In situ QXAS study of sulfidation/oxidative regeneration reactions of zinc molybdate (ZnMoO4) and ZnO-MoO3 materials.

Recent technologies such as those using coal, natural gas or biomass as fuel are often facing the challenge of removing H2S impurities. Among the various existing routes for sulfur removal, the conversion of transition metal oxides into sulfides is often considered for deep gas purification. The ideal regenerative system, preventing waste generation, should combine a high affinity material towards H2S and an easy way for its regeneration into the initial oxide form. The present paper describes the reactivity of the ZnMoO4 mixed oxide material and ZnO-MoO3 oxides mixture as potential candidates for the regenerative H2S sorption process. The use of the QXAS technique allowed us to get time resolved information about both sulfidation and oxidative regeneration processes at Mo and Zn K-edges. Faced with the complexity of gas-solid reactions involving several phases, QXAS in combination with multivariate data analysis enabled us to follow the sulfidation and oxidative regeneration kinetics of both materials, with a description of the evolution of several intermediate phases. Both Mo and Zn K-edge spectroscopic data were analyzed and comparison of the evolution of ternary oxides containing the two elements proved to be an effective way for validating the results.

Use of the Distance Transform for Integration of Local Measurements: Principle and Application in Chemical Engineering.

We propose an original methodology to integrate local measurement for nontrivial object shape. The method employs the distance transform of the object and least-square fitting of numerically computed weighting functions extracted from it. The method is exemplified in the field of chemical engineering by calculating the global metal concentration in catalyst grains from uneven metal distribution profiles. Applying the methodology on synthetic profiles with the help of a very simple deposition model allows us to evaluate the accuracy of the method. For high symmetry objects such as an infinite cylinder, relative errors on global concentration are lower than 1% for well-resolved profiles. For a less symmetrical object, a tetralobe, the best estimator gives a relative error below 5% at the cost of increased measurement time. Applicability on a real case is demonstrated on an aged hydrodemetallation catalyst. Sampling of catalyst grains at the inlet and outlet of the reactor allowed conclusions concerning different reactivity for the trapped metals.

Superstructure of a substituted zeolitic imidazolate metal-organic framework determined by combining proton solid-state NMR spectroscopy and DFT calculations.

We report the supercell crystal structure of a ZIF-8 analog substituted imidazolate metal-organic framework (SIM-1) obtained by combining solid-state nuclear magnetic resonance and powder X-ray diffraction experiments with density functional theory calculations.