| Pyrolysis gasoline (PyGas) is a valuable byproduct and it accounted for more than half of the ethylene production. The main purpose of the first stage hydrogenation of PyGas is that diene and alkenyl aromatic are selective hydrogenated into mono-olefins and alkyl aromatics, where the unsaturated compound and the polymer generation can be avoided and further utilized. The development of relating to the hydrogenation catalysts has received more and more attention.Bimetallic catalyst materials show a lot of physical and chemical properties different from the corresponding single metal systems in the joint action of confinement effect, size effect and alloying effect. The excellent bimetallic catalysts can be prepared by modulating composition and its mass ratio. Currently, Ni-based catalysts are an important catalyst for PyGas hydrogenation, not only it has good ability of anti-gum, but also has a strong anti-arsenic metal poisoning, and there is a very good price competition force. In this paper, based on previous laboratory supported Ni-based catalyst materials research,Al2O3 was not only the source of Al3+ but also the catalyst support, a series of supported NiCo/Al2O3 bimetallic catalysts are prepared and further evaluate their the catalytic performance. The physical and chemical performance of the supported catalysts is characterized in virtue of several characterization techniques and investigated the effect of different mass fraction ratio of Ni and Co on catalytic properties. The results of this paper are as follows:1. Firstly, NiCoAl-LDHs and NiAl-LDHs/Al2O3 and COAl-LDHs/Al2O3 were in-situ grown(LP) on the γ-Al2O3 spheres with adjusting Ni:Co mass ratio. Then NiCo/Al2O3 samples are obtained after calcination at 450℃ and reduction at 500 ℃ of LDHs/Al2O3 precursor materials. Compared with the samples by impregnation method(IM), the LP nanoparticles are smaller than 8 nm and display a narrow distribution, while IM are larger than 16 nm and the proportion reaches 53%. With the addition of Co, the proportion of LP between 1 and 4 nm is enhanced from 53% to 63%. Also, NiCo bimetallic catalysts form NiCo alloy phase. Futhermore, the confinement effect of the Ni-O-Al or Co-O-Al structure in the LDHs gives rise to the relatively stronger interaction between Ni or Co and support for LP. Meanwhile, the addition an appropriate amounts of Co is conducive to prompte the reduction of the Ni species.2. This paper report the preparation of the novel highly dispersion supported NiCo/Al2O3 bimetallic catalysts for selective hydrogenation of PyGas. The catalytic evaluation results indicate that the mass fraction ratio of NiCo bimetallic plays an important role in catalytic performance. Compared with the Ni/Al2O3 catalyst, the appropriate amounts of Co can significantly enhance the catalytic activity, selectivity and stability of the catalytic reaction. However, the opposite results are obtained with further increase the addition of Co. It is likely that the catalyst active sites surface and structure properties are alterd by modulating the content of Co, thus affecting the synergistic effect of Ni and Co. At the same time, the IM sample displays a lower catalytic activity and selectivity than the LP and stability of the catalytic reaction is also poor.3. Finally, this paper introduces H2-TPD characterization method to analyze LP and IM samples. It can be found that the desorption peaks of IM sample are higher than LP samples. And LP-2Ni1Co/Al2O3 has a lower desorption peaks in LP samples. This phenomenon may indicate that binding energy of the adsorbed hydrogen of the catalyst active sites has noticeably reduced for LP samples, which is crucial importance for the hydrogenation reaction. Also, the total hydrogen desorption amounts are further analyzed. According to above analysis, it has explained the experimental results of excellent catalytic performance of LP-NiCO/Al2O3 catalysts samples. |
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