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1.
In this study, the silicic acid produced from sodium metasilicate hydrate and titanium tetraisopropylate were chosen as the ceramic precursors for the modification of biodegradable polylactide (PLA) through an in situ sol-gel process and the melt blending method. In addition, acrylic acid grafted polylactide (PLA-g-AA) was studied as an alternative to PLA. Hybrids were characterized by Fourier transform infrared spectroscopy, 29 Si solid-state nuclear magnetic resonance (NMR), thermogravimetry analysis (TGA), scanning electron microscope (SEM), and Instron mechanical tester. The result was that properties of the PLA-g-AA/SiO2–TiO2 hybrid were superior to those of the PLA/SiO2–TiO2 hybrid. This was because the carboxylic acid groups of acrylic acid acted as coordination sites for the silica-titania phase to allow the formation of stronger chemical bonds. The 29 Si solid-state NMR showed that Si atoms coordinated around SiO4 units were predominantly Q3 and Q4. The 10 wt.% SiO2–TiO2 content gave the maximum values of tensile strength and glass transition temperature in PLA/SiO2–TiO2 and PLA-g-AA/SiO2–TiO2 both because excess SiO2–TiO2 particles caused separation between the organic and inorganic phases. 相似文献
2.
ZrO2–SiO2 complex oxides with Si/Zr mole ratio of 3 (SZ-3) were synthesized. ZrO2–SiO2 supported Ni and NiCu catalysts were prepared by impregnation method. Their catalytic performances were evaluated in the hydrodeoxygenation (HDO) upgrading of model reactant guaiacol to hydrocarbons. The physicochemical properties of the support materials and catalysts were characterized by FTIR, XRD, TPD, TPR, and BET techniques. The addition of Cu significantly affected the acidity, and thus influenced their catalytic performance for product distributions. Over the Ni5Cu/SZ-3 catalyst, the cyclohexane selectivity of 80.8% and the methylcyclohexane selectivity of 12.4% were obtained with complete conversion of guaiacol under the 300 °C, 5.0 MPa H2 pressure. 相似文献
3.
M. Tóth J. Kiss A. Oszkó G. Pótári B. László A. Erd?helyi 《Topics in Catalysis》2012,55(11-13):747-756
Supported gold, rhodium and bimetallic rhodium-core?Cgold-shell catalysts were prepared. The supports were TiO2 as well as titanate nanotube and nanowire formed in the hydrothermal conversion of titania. The catalytic properties were tested in the CO2 hydrogenation at 493?K. The amount and the reactivity of the surface carbonaceous deposit were determined by temperature-programmed reduction. The surfaces of the materials were characterized by X-ray photoelectron and low-energy ion scattering spectroscopy (LEIS). The surface forms during the catalytic reaction were identified by DRIFT spectroscopy. On the XP spectra of bimetallic catalysts the existence of highly dispersed gold particles could be observed besides the metallic form on all supports. Small Rh particles could also be identified on the titanate supports. LEIS spectra demonstrated that Rh-core?CAu-shell particles formed, since no scattering from Rh was detected. The main product of CO2 hydrogenation was CH4 on all catalysts. IR spectra revealed the existence of CO and formate species on the surface. In addition, a new band was observed around 1,770?cm?1 which was assigned as tilted CO. It is bonded to Rh and interacts with a nearby the oxygen vacancy of the support. Agglomeration of highly dispersed Rh was observed on bimetallic samples induced by reaction or reactant. 相似文献
4.
Very tiny Au particles on TiO2 show excellent activity and selectivity in a number of oxidation reactions. We have studied the vapor deposition of Au onto a TiO2(110) surface using XPS, LEIS, LEED and TPD and found that we can prepare Au islands with controlled thicknesses from one to several monolayers. In order to understand at the atomic level the unusual catalytic activity in oxidation reactions of this system, we have studied oxygen adsorption on Au/TiO2(110) as a function of Au island thickness, and have measured the titration of this adsorbed oxygen with CO gas to yield CO2, as function of Au island thickness, CO pressure and temperature. A hot filament was used to dose gaseous oxygen atoms. TPD results show higher O2 desorption temperatures (741 K) from ultrathin gold particles on TiO2(110) than from thicker particles (545 K). This implies that Oa bonds much more strongly to ultrathin islands of Au. Thus from Brønsted relations, ultrathin gold particles should be able to dissociatively adsorb O2 more readily than thick gold particles. Our studies of the titration reaction of oxygen adatoms with CO (to produce CO2) show that this reaction is extremely rapid at room temperature, but its rate is slightly slower for the thinnest Au islands. Thus the association reaction (COg + Oa → CO2,g) gets faster as the oxygen adsorption strength decreases, again as expected from Brønsted relations. For islands of about two atomic layers thickness, the rate increases slowly with temperature, with an apparent activation energy of 11.4 ± 2.8 kJ/mol, and shows a first‐order rate in CO pressure and oxygen coverage, similar to bulk Au(110). 相似文献
5.
