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摘要: 以三聚氰胺苯甲酸盐为碳源和氮源、以三聚氰胺磷钼酸盐为钼源、磷源和氮源，采用程序升温的方法制备了系列N，P掺杂型C@Mo2C催化剂。采用XRD、SEM、TEM和XPS等对催化剂的结构、形貌和表面特性进行了表征，研究了三聚氰胺苯甲酸盐中n（三聚氰胺）/n（苯甲酸）、前驱体中n（C）/n（Mo）等因素对所制备催化剂的结构及其在二氧化碳加氢反应中催化性能的影响。在反应温度为220℃、反应压力为3.0 MPa、空速为3 600 mL/（g·h）的条件下，在N，P掺杂型C@Mo2C的催化作用下，CO2转化率可以达到12.2%，此时产物中CH3OH的选择性达到52.2%。
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关键词:
- N, P掺杂型C@Mo2C /
- β-Mo2C /
- CO2加氢 /
- 甲醇
Abstract: The N, P-doped C@Mo2C catalysts were prepared using melamine benzoate as the source of nitrogen and carbon, melamine phosphomolybdate as the source of phosphorus, nitrogen and molybdenum, respectively. The surface structures of the prepared catalysts were characterized by XRD, SEM, TEM and XPS. The effects of the ratio of benzoic acid to melamine in melamine benzoate and n(C)/n(Mo) of the precursor on the catalysts were investigated. The activity of the catalysts was evaluated by using CO2 hydrogenation as a model reaction in a fixed-bed reactor, in which a mixed gas of CO2/H2 (VH2:VCO2=3:1) was used as the feed gas, and it was found that the N, P-doped C@Mo2C showed a good catalytic performance with CO2 conversion of 12.2% and methanol selectivity of 52.2% under the optimal reaction conditions (reaction temperature 220℃, reaction pressure 3.0 MPa, space velocity 3 600 mL/(g·h).-
Key words:
- N, P-doped C@Mo2C /
- β-Mo2C /
- CO2 hydrogenation /
- methanol
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图 2 不同催化剂的SEM照片
(a): N, P-dC@Mo2C-1-35; (b): N, P-dC@Mo2C-2-35; (c): N, P-dC@Mo2C-2-25; (d): N, P-dC@Mo2C-2-45
Figure 2 SEM images of the catalysts
图 3 不同催化剂的TEM照片 ((a)，(b))，N, P-dC@Mo2C-2-35的HRTEM照片 (c) 和EDXS谱图 (d)
Figure 3 TEM images of the catalysts ((a), (b)), HRTEM image (c) and EDXS pattern of N, P-dC@Mo2C-2-35(d)
表 1 不同催化剂中Mo2C的平均颗粒粒径
Table 1 Average Mo2C crystallite size of the catalystsa
Catalyst Average Mo2C crystallite size d/um N, P-dC@Mo2C-1-35 21.3 N, P-dC@Mo2C-2-35 16.1 N, P-dC@Mo2C-2-25 17.2 N, P-dC@Mo2C-2-45 18.2 a: calculated by the Scherrer formula 
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表 2 不同催化剂表面的Mo、N、P的原子含量
Table 2 Surface Mo, N and P atom content of the catalysts
Catalyst Content wmol/% Mo N P N, P-dC@Mo2C-1-35 9.53 24.13 2.46 N, P-dC@Mo2C-2-35 10.58 12.26 1.88 N, P-dC@Mo2C-2-25 11.75 4.56 2.67 N, P-dC@Mo2C-2-45 12.35 9.69 2.88
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表 3 不同催化剂表面的Mo 3d5/2电子结合能和 (MoⅣ+ Moδ)/ Mototal
Table 3 Mo 3d5/2 binding energies and (MoⅣ + Moδ)/Mototal of the catalystsa
Catalyst Mo 3d5/2 (eV)(mol%)b (MoⅣ+ Moδ)/
Mototal (%)MoⅡ MoⅢ MoⅣ Moδ MoⅥ N, P-dC@Mo2C-1-35 228.6(1.15) 229.0(0.17) 229.6(0.61) 232.1(2.66) 233.1(4.94) 34.3 N, P-dC@Mo2C-2-35 228.6(1.02) 228.9(1.17) 229.6(1.31) 232.1(2.81) 233.3(4.27) 38.9 N, P-dC@Mo2C-2-25 228.5(1.90) 228.8(3.72) 229.7(1.24) 232.1(2.36) 233.1(2.53) 30.6 N, P-dC@Mo2C-2-45 228.5(1.97) 228.9(2.05) 229.5(1.73) 232.1(2.76) 233.1(3.84) 36.4 a: Mototal= MoⅡ+MoⅢ+MoⅣ +Moδ +MoⅥ; b: the molar fraction of Mo in the parentheses
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表 4 不同催化剂表面的N 1s电子结合能
Table 4 N 1s binding energies of the catalysts
Catalyst N 1s (eV) (mol%)a N-Mo pyridinic pyrrolic graphitic N, P-dC@Mo2C-1-35 396.5(3.62) 398.3(11.39) 399.9(5.84) 401.7(3.28) N, P-dC@Mo2C-2-35 396.4(1.72) 398.3(5.99) 399.8(3.15) 401.7(1.40) N, P-dC@Mo2C-2-25 396.4(0.72) 398.3(2.53) 399.9(0.68) 401.7(0.63) N, P-dC@Mo2C-2-45 396.4(1.39) 398.3(5.26) 399.9(2.07) 401.7(0.97) a: the molar fraction of N in the parentheses
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表 5 不同催化剂表面的P 2p电子结合能
Table 5 P 2p binding energies of the catalystsa
Catalyst P 2p E/eV P(o)/Ptotal(%) P-Mo(P 2p3/2) P-Mo(P 2p1/2) P-C P-O N, P-dC@Mo2C-1-35 129.5 130.4 133.1 134.0 63.2 N, P-dC@Mo2C-2-35 129.4 130.4 133.1 134.0 75.2 N, P-dC@Mo2C-2-25 129.5 130.4 133.0 133.9 61.2 N, P-dC@Mo2C-2-45 129.5 130.4 133.1 133.9 69.0 a: Ptotal= P(c)+P(o), P(c)=P-C, P(o)=P-O
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表 6 不同催化剂的活性评价
Table 6 Catalytic performance of the catalystsa
Catalyst CO2 conversion x/% Selectivity s/% CH3OH CO CH4 CH3OCH3 N, P-dC@Mo2C-1-35 14.5 40.5 4.8 51.5 3.2 N, P-dC@Mo2C-2-35 12.2 52.2 4.0 34.4 9.4 N, P-dC@Mo2C-2-25 10.4 26.9 8.7 62.6 1.8 N, P-dC@Mo2C-2-45 12.0 45.5 4.5 40.7 9.3 a: reaction conditions: VH2:VCO2=3:1, t=220 ℃, p=3.0 MPa, GHSV (gas hourly space velocity)=3 600 mL/(g·h)
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表 7 CO2加氢反应工艺条件
Table 7 Optimized reaction conditions for hydrogenation of CO2a
Pressure p/MPa Temperature t/℃ CO2 conversion
x/%Selectivity s/% CH3OH CO CH4 CH3OCH3 1.0 220 9.4 46.8 3.9 39.5 9.8 2.0 220 10.2 50.5 3.8 36.2 9.5 3.0 220 12.2 52.2 4.0 34.4 9.4 3.0 200 10.4 52.3 1.4 39.2 7.1 3.0 240 14.2 47.8 8.6 32.5 11.1 a：reaction conditions: VH2:VCO2= 3:1, GHSV=3 600 mL/(g·h)
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