焙烧气氛对二甲醚低温选择氧化MoO<sub>3</sub>-SnO<sub>2</sub>催化剂结构及性能的影响

顾颖颖; 张振洲; 王文峰; 高秀娟; 张清德; 韩怡卓; 谭猗生

焙烧气氛对二甲醚低温选择氧化MoO₃-SnO₂催化剂结构及性能的影响

顾颖颖^{1, 2},
张振洲^{1, 2},
王文峰^{1, 2},
高秀娟^{1, 2},
张清德^1, ,,
韩怡卓¹,
谭猗生¹

1.
中国科学院山西煤炭化学研究所煤转化国家重点实验室, 山西太原 030001
2.
中国科学院大学, 北京 100049

基金项目:

国家自然科学基金 21373253

国家自然科学基金 20903114

中国科学院青年创新促进会 2014155

详细信息

通讯作者:
张清德, Tel/Fax: 0351-4044388, E-mail: qdzhang@sxicc.ac.cn

中图分类号: O643.3
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出版历程
- 收稿日期: 2017-01-24
- 修回日期: 2017-03-31
- 网络出版日期: 2021-01-23
- 刊出日期: 2017-05-10

Effects of calcination atmosphere on the structure and performance of MoO₃-SnO₂ catalyst for the oxidation of dimethyl ether at low temperature

1.
State Key Laboratory of Coal Conversion, Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China
2.
University of Chinese Academy of Sciences, Beijing 100049, China

Funds:

the National Natural Science Foundation of China 21373253

the National Natural Science Foundation of China 20903114

Youth Innovation Promotion Association CAS 2014155

摘要

摘要: 采用共沉淀法制备了Mo/Sn物质的量比为1：3的MoO₃-SnO₂催化剂，考察了焙烧气氛（O₂、air、N₂和H₂）对催化剂结构及二甲醚（DME）低温氧化制甲酸甲酯（MF）性能的影响。结果表明，在O₂中焙烧的催化剂上DME转化率高达25.10%，MF选择性为72.21%，催化剂具有较高的反应活性。而在H₂中焙烧催化剂上DME转化率仅为7.01%，MF选择性为75.82%。不同气氛焙烧催化剂上DME转化率由大到小的顺序：O₂ > air> N₂> H₂。采用XRD、Raman、XPS及ESR等对催化剂进行深入表征。结果表明，共沉淀制备Mo1Sn3催化剂中钼物种以高分散MoO_x形式存在。O₂中焙烧催化剂表面Mo=O及存在于Mo-Sn界面处五配位钼氧化物中Mo⁵⁺含量均高于其他三种催化剂，即低聚态MoO_x末端Mo=O可能是反应活性位点之一，五配位钼氧化物中Mo⁵⁺的存在有利于催化剂活性的提高，也有助于MF的生成。结合in suit DRIFTS证实了吸附于Mo⁵⁺上的CH₃O，在催化剂表面Mo=O作用下氧化为HCHO后与另一分子CH₃O耦合为MF。
- MoO₃-SnO₂催化剂 /
- 焙烧气氛 /
- 二甲醚氧化 /
- 甲酸甲酯
Abstract: MoO₃-SnO₂ catalysts with a Mo/Sn molar ratio of 1:3 was prepared by the co-precipitation method and calcined in different atmospheres (O₂, air, N₂ and H₂); the effect of calcination atmosphere on the catalytic performance of MoO₃-SnO₂ in the oxidation of dimethyl ether (DME) to methyl formate (MF) was investigated. The results show that the MoO₃-SnO₂ catalyst prepared by calcination in O₂ exhibits the highest activity; the conversion of DME reaches 25.10%, with the selectivity of 72.21% to MF. Over the catalyst calcined in H₂, the conversion of DME is only 7.01%, with the selectivity of 75.82% to MF. The activity of the MoO₃-SnO₂ catalysts calcined at different atmospheres follows the order of O₂ > air > N₂ > H₂. The results of XRD, Raman, XPS and ESR characterization indicate the presence of MoO_x domains on the surface of the MoO₃-SnO₂ catalyst with a Mo/Sn molar ratio of 1:3. The terminal Mo=O groups of oligomeric MoO₃ may be the active sites for the methoxy intermediate and the penta-coordinated Mo⁵⁺ species in the Mo-Sn interface may be able to promote the oxidation of DME to MF. Consequently, methoxy species are absorbed on the Mo⁵⁺ species in the Mo-Sn interfaces, which are oxidized to HCHO on the terminal Mo=O groups; after that, the absorbed HCHO may then react with the neighboring absorbed methoxy species, forming MF.
- MoO₃-SnO₂ catalysts /
- calcination atmosphere /
- dimethyl ether oxidation /
- methyl formate

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图 1 二甲醚在不同焙烧气氛MoO₃-SnO₂催化剂上的选择性氧化性能

Figure 1 Performance of the Mo1Sn3 catalyst calcined in different atmospheres for the oxidation of dimethyl ether (DME) to methyl formate (MF)

the reactions were conducted at atmospheric pressure and 150 ℃, with GHSV of 1 800 h^-1 and DME/O₂ ratio of 1:1 for MF selectivity: ▼: N₂; ▶: air; ◀: H₂; : O₂; for DME conversion: ▶: O₂; ■: air; ▲: N₂; ◆: H₂