《Journal of Catalysis》1999,181(2):244-255
Various Pt/NaCsβ catalysts with decreasing Na/Cs ratios and a Pt/KL sample taken as a reference catalyst for aromatization ofn-hexane, have been prepared by exchange of NaCsβ and KL zeolites in a Pt tetraammine solution then calcination and reduction. The increase of the Cs content in the NaCsβ zeolitic support results in a decrease of the cyclohexane adsorption and Pt exchange capacities. The Pt/Csβ and Pt/KL samples show similar behaviors which strongly differ from those of the Na-containing Pt/NaCsβ samples in terms of (i) reducibility of the Pt ions after calcination, (ii) shape of the FTIR spectra of CO adsorbed on the Pt clusters after reduction, and (iii) catalytic activity of these clusters in the conversion ofn-hexane. In particular, the selectivity to aromatization is much higher on the Pt/Csβ and Pt/KL catalysts than on the Na-containing Pt/NaCsβ ones. The reasons for the specific behaviors of the Pt/Csβ and Pt/KL samples are discussed. 相似文献
6.
A. Kelaidopoulou E. Abelidou G. Kokkinidis 《Journal of Applied Electrochemistry》1999,29(11):1255-1261
Platinum particles dispersed in a poly(2-hydroxy-3-aminophenazine) film (pHAPh/Pt) provide a better catalyst than smooth Pt for the electrooxidation of methanol and formic acid in perchloric acid aqueous solutions. The catalytic activity of the Pt particles is further enhanced when Sn is codeposited in the polymer film. In the case of formic acid oxidation, the activity of Pt nanoparticles is influenced by adatoms of Tl, Pb and Bi deposited undepotential conditions. The upd-modified Pt particles are much more active than bare Pt particles. The morphology and identity of the metallic dispersion were examined by transmission electron microscopy. 相似文献
7.
Teresita F. Garetto María S. Avila Charito I. Vignatti V. Venkat Rao Komandur Chary Carlos R. Apesteguía 《Catalysis Letters》2009,130(3-4):476-480
The combustion of benzene was studied on Pt supported on V2O5–TiO2 samples containing different amounts of V2O5. Vanadium was highly dispersed as V4+ for low V2O5 loadings, forming a vanadia monolayer on titanium dioxide for a V2O5 concentration of about 5%wt. V2O5–TiO2 samples were more active than V2O5 and TiO2 single oxides, and the activity increased with the vanadia content. The platinum dispersion in Pt/V2O5–TiO2 catalysts increased with the V2O5 loading but the activity for the deep oxidation of benzene exhibited an opposite trend. Benzene combustion was a structure sensitivity reaction promoted on larger metallic Pt crystallites which were preferentially formed when the V2O5 content in the sample was decreased. 相似文献
8.
Obulapathi Eggidi Ajoy Kumar Pandey 《International Journal of Applied Ceramic Technology》2023,20(1):294-305
Effect of two-step sintering (TSS) on microstructure and mechanical properties of ceria-stabilized zirconia-toughened alumina with added TiO2 (CSZTA–TiO2) was studied. A coprecipitation technique was used to produce the CSZTA–TiO2 powders. The synthesized powders were compacted using a uniaxial hydraulic press and conventionally sintered in air. The phase and microstructure of sintered samples were studied using X-ray diffraction and scanning electron microscopy techniques. Phases were quantified using the Rietveld refinement method. Different TSS schedules were followed to optimize microstructure and mechanical properties. Mechanical properties of the CSZTA-4TiO2 composite were evaluated and found as follows: Vickers's hardness of 1650 ± 9.6 HV10, indentation fracture toughness of 8.45 ± .14 MPa √m, compressive strength of 2088 MPa, and Young's modulus of 158 GPa. 相似文献
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11.
