Promotion temperature programmed reaction

Important information on reaction mechanisms and on the influence of promoters can be deduced from temperature programmed reactions [2], Figure 2.8 illustrates how the reactivity of adsorbed surface species on a real catalyst can be measured with Temperature Programmed Reaction Spectroscopy (TTRS). This figure compares the reactivity of adsorbed CO towards H2 on a reduced Rh catalyst with that of CO on a vanadium-promoted Rh catalyst [13]. The reaction sequence, in a simplified form, is thought to be as follows ... 

As stated earlier, it should be possible to epoxidize non-allylic olefins other than butadiene, or even olefins with allylic hydrogen atoms, as long as the allylic hydrogens are kinetically non-reactive. The olefins in Table 4 indicate this is indeed the case. In all cases, the catalysts were promoted with CsCI the unpromoted catalysts were either inactive or exhibited very low and transient activities. The data for the epoxidation of styrene and 4-vinylpyridine are discussed in greater detail in an earlier patent (12). The epoxidation of styrene over silver surfaces has also been observed by Blum (13) and Hawker, Lambert eta (14), although the catalysts evaluated in Table 4 are much more active and selective than those described by Blum. The transient temperature programmed reaction spectroscopy (TPRS)... 

Mossbauer spectroscopic studies showed that alkali promotes the reduction of Fc203 to Fe at 300 °C [111,138,139]. Yet more direct measurements by temperature programmed reactions demonstrate that K decreases the rate of reduction for (Fe,K)-oxide samples [121] and for (Fe,Al,K)-oxide samples [121]. The rate of reduction increases through the sequence (Fe, A1,M), M = Li, Na, K, Rb, Cs for Fe203 based catalysts [139]. 

The promoter role of ceria in WGS reaction is demonstrated in Figure 8.6. Temperature-programmed conversion of CO was carried out in an oxygen-deficient medium. The oxygen content was adjusted to obtain a maximum conversion of 40% by... 

Temperature programmed reduction measures the reaction of hydrogen with a sample at various temperatures. The results are interpreted in terms of the different species present in the sample and their amenability to reduction. Therefore, these results can give information on the presence of different oxidation states or the effect of a dopant in a lattice. It is useful for measuring the temperature necessary for the complete reduction of a catalyst and is commonly used to investigate the interaction of a metal catalyst with its support, or of the effect of a promoter on a metal catalyst. 

Insight into chemisorption bonds is important for the interpretation of photoemission and vibrational spectra of adsorbed molecules, of temperature-programmed desorption data, and for the understanding of catalytic reactions. If we have a feeling for how electrons rearrange over orbitals when a molecule adsorbs, we may be able to understand why molecules dissociate or not, to what extent they are activated, or also how a promoter influences the reactions on the surface. 

Co. surface area = 300 m2/g ) with aqueous solutions of Cu, Cr, Mg, Ca, Sr, and Ba in Nitrate. All the catalysts have Cu to Si02 weight ratio of 14/86. For promoted catalyst, the Cr to Cu molar ratio was varied from 1/4 0 to 1/4, and the alkaline earth metal to Cu molar ratio was kept at 1/10. The impregnated catalysts were dried at 100 °C overnight, calcined at 450 for 3 h and then reduced in a stream of 10% H2 in Ar at 300 °C for 2 h. The copper surface areas of catalysts were determined by the N20 decomposition method described elsewhere [4-5J. The basic properties of the catalysts were determined by temperature-programmed desorption ( TPD ) of adsorbed carbon dioxide. Ethanol was used as reactant for dehydrogenation reaction which was performed in a microreactor at 300°C and 1 atm. 

Fig. 5.3. Arrhenius plot for temperature programmed surface reaction ln(rate) as a function of 1/T, for the reaction of a pre-adsorbed CO in the flow of H2. Promoted and unpromoted Rh/Si02...

In this study, suboxides of vanadia catalysts were used in pentane, pentene, dicyclopentadiene and cyclopentane oxidation reactions. In the previous phase of the work [12,13], the role of alkali promoters on the catalyst selectivity was examined. The catalysts were reduced in situ at different temperatures and the effect of pre-reduction temperature was investigated. Controlled-atmosphere characterization of pre-reduction, post-reduction, and post-reaction catalysts were performed using X-ray diffraction. X-ray photoelectron spectroscopy, laser Raman spectroscopy and temperature-programmed desorption experiments. The objectives of this study were to determine the activity and selectivity of different suboxides of vanadia in... 

The Influence of Oxygen Poisoning on a Multiply Promoted Iron Catalyst Used for Ammonia Synthesis A Temperature-Programmed Desorption and Reaction Study... 

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