reaction, was observed.  相似文献   

4.
We report structure and photocatalytic activity of solid nanotubes comprising iron oxide (hematite, α-Fe2O3) nanoparticles. The initial precursor cylinders were prepared by alternating layer-by-layer assembly of poly-l-arginine (PLA) and iron-storage protein ferritin in a track-etched polycarbonate membrane (pore diameter: 400 nm) with subsequent dissolution of the template. The obtained (PLA/ferritin)3 nanotubes (outer diameter: 410 ± 14 nm) were calcinated at 500 or 700 °C under air, yielding iron oxide nanotubes. After the calcination, the cylindrical hollow structure completely remained, but its diameter, wall thickness, and maximum length were significantly diminished. SEM measurements revealed that the nanotubes prepared at 500 °C consist of uniform hematite nanoparticles with ca. 5 nm diameter and the nanotubes calcinated at 700 °C are composed of ca. 20 nm hematite nanoparticles. These nanotubes showed efficient photocatalytic activity for degradation of 4-chlorophenol; higher catalytic activity was observed in the reaction with 5 nm hematite nanoparticle nanotubes.  相似文献   

5.
The denitridation behaviour of binary iron, cobalt and rehnium nitrides under H2 /Ar has been investigated. The iron nitride was found to lose over 70 % of its as prepared nitrogen content at 400 °C. The cobalt nitride was completely denitrided at 250 °C. Rhenium nitride lost close to 90 % of its nitrogen at 350 °C. In addition, Co-Re4 prepared by ammonolyis was investigated, whilst only traces of NH3 were lost from this material under H2/Ar at 400 °C, with H2/N2 it proved to be an active ambient pressure ammonia synthesis catalyst in accordance with previous literature.  相似文献   

6.
Solid acid catalysts based on graphite-like mesoporous carbon material Sibunit were developed for the one-pot solubilization–hydrolysis–dehydration of cellulose into glucose and 5-hydroxymethylfurfural (5-HMF). The catalysts were produced by treating Sibunit surface with three different procedures to form acidic and sulfo groups on the catalyst surface. The techniques used were: (1) sulfonation by H2SO4 at 80–250 °C, (2) oxidation by wet air or 32 v/v% solution of HNO3, and (3) oxidation-sulfonation what meant additional sulfonating all the oxidized carbons at 200 °C. All the catalysts were characterized by low-temperature N2 adsorption, titration with NaOH, TEM, XPS. Sulfonation of Sibunit was shown to be accompanied by surface oxidation (formation of acidic groups) and the high amount of acidic groups prevented additional sulfonation of the surface. All the Sibunit treatment methods increased the surface acidity in 3–15 times up to 0.14–0.62 mmol g?1 compared to pure carbon (0.042 mmol g?1). The catalysts were tested in the depolymerization of mechanically activated microcrystalline cellulose at 180 °C in pure water. The main products 5-HMF and glucose were produced with the yields in the range of 8–22 wt% and 12–46 wt%, respectively. The maximal yield were achieved over Sibunit sulfonated at 200 °C. An essential difference in the composition of main products obtained with solid acid Sibunit carbon catalysts (glucose, 5-HMF) and soluble in water H2SO4 catalysts (formic and levulinic acids) as well as strong dependence of the reaction kinetics on the morphology of carbon catalysts argue for heterogenious mechanism of cellulose depolymerization over Sibunit.  相似文献   

7.
Tin dioxide nanoparticles were prepared in the presence of graphitized carbon nitride (g-C3N4) forming nanocomposites with different contents of SnO2 up to 40 %. G-C3N4 was synthetized by heating of melamine at 550 °C in the open air and Sn2+ ions were precipitated by sodium hydroxide in g-C3N4 aqueous dispersions. Resulting mixtures were dried by freezing at ?20 °C and calcined at 450 °C to obtain SnO2/g-C3N4 nanocomposites.The nanocomposites were characterized by common characterization methods in solid state and in their aqueous dispersions using dynamic light scattering (DLS) analysis and photocatalysis. SnO2 nanoparticles in the nanocomposites were found to have an average size of 4 nm, however, those precipitated without g-C3N4 had an average size of 14 nm. Separation of photoinduced electron and holes via heterojunction between SnO2 and g-C3N4 was demonstrated by photocatalytic decomposition of Rhodamine B (RhB) under LED visible irradiation (416 nm) and photocurrent measurements. The most photocatalytically active nanocomposite contained 10 % of SnO2. Graphitized carbon nitride was assumed to serve as a template structure for the preparation of SnO2 nanoparticles with a narrow size distribution without using any stabilizing additives.  相似文献   