Sai Peng Yong Jiang Canhui Xu Shuanglin Hu Yinglou Wang 《Journal of the American Ceramic Society》2019,102(10):6256-6266
First-principles calculations and thermodynamics analyses were combined to study the surface stabilities of 3C–SiC and H2O adsorption on the (110) surface. The stoichiometric (110) surface was predicted to be generally the most stable. Only at the extremely C-poor condition, the nonstoichiometric Si-terminated (100) could become more energetically favored. The adsorption and dissociation of single H2O molecule on the 3C–SiC (110) were then comparatively investigated. Calculations show that H2O molecules prefer to partially dissociate into one hydroxyl OH and one H adsorbed at the top-most Si and C sites, respectively, leading to the formation of a hydrogen network on the surface. The calculated equilibrium adsorption diagram further suggested that the 3C–SiC (110) surface can be only either completely clean or fully covered by the partially dissociated species of H2O, for a wide range of temperature and the partial potential of H2O. 相似文献
12.
The properties of the adsorbed NHx species (x=0,1,2,3) on platinum(111) and (100)‐(1×1) single‐crystal planes are studied by the semi‐empirical method of interacting bonds. Both surfaces reveal similar features. The adsorbed species NH and NH2 are stable on the surface, and stable NH3(ads) species cannot form. The NH2(ads) species is favourable in adsorbed hydrogen excess, but lack of the latter results in NHads becoming dominant. Both NH and NH2 species are expected to diffuse easily over the surface due to the small difference between their bond strengths to various adsorption sites. This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
K. C. Waugh 《Catalysis Letters》2010,134(1-2):2-4
This letter is a re-examination of the ethylene oxide (EO) temperature programmed desorption (tpd) peak shapes (reported in references 1 and 2) which were obtained by tpd after having adsorbed EO at 250 K on to Ag(110) and Ag(111) surfaces. In these papers, the peaks were deemed to originate from a unimolecular rearrangement of an adsorbed oxametallacycle, producing EO, which desorbed on formation. Consequently, on the basis of this thesis, the activation energy of the composite process of internal rearrangement of the oxametallacycle and desorption of EO was determined by solution of the first order Redhead equation [3] at the peak maximum temperature, using an assumed value of 1013 s?1 for the desorption pre-exponential term. The conclusions of this re-examination are that the m/z = 29 desorption peaks shown in Fig. 1 derive from a second order surface reaction of an adsorbed O atom and adsorbed ethylene molecule and that this is the rate determining step in the desorption of EO. An important corollary of these conclusions is that an oxametallacycle is not involved in the ethylene epoxidation reaction coordinate as the papers suggest. Fig. 1
The m/z 29 desorption spectra following ethylene oxide adsorption at 250 K on Ag(110): ethylene oxide exposure—(a) 10L, (b) 5L, (c) 0.5L and (d) 0.1L 相似文献
14.
S. T. Aruna M. Muniprakash V. K. William Grips 《Journal of Applied Electrochemistry》2013,43(8):805-815
In this paper, the effect of titania particles preparation on the properties of Ni–TiO2 electrocomposite coatings has been addressed. Titania particles were prepared by precipitation method using titanium tetrachloride as the precursor. The titanyl hydroxide precipitate was subjected to two different calcinations temperatures (400 and 900 °C) to obtain anatase and rutile titania particles. These particles along with commercial anatase titania particles were separately dispersed in nickel sulfamate bath and electrodeposited under identical electroplating conditions to obtain composite coatings. The electrodeposited coatings were evaluated for their microhardness, wettability, corrosion resistance, and tribological behavior. The variation of microhardness with current density exhibited a similar trend for all the three composite coatings. The composite coating containing anatase titania particles exhibited higher microhardness and improved wear resistance. However, the corrosion resistance of the composite coating containing commercial titania powder was superior to that of plain nickel, Ni–TiO2 composite coatings containing anatase and rutile titania particles. The poor corrosion resistance of these composite coatings was attributed to the higher surface roughness of the coatings. This problem was alleviated by incorporating ball-milled titania powders. The composite coatings with higher surface roughness were modified with a low surface energy material like fluoroalkyl silane to impart hydrophobic and superhydrophobic properties to the coatings. Among these coatings, Ni–TiO2–9C coating exhibited the highest water contact angle of 157°. 相似文献
15.
