Specific Surface Area Of Catalyst Research Articles

Catalytic activity of oxides and halides on hydrogen storage of MgH 2

Hydrogen sorption kinetics of ball milled MgH 2 with and without chemical additives were studied. We observed kinetics and capacity improvement with increasing the number of sorption cycles that contributed to the micro/nano cracking of MgH 2 particles, shown by XRD and SEM studies. In addition, to investigate the proposed specific role of O 2−-based additives on the sorption kinetics of MgH 2, we have undertaken a comparative study evaluating the performances of MgH 2 containing the NbCl 5, CaF 2 or Nb 2O 5 additives. At 300 °C, addition of NbCl 5 and CaF 2 improved the sorption capacity to 5.2 and 5.6 wt% within 50 min, respectively, in comparison to the required 80 min in the case of Nb 2O 5. This suggests the importance of the chemical nature of the catalyst for hydrogen sorption in MgH 2. In addition, the catalyst specific surface area was shown to be very critical. High surface area Nb 2O 5 (200 m 2 g −1), prepared by novel precipitation method, exhibits an excellent catalytic activity and helped to desorb 4.5 wt% of hydrogen from MgH 2 within 80 min at a temperature as low as 200 °C.

Non‐Isothermal Crystallization Behavior of Poly(trimethylene terephthalate) Synthesized with Different Catalysts

AbstractSummary: Non‐isothermal crystallization behavior of PTT resins synthesized with different catalysts was studied by using differential scanning calorimetry (DSC) and polarized light microscopy (PLM). The results showed that with the increase of the cooling rate, the crystallization temperature for poly(trimethylene terephthalate) (PTT) resin decreased, which indicated that the crystallization process was controlled by the nucleation. Catalyst had no effect on the crystallization development process, but had somewhat effect on the non‐isothermal crystallization mechanism. The average values of Avrami exponent, for PTT with different catalysts were between 3 and 4. It was assumed that the non‐isothermal crystallization mechanism for PTT with or without catalyst was the combination of homogenous and heterogeneous nucleation and spherulite growth, but it mainly depended on the latter. For sample 4, the non‐isothermal crystallization underwent secondary crystallization process when cooling rate was over 20 °C/min. At the same cooling rate, the crystallization temperature, the crystallization ability and the crystallization rate of PTT resins followed the sequence as: sample 2 > sample 1 ≈ sample 3 ≈ sample 4, which proved that catalysts could significantly prompt crystallization. The cooling rate had significant effect on the crystallization ability parameters of PTT, i.e., with the increase of cooling rate, the crystallization ability declined. Although catalyst could increase the crystallization ability of PTT, the effect was very limited because the effect of the molecular weight on the crystallization ability would be superior to the catalyst when the molecular weight of PTT was significantly high. The specific surface area of catalyst had also a great influence on the spherulitic morphology of PTT formed in the cooling process. The spherulite dimensions decrease with increasing the specific surface area of catalyst because of an increase in the nucleation rate, which produces more and smaller spherulites that can not grow larger before impinging on each other. magnified image

The catalytic oxidation of aromatic hydrocarbons over supported metal oxide

The catalytic activity of metals (Cu, Mn, Fe, V, Mo, Co, Ni, Zn)/γ-Al 2O 3 was investigated to bring about the complete oxidation of benzene, toluene and xylene (BTX). Among them, Cu/γ-Al 2O 3 was found to be the most promising catalyst based on activity. X-ray diffraction (XRD), Brunauer Emmett Teller method (BET), electron probe X-ray micro analysis (EPMA) and temperature programmed reduction (TPR) by H 2 were used to characterize a series of supported copper catalysts. Increasing the calcination temperature resulted in decreasing the specific surface areas of catalysts and, subsequently, the catalytic activity. Copper loadings on γ-Al 2O 3 had a great effect on catalytic activity, and 5 wt.% Cu/γ-Al 2O 3 catalyst was observed to be the most active, which might be contributed to the well-dispersed copper surface phase. Using TiO 2 (anatase), TiO 2 (rutile), SiO 2 (I) and SiO 2 (II) as support instead of γ-Al 2O 3, the activity sequence of 5 wt.% Cu with respect to the support was γ-Al 2O 3>TiO 2 (rutile)>TiO 2 (anatase)>SiO 2 (I)>SiO 2 (II), and this appeared to be correlated with the distribution of copper on support rather than with the specific surface area of the catalyst. The smaller particle size of copper, due to its high dispersion on support, had a positive effect on catalytic activity. The activity of 5 wt.% Cu/γ-Al 2O 3 with respect to the VOC molecule was observed to follow this sequence: toluene>xylene>benzene. Increasing the reactant concentration exerted an inhibiting effect on the catalytic activity.

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

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.

Design, modelling and experimentation of a new large-scale photocatalytic reactor for water treatment

Recent literature has demonstrated on a laboratory scale the potential of semiconductor photocatalysis technology to completely destroy organic pollutants present in water. However, to date no viable pilot plant exists using this technology. In this paper, a new reactor design is presented that addresses the two most important parameters, namely, light distribution inside the reactor and high specific surface area of catalyst. The reactor consists of several hollow tubes employed as a means of light delivery to the catalyst present on the outside surface of the tubes. Simple model calculations were performed to evaluate the radial light intensity profile as a function of input light intensity and angle of incidence, diameter, length, wall thickness and surface roughness of tubes. A reactor was designed and constructed based on the modelling results, and when experiments were conducted showed very promising results. The new reactor aims at developing a technical solution to the design of a commercial scale photocatalytic reactor.

