Sulfide catalysts stability

Similarly to the case of direct-oxidation anode materials, sulfur-tolerant anode materials based on sulfides [6, 7] or double-perovskite oxides have special requirements for their processing into SOFC layers. For example, nickel sulfide-promoted molybdenum sulfide is tolerant to high sulfur levels [7], However, it has a low melting temperature [6] that has resulted in the development of cobalt sulfide as a stabilizer of the molybdenum sulfide catalyst [6], CoS-MoS2 admixed with Ag has an even higher performance in H2S-containing fuels than in pure H2 [6]. However, processing methods such as PS, infiltration, or sol-gel techniques that can process... 

In summary, the presence of a relatively strong Mo5+ signal found on A1203 catalysts but not on Si02 catalysts can be considered as additional evidence for an interaction between the molybdena and the alumina, which permits stabilization of the Mo5+ state in the reduced and sulfided catalyst. An H-containing specie seems a reasonable hypothesis for this state. The Co may be in tetrahedral or octahedral environment or both. 

Method of Operation. The catalyst was activated in the reactor by first calcining at 232.2 C (450 F) and then sulfiding with a mixture of 5.14 volume percent H2S in H2. The reactor was then brought to the operating conditions and the flow of hydrogen and oil started. After about 32 hours of operation for catalyst stabilization, representative product oil samples were taken at specified reactor conditions. The product oil samples were analyzed for sulfur and nitrogen contents with the help of a Leco Model 634-700 automatic sulfur analyzer and Perkin Elmer Model 240 elemental analyzer, respectively. 

Stability of catalysts not affected by drying temperatures, but is affected by sulfiding. Sulfided catalyst fouled by different mechanism.81 ... 

Both catalyst types preserve activity for several hours (Fig. 1). The activity and stability of the bimetallic catalysts strongly depend on their type. The oxide catalysts exhibit higher activity and stability than the sulfide catalysts. In three hours, the activity of sulfide catalysts decreases by 20%, and that of the sulfide catalysts, by a factor of 3. For bimetallic catalysts, there is the synergetic effect. 

This section is concerned with transition metal clusters that, in addition to metal atoms, contain sulfur atoms in the cluster core (rather than just in the peripheral ligands). Metal-metal bonds often supplement sulfur-atom bridges in stabilizing the structures encountered. Generally, such clusters are likely to resemble the HDS active phases of heterogeneous metal-sulfide catalysts to some extent, e.g. in terms of coordination sphere and metallic oxidation states. Because of the large number of molecular metal-sulfide clusters now known, we shall focus on homometallic clusters of Mo(W) and heterobimetallic clusters of Mo(W)-Co(Ni) (next two sections), i.e. molecular clusters containing the elements that are relevant for industrial... 

In certain commercial catalysts, nickel sulfide is used in admixture with sulfides of chromium, vanadium, molybdenum, or tungsten. There is no information available on these mixed sulfide catalysts. It can be conjectured that the nickel sulfide reacts with the other sulfides to form thio salts such as NiCr2S , NiMoSs, etc., and that either these thio salts act as stabilizing supports for Ni3S2 catalyst, or are catalysts themselves. 

Stability of Sulfide Catalysts under Hydrotreating Conditions 326... 

Determination of the nature of the catalytically stabilized phase under operating conditions is fundamental if one wants to understand the activity and selectivity properties of a given sulfide. It is even more important since sulfide catalysts have to work under very harsh conditions in a hydrotreating reactor. Significant restructuring can be expected. However,... 

In Chapter 1 we emphasized that the properties of a heterogeneous catalyst surface are determined by its composition and structure on the atomic scale. Hence, from a fundamental point of view, the ultimate goal of catalyst characterization should be to examine the surface atom by atom under the reaction conditions under which the catalyst operates, i.e. in situ. However, a catalyst often consists of small particles of metal, oxide, or sulfide on a support material. Chemical promoters may have been added to the catalyst to optimize its activity and/or selectivity, and structural promoters may have been incorporated to improve the mechanical properties and stabilize the particles against sintering. As a result, a heterogeneous catalyst can be quite complex. Moreover, the state of the catalytic surface generally depends on the conditions under which it is used. 

Recently, rhodium and ruthenium-based carbon-supported sulfide electrocatalysts were synthesized by different established methods and evaluated as ODP cathodic catalysts in a chlorine-saturated hydrochloric acid environment with respect to both economic and industrial considerations [46]. In particular, patented E-TEK methods as well as a non-aqueous method were used to produce binary RhjcSy and Ru Sy in addition, some of the more popular Mo, Co, Rh, and Redoped RuxSy catalysts for acid electrolyte fuel cell ORR applications were also prepared. The roles of both crystallinity and morphology of the electrocatalysts were investigated. Their activity for ORR was compared to state-of-the-art Pt/C and Rh/C systems. The Rh Sy/C, CojcRuyS /C, and Ru Sy/C materials synthesized by the E-TEK methods exhibited appreciable stability and activity for ORR under these conditions. The Ru-based materials showed good depolarizing behavior. Considering that ruthenium is about seven times less expensive than rhodium, these Ru-based electrocatalysts may prove to be a viable low-cost alternative to Rh Sy systems for the ODC HCl electrolysis industry. 

---