1,250 research outputs found
Thermal stability of the cu-ceo2 interface on silica and alumina, and its relation with activity in the oxidation reaction of co and the decomposition of n2o
Indexación: Scopus; Scielo.The effect of the support on the formation of the Cu-CeO2 interface and its thermal stability after calcination at 500, 700 and 900 °C is studied. The supports used are SiO2, because of its inert character, and Al2O3, because it can interact with the Cu and Ce species on the surface. The catalysts were characterized by BET, XRD, UV-vis DRS, and TPR with H2. The catalytic activity in the CO oxidation reactions with O2 at low temperature and the decomposition of N2O were selected to visualize the effect of temperature on the concentration of Cu-CeO2 interfacial sites. The results show that at a calcination temperature of 500 °C the formation of the Cu-CeO2 interface is favored over the SiO2 support. However, the stability of the Cu-CeO2 interface on SiO2 is much lower than on Al2O3, causing a substantial decrease of the interfacial sites calcining at 700 °C, and segregation of the Cu and Ce species on the surface of the silica, with complete loss of the catalytic activity in both reactions when calcining at 900 °C. In contrast, on alumina the Cu-CeO2 interface is more stable and presents a significant catalytic activity in both reactions, even when calcining at 900 °C. The characterization results show that the sintering process of Cu species and CeO2 particles is less on the alumina support due to the greater interaction of the Cu and Ce with this support. © 2018 Sociedad Chilena de Quimica.all rights reserved.https://scielo.conicyt.cl/scielo.php?script=sci_arttext&pid=S0717-97072018000304102&lng=en&nrm=iso&tlng=e
Activity of alumina supported fe catalysts for N2O decomposition: Effects of the iron content and thermal treatment
Indexación: Scopus.The activity of Fe2O3/Al2O3 catalysts prepared by impregnation of Al2O3 with different amounts of Fe and calcination temperatures (650 and 900 °C) in the direct N2O decomposition reaction was studied. High calcination temperature was introduced to study the effect of "aging", which are the conditions prevailing in the process-gas option for N2O abatement. The catalysts were characterized by BET, XRD, UV-DRS, and H2-TPR. The incorporation of Fe promotes the alumina phase transition (g-Al2O3 to a-Al2O3) when the catalysts are calcined at 900 °C, which is accompanied by a decrease in the specifc area. The activity of the catalysts and the specifc surface area depend on Fe loading and calcination temperature. It was found that highly dispersed Fe species are more active than bulk type Fe2O3 particles. We conclude that Fe2O3/Al2O3 catalysts prepared by impregnation method are active in the decomposition of N2O, to be used at low or high reaction temperatures (tail-gas or process-gas treatments, respectively), as part of nitric acid production plant. © 2018 Sociedad Chilena de Quimica. All rights reserved.https://scielo.conicyt.cl/pdf/jcchems/v62n4/0717-9324-jcchems-62-04-3752.pd
Effective description of brane terms in extra dimensions
We study how theories defined in (extra-dimensional) spaces with localized
defects can be described perturbatively by effective field theories in which
the width of the defects vanishes. These effective theories must incorporate a
``classical'' renormalization, and we propose a renormalization prescription a
la dimensional regularization for codimension 1, which can be easily used in
phenomenological applications. As a check of the validity of this setting, we
compare some general predictions of the renormalized effective theory with
those obtained in a particular ultraviolet completion based on deconstruction.Comment: 28 page
Comment on SU(16) grand unification
In a recent paper on SU(16) grand unification, because of the presence of
intermediate-energy gauge groups containing products of U(1) factors which are
not orthogonal among themselves, the renormalization-group treatment has a few
small errors. I correct it. I emphasize that one should not switch gauge
couplings at the various thresholds. It is easier, and it avoids errors, to use
throughout the gauge couplings of the standard model, and compute at each
threshold, in the usual way, the extra contributions to the beta functions from
the extra non-decoupled fields. I also point out that the SU(16) grand
unification theory, due to the large number of scalars present in it, is not
asymptotically free. It becomes a strong-coupling theory at energies only
slightly larger than the unification scale.Comment: 5 latex pages, 2 tables, no figure
Lorentz Violation in Extra Dimensions
In theories with extra dimensions it is well known that the Lorentz
invariance of the -dimensional spacetime is lost due to the compactified
nature of the dimensions leaving invariance only in 4d. In such theories
other sources of Lorentz violation may exist associated with the physics that
initiated the compactification process at high scales. Here we consider the
possibility of capturing some of this physics by analyzing the higher
dimensional analog of the model of Colladay and Kostelecky. In that scenario a
complete set of Lorentz violating operators arising from spontaneous Lorentz
violation, that are not obviously Planck-scale suppressed, are added to the
Standard Model action. Here we consider the influence of the analogous set of
operators which break Lorentz invariance in 5d within the Universal Extra
Dimensions picture. We show that such operators can greatly alter the
anticipated Kaluza-Klein(KK) spectra, induce electroweak symmetry breaking at a
scale related to the inverse compactification radius, yield sources of parity
violation in, e.g., 4d QED/QCD and result in significant violations of
KK-parity conservation produced by fermion Yukawa couplings, thus destabilizing
the lightest KK particle. LV in 6d is briefly discussed.Comment: 26 pages, 2 figures; additional references and discussio
Off-the-Wall Higgs in the Universal Randall-Sundrum Model
We outline a consistent Randall-Sundrum (RS) framework in which a fundamental
5-dimensional Higgs doublet induces electroweak symmetry breaking (EWSB). In
this framework of a warped Universal Extra Dimension, the lightest Kaluza-Klein
(KK) mode of the bulk Higgs is tachyonic leading to a vacuum expectation value
(vev) at the TeV scale. The consistency of this picture imposes a set of
constraints on the parameters in the Higgs sector. A novel feature of our
scenario is the emergence of an adjustable bulk profile for the Higgs vev. We
also find a tower of non-tachyonic Higgs KK modes at the weak scale. We
consider an interesting implementation of this ``Off-the-Wall Higgs'' mechanism
where the 5-dimensional curvature-scalar coupling alone generates the tachyonic
mode responsible for EWSB. In this case, additional relations among the
parameters of the Higgs and gravitational sectors are established. We discuss
the experimental signatures of the bulk Higgs in general, and those of the
``Gravity-Induced'' EWSB in particular.Comment: 27 pages, 4 figure
Antisymmetric tensor unparticle and the radiative lepton flavor violating decays
We study the contribution of the tensor unparticle mediation to the branching
ratios of the radiative lepton flavor violating decays and predict a
restriction region for free parameters of the scenario by using experimental
upper limits. We observe that the branching ratios of the radiative lepton
flavor violating decays are sensitive to the fundamental mass scales of the
scenario and to the scale dimension of antisymmetric tensor unparticle. We
obtain a more restricted set for the free parameters in the case of the
\mu\rightarrow e \gamma decayComment: 15 pages, 10 figure
Tree FCNC and non-unitarity of CKM matrix
We discuss possible signatures of the tree level FCNC, which results from the
non-unitarity of CKM matrix. We first define the unitaity step-by-step, and
possible test of the non-unitaity through the 4-value-KM parametrization. We,
then, show how the phase angle of the unitary triangle would change in case of
the vector-like down quark model. As another example of tree FCNC, we
investigate the leptophobic model and its application to the recent
mixing measurements.Comment: Talk given at Neutrino Masses and Mixings 2006 (NMM2006), Shizuoka,
Japan (December 2006
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