scholarly journals The Effect of Thermal Treatment under Different Atmospheric Conditions on the Catalytic Performance of Nickel Supported on Porous Silica in the Gas-Phase Hydrogenation of Acetonitrile

2007 ◽  
Vol 25 (3-4) ◽  
pp. 185-198 ◽  
Author(s):  
Pilar Braos-García ◽  
Desireé Durán-Martín ◽  
Antonia Infantes-Molina ◽  
Dolores Eliche-Quesada ◽  
Enrique Rodríguez-Castellón ◽  
...  
Keyword(s):  
Thermal Treatment ◽  
Gas Phase ◽  
Porous Silica ◽  
Catalytic Performance ◽  
Atmospheric Conditions

SiO2 Entrapment of Animal Cells for Hybrid Bioartificial Organs

2000 ◽  
Vol 628 ◽  
Author(s):  
Giovanni Carturan ◽  
Renzo Dal Monte ◽  
Maurizio Muraca
Keyword(s):  
Gas Phase ◽  
Mechanical Stability ◽  
Porous Silica ◽  
Collagen Matrix ◽  
Homogeneous Layer ◽  
Animal Cells ◽  
Bioartificial Organs ◽  
Liver And Pancreas ◽  
Encapsulation Method ◽  
Metabolic Activities

ABSTRACTSi-alkoxides in gas phase are reactive towards the surface of animal cells, depositing a homogeneous layer of porous silica. This encapsulation method preserves cell viability and does not alter the hindrance of the biological load.In the prospective use for the design of a hybrid bioartificial liver, hepatocytes in a collagen matrix can be entrapped by the siliceous deposit which provides definite mechanical stability to the collagen matrix and molecular cutoff vs. high molecular weight proteins, including immunoglobulins. The functionality of the encapsulated cell load is maintained for the expressions of typical liver and pancreas metabolic activities.

scholarly journals Quantitative estimates of the volatility of ambient organic aerosol

2010 ◽  
Vol 10 (1) ◽  
pp. 1901-1938 ◽  
Author(s):  
C. D. Cappa ◽  
J. L. Jimenez
Keyword(s):  
Los Angeles ◽  
Gas Phase ◽  
Organic Aerosol ◽  
Basis Sets ◽  
Volatile Fraction ◽  
Volatile Components ◽  
Atmospheric Conditions ◽  
Volatile Material ◽  
Evaporation Coefficient ◽  
Quantitative Estimates

Abstract. Measurements of the sensitivity of organic aerosol (OA, and its components) mass to changes in temperature were recently reported by Huffman et al. (2009) using a tandem thermodenuder-aerosol mass spectrometer (TD-AMS) system in Mexico City and the Los Angeles area. Here, we use these measurements to derive quantitative estimates of aerosol volatility within the framework of absorptive partitioning theory using a kinetic model of aerosol evaporation in the TD. OA volatility distributions (or "basis-sets") are determined using several assumptions as to the enthalpy of vaporization (ΔHvap). We present two definitions of "non-volatile OA," one being a global and one a local definition. Based on these definitions, our analysis indicates that a substantial fraction of the organic aerosol is comprised of non-volatile components that will not evaporate under any atmospheric conditions, on the order of 50–80% when the most realistic ΔHvap assumptions are considered. The sensitivity of the total OA mass to dilution and ambient changes in temperature has been assessed for the various ΔHvap assumptions. The temperature sensitivity is relatively independent of the particular ΔHvap assumptions whereas dilution sensitivity is found to be greatest for the low (ΔHvap = 50 kJ/mol) and lowest for the high (ΔHvap = 150 kJ/mol) assumptions. This difference arises from the high ΔHvap assumptions yielding volatility distributions with a greater fraction of non-volatile material than the low ΔHvap assumptions. If the observations are fit using a 1 or 2-component model the sensitivity of the OA to dilution is unrealistically high. An empirical method introduced by Faulhaber et al. (2009) has also been used to independently estimate a volatility distribution for the ambient OA and is found to give results consistent with the high and variable ΔHvap assumptions. Our results also show that the amount of semivolatile gas-phase organics in equilibrium with the OA could range from ~20% to 400% of the OA mass, with smaller values generally corresponding to the higher ΔHvap assumptions. The volatility of various OA components determined from factor analysis of AMS spectra has also been assessed. In general, it is found that the fraction of non-volatile material follows the pattern: biomass burning OA < hydrocarbon-like OA < semivolatile oxygenated OA < low-volatility oxygenated OA. Correspondingly, the sensitivity to dilution and the estimated amount of semivolatile gas-phase material for the OA factors follows the reverse order. Primary OA has a substantial semivolatile fraction, in agreement with previous results, while the non-volatile fraction appears to be dominated by oxygenated OA produced by atmospheric aging. The overall OA volatility is thus controlled by the relative contribution of each aerosol type to the total OA burden. Finally, the model/measurement comparison appears to require OA having an evaporation coefficient (γe) substantially greater than 10−2; at this point it is not possible to place firmer constraints on γe based on the observations.

scholarly journals Catalytic Performance of Nitrogen-Doped Activated Carbon Supported Pd Catalyst for Hydrodechlorination of 2,4-Dichlorophenol or Chloropentafluoroethane

