II. ELECTRICAL PROPERTIES OF NI/SILICA GEL AND PT/ Γ-Alumina CATALYSTS IN RELATION TO CATALYTIC ACTIVITY

Gobara, Heba M.; Gomaa, Mohamed M.

doi:10.21608/iccee.2008.38370

Cited by 3 publications

(5 citation statements)

References 32 publications

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“…Samples generally showed the same general trend for the frequency dependence of the dielectric constant in the supposed range [21,[53][54][55][56][57][58][59][60][61][62][63]. Figure 4 showed the variation of conductivity with frequency for different samples containing various proportions of Ag 2 O/Li 2 O replacements.…”

Section: Electrical Properties Of the Studied Samplesmentioning

confidence: 90%

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Electrical and physicochemical properties of some Ag2O-containing lithia iron silica phosphate glasses

Ibrahim

Darwish

Gomaa

2011

J Mater Sci: Mater Electron

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The present paper reports the influence of Ag 2 O addition at the expense of Li 2 O on the local structure of xAg 2 OÁ(30 -x)Li 2 OÁ10Fe 2 O 3 Á10SiO 2 Á50P 2 O 5 glass matrix (with x = 0, 0.5, 1, 1.5 and 2 mol %). The phosphate structural units of the network former are assessed from Fourier transform infrared (FT-IR) spectroscopy. The addition of Ag 2 O to the glass network matrix B1 mol % leads to the occurrence of a depolymerization process of the phosphate structure and consequently, to the appearance of a distortion of the PO 4 tetrahedra. When the content of Ag 2 O is increased from 1.5 up to 2 mol %, a remarkable polymerization process has been observed. The density, molar volume, microhardness and chemical durability have been investigated in order to study the effect of Ag 2 O/Li 2 O replacements on the physicochemical properties the studied glasses. The AC electrical properties are affected to a great extent with composition. These results are related to the internal structure of the glass samples. The conductivity, dielectric constant and dielectric loss of the studied glasses were studied using the frequency response in the interval 100 Hz-100 kHz and the effect of compositional changes on the measured properties was investigated. Measurements showed that the electrical responses of glass samples were different and complex for interpretation. The increase of Ag 2 O addition at the expense of Li 2 O contents (from 0 to 1 mol %) led to increase the conductivity, dielectric constant and dielectric losses of samples. The addition of more Ag 2 O at the expense of Li 2 O (from 1.5 to 2 mol %), resulting into decreasing the conductivity, the dielectric constant and dielectric losses of the studied glasses. The experimental data of the glass samples were argued to the internal structure of the glasses and the nature and role-played by weakening or increasing the rigidity of the structure of the sample. It could be concluded, therefore, that the AC electrical properties of the samples were influenced by the distribution of its constituents, connectivity, and number of free charges.

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Section: Electrical Properties Of the Studied Samplesmentioning

confidence: 90%

“…However, the increase of Ag 2 O/Li 2 O replacements in the samples G 3 and G 4 led to decrease the A.C. conductivity of the samples. Sample G 1 has the lowest conductivity value [54][55][56][57][58]. Figure 6 showed the dielectric loss (Tan d) of the different samples.…”

Section: Electrical Properties Of the Studied Samplesmentioning

confidence: 99%

Electrical and physicochemical properties of some Ag2O-containing lithia iron silica phosphate glasses

Ibrahim

Darwish

Gomaa

2011

J Mater Sci: Mater Electron

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“…Data were measured in the frequency range from 42 Hz to 5 MHz. The samples were connected to non-polarizing electrodes (Cu/CuSO 4 ) [15,16] and the oscillation amplitude was set at 1 volt (small signal).…”

Section: Electrical Properties Measurementmentioning

confidence: 99%

“…Dielectric measurements are acceptable means for studying the dynamic properties (capacitance, conductance, permittivity and loss factor) of dielectrics. The previous works [15,16] have focused on mobility of the exchangeable cations (Pt and Ni) loaded on different supports. Recently, the enhancement of electrical conductivity of the hybrid prepared from Pt NPs and reduced graphine oxide (rGO) using the aniline stabilizer was reported to originate from the small particle size, uniform dispersion of Pt NPs and good interfacial interaction between the Pt NPs and r-GO hybrid [17].…”

Section: Introductionmentioning

confidence: 99%

Can microwave assisted in situ reduction of supported Pt nanoparticles challenge the chemical method in controlling the dispersion profile-catalytic performance relationship?

et al. 2015

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In this study, Pt (of 0.3, 0.6 and 0.9 wt % loadings) was supported on mesoporous silica surface via microwave-assisted solution (MAS) method or rotary chemical evaporation (RCE) method in the in situ reduction step. The as-synthesized Pt nanocatalysts were characterized through XRD, XRF, TGA/ DSC, TEM, N 2 -adsorption-desorption, H 2 -pulse titration and electrical conductivity techniques. The samples prepared by MAS method exhibited higher surface area and a better dispersion profile of Pt NPs, of average sizes not exceeding 10 nm with increasing the Pt loading. In contrast, although RCE method showed higher efficacy in decomposing the used precursor, uneven distribution of larger Pt nanoparticles (≥ 33 nm) was displayed. Electrical properties in terms of AC conductivity and dielectric constant confirmed the enhancement of even distribution of smaller Pt NPs with higher concentration of grain boundaries affected by microwave electromagnetic radiations. Highly mobile electrons and lattice vibrations (phonons) were favored, as compared with aggregated NPs produced during RCE method. The TOF values calculated for reactions to selectively produce ethylene (from ethanol) or benzene (from cyclohexane) decreased with Pt loadings on catalyst samples synthesized by MAS method. The highly dispersed NPs (of 3-7 nm) seemed to be responsible of the activity in both reactions, tending probably to be structure insensitive. However, samples reduced by RCE method, with enlarged average sizes of surface Pt NPs (approaching 15.5 nm), exhibited increasing TOF values with Pt loading, i.e., turning the reactions most probably to be structure sensitive.

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“…Recently, we modified the Ni/HZSM-5 catalyst by silica gel (SG, amorphous structure, formed by Si-O tetrahedron, adsorption performance increasing as the hydrogen bonding with the Si-OH and Si-O-Si on surface) [32,[35][36][37], and found that the modified catalyst showed high biomass sugar polyol conversion into gasoline (C5-C12 alkanes) by one-pot aqueous phase catalysis process. Interestingly, the produced oil products were predominantly straight-chain alkanes (pentane, hexane, heptane, octane, nonane, decane, undecance, odecane, etc.)…”

Section: Introductionmentioning

confidence: 99%

One-pot aqueous phase catalytic conversion of sorbitol to gasoline over nickel catalyst

Weng

Qiu

et al. 2015

Energy Conversion and Management

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II. ELECTRICAL PROPERTIES OF NI/SILICA GEL AND PT/ Γ-Alumina CATALYSTS IN RELATION TO CATALYTIC ACTIVITY

Cited by 3 publications

References 32 publications

Electrical and physicochemical properties of some Ag2O-containing lithia iron silica phosphate glasses

Electrical and physicochemical properties of some Ag2O-containing lithia iron silica phosphate glasses

Can microwave assisted in situ reduction of supported Pt nanoparticles challenge the chemical method in controlling the dispersion profile-catalytic performance relationship?

One-pot aqueous phase catalytic conversion of sorbitol to gasoline over nickel catalyst

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