2008 Volume 51 Issue 3 Pages 119-133
The reaction pathway for hydrogenation of 2-butyne-1,4-diol involves parallel and consecutive isomerization as well as hydrogenation reactions forming other side products along with cis-2-butene-1,4-diol and butane-1,4-diol. Hence, achieving the highest selectivity to butene- and/or butanediol is critical from industrial point of view. Hydrogenation of butynediol is also of fundamental significance, due to its adsorption characteristics leading to the formation of active species and their role in determining the product distribution. Studies on designing various catalyst systems including colloidal as well supported palladium nanoparticles for the hydrogenation of butynediol, role of additives, catalyst pretreatment, kinetic studies carried out in our group has been presented in this review. Interestingly, almost complete selectivity to the intermediate olefinic diol was achieved with 1% Pd/CaCO3-NH3 catalyst system. This could be due to the competitive adsorption of ammonia on the palladium surface along with the substrate 2-butyne-1,4-diol. Studies on catalyst pretreatment and kinetics using palladium catalyst have also been presented here. Nanostructure palladium both colloidal as well as supported catalysts showed a very high catalytic activity (10-40 times more) in the hydrogenation 2-butyne-1,4-diol to cis-2-butene-1,4-diol compared with the corresponding conventional Pd catalysts. For platinum based catalysts, formation of side products was completely eliminated in the hydrogenation of butyne diol. The increase in the basic strength of alkali metal doped Pt catalysts measured by CO2-TPD, led to the increase in electron density of Pt hence, faster desorption and higher selectivity to butenediol. In the case of continuous hydrogenation, the selectivity pattern was completely different from that found in the case of batch slurry reactor and by varying the contact time, the selectivity to both butene- and butanediols could be varied over a wide range of conditions.
