Determination of metal dispersity of Pd/SiO2 catalysts by transmission electron microscopy and H2?O2 chemisorption

Dispersity of palladium for a series of Pd/SiO₂ catalysts has been determined by TEM and H₂–O₂ chemisorption. The mean crystallite dimensions obtained by these methods have been compared. Assuming O/Pd_s to be 0.6 for Pd crystallites larger than 9 nm, good agreement has been observed between the results of the two experimental methods.

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Pd/SiO₂ H₂–O₂. , . O/Pd_s0.6, Pd 9 , .

     

Effect of dispersity on some catalytic reactions on Pt/SiO2

The effect of the dispersity of a Pt/SiO₂ catalyst has been investigated in the hydrogenolysis of ethane, n-butane and in cyclohexane exchange. Turnover number, N_T, for ethane hydrogenolysis increases with decreasing particle size, which may be interpreted by the formation of a surface intermediate in which both carbon atoms are bonded to one platinum atom. Cyclohexane exchange is not influenced by the change in particle size.

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Pt/SiO₂ , - . N_T, , , . .

     

Hydrogenolysis of n-butane over Ru/SiO2 catalysts of high ruthenium dispersity

Ruthenium catalysts Ru/SiO₂ were obtained from 2RuOHCl₂. 7NH₃ solution by means of ion exchange between the OH groups on the SiO₂ surface and using classical impregnation from acid RuCl₃ solution. The measurement of the rate of n-butane hydrogenolysis was carried out in a gradientless reactor. Measurements were made within the temperature range of 470–670 K at H₂C₄H₁₀ ratio equal to 61. The results obtained indicate a definite influence of the dispersity of ruthenium on the reaction rate of the hydrogenolysis of n-butane and on the selectivity of this process. The effect of the degree of Ru dispersity on the rate of n-butane hydrogenolysis was examined A correlation was found between the dispersity of Ru and the selectivity to methane, ethane and propane.

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Ru/SiO₂ 2RuOHCl₂. 7NH₃ OH SiO₂ , RuCl₃. - . 470–670 H₂C₄H₁₀, 61. -, . -. Ru , .

     

Investigation of the acidity of Ni/Al2O3 and Ni/SiO2?Al2O3 catalysts

Acidity of Ni-modified alumina and silica-alumina catalysts was determined using n-butylamine titration and pyridine adsorption methods. Strong influence of Ni²⁺ ions on the Brönsted acidity of silicaalumina was observed. Improved Brönsted acidity of such system was confirmed by the results of the test reaction.     

Structure sensitivity of methane oxidation on Pt/SiO2 of widely varying dispersity

Methane oxidation on Pt/SiO₂ is a structure sensitive reaction at 260–335°C. The higher the percentage exposed, the lower the turnover frequency with decreasing reaction order in P_{CH 4} from 1.0 to 0.5 and slightly decreasing the activation energies of reaction from 90 to 80 kJ/mol, caused by the shift of rate-determining step.

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Pt/SiO₂ 260–335°C . , P_{CH 4} 1,0 0,5 90 80 /. , .

     

Temperature-programmed desoprtion of H2 from the surfaces of pd/support and Pd-Ag/support catalysts (support = Al2O3, SiO2)

Thermal desorption of H₂ from the surface of Pd/support and Pd-Ag/support (support = Al₂O₃, SiO₂) catalysts has been investigated. Two wide desorption peaks can be observed for the 5% Pd/support catalyst. The presence of these peaks in the thermogram indicates that several adsorption states exist, which is the result of occurrance of different adsorption centers of specific bond strengths for hydrogen. The addition of silver to the palladium catalysts causes a considerable decrease in the size of the high temperature desorption peak. It is also worth noting that the temperature of the maximum of the desorption rate remains practically constant for all bimetallic catalysts studied. This means that the activation energy of the hydrogen desorption process does not change after the introduction of silver to the palladium catalyst.     

Influence of anchored cerium ions on the dispersity and activity of Pd/SiO2 catalysts

(Pd+Ce)/SiO₂ catalysts prepared by decomposition of organometallic complexes of Ce and Pd have higher activity, dispersity and selectivity in methanol synthesis than Pd/SiO₂ catalysts.

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, (Pd+Ce)/SiO₂ , Ce Pd, Pd/SiO₂.

     

The activity of Ni/AlPO4, Ni/AlPO4?Al2O3 and Ni/AlPO4?SiO2 catalysts in the hydrogenation of e-cinnamaldehyde

Liquid-phase catalytic hydrogenatio of E-cinnamaldehyde was carried out by using new supported nickel catalysts (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ and Ni/AlPO₄–SiO₂) in methanol as solvent under low hydrogen pressure (4.1 bar) and 298 K. The kinetic orders are zero in H₂ and aldehyde. The selectivity to the hydrogenaton of the C=C double bond is very high (>99%)

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- (Ni/AlPO₄, Ni/AlPO₄–Al₂O₃ Ni/AlPO₄–SiO₂) (4,1 ) 298 . H₂ . C–C (>90%).

