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1.
TiO2 supported on SiO2 surface is effective on the recovery of photocatalyst, morphological control, and coating on the substrate. Furthermore, it shows much higher photocatalytic activity than pure TiO2. The silica support is quite influential on the surface properties of TiO2 supported on SiO2. The enhanced photocatalytic activity of TiO2–SiO2 could be explained by the effects of surface area, adsorption, band-gap energy and local structure. However, it is difficult to say which one is the most important factor responsible for the photocatalytic property of TiO2–SiO2. For example, the reduction of particle size could effect on both of the surface area and band-gap energy. And, Ti–O–Si bonds could modify the band-gap energy and local structure. Therefore, the photocatalytic properties of TiO2–SiO2 should be expressed by sum of many factors such as surface area, adsorption, band-gap energy and local structure.  相似文献   

2.
The oxidation of CH4 with O2 at low pressure was carried out over SiO2 prepared from metal Si. The Si showed only total oxidation activity while the Si partly oxidized to SiO2 showed high selectivities to CH3OH and HCHO. The results on SiO2 prepared from Si were compared with those over commercial silicas. The role of SiO2 in the CH4 oxidation was discussed.  相似文献   

3.
The ((Bi3.5La0.5)Ti3O12(BLT) thin-films used in this study were fabricated on a Pt(111)/SiO2/Si(100) substrate by a Liquid Source Misted Chemical Deposition (LSMCD) technique. X-ray diffraction patterns showed that the BLT films were crystallized and no other phases were observed when annealed above 650 ‡C. Grain size and remnant polarizations increased with increase in the annealing temperature, while leakage current densities decreased. The remnant polarizations (Pr) increased from 2.0 to 4.8 and 19.0 μC/cm2 with increase in the annealing temperature from 650 to 700 and 750 ‡C, respectively. The BLT films annealed at 700 ‡C in O2 showed a good fatigue resistance of reduced polarization by 10% after 109 switching cycles when 9 V of bipolar voltage was applied at a frequency of 40 kHz.  相似文献   

4.
Titanium oxide thin films were deposited on p-type Si(100), SiO2/Si, and Pt/Si substrates by plasma enhanced chemical vapor deposition using high purity Ti(O-i-C3H7)4 and oxygen. As-deposited amorphous TiO2 thin films were treated by rapid thermal annealing (RTA) in oxygen ambient, and the effects of RTA conditions on the structural and electrical properties of TiO2 films were studied in terms of crystallinity, microstructure, current leakage, and dielectric constant. The dominant crystalline structures after 600 and 800 ‡C annealing were an anatase phase for the TiO2 film on SiO2/Si and a rutile phase for the film on a Pt/Si substrate. The dielectric constant of the as-grown and annealed TiO2 thin films increased depending on the substrate in the order of Si, SiO2/Si, and Pt/ Si. The SiO2 thin layer was effective in preventing the formation of titanium silicide at the interface and current leakage of the film. TEM photographs showed an additional growth of SiOx from oxygen supplied from both SiO2 and TiO2 films when the films were annealed at 1000 ‡C in an oxygen ambient. Intensity analysis of Raman peaks also indicated that optimizing the oxygen concentration and the annealing time is critical for growing a TiO2 film having high dielectric and low current leakage characteristics.  相似文献   

5.
The V2O5 catalysts supported on TiO2–SiO2–MoO3 (TSM) prepared by the coprecipitation method were investigated for the selective catalytic reduction (SCR) of NO by NH3 at low temperatures. The V2O5/TSM catalyst with 7–13 wt% SiO2 was found to exhibit a superior SCR activity and a good sulfur tolerance at low temperatures (<250 °C). The presence of highly active polymeric vanadates formed by the incorporation of MoO3 to TiO2–SiO2 and superior redox properties seems to enhance SCR activity, and furthermore the very lower SO2 oxidation activity due to the higher acidity leads to the remarkable improvement of sulfur tolerance.  相似文献   