Preparation of high loading silica supported nickel catalyst: simultaneous analysis of the precipitation and aging steps

The precipitation and aging steps used for the preparation of high loading silica supported nickel catalysts were simultaneously analyzed with the aid of statistical design of experiments. Empirical models relating catalyst final properties and preparation variables were developed. It was found that the precipitation step determines the final catalyst nickel content, and that at low nickel concentrations high metallic area per gram of reduced nickel may be attained with the precipitated precursor without performing the aging step. When it is performed, the aging step has a strong influence on final catalyst properties, such as specific surface area, metallic area per gram of nickel and degree of reduction. Therefore, catalyst aging may be an effective method to control dispersion, reducibility and active phase accessibility. The importance of the aging step was shown to increase with the aging temperature, which is linked to the larger rates of silicate formation at high temperatures. A semi-empirical model was developed to describe the final catalyst specific surface area as a function of the rate of silicate formation. This model is able to describe changes of the catalyst surface area fairly well and allow the proper manipulation of preparation conditions in order to maximize the catalyst specific area, leading to maximum catalyst activities.

Structure and Texture of Nickel‐Molybdenum Catalysts on Alumina Support Modified with Fluoride or Chloride Ions

AbstractThe performed study involves measurements of a specific surface area via a BET method, of the pore volume, FT‐IR, and a derivatographic study of a series of Al2O3‐supported nickel‐molybdenum catalysts modified with fluoride and chloride ions. It was found that fluoride ions lead to a decrease in the specific surface area of catalysts, whereas chloride ions have a small effect on this parameter. Modification does not change the type of pores of the catalysts, yet it affects their size and increases concentration of OH groups adsorbed on the surface of the catalysts relative to the carrier and the unmodified catalyst. Addition of fluoride ions decreases the thermal stability of the catalyst, whereas chloride ions does not cause any change.

MgCl2·6H2O‐based titanium catalysts for propylene polymerization. Chemical composition and productivity

AbstractMgCl2·6H2O was reacted with dichlorodiphenylsilane to obtain anhydrous magnesium dichloride. MgCl2 thus obtained was solubilized in 2‐ethyl‐1‐hexanol to prepare titanium catalysts for propylene polymerization through regeneration of magnesium dichloride by reaction with titanium tetrachloride. The nature of internal lewis base dialkyl phthalate [Ph(COOR)2, where R = Me, Et, and n‐Bu] and reactants concentration (alcohol and dialkyl phthalate) influence the chemical composition and specific surface area of catalysts. The activity of the catalysts changes in the order ßmethyl < ethyl < butyl. The polymerization parameters such as Al/Ti mole ratios, aging time of catalysts and cocatalysts (triethylaluminium) also control the activity. The concentration of the external Lewis base (dimethoxydiphenylsilane) improves the stereospecifity of the catalyst system.

Electrocatalysis by ad-atoms Part XIII. Preparation of ad-electrodes with tin ad-atoms for methanol, formaldehyde and formic acid fuel cells

The practical application of the electrocatalysis by tin ad-atoms to organic fuel cell anodes has been studied. A simplified and versatile preparation method of the electrode having high specific surface area platinum with a well-defined tin coverage has been developed. It consists of underpotential deposition of ad-atoms and subsequent anodic treatment resulting in uniform dispersion of the ad-atoms over all the platinum clusters in the catalyst layer of the electrode. The resulting electrode exhibits enhancement effects in the specific activity over the pure platinum black electrode by a factor of 100 for methanol oxidation, of more than 1000 for formaldehyde oxidation and of 250 for formic acid oxidation, respectively. This method has the advantage that a much higher specific surface area of catalyst is obtained, as well as an optimum composition, compared with the electrochemical co-deposition or immersion methods proposed previously.

Electrocatalysis by AD-atoms: Part XIII. Preparation of ad-electrodes with tin ad-atoms for methanol, formaldehyde and formic acid fuel cells

The practical application of the electrocatalysis by tin ad-atoms to organic fuel cell anodes has been studied. A simplified and versatile preparation method of the electrode having high specific surface area platinum with a well-defined tin coverage has been developed. It consists of underpotential deposition of ad-atoms and subsequent anodic treatment resulting in uniform dispersion of the ad-atoms over all the platinum clusters in the catalyst layer of the electrode. The resulting electrode exhibits enhancement effects in the specific activity over the pure platinum black electrode by a factor of 100 for methanol oxidation, of more than 1000 for formaldehyde oxidation and of 250 for formic acid oxidation, respectively. This method has the advantage that a much higher specific surface area of catalyst is obtained, as well as an optimum composition, compared with the electrochemical co-deposition or immersion methods proposed previously.

Catalyzed burning rates of ammonium perchlorate and polymethylmethacrylate mixtures

The catalytic effect of Fe2O3, carbon black and SiO2 (“Aerosil”) on the burning rates, u, of ammonium perchlorate (AP) and AP-polymethylmethacrylate (PMMA) mixtures was studied. An increase in the catalyst weight percent, C, in the mixture caused a significant increase in u only at C ≤ 5–10% (in some cases even at C ≤ 1–2%). Dependence of the burning rate on the catalyst specific surface area, S, is slight (if S is not too small). Strong catalyst agglomeration (especially for Aerosil) was observed in the burning zone. The rate of catalytic reaction, W, in the burning zone was calculated. The comparison of W with catalytic reaction rates measured in conventional chemical reactors leads to the conclusion that the weight part of the mixture reacting on catalyst under the burning condition is very small. A heterogeneous-homogeneous mechanism of catalysis in flames is suggested.