Confined Synthesis Of Pt And NiMo Bimetallic Component Catalysts And Their Performance For The Catalytic Hydrogenation

Oil resources are still the main energy sources of modern industry and transportation industry in China.As global oil reserves decline,the trend of heavy quality and inferior quality of petroleum is becoming more and more serious,it is urgent to improve the utilization rate of petroleum products and reduce the emission of environmental pollutants caused by their use.Hydrogenation processes,such as n-alkane hydroisomerization,can be used to produce gasoline with high octane number,diesel oil with low freezing point and lubricating oil with high viscosity index;hydrodesulfurization(HDS)technology can remove sulfur-containing components in crude oil to obtain clean fuel oil.These two reactions are important catalytic processes in the petroleum industry to ensure clean and efficient fuel oil production.Developing high-efficient and low-cost catalyst is the key to upgrading of hydroisomerization and hydrodesulfurization technologies.Noble metal-based catalysts are commonly used as catalytic materials in hydroisomerization and hydrodesulfurization,but their large-scale use is limited by limited reserves and high cost.Increasing the utilization of noble metals to reduce its amount or replacing noble metals with transition metals are two common ways to reduce the cost of catalysts.Based on the above analysis,this paper is devoted to the development of strategies,including improving the utilization efficiency of noble metals and developing high-efficient non-noble metal catalysts,to obtain low-cost and high-efficient catalytic materials,through size-control and electronic structure-control methods.The main research contents are as follows:(1).Pt clusters can expose more active sites,thus improving the catalytic efficiency of Pt and reducing the amount of noble metals and catalyst-cost.However,the synthesis of 1 nm Pt clusters remains a challenge.We immobilized the Pt precursors at the pore mouth location of the zeolite based on a“vacuum-assisted”strategy.Highly dispersed Pt clusters(about 1 nm)anchored on the SAPO-11 molecular sieve(S-11)surface were obtained by the confinement effect.The highly dispersed Pt clusters not only exposed abundant active sites,but also facilitated the contact between metal sites and acid sites,promoting the synergy between the two sites.S-11 loading trace Pt clusters(0.15 wt.%)showed excellent catalytic performance in the hydroisomerization of n-hexadecane,the C₁₆ isomer yield reached 89.0%,which was much higher than that over I-0.15 Pt/S-11catalyst prepared via impregnation method and commercial C-0.5 Pt/S-11 catalyst(the maximum isomer yield was about 80%).In addition,V-Pt/S-11 catalyst also shows good hydroisomerization performance for diesel oil.(2).Transition metal Ni,which is in the same main group as Pt,is a potential non-noble metal catalytic material for hydrogenisomerization reaction.Due to its electronic structure and large size,Ni can lead to the hydrolysis of C-C bonds of n-alkanes,which is not conducive to the hydroisomerization performance.Based on the“vacuum-assisted”strategy,we constructed small-size“Ni-Mo O_x”structural units on the surface of S-11molecular sieve.The interaction between the two components leads to electron transfer from the Mo O_x species to the metal Ni,which increases the electron density in the the d-band center of Ni and enhances the activation and desorption of H at the Ni site.In addition,the strong interaction between Mo O_x and S-11 support makes the size of the Ni particles in the“Ni-Mo O_x”structural unit smaller,which exposes more surface active sites.Under the optimized conditions,3.0 Ni-0.5 Mo/S-11 catalyst exhibited similar isomerization performance and isomerization/cracking mechanism as 0.5Pt/S-11 catalyst,the optimal isomer yield reached 81.4%,which was much better than the mono-metal Ni based catalysts and non-noble metal-based catalysts reported in the literature.(3).Electronic modulation of Mo by Ni species in the Ni-Mo bimetallic based system can also promote the catalytic performance of Mo species.For example,using Ni to modulate the electronic structure of Mo S₂ can improve its HDS performance,but this promotion effect is also related to the size and the sulfurization degree of the active phase.We used phosphomolybdate(PMo₁₂)as Mo source and polyethylenimine(PEI)as coupling agent to anchor highly dispersed Mo and Ni sources on PEI-modified graphite oxide(GO).After calcination and sulfidation,a small-size Ni-Mo sulfide catalyst(Ni-Mo-S/RGO-A)was synthesized.The anchoring effect of PEI effectively inhibits the migration and aggregation of metal components during heat treatment,resulting in the formation of small-size sulfide.In addition,the appropriate interaction between the graphene substrate and the metal components is conducive to the full sulfidation of the active phase species,which promotes the formation of sulfur vacancy.The prepared Ni-Mo-S/RGO-A catalyst exhibited excellent catalytic activity in the HDS reaction of dibenzothiophene(DBT),its catalytic activity was 1.7 times and 4.3 times that of the Ni-Mo-S/RGO-I catalyst prepared by impregnation method and commercial Ni-Mo-S/Al₂O₃catalyst,respectively,which was the best HDS catalyst reported in literature at present.