6.
The selective reduction of NO by C3H8 is performed on copper-based catalysts: Cu/Al2O3, Cu/SiO2, Cu/SiO2–Al2O3 solids, fresh and hydrothermally-treated Cu-MFI with various Si/Al ratios. For all the Cu-MFI solids and for the non-zeolitic supported-copper solids with low copper loadings, O2 promotes the reduction of NO. The C3H8–NO reaction rate correlates with the number of accessible and isolated Cun+ ions deduced from the infrared spectroscopy of adsorbed CO. When only one type of sites is detected, the FTIR spectroscopy of adsorbed CO allows an estimation of the copper dispersion. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

7.
The atmospheric hydroformylations of ethylene and propylene were investigated over SiO2-supported Rh4(CO)12, Co2(CO)8, Rh2Co2(CO)12 and RhCo3(CO)12-derived catalysts. The bimetal cluster-derived catalysts showed excellent activities for the formation of oxygenates. In situ IR study on partially dehydroxylated SiO2-supported RhCo3(CO)12 suggested that the bimetal cluster framework may be preserved after decarbonylation under H2 at 623 K and may be recarbonylated at room temperature. A strong physisorption of RhCo3 (CO)12 on SiO2 is proposed, due to a nucleophilic attack of surface oxygen on the Co atoms, which promotes a metal-support interaction and thus stabilizes the bimetal cluster framework. A subcarbonyl bimetal cluster is thought to be the actual catalytic species on the surface.  相似文献   

8.
TiO2–SiO2 mixed oxide with large pore size was synthesized by the xerogel method and it was then used to prepare the WO3/TiO2–SiO2 catalyst by an incipient wetness method. The as‐prepared WO3/TiO2–SiO2 sample was employed as the first heterogeneous catalyst in the liquid‐phase cyclopentene oxidation by aqueous H2O2, which exhibited higher selectivity (about 75%) to glutaraldehyde (GA) and, in turn, higher GA yield than the WO3/SiO2 heterogeneous catalyst and even the tungstic acid homogeneous catalyst under the same reaction conditions. The amorphous WO3 phase was identified as the active sites and the loss of the active sites was proved to be not important. The lifetime of the catalyst was determined and its regeneration method was proposed. The effects of various factors on the catalytic behaviors, such as the WO3 loading, the calcination temperature, the surface acidity and the reaction media, were investigated and discussed based on various characterizations including BET, XRD, XPS, FTIR, EXAFS and Raman spectra etc. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

9.
The ammonia method has been successfully used for preparing thermostable and well dispersed alumina‐supported catalysts with a surface average size of cobalt particle D s= 5.7 nm. The disproportionation reaction of CO over this Co/Al2O3 catalyst and a similar Co/SiO2 catalyst leads to the formation of carbon nanotubes demonstrating the same morphology. The amount of nanotubes over Co/Al2O3, however, is much larger than that obtained over Co/SiO2, because of a faster ageing in the latter solid. Similar support effects have already been reported for other catalytic reactions involving carbon oxides. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

10.
L. Huang  Y. Xu 《Catalysis Letters》1998,55(3-4):227-234
The preparation of a highly active bimetallic SiO2‐supported Rh–Co catalyst from RhCl3 and Co2(CO)8 (Rh:Co= 1 : 3 atomic ratio) has been studied by IR spectroscopy and ethylene hydroformylation, etc. Two steps are involved in the preparative process: (1) surface‐mediated synthesis of Rh+(CO)2/SiO2 from calcined RhCl3/SiO2; (2) impregnation of Rh+(CO)2/SiO2 with a Co2(CO)8 solution followed by H2 reduction at 623 K. The IR results of reductive carbonylation of calcined RhCl3/SiO2 have been compared to those of uncalcined RhCl3/SiO2 at 373 K. In situ IR observations, extraction results and elemental analysis suggest that approximately 50% of RhCl3 are transformed to Rh2O3 on the SiO2 surface and that calcined RhCl3/SiO2 is converted to a mixture of [Rh(CO)2Cl]2 and [Rh(CO)2O2 (Os: surface oxygen) under CO at 373 K. When this SiO2‐supported mixture was submitted to impregnation with a Co2(CO)8 solution at room temperature, IR study and elemental analysis show that [Rh(CO)2Cl]2 reacts easily with Co2(CO)8 on the surface to give RhCo3(CO)12, whereas [Rh(CO)2O2 does not react with Co2(CO)8. Catalytic study in steady‐state ethylene hydroformylation shows that a catalyst thus derived is more active than a catalyst derived from RhCo3(CO)12/SiO2 and a catalyst derived by coimpregnation of [Rh(CO)2Cl]2 and Co2(CO)8 on SiO2. This result suggests that the high rhodium dispersion of [Rh(CO)2O2 plays a crucial role in the formation of highly dispersed bimetallic Rh–Co sites. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

