Faster Algorithms for Bound-Consistency of the Sortedness and the Alldifferent Constraint

We present narrowing algorithms for the sortedness and the alldifferent constraint which achieve bound-consistency. The algorithm for the sortedness constraint takes as input 2n intervals X1 , ..., Xn , Y1 , ..., Yn from a linearly ordered set D. Let S denote the set of all tuples t 2 X1 Xn Y1 Yn such that the last n components of t are obtained by sorting the first n components. Our algorithm determines whether S is non-empty and if so reduces the intervals to bound-consistency. The running time of the algorithm is asymptotically the same as for sorting the interval endpoints. In problems where this is faster than O(n log n), this improves upon previous results. The algorithm for the alldifferent constraint takes as input n integer intervals Z1 , ..., Zn . Let T denote all tuples t 2 Z1 Zn where all components are pairwise different. The algorithm checks whether T is non-empty and if so reduces the ranges to bound-consistency. The running time is also asymptotically the same as for sorting the interval endpoints. When the constraint is for example a permutation constraint, i.e. Z i [1; n] for all i, the running time is linear. This also improves upon previous results

Compensation effect and volcano curve in toluene hydrogenation catalyzed by transition metal sulfides

Guernalec, N. Geantet, C. Cseri, T. Vrinat, M. Toulhoat, H. Raybaud, P.Within the framework of volcano curves, a kinetic study of toluene hydrogenation catalyzed by transition metal sulfides highlights the variation of the apparent kinetic parameters as a function of the ab initio sulfur-metal bond energy descriptor and sulfo-reductive reaction conditions

Dual Effect of H

Recent progresses achieved by quantum molecular modeling techniques enabled the rational interpretation of catalytic trends of series of transition metal sulfide catalysts. Empirical volcano curves can be explained by microkinetic models including chemical descriptors calculated at an ab initio level. This approach was successfully applied in the field of hydrotreating catalysis using the metal-sulfur bond energy descriptor. The purpose of the present work was to extend this approach by exploring the effect of reaction conditions (partial pressure of H2S) on the volcano curve. On the one hand, high resolution transmission electron microscopy (HRTEM) images combined with molecular modeling of morphologies and surfaces exposed by catalysts provide an estimate of the number of potential active sites. This approach is illustrated for the relevant case of unsupported or alumina supported Co9S8 sulfide. On the other hand, an improved microkinetic model is proposed in order to reflect the dual effects of H2S observed in the hydrogenation of toluene : an inhibiting effect for MoS2, Rh2S3, RuS2, NiMoS and a promoting effect for Cr2S3 et Co9S8. The experimental results and kinetic modeling reveal that the maximum of the volcano curve and thus the optimal sulfide catalyst depends closely on the partial pressure of H2S