scholarly journals The influence of thermal treatment on properties of kaolin

2016 ◽  
Vol 70 (5) ◽  
pp. 595-601 ◽  
Author(s):  
Elizabeth Erasmus
Keyword(s):  
South African ◽  
Spinel Phase ◽  
Surface Group ◽  
Atomic Ratio ◽  
Pozzolanic Activity ◽  
Diffusion Control ◽  
Hydroxyl Groups ◽  
Surface Hydroxyl ◽  
First Order Kinetics ◽  
Different Temperatures

The kinetics of dehydroxylation of South African kaolin revealed that both the inner and the surface hydroxyl groups disappear according to first order kinetics, however, the surface group disappeared faster than the inner groups, showing that diffusion control kinetics is also important. The temperature dependent transformations of the kaolin was measure by means of fractional conversion of the ratios between AlO6:AlO4 and Si-O-Al:Si-O-Si, which showed kobs values 0.0168 s-1 and 0.0089 s-1 for the transformation to the spinel phase and values of 0.0165 s-1 and 0.0156 s-1 for the transformation to mullite respectively. The pozzolanic activities of the kaolin calcined at different temperatures showed a maximum pozzolanic activity when the kaolin is calcined at 650?C and the pozzolanic activity for mullite is even less than for the uncalcined kaolin. XPS revealed that the atomic ratio between Si and Al did not change from kaolin to metakaolin (Si:Al = ca. 1.2) however the mullite showed a atomic ratio of Si:Al = 1.52, implying that some deallumination occurred during calcination at high temperatures.

scholarly journals Evaluation of a Novel Water Treatment Residual Nanoparticles as a Sorbent for Arsenic Removal

2015 ◽  
Vol 2015 ◽  
pp. 1-10 ◽  
Author(s):  
Elsayed Elkhatib ◽  
Ahmed Mahdy ◽  
Fatma Sherif ◽  
Hala Hamadeen
Keyword(s):  
Water Treatment ◽  
Arsenic Removal ◽  
Batch Adsorption ◽  
Hydroxyl Groups ◽  
Surface Complexes ◽  
Surface Hydroxyl ◽  
Ph Values ◽  
First Order Kinetics ◽  
The Stability ◽  
Water Treatment Residual

A novel sorbent, water treatment residual nanoparticles (nWTR), was synthesized and used to remove As(V) from water solutions. The kinetics and equilibrium of As(V) adsorption by nWTR were evaluated. The kinetic data for nWTR at 3 different pH values indicate that As(V) sorption is biphasic, is favored at low pH values, and followed the power function and first-order kinetics models fit. The results of the batch adsorption study showed that nWTR was effective in As(V) removal and its removal capability was 16 times higher than that of bulk WTR. Fourier transmission infrared (FTIR), SEM-EDX spectra, and As fractionation results indicate the crucial role of surface hydroxyl groups in As retention onto nWTR and the high capability of nWTR to immobilize As(V). The stability of As-nWTR surface complexes is suggested as less than 2% of adsorbed As(V) was released from nWTR after 4 consecutive desorption cycles.

The synthesis and structure of silica-supported bis(h5-cyclopentadienyl)dichlorotitanium(IV) complexes

1986 ◽  
Vol 51 (7) ◽  
pp. 1430-1438 ◽  
Author(s):  
Alena Reissová ◽  
Zdeněk Bastl ◽  
Martin Čapka
Keyword(s):  
Free Surface ◽  
Hydroxyl Groups ◽  
Titanium Complex ◽  
Surface Hydroxyl ◽  
Surface Hydroxyl Groups ◽  
Free Hydroxyl ◽  
Cyclopentadienyl Anion

The title complexes have been obtained by functionalization of silica with cyclopentadienylsilanes of the type Rx(CH3)3 - xSi(CH2)nC5H5 (x = 1-3, n = 0, 1, 3), trimethylsilylation of free surface hydroxyl groups, transformation of the bonded cyclopentadienyl group to the cyclopentadienyl anion, followed by coordination of (h5-cyclopentadienyl)trichlorotitanium. The effects of single steps of the above immobilization on texture of the support, the number of free hydroxyl groups, the coverage of the surface by cyclopentadienyl groups and the degree of their utilization in anchoring the titanium complex have been investigated. ESCA study has shown that the above anchoring leads to formation of the silica-supported bis(h5-cyclopentadienyl)dichlorotitanium(IV) complex.

scholarly journals High catalytic activity for formaldehyde oxidation of an interconnected network structure composed of δ-MnO2 nanosheets and γ-MnOOH nanowires

2020 ◽  
Vol 8 (4) ◽  
pp. 429-439
Author(s):  
Ying Tao ◽  
Rong Li ◽  
Ai-Bin Huang ◽  
Yi-Ning Ma ◽  
Shi-Dong Ji ◽  
...  
Keyword(s):  
Catalytic Activity ◽  
Network Structure ◽  
Manganese Oxides ◽  
Active Oxygen Species ◽  
Low Cost ◽  
High Dispersion ◽  
Hydroxyl Groups ◽  
High Catalytic Activity ◽  
Interconnected Network ◽  
Surface Hydroxyl

AbstractAmong the transition metal oxide catalysts, manganese oxides have great potential for formaldehyde (HCHO) oxidation at ambient temperature because of their high activity, nontoxicity, low cost, and polybasic morphologies. In this work, a MnO2-based catalyst (M-MnO2) with an interconnected network structure was successfully synthesized by a one-step hydrothermal method. The M-MnO2 catalyst was composed of the main catalytic agent, δ-MnO2 nanosheets, dispersed in a nonactive framework material of γ-MnOOH nanowires. The catalytic activity of M-MnO2 for HCHO oxidation at room temperature was much higher than that of the pure δ-MnO2 nanosheets. This is attributed to the special interconnected network structure. The special interconnected network structure has high dispersion and specific surface area, which can provide more surface active oxygen species and higher surface hydroxyl groups to realize rapid decomposition of HCHO.

