Abstract Here, different loading of palladium (Pd), ranged from 0.5 to 5 wt%, was incorporated into the three dimensional siliceous mesoporous material; TUD-1. The synthesis procedure was carried out without the use of solvents, surfactants, and/or copolymers. Only triethanolamine and water with the precursors of Si and Pd were applied in one-pot synthesis procedure to prepare Pd-TUD-1 materials. The prepared materials were characterized by means of elemental analysis, XRD, Raman spectroscopy, N 2 sorption measurements, SEM and TEM. Characterization data confirmed the formation of PdO particles inside the pores of TUD-1 matrix, moreover bulky PdO particles were also detected as an extra-framework separated phase in the high loading samples. The prepared samples were divided into two batches, the first was activated by hydrogenation at 300 °C for 3 h, and the second batch did not activated. The catalytic activity of the two batches was examined in the selective hydrogenation of 1,5-cyclooctadiene (COD) at 80 °C under solvent-free condition to produce cyclooctene (COE). The obtained results showed that the samples of the two batches were able to catalyze the reaction with a very comparable activity. The non-hydrogenated sample with a 0.5% Pd gave 98.5% COD conversion with a COE selectivity of 92.8%, while the same sample which pre-hydrogenated gave 96.8% of COD conversion and 93.5% selectivity towards COE. The characterization of the used catalysts confirmed that PdO was in-situ reduced to Pd nanoparticles during the reaction. Graphical abstract Image 1 Highlights • PdO nanoparticles were incorporated with different loading in TUD-1 mesoporous material. • Pre-activation of PdO nanoparticles was performed by hydrogenation to generate Pd0 active sites. • The reduction of 1,5-cyclooctaniene was used to evaluate the catalytic activity of the pre-activated catalysts and the as-synthesized ones. • The activity data shows that the pre-activation (hydrogenation) step is not necessary at low Pd loading. [ABSTRACT FROM AUTHOR]