Ni/SAPO-11 catalysts with highly dispersed Ni (TA-Ni/SA-11) were prepared using tartaric acid as a dispersant. The effect of the tartaric acid content on the physiochemical properties of the TA-Ni/SA-11 catalysts and their n-heptane hydroisomerization performance were investigated. TA-Ni/SA-11 exhibits smaller Ni particles and more Ni active sites in comparison to conventional Ni/SAPO-11 prepared via the impregnation method due to the interaction between tartaric acid and Ni 2+ . As the molar ratio of tartaric acid and Ni 2+ (n TA /n Ni ) increases, the number of Ni active sites in TA-Ni/SA-11 rises, while the surface area and relative crystallinity decrease because of the dealumination of SAPO-11. When n TA /n Ni is 0.75, 0.75TA-Ni/SA-11 presents the highest n-heptane conversion of 82.4% and isomer selectivity of 90.5%, as well as the lowest cracking selectivity of 9.0% at 380 °C, 1.5 MPa, 2 h − 1 , and a volume ratio of H 2 to n-heptane of 400 among these catalysts. Graphical
Lei Fan,Lianming Zhao,Yuchao Lv,Tinghu Wang,Yupeng Tian,Jianye Fu,Xinmei Liu
The synthesis of highly-dispersed non-noble metal based catalysts and their application in hydrogenation/dehydrogenation still remain challenging. Therefore, it is of great importance to protect metals from aggregation in both calcination and reduction processes. In this research, density functional theory (DFT) calculations were used to elucidate the stabilization effect of ionic liquid [Bmim][BF4] on Ni in the reduction process, showing that [Bmim][BF4] could efficiently inhibit Ni aggregation on the support. By further analysis combined with theoretical calculations, we found that the degree of metal dispersion before reduction directly determines the effect of [Bmim][BF4]. Guided by the DFT results, the method of co-assisted preparation of Ni/SAPO-11 using [Bmim][BF4] and lysine was adopted. Lysine forms a coordination compound with nickel oxides. The steric hindrance generated by the Ni–lysine complex can effectively inhibit the aggregation of nickel oxides during the calcination process. The DFT calculations revealed that during the reduction process, [BF4−] plays a dominant role in stabilization and electronic modulation by directly interacting with Ni on the support. The combination effects of [Bmim][BF4] and lysine effectively inhibit metal aggregation, leading to ultra-small nickel particles with a mean size of 4.4 nm over the obtained catalyst. Furthermore, the presence of [Bmim][BF4] also tunes the electronic state of Ni species. Using hexane isomerization as a probe reaction, the result indicates the excellent catalytic activity of the obtained catalyst (≈93.7% isomer selectivity at 63.5% conversion), much superior to that of Ni/SAPO-11 obtained from the traditional impregnation route (≈75.8% isomer selectivity at 64.6% conversion). This work provides a new method for the preparation of highly effective non-noble metal supported catalysts.
Wei-Long Zhan,Yu-Chao Lyu,Xin-Mei Liu,Lei Fan,Fu-Rang Li,Ye Yang
The Ni/SAPO-11 catalyst used for n-hexane hydroisomerization was prepared via a novel two-step crystallization strategy. It involves introduction of nickel salt into the pre-crystalized system of SAPO-11 by grinding followed by a second crystallization step. No extra solvent is introduced during the whole synthesis procedure which reduces waste liquid emissions significantly. More importantly, interaction between nickel and support is effectively regulated by the novel method to achieve a well dispersed nickel species and inhibit formation of inert nickel spinel simultaneously. Chemical environments of framework Si are tuned to enhance surface acidity of the Ni/SAPO-11 catalyst. It also shows smaller particle size which favors fast diffusion of reactants and products. Insights into the two-step crystallization indicate that accumulation of SAPO-11 precursors in the pre-crystallization stage, pH regulation by nickel salt and structural directing effect of Ni 2+ during the second crystallization period account for the rapid crystal growth and smaller particle size of the Ni/SAPO-11 catalyst. All the unique features endow the Ni/SAPO-11 catalyst higher activity and isomers selectivity than the Pt/SAPO-11 catalyst in n-hexane hydroisomerization.
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