Lifting representations of finite reductive groups: a character relation

Given a connected reductive group $\tilde{G}$ over a finite field $k$, and a semisimple $k$-automorphism $\varepsilon$ of $\tilde{G}$ of finite order, let $G$ denote the connected part of the group of $\varepsilon$-fixed points. Then there exists a lifting from packets of representations of $G(k)$ to packets for $\tilde{G}(k)$. In the case of Deligne-Lusztig representations, we show that this lifting satisfies a character relation analogous to that of Shintani.Comment: Minor errors corrected, proofs streamlined. Main result slightly generalized, restated to emphasize analogy with stabilit

On the elliptic nonabelian Fourier transform for unipotent representations of p-adic groups

In this paper, we consider the relation between two nonabelian Fourier transforms. The first one is defined in terms of the Langlands-Kazhdan-Lusztig parameters for unipotent elliptic representations of a split p-adic group and the second is defined in terms of the pseudocoefficients of these representations and Lusztig's nonabelian Fourier transform for characters of finite groups of Lie type. We exemplify this relation in the case of the p-adic group of type G_2.Comment: 17 pages; v2: several minor corrections, references added; v3: corrections in the table with unipotent discrete series of G

The structure of blocks with a Klein four defect group

We prove Erdmann’s conjecture [16] stating that every block with a Klein four defect group has a simple module with trivial source, and deduce from this that Puig’s finiteness conjecture holds for source algebras of blocks with a Klein four defect group. The proof uses the classification of finite simple groups

Adsorption and reaction of CO on (Pd–)Al2O3 and (Pd–)ZrO2: vibrational spectroscopy of carbonate formation

γ-Alumina is widely used as an oxide support in catalysis, and palladium nanoparticles supported by alumina represent one of the most frequently used dispersed metals. The surface sites of the catalysts are often probed via FTIR spectroscopy upon CO adsorption, which may result in the formation of surface carbonate species. We have examined this process in detail utilizing FTIR to monitor carbonate formation on γ-alumina and zirconia upon exposure to isotopically labelled and unlabelled CO and CO2. The same was carried out for well-defined Pd nanoparticles supported on Al2O3 or ZrO2. A water gas shift reaction of CO with surface hydroxyls was detected, which requires surface defect sites and adjacent OH groups. Furthermore, we have studied the effect of Cl synthesis residues, leading to strongly reduced carbonate formation and changes in the OH region (isolated OH groups were partly replaced or were even absent). To corroborate this finding, samples were deliberately poisoned with Cl to an extent comparable to that of synthesis residues, as confirmed by Auger electron spectroscopy. For catalysts prepared from Cl-containing precursors a new CO band at 2164 cm−1 was observed in the carbonyl region, which was ascribed to Pd interacting with Cl. Finally, the FTIR measurements were complemented by quantification of the amount of carbonates formed via chemisorption, which provides a tool to determine the concentration of reactive defect sites on the alumina surface

Determining adsorbate configuration on alumina surfaces with 13C nuclear magnetic resonance relaxation time analysis

Relative strengths of surface interaction for individual carbon atoms in acyclic and cyclic hydrocarbons adsorbed on alumina surfaces are determined using chemically resolved 13C nuclear magnetic resonance (NMR) T1 relaxation times. The ratio of relaxation times for the adsorbed atoms T1,ads to the bulk liquid relaxation time T1,bulk provides an indication of the mobility of the atom. Hence a low T1,ads/T1,bulk ratio indicates a stronger surface interaction. The carbon atoms associated with unsaturated bonds in the molecules are seen to exhibit a larger reduction in T1 on adsorption relative to the aliphatic carbons, consistent with adsorption occurring through the carbon-carbon multiple bonds. The relaxation data are interpreted in terms of proximity of individual carbon atoms to the alumina surface and adsorption conformations are inferred. Furthermore, variations of interaction strength and molecular configuration have been explored as a function of adsorbate coverage, temperature, surface pre-treatment, and in the presence of co-adsorbates. This relaxation time analysis is appropriate for studying the behaviour of hydrocarbons adsorbed on a wide range of catalyst support and supported-metal catalyst surfaces, and offers the potential to explore such systems under realistic operating conditions when multiple chemical components are present at the surface

