Reaction alumina

Other reactions taking place throughout the hardening period are substitution and addition reactions (29). Ferrite and sulfoferrite analogues of calcium monosulfoaluminate and ettringite form soHd solutions in which iron oxide substitutes continuously for the alumina. Reactions with the calcium sihcate hydrate result in the formation of additional substituted C—S—H gel at the expense of the crystalline aluminate, sulfate, and ferrite hydrate phases. 

Fig. 1. P MAS NMR spectrum of (a)Ru-BrNAP/PTA/y-Al203, and (b)Ru-BINAP crt rlex In order to find the characteristics of the immobilized catalyst, asymmetric hydrogenation of the prochiral C=C bond was performed as a model reaction. Firstly, three different homogeneous Ru-BINAP complexes including [RuCl2((R)-BINAP)], [RuCl((R)-BINAP)(p-cymene)]Cl and [RuCl((R)-BINAP)(Benzene)]Cl were immobilized on the PTA-modified alumina. Reaction test of immobilized catalysts showed that [RuCl2((R)-BINAP)] was the most active and selective so all the experiment were done using this catalyst afterwards.

NaCl and subsequent heating (68) or by treating with acetonitrile (69) failed to alter the spectrum, but the rate of the reaction of Nb(7r-allyl)4 with NaCl-treated alumina was markedly reduced. An alternative explanation for the spectrum (Figure 13) could be that all the niobium atoms are attached to the alumina surface by multiple oxide bridges, a conclusion which was also reached from the ESR spectrum of the VC14/ alumina reaction product (60). This is not confirmed by the stoichiometric results of the reaction of Zr( benzyl )4 with alumina previously dried at 750° (Table II). 

Platinum Platinum Platinum (2%) on (2%) on (0.75%) on silica-silica gel alumina alumina Reaction temperature (°C) Silica- alumina... 

In summary, catalytic C-H transformations in small unfunctionalized alkanes is a technically very important family of reactions and processes leading to small olefins or to aromatic compounds. The prototypical catalysts are chromia on alumina or vanadium oxides on basic oxide supports and platinum on alumina. Reaction conditions are harsh with a typical minimum temperature of 673 K at atmospheric pressure and often the presence of excess steam. A consistent view of the reaction pathway in the literature is the assumption that the first C-H abstraction should be the most difficult reaction step. It is noted that other than intuitive plausibility there is little direct evidence in heterogeneous reactions that this assumption is correct. From the fact that many of these reactions are highly selective toward aromatic compounds or olefins it must be concluded that later events in the sequence of elementary steps are possibly more likely candidates for the rate-determining step that controls the overall selectivity. A detailed description of the individual reactions of C2-C4 alkanes can be found in a comprehensive review [59]. 

The XRD output in Fig. 11.4 shows clear peaks of unreacted AI2O3 and the reaction product, A1H3(P04)2 H20. Formation of this reaction product is consistent with the observations made by earlier investigators [14]. Sharper and taller peaks in the X-ray patterns of samples cured for longer time indicate that their concentration in the gel is time dependent. This implies that in order to form a chemically bonded ceramic, sufficient hydrothermal curing is necessary to allow the water-alumina reactions to occur, and the dissolution of alumina to take place. This confirms the importance of the role of water in these reactions as noted by Bothe and Brown [12]. 

The advantage afforded by the 60% alumina brick over the super duty fireclay bricks mentioned above is a higher service temperature limit. The majority of the alumina in a 60% alumina brick is combined with silica to form mullite, and is therefore protected from the alkali/alumina reaction. 

From 2400°F up, 88% plus alumina brick is suggested. Although the alkali/alumina reaction will occur, the higher refractoriness of the alumina brick is necessary to ensure that the lining does not soften and sag during service in the high temperature exposure. 

Kasprzyk-Hordem, B., Chemistry of alumina, reactions in aqueous solution and its application in water treatment, Adv. Colloid Intetf. Sci., 110, 19, 2004. 

Our study also showed that the catalyst deactivates with time-on-stream even at low conversions. The activity dropped 30% from its initial value over a few hours. The present work further investigates this deactivation phenomenon in order to evaluate more thoroughly the potential application of copper oxide catalysts for OMR. Experiments were conducted to determine the cause of deactivation and the effect of the support on deactivation rate. Zirconia has been explored as an alternative support to ZnO and/or alumina. Reaction and deactivation rate data for 18-hour OMR reactions are reported for these catalysts. 

Figure 4.28 Effect of 21 ppm sulfur dioxide on the activity of a ruthenium/alumina catalyst for the preferential oxidation of carbon monoxide the catalyst contained 1.6 wt.% ruthenium on alumina reaction temperature 150°C [338].

This problem can be eliminated by recourse to alumina reaction vessels but this leads to experimental complications which are... 

Table 1. Variation of cyclohexane conversion and selectivity of products with different VPO alumina. Reaction conditions H2O2 cyclohexane mole ratio is 5 1, temperature 333K, 24 h.

In absence of alumina, reaction time ranges from 4.5-9 min and yield of product ranges from 45-65% whereas in presence of alumina, reaction time was reduced to approximately half (2.5-4 min) and yield was also far better (64-90%). 

Samples were sintered in air at different temperatures between 900 and 1100 C using heating rates of 5 K/min and a dweU time of 3 h. After sintering, specimens were exposed in an electrically heated furnace with alumina reaction tube and repeatedly reduced and oxidized (redox-cycled) at 800 °C in Ar-2%H2 and Ar-2%H2-7%H20 respectively correlating with the above mentioned oxygen partial pressures. For every half-cycle (one half-cycle corresponds to either an oxidation or a reduction step) a flow rate of 10 Nl/min for a time of 10 h was applied. 

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