Gas phase semi-hydrogenation of 1,3-butadiene has been investigated over Pd catalysts of egg-shell type containing 0.03-0.05 wt% Pd. The measurements concentrated on the effect of the hydrocarbonaceous deposits formed from methane or butadiene at 473-523 K. The carbonaceous material has influenced the over-hydrogenation selectivity (n-butane formation) and the distribution of n-butenes. Under the reported conditions the deposits form three-dimensional islands and in the case of diene they are also present on the support sites. The poisoning experiments with Pd-powder confirmed the formation of PdCx phase from both methane and butadiene. Deliberate diene and prolonged methane poisoning at 513 K (18 h) increased the n-butane selectivity and decreased the 1-butene/2-butene and trans-/cis-2-butene ratios with simultaneous decrease of the apparent activation energy of hydrogenation. The results are interpreted by transport hinderance which affects mainly the surface fugacity of diene.