Catalyst oxide phase

In this paper, the phenomena occuring in catalysts used to hydrocrack petroleum residua are discussed. Reaction sites are provided by the catalyst sulphide phase (Mo is the majority cation) and by the catalyst oxide phase (A1 is the majority cation). The influence of the promoter cations (typically Co or Ni) is also described. The catalyst is deactivated by coke and by metals. Furthermore, the reaction rate is often controlled by the rate of diffusion of the large carbonaceous molecules in the residua. All of these factors have been considered in mathematical simulations of the phenomena occuring in the catalyst. 

Arsenic-Catalyzed Liquid-Phase Process. An arsenic catalyst Liquid-phase process for olefin oxides has been patented by Union Carbide... 

The scope of reactions involving hydrogen peroxide and PTC is large, and some idea of the versatility can be found from Table 4.2. A relatively new combined oxidation/phase transfer catalyst for alkene epoxidation is based on MeRe03 in conjunction with 4-substituted pyridines (e.g. 4-methoxy pyridine), the resulting complex accomplishing both catalytic roles. 

Transition metal oxides, rare earth oxides and various metal complexes deposited on their surface are typical phases of DeNO catalysts that lead to redox properties. For each of these phases, complementary tools exist for a proper characterization of the metal coordination number, oxidation state or nuclearity. Among all the techniques such as EPR [80], UV-vis [81] and IR, Raman, transmission electron microscopy (TEM), X-ray absorption spectroscopy (XAS) and NMR, recently reviewed [82] for their application in the study of supported molecular metal complexes, Raman and IR spectroscopies are the only ones we will focus on. The major advantages offered by these spectroscopic techniques are that (1) they can detect XRD inactive amorphous surface metal oxide phases as well as crystalline nanophases and (2) they are able to collect information under various environmental conditions [83], We will describe their contributions to the study of both the support (oxide) and the deposited phase (metal complex). 

Raman spectroscopy has been used for a long time in order to study supported and promoted metal catalysts and oxide catalysts [84] since many information can be obtained (1) identification of different metal oxide phases (2) structural transformations of metal oxide phases (3) location of the supported oxide on the oxide substrate and... 

Within the inverse model catalyst approach, the y/7-V309-Rh(l 11) nanostructures have been used to visualize surface processes in the STM with atomic-level precision [104]. The promoting effect of the V-oxide boundary regions on the oxidation of CO on Rh(l 1 1) has been established by STM and XPS by comparing the reaction on two differently prepared y/7-V309-Rh(l 11) inverse catalyst surfaces, which consist of large and small two-dimensional oxide islands and bare Rh areas in between [105]. A reduction of the V-oxide islands at their perimeter by CO has been observed, which has been suggested to be the reason for the promotion of the CO oxidation near the metal-oxide phase boundary. 

The oxidation of cobalt metal to inactive cobalt oxide by product water has long been postulated to be a major cause of deactivation of supported cobalt FTS catalysts.6 10 Recent work has shown that the oxidation of cobalt metal to the inactive cobalt oxide phase can be prevented by the correct tailoring of the ratio Ph2cJPh2 and the cobalt crystallite size.11 Using a combination of model systems, industrial catalyst, and thermodynamic calculations, it was concluded that Co crystallites > 6 nm will not undergo any oxidation during realistic FTS, i.e., Pi[,()/I)i,2 = 1-1.5.11-14 Deactivation may also result from the formation of inactive cobalt support compounds (e.g., aluminate). Cobalt aluminate formation, which likely proceeds via the reaction of CoO with the support, is thermodynamically favorable but kinetically restricted under typical FTS conditions.6... 

After calcinations, the precipitated iron catalyst is composed of a mixture of iron oxide phases before activation. The exact nature of this phase is not critical for the discussion and will be referred to in general as an oxide phase. During activation the catalyst is subjected to a reducing environment that will lead to the formation of either metallic iron if pure hydrogen is used or some iron carbide if the reduction is done with either CO or syngas. During reduction with a gas... 

Table 117 Influence of Fe oxide phase on water-gas shift rates of Ru/Fe oxide catalysts (0.25 g) using a feed containing a H2O/CO ratio of 2.5 and a flow rate of 3.5 dm3/h at a temperature of 350 °C. Catalysts were calcined at 600 °C. Data based on RuC13 precursor in preparation510...

Bismuth Molybdates. Bismuth molybdates are used as selective oxidation catalysts. Several phases containing Bi and/or Mo may be mixed together to obtain desired catalytic properties. While selected area electron diffraction patterns can identify individual crystalline particles, diffraction techniques usually require considerable time for developing film and analyzing patterns. X-ray emission spectroscopy in the AEM can identify individual phases containing two detectable elements within a few minutes while the operator is at the microscope. 

Fig. 14.20 Schematic representation of the relevant SOFC reactions. The steam reform reaction needs nickel as the catalyst. Oxidation of H2 and CO takes place at the triple phase boundaries (TPBs represented as smaller dots) in the anode, and is catalyzed by the Ni. At the cathode, 02 reduction also occurs at TPBs and is catalyzed by LSM.

Dynamic effects are a potentially important but easily overlooked aspect of heterogeneous catalysis that can nonetheless impact the accuracy of our knowledge and predictions. For example, multiple co-existing meta-stable surface oxide phases have been identified for Pd and Ag interacting with oxygen, which suggests that the catalyst surfaces may be in a state of flux under reaction conditions, adding new uncertainty to the nature of the... 

The vanadium oxide species is formed on the surface of the oxide support during the preparation of supported vanadium oxide catalysts. This is evident by the consumption of surface hydroxyls (OH) [5] and the structural transformation of the supported metal oxide phase that takes place during hydration-dehydration studies and chemisorption of reactant gas molecules [6]. Recently, a number of studies have shown that the structure of the surface vanadium oxide species depends on the specific conditions that they are observed under. For example, under ambient conditions the surface of the oxide supports possesses a thin layer of moisture which provides an aqueous environment of a certain pH at point of zero charge (pH at pzc) for the surface vanadium oxide species and controls the structure of the vanadium oxide phase [7]. Under reaction conditions (300-500 C), moisture desorbs from the surface of the oxide support and the vanadium oxide species is forced to directly interact with the oxide support which results in a different structure [8]. These structural... 

---