8.
《Ceramics International》2016,42(4):4853-4859
A hard and optically transparent amorphous Hf7B23Si17C4N45 film with a contamination level less than 4 at%, prepared by reactive pulsed dc magnetron sputtering, was subjected to systematic investigation of high-temperature oxidation behavior in air up to 1700 °C. We focus on thermogravimetric analysis of the film in air and on the evolution of the film structure, microstructure and elemental composition with an annealing temperature ranging from 1100 °C to 1700 °C. The film exhibits a superior oxidation resistance up to 1600 °C due to a formation of a nanocomposite protective oxide layer on the surface above 1000 °C. The layer consists of monoclinic and tetragonal (or orthorhombic) HfO2 nanocrystallites surrounded by a SiO2-based amorphous matrix, most probably containing boron. The HfO2 nanocrystallites exhibit a gradient in size with a dense population of small (a couple of nm) crystallites next to the interface and larger but dispersed crystallites close to the surface.  相似文献   

9.
β-Si3N4 rodlike seed crystallites were successfully produced by single-step heat treatment of commercial α-Si3N4 powder at 1900°C for 20 h under an N2 gas pressure of 980 kPa. The average diameter, length, and aspect ratio of the seed crystallites were 0.73 μm, 1.37 μm, and 1.86, respectively. The α- ⇀ β-Si3N4 phase transformation proceeded mainly at 1900°C, and this temperature was lower than the theoretical α-Si3N4 dissociation temperature (1933°C) under N2 gas pressure of 980 kPa. The formation of metastable solid solution due to the dissolution of O impurity into the α-Si3N4 crystal lattice was suggested as the driving force for the present oxide additive-free α- ⇀ β-Si3N4 phase transformation. β-Si3N4 ceramics were fabricated by liquid phase sintering promoted by an additive system of 1 wt% MgO with 3 wt% Gd2O3. Starting α-Si3N4 powder with 10 vol% rodlike β-Si3N4 seed crystallites prepared in this study and an extended sintering time for up to 20 h at 1950°C resulted in the formation of bimodal microstructure composed of fine matrix grains and large elongated grains originated from the seed crystallites. The β-Si3N4 ceramics exhibited improved fracture toughness and thermal conductivity of 5.9 ± 0.8 MPa m−1/2 and 109.3 ± 0.4 W m−1 K−1, respectively, retaining a high fracture strength of about 1 GPa.  相似文献   

10.
We have investigated the effect of cobalt nanoparticle size in Fischer–Tropsch synthesis (CO/H2) and have compared it to data obtained for carbon dioxide hydrogenation (CO2/H2) using model catalysts produced by colloidal methods. Both reactions demonstrated size dependence, in which we observed an increase of the turnover frequency with increasing average particle size. In both case, a maximum activity was found for cobalt particles around 10–11 nm in size. Regarding the selectivity, no size-dependent effect has been observed for the CO2 hydrogenation, whereas CO hydrogenation selectivity depends both on the temperature and on the size of the particles. The hydrogenation of CO2 produces mainly methane and carbon monoxide for all sizes and temperatures. The Fischer–Tropsch reaction exhibited small changes in the selectivity at low temperature (below 250 °C) while at high temperatures we observed an increase in chain growth with the increase of the size of cobalt particles. At 250 °C, large crystallites exhibit a higher selectivity to olefin than to the paraffin equivalents, indicating a decrease in the hydrogenation activity.  相似文献   

11.
Cubic solid solution nanocrystals in the zirconia (ZrO2)–yttrium niobate (Y3NbO7) system were directly formed at 180°C–240°C from the precursor solution mixtures of NbCl5, ZrOCl2, and YCl3 under mild hydrothermal conditions in the presence of aqueous ammonia. The lattice parameter corresponding to cubic phase linearly changed according to the Vegard's law in the wide composition range of ZrO2 (mol%) = 10–90 in the ZrO2–1/4Y3NbO7 system. The progress of the formation of nanocrystalline solid solutions based on the Y3NbO7 was assisted via the presence of ZrO2 component as a promoter with the same fluorite‐type structure. The optical band gap of the solid solutions was in the range 3.4–3.7 eV. Broadband emissions centered at 360–380 and 390 nm were observed for the nanocrystalline cubic solid solutions and pure cubic Y3NbO7, respectively, under excitation at 240 nm Xe lamp. The nanosized cubic crystallites of the solid solutions were maintained after heat treatment up to 800°C for 1 h air. The cubic phase of the solid solutions in the ZrO2–1/4Y3NbO7 system was maintained after heat treatment at 1400°C in air.  相似文献   

