Crystallite sizes and surface areas of catalysts

1972 ◽  
Vol 5 (2) ◽  
pp. 127-130 ◽  
Author(s):  
W. L. Smith
Keyword(s):  
Surface Areas ◽  
Crystallite Sizes

Drop Solution Calorimetric Studies of Interface Enthalpy of Cubic Silver (I) Oxide (Ag2O) Nanocrystals

2021 ◽  
Vol 878 ◽  
pp. 73-80
Author(s):  
Khansaa Al-Essa ◽  
A V Radha ◽  
Alexandra Navrotsky
Keyword(s):  
Thermodynamic Cycle ◽  
Solution Calorimetry ◽  
X Ray Diffraction ◽  
X Ray ◽  
Surface Areas ◽  
Chemical Technique ◽  
Crystallite Sizes ◽  
Wet Chemical ◽  
Wet Chemical Technique ◽  
Calorimetric Studies

The nanoscale, cubic silver (I) oxide (Ag2O.nH2O) with different particles sizes and surface areas were synthesized by a wet chemical technique. The prepared crystallite size ranges were from (33.3±0.3 to 39.4±0.4 nm). Interface areas were estimated by comparing the surface areas measured by N2 adsorption to the crystallite sizes refined from X-ray diffraction data. The interface enthalpy of Ag2O.nH2O nanocrystal was measured using isothermal acid solution calorimetry in 25%HNO3 at 26°C. The interface enthalpy was verified by utilizing thermodynamic cycle. The enthalpies of drop solution (ΔHds) for Ag2O.nH2O are exothermic and range from (-62.228±0.197) to (-64.025±0.434 kJ/mol), while its interface enthalpy is (0.842±0.508 J/m2). This work provides the first calorimetric measurement of the interface enthalpy of nanocrystalline silver (I) oxide (Ag2O.nH2O).

Effect of Palladium on Photocatalytic Activity of SnO2 Nanoparticles

2008 ◽  
Vol 55-57 ◽  
pp. 777-780 ◽  
Author(s):  
R. Janmanee ◽  
P. Pirakitikulr ◽  
Natda Wetchakun ◽  
Chaikarn Liewhiran ◽  
Sukon Phanichphant
Keyword(s):  
Photocatalytic Activity ◽  
Specific Surface ◽  
Sno2 Nanoparticles ◽  
Ammonium Hydroxide ◽  
Decomposition Methods ◽  
Impregnation Method ◽  
Pure Sno2 ◽  
Surface Areas ◽  
Uva Light ◽  
Crystallite Sizes

SnO2 nanoparticles were successfully synthesized with either the presence (PS) or absence (NPS) of the Broussonetia papyrifera (L.) Vent Pulp as the dispersant by the precipitation coupling with the thermal decomposition methods using tin tetrachloride pentahydrate (Sn4Cl.5H2O) and ammonium hydroxide (NH4OH) as the starting material and precipitant respectively. The pulp was soaked in SnCl4 solution and NH4OH was slowly added dropwise. The white gelable precipitate of Sn(OH)4 was obtained. Afterward, the white precipitate was filtered and washed until it was free from chloride. The white precipitate was then dried at 80°C for 24h and calcined for 1h at 600°C, 650°C, and 700°C respectively. The synthesized products were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM) and Brunauer-Emmett-Teller (BET) measurement of specific surface area. The crystallite sizes of SnO2 nanoparticles with the presence and absence of the pulp were found to be ranging from 5-15 nm and 5-30 nm respectively. The specific surface areas (SSABET) were 62.53 m2/g and 26.60 m2/g for PS and NPS samples respectively. SnO2 nanoparticles were doped with palladium in the range from 0.25-1.00 mol% by the impregnation method. The photocatalytic activity of SnO2 and Pd-doped SnO2 nanoparticles were investigated for the degradation of sucrose and glucose under UVA-light irradiation. The results showed that the photocatalytic activity of Pd-doped SnO2 was higher than pure SnO2 and the best photocatalytic activity for the degradation of sucrose and glucose were obtained in the case of Pd-doped SnO2 nanoparticles with 0.5 mol % and 1.0 mol % Pd loading respectively.

