University of Patras

About: University of Patras is a education organization based out in Pátrai, Greece. It is known for research contribution in the topics: Population & Catalysis. The organization has 13372 authors who have published 31263 publications receiving 677159 citations. The organization is also known as: Panepistímio Patrón.

Selective methanation of CO over supported Ru catalysts

Abstract: The catalytic performance of supported ruthenium catalysts for the selective methanation of CO in the presence of excess CO 2 has been investigated with respect to the loading (0.5–5.0 wt.%) and mean crystallite size (1.3–13.6 nm) of the metallic phase as well as with respect to the nature of the support (Al 2 O 3 , TiO 2 , YSZ, CeO 2 and SiO 2 ). Experiments were conducted in the temperature range of 170–470 °C using a feed composition consisting of 1%CO, 50% H 2 15% CO 2 and 0–30% H 2 O (balance He). It has been found that, for all catalysts investigated, conversion of CO 2 is completely suppressed until conversion of CO reaches its maximum value. Selectivity toward methane, which is typically higher than 70%, increases with increasing temperature and becomes 100% when the CO 2 methanation reaction is initiated. Increasing metal loading results in a significant shift of the CO conversion curve toward lower temperatures, where the undesired reverse water–gas shift reaction becomes less significant. Results of kinetic measurements show that CO/CO 2 hydrogenation reactions over Ru catalysts are structure sensitive, i.e., the reaction rate per surface metal atom (turnover frequency, TOF) depends on metal crystallite size. In particular, for Ru/TiO 2 catalysts, TOFs of both CO (at 215 °C) and CO 2 (at 330 °C) increase by a factor of 40 and 25, respectively, with increasing mean crystallite size of Ru from 2.1 to 4.5 nm, which is accompanied by an increase of selectivity to methane. Qualitatively similar results were obtained from Ru catalysts supported on Al 2 O 3 . Experiments conducted with the use of Ru catalyst of the same metal loading (5 wt.%) and comparable crystallite size show that the nature of the metal oxide support affects significantly catalytic performance. In particular, the turnover frequency of CO is 1–2 orders of magnitude higher when Ru is supported on TiO 2 , compared to YSZ or SiO 2 , whereas CeO 2 - and Al 2 O 3 -supported catalysts exhibit intermediate performance. Optimal results were obtained over the 5%Ru/TiO 2 catalyst, which is able to completely and selectively convert CO at temperatures around 230 °C. Addition of water vapor in the feed does not affect CO hydrogenation but shifts the CO 2 conversion curve toward higher temperatures, thereby further improving the performance of this catalyst for the title reaction. In addition, long-term stability tests conducted under realistic reaction conditions show that the 5%Ru/TiO 2 catalyst is very stable and, therefore, is a promising candidate for use in the selective methanation of CO for fuel cell applications.

Development of nickel based catalysts for the transformation of natural triglycerides and related compounds into green diesel: a critical review

Abstract: The accumulation of greenhouse gases in the atmosphere resulting from the extensive use of fossil fuels and the depletion of oil reserves due to the increasing demands for energy compel the progressive replacement of fossil fuels by renewable energy sources among which biomass. Triglycerides-based biomass such as plant oils, animal fats, waste cooking and micro-algal oils should be upgraded by transesterification, cracking/hydrocracking and selective deoxygenation (SDO) to provide, respectively, biodiesel (fatty acid methyl esters), the so-called organic liquid product (mixture of hydrocarbons in the range of gasoline, kerosene and diesel) and green diesel (hydrocarbons in the diesel range). Problems related to the production, storage and use of the already produced biodiesel shifts the research to the second and third upgrading route. Intensive work in the last ten years has shown that the noble metals (mainly palladium) and the NiMo, CoMo and NiW sulphide catalysts supported on high surface area carriers, are promising concerning SDO for producing green diesel in the context of a stand-alone process of natural triglycerides. However, the high cost of the noble metal catalysts and the eventual S-contamination of the end product when using the aforementioned sulfided catalysts have rise intensive parallel research in the last three years for developing low cost Ni-based non-sulphide catalysts. The research effort in this area seems to focus on the following issues: (i) effect of supports, nickel loading and promoters on the catalytic performance of Ni-based non-sulphide catalysts, (ii) SDO pathways over these catalysts, (iii) effect of preparation method on their catalytic performance, (iv) comparison of nickel catalysts with other metallic and sulphide catalysts, (v) development of nickel phosphide catalysts, (vi) development of NiMo, CoMo or NiW non-sulphide catalysts (reduced, carbides, nitrides) and (vii) deoxygenation in low or no hydrogen containing atmosphere. In the present article we critically review the contributions relevant to each one of the aforementioned subjects for obtaining a synthetic picture concerning the progress pointed out so far and the future perspectives as well.

Vibration isolation using open or filled trenches

Abstract: The problem of structural isolation from ground transmitted vibrations by open or infilled trenches under conditions of plane strain is numerically studied. The soil medium is assumed to be linear elastic or viscoelastic, homogeneous and isotropic. Horizontally propagating Rayleigh waves or waves generated by the motion of a rigid foundation or by surface blasting are considered in this work. The formulation and solution of the problem is accomplished by the boundary element method in the frequency domain for harmonic disturbances or in conjunction with Laplace transform for transient disturbances. The proposed method, which requires a discretisation of only the trench perimeter, the soil-foundation interface and some portion of the free soil surface on either side of the trench appears to be better than either finite element or finite difference techniques. Some parametric studies are also conducted to assess the importance of the various geometrical, material and dynamic input parameters and provide useful guidelines to the design engineer.

Adipokines in periaortic and epicardial adipose tissue: differential expression and relation to atherosclerosis.

Abstract: Aim: Adipokines are protein products of adipose tissue with paracrine and endocrine actions, which have been implicated in the pathogenesis of cardiovascular disease. Locally produced adipokines, especially by periadventitial adipose tissue, may affect vascular physiology and pathology. We investigated the expression of adiponectin, visfatin, leptin and novel adipokines chemerin and vaspin in human periaortic and epicardial adipose tissue, as well as their correlation to aortic and coronary atherosclerosis.Methods: Standard immunohistochemical staining for the adipokines was performed on samples of human periaortic, pericoronary and apical epicardial adipose tissue. Atherosclerotic lesions of the adjacent vascular wall were assessed using the AHA classification.Results: Adipokines were expressed in periadventitial and apical epicardial adipose tissue and - except for adiponectin - in vascular smooth muscle cells and foam cells in atherosclerotic lesions. Aortic atherosclerosis was positively correlated with chemerin, vaspin, visfatin and leptin periaortic fat expression. Coronary atherosclerosis was positively correlated with chemerin and visfatin pericoronary fat expression. Adipose tissue adiponectin expression was negatively correlated to atherosclerosis in both locations. Expression of adipokines in apical epicardial fat was not associated with atherosclerosis.Conclusions: Our results show: a) a different expression pattern of adiponectin, visfatin, leptin, chemerin and vaspin in periaortic, pericoronary and apical epicardial adipose tissue, b) a correlation of these adipokines with either aortic or coronary atherosclerosis or both in a pattern characteristic for each adipokine and suggest that locally produced adipokines might differently affect the atherosclerotic process in different locations.