12.
《Ceramics International》2019,45(13):16554-16563
Phase pure CaCu3Ti4O12 CCTO ceramics are prepared by solid-state synthesis route. The effect of measuring atmospheres (air and dry N2) on the stability and reproducibility of electrical properties of CCTO as a function of sample thickness (as-prepared to thinned down) is investigated. As-sintered CCTO prepared at 1080 °C for 5 h with an initial thickness of 2.31–2.32 mm is reduced subsequently by fine grinding to 1.835 mm and then to 1.65–1.5 mm. Large inconsistency in the impedance spectra is observed when the samples are measured in air despite the thickness variations. Stable and reproducible dielectric properties are obtained in dry N2. A relatively closer resistivity (∼2 × 108 Ωcm at 23 °C in N2) regardless of the sample thickness suggests the absence of any barrier layer at the sample surface. Increased space charge accumulation at grain boundaries (GBs) leading to much larger dielectric constant (ε′) was observed in air at 23 °C. A temperature (from 23 °C to 225 °C) and frequency (from 1 Hz to 1 MHz) independent and stable ε′ is observed when samples are tested in N2. Much lower tan δ values with large ε′ are observed for both as prepared (0.010 ± 0.001 with ε′ of 9,663 ± 4 at 1.4 kHz) and the thinned down (0.015 ± 0.000 with ε′ of 9,352 ± 5 and 4.5 kHz) samples at 23 °C in N2.  相似文献   

13.
Nitromethane (NM) is a very efficient reductant for converting NO2 to N2 over Ag/Y: Between 140 °C and 400 °C, the N2 yield is close to 100%. This high N2 yield results from the ability of Ag/Y to effectively catalyze the reaction between NM and NO2. This high catalytic activity of Ag/Y is minimally affected by surface bound CN, NC, or acetate, all of which are stable at temperatures below ∼300 °C. At T ≥ 400 °C, there is a reaction path that yields N2 from NM even in the absence of NO2. However even at 400 °C, under typical deNO x conditions, most N2 molecules are formed as a result of the reaction of NM and NO2.  相似文献   

14.
The effect of substrate temperature on the formation of β-C3N4-like crystallites by an inductively coupled plasma sputtering method has been investigated. Transmission electron diffraction patterns reveal that the structure of the microcrystallites formed is close to the theoretically predicted structure of β-C3N4. By using 100 W of radio-frequency (RF) power for the deposition, the N/C atomic ratio in the film decreases from 0.35 to 0.07 upon increasing the substrate temperature from 100°C to 500°C. However, the crystallinity of the grains improves upon increasing the substrate temperature from 100°C to 400°C and then deteriorates drastically at 500°C, probably due to a deficiency of nitrogen in the film. By using 500 W of RF power to increase the degree of gas dissociation, the formation of β-C3N4 crystallites is enhanced upon increasing the substrate temperature from 400°C to 800°C, with the N/C atomic ratio in the film decreasing only slightly from 1.0 to 0.85. At 800°C, the film deposited consists of large sizes of crystallites, as evidenced from the highly spotty electron diffraction pattern, and contains a high percentage (90%) of sp3 CN bonding (i.e., the bonding of C3N4 crystallites) as estimated from X-ray photoelectron spectroscopy. The results suggest that, at a high degree of gas dissociation, the high substrate temperature is favorable for the synthesis of β-C3N4 crystallites.  相似文献   

15.
The CO2 absorption properties of potassium-based TiO2 sorbents prepared by calcining at various temperatures from 300 to 700 °C under N2 and air were investigated in a fixed bed reactor at 60 °C. The CO2 capture capacity of the sorbent was changed dramatically depending on the structure of the sorbent, which was affected by calcination atmosphere, as well as calcination temperature.  相似文献   

16.
《Ceramics International》2021,47(23):33078-33088
The wetting behaviour and interfacial reaction mechanism between Ag–Cu alloy fillers (with varying copper contents) and Si3N4 ceramics using reactive air brazing at 970 °C were systematically investigated. As the copper content increased, the contact angles of the Ag–Cu filler on the Si3N4 ceramics decreased. A violent boiling-like interfacial reaction was observed during the experiment, and mass spectrometry analysis identified the gaseous products as N2, NO and NO2. The solid products SiO2 and Cu–O formed at the interface, and the interfacial reactions improved the wettability of the Ag–Cu filler on the Si3N4 ceramics. Owing to buoyancy and the pushing of the gases, the interfacial products floated to the surface of the filler and their distribution increased along with the increasing copper content. Two different microstructures were formed at the interface near the triple line. Thick and thin SiO2 layers were respectively formed on the triple line interface of the fillers with low (Ag–3Cu/Ag–5Cu) and high (Ag–6.6Cu/Ag–16Cu) copper content. The interfacial bonding zones formed in Ag–5Cu, Ag–6.6Cu, and Ag–16Cu samples indicated that the corresponding Ag–Cu fillers were effectively brazed with the Si3N4 ceramics.  相似文献   

