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摘要: 采用共沉淀法和水热法制备了三种不同粒径、不同结构的纳米氧化锆催化剂, 借助XRD、TEM、Raman光谱、N2物理吸附、XPS、NH3-TPD表征了催化剂的物理化学性质, 并研究了其合成气催化转化性能。在400 ℃、3 MPa、空速500 mL/(gcat·h)、进料组成H2/CO/Ar (体积比) 为5:5:1时, 氧化锆能够一步催化合成气转化为高辛烷值烃类产物, 主要是异构烯烃、环状烯烃及芳烃。在烃类产物中, C5+选择性高达48%, C5+中芳烃含量为30%-53%。结果表明, 单斜相氧化锆比四方相更有利于CO转化, 其中, 比表面积较大、酸量较大的小粒径氧化锆表现出最高的CO转化率及产物收率; 而大晶粒单斜相氧化锆表现出最高的芳烃选择性, 这与其较高的酸性位密度相对应。因此, CO转化在ZrO2催化剂上是酸催化反应, 酸量影响催化剂的活性, 而酸性位密度是影响芳烃等较大分子量产物生成的主要因素。Abstract: A series of ZrO2 nanoparticles with different particle sizes and different crystalline phases were prepared using coprecipitation and hydrothermal methods. Their physico-chemical properties were characterized by N2 physisorption, XRD, TEM, Raman spectroscopy, XPS, and NH3-TPD techniques. The catalytic performances for syngas conversion were tested at 400 ℃, 3 MPa, gas hourly space velocity (GHSV) of 500 mL/(gcat·h), and H2/CO/Ar (volume ratio)=5:5:1. It was found that syngas can be directly converted into hydrocarbons over ZrO2 nanoparticles. The hydrocarbon products are mainly composed of isomerized olefins, cyclenes, and aromatics. The selectivity of C5+ hydrocarbons is up to 48%. Moreover, the aromatic concentration in C5+ ranges from 30% to 53% depending on ZrO2 structures. It is also found that the monoclinic ZrO2 shows higher activity than the tetragonal one. Monoclinic ZrO2 with larger specific surface area and acid amount show highest CO conversion as well as the yield of target products, but the monoclinic ZrO2 with lager particle size has the higher acid surface density and results in the higher aromatic selectivity. Consequently, acidity is the key factor for CO conversion. And high acid surface density promotes the formation of aromatics but acid amount affects the activity.
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Key words:
- zirconia /
- isosynthesis /
- syngas /
- one-step /
- aromatics
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图 1 不同方法制备的氧化锆X射线粉末衍射谱图
Figure 1 XRD patterns of ZrO2 synthesized by different methods
图 2 不同方法制备的氧化锆的拉曼(Raman) 光谱谱图
Figure 2 Raman spectra of ZrO2 synthesized by different methods
图 3 不同氧化锆样品的透射电子显微镜照片
Figure 3 TEM (scale bar 20 nm) and HRTEM (scale bar 5 nm) images of ZrO2
(a), (b); m-ZrO2 (30 nm); (c), (d); m-ZrO2 (9 nm); (e), (f); t-ZrO2(9 nm)
图 4 不同氧化锆样品的NH3程序升温脱附曲线(NH3-TPD)
Figure 4 NH3-TPD profiles of ZrO2 prepared by different methods
图 5 三种催化剂样品的CO程序升温脱附(CO-TPD) 曲线
Figure 5 CO-TPD profiles of ZrO2 prepared by different methods
图 7 不同氧化锆样品的XPS谱图
Figure 7 XPS spectra of ZrO2 prepared by different methods
(a): Zr 3d; (b): O 1s
图 8 m-ZrO2 (30 nm) 液相烃类产物气相色谱图(来自色-质联用)
Figure 8 GC spectrum of liquid hydrocarbons produced over on m-ZrO2 (30 nm) catalyst using GC-MS analysis
(t=400 ℃, GHSV=500 mL/(gcat·h-1), p=3 MPa, H2/CO/Ar (volume ratio)=5:5:1)
图 9 m-ZrO2 (30 nm) 水相产物气相色谱图(来自色-质联用)
Figure 9 GC spectrum of aqueous products produced over m-ZrO2 (30 nm) catalyst using GC-MS analysis
(t=400 ℃, p=3 MPa, GHSV=500 mL/(gcat·h-1), H2/CO/Ar (volume ratio)=5:5:1)
表 1 不同氧化锆的物理化学性质
Table 1 Physico-chemical properties of ZrO2 prepared by different methods
Catalyst Phase Crystal sizea/nm ABETb/(m2·g-1) Acidityc/(μmol·g-1) Acid surface density/(μmol·m-2) m-ZrO2 (30 nm) m 30 53 61.3 1.156 m-ZrO2(9 nm) m 9 134 118.5 0.884 t-ZrO2(9 nm) t 9 109 64.4 0.591 a: crystal size was calculated by Scherrer equation using XRD patterns and confirmed by TEM; b: BET surface area was calculated using N2 sorption; c: acidity was measured from ammonia temperature programmed desorption 
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表 2 不同氧化锆XPS谱图Zr 3d轨道拟合结果
Table 2 XPS parameters of different ZrO2 samples
Sample Zr 3d5/2E/eV ZrⅠspecies ZrⅡspecies m-ZrO2(30 nm) 181.9 (58.4)a 184.6 (41.6)a m-ZrO2 (9 nm) 181.8 (66.5) 183.9 (33.5) t-ZrO2(9 nm) 182.1 (82.7) 184.5 (17.3) a：percentage of Zr species respectively
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表 3 不同方法制备的氧化锆的催化反应性能
Table 3 Catalytic performances of ZrO2 catalysts prepared by different methods
Catalyst CO conv. x/% Yield w/% Selectivitys/% Distribution of HC /% Aro. in C5+ /% HC CO2 CHO HC CO2 CHO C1 C2-4 C5+ m-ZrO2 (30 nm) 17.7 9.7 8.0 0.003 5 54.7 45.3 0.020 20.3 31.5 48.2 52.3 m-ZrO2(9 nm) 26.2 13.6 12.5 0.013 0 52.0 47.9 0.048 24.5 38.2 37.4 40.7 t-ZrO2 (9 nm) 16.1 8.1 8.0 0.008 9 50.1 49.8 0.055 35.4 39.8 24.9 29.2 reaction conditions: t=400 ℃, p=3 MPa, GHSV=500 mL/(gcat·h), H2/CO/Ar=5：5：1，steady state of reaction was reach at 3 h
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