     

稀土掺杂SiO2与SiO2@Au纳米球

By using EDTA-lanthanide (Eu³⁺， Tb³⁺) coordination compound as precursor， multicolor luminescent SiO₂ nanoshperes were prepared. Also， without any pre-treatment to the surface of SiO₂ nanosphere， a facile strategy was developed for the synthesis of SiO₂@Au core-shell nanospheres.     

Hydrogenation of Benzonitrile on Sn-Pt/SiO2 Catalysts Prepared by Introducing SnEt4 to Pt/SiO2: Role of Tin

Liquid phase hydrogenation of benzonitrile was studied over Sn-Pt/SiO₂ catalysts prepared by introducing tetraethyl tin onto the 3 wt.% Pt/SiO₂ catalyst. Tin content of the catalysts ranged from 0.05 to 0.63 wt.%, whereas Sn/Pt surface atomic ratios determined by chemisorption measurements were between 0.1 to 3.5. Dibenzylamine selectivity influenced to a small extent by the level of conversion and the Sn/Pt ratio wasca. 75 %. The addition of tin to Pt in the range of (Sn/Pt)_surface = 0.50–1.25 led to an increase in the turnover frequency (TOF) by a factor of 2. TOF showed a maximum at a surface atomic ratio of Sn/Pt = 1. The enhancement of catalyst activity upon the addition of tin is explained by the formation of Sn⁺-Pt ensemble sites on the surface of bimetallic nanoclusters. It is suggested that highly dispersed positively charged tin species, by polarizing the triple bond, enhance the reactivity of the -CN group. Calcination at 300°C followed by re-reduction of the catalysts resulted in a monotonic decrease of specific activity with increasing Sn/Pt ratio.     

Cyclohexanol dehydrogenation over Cu/SiO2 and CuO/SiO2: A comparison

Various CuO/SiO₂ catalysts were prepared and characterized by XRD, surface area and metal area measurements. While dehydrogenation activity for cyclohexanol was observed at 473–573 K on reduced catalysts, it was observed only at 573 K on the unreduced catalyst.IICT Communication No: 3261     

Acidity of SiO2, SiO2?Al2O3 and γ-Al2O3 supports and supported molybdena catalysts

Acidity of SiO₂, -Al₂O₃ and SiO₂–Al₂O₃ supports and supported Mo-catalysts in oxidized and reduced state are characterized by IR-spectroscopic and gravimetric pyridine (py) adsorption measurements. Differences in surface acidities are interpreted as results of differences in chemical compositions, molybdena-support interactions and molybdena dispersities.

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SiO₂, -Al₂O₃ SiO₂–Al₂O₃, Mo -- . , .

     

Hydrogenolysis of ethane over Ni/Al2O3 catalysts of high nickel dispersity

The effect of nickel dispersity on the rate of ethane hydrogenolysis and the number of B₅ centers has been studied. A maximum in the rate of ethane hydrogenolysis is observed in the range of nickel dispersity of 2–3.5 nm. There is a minimum of the apparent activation energy of ethane hydrogenolysis in this range of metal crystallite size.

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₅. 2–3,5 . .

     

高镍负载量Ni/SiO2和低镍负载量Ni-Ce/SiO2催化CO甲烷化的比较研究

采用等体积浸渍法制备了高镍负载量的13%Ni/SiO₂(13Ni/Si)催化剂和低镍负载量的7%Ni-2%Ce/SiO₂(7Ni-2Ce/Si)催化剂.通过N₂物理吸附、XRD、FT-IR、TEM、H₂-TPR/TPD等技术对催化剂进行表征,在连续流动微反装置上考察了催化剂的CO甲烷化活性.结果表明,在7Ni-2Ce/Si催化剂中NiO、CeO₂和SiO₂之间产生的相互作用,改变了Ni-O-Si键的化学环境,促进了氧化镍物种的分散和还原,进而提高了催化剂的活性比表面积,同时在催化剂表面形成了新的中等强度的CO吸附中心.与高镍负载量的13Ni/Si催化剂相比,低镍负载量的7Ni-2Ce/Si表现出更高的CO吸附能力和甲烷化活性.常压下,在CO体积分数1%和空速7 000 h^-1的反应条件下,低镍负载量的7Ni-2Ce/Si催化剂上CO完全甲烷化最低温度为230 ℃,比高镍负载量的13Ni/Si低了30 ℃.     

Characterization of MoS2/SiO2 by ESR and NO adsorption

Six MoS₂/SiO₂ samples were characterized by XRD, BET surface area, ESR and NO adsorption measurements. Correlation was found between the amount of Mo⁵⁺, sulfur radicals and adsorption capacity for oxygen and NO.

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MoS₂/SiO₂ , , , NO. Mo⁵⁺, NO.

