ZrO_2助剂对Ni/SiO_2催化剂CO甲烷化催化活性及其吸附性能的影响

Effect of ZrO_2 promoter on the catalytic activity for CO methanation and its adsorption performance of the Ni/SiO_2 catalyst

采用连续流动微反装置和原位漫反射红外光谱法考察了Ni/SiO2及添加ZrO2助剂的Ni/ZrO2-SiO2催化剂CO甲烷化催化活性和吸附性能。结果表明,在CO体积分数1%、空速5000 h-1、常压的反应条件下,200℃时Ni/ZrO2-SiO2催化剂可将CO完全转化。而相同反应条件下Ni/SiO2催化剂上CO的转化率仅为35%,直至270℃时方可将CO完全转化。由此可见,ZrO2助剂的添加明显提高了Ni/ZrO2-SiO2催化剂的CO甲烷化催化活性。同时,ZrO2助剂的添加显著提高了Ni/ZrO2-SiO2催化剂对CO的吸附能力,H2存在时可通过在较低温度时形成较多的桥式羰基氢化物来提高Ni/ZrO2-SiO2催化剂的CO甲烷化催化活性;CO甲烷化反应条件下,Ni/SiO2和Ni/ZrO2-SiO2催化剂上C—O键的削弱和断裂是经由羰基氢化物-多氢羰基氢化物的途径,而不是经由C—O键的直接断裂途径。

The catalytic activities for CO methanation and adsorption performances of the Ni/SiO2 and Ni/ZrO2- SiO2 catalysts were investigated by a continuous flowing microreactor apparatus and in-situ diffuse reflectance fourier transform infrared spectroscopy. The results showed that CO was completely transformed at 200℃ under the reaction conditions： CO 1% ,GHSV 5000h^-1 and an atmosphere pressure over the Ni/ZrO2-SiO2 catalyst, while under the same reaction conditions the CO conversion was only 35% and CO was not completely transformed until 270℃ over the Ni/SiO2 catalyst, which suggested the catalytic activity of the Ni/ZrO2-SiO2 catalyst increased with the addition of ZrO2 promoter. Meanwhile, the addition of ZrO2 promoter enhanced the adsorption capacity of the Ni/ZrO2-SiO2 catalyst for CO, and that in the presence of H2 a larger amount of bridged carbonyl hydride formed over the Ni/ZrO2-SiO2 catalyst at lower temperature, resulting in the increase of its catalytic activity. In CO methanation reaction, the breaking of C-O bond over those catalysts was via multi-hydrogen carbonyl hydride rather than via direct breaking.