Chemisorption

About: Chemisorption is a research topic. Over the lifetime, 16298 publications have been published within this topic receiving 554989 citations.

Kinetics of deep oxidation of n-hexane and toluene over Pt/Al2O3 catalysts: Platinum crystallite size effect

Abstract: The kinetics of n-hexane and toluene complete oxidation has been studied over 0.12% Pt/Al2O3 catalysts. Measurements were performed in an external recycle reactor. Reaction rates were measured as a function of temperature and reactants concentrations for two platinum crystallite sizes, 1.0 and 15.5 nm. The turnover frequency (TOF) for the oxidation of both hydrocarbons is about 10 times higher for the 15.5 nm than for the 1.0 nm Pt crystallite size. The reaction constants are calculated according to Mars van Krevelen (MVK) mechanism. The oxygen chemisorption rate constant (kO) is the same during the n-hexane and the toluene oxidation for each sizes of platinum crystallite. For both hydrocarbons the oxygen chemisorption rate constant and the surface reaction rate constant (ki) are higher for 15.5 nm than for 1.0 nm crystallite size. The activation energy for kO decreases with the increase of the Pt crystallite size. The activation energy for ki is independent on the Pt crystallite size for both hydrocarbons. The values of kinetic constants reveal that the increase of the reaction rate for large Pt crystallites could be related to the lower activation energy for kO. This implies that on large Pt crystallites oxygen is held on Pt atoms with a lower bond strength that on small Pt crystallites, which explains the structure sensitivity found for n-hexane and toluene oxidation.

Synthesis of highly coke resistant Ni nanoparticles supported MgO/ZnO catalyst for reforming of methane with carbon dioxide

Abstract: Ni-nanoparticles supported on MgO promoted nanocrytalline zinc oxide catalyst was prepared by hydrothermal method in presence of cationic surfactant cetyltrimethylammonium bromide. The catalyst showed very good activity for the reforming of methane with carbon dioxide to produce synthesis gas, where H 2 /CO ratio was almost 1 and the catalyst showed no deactivation for more than 100 h. The prepared catalyst was characterized using the analytical techniques like N 2 -physisorption studies, X-ray diffraction (XRD), Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), Temperature programmed desorption (TPD), Temperature programmed reduction (TPR), Temperature programmed oxidation (TPO), H 2 -chemisorpton, Thermo-gravimetric analysis (TGA), Inductively coupled plasma atomic emission spectroscopy (ICP-AES), X-ray photoelectron spectroscopy (XPS), and Extended X-ray absorption fine structure (EXAFS). Transmission electron microscopy and H 2 -chemisorption analysis indicated that highly dispersed Ni nanoparticles with average size 5.7 nm, present on ZnO when MgO was added with the catalyst. The strong Ni–ZnO interaction was evidenced from TPR and EXAFS analysis. The presence of highly dispersed Ni nanoparticles and strong metal support interaction enhanced the reduction behaviour of the Ni-MgO/ZnO catalyst. The presence of MgO increased the adsorption behaviour of CO 2 , enhanced the dissociation of CO 2 and accelerated the carbon elimination.

Kinetic study and the effect of particle size on low temperature CO oxidation over Pt/TiO2 catalysts

Abstract: A series of Pt/TiO2 catalysts with various Pt particle sizes were prepared and tested for low temperature CO oxidation. The effect of Pt particle sizes on the reaction was investigated. It was found that turnover frequencies based on Pt dispersion varied as declined with increasing Pt particle size as a function of d−0.86. However, turnover frequency based on Pt atoms located on the periphery of Pt–TiO2 interface remained constant at 40 °C, implying that these periphery Pt atoms were the active sites. Kinetic study was conducted to investigate reaction pathway on the catalyst. The derived power rate law expression was r = 1.98 x 10−7 PCO0.29PO20.19 at 40 °C. Based on the kinetic results, elementary steps of this reaction were proposed, which involved chemisorption of CO on Pt atoms and chemisorption of O2 on TiO2 and a reaction of these two species at the Pt–TiO2 interface.