Monitoring Hydrotreating Catalysts Synthesis and Deactivation using Raman Spectrometry

Raman spectrometry has become a popular characterization technique for hydrotreatment catalysts: it provides important information on chemical structures along all the synthesis cycle, from the impregnation solution to the sulfided catalyst. Aspects of physico-chemical processes taking place on the catalyst surface can be monitored using this technique. This article describes some examples where Raman spectrometry has been used to evaluate the impact of experimental parameters (choice of metallic precursors, presence of impurity, influence of calcination temperature, coke deposit) on the catalyst structure

Probing the structure of iron(III)-mitriloacetate complexes in aqueous solution using Raman spectroscopy

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DFT Study of the Interaction of a single Palladium Atomwith γ\gamma -Alumina Surfaces: the Role of Hydroxylation

International audienceConsidering the crucial role of the $\gamma$-alumina solid phase in heterogeneous catalysis as a support of numerous active phases, a revised and improved atomistic description of $\gamma$-alumina surfaces was mandatory to furnish new highlights in the field of $\gamma$-alumina supported catalysts. Two important scientific challenges in heterogeneous catalysis have recently been taken up by modern Density Functional Theory (DFT) simulations. The first challenge described in this paper is to show that DFT calculations combined with simple thermodynamic model provide an elegant way of determining the stable chemical species at the $\gamma$-alumina surface (such as hydroxyls or Lewis sites) as a function of reaction conditions. The (100) and (110) surfaces exposed mainly by the $\gamma$-alumina nanocrystallites exhibit two distinct behaviors regarding their hydroxylation states. The (110) surface maintains a high degree of hydroxyl coverage even at high temperature, whereas the (100) surface is dehydrated at low temperature. This first important step being achieved, a second challenge in heterogeneous catalysis is the interaction of the active phase with $\gamma$-alumina. In the second part of this paper, we present the adsorption of a single palladium atoms (Pd1) on the (100) and (110) $\gamma$-alumina surfaces. By determining the potential energy surface of Pd on $\gamma$-alumina, the relationship between structure and metal-oxide interaction energy at the interface is depicted. Furthermore, new insights are provided on the chemisorption and diffusion processes of Pd on the two surfaces. The adsorption energy and the hopping rate of Pd are strongly reduced when the hydroxyl coverage increases such as found on the (110) surface. As a consequence, the surface hydroxylation appears as a key parameter for understanding the active phase/support interaction and enables the interpretation of available experimental data

New insights into the role of glycol-based additives in the improvement of hydrotreatment catalyst performances

International audienceThe introduction of a glycol-type additive in hydrotreating catalysts is an efficient procedure to improve catalytic activity. Nevertheless, controversial explanations about the activity enhancement mechanism exist in the literature. This may be due to different catalyst preparation procedures, different location of the additive impregnation step, or simply because several phenomena are implied in this improvement. The aim of this work is thus to rationalize the roles of these additives with respect to (i) species present in the impregnation solution as well as on the catalyst surface and (ii) the preparation step where the additive impregnation is performed, i.e. after drying or after calcination. Different impregnation solutions have been used containing (a) ammonium heptamolybdate or cobaltomolybdate heteropolyanions for CoMo catalysts and (b) phosphomolybdate heteropolyanion with different P/Mo molar ratio for CoMoP catalysts. Surface species have been thoroughly characterized for dried and calcined catalysts prior to and after the additive impregnation using triethyleneglycol. For all dried and calcined CoMo and CoMoP catalysts, a redissolution phenomenon has been evidenced after the additive impregnation, leading to the formation of the Anderson heteropolyanion AlMo6O24H6 3-. This redissolution phenomenon is however limited by the low solubility of AlMo6O24H6 3-. Moreover, in the case of CoMoP dried catalysts (P/Mo molar ratio 0.4), characterization of additive-containing catalysts evidenced PCoMo11O40 7- formation. Redissolution and redispersion due to the additives are thus enhanced because phosphomolybdic species have a much higher solubility than AlMo6O24H6 3-. Similar observations, although less pronounced, may be drawn for calcined catalysts. Indeed, a stronger precursor-support interaction has been created during calcination. Catalysts performances were evaluated in toluene hydrogenation and activities obtained match perfectly