     

Preparation, thermal properties, morphology, and microstructure of phosphorus-containing epoxy/SiO2 and polyimide/SiO2 nanocomposites

A phosphorus-containing tri-ethoxysilane (dopo-icteos) reacting from the nucleophilic addition reaction of 9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (dopo) and 3-(trieoxysilyl) isocyanate (icteos) was synthesized. The structure of dopo-icteos was confirmed by ¹H, ¹³C, ³¹P NMR and IR spectra. A triethylamine catalyzed mechanism for the dopo-icteos synthesis was proposed and verified by NMR spectra. The phosphorus-containing epoxy/SiO₂ and polyimide/SiO₂ nanocomposites were prepared from the in-situ curing of diglycidyl ether of bisphenol A (DGEBA)/4,4-diaminodiphenylmethane(DDM)/dopo-icteos, and imidization of poly(amic acid) of pyromellitic dianhydride (PMDA)/4,4′-oxydianiline (ODA)/dopo-icteos, respectively. The microstructure and morphology were investigated by ²⁹Si NMR, scanning electron microscope (SEM), EDS (Si and P mapping) analysis and atomic force microscope (AFM). The thermal properties, flame retardancy and dielectric properties of the organic-inorganic hybrids were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), limiting oxygen index (LOI), thermal gravimetric analysis (TGA) and dielectric analyzer (DEA).     

Modification of the catalytic activity of Ni/SiO2 in ethane hydrogenolysis, benzene and co hydrogenation by reduction at high temperatures and restoration by O2?H2 treatments

An increase of the temperature of reduction of Ni/SiO₂ from 900 to 1120 K results in a decrease of catalytic activity per unit area in benzene hydrogenation and ethane hydrogenolysis. O₂–H₂ treatments restore the activities. This behavior is similar to that observed on Pt-based catalysts. In contrast, the CO+H₂ reaction on nickel is not affected by such treatments.

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Ni/SiO₂ 900 1120 . O₂–H₂ . , , CO+H₂ .

     

The role of acidity of MoO3?SiO2 and WO3?SiO2 catalysts

The acidity of various MoO₃–SiO₂ and WO₃ catalysts has been measured by means of ammonia adsorption. Whereas the acidity of silica and pure metal oxides is very low, an increase of surface acidity results from a reaction between silica support and metal oxides. A significant correlation between surface acidity and catalytic activity for aromatization of lower olefines could be found.

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MoO₃–SiO₂ WO₃ . SiO₂ . , SiO₂ . .

     

La2O3助剂对Rh/SiO2催化CO加氢反应性能的影响

采用溶胶凝胶法制备了SiO_2和La_2O_3-SiO_2载体,再通过浸渍法分别引入Rh-La和Rh组分,研究考察了La引入方式对Rh/SiO_2催化CO加氢反应性能的影响。结果表明,La的添加有利于提高Rh的分散度,促进Rh+中心数的增加,有效地抑制产物中CO2的生成,提高含氧化合物选择性。此外,La的引入方式会影响La与Rh间的相互作用强弱,Rh和La共浸渍制得的2Rh-5La_2O_3/SiO_2催化剂中Rh-La相互作用较强,削弱的Rh-CO键有利于反应过程中CO的插入反应,使得产物以C_(2+)含氧化合物为主。而La以助剂形式掺入SiO_2制得的2Rh/5La_2O_3-SiO_2催化剂具有较弱的La-Rh相互作用,其产物则以甲醇、乙醇等低碳醇为主。     

High pressure and high temperature investigations in the system MgOSiO2H2O

The system MgOSiO₂H₂O was investigated at pressures between 40 and 95 kbar and at temperatures between 500 and 1400°C. The reaction products were examined by X-ray, optical and thermal analysis techniques and the density of phase A discovered by Ringwood and Major was also measured. It was found that phase A was hydrated and its chemical formula was H₆Mg₇Si₂O₁₄. When the $\text{Mg}\text{Si}$ ratio of the system is 2, phase A + clinoenstatite, and forsterite are stable at temperatures lower and higher than a boundary curve T (°C) = 10P (kbar), respectively. When the $\text{Mg}\text{Si}$ ratio of the system is 3, phase A + phase D (which is completely different from the phases, A, B and C discovered by Ringwood and Major, and any other known phases of magnesium silicate) and phase D + brucite are stable at temperatures lower and higher than a boundary curve T(°C) = 10P (kbar) + 200. Phase A has approximately an hexagonal symmetry and the space group and the lattice parameters are determined as P6₃ or $\text{P6}{}_3\text{m}$ and a = 7.866(2) Å and c = 9.600(3) Å, respectively. The measured density is 2.96 ± 0.02 g/cm³. The optical observations show that phase A is biaxial positive crystal with refractive indices α = 1.638 ± 0.001, β = 1.640 ± 0.002, and γ = 1.649 ± 0.001. Some interpretation is given on the inconsistency between the symmetry determined by the X-ray diffraction and the optical observation. The new phase D belongs to the space group $\text{P2}{}_1\text{c}$ with lattice parameters a = 7.914(2)Å, b = 4.752(1) Å, c = 10.350(2) Å and β = 108.71(5)° and is a biaxial crystal with refractive indices α = 1.630 ± 0.002, β = 1.642 ± 0.002 and γ = 1.658 ± 0.001.