Catalyst hydrogenolysis

Catalytic transfer hydrogenation (entries 2 and 3 below) can be used to cleave benzyl esters in some compounds that contain sulfur, a poison for hydrogenolysis catalysts. 

Diphenylmethyl esters are similar in acid lability to r-butyl esters and can be cleaved by acidic hydrolysis from 5-containing peptides that poison hydrogenolysis catalysts. 

Comparison of the catalysts in Figure 1 demonstrates that the Ni/Re catalyst yielded the highest activity of the catalysts under the conditions tested. The Rh/Re catalyst also showed excellent conversion at 240°C as did the Ru catalyst which is also known to be an excellent hydrogenolysis catalyst for conversion of sorbitol to these products [4,5], The Ru/Re and Ru/Re+ catalysts also demonstrated high conversion, especially at high temperatures. 

Reaction Modeling Studies Related to Cluster-Derived Butane Hydrogenolysis Catalysts... 

The traditional catalysts have usually a short period of operation because of high rates of deactivation processes, such as polymerization, carbonization, and decomposition of the active component. The catalysts are routinely prepared by precipitation, which results in formation of a wide range of surface species, providing a number of side reactions. The side reactions may also occur on alumina, the main support for the hydrogenolysis catalysts. Alumina is an active catalyst for dehydration processes as well ... 

Cyclopentane hydrogenolysis. Catalysts were tested with cyclopentane hydrogenolysis imder the following conditions 0.9 bar hydrogen and 0.1 bar of cyclopentane at 290°C. 

Figure 1 Activity for cyclopentane hydrogenolysis. Catalysts A catalytic reduction B coimpregnation, C successive impregnation CR calcined and reduced R only reduced catalyst.

Hydrogenolysis [1, 779, after citation of ref. 4], Homing and Reisner4 found palladium-on-charcoal very effective as a hydrogenation-hydrogenolysis catalyst without addition of perchloric or sulfuric acid. They found the catalyst effective also... 

Hydrogenation of ketones in alkaline medium at room T and atmospheric P, catalyzed by [Rh(2,2 -bipyridine) (diene)]PFg type complexes occurs with selectivity for reduction of carbon-oxygen double bonds to hydroxyl groups even in the presence of olefinic bonds. The system acts as a hydrogenolysis catalyst for molecular O2, and hydrogenation activity is retained even if large amounts of 62 are present. ... 

Metal phthalocyanines MPc (M=V, Mn, Fe, Co, and especially Pd) as very stable and selective hydrogenation or hydrogenolysis catalysts with adjustable chemospecificity, sometimes pH dependent. 

On activity, comparison of runs 4 and 5 illustrates an increase by a factor of two on going from ethanol to methanol (polarity effect [3]). Addition of a catalytic quantity of sulfuric acid (run 4 compared to run 3) increases activity by a factor of ten [hydrogenolysis catalyst - [5]]. On selectivity, using alcohols in place of ether gives different intermediates (4h in EtOH, 4e in MeOH and 4g in dimethoxyethane) illustrating the concept of "reactive solvent" in the case of alcohols [6]. 

Reduction of 0.1 % Ru/TiOa at 758 K led to high values of 5,- in the n-hexane reaction at 633 K, reacting 94% when the precursor had been made by ion exchange lower values were found with 0.5% RU/HO2, and very low values after reduction at only 433 K. Thus as with the effect of sulfur, even the character of the most active hydrogenolysis catalyst is susceptible to modification. 

In fact, the acid-catalysed ring contraction of alkylcyclohexanes to al-kylcyclopentanes is potentially important as a reaction, because cyclopentanes are more readily ring-opened than alkylcyclohexanes over precious metal hydrogenolysis catalysts to give linear hydrocarbons. Such linear alkanes are suitable for diesel fuel. Addition of an acidic function therefore enables both cyclopentanes and cyclohexanes to be transformed at a similar rate in this way. 

---