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.

Methanol dehydration to dimethylether over Al2O3 catalysts

Abstract: The vapor-phase dehydration of methanol to dimethylether (DME) has been investigated over a set of eight commercial and self-prepared Al2O3 catalysts with different physicochemical characteristics. Materials were characterized with respect to their textural properties (B.E.T. and B.J.H. methods), acidity (TPD of ammonia), crystallinity, phase composition and morphology (XRD, TEM). Catalytic activity and selectivity have been evaluated in the temperature range of 150–400 °C in the absence and in the presence of water in the feed. The adsorption/desorption properties of catalysts toward methanol and water as well as some aspects of the reaction mechanism have been investigated with the use of transient-MS and in situ DRIFTS techniques. Results show that catalytic activity per gram of catalyst varies by two orders of magnitude from one sample to another in a manner that depends on the physicochemical characteristics of Al2O3. All samples investigated are highly selective to DME at temperature lower than ca. 325 °C, whereas small amounts of CO and CH4 are formed at higher reaction temperatures. As a general trend, activity per gram of catalyst increases with increase of SSA (amount of acidic surface sites) and is enhanced over samples characterized by high crystallinity and relatively high porosity. The presence of water vapor in the feed suppresses conversion of methanol at a given temperature due to competition for active sites and thermodynamic limitations. Methanol adsorbs on the Al2O3 surface both molecularly and in the form of methoxy species. Evidence is provided that formation of DME involves weakly adsorbed methoxy species whereas methoxy species that are bonded more strongly on the Al2O3 surface are converted to surface formates, which decompose to yield CO, H2 and CH4 in the gas-phase.

Deposition of aluminium on magnesium by a CVD process

Abstract: The feasibility of Al deposition on Mg and Mg-alloys by means of Fluidized Bed CVD (FBCVD) or Pack Bed CVD (PBCVD) processes is evaluated by means of thermochemical computations and experimentation. For the thermodynamic analysis, a closed system consisting of Al2O3 as filler, Al as donor, halide or halide compound as process activator and Ar as inert gas was considered. Different activators were evaluated in the temperature range from 280 to 420 °C. Among them NH4Cl, and iodine are the best candidate compounds due to the relatively high partial pressures of the formed aluminium halides. The analysis indicates that the deposition of aluminium on magnesium takes place through a displacement reaction mechanism on the surface followed by limited inward diffusion of Al. Pack bed experiments have shown that by use of NH4Cl activator, aluminium is deposited locally. Iodine activator results in more even but porous coatings. The process is simple and promising for the formation of corrosion and wear resistant coatings on magnesium. However, in order to provide a long-term protection, the coating should be deposited under conditions that eliminate through-thickness pores. Further developments are required in order to achieve dense, pore-free coatings.

Multilane traffic flow dynamics: Some macroscopic considerations

Abstract: The subject of macroscopic modelling and analysis of multilane homodirectional freeway flow is discussed in this paper. Two existing models are extended and treated numerically so that their simplifying assumptions are relaxed. Further, two new formulations are developed; the first is two dimensional with respect to space (i.e. in addition to the street length it includes the street width explicitly) while the second is one dimensional high order dynamic (i.e. it incorporates a momentum equation in order to take into acount acceleration and inertia effects). All modelling alternatives are implemented into a few exemplary situations representing uninterrupted and interrupted flow conditions. Finally, comparisons with aggregate results obtained from microscopic simulation are presented.