Propylene oxide oxidation— temperature effect

Figures 1 shows the catalytic performance of the Fe-BEA catalysts in the temperature range of 250-550 °C. It is clear from the figure that propylene yield depends on particle size of the parent BEA zeolite. Effect of the N20 concentration has been analyzed under reaction regimes RS-1 and RS-2. Increase in N20 concentration resulted in the same propene yields but increased the N20 conversion and decreased the selectivity toward propylene. At higher temperature has been obtained increases in the formation of the molecular oxygen which further accelerates production of the undesired carbon oxides. Thus, at lower feed concentration of N20, i.e. at 1 1 feed ratio of reactants (RS-1), formation of carbon oxides is suppressed and the selectivity of ODHP reaction is...

Bromine, chlorinated solvents, amines, propylene oxide and tetrahydrofuran (THF) can have more or less severe effects at room temperature. Alterations increase when the temperature rises. 

In most cases the catalytically active metal complex moiety is attached to a polymer carrying tertiary phosphine units. Such phosphinated polymers can be prepared from well-known water soluble polymers such as poly(ethyleneimine), poly(acryhc acid) [90,91] or polyethers [92] (see also Chapter 2). The solubility of these catalysts is often pH-dependent [90,91,93] so they can be separated from the reaction mixture by proper manipulation of the pH. Some polymers, such as the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers, have inverse temperature dependent solubihty in water and retain this property after functionahzation with PPh2 and subsequent complexation with rhodium(I). The effect of temperature was demonstrated in the hydrogenation of aqueous allyl alcohol, which proceeded rapidly at 0 °C but stopped completely at 40 °C at which temperature the catalyst precipitated hydrogenation resumed by coohng the solution to 0 °C [92]. Such smart catalysts may have special value in regulating the rate of strongly exothermic catalytic reactions. 

Temperature Programmed Reaction. Examination of another redox system, propylene oxidation on M0O3, provides further insight. It is well accepted that propylene oxidation on molybdenum-based catalysts proceeds through formation of allylic intermediates. From isotopic studies it has been demonstrated that formation of the allylic intermediate is rate-determining (H/D effect), and that a symmetric allylic species is formed ( C labelling). 

Polyurethane Networks. Andrady and Sefcik (1983) have applied the same relationship as Rietsch et al. (1976), to the glass transition temperature of networks based on poly(propylene oxide) diols with a controlled molar mass distribution, crosslinked by aromatic triisocyanates. They obtained a Kr value of 25 K kg mol-1, about twice that for PS networks. They showed that the length distribution of elastically active chain lengths, directly related to the molar mass distribution of the starting poly(propylene oxide), has practically no effect on Tg. 

The reaction kinetics were studied at temperatures between 240°C and 400°C, propylene oxide partial pressures between. 4 10 bar and 4.0 10 J bar and oxygen partial pressures between. 02 bar and. 2 bar. At steady state external diffusional limitations as well as diffusional effects inside the porous silver film were negligible (4). The kinetics and potentiometric results can be summarized as follows (4) ... 

A series of additional experiments was performed with a Ag(poly) foil [rather than a Au(poly)] foil to examine in more detail the nature of the reaction products of d6-PC with metallic Li, and possible substrate effects. According to data compiled in the literature (Table 3), all of these fragments, except mle = 4, are consistent with, albeit not unique to, ethylene oxide, e.g., acetaldehyde. No features could be identified for mle = 32 and 64, indicating that propylene oxide, if produced, yields signals too small to be detected. Furthermore, no differences were found between the peak shapes and temperatures obtained for these experiments and those observed using Au(poly) hence, the reaction pathway does not seem to be affected by the nature of the substrate. Based on the behavior found for BuOLi, for which the series of high temperature peaks are found in the range... 

The stereoregularity—i.e., distribution of the stereosequence length in these polymers—has a marked effect on the crystallization rates and the morphology of the crystalline aggregates. These differences, in turn, influence the dynamic mechanical properties and the temperature dependence of the dynamic mechanical properties. In order to interpret any differences in the dynamic mechanical properties of polymers and copolymers of propylene oxide made with different catalysts, it was interesting to study the differences in the stereosequence length in the propylene oxide polymers made with a few representative catalysts. 

Washington, C. King, S.M. Effect of electrolytes and temperature on the structure of a poly(ethylene oxide) poly(propylene oxide) poly(ethylene oxide) block copolymer adsorbed to a perfluorocarbon emulsion. Langmuir 1997, 13, 4545-4550. 

Gold nanoparticles have received significant attention in recent years because of their unique catalytic activity [37 3]. Supported gold nanoparticles in the range of 2-5 nm are effective as catalysts for a variety of reactions including selective oxidation of propane to propylene oxide [44] and low-temperature CO oxidation [45]. Numerous experimental studies have focused on understanding the effect of particle size in gold catalysts however, the picture is often complicated by the lack of a monodisperse size distribution. 

Increased amounts of palladium on the charcoal surface increased the rate of hydrogen chemisorption, but exerted little effect on the equilibrium amounts of hydrogen chemisorbed. Extensive evacuation of the chemisorbed catalyst at elevated temperatures gave little hydrogen desorbed, but large amounts of water, methane, propylene, oxides of carbon, and so on. 

TABLE 14.2 Effects of deposition temperature (Tj), oxidants, and supports on propylene oxide selectivity (%)... 

Competition experiments of propane and propylene [12] reveal that propane and propylene compete with similar effectiveness for the catalytic metal oxide sites, albeit as expected propylene is favored by a factor of 2.3. Since the operating temperature is rather high, the results also imply that the thermal contribution to the respective C-H bond breaking is significant, diminishing the customary importance of the a-hydrogen bond weakening in propylene due to the jt-bond interaction of the olefin with the catalyst surface. 

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