Search results for "heterogeneous"
showing 10 items of 460 documents
Understanding selective reduction reactions with heterogeneous Pd and Pt : climbing out of the black box
2016
Total oxidation of propene at low temperature over Co3O4–CeO2 mixed oxides: Role of surface oxygen vacancies and bulk oxygen mobility in the catalyti…
2008
Liotta, L. F. Ousmane, M. Di Carlo, G. Pantaleo, G. Deganello, G. Marci, G. Retailleau, L. Giroir-Fendler, A.; Co3O4, CeO2 and Co3O4-CeO2 mixed oxides with Co/Ce nominal atomic ratio 0.1:5, prepared by co-precipitation method with sodium carbonate, were tested in the oxidation of propene under lean condition and the catalyst stability was checked by performing three consecutive heating-cooling cycles. Characterization of the textural properties were performed by surface area measurement BET, X-ray diffraction (XRD) and scanning electron microscopy (SEM) measurements. Among the Co3O4-CeO2 mixed oxides, Co3O4 (30 Wt%)-CeO2 (70 wt%) gives the best activity attaining full propene conversion at …
Understanding Structure and Stability of Monoclinic Zirconia Surfaces from First-Principles Calculations
2017
Under the water-rich pre-treatment and/or reaction conditions, structure and chemistry of the monoclinic zirconia surfaces are strongly influenced by oxygen vacancies and incorporated water. Here, we report a combined first-principles and atomistic thermodynamics study on the structure and stability of selected surfaces of the monoclinic zirconia. Our results indicate that among the studied surfaces, the most stable (111) surface is the least vulnerable towards oxygen vacancies in contrast to the less stable (011) and (101) surfaces, where formation of oxygen vacancies is energetically more favorable. Furthermore, we present a vigorous, systematic screening of water incorporation onto the s…
Heterogeneous photocatalysis: guidelines on experimental setup, catalyst characterization, interpretation, and assessment of reactivity
2019
Soon after the publication of the first pioneering works on heterogeneous photocatalysis, the number of papers on this topic continuously increased. This intriguing field of research is very complex as it endows with an interdisciplinary overview that involves different aspects of chemistry, physics, material and environmental sciences. Even if photocatalytic applications in real processes are often difficult to be implemented and scaled-up, investigations at laboratory scale are easy to be performed, and in some cases they may give rise to misconceptions. For this reason, the present work aims to sum up most of the common experimental techniques and procedures generally used in heterogeneo…
Catalytic applications of TiO2
2021
Abstract The use of TiO2 as heterogeneous catalyst and/or active support for metals or other oxides is here reported. Many reactions of industrial relevance involve, in fact, titania-based catalysts, among them, NOx abatement, Fischer–Tropsch and water–gas shift, Deacon and Claus processes, hydrodesulfurizations and hydrogenations, selective reductions and selective oxidations. This chapter aims to discuss the main applications of TiO2, in its different forms, as effective support or catalyst for thermocatalytic and photo-thermocatalytic reactions, focusing on the role of its structural and physicochemical properties on the catalytic performance (activity, selectivity, stability).
Thermodynamics: Classical Framework
2016
This chapter starts with a summary of the thermodynamic potentials and the relationships between them which are obtained from Legendre transformation. This is followed by an excursion to some important global properties of materials such as specific heat, expansion coefficients and others. The thermodynamic relations provide the basis for a discussion of continuous changes of state which are illustrated by the Joule-Thomson effect and the Van der Waals gas. These are models which are more realistic than the ideal gas. The discussion of Carnot cycles leads to and illustrates the second and third laws of thermodynamics. The chapter closes with a discussion of entropy as a concave function of …
Random Walk and Diffusion
2014
The concept of random walk as introduced by Einstein is introduced. It is shown that a random walk on a lattice can be descrbed by a difference equation, which becomes a partial differential equation (diffusion equation) in the continuum limit. The equation is solved with the help of Fourier and Laplace transformations.
Photolytic and TiO2-Assisted Photodegradation of Aqueous Solutions of Tetracycline
2004
Aqueous solutions of tetracycline were UV-irradiated in homogeneous and heterogeneous systems. Tetracycline disappeared in both systems, but the presence of TiO2 accelerated the photodegradation of the antibiotic in comparison with direct photolysis. The rate of decomposition was dependent on the concentration of tetracycline and its degradation on the surface of TiO2 can be described by means of a pseudo-first order kinetics. Photolysis involved only the photodeamination of tetracycline and a partial mineralization. Unlikely, the treatment with TiO2 and UV-light resulted in a complete mineralization of the antibiotic drug.
ULTRASONIC WAVES IN HETEROGENEOUS MATERIALS - MECHANICAL CHARACTERIZATION OF HETEROGENEOUS MATERIALS BY MEANS OF ULTRASONIC TESTS AND NUMERICAL MODEL…
2014
This Ph.D thesis treats the propagation of ultrasonic waves in heterogeneous materials. It is widely known how waves propagate in homogeneous materials like metallic ones. But very few aspects are known about the propagation in the heterogeneous materials because of the complex behavior regarding these materials. The heterogeneity can be related with the intrinsic properties, elastic and chemical, of each phase of the material, or with the periodic or random arrangement of inclusions of constant or different shapes. Concrete is a common case. In this work the first chapter gives a description of the main characteristics of heterogeneous materials.. In the second one, the methods of inspecti…
High-density electromyography activity in various hamstring exercises
2019
Proximal‐distal differences in muscle activity are rarely considered when defining the activity level of hamstring muscles. The aim of this study was to determine the inter‐muscular and proximal‐distal electromyography (EMG) activity patterns of hamstring muscles during common hamstring exercises. Nineteen amateur athletes without a history of hamstring injury performed 9 exercises, while EMG activity was recorded along the biceps femoris long head (BFlh) and semitendinosus (ST) muscles using 15‐channel high‐density electromyography (HD‐EMG) electrodes. EMG activity levels normalized to those of a maximal voluntary isometric contraction (%MVIC) were determined for the eccentric and concentr…