Effect of Calcination Temperatures of Cu/CeO2-Containing Co on Physiochemical Properties and Catalytic Activity to Selective CO Oxidation

2015 ◽  
Vol 1131 ◽  
pp. 175-181 ◽  
Author(s):  
Pornthip Aunbamrung ◽  
Akkarat Wongkaew
Keyword(s):  
Co Oxidation ◽  
Mesoporous Structure ◽  
Selective Co Oxidation ◽  
Calcination Temperatures ◽  
Surface Areas ◽  
Type Iv ◽  
Negative Effect ◽  
Crystallite Sizes ◽  
Co Precipitation ◽  
Shift Reaction

The CuO/CeO2-Co3O4 catalysts were prepared via co-precipitation at different calcination temperatures and evaluated catalytic activities in the reaction of selective CO oxidation. The catalysts were characterized by BET, XRD and FESEM-EDX techniques. As determined by BET studies, the catalysts have type IV adsorption isotherm which indicated mesoporous structure. An increase in calcination temperatures decreased the specific surface areas of the catalysts. XRD was used for determination of crystallite sizes of each oxide. It was found that CuO and Co3O4 existed in highly dispersed at every calcination temperatures. For CeO2, an increase in calcination temperatures increased the crystallite sizes. Surface morphology of the catalysts was also investigated by FESEM. The catalyst calcined at 500°C showed the highest performance to completely convert CO to CO2 at 150°C. Furthermore, the effect of CO2 and H2O to activity of catalyst was studied. The result showed that both CO2 and H2O has negative effect to activity of catalyst. CO conversion and selectivity decreased to 93.8% and 48.5% at 210°C, respectively. This may be due to the adsorption of CO2 and H2O molecules on active site and due to the reverse water gas shift reaction occurred at temperature above 190°C.

Activated Carbon Production by Co-Pyrolysis of Vacuum Residue and Gum Rosin

2020 ◽  
Vol 988 ◽  
pp. 137-143
Author(s):  
Anisa Maulida ◽  
Dijan Supramono
Keyword(s):  
Activated Carbon ◽  
Surface Area ◽  
Liquid Crystalline ◽  
Low Cost ◽  
Holding Time ◽  
Vacuum Residue ◽  
Atom Ratio ◽  
Surface Areas ◽  
Gum Rosin ◽  
Crystallite Sizes

Vacuum residue (VR) is potential to be used as a feedstock for mesophase pitch (MP) production because of its low cost and aromatic content. MP, which is a liquid-crystalline state of VR, may be used as precursor of activated carbon (AC). Gum rosin containing conjugated double bonds may be added to and can improve crystallinity and pore surface area in further processes of carbonisation and activation. In the present study, co-pyrolysis was carried out in a stirred tank reactor at 450°C with holding time for 120 minutes. The amount of gum rosin mixed with VR was varied 0, 5, 10 and 15% wt of VR. The precursor products had C/H mole ratio of about 2.43, 2.37, 2.28, and 2.01 by increasing gum rosin added. Subsequently, this precursor underwent carbonization at 700°C with holding time for 120 minutes under N2 flow and activation. KOH solution was used as activating agent to the precursor of activated carbon. Activated carbon gave higher surface area and lower C/H atom ratio with increasing gum rosin added during co-pyrolysis. With gum rosin addition, surface areas of ACs were 120.81, 194.56, 312.36, dan 462.19 m2/g, respectively, and crystallite sizes increased from 8 to 22 Å.

Photocatalytic decoloration of Acid Red 27 in presence of SnO2 nanoparticles

2010 ◽  
Vol 62 (6) ◽  
pp. 1256-1264 ◽  
Author(s):  
A. Esmaielzadeh Kandjani ◽  
M. Farzalipour Tabriz ◽  
N. A. Arefian ◽  
M. R. Vaezi ◽  
F. Halek ◽  
...  
Keyword(s):  
Rate Constant ◽  
Sno2 Nanoparticles ◽  
High Surface ◽  
Hydrothermal Process ◽  
High Surface Area ◽  
Reaction Rate Constant ◽  
Kinetic Rate Constant ◽  
Kinetic Rate ◽  
Surface Areas ◽  
Crystallite Sizes

