Support acidity effect

Pt-Re-alumina catalysts were prepared, using alumina containing potassium to eliminate the support acidity, in order to carry out alkane dehydrocyclization studies that paralleled earlier work with nonacidic Pt-alumina catalysts. The potassium containing Pt-Re catalyst was much less active than a similar Pt catalyst. It was speculated that the alkali metal formed salts of rhenic acid to produce a catalyst that was more difficult to reduce. However, the present ESCA results indicate that the poisoning effect of alkali in Pt-Re catalysts is not primarily due to an alteration in the rhenium reduction characteristics. 

To the product of the previous reaction are added DMF (7.0 mL) and DBU (1.6 mL). After shaking for 15 h, the resin is extensively washed with DMF, dichloromethane and methanol (note 7). Cleavage from the support is effected by treatment with 50% trifluoroacetic acid in dichloromethane (6.0 mL) for 1 h. Concentration of the filtrate yields 273 mg (80%) of the title compound as an oil (85% pure by HPLC, 254 nm), which crystallizes upon addition of methanol (2.0 mL). Filtration and drying yields 82 mg (24%) of slightly yellow crystals, 93% pure by HPLC (254 nm note 8). 

Of the two, valproic acid is somewhat easier to tolerate, is less likely to cause interactions with other medications, and has more data supporting its effectiveness... 

The initial step of the reaction, Eq. (7), provides the individual metal sulfide molecules via reaction of the M2+ ions with H2S. In the case of films derived from fatty acids, the two carboxylate functions, associated with the M2+ ion, are the sink for the two protons released from the reaction. The diffusion and coalescence of the individual MS molecules to give MS particles are depicted in Eq. (8). Despite an abundance of literature concerning Q-state particle formation in LB films, there has been little discussion relating to mechanistic aspects of how the nature of the LB support matrix effects the processes depicted in Eq. (7) and (8). The remainder of this section outlines the mechanistic and kinetic insights gained into these processes over the course of study of metal chalcogenide formation in LB films. 

Recent work by Schlatter and Boudart (20) demonstrated the possibility of contamination of the metal by impurities released by the support this effect can be minimized by diluting the catalyst with an acidic oxide which strongly adsorbs these impurities. In such a case, the lower activity... 

The possible catalyst components have been classified into three groups metal oxide support, acidity enhancers, and promoters. As metal oxide supports, y-Al203, Zr02, Ti02 have been considered. Acidity enhancers SO4, BOf, POl and WO were used, for which the content of SO4-, BOf, PO ranged from 0.5-6 wt% and of WO from 0.5-36%. For promoters (water and thioresistance) the effect of Pt, Ce, Pd, Sn, Ni, Mn and Nb was explored (0.5-6 wt% for each metal). Each material contains one support, one acidity promoter and at least two metallic promoters, of which one is Pt (0.5 wt%). 

The results of this work will show that the support acid/base properties has the largest influence on the adsorption of H, while the effect of the support on CH3 and CH2 adsorption is much smaller. These new results can explain several support-induced changes in the catalytic properties of supported Pt catalysts. These changes are mainly driven by the strength of the Pt-H bond. 

In Chapter 4 the H/D exchange of cyclopentane was measured for Pt catalysts with supports of various acidity. With the earlier developed Monte-Carlo model the contributions of the various possible intermediates in the H/D exchange can directly be measured. It was shown that the activity and the selectivity in the H/D exchange over the supported Pt catalysts strongly depend on the support acid/base properties. The activities of the various catalysts show a compensation effect. The compensation effect can directly be correlated to the contribution of the various exchange mechanisms, which proceed via different intermediates. The contribution of each intermediate depends on the electronic properties of the Pt particles, which in turn depend on the support acidity. This shows that the compensation effect is caused by support induced changes in the adsorption modes of cyclopentane. 

Although MgO can be considered a basic oxide, the presence of A1 in the mixed oxide may induce some surface acidity. For example, decomposition of 2-propanol over calcined hydrotalcite results in the formation of both propene and propanone which is consistent with the presence of both surface acid and base sites (16). We therefore wanted to test the effect of neutralizing all of the support acidity by... 

Recently, Pt/Nb20s catalysts have been investigated on dehydrogenation of alkanes. These systems have presented advantages on selectivity towards olefins when compared to Pt/ALOs or even Pt-Sn/A]20 , catalysts [4-6]. The promoting mechanism is related to both the SMSI (Strong Metal Support Interaction) effect and the low acidity of the support, which produce a sharp decrease in hydrogenolysis and aromatization, respectively [5]. 

Clinical Studies with Ha-Receptor Antagonists. HA Hz-receptor antagonists are potent and selective inhibitors of gastric acid secretion, with numerous clinical studies to support their effectiveness in ulcer disease. Table 3.4 outlines the clinical effectiveness and pharmacokinetic profile of Hz-receptor antagonists currently available in the UK. 

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