Synthesis of small crystal NiY zeolites and their catalytic performance in hydrocracking
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摘要: 通过在小晶粒Y分子筛合成的过程中原位引入Ni源合成了一系列不同Ni掺入量的小晶粒Y-xNi分子筛,将活性金属Ni预浸渍到Y分子筛的骨架中。将Y-xNi分子筛和ASA混合物作为载体并采用等体积浸渍法负载Ni和W,制备了系列Cat-xNi加氢裂化催化剂,以正十六烷为反应物,探究其加氢裂化催化反应性能。采用扫描电子显微镜(SEM)、X射线衍射(XRD)、N2吸附-脱附、氨气程序升温脱附(NH3-TPD)、氢气程序升温还原(H2-TPR)、透射电子显微镜(TEM)和X射线光电子能谱(XPS)等表征手段分析了Ni的掺入对Y分子筛及Cat-xNi催化剂理化性质的影响。结果表明,Ni主要取代Al引入Y分子筛骨架;在Y分子筛中适量掺入Ni会提高Y分子筛的相对结晶度以及Brønsted酸和Lewis酸位点的数量,但过量的Ni掺入不利于Y分子筛的结晶。Ni的掺入削弱了金属与载体间的相互作用,提高了活性金属的硫化度及NiWS活性相的堆积数及分散度,调节了催化剂上金属中心与酸中心的匹配。催化性能评价结果显示,由于Ni改性能同时增加Brønsted酸中心与NiWS活性中心数量,增强金属中心与酸中心之间的协同作用,因而在提高正十六烷加氢裂化活性的同时可避免其过度裂化,获得较高的中间馏分产物(C8–C12)选择性及收率。在360 °C反应条件下,与Cat-0Ni催化剂相比,Cat-0.2Ni催化剂具有较高的n-C16转化率和C8–C12产物收率(达65.4%)。综上可知,采用原位合成法将活性金属Ni预浸渍在Y分子筛上可以有效调节裂化活性中心与加氢活性中心之间的平衡,从而提高其催化活性和中间馏分产物的收率。Abstract: A series of small crystal Y-xNi zeolites with different amounts of Ni doping were synthesized by in situ introducing the Ni precursors during the synthesis, through which the active Ni metal was incorporated into the framework of the Y zeolites. With the mechanical mixture of Y-xNi zeolites and amorphous silica-alumina (ASA) as the support, a series of Cat-xNi catalysts were prepared through loading the Ni and W components by incipient wet impregnation and the catalytic performance of Cat-xNi in the hydrocracking of n-hexadecane was then investigated. In addition, the effect of Ni doping on the physicochemical properties of Y zeolite and Cat-xNi catalysts was elucidated with the help of scanning electron microscopy (SEM), X-ray diffraction (XRD), N2-adsorption desorption, NH3 temperature programmed desorption (NH3-TPD), H2 temperature programmed reduction (H2-TPR), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and so on. The results indicate that Ni can replace Al to enter the framework of the Y zeolites. The incorporation of appropriate amount of Ni into the Y zeolites can increase their relative crystallinity and the number of Brønsted and Lewis acid sites; however, excessive Ni incorporation is detrimental to the crystallization of Y zeolite and excessive non-framework Ni species will cover the surface Brønsted acid sites. Moreover, Ni doping can weaken the metal-support interaction, increase the sulfation extent of the active metal and the stacking number and dispersion of the active NiWS phase, and then improve the matching between the metal and acid sites on the Cat-xNi catalysts. As a results, in comparison with the counterpart Cat-0Ni catalyst, the Cat-xNi catalysts display more Brønsted acid sites and active NiWS sites as well as improved the synergy between the metal sites and acid sites, which can enhance the conversion of n-hexadecane whereas inhibit the over-cracking, and then booster the yield of the middle distillate products (C8–C12). In particular, for the n-hexadecane hydrocracking at 360 °C, the Cat-0.2Ni catalyst exhibits a C8–C12 product yield of 65.4%, with a much higher n-C16 conversion than the Cat-0Ni counterpart. All these suggest that the pre-impregnation of active metal Ni on the Y zeolites can effectively regulate the balance between the hydrogenation and cracking performance and improve the catalytic activity and the yield of middle distillate products in the hydrocracking of paraffins.
