MoO3-SnO2 catalyst prepared by hydrothermal synthesis method for dimethyl ether catalytic oxidation
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摘要: 采用无沉淀剂水热法一步合成了MoO3-SnO2复合金属氧化物催化剂，通过调变Mo/Sn物质的量比，考察了催化剂上活性组分MoOx分散程度对二甲醚（DME）低温氧化生成甲酸甲酯（MF）反应性能的影响。当Mo/Sn=1:2，反应条件为150℃时，催化剂表现出较好的催化性能，DME转化率为22.0%，MF选择性达到77.6%。实验中采用TEM、XRD、Raman、FT-IR、NH3-TPD及H2-TPR等表征对催化剂晶体结构及表面性质进行了分析。结果发现，Mo/Sn物质的量比变化会对催化剂晶体结构产生显著影响，钼氧化物在SnO2表面形成不同分散程度的MoOx结构，这种钼氧化物结构的变化进一步影响了催化剂表面的酸性及氧化还原性，是造成催化性能差异的主要原因。Abstract: MoO3-SnO2 composite metal oxide catalyst was synthesized by one-step hydrothermal synthesis method without precipitant. The effect of MoOx dispersion state on the catalytic performance of MoO3-SnO2 catalysts with different Mo/Sn molar ratios was investigated for dimethyl ether (DME) low-temperature oxidation to methyl formate (MF). MF selectivity reaches 77.6% with DME conversation of 22.0% over Mo1Sn2 at 150 ℃. The physiochemical properties of these catalysts were characterized by TEM, XRD, Raman, FT-IR, NH3-TPD and H2-TPR. The results showed that the addition of SnO2 into MoO3 affected the crystal structure of catalysts, forming MoOx species with different degree of dispersion on the surface of SnO2. The special architecture of MoOx-SnO2 plays a major role in modifying the acidity and the oxidizability of MoO3-SnO2 catalysts, leading to the obvious differences on catalytic activity.
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Key words:
- hydrothermal synthesis /
- dimethyl ether /
- selective oxidation /
- methyl formate /
- MoOx
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图 1 不同Mo/Sn催化剂的TEM照片
Figure 1 TEM images of MoO3-SnO2 catalysts with different Mo/Sn mole ratios
(a): Mo3Sn1; (b): Mo1Sn1; (c): Mo1Sn2; (d): Mo1Sn10
图 2 不同Mo/Sn比例催化剂的XRD谱图
Figure 2 XRD patterns of MoO3-SnO2 catalysts with different Mo/Sn mole ratios
a: Mo3Sn1; b: Mo2Sn1; c: Mo1Sn1; d: Mo1Sn2; e: Mo1Sn3; f: Mo1Sn4; g: Mo1Sn5; h: Mo1Sn10
图 3 不同Mo/Sn比例催化剂的Raman谱图
Figure 3 Raman patterns of MoO3-SnO2 catalysts with different Mo/Sn mole ratios
a: MoO3; b: Mo3Sn1; c: Mo2Sn1; d: Mo1Sn1; e: Mo1Sn2; f: Mo1Sn3; g: Mo1Sn4; h: Mo1Sn5; i: Mo1Sn10; j: SnO2
图 4 不同Mo/Sn比例催化剂的FT-IR谱图
Figure 4 FT-IR spectra of MoO3-SnO2 catalysts with different Mo/Sn mole ratios
a: Mo3Sn1; b: Mo2Sn1; c: Mo1Sn1; d: Mo1Sn2; e: Mo1Sn3; f: Mo1Sn4; g: Mo1Sn5; h: Mo1Sn10
图 5 不同Mo/Sn比例催化剂的NH3-TPD谱图
Figure 5 NH3-TPD spectra of MoO3-SnO2 catalysts with different Mo/Sn mole ratios
a: Mo3Sn1; b: Mo2Sn1; c: Mo1Sn1; d: Mo1Sn2; e: Mo1Sn3; f: Mo1Sn4; g: Mo1Sn5; h: Mo1Sn10
图 6 不同Mo/Sn比例催化剂的H2-TPR谱图
Figure 6 H2-TPR spectra of MoO3-SnO2 catalysts with different Mo/Sn mole ratios
a: Mo3Sn1; b: Mo2Sn1; c: Mo1Sn1; d: Mo1Sn2; e: Mo1Sn3; f: Mo1Sn4; g: Mo1Sn5; h: Mo1Sn10
图 7 MoOx物种在SnO2表面的可能分散形式
Figure 7 Possible distribute mode of MoOx species on the surface of SnO2
(a): MoO3 clusters; (b): MoOx oligomers; (c): MoOx monomers
表 1 不同Mo/Sn比例的MoO3-SnO2催化剂对二甲醚选择性氧化制备甲酸甲酯的影响
Table 1 Effects of different Mo/Sn mole ratio on the reaction of DME to MF over MoO3-SnO2 catalysts
Catalyst DME conversion x/% Cmol-selectivity s/% MF CH3OH HCHO DMM CO MoO3 3.4 0 98.8 1.2 0 0 Mo3Sn1 6.6 54.3 34.0 5.4 2.2 4.1 Mo2Sn1 8.5 67.0 25.8 3.9 0.2 3.1 Mo1Sn1 17.1 75.9 6.3 0 3.9 13.9 Mo1Sn2 22.0 77.6 8.6 0 1.4 12.4 Mo1Sn3 15.6 77.1 9.5 0 0 13.4 Mo1Sn4 10.6 76.4 23.2 0.4 0 0 Mo1Sn5 6.6 71.1 28.0 0.9 0 0 Mo1Sn10 4.2 41.9 58.1 0 0 0 SnO2 2.8 0 100 0 0 0 reaction conditions: tR=150 ℃, atmospheric pressure, n(DME):n(O2)=1:1, GHSV=1800 h-1; MF: HCOOCH3, MeOH: CH3OH, FA: HCHO, DMM: CH3OCH2OCH3 
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