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图 2 二甲醚在不同焙烧气氛MoO₃-SnO₂催化剂上的选择性氧化产物分布

Figure 2 Distribution of products from the catalytic oxidation of DME over the MoO₃-SnO₂ catalysts calcined in different atmospheres

the reactions were conducted at atmospheric pressure and 150 ℃, with GHSV of 1 800 h^-1 and DME/O₂ ratio of 1:1

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图 3 不同焙烧气氛MoO₃-SnO₂催化剂的XRD谱图

Figure 3 XRD patterns of the MoO₃-SnO₂ catalysts prepared with different calcination atmospheres

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图 4 不同焙烧气氛MoO₃-SnO₂催化剂的Raman谱图

Figure 4 Raman spectra of the MoO₃-SnO₂ catalysts prepared with different calcination atmospheres

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图 5 不同焙烧气氛MoO₃-SnO₂催化剂的XPS谱图

Figure 5 XPS spectra of the MoO₃-SnO₂ catalysts prepared with different calcination atmospheres

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图 6 不同焙烧气氛MoO₃-SnO₂催化剂的ESR谱图

Figure 6 ESR patterns of the MoO₃-SnO₂ catalysts prepared with different calcination atmospheres

(a): ESR spectrum; (b): enlargement of spectrum Mo⁵⁺

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图 7 Mo1Sn3-air在150 ℃下脉冲二甲醚氧化反应的in suit DRIFTS谱图

Figure 7 Evolution of dimethyl ether oxidation with time on steam over the Mo1Sn3-air catalyst at 150 ℃, detected by an in suit DRIFTS pulsed method

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表 1 反应温度对空气气氛中焙烧Mo1Sn3催化剂上DME的氧化反应性能

Table 1 Performance of the Mo1Sn3 catalyst calcined in air for the oxidation of dimethyl ether (DME) to methyl formate (MF) under different temperatures

Temperature t/℃	DME conversion x/%	Product selectivity s/%
Temperature t/℃	DME conversion x/%	MF	FA	CH₃OH	CH₄	CO	CO₂
140	12.40	80.35	0.09	12.06	0.00	7.50	0.00
150	17.42	77.00	0.02	7.68	0.00	15.30	0.00
160	97.72	0.12	0.00	0.06	0.00	99.82	0.00
reaction conditions: atmospheric pressure, GHSV=1 800 h^-1, DME:O₂= 1:1

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表 2 反应空速对空气气氛中焙烧Mo1Sn3催化剂上DME的氧化反应性能

Table 2 Performance of the Mo1Sn3 catalyst calcined in air for the oxidation of dimethyl ether (DME) to methyl formate (MF) under different space velocities (GHSV)

GHSV /h^-1	DME conversion x/%	Product selectivity s/%
GHSV /h^-1	DME conversion x/%	MF	FA	CH₃OH	CH₄	CO	CO₂
900	25.50	75.95	0.01	5.10	0.00	18.94	0.00
1 800	17.42	77.00	0.02	7.68	0.00	15.30	0.00
3 600	14.69	68.23	6.76	13.31	0.00	11.70	0.00
reaction conditions: atmospheric pressure, temperature=150 ℃, DME:O₂=1:1

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表 3 反应温度对氧气气氛中焙烧Mo1Sn3催化剂上DME的氧化反应性能

Table 3 Performance of the Mo1Sn3 catalyst calcined in oxygen for the oxidation of dimethyl ether (DME) to methyl formate (MF) under different temperatures

Temperature t/℃	DME conversion x/%	Product selectivity s/%
Temperature t/℃	DME conversion x/%	MF	FA	CH₃OH	CH₄	CO	CO₂
120	16.58	76.57	0.16	23.27	0.00	0.00	0.00
130	16.78	81.92	0.03	10.81	0.00	7.24	0.00
140	14.47	81.02	0.05	9.11	0.00	9.82	0.00
150	21.23	74.88	0.03	9.64	0.00	15.45	0.00
160	25.92	70.83	0.01	7.07	0.00	22.09	0.00
reaction conditions: atmospheric pressure, GHSV=1 800 h^-1, DME:O₂=1:1

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表 4 不同焙烧气氛MoO₃-SnO₂催化剂的XPS表征

Table 4 XPS results of the MoO₃-SnO₂ catalysts prepared with different calcination atmospheres

Catalyst	O 1s E/eV		Sn 3d E /eV		Mo 3d E /eV		O_lat/(O_sur+O_lat)
Catalyst	O_sur	O_lat	Sn 3d_3/2	Sn 3d_5/2	Mo 3d_3/2	Mo 3d_5/2
Mo1Sn3-O₂	533.3	530.8	495.3	486.8	236.0	232.9	0.77
Mo1Sn3-air	533.1	530.3	494.9	486.3	235.6	232.5	0.73
Mo1Sn3-N₂	532.7	530.1	494.5	486.1	235.3	232.2	0.78
O_sur =surface active oxygen; surface hydroxyl oxygen and chemisorbed oxygen；O_lat = lattice oxygen

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