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 H2 Production from Catalytic Methane Decomposition Using Fe/x-ZrO2 and Fe-Ni/(x-ZrO2) (x = 0, La2O3, WO3) Catalysts

Catalysts ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 793
Author(s):  
Fahad Al-Mubaddel ◽  
Samsudeen Kasim ◽  
Ahmed A. Ibrahim ◽  
Abdulrhman S. Al-Awadi ◽  
Anis H. Fakeeha ◽  
...  
Keyword(s):  
Supported Catalysts ◽  
Thermo Gravimetric Analysis ◽  
Space Velocity ◽  
H2 Production ◽  
Methane Decomposition ◽  
Gravimetric Analysis ◽  
Impregnation Method ◽  
Carbon Deposits ◽  
Surface Areas ◽  
H2 Yield

An environmentally-benign way of producing hydrogen is methane decomposition. This study focused on methane decomposition using Fe and Fe-Ni catalysts, which were dispersed over different supports by the wet-impregnation method. We observed the effect of modifying ZrO2 with La2O3 and WO3 in terms of H2 yield and carbon deposits. The modification led to a higher H2 yield in all cases and WO3-modified support gave the highest yield of about 90% and was stable throughout the reaction period. The reaction conditions were at 1 atm, 800 °C, and 4000 mL(hgcat)−1 space velocity. Adding Ni to Fe/x-ZrO2 gave a higher H2 yield and stability for ZrO2 and La2O3 + ZrO2-supported catalysts whose prior performances and stabilities were very poor. Catalyst samples were analyzed by characterization techniques like X-ray diffraction (XRD), nitrogen physisorption, temperature-programmed reduction (TPR), thermo-gravimetric analysis (TGA), and Raman spectroscopy. The phases of iron and the supports were identified using XRD while the BET revealed a significant decrease in the specific surface areas of fresh catalysts relative to supports. A progressive change in Fe’s oxidation state from Fe3+ to Fe0 was observed from the H2-TPR results. The carbon deposits on Fe/ZrO2 and Fe/La2O3 + ZrO2 are mainly amorphous, while Fe/WO3 + ZrO2 and Fe-Ni/x-ZrO2 are characterized by graphitic carbon.

SURFACE CHEMISTRY AND CATALYTIC PROPERTIES OF BORON PHOSPHATE: 1. SURFACE AREA AND ACIDITY

1965 ◽  
Vol 43 (6) ◽  
pp. 1680-1688 ◽  
Author(s):  
J. B. Moffat ◽  
H. L. Goltz
Keyword(s):  
Surface Area ◽  
Active Sites ◽  
Elevated Temperatures ◽  
Catalytic Properties ◽  
Nitrogen Adsorption ◽  
Weight Changes ◽  
Kcal Mole ◽  
Boron Phosphate ◽  
Surface Areas ◽  
Nitrogen Adsorption Isotherms

Surface properties of the dehydration catalyst, boron phosphate (BP), prepared by the reaction of triethyl borate and phosphoric acid, were investigated by the use of a microbalance system. During evacuation at elevated temperatures, weight changes of the BP were obtained. Nitrogen adsorption isotherms were measured after each treatment. Surface areas appear to increase, and reach a maximum in the range 200–300 °C. Weight changes are initially large but begin to level off as the temperature is increased. Ammonia isotherms were obtained at 25.00 °C on aliquots of the same BP sample after various pretreatments. Amounts of ammonia remaining adsorbed after evacuation overnight were taken as the quantity chemisorbed. An approximate value of 8.9 kcal/mole of ammonia was obtained for the heat of chemisorption of ammonia by measuring the pressure and weight change as the amount of chemisorbed ammonia is decreased on heating the BP to various temperatures in a closed system. Results are interpreted in terms of change of number of active sites with surface area and the deactivation of sites on loss of water.

