Phase cooperation

These reactions require a lot more research to reach fruition, most specifically in the field of long-term catalyst stability and selectivity. Furthermore, in many instances the reaction mechanism and the active catalytic site are still poorly understood. Issues such as the importance of site isolation and phase cooperation... 

The Role of Site Isolation and Phase Cooperation in Selective Oxidation Catalysis, R. K. Grasselli and J. M. Thomas, eds., Kloster Irsee, 2000 Top. Catal. 15, 83-289 (2001). 

The fact that the active site is already partly reduced will diminish its ability (nucleophilicity) to activate all C—H bonds. In this way the oxygen activation on a site that is partly reduced will create a situation in which oxygen transfer can occur selectively without simultaneous activation of many reactive sites at the alkoxide. Obviously, for such a fortunate situation no external regeneration of the active site by lattice oxygen or by withdrawal of electrons to distant electron sinks (phase cooperation) must occur. The concept of site isolation finds in such an interpretation a natural cause a catalytic site must be constructed in such a way that its electronic structure is allowed to fluctuate between a highly active initial state and moderate consecutive states as the conversion of the substrate molecule proceeds. The site is... 

The multifunctionality is achieved through either the combination of two different compounds (phase-cooperation) or the presence of different elements inside a single crystalline structure. In antimonates-based systems, cooperation between the metal antimonate (having a rutile crystalline structure), employed for propane oxidative dehydrogenation and propene activation, and the dispersed antimony oxide, active in allylic ammoxidation, is made more efficient through the dispersion of the latter compound over the former. In metal molybdates, one single crystalline structure contains both the element active in the oxidative dehydrogenation of the hydrocarbon (vanadium) and those active in the transformation of the olefin and in the allylic insertion of the N H2 species (tellurium and molybdenum). 

Another observed transition deals with the 1st and 2nd phenyl rings, which are attached to the 1st isopropylidene unit. Figure 66 shows that 02 of the 1st phenyl ring changes from 60° to - 50° between 55 and 80 ps, while 02 of the 2nd phenyl ring changes in the same direction exactly within the same duration. This is an in-phase cooperative rotation of the rings attached to the... 

FIGURE 11 Hierarchy of phases in catalysts developed from their function. At the level of the active phase confusion can arise from spectators and unnecessary admixtures or deactivated phases. Phase cooperation phenomena are frequently ascribed to beneficial effects these admixtures without much experimental evidence. 

Planning and control of operations are keys to moving an organization or supply chain in a desired direction. The extent of joint planning is expected to bear heavily on the success of the supply chain. Different components may be emphasized at different times during the life of the supply chain, but planning transcends the phases (Cooper and Ellram 1993). The control aspects can be operationalized... 

In the ordered phase Cooper and Reddington (1965) first reported that the optical transition across the band gap created by magnetic ordering was independent of the type of ordering in Dy, whether it was ferromagnetic or helical. Krizek and Taylor made the same observation in Tb, Dy, and Ho. The band gaps were found to be 0.65 in Tb (Krizek and Taylor, 1974), 0.44 in Dy (Cooper and... 

B. (2002) Evidence of phase cooperation in the LaCoOs-Ce02-Co304 catalytic system in relation to activity in methane combustion. Appl Catal A- Gen, 231 (1-2), 65-80. 

B. (2002) Evidence of phase cooperation in the LaCo03-Ce02-Co304 catalytic system... 

Andersson, A., Hanse, S. and Wickman, A. (2001). The Importance of Site Isolation and Phase Cooperation in Propane Ammoxidation on Rutile-type Vanadia Catalysts, Top. Catal., 15, pp. 103-110. 

Grasselli, R.K. Genesis of site isolation and phase cooperation in selective oxidation catalysis. Top. Catal 2001,15, 93-101. 

---