Ni改性Mo2C/Al2O3催化剂在逆水气变换反应中的应用

Performance of Ni modified Mo2C/Al2O3 catalyst in the reverse water-gas shift

摘要:

以掺杂分子筛的大孔氧化铝为载体，添加Ni作为改性助剂，通过共浸渍和程序升温碳化法制备了Mo2C/Al2O3和Ni-Mo2C/Al2O3催化剂。采用XRD、TEM和N2吸附-脱附等手段对催化剂晶体结构、微观形貌及孔结构等性质进行表征，考察了其在逆水气变换反应中的性能。XRD结果表明，Ni改性后的催化剂MNCAS在23.2?、30.2?、40.8?、43.1?、45.4?、51.6?、59.6?、62.7?和71.0?处出现了Ni3Mo3N的特征衍射峰，这可能是Ni的加入导致碳含量不足所致。TEM的结果也表明，在MNCAS催化剂中出现了Ni3Mo3N的0.21nm、0.22nm和0.27nm的晶格间距，Ni的加入有效改善了Mo2C的聚集现象。N2吸附-脱附表明催化剂具有良好的介孔结构。反应评价结果表明，催化剂MCAS对逆水气反应有较高的催化活性，CO选择性为93.87 %，Ni改性后的MNCAS-8催化剂向甲烷选择性转变，在低温段甲烷选择性达到84.37 %，这是由于Ni加入后生成的Ni3Mo3N有更高的甲烷选择性。

Abstract:

Mo2C/Al2O3 and Ni-Mo2C/Al2O3 catalysts were prepared by co-impregnation and temperature-programmed carbonization, using macroporous alumina doped with molecular sieve as the carrier and Ni as the modification agent. The crystal structure, micro-morphology and pore structure of the catalysts were characterized by XRD, TEM and N2 adsorption-desorption, and their performances in the reverse water-gas shift were investigated. The XRD results reveal that the characteristic diffraction peaks of Ni3Mo3N appeared at 23.2?, 30.2?, 40.8?, 43.1?, 45.4?, 51.6?, 59.6?, 62.7? and 71.0? for the modified Ni catalyst MNCAS, this may be ascribed to insufficient carbon content due to the addition of Ni. TEM results also showed that that the lattice spacing of Ni3Mo3N in MNCAS catalyst is 0.21 nm, 0.22 nm and 0.27 nm respectively, and the addition of Ni effectively improved the aggregation of Mo2C. N2 adsorption-desorption demonstrate that the catalyst had good mesoporous structure. The catalytic evaluation results indicate that MCAS catalyst exhibits high activity for the RWGS reaction, the selectivity of CO is 93.87 %. Ni modified MNCAS-8 catalyst shifts the reaction further to methanation, and the methane selectivity reached 84.37 % at low temperature. This is ascribed to the formation of Ni3Mo3N after Ni addition, which has higher methane selectivity.