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.

scholarly journals Comparison of Nitrogen Adsorption and Mercury Penetration Results

1988 ◽  
Vol 5 (1) ◽  
pp. 76-93 ◽  
Author(s):  
Bruce D. Adkins ◽  
Burtron H. Davis
Keyword(s):  
Surface Area ◽  
Pore Volume ◽  
Narrow Range ◽  
Nitrogen Adsorption ◽  
Bet Surface Area ◽  
Pore Sizes ◽  
Surface Areas ◽  
Bet Method ◽  
Crystallite Sizes ◽  
Materials Used

Mercury penetration pore volumes obtained for four materials (two silicas, alumina and zirconia) agreed closely with the “Gurvitsch Volume” obtained from nitrogen adsorption. The pore volume of the materials used in this study was found in a narrow range of pore sizes that are amenable to both mercury penetration and nitrogen adsorption measurements. The average crystallite sizes calculated from the BET surface area and from TEM measurements agreed closely except for the highest surface area (310 m2/g) material. The surface areas obtained from mercury penetration or the BET method agree closely for the two lower area materials but the mercury penetration is much higher than the nitrogen surface area for the two higher area materials.

Cell morphology, volume, and surface area determinations from multilevel contouring within HVEM micrographs of serial sections and whole-cell mounts

1987 ◽  
Vol 45 ◽  
pp. 588-589
Author(s):  
M. Marko ◽  
A. Leith ◽  
D. Parsons
Keyword(s):  
Surface Area ◽  
Electron Micrographs ◽  
Cell Morphology ◽  
Individual Variation ◽  
Serial Section ◽  
Stereo Pair ◽  
Complex Structures ◽  
Serial Sections ◽  
Surface Areas ◽  
Computer Based

The use of serial sections and computer-based 3-D reconstruction techniques affords an opportunity not only to visualize the shape and distribution of the structures being studied, but also to determine their volumes and surface areas. Up until now, this has been done using serial ultrathin sections.The serial-section approach differs from the stereo logical methods of Weibel in that it is based on the Information from a set of single, complete cells (or organelles) rather than on a random 2-dimensional sampling of a population of cells. Because of this, it can more easily provide absolute values of volume and surface area, especially for highly-complex structures. It also allows study of individual variation among the cells, and study of structures which occur only infrequently.We have developed a system for 3-D reconstruction of objects from stereo-pair electron micrographs of thick specimens.

scholarly journals Influence of the Reduction Temperature and the Nature of the Support on the Performance of Zirconia and Alumina-Supported Pt Catalysts for n-Dodecane Hydroisomerization

Catalysts ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 88
Author(s):  
Diana García-Pérez ◽  
Maria Consuelo Alvarez-Galvan ◽  
Jose M. Campos-Martin ◽  
Jose L. G. Fierro
Keyword(s):  
Catalytic Activity ◽  
Surface Area ◽  
Catalytic Properties ◽  
Catalytic Performance ◽  
Major Influence ◽  
Pt Catalysts ◽  
Reduction Temperature ◽  
Metal Dispersion ◽  
Tungsten Oxides ◽  
Supported Pt Catalysts

Catalysts based on zirconia- and alumina-supported tungsten oxides (15 wt % W) with a small loading of platinum (0.3 wt % Pt) were selected to study the influence of the reduction temperature and the nature of the support on the hydroisomerization of n-dodecane. The reduction temperature has a major influence on metal dispersion, which impacts the catalytic activity. In addition, alumina and zirconia supports show different catalytic properties (mainly acid site strength and surface area), which play an important role in the conversion. The NH3-TPD profiles indicate that the acidity in alumina-based catalysts is clearly higher than that in their zirconia counterparts; this acidity can be attributed to a stronger interaction of the WOx species with alumina. The PtW/Al catalyst was found to exhibit the best catalytic performance for the hydroisomerization of n-dodecane based on its higher acidity, which was ascribed to its larger surface area relative to that of its zirconia counterparts. The selectivity for different hydrocarbons (C7–10, C11 and i-C12) was very similar for all the catalysts studied, with branched C12 hydrocarbons being the main products obtained (~80%). The temperature of 350 °C was clearly the best reduction temperature for all the catalysts studied in a trickled-bed-mode reactor.

scholarly journals Tuning the hierarchical pore structure of graphene oxide through dual thermal activation for high-performance supercapacitor

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
Jeongpil Kim ◽  
Jeong-Hyun Eum ◽  
Junhyeok Kang ◽  
Ohchan Kwon ◽  
Hansung Kim ◽  
...  
Keyword(s):  
Graphene Oxide ◽  
Pore Structure ◽  
Specific Capacitance ◽  
Surface Area ◽  
Thermal Annealing ◽  
High Performance ◽  
Annealing Process ◽  
Supercapacitor Electrode ◽  
Simple Method ◽  
Surface Areas