11.
We present here the decomposition of methanol over Pt nanoparticles supported on a series of oxide powders. The samples tested may be roughly grouped in two categories consisting of large (∼15–18 nm) and small (∼8–9 nm) Pt particles deposited on reducible (CeO2, TiO2) and non-reducible (SiO2, ZrO2, Al2O3) supports. The smallest particles (∼8 nm), deposited on ZrO2, were found to be cationic and the most active for the decomposition of methanol. Furthermore, the stability of metallic Pt and its oxides was observed to be dependent on the choice of support. In all Pt containing samples the reaction proceeds via he direct decomposition of methanol, as no significant amounts of by-products were detected in the experimental range of 100–300 °C.  相似文献   

12.
This paper describes the synthesis of cements, chemically and structurally related to Ca2SiO4. Silica was obtained from rice hull after heating at 600 °C. Calcium oxide and small amounts of barium chloride were mixed in order to obtain a final (Ca/Si) or (Ca+Ba)/Si ratio equal to 1.95, 1.90, and 1.80, which is lower than in the conventional cement. The solids were mixed and ultrasonically treated for 1 h with a water/solid ratio of about 20. After drying and grinding, the mixtures were heated up to 1100 °C. It was possible, in some cases, to obtain a cementitious material. These cements are structurally related to β-Ca2SiO4 and the lower (Ca+Ba)/Si ratio obtained was 1.95. The initial chemical compositions of these cements are: (Ca1.83+Ba0.12)SiO4 and (Ca1.79+Ba0.16)SiO4. A further lowering in the (Ca+Ba)/Si ratio changes the nature of the silicates.  相似文献   

13.
The effect of gold particle size and Au/FeO x interface on the electronic properties and catalytic activity using samples of Au/SiO2/Si(100), Au/FeO x /SiO2/Si(100), FeO x /Au/SiO2/Si(100) has been modelled. Nanosize gold particles of varying size were fabricated by deposition of a 10 nm thick gold film onto SiO2/Si(100) substrate by electron beam evaporation followed by modification using low energy Ar+ ion bombardment or Ar+ ion implantation. These modifications formed Au islands of decreasing size accompanied by the strong redistribution of the Au 5d valence band structure determined by ultraviolet and X-ray photoelectron spectroscopy (UPS, XPS) and increased activity in catalytic CO oxidation. The gold/iron oxide interface was prepared by deposition of iron oxide using pulsed laser deposition (PLD). The structural properties of gold and iron oxide were characterized by XPS, atomic force microscopy (AFM), transmission electron microscopy (TEM) and secondary ion mass spectroscopy (SIMS). Generally, the formation of gold/iron oxide interface increases the catalytic activity in CO oxidation regardless of the sequence of deposition, namely either Au/FeO x /SiO2/Si(100) or FeO x /Au/SiO2/Si(100) is formed. Furthermore, the interface formed is operative in determining the catalytic activity even if gold is not exposed to the surface, but it is located underneath the iron oxide layer. This is a promoting effect of the Au nanoparticles, which is more efficient than that of the bulk like Au films.  相似文献   

14.
The promotional effects of ZrO2 on Ni/ZrO2–SiO2 catalysts were investigated by the comparison of Ni/SiO2 and Ni/ZrO2–SiO2 activity in the hydrogenation of maleic anhydride (MA) to γ-butyrolactone (GBL), and by the measurements of X-ray diffraction (XRD), Fourier transform infrared (FT-IR), temperature-programmed reduction (TPR) and ammonia temperature-programmed desorption (NH3-TPD). The presence of ZrO2 led to an obvious increase of GBL yield. The promotion effect could be attributed to the possible presence of Zr4+ species on the catalyst surface owing to the higher ionicity of the Zr–O bonds, and to the proper interaction of Ni with the ZrO2-SiO2 support that is regulated by the presence of ZrO2.  相似文献   

