![]() On the other hand, Brønsted (Mo OH) acidic function was found to form on the surface of the MoO 2 structure, thereby producing a metal-acid (bifunctional) MoO 2− x(OH) y catalyst. ![]() Results obtained enabled revealing the presence of density of states (DOS) at the Fermi level and, hence, metallic properties related to the deformed rutile structure of MoO 2. The modified and unmodified catalysts were characterized, before and after H 2-reduction at 673 K, by means of ISS, XPS, UPS and FT-IR spectroscopy techniques. Then, potassium-modified versions of the catalyst were prepared at 0.5–5 wt%-K. Titania-supported molybdena catalyst was prepared by calcination at 773 K of ammonium heptamolybdate-impregnated TiO 2 pellets with the equivalent of 5 monolayers of MoO 3. Above 5.8 GPa, however, this phase transition becomes thermodynamically favourable, making hydrogenation of Pd 5As likely to occur. The lack of reactivity might be due to kinetic hindrance because of an endothermic rearrangement of the metal matrix necessary for hydrogen incorporation. Quantum-mechanical calculations using DFT methods using an ab initio evolutionary algorithm confirm the crystal structure of Pd 5As and reveal the stability of a hypothetical hydride Pd 5AsH. Pd 5As does not take up hydrogen up to 5.0 MPa hydrogen pressure and temperatures up to 723 K. The crystal structure of Pd 5As represents a strongly distorted cubic closest packing as proven by crystallographic group–subgroup relationships. Palladium has got coordination numbers of 11 (average distance 276 pm) or 12 (average distance of 278 pm). Two such polyhedra are connected by a common edge to double prisms (average distance As–Pd 252 pm). ![]() Eight palladium atoms form a bicapped trigonal prism around arsenic. This is in contrast to earlier work, which describes the structure in the non-centrosymmetric space group C2. The crystal structure of Pd 5As was refined simultaneously from laboratory X-ray, synchrotron and neutron powder diffraction data (space group C2/ m, a = 551.82(2) pm, b = 774.50(3) pm, c = 842.13(4), β = 99.037(2)°, Z = 4). La préparation des solides Co–Mo–S et Ni–Mo–S basés sur la structure MoS 2 et éminemment importants pour la catalyse a été également considérée. En particulier, la relation entre les techniques de préparation et les propriétés des matériaux obtenus a été analysée. Un certain nombre de méthodes de préparation ont été comparées dans cette revue, y compris la décomposition des précurseurs, les synthèses hydrothermales, les synthèses en solution par méthodes de chimie douce, les préparations en présence de tensioactifs, l'intercalation–exfoliation, et les réactions gaz–solide. Preparation of bulk Co–Mo–S and Ni–Mo–S mixed sulfides based on the MoS 2 structure and eminently important for catalysis was also considered.ĭes aspects synthétiques des matériaux à base de sulfure de molybdène ont été considérés, en insistant sur les matériaux catalytiques. In particular, the relationship between the preparation techniques and the properties of the materials obtained was analyzed. A number of preparation methods were critically compared in this review, including molecular precursor decomposition, hydrothermal, soft chemistry aqueous, surfactant-aided, intercalation–exfoliation, and solid–gas reactions. Synthetic aspects of the molybdenum sulfide-based materials were reviewed, with emphasis on the catalytic materials.
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