AbstractHerein, we introduce a simple method to prepare hierarchical graphene with a tunable pore structure by activating graphene oxide (GO) with a two-step thermal annealing process. First, GO was treated at 600 °C by rapid thermal annealing in air, followed by subsequent thermal annealing in N2. The prepared graphene powder comprised abundant slit nanopores and micropores, showing a large specific surface area of 653.2 m2/g with a microporous surface area of 367.2 m2/g under optimized conditions. The pore structure was easily tunable by controlling the oxidation degree of GO and by the second annealing process. When the graphene powder was used as the supercapacitor electrode, a specific capacitance of 372.1 F/g was achieved at 0.5 A/g in 1 M H2SO4 electrolyte, which is a significantly enhanced value compared to that obtained using activated carbon and commercial reduced GO. The performance of the supercapacitor was highly stable, showing 103.8% retention of specific capacitance after 10,000 cycles at 10 A/g. The influence of pore structure on the supercapacitor performance was systematically investigated by varying the ratio of micro- and external surface areas of graphene.

scholarly journals Action Time-Effect and Mechanism of Low-Calcium Fly Ash in Cement-Based Composites

Crystals ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 681
Author(s):  
Na Yan ◽  
Qingqing Tang ◽  
Ying Zhang ◽  
Guowen Sun
Keyword(s):  
Fly Ash ◽  
Nitrogen Adsorption ◽  
Chemical Effect ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Degree Of Hydration ◽  
Surface Areas ◽  
Activity Effect ◽  
Low Calcium ◽  
Pore Size Distributions

This study was conducted in order to investigate when low-calcium fly ash plays a physical or chemical effect and what is the chemical effect proportion of low-calcium fly ash. Two types of low-calcium fly ash and quartz powder, with similar fineness as active and inert admixtures, were used as materials in this study. Under different water/binder ratios and hydration ages, the effects of the different types of admixtures and their dosages on the flexural and compressive strength of the composites were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and nitrogen adsorption methods, in addition to an assessment of the degree of hydration of the fly ash, were employed to observe the hydration products at different ages, the microstructures of the hydration products, as well as their surface areas and pore size distributions. The results show that during the hydration period of 28 days, the low-calcium fly ash has a micro-aggregate filling physical effect. However, after 56 days, the hydration degree of fly ash begins to exceed 1%. This illustrates that the low-calcium fly ash has both the pozzolanic activity effect and micro-aggregate filling effect. In contrast, the low-calcium fly ash hydrated for 90 days is still dominated by the physical filling effect.

Effect of Synthesis Temperature on Particles Size and Morphology of Zirconium Oxide Nanoparticle

2017 ◽  
Vol 50 ◽  
pp. 18-31 ◽  
Author(s):  
Rudzani Sigwadi ◽  
Simon Dhlamini ◽  
Touhami Mokrani ◽  
Patrick Nonjola
Keyword(s):  
Electron Microscopy ◽  
Particle Size ◽  
Zirconium Oxide ◽  
Thermo Gravimetric Analysis ◽  
Gravimetric Analysis ◽  
X Ray Diffraction ◽  
X Ray ◽  
Transmission Electron ◽  
Crystallite Sizes ◽  
Ft Ir

The paper presents the synthesis and investigation of zirconium oxide (ZrO2) nanoparticles that were synthesised by precipitation method with the effects of the temperatures of reaction on the particles size, morphology, crystallite sizes and stability at high temperature. The reaction temperature effect on the particle size, morphology, crystallite sizes and stabilized a higher temperature (tetragonal and cubic) phases was studied. Thermal decomposition, band structure and functional groups were analyzed by Brunauer-Emmett-Teller (BET), Scanning Electron Microscopy (SEM), Transmission electron microscopy (TEM), X-ray diffraction (XRD), Thermo-gravimetric analysis (TGA) and Fourier transform infrared (FT-IR). The crystal structure was determined using X-ray diffraction. The morphology and the particle size were studied using (SEM) and (TEM). The shaped particles were confirmed through the SEM analysis. The transmission electron microscopic analysis confirmed the formation of the nanoparticles with the particle size. The FT-IR spectra showed the strong presence of ZrO2 nanoparticles.

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