15.
The reforming of CH4 with CO2 over supported Rh catalysts has been studied over a range of temperatures (550–1000 K). A significant effect of the support on the catalytic activity was observed, where the order was Rh/Al2O3>Rh/TiO2>Rh/SiO2. The catalytic activity of Rh/SiO2 was promoted markedly by physical mixing of Rh/SiO2 with metal oxides such as Al2O3, TiO2, and MgO, indicating a synergetic effect. The role of the metal oxides used as the support and the physical mixture may be ascribed to the promotion in dissociation of CO2 on the surface of Rh, since the CH4 + CO2 reaction is first order in the pressure of CO2, suggesting that CO2 dissociation is the rate-determining step. The possible model of the synergetic effect was proposed.  相似文献   

16.
The hydrogenation of CO over a RhVO4/SiO2 catalyst has been investigated after H2 reduction at 773 K. A strong metal–oxide interaction (SMOI) induced by the decomposition of RhVO4 in H2 enhanced not only the selectivity to C2 oxygenates but also the CO conversion drastically, compared with an unpromoted Rh/SiO2 catalyst. The selectivity of the RhVO4/SiO2 catalyst was similar to those of conventional V2O5‐promoted Rh/SiO2 catalysts (V2O5–Rh/SiO2), but the CO dissociation activity (and TOF) was much higher than for V2O5–Rh/SiO2, and hence the yield of C2 oxygenates was increased. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

17.
Model supports consisting of a thin layer of SiO2 on a silicon single crystal have been used to study ZrO2/SiO2/Si model catalysts made by wet chemical preparation methods. Auger depth profiling and angle-dependent X-ray photoelectron spectroscopy show that catalysts prepared by a surface reaction between zirconium ethoxide and hydroxyl groups on the SiO2 contain a highly dispersed zirconium phase that is converted to ZrO2 upon calcination.  相似文献   

18.
Methanethiol has been synthesized by one‐step catalytic reaction from H2S‐content syngas on K2MoS4/SiO2 catalyst with selectivity over 95% under the optimum reaction conditions of 563 K, 2.0–3.0 MPa and 5–6% H2S content in the feed syngas. The results of XRD and XPS showed that Mo–S–K phase on the surface of the catalyst K2MoS4/SiO2 was responsible for the high activity and selectivity to methanethiol, and which may be restrained by the existence of (S–S)2- species. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

19.
The effects of support pretreatment with nC1–C5 alcohols on the performance of Rh–Mn–Li/SiO2 catalyst in the synthesis of C2-oxygenates from syngas have been investigated by CO hydrogenation reaction, transmission electron microscopy (TEM), pulse adsorption of CO and H2, and Fourier Transform infrared (FT-IR) spectroscopy. The catalysts prepared from the pretreated silica supports exhibited higher space time yields of C2-oxygenates (STYC2-oxy) and selectivities towards C2-oxygenates (SC2-oxy) than that prepared from the untreated silica support. The enhancement in the hydrophobicity of the pretreated silica supports would be favorable for increasing Rh dispersion and ratio of Rh+/Rh0 sites, therefore increasing the number of active sites, especially the active sites for CO insertion. Such variations are responsible for the improvements in the catalytic performance of the Rh–Mn–Li/SiO2 catalyst.  相似文献   

20.
Using hydrofluoric acid as acid catalyst, F doped nanoporous low-k SiO2 thin films were prepared through sol-gel method. Compared with the hydrochloric acid catalyzed film, the films showed better micro structural and electrical properties. The capacitance-voltage and current-voltage characteristics of F doped SiO2 thin films were then studied based on the structures of metal-SiO2-semiconductor and metal-SiO2-metal, respectively. The density of state (DOS) of samples deposited on metal is found to decrease to a level of 2 × 1017 eV−1 cm−3. The values of mobile ions, fix positive charges, trapped charges and the interface state density between the SiO2/Si interfaces also decrease obviously, together with the reduction of the leakage current density and the dielectric constant, which imply the improvement of the electrical properties of thin films. After annealing at a temperature of 450C, the lower values of the leakage current density and dielectric constant could be obtained, i.e. 1.06 × 10−9 A/cm2 and 1.5, respectively.  相似文献   

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