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Key words:
- Y zeolite /
- in-situ Ni modification /
- catalyst /
- hydrocracking /
- middle distillate
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图 11 Cat-xNi系列硫化催化剂在不同反应温度下n-C16的转化率(a)、C8−C12的选择性(b)和收率(c)以及在360 ℃条件下重复三次实验后不同催化剂的C8−C12的收率(d)
Figure 11 Conversion of n-C16 (a), selectivity of C8−C12 (b) and yield of C8−C12 (c) over the sulfided NiW catalysts at different reaction temperature; the average yield of C8–C12 (with the error bar) derived from three repetitive tests at 360 °C for different sulfided Cat-xNi catalysts (d)
表 1 不同Ni含量杂原子Y-xNi分子筛的理化性质
Table 1 Physicochemical properties of the synthesized Y-xNi zeolites with different Ni contents
Sample n(NiO/Al2O3) Relative crystallinityb/
%Crystal sizec/
nmSBET/
(m2·g−1)vtotal/
(cm3·g−1)Average pore diameter/
nmtheoretical actuala Y-0Ni 0 0 100 125 634.4 0.64 6.7 Y-0.1Ni 0.1 0.09 102 136 612.1 0.62 6.4 Y-0.2Ni 0.2 0.17 97 141 600.6 0.61 6.1 Y-0.3Ni 0.3 0.26 92 146 588.4 0.59 5.9 Y-0.4Ni 0.4 0.37 88 152 560.2 0.55 5.1 a: Calculated from XRF results (test sample was HY-xNi zeolites after ion-exchange); b: Calculated from XRD results and Eq. (1); c: Statistically calculated from SEM image results. 表 2 Y-xNi系列分子筛上各物种分峰拟合
Table 2 XPS deconvolution results of the synthesized Y-xNi zeolites
Catalyst Si−O−Si/% Si−O−H/% Si−O−Al/% Ni−O/% Ni2+/% Ni3+/% Y-0Ni 39.6 28.1 32.3 − − − Y-0.1Ni 37.3 25.8 23.5 13.4 43.0 57.0 Y-0.2Ni 38.1 29.1 17.6 15.2 46.7 53.3 Y-0.3Ni 38.8 30.0 13.4 17.8 50.1 49.9 Y-0.4Ni 39.1 30.8 10.9 19.2 55.4 44.6 表 3 Y-xNi系列分子筛的酸类型及酸量
Table 3 Acidity of the synthesized Y-xNi zeolites
Sample Acidity/(μmol·g−1) total acid sites (200 ℃) medium and strong acid sites (350 ℃) totald L B L+B B/L L B L+B B/L Y-0Ni 96 220 316 2.3 45 158 206 3.5 414 Y-0.1Ni 125 233 358 1.9 63 164 227 2.6 452 Y-0.2Ni 162 242 404 1.5 88 171 259 1.9 486 Y-0.3Ni 193 254 447 1.3 107 182 289 1.7 522 Y-0.4Ni 228 257 485 1.1 124 189 313 1.5 591 d: Calculated from NH3-TPD results. 表 4 硫化催化剂上WS2的平均长度、堆垛层数、fw值
Table 4 Average length, stacking number, fw values of WS2 slabs for the sulfided Cat-xNi catalysts
Catalyst Length/nm Stacking number fw Cat-0Ni 3.65 3.54 0.34 Cat-0.1Ni 3.61 3.55 0.35 Cat-0.2Ni 3.56 3.58 0.36 Cat-0.3Ni 3.48 3.58 0.37 Cat-0.4Ni 3.65 3.47 0.32 表 5 硫化NiW系列催化剂上各物种分峰拟合结果
Table 5 XPS deconvolution results of the sulfide NiW series catalysts
Catalyst WS2/% WOxSy/% WO3/% Nisulfidation/% NiWS/% NixSy/% NiO/% Cat-0Ni 68.1 10.2 21.7 70.1 58.6 11.5 32.9 Cat-0.1Ni 68.7 11.4 19.9 68.3 59.1 9.2 31.7 Cat-0.2Ni 69.0 11.8 19.2 69.5 59.7 9.8 30.5 Cat-0.3Ni 69.2 12.1 18.7 70.2 60.8 9.4 29.8 Cat-0.4Ni 51.8 9.8 38.4 63.6 52.9 10.7 36.4 表 6 360 ℃下五种催化剂的n-C16加氢裂化活性数据
Table 6 Results of the n-C16 hydrocracking reaction over five catalysts at 360 ℃
Catalyst ka/(mol·g–1·h−1) TOFa,b/h−1 n-C16 conversion/% C8−C12 selectivity/% C8−C12 yield/% Cat-0Ni 1.09×10−2 25.79 65.2 88.9 58.1 Cat-0.1Ni 1.22×10−2 27.32 71.3 86.6 61.7 Cat-0.2Ni 1.31×10−2 28.05 75.1 86.0 64.6 Cat-0.3Ni 1.44×10−2 29.44 76.2 75.4 57.5 Cat-0.4Ni 1.68×10−2 38.19 81.0 68.9 55.8 a: The rate constant k and TOF values were determined at an n-C16 conversion of about 30% by changing the LHSV for reaction; b: The TOF value is number of n-C16 molecules converted per hour per mole of W atoms. -
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