17.
The present study indicates that solid acid catalysis of crude tall oil (CTO) over a WO3/ZrO2 catalyst is effective in converting the CTO fatty acids components into biodiesel in high yield. Preparation of the catalyst by an impregnation method was selected and WO3 activity was best at a loading mass fraction of 5% to ZrO2 support and activation at 500°C for five hours under air at atmospheric pressure. Optimal reaction conditions were reaction temperature at 250°C; methanol to CTO molar ratio at 10; reaction time four hours, catalyst mass fraction of 3%; and stirring intensity at 625 rpm. The conversion at optimal reaction conditions was 70%. The catalyst was highly active at temperatures higher than 200°C. The biodiesel produced met some, but not all, the diesel quality parameters stipulated by standard specifications such as ASTM D6751 and EN14214.  相似文献   

18.
High-molecular-weight poly(p-arylene sulfide ketone) (PPSK) was prepared by nucleophilic substitution reaction of 4,4’-diflurobenzophenone (DFBP) and sodium sulfide in the compound solvents of diphenyl sulfone (DPS) and 1,3-dimethyl-2-imidazolidinone (DMI) with catalysts under elevated temperature. The inherent viscosity (ηint) of the PPSK synthesized was 0.703 dl/g. PPSK was characterized by Fourier-transform infrared spectroscopy, elemental analysis, x-ray diffraction, differential scanning calorimetry, and thermogravimetric analysis. It was found that the polymer had excellent thermal properties: glass transition temperature (Tg) was 142.8 °C, melting temperature (Tm) was 362.3 °C. Under nitrogen atmosphere, 5 % (T5%) and 10 % (T10%) weight-loss temperatures were about 498.5 °C and 526.2 °C, respectively, while in the air the T5% and T10% were about 517 °C and 535.8 °C, respectively. The PPSK was found to be a semi-crystalline polymer, as confirmed by XRD. The polymer was insoluble in any solvent except concentrated sulfuric acid at room temperature. A series of the PPSK separating membranes were prepared by dissolving PPSK to concentrated sulfuric acid. The fluxes and the porosities of the separating membranes were in the range of 230–43 L/(m2?·?h) and 77.7-84.7 %, respectively. At the same time, these separating membranes showed moderate tensile strength of 1.02-1.88 MPa.  相似文献   

19.
A simple and effective way to manufacture graphene from a coal tar pitch (CTP) is demonstrated. Silica (SiO2) nanoparticles were used to modify the CTP as carbon precursor. A silica nanofiller introduced into the CTP matrix underwent carboreduction during heat treatment to 2000 °C, resulting in the formation of silicon carbide. Surfaces of SiC grains were sites for graphene formation. The influence of SiO2 on the structure and microstructure of CTP- based carbon matrix, after annealing up to 2800 °C, was studied. Carbon samples were analyzed using X- ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Raman Spectroscopy. Crystallite sizes (La, Lc) and interplanar distance (d002) were determined. The presence of SiO2 in CTP carbon precursor favored the crystallites’ growth in the ‘a′ crystallographic graphite direction, and inhibited their growth on the ‘c′ axis. The crystallites composing of graphene layers, were characterized by an elongated dimension in the ‘a′ axis direction. Above 2000 °C silicon carbide decomposed, followed by the sublimation of silicon from the carbon matrix.  相似文献   

20.
《Ceramics International》2021,47(18):25324-25336
CrNx/Ag nanocomposite films with varying Ag content were prepared by reactive magnetron sputtering under a constant Ar/N2 stream. The films were annealed between 500 – 800 °C in the air. The microstructure and elemental composition of films were studied by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The mechanical properties were characterized with respect to nano-hardness and high-temperature tribology. The results reveal that the incorporation and concentration of Ag influence the morphology and microstructure of films. The microstructure of films evolves by annealing, and the films with higher Ag concentration exhibit more severe structure evolution. Annealing at 650 °C results in the sublimation of Ag, and the oxide emerges on the film surface. Annealing at 800 °C reveals that the film with 6.2 at.% Ag exhibits superior structural stability, while the one with 20.2 at.% Ag deteriorates. The hardness of films decreases with the increasing Ag concentration and heating temperature. Films with 12.6 at.% Ag and above possess solid lubrication during the sliding at 350–650 °C. Both the friction coefficient and wear resistance are found dependent on the Ag concentration and sliding temperature.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号