Study On Ligand Modified Palladium Catalyst For Acetylene Hydrogenation

The property of supported metals catalysts were greatly affected by inorganic additives,organic ligands and property of supports.In this dissertation,the effects of the ligand and its structure on the hydrogenation of acetylene by Pd catalyst were investigated by adjusting the size of Pd nanoparticles and controlling the surface electronic properties and the spatial structure of the Pd catalyst by ligands.?1?Adsorption of Pd²⁺by N₃-containing organosilicone-modified silica?N₃-SiO₂?support and subsequent reduction by addition of NaBH₄ to synthesize a supported Pd catalyst.The impregnated Pd solution was impregnated with Al₂O₃ and C?multi-walled carbon nanotubes?in equal volume to synthesize supported Pd catalysts,The catalysts prepared with N₃-SiO₂ and C as carriers showed better catalytic performance,with conversion rates of 95%and 99%at 130?and ethylene selectivity of 90%and 94%,respectively.?2?With[N₃-SiO₂]as the carrier,the catalytic performance of Pd-based nanostructured catalysts with and without ligands was investigated.Acetylene hydrogenation results show that,under the same temperature conditions,the Pd catalyst with ligand addition than the Pd catalyst without ligand,ethylene selectivity decreased significantly.The hydrogenation of acetylene over Pd catalysts modified with triphenylphosphine?PPh3?ligand,pyridine?Py?and 1-Dodecanethiol?HSC12?was studied.The results show that,compared with the use of PPh3 and Py ligand,the use of HSC12 as a ligand can increase product selectivity.A series of characterizations indicate that the ligand-modified Pd nanocatalysts have smaller particle size and higher dispersibility;the ligands are adsorbed on the metal Pd.?3?Using[N₃-SiO₂]as a carrier,the effect of different alkyl S ligands on the supported Pd nanocatalysts was further investigated.The results of the catalyst tests show that under the same temperature conditions,the conversion of acetylene gradually increases and the selectivity to ethylene increases with the increase of chain lengths of alkyl S ligands.At the same temperature,the catalytic performance of the same ligand chains with different structures I,possessing a heterocyclic structure ligand has better catalytic performance in the reaction.The results of characterizations indicate that the sizes of Pd-based catalysts with different alkyl S ligands are similar and the Pd loadings are similar.The effects of different chain length and chain alkyl S ligands on the metal Pd are different,Thus affecting its catalytic performance.?4?The effects of different particle sizes on the catalytic performance of the catalysts were investigated with[N₃-SiO₂]and Al₂O₃ as carriers.When the loadings are the same,the dropping rate of the reductant will affect the size of Pd particles and further affect the catalytic activity;with different loadings,the higher the loading,the larger the particle size of Pd,leading to the increase of catalytic activity and reduce selectivity.