Various characteristics of Ni and Pt–Al2O3 nanocatalysts prepared by microwave method to be applied in some petrochemical processes

AbstractAlumina-supported metal nanocatalysts were prepared via the microwave method, by loading nano Ni particles (at 1, 3 and 5wt%) or nano Pt particles (at 0.3, 0.6 and 0.9wt%). Structural and adsorption features of the nano catalysts were revealed through XRD, DSC-DTA, TEM, H2-chemisorption and N2-physisorption. N2-adsorption–desorption isotherms of type IV were related typically to mesoporous materials with H2 class of hysteresis loops characterizing ink bottle type of pores. The well dispersed nano-sized metal particles were evidenced in the studied catalytic systems, exhibiting marked thermal stability up to 800°C. The catalytic performances of different catalyst samples were assessed during cyclohexane, normal hexane and ethanol conversions, using the micro-catalytic pulse technique at different operating conditions. The 5% Ni–γ–Al2O3 sample was found to be the most active in dehydration of ethanol to produce ethylene, as well as in n-hexane cracking. However, the 1% Ni–Al2O3 sample showed the highest dehydrogenation activity for selective production of benzene from cyclohexane. On the other hand, the 0.9% Pt–γ–Al2O3 sample exhibited the highest activity in the dehydration of ethanol and in the dehydrogenation of cyclohexane. The 0.3% Pt–γ–Al2O3 sample was the most active in the dehydrocyclization of normal hexane, as compared to the other catalyst samples under study

The use of black pepper (Piper guineense) as an ecofriendly antimicrobial agent to fight foodborne microorganisms

Consumers demand clean-label food products, necessitating the search for new, natural antimicrobials to meet this demand while ensuring food safety. This review aimed at investigating the antimicrobial properties of black pepper (Piper guineense) against foodborne microorganisms. The existence of foodborne illness, food spoilage, food waste, the resulting negative economic impact of these issues, and consumer interests have all pushed the food industry to find alternative, safe, and natural antimicrobials to be used in foods and beverages. Consumers have also influenced the demand for novel antimicrobials due to the perceived association of current synthetic preservatives with diseases and adverse effects on children. They also have a desire for clean-label products. These combined concerns have prompted researchers at investigating plant extracts as potential sources for antimicrobials. Plants possess many antimicrobial properties; therefore, evaluating these plant extracts as a natural source of antimicrobials can lead to a preventative control method in reducing foodborne illness and food spoilage, inclusively meeting consumer needs. In most regions, P. guineense is commonly utilized due to its potent and effective medicinal properties against foodborne microorganisms

Homogeneous nucleation of liquid from the vapor phase in an expansion cloud chamber

A Wilson expansion cloud chamber has been used to measure the homogeneous vapor-to-liquid nucleation of several materials over the past decade. These data, representing nucleation rate as a function of temperature and supersaturation ratio for toluene, nonane, and water measured in our center, have been re-examined and are presented both in graphical form and as a table of selected data points. The latter is included for ease of comparison with theory. Measurements of the binary homogeneous nucleation of ethanol-water (E-W) mixtures are also presented. The expansion chamber experimental technique and data reduction technique are discussed

Scaling of Nucleation Rates

The homogeneous nucleation rate, J, for T ≪ Tc can be cast into a corresponding states form by exploiting scaled expressions for the vapor pressure and for the surface tension, σ. In the vapor-to-liquid case with σ = σ0[Tc-T], the classical cluster energy of formation /kT = [16π/3]·Ω3[Tc/T-1]3/(ln S)2 ≡ [x0/x]2, where Ω ≡ σ0[k ñ2/3] and ñ is liquid number density. The Ω ≈ 2 for normal liquids. (A similar approach can be applied to homogeneous liquid to solid nucleation and to heterogeneous nucleation formalisms using appropriate modifications of σ and Ω.) The above [x0/x]2 is sufficiently tenable that in some cases, one can use it to extract approximate critical temperatures from experimental data. In this work, we point out that expansion cloud chamber data (for nonane, toluene, and water) are in excellent agreement with ln J ≈ const. - [x0/x]2 [centimeter-gram-second (cgs) units], and that the constant term is well approximated by ln (Γc), where Γc is the inverse thermal wavelength cubed per second at T = Tc. The ln (Γc) is ≈ 60 in cgs units (74 in SI units) for most materials. A physical basis for the latter form, which includes the behavior at small n, the discrete integer behavior of n, and a configurational entropy term, τ ln (n), is presented