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Nonacidic catalysts

Rea.ctlons, The chemistry of butanediol is deterrnined by the two primary hydroxyls. Esterification is normal. It is advisable to use nonacidic catalysts for esterification and transesterification (122) to avoid cycHc dehydration. When carbonate esters are prepared at high dilutions, some cycHc ester is formed more concentrated solutions give a polymeric product (123). With excess phosgene the usefiil bischloroformate can be prepared (124). [Pg.108]

Studies of the synthesis of quiaolines usiag transition-metal catalysts and nonacidic conditions (55) have determined that mthenium(III) chloride is the most effective of a wide range of catalysts. The reaction between nitrobenzene and 1-propanol or 1-butanol gives 65 and 70% yields of 2-ethyl-3-methylquiQoline [27356-52-1] and 3-ethyl-2-propylquiQoline, respectively. [Pg.392]

For more selective hydrogenations, supported 5—10 wt % palladium on activated carbon is preferred for reductions in which ring hydrogenation is not wanted. Mild conditions, a neutral solvent, and a stoichiometric amount of hydrogen are used to avoid ring hydrogenation. There are also appHcations for 35—40 wt % cobalt on kieselguhr, copper chromite (nonpromoted or promoted with barium), 5—10 wt % platinum on activated carbon, platinum (IV) oxide (Adams catalyst), and rhenium heptasulfide. Alcohol yields can sometimes be increased by the use of nonpolar (nonacidic) solvents and small amounts of bases, such as tertiary amines, which act as catalyst inhibitors. [Pg.200]

Dehydrogenation method and nonacidic multimetallic catalytic composite for use therein Catalyst development Pt, Co, U 77... [Pg.59]

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. [Pg.63]

Bond rupture probabilities have also been reported by Myers and Munns (160) for hydrogenolysis reactions over a number of supported catalysts containing platinum in the range 0.1-1%. The reactions were carried out in the region of 350°-480°C. Provided one confines the comparison to nonacidic supports, these results are in tolerable agreement with the data in Table XI. [Pg.66]

A wide range of nonacidic metal oxides have been examined as catalysts for aromatization and skeletal isomerization. From a mechanistic point of view, chromium oxide catalysts have been, by far, the most thoroughly studied. Reactions over chromium oxide have been carried out either over the pure oxide, or over a catalyst consisting of chromium oxide supported on a carrier, usually alumina. Depending on its history, the alumina can have an acidic function, so that the catalyst as a whole then has a duel function character. However, in this section, we propose only briefly to outline, for comparison with the metal catalyzed reactions described in previous sections, those reactions where the acidic catalyst function is negligible. [Pg.81]

Although reactions over nonacidic metal oxide catalysts possess some superficial similarities to reactions over platinum catalysts, on the whole, the two systems are sufficiently distinct that, at a mechanistic level, they are worth treating independently. [Pg.84]

The use of mechanical mixtures of metals on nonacidic supports and acidic catalysts showed that dual function effect appears without an intimate contact between the two functions 114,117,118). [Pg.312]

Skeletal ring contraction steps of primary C7 and Cg rings are more probable than bicyclic intermediates (132b). Aromatization of methylcyclo-pentane indicated no carbonium mechanism with a nonacidic catalyst. Instead, Pines and Chen (132b) proposed a mechanism similar to that defined later as bond shift. This is a methyl shift. Two additional isomerization pathways characteristic of chromia have also been demonstrated vinyl shift (94) and isomerization via C3 and C4 cyclic intermediates (90a). These were discussed in Section III. 1,1-Dimethylcyclohexane and 4,4-dimethyl-cyclohexene gave mainly toluene over various chromia catalysts. Thus, both skeletal isomerization and demethylation activities of chromia have been verified. The presence of an acidic almnina support enhances isomerization dual function effects are thus also possible. [Pg.317]

The key to the development of C02-resistant protonconducting oxides was the maximization of the en-tropic stabilization of protonic defects. If this approach also led to stable hydroxides with sufficiently high conductivity, AFCs using such electrolytes may operate even with air as the cathode gas. This would be tremendously advantageous, because fuel cells with nonacidic electrolytes may operate with non-noble-metal catalysts such as nickel for the anode and silver for the cathode. [Pg.435]

When a nonacidic catalyst such as nickel on kieselguhr is used, demethylation of alkanes occurs almost exclusively.66 It is significant that the demethylation is very selective—a methyl group attached to secondary carbon is more readily cleaved off than is one attached to a tertiary, which in turn is more readily eliminated than one at a quaternary carbon. Demethylation of 2,2,3-trimethylpentane yielded product consisting of 90% 2,2,3-trimethylbutane, and only 7% 2,3- and 3% 2,2-dimethylpentane. [Pg.36]

Additional evidence to this scheme was reported applying temporal analysis of products. This technique allows the direct determination of the reaction mechanism over each catalyst. Aromatization of n-hexane was studied on Pt, Pt—Re, and Pd catalysts on various nonacidic supports, and a monofunctional aromatization pathway was established.312 Specifically, linear hydrocarbons undergo rapid dehydrogenation to unsaturated species, that is, alkenes and dienes, which is then followed by a slow 1,6-cyclization step. Cyclohexane was excluded as possible intermediate in the dehydrocyclization network. [Pg.61]

