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 s electivity and activity for hydrogenation of 1,3-butadiene without isomeriz ation and over-hydrogenation of the 1-butene. The activity of 1,3-butadiene in hydrogenation increased linearly with lithium loading. This behavior in dicates 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 l ithium aided Pd particles to be the metallic state as active site. The addi tion of lithium greatly improves 1-butene selectivity till a certain level, but over which it decreased and trans-2-butene increased due to isomerizat ion. The ratio of trans- and cis-2-butene from the result of hydrogenation of l-butene was about 2:1, i.e., 1-butene favored the trans isomer. Therefo re, 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 i t is suggested that the addition of lithium affects the adsorption of react ant and product and consequently 1-butene selectivity, 1-Butene selectivity results also indicated there is an optimum value creating a better environ ment for the desorption of 1-butene without isomerization at a certain leve l of the lithium loading.