In this paper, the photocatalytic decoloration of Acid Red 27 (AR27) has been investigated using ultraviolet (UV) irradiation in presence of SnO2 nanoparticles. SnO2 nanoparticles were synthesized via hydrothermal process. The SnO2 nanoparticles' average crystallite sizes derived from X-ray analyses which were synthesized for 2, 12 and 24 hrs were about 3.73, 5.31 and 7.6 nm, respectively. Brunauer-Emmett-Teller (BET) analyses showed high surface area of about 183, 120 and 90(m2/g), respectively for aforementioned synthesized samples. Our investigations indicated that reaction rate constant and photocatalytic efficiency of AR27 decoloration have a direct relation with SnO2 nanoparticles' specific surface areas and band gap energies. Decoloration kinetics was investigated by using Langmuir–Hinshelwood model. The values of the adsorption equilibrium constant, K[AR27], and the kinetic rate constant of surface reaction, kc, were found to be 0.0924 (l/mg) and 0.2535 (mg/l min), respectively.

scholarly journals Plasma Oxidation of H2S over Non-stoichiometric LaxMnO3 Perovskite Catalysts in a Dielectric Barrier Discharge Reactor

Catalysts ◽  
2018 ◽  
Vol 8 (8) ◽  
pp. 317 ◽  
Author(s):  
Kejie Xuan ◽  
Xinbo Zhu ◽  
Yuxiang Cai ◽  
Xin Tu
Keyword(s):  
Dielectric Barrier Discharge ◽  
Barrier Discharge ◽  
Relative Concentration ◽  
Dielectric Barrier ◽  
Surface Areas ◽  
Crystallite Sizes ◽  
Reaction Performance ◽  
Catalytic Removal ◽  
Sulfur Balance ◽  
Catalyst Surfaces

In this work, plasma-catalytic removal of H2S over LaxMnO3 (x = 0.90, 0.95, 1, 1.05 and 1.10) has been studied in a coaxial dielectric barrier discharge (DBD) reactor. The non-stoichiometric effect of the LaxMnO3 catalysts on the removal of H2S and sulfur balance in the plasma-catalytic process has been investigated as a function of specific energy density (SED). The integration of the plasma with the LaxMnO3 catalysts significantly enhanced the reaction performance compared to the process using plasma alone. The highest H2S removal of 96.4% and sulfur balance of 90.5% were achieved over the La0.90MnO3 catalyst, while the major products included SO2 and SO3. The missing sulfur could be ascribed to the sulfur deposited on the catalyst surfaces. The non-stoichiometric LaxMnO3 catalyst exhibited larger specific surface areas and smaller crystallite sizes compared to the LaMnO3 catalyst. The non-stoichiometric effect changed their redox properties as the decreased La/Mn ratio favored the transformation of Mn3+ to Mn4+, which contributed to the generation of oxygen vacancies on the catalyst surfaces. The XPS and H2-TPR results confirmed that the Mn-rich catalysts showed the higher relative concentration of surface adsorbed oxygen (Oads) and lower reduction temperature compared to LaMnO3 catalyst. The reaction performance of the plasma-catalytic oxidation of H2S is closely related to the relative concentration of Oads formed on the catalyst surfaces and the reducibility of the catalysts.

Catalytic Properties of Vanadium Nitride and the Effect of Preparative Parameters on its Microstructure

1996 ◽  
Vol 454 ◽  
Author(s):  
Heock-Hoi Kwon ◽  
Levi T. Thompson
Keyword(s):  
Surface Area ◽  
Catalytic Properties ◽  
Space Velocity ◽  
Reaction Rates ◽  
Vanadium Nitride ◽  
Gravimetric Analysis ◽  
Vanadium Nitrides ◽  
Surface Areas ◽  
Pore Size Distributions ◽  
Crystallite Sizes

AbstractIn this paper we describe the synthesis, morphologies, and catalytic properties of vanadium nitrides prepared via the temperature programmed reaction (TPR) of V2O5 (7 m2/gr) with ammonia. This reaction yielded VN with surface areas up to 60 m2/gr. Among the synthesis parameters, the molar hourly space velocity had the most significant influence on the BET surface areas, crystallite sizes, and pore size distributions. Thermal gravimetric analysis (TGA) and x-ray diffraction indicated that the solid state reaction of V2O5 with NH3 occurred as follows: V2O5 → V4O9 → VO2 → V2O3 → VO0.9 → V.N. Scanning electron microscopy revealed that the surface roughness increased as the transformation proceeded, which corresponds to the increase in surface area. The vanadium nitrides were exceptionally active for the dehydrogenation of butane with selectivities greater than 98 % to C4 olefins. The deactivation was very slow for these catalysts. The reaction rates increased with increasing surface area and were comparable to that of a commercial Pt-Sn/Al2O3 dehydrogenation catalyst.

