A study on the selective hydrogenation of 1,3-butadiene over Pd-Li/SiO₂ catalysts

Lithium addition to Pd supported on silica markedly improves the 1-butene selectivity and activity for hydrogenation of 1,3-butadiene without isomerization and over-hydrogenation of the 1-butene. The activity of 1,3-butadiene in hydrogenation increased linearly with lithium loading. This behavior indicates that there is not a physical blockage of the surface active sites. These results are in good agreement with XPS results that the addition of lithium aided Pd particles to be the metallic state as active site. The addition of lithium greatly improves 1-butene selectivity till a certain level, but over which it decreased and trans-2-butene increased due to isomerization. The ratio of trans- and cis-2-butene from the result of hydrogenation of 1-butene was about 2:1, i.e., 1-butene favored the trans isomer. Therefore, it was reasonably assumed that the increase in 1-butene selectivity was reflected in an decrease in the trans-2-butene selectivity. From NH₃-TPD it is suggested that the addition of lithium affects the adsorption of reactant and product and consequently 1-butene selectivity. 1-Butene selectivity results also indicated there is an optimum value creating a better environment for the desorption of 1-butene without isomerization at a certain level of the lithium loading.