Carbon Nanotunes Supported Pt and Pt-Ru Catalysts for Selective Hydrogenation of Citral: Effect of Promoters and Thermal Activation of Catalysts

2012 ◽  
Vol 584 ◽  
pp. 229-233 ◽  
Author(s):  
Sakunthala Angamuthu Ananthan ◽  
Narayanan Vengidusamy ◽  
Krishnamoorthy Giribabu ◽  
Ranganathan Suresh
Keyword(s):  
Selective Hydrogenation ◽  
Bimetallic Catalyst ◽  
Surface Group ◽  
Inert Atmosphere ◽  
Area Measurement ◽  
Bet Surface Area ◽  
Metallic State ◽  
Environment Friendly ◽  
Ru Catalysts ◽  
Different Temperatures

MWCNT supported Pt, Ru, and Pt–Ru catalysts were prepared and reduced at two different temperatures, 375°C (LTR) and 675°C (HTR) for the selective hydrogenation of citral to the corresponding unsaturated alcohols (geraniol and nerol). The catalysts were characterized by BET Surface area measurement, TPD, SEM, EDAX, TEM, XRD and XPS. It was found that the XRD of Pt and Ru shows fcc and hcp crystalline structure respectively, which is uniformly dispersed with an average particles size of 3.5 nm and zero valence metallic state. The removal of acidic oxygen surface group is observed when heat- treatments in a inert atmosphere at 675°C were performed. The bimetallic catalyst of Pt-Ru/MWCNT (HTR) was found to afford remarkably high conversion levels (85%) and high selectivity (95%) provided that a thermal pretreatment was performed on the catalyst. These results can be rationalized in terms of electron transfer from the support to the metal. The catalysts are environment friendly and can be recycled for more than eight times.

Structural and Electrical Properties of Mn-Co-Ni-O Thin Films Prepared by Dip-Coating Technique

1992 ◽  
Vol 271 ◽  
Author(s):  
Shoji Kaneko ◽  
Naoto Mazuka ◽  
Tamotsu Yamada
Keyword(s):  
Thin Films ◽  
Spinel Phase ◽  
Dip Coating ◽  
Atomic Ratio ◽  
Heating Process ◽  
Electric Resistance ◽  
Glass Substrates ◽  
Methanol Solutions ◽  
Structural And Electrical Properties ◽  
Dip Coating Technique

ABSTRACTMn-Co-Ni-O thin films of metal atomic ratio 3.0 : 1.9 : 1.0 were prepared on glass substrates from methanol solutions of the corresponding metal β-diketonates by dip-coating. As-prepared films were heated at 900°C for 1 h mostly after being calcined at 450°C for 5 min. The film thickness increased with increasing concentration of the solution as well as the number of lifting times. However, the effect was not apparent with the sample prepared without calcination. The prepared films were observed to crystallize into a complicated spinel phase by the heating process at 900°C for 1 h. The surface of the dense film composed of particles of about 0.2 μm diameter, was almost even. The thermal and aging responses of electric resistance showed the film to be a good material as a thermistor.

Kinetics and Mechanism of Oxidation of Aliphatic Secondary Alcohols by Benzimidazolium Fluorochromate in Dimethyl Sulphoxide Solvent

2021 ◽  
Vol 37 (3) ◽  
pp. 626-633
Author(s):  
Bhawana Arora ◽  
Jitendra Ojha ◽  
Pallavi Mishra
Keyword(s):  
Activation Parameters ◽  
Sigmatropic Rearrangement ◽  
Dimethyl Sulphoxide ◽  
Secondary Alcohols ◽  
Hydrogen Ions ◽  
Reaction Conditions ◽  
First Order Kinetics ◽  
Aqueous Solvent ◽  
Ester Formation ◽  
Different Temperatures

Oxidation of secondary alcohols is an important part of synthetic organic chemistry. Various studies are carried out at different reaction conditions to determine the best mechanistic pathways. In our study, oxidation of different secondary alcohols was done by using Benzimidazolium Fluorochromate in Dimethyl Sulphoxide, which is a non-aqueous solvent. Oxidation resulted in the formation of ketonic compounds. The reaction showed first order kinetics both in BIFC and in the alcohols. Hydrogen ions were used to catalyze the reaction. We selected four different temperatures to carry out our study. The correlation within the activation parameters like enthalpies and entropies was in accordance with the Exnerʼs criterion. The deuterated benzhydrol (PhCDOHPh) oxidation exhibited an important primary kinetic isotopic effect (kH / kD = 5.76) at 298 K. The solvent effect was studied using the multiparametric equations of Taft and Swain. There was no effect of addition of acrylonitrile on the oxidation rate. The mechanism involved sigmatropic rearrangement with the transfer of hydrogen ion taking place from alcohol to the oxidant via a cyclic chromate ester formation.

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