Steam reforming of phenol for producing hydrogen over nickel support on MgO prepared by different methods
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摘要: 利用浸渍法和水热共沉淀法两种方法，制备了介孔Ni/MgO催化剂，用于水蒸气重整生物质油模型物苯酚制取氢气；利用XRD、N2吸附/脱附、H2-TPR、TEM以及TG等手段对催化剂进行了表征。结果表明，以介孔MgO为载体，采用浸渍法制备的介孔NiO/MgO固溶体，具有较高的比表面积（60.6 m2/g）以及较大的孔径（10.1 nm）。与水热共沉淀法制备的催化剂相比，浸渍法制备的NiO/MgO前驱体经还原后的所得到介孔Ni/MgO催化剂Ni颗粒较小（5.0-6.0 nm），分布均匀，具有较高的分散度（19.44%）。较大的比表面积能有效地促进活性金属颗粒的分散，而介孔有利于反应物和产物在催化剂孔道中的扩散。因此，该Ni/MgO催化剂在水蒸气重整苯酚制氢反应中具有较高的催化活性、稳定性和优异的抗积炭能力。Abstract: MgO-supported nickel catalysts were prepared by impregnation and hydrothermal coprecipitation methods; they were characterized by XRD, N2 sorption, H2-TPR, TEM and TG and used in the steam reforming of biomass oil model compound-phenol for hydrogen production. The results indicated that the NiO/MgO solid solution prepared by the impregnation method displays higher surface area (60.6 m2/g) and larger pore diameter (10.1 nm), in comparison with that prepared by hydrothermal coprecipitation. After reduction, the mesoporous Ni/MgO catalyst obtained from impregnation exhibits small and uniform Ni nanoparticles (5.0-6.0 nm) with high dispersion (19.44%). As high surface area is favorable for the dispersion of Ni nanoparticles and mesoporous structure can promote the mass transfer of reactants and products, the Ni/MgO catalyst exhibits high activity as well as excellent coke resistance ability and long-term stability in the steam reforming of phenol.
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Key words:
- mesoporous MgO /
- Ni/MgO catalyst /
- steam reforming /
- phenol /
- hydrogen
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图 1 Mm、NiO/Mm以及NiO-Mm的N2吸附/脱附等温线以及BJH法孔径分布图(内嵌)
▲: Mm; ●: NiO/Mm; ■: NiO-Mm
Figure 1 N2 adsorption-desorption isotherm plots and BJH cumulative pore distribution (inset) of various catalysts
图 2 NiO/Mm和NiO-Mm催化剂的H2-TPR谱图
Figure 2 H2-TPR profiles of the NiO/Mm catalyst (a) and NiO-Mm catalyst (b)
图 3 Mm、Ni/Mm、Ni-Mm的广角以及小角的XRD谱图
Figure 3 XRD patterns at wide angle and low angle (inset) of the Mm (a), Ni/Mm (b) and Ni-Mm (c) catalysts
图 4 还原后Ni/Mm以及Ni-Mm的TEM照片及其Ni粒径分布
Figure 4 TEM images and Ni particle size distribution patterns of the Ni/Mm ((a) and (b)) and Ni-Mm ((c) and (d)) catalysts
图 5 Ni/Mm催化剂和Ni-Mm催化剂的苯酚转化率、H2产率以及H2选择性
Figure 5 Phenol conversion (○, ●), H2 yield (■, □), H2 selectivity (△, ▲) vs.reaction time over the Ni/Mm catalyst (solid symbols) and Ni-Mm catalyst (hollow symbols) reaction conditions: 0.3 g catalyst, 450 ℃, N2 flow rate=45 mL/min, liquid flow rate=5.2 mL/h, S/C (mol ratio)=20
图 6 反应6 h后Ni/Mm和Ni-Mm催化剂的热重等温线
Figure 6 TGA curves of the Ni/Mm (a) and Ni-Mm (b) catalysts after reaction for 6 h
表 1 不同方法制备的催化剂的物理性质
Table 1 Physical properties of the catalysts prepared by different methods
Catalyst BET surface areaa A/(m2·g-1) Pore sizeb d/nm Pore volumeb v/(cm3·g-1) Mm 66.4 8.5 0.30 NiO/Mm 60.6 10.1 0.26 NiO-Mm 49.5 8.0 0.25 a: surface areas were obtained from nitrogen adsorption data by BET method;
b: total pore volume and average pore size were calculated from desorption branch isotherm by BJH method
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表 2 Ni基MgO催化剂的物理化学性质
Table 2 Physical and chemical properties of MgO supported Ni-based catalysts
Catalyst Ni loading
w/%Ni reducibilitya
/%Ni size d/nm Ni dispersiond
/%Ni surface aread
/(m2·(g-Ni)-1)by TEMb by XRDc Ni/Mm 10.98 12.29 5.42 5.17 19.44 16.02 Ni-Mm 10.98 13.32 6.93 6.79 14.84 14.81 a: Ni reducibility was calculated from H2-TPR profiles;
b: Ni particle size was calculated by using weighted average from the TEM results;
c: Ni particle size was determined by XRD;
d: Ni dispersion and Ni surface area were calculated according to literature[15]
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表 3 不同催化剂的苯酚转化率、氢气产率和产物选择性
Table 3 Phenol conversion, H2 yield and product selectivity for phenol steam-reforming over various catalysts
Catalyst xphenol /% wH2 /% Selectivity s/% H2 CO CO2 CH4 Ni/Mm 83.1 49.9 85.2 2.5 12.3 - Ni-Mm 72.7 45.2 77.1 4.9 18.0 - reaction conditions: 0.3 g catalyst, 450 ℃, N2 flow rate=45 mL/min, liquid flow rate=5.2 mL/h, S/C (mol ratio)=20, TOS=6 h
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