The Effect of Thiophene on the Aromatization of n-Nonane over Nonacidic Platinum on Alumina-K Catalyst in the Presence of H-/xh... [Pg.304]

A third possible pathway could yield indan through cyclononane intermediate. We know that cyclononane undergoes transannular dehydrocycli-zation over platinum-on-charcoal catalyst at 300°C, to perhydroindan and then to indan (38) but so far there is no evidence for the direct cyclization of n-nonane to cyclononane. Unfortunately, Il in and Usov used an acidic catalyst and we cannot separate the contributions of acid and metal catalysis to the two mechanisms. Experiments over nonacidic platinum catalysts could show the relative importances of the platinum metal in the two cyclization pathways. [Pg.314]

It is interesting to compare the dehydrocyclization activity of platinum with that of chromia-alumina. Pines and Goetschel reacted different butyl-benzene isomers over acidic and nonacidic chromia-alumina catalysts between 480°C and 492°C (41). Dehydrocyclization is much slower over... [Pg.314]

C6-dehydrocyclization does not (50). As a consequence, over nonacidic platinum catalysts above 400°C, C6-dehydrocyclization predominates over C5-dehydrocyclization (27). Furthermore, the phenanthrene/anthracene ratio is independent of catalyst acidity (52). The effect of reaction temperature is, however, very interesting. Over platinum-on-carbon catalyst between 350°C and 400°C, more anthracene is formed than phenanthrene. Above 450°C phenanthrene is the main product (55). Phenanthrene is also the main product over chromia-alumina between 360°C and 440°C whereas, as seen above, anthracene is formed in this temperature range over platinum-on-carbon catalyst (54). [Pg.317]

Platinum can catalyze C5- and C6-dehydrocyclizations. The two reactions are parallel. Interconversion is very limited between five- and six-membered ring products over nonacidic platinum catalysts. Platinum-catalyzed dehydrocyclization does not involve carbonium ions. [Pg.319]

Most experimental data are reported on the use of Pd-Ti02 catalysts in the hydrogenation. As equation 24 shows, product distribution is considerably affected by the para substituent. The formation of benzyl alcohols is favorable on nonacidic supports while acidic supports promote hydrogenolysis. Hydrogenolysis can also be avoided under strongly acidic conditions in the presence of ethanol. In this case, the product benzyl alcohol readily undergoes dehydration to form benzyl ethyl ether. [Pg.876]

Hydrocracking Condensed-Ring Aromatics Over Nonacidic Catalysts... [Pg.70]

Wu, W. Haynes, H. W., Jr. Hydrocracking Condensed-Ring Aromatics Over Nonacidic Catalysts. ACS Div. Petrol. Chem. Preprints, 1975, 20 (2), 446-478. [Pg.45]

Michael reactionsThis reagent serves as a nonacidic catalyst for Michael reactions of ketene silyl acetals with a,P-enones, and is more effective than dialkoxy-titanium oxides, (R0)2Ti=0. The reaction proceeds at -78° in various solvents, CH2C12, ether, and toluene. [Pg.19]

The alkane conversion data, like the catalyst characterization, should not be considered to fit only one model. In the discussion that follows we consider first a catalyst with a nonacidic support and then consider the case where the support is acidic. An interpretation of the conversion data for atmospheric or lower pressure conversions are complicated by rapid catalyst aging. Thus, we will rely on data generated at greater than one atmosphere (i.e., 100 to 400 psig) in the following discussion. [Pg.125]

For PtSn supported on a nonacidic alumina the addition of Sn causes an increase in activity up to Sn/Pt = 4, and then a decline in activity for low pressure operation (42). The increase in activity is much less at 400 psig operation than the two-fold increase observed at atmospheric pressure. However, there is a change in the selectivity of aromatic isomers produced from n-octane at both 15 and 400 psig as Sn is incorporated into the catalyst. Thus, both Pt and Pt/Sn catalysts produce only (> 90-95%) ethylbenzene and o-xylene as the dehydrocyclization products from n-octane. However, Pt produces ethylbenzene o-xylene = 1 1 whereas a catalyst with Sn/Pt = 4 produces ethylbenzene o-xylene = 1 2. This change in aromatic isomerization leads to two postulates ... [Pg.125]


See other pages where Nonacidic catalysts is mentioned: [Pg.489]    [Pg.108]    [Pg.806]    [Pg.274]    [Pg.58]    [Pg.59]    [Pg.61]    [Pg.282]    [Pg.177]    [Pg.302]    [Pg.312]    [Pg.325]    [Pg.836]    [Pg.225]    [Pg.47]    [Pg.49]    [Pg.57]    [Pg.300]    [Pg.306]    [Pg.315]    [Pg.216]    [Pg.71]    [Pg.82]    [Pg.113]   
See also in sourсe #XX -- [ Pg.65 ]

See also in sourсe #XX -- [ Pg.65 ]




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