Molecules ◽  
2019 ◽  
Vol 24 (4) ◽  
pp. 674 ◽  
Author(s):  
Haodong Tang ◽  
Bin Xu ◽  
Meng Xiang ◽  
Xinxin Chen ◽  
Yao Wang ◽  
...  
Keyword(s):  
Activated Carbon ◽  
Liquid Phase ◽  
Gas Phase ◽  
Nitrogen Doping ◽  
Catalyst Surface ◽  
Catalytic Performance ◽  
Atomic Ratio ◽  
Pd Catalyst ◽  
Nitrogen Doped ◽  
The Stability

Nitrogen-doped activated carbon (N-AC) obtained through the thermal treatment of a mixture of HNO3-pretreated activated carbon (AC) and urea under N2 atmosphere at 600 °C was used as the carrier of Pd catalyst for both liquid-phase hydrodechlorination of 2,4-dichlorophenol (2,4-DCP) and gas-phase hydrodechlorination of chloropentafluoroethane (R-115). The effects of nitrogen doping on the dispersion and stability of Pd, atomic ratio of Pd/Pd2+ on the surface of the catalyzer, the catalyst’s hydrodechlorination activity, as well as the stability of N species in two different reaction systems were investigated. Our results suggest that, despite no improvement in the dispersion of Pd, nitrogen doping may significantly raise the atomic ratio of Pd/Pd2+ on the catalyst surface, with a value of 1.2 on Pd/AC but 2.2 on Pd/N-AC. Three types of N species, namely graphitic, pyridinic, and pyrrolic nitrogen, were observed on the surface of Pd/N-AC, and graphitic nitrogen was stable in both liquid-phase hydrodechlorination of 2,4-DCP and gas-phase hydrodechlorination of R-115, with pyridinic and pyrrolic nitrogen being unstable during gas-phase hydrodechlorination of R-115. As a result, the average size of Pd nanocrystals on Pd/N-AC was almost kept unchanged after liquid-phase hydrodechlorination of 2,4-DCP, whereas crystal growth of Pd was clearly observed on Pd/N-AC after gas-phase hydrodechlorination of R-115. The activity test revealed that Pd/N-AC exhibited a much better performance than Pd/AC in liquid-phase hydrodechlorination of 2,4-DCP, probably due to the enhanced stability of Pd exposed to the environment resulting from nitrogen doping as suggested by the higher atomic ratio of Pd/Pd2+ on the catalyst surface. In the gas-phase hydrodechlorination of R-115, however, a more rapid deactivation phenomenon occurred on Pd/N-AC than on Pd/AC despite a higher activity initially observed on Pd/N-AC, hinting that the stability of pyridinic and pyrrolic nitrogen plays an important role in the determination of catalytic performance of Pd/N-AC.

scholarly journals Enhanced Phenol Tert-Butylation Reaction Activity over Hierarchical Porous Silica-Alumina Materials

Catalysts ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 1098
Author(s):  
Ling Xu ◽  
Fan Wang ◽  
Zhi Xiu ◽  
Limei Duan ◽  
Zongrui Liu ◽  
...  
Keyword(s):  
Physical Adsorption ◽  
Porous Silica ◽  
Mesoporous Structure ◽  
Catalytic Performance ◽  
Crystallization Time ◽  
Hydrothermal Conditions ◽  
Transmission Electron ◽  
Hierarchical Porous ◽  
Silica Alumina ◽  
Ft Ir

Hierarchical aluminum-silicon materials have been successfully prepared by mixing pre-crystallization of silica-alumina sol and citric acid under hydrothermal conditions. The influence of pre-crystallization time on the micro-mesoporous structure is studied using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), N2 physical adsorption, and high-resolution transmission electron microscopy (HRTEM). The catalytic performance of hierarchical silica-alumina material is evaluated by alkylation of phenol with tert-butanol. The results show that the silica-alumina materials with a pre-crystallization time of 16 h show micro-mesoporous structure and excellent catalytic activity.

Facile One-Step Dialysis Strategy for Preparation of Porous Silica Nanoparticles with Rough Surface

NANO ◽  
2020 ◽  
Vol 15 (03) ◽  
pp. 2050038
Author(s):  
Zhe Chen ◽  
Jiaqiong Xu ◽  
Xuechen Xiang ◽  
Dongfang Ren ◽  
Ning Chen ◽  
...  
Keyword(s):  
Silica Nanoparticles ◽  
Rough Surface ◽  
Mesoporous Silica Nanoparticles ◽  
Porous Silica ◽  
Catalytic Performance ◽  
Ammonia Solution ◽  
Type Iv ◽  
Organic Surfactant ◽  
One Step ◽  
Adsorption Desorption

In this study, porous silica nanoparticles were fabricated in the absence of organic surfactant template at room temperature by a facile one-step dialysis method. By using a dialysis system comprising an ammonia solution as the dialysate, a series of porous silica nanoparticles with a rough surface (e.g., raspberry-like) were obtained by the initiation of a homogeneous ternary tetraethylsilicate-water-ethanol system with different ammonia solution concentrations. The specific surface area and pore volume of porous nanoparticles were regulated by changing the dialysate concentrations. N2 adsorption–desorption measurements revealed that the porous silica nanoparticles owned both mesopores and micropores and exhibited a type IV isotherm, hence, these nanoparticles can be used as mesoporous silica nanoparticles (MSNs). The Au@MSN nanocomposite can be used as a catalyst for the typical reduction of 4-nitrophenol to 4-aminophenol by NaBH4 and exhibited excellent catalytic performance.

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