Abstract:

Selective hydrogenation of CO₂ to methanol is one of the most important ways of resource utilization of CO₂, so it is very necessary to develop efficient methanol synthesis catalysts. In this study, the Sn promoter has been incorporated into In₂O₃ to modify its reducibility and the surface oxygen vacancy, in order to optimize the catalytic performance of In₂O₃ catalyst for CO₂ hydrogenation to methanol. Several characterizations including XRD, TEM, H₂-TPR, H₂-D₂-TPSR, Raman, XPS, and CO₂-TPD were conducted to reveal the effect of Sn promoter on the structure and chemistry of the catalysts. The activity tests were performed in a high pressure fixed-bed reactor to study the catalytic performance. The results showed that the Sn atoms were highly dispersed in In₂O₃ and tended to accumulate on the surface through forming Sn—O—In structure, which promotes the formation of surface oxygen vacancy, and can inhibit the excessive reduction of In₂O₃. As a result, the Sn promoted In₂O₃ catalysts exhibited higher methanol selectivity and productivity. The Sn-In₂O₃ catalyst with a Sn/In molar ratio of 0.5% possessed the optimized catalytic performance, which showed a CO₂ conversion of 6.2% and methanol selectivity of 70.4% at the reaction conditions of 300℃ and 3 MPa with GHSV of 15000 ml·g^-1·h^-1. With further increment of Sn content, the CO₂ conversion would slightly decrease, while the methanol selectivity would increase to 80.8%, significantly higher than that of 55.4% on the pure In₂O₃ catalyst.

Key words: catalyst, CO₂, hydrogenation, In₂O₃, Sn incorporation, oxygen vacancy, methanol production

摘要：

选择性加氢制甲醇是CO₂资源化利用最主要的方式之一，因此十分需要开发高效的合成甲醇催化剂。本研究采用共沉淀法在In₂O₃中掺杂Sn来调控In₂O₃的还原能力和表面氧空位浓度，以提升In₂O₃催化剂在CO₂加氢制甲醇中的催化性能。通过XRD、TEM、H₂-TPR、H₂-D₂-TPSR、Raman、XPS、CO₂-TPD等表征手段，研究了Sn助剂对催化剂结构和表面化学性质的影响；并通过高压固定床装置测试了催化剂的催化性能。结果表明，Sn在In₂O₃中高度分散并倾向于在表面富集，与In₂O₃形成Sn—O—In结构，促进了表面氧空位的生成，且能抑制In₂O₃的过度还原，从而使得Sn-In₂O₃催化剂表现出更高的甲醇选择性和产率。在300℃、3 MPa、空速为15000 ml·g^-1·h^-1的反应条件下，Sn/In摩尔比为0.5%的Sn-In₂O₃催化剂具有最优的催化性能，此时CO₂转化率为6.2%，甲醇选择性为70.4%，当Sn含量进一步增加时，CO₂转化率会略有下降，而甲醇选择性提升至80.8%。

关键词: 催化剂, 二氧化碳, 加氢, In₂O₃, Sn掺杂, 氧空位, 甲醇合成