Product selectivity hydrogen concentration effect

Both of these reactions have very important industrial uses (Section 14.3.9). In order to obtain alkene streams of sufficient purity for further use, the products of steam-cracking or catalytic cracking of naphtha fractions must be treated to lower the concentration of alkynes and alkadienes to very low levels (<5ppm). For example, residual alkynes and dienes can reduce the effectiveness of alkene polymerisation catalysts, but the desired levels of impurities can be achieved by their selective hydrogenation (Scheme 9.4) with palladium catalysts, typically Pd/A Os with a low palladium content. A great deal of literature exists,13,37 particularly on the problem of hydrogenating ethyne in the presence of a large excess of... 

This paper examines the hydrogenation of aniline, /Moluidinc. and 4-fcrt-butylanilinc over a series of 2.5 % Rh/Si02 catalysts, comparing reaction rates and product selectivities. Further studies concentrated on examining support particle size and average metal crystallite size effects on /Moluidinc hydrogenation and the support pore size effects on 4-tert-butylaniline hydrogenation. 

The effects have been studied of the total or partial substitution of Ni by Cu or Co on the physicochemical properties and catalytic activity of Ni (Co,Cu)-Zn-Al catalysts used for the selective hydrogenation of acetylene. In addition, the influence of the hydrogen concentration in the feed on the activity, selectivity and coke formation on the catalysts has been investigated. The results obtained in this work could be explained by the formation, to different degrees, of bimetallic clusters of Ni-Cu and Ni-Co in the quaternary Ni-Co-Zn-Al and Ni-Cu-Zn-Al catalysts. The formation of these bimetallic clusters would be responsible for the diminution of methane and ethane, both undesirable products. 

Catalytic activity was measured as a function of turnover frequency [moles product/(mole catalyst) (hour)]. The standard run has a turnover frequency of 105 10. All the parameters investigated were perturbed about this standard and included the effects of catalyst, aldehyde, KOH and water concentration, initial CO pressure, and reaction time. In addition, a few selected runs were also conducted to examine the effects of hydrogen in the gas phase as well as the relative ease with which other aldehydes could be reduced. 

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