Preparation Of The High Dispersion Ⅷ Group Transition Metal Catalysts And Their Catalytic Performance For Oxidative Dehydrogenation Of Light Alkanes

For supported metal catalyst,the high dispersion of active metal center is of vital importance to their catalytic performance for specific reactions.The thesis aims to develop a new method to prepare supported VIII group metal catalyst with isolated metal center and higher stability and investigate their performance for oxidative dehydrogenation of light alkanes.Research mainly focuses on the following aspects:Design and install the vapor deposition device and prepare supported Ni/γ-Al₂O₃ 、Ni/5A 、 Ni/Hβ catalysts using nickel acetylacetonate as the precursor under vacuum atmosphere,explore the impact of deposition temperature,weight of precursor and deposition times for the nickel content of catalyst.Results show that catalyst with nickel content of 8%could be prepared in this device under the condition of 240℃,-101.3kPa,with the deposition time of 1 hour,4 times by 1g precursor.Performance for ODHE reactions of catalyst with close nickel content prepared by vapor deposition and impregnation were studied.Research found that catalysts prepared by vapor deposition with lower nickel content（less than 4.2%）could better enhance ethane conversion,oxygen conversion and gain higher ethylene yield compared with catalyst prepared by impregnation.When using γ-Al₂O₃ as the supporter,catalyst with higher nickel content（more than 6%）prepared by vapor deposition can’t get a better ethylene selectivity for the reaction.Preliminary results show that covering the silica layer on supported platinum catalyst can effectively prevent the accumulating and sintering of metal particles under high temperature.Using TEOS as precursor,when calcinated under 300℃ catalysts with inert silica layer still possess considerably isolated bare active center and obvious particle accumulation won’t happen even though the calcination temperature rises to 600 ℃.ODHE reaction results indicate that catalysts with silica inert layer could maintain higher stability and activity in the course of the reaction process.This method can also be extended to the preparation of other supported transition metal catalyst.