Preparation Of Metal Oxide-loaded Palladium Based Catalyst And Selective Hydrogenation Of Acetylene

Ethylene is one of the important raw materials in chemical production,which is mainly used in the production of polyethylene and is also a commonly used inter-mediate in the pharmaceutical,agricultural and fine chemical industries.However,the process of industrial cracking to ethylene generates a small amount of acetylene,which can poison the catalyst for downstream ethylene polymerization reactions and therefore needs to be removed prior to the polymerization reaction.Among many production methods,selective hydrogenation of acetylene to ethylene is considered the most efficient,environmentally friendly and economical strategy,and the commonly used loaded palladium-based（Pd-NPs）catalysts tend to over-hydrogenate acetylene to ethane due to their high activity,therefore,improving the selectivity of Pd-based catalysts to ethylene is the key to achieve efficient acetylene hydrogenation.Also,due to the high price of Pd-based materials,the development of low-loading Pd catalysts to reduce the catalyst fabrication cost is an important research direction in the field of catalysis.In this thesis,a series of Pd-based catalysts with graphene coating,Zn O nanowires,Zn O nanoparticles,Cerium oxide nano-particles and Tita-nium oxide nanoparticles were prepared by deposition-precipitation,hydrogen red-uction and CVD methods,and the loading of Pd was controlled to be below 0.5 wt%.Finally,the prepared series of catalysts were applied to acetylene selective hydro-genation to investigate their practical catalytic performance.The main research of this thesis contains the following two aspects:（1）Preparation and structural characterization of palladium-based catalysts:a series of loaded Pd/Zn O,Pd/CeO₂,and Pd/TiO₂ catalysts were prepared by deposition precipitation method using Zn O,cerium oxide,and titanium oxide as carriers and palladium nitrate solution as precursors,followed by hydrogen reduction and high-temperature cracking deposition of organic precursors at 700℃to prepare a series of graphene layers with coated C@Pd/Zn O,C@Pd/CeO₂,and C@Pd/TiO₂ catalysts.The species composition,structure,and chemical valence of the fabricated catalytic materials were subsequently characterized and analyzed by TEM,XRD,Raman,and XPS.（2）On the basis of the above work,the performance of the prepared series of catalysts was investigated for the selective hydrogenation of acetylene,and the results showed that the ethylene selectivity of the catalysts was significantly enhanced after the graphene layer encapsulation of the restricted domain:the C@Pd/Zn O（nanowire）catalyst showed 92.5%conversion and 96%selectivity at 150°C;the C@Pd/CeO₂-0.75 m L catalyst at 150℃with 94%conversion and 75%selectivity;C@Pd/TiO₂catalyst at 110℃with 95.5%conversion and 79%selectivity.Meanwhile,combined with the XPS and other characterization results,it was found that the interaction between the active center Pd and the carrier would regulate the catalytic performance of the catalyst,and there was the generation of Pd-Zn bond between the Zn O carrier and the Pd nanoparticles,which had a significant contribution to the improvement of the catalyst selectivity;the cladding of the graphene layer constructed a domain-limited spatial environment,which helped the rapid desorption of ethylene on the catalyst surface and prevented the excessive hydrogenation of ethylene to ethane.