scholarly journals Thermoanalytical, optical, and magnetic investigations on nanocrystalline Li0.5Fe2.5O4 and resulting ceramics prepared by a starch-based softchemistry synthesis

2020 ◽  
Author(s):  
Roberto Köferstein
Keyword(s):  
Sintering Temperature ◽  
Magnetic Measurements ◽  
Soft Chemistry ◽  
Temperature Dependent ◽  
Disorder Phase Transition ◽  
Surface Areas ◽  
Dsc Measurements ◽  
Enthalpy Changes ◽  
Superparamagnetic Behaviour ◽  
Crystallite Sizes

Nanocrystalline Li0.5Fe2.5O4 was prepared by a starch-based soft-chemistry synthesis. Calcining of the (LiFe)-gel between 350 and 1000 °C results in Li0.5Fe2.5O4powders with crystallite sizes from 13 to 141 nm and specific surface areas between 35 and 7.1 m2 g−1. XRD investigations reveal the formation of ordered Li0.5Fe2.5O4. Sintering between 1050 and 1250 °C leads to ceramics with relative densities of 67−95 % consisting ofgrains between 0.3 and 54 μm. As the sintering temperature increases a rising weight loss ofthe ceramic samples was observed due to the loss of Li2O. Temperature-dependent magnetic measurements indicate a superparamagnetic behaviour for the nano-sized samples. Field-dependent measurements at 3 K of ceramics sintered between 1050 and 1200 °C showincreasing saturation magnetization values (Ms) of 70.0 to 73.0 emu g−1 most likely due to the formation of lithium vacancies and a decrease of the inversion parameter. The magnetization drops down to 67.7 emu g−1 after sintering at 1250 °C caused by the formation of hematite.Diffuse reflectance spectra reveal an indirect allowed band gap decreasing from 1.93 to 1.60 eV depending on thermal treatment. DSC measurements of the order - disorder phase transition on nano-sized powders and bulk ceramics exhibit transition temperatures between 734 and 755 °C and enthalpy changes (ΔtrsH) ranging from 5.0 to 13.5 J g−1. The linear starch was found to be 11.4⋅10−6 K−1.

Preparation and Characterization of Metal Sulfide Electro-catalysts for PEM Fuel Cells

2002 ◽  
Vol 756 ◽  
Author(s):  
Hua Zhang ◽  
Ysmael Verde-Gómez ◽  
Allan J. Jacobson ◽  
Alejandra Ramirez ◽  
Russell R. Chianelli
Keyword(s):  
Carbon Monoxide ◽  
Hydrogen Sulfide ◽  
Hydrogen Oxidation ◽  
Metal Sulfide ◽  
Pem Fuel Cells ◽  
Gas Diffusion ◽  
Pure Hydrogen ◽  
Surface Areas ◽  
Ruthenium Sulfide ◽  
Crystallite Sizes

ABSTRACTRuthenium sulfide samples were prepared by flowing pure hydrogen sulfide into an aqueous solution of ruthenium chloride followed by further sulfidation in hydrogen sulfide. The final products were characterized by X-ray diffraction and crystallite-sizes were estimated from line broadening. The specific surface areas of catalysts were measured using the multipoint BET method and compositions were determined by thermogravimetric analysis. Ruthenium sulfide loaded gas diffusion electrodes were fabricated by a spraying technique and their electrochemical behavior studied. The electrochemical oxidation of hydrogen was investigated in a three -electrode cell using a ruthenium sulfide loaded gas diffusion electrode as the working electrode with humidified hydrogen containing small amounts of carbon monoxide. Results on the activity and the effects of carbon monoxide with reference to a standard platinum electrode measured at the same conditions show that ruthenium sulfide has a lower activity for hydrogen oxidation but is not susceptible to CO poisoning.

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