【摘要】 本文运用红外光谱研究了CO和H₂O在Ni基催化剂上的吸附和反应规律。证实了H₂O在催化剂上是解离吸附,以OH的形式吸附在催化剂上,在OH之间可能有氢键形成。CO有两种吸附态:线式和桥式。预吸附H₂O使CO线式吸附态几乎消失,桥式吸附峰红移了约30cm^-1。在不同温度时,对比了CO或表面碳与H₂O的反应,发现表面碳更容易同水反应生成甲烷。更多还原

【Abstract】 The adsorption and reaction of CO and H₂O on Ni catalyst were studied using infrared spectroscopy. Some valuable results were obtained. 1. Adsorption of H₂O and CO Two types of adsorbed CO on Ni catalyst were identified by IR spectroscopy, the linear state (2060 cm^-1) and bridged state (1960 cm^-1).Above 200℃, disproportionation reaction of CO could occur, forming CO₂ and surface carbon. A wide absorption band at 3600—3100 cm^-1 was observed when H₂O was adsorbed on the catalyst. The band belongs to the stretch-vibration of OH bond. The bent-vibration band of H₂O disappeared when it was adsorbed on the catalyst. This result showed that H₂O was dissociated into OH and H on the catalyst. The wave number of adsorbed H₂O was lower than that of gas phase H₂O, but was equal to that of liquid H₂O. This implys that the hydrogen-bond formed between adsorbed OH. When H₂O was preadsorbed, the absorption band of bridged state CO gave a red shift about 30cm^-1, and the band of linear state CO almost disappeared. This means that the C-O bond of adsorbed CO was weakened by H₂O. 2. Reaction of CO with Preadsorbed H₂O Above 200℃, CO could react with preadsorbed H₂O, forming CH₄ and CO₂. It was found that only bridged state CO existed, no linear state CO formed when the reaction proceeded. 3. Reaction of H₂O with surface carbon The surface carbon formed by disproportionation of CO at 400℃ could react with H₂O at 100℃. CH₄ and CO₂ were produced. This reaction was different from that between CO and H₂O which could proceeded only above 200℃ .It shows the surface carbon with H₂O more easily, indicating that the surface carbon is an intermediate species of shift-methanation reaction. The bridged state CO was formed when surface carbon reacts with H₂O. When a large amount of surface carbon was accumulated on the catalyst surface, neither bridged nor linear CO was detected, this implied that the Ni atoms on the surface were all covered by carbon. The catalyst still had good catalytic activity.This result indicates a posibility that the surface carbon itself is an active center.更多还原