Qing Li Zhijun Sui Xinggui Zhou Yian Zhu Jinghong Zhou De Chen 《Topics in Catalysis》2011,54(13-15):888-896
The influences of gas compositions on the rates of coke formation over a Pt?CSn/Al2O3 catalyst are studied. The coke formed on the catalyst is characterized by thermal gravimetric analysis, IR spectroscopy, Raman spectroscopy and elemental analysis. Two kinds of coke are identified from the TPO profiles and assigned to the coke on the metal and the coke on the support, respectively. The coke formed on the metal is softer (containing more hydrogen) than that formed on the support. The rate of coke formation on the metal is weakly dependent on the propylene and hydrogen pressures but increasing with the propane pressure, while the rate of coke formation on the support is increasing with the propane and propylene pressures and decreasing with the hydrogen pressure. Based on the kinetic analysis, a mechanism for the coke formation on the Pt?CSn/Al2O3 catalyst is proposed, and the dimerization of adsorbed C3H6 is identified to be the kinetic relevant step for coke formation on the metal. 相似文献
16.
TPR, CO-FTIR and129Xe NMR spectroscopic techniques were used to measure the distribution of platinum species after the calcination of Pt/L and Pt/ zeolites. Autoreduction which occurred in Pt/ zeolite was avoided in the channel of L zeolite. Pt particles dispersed well and exhibited excellent reactivity for the aromatization ofn-hexane in L zeolite. 相似文献
17.
Takeshi Kubota Hiroaki Kubota Toshihisa Kubota Emi Moriyasu Takayuki Uchida Yuriko Nitta Takashi Sugimura Yasuaki Okamoto 《Catalysis Letters》2009,129(3-4):387-393
The effects of the catalyst support, reaction temperature, and concentration of the modifier were examined to optimize supported Pd-catalysts and reaction conditions for the achievement of higher enantiomeric excess in the hydrogenation of (E)-α-phenylcinnamic acid. Over 90% of enantioselectivity was achieved using a cinchonidine-modified 40 wt% Pd/TiO2 catalyst at 288 K. 相似文献
18.
Zeolite P was synthesized through hydrothermal method based on a kind of Class C fly ash(FA). X-ray diffraction(XRD), scanning electron microscopy(SEM), and Brunauer–Emmett–Teller(BET) were used to analyze and characterize the synthetic sample. The kinetics and thermodynamics of copper and nickel ions removed by the zeolite samples were experimentally explored in detail. The results of kinetic treatment showed the second-order exchange second-order saturation model(SESSM) can well describe the removal process of copper ions, while the first-order empirical kinetic model(FEKM) is the best kinetic model for nickel ions. Langmuir and Freundlich isotherms were used to fit the equilibrium concentration of Cu(Ⅱ) or Ni(Ⅱ) under certain conditions. Whether for copper or nickel ion, the Langmuir model is in good agreement with the experimental equilibrium concentration.The apparent theoretical removal capacities for Cu(Ⅱ) and Ni(Ⅱ) can reach to 138.1 mg·g~(-1) and 77.0 mg·g~(-1),respectively. 相似文献
19.
采用快速冷冻沉淀法首次成功制备出Fe(Ⅲ)和Al(Ⅲ)复合掺杂非晶态Ni(OH)2粉体材料。通过XRD、SAED、SEM、IR、Raman光谱及DSC-TG等对样品粉体的结构形态进行表征和分析,同时将样品合成电极材料并组装成MH/Ni模拟电池进行电化学性能测试,结果表明,样品材料内部结构缺陷多、无序性强、材料微粒大小比较均匀,并具有较好的分散性,结合水含量较多。将复合掺杂Fe(Ⅲ) 5%和Al(Ⅲ) 8%的样品材料制备镍正极并组装成MH/Ni模拟电池,在以80 mA·g-1恒流充电5.5 h,40 mA·g-1恒流放电,终止电压1.0 V的充放电制度下,进行充放电性能、比容量及其循环性能等电化学性能的测试,放电平台平稳,工作电压高达1.30 V,放电比容量达到357.6 mAh·g-1,且在电极过程中材料的稳定性增强、电化学阻抗较小,循环可逆性较好。 相似文献