Effects of ZrO2 and Al2O3 on the performance of Mo-based catalysts in methanation
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摘要: 通过共沉淀法制备了ZrO2和Al2O3载体，采用等体积浸渍法制备了MoO3质量分数为5%的Mo/ZrO2和Mo/Al2O3催化剂，并用于甲烷化反应。在三种反应气氛下对两种预硫化的Mo基催化剂进行评价，发现ZrO2载体均可显著促进甲烷化反应，同时能够促进水汽变换（WGS）反应。通过XRD、H2-TPR、XPS和TEM等表征发现，两种载体上Mo物种的硫化程度以及暴露的活性位数量不同，从而导致两种催化剂上催化性能差异显著。与Mo/Al2O3相比，Mo/ZrO2催化剂上的MoO3更易被还原，硫化程度也更高，并且Mo4+的含量更高，Mo6+的含量更低。虽然ZrO2载体上MoS2尺寸较大，边位置的Mo比例有所降低，但是由于MoS2沿ZrO2颗粒表面弯曲生长，使得MoS2基面成为反应的活性位；因此，Mo/ZrO2催化剂在甲烷化与WGS反应中表现出更优异的催化性能。Abstract: Mo/ZrO2 and Mo/Al2O3 catalysts with a MoO3 loading of 5% were prepared by incipient wetness impregnation method; the effect of support on the performance of Mo-based catalysts in methanation was then investigated in three different feeds. The results indicate that ZrO2 as a support can promote the methanation and water-gas shift (WGS) reaction. ZrO2 is beneficial to the sulfuration and reduction of MoO3. The Mo sulfidation degree and the content of Mo4+ on Mo/ZrO2 are higher than that on Mo/Al2O3. Besides, the curved MoS2 basal plane on Mo/ZrO2 can provide the active sites for methanation and WGS, which is effective to enhance the performance of Mo-based catalysts in methanation.
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Key words:
- CO/CO2 hydrogenation /
- methanation /
- oxide supports /
- sulfidation degree
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图 1 Mo/Al2O3和Mo/ZrO2催化剂的COx加氢催化性能
Figure 1 Catalytic performance of the Mo/Al2O3 and Mo/ZrO2 catalysts in methanation
(a): CO and CO2 conversion; (b): COx conversion and CH4 selectivity reaction conditions: H2:CO:CO2=1.4:0.8:1, φ=0.3% H2S, GHSV=5 000 h-1, 3 MPa ▲: Mo/Al2O3; ■: Mo/ZrO2
图 2 Mo/Al2O3和Mo/ZrO2催化剂CO加氢催化性能
Figure 2 Catalytic performance of the Mo/Al2O3 and Mo/ZrO2 catalysts in methanation
(a): CO conversion; (b): CH4 and CO2 selectivity reaction conditions: H2:CO =3:1, φ=0.3% H2S, GHSV=5 000 h-1, 3 MPa ▲: Mo/Al2O3; ■: Mo/ZrO2
图 3 Mo/Al2O3和Mo/ZrO2催化剂CO2加氢催化性能比较
Figure 3 Catalytic performance of the Mo/Al2O3 and Mo/ZrO2 catalysts in methanation
(a): CO2 conversion; (b): CH4 and CO selectivity reaction conditions: H2:CO2 =4:1, φ=0.3% H2S, GHSV=5 000 h-1, 3 MPa ▲: Mo/Al2O3; ■: Mo/ZrO2
图 4 载体与对应的各种状态催化剂的XRD谱图
Figure 4 XRD patterns of the Mo/Al2O3 and Mo/ZrO2 catalysts
(a): Al2O3 and corresponding catalysts; (b): ZrO2 and corresponding catalysts the symbols of ●, ♦and □ denote MoO3, monoclinic phase ZrO2 and tetragonal phase ZrO2, respectively ●: MoO3; ♦: m-ZrO2; □: t-ZrO2
图 5 Mo/Al2O3和Mo/ZrO2催化剂的H2-TPR谱图
Figure 5 H2-TPR profiles of the Mo/Al2O3 and Mo/ZrO2 catalysts
(a): oxidized catalysts; (b): sulfurized catalysts
图 6 催化剂XPS分峰拟合谱图
Figure 6 XPS spectra of the Mo/Al2O3 and Mo/ZrO2 catalysts
(a), (b): fresh catalysts; (c), (d): used catalysts
图 7 催化剂的TEM照片与分析
Figure 7 TEM images of the Mo/Al2O3 (a) and Mo/ZrO2 catalysts (b) and the size distribution results (c)
表 1 Mo/Al2O3和Mo/ZrO2催化剂在三种反应气氛下的CH4收率
Table 1 CH4 yields for methanation over the Mo/Al2O3 and Mo/ZrO2 catalysts in three different feed gases
表 2 反应前后催化剂表面Mo与S物种组成
Table 2 Composition of Mo and S species for the Mo/Al2O3 and Mo/ZrO2 catalysts
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