CO、H_2及HO_2在Co/SiO_2催化剂上吸附的原位红外光谱

IN SITU IR STUDY OF ADSORPTION OF CO,H_2 AND H_2O ON Co/SiO_2 CATALYST

用原位IR研究了CO在Co/SiO_2催化剂上的吸附,并考察了吸附的CO与H_2、H_2O的相互作用。CO在Co/SiO_2上的吸附显示出四种不同的吸收峰。2002、2027cm^(-1)归属于端基CO吸附;2120cm^(-1)归属于CO在钴离于上的吸附;1870cm^(-1)为CO的桥式吸附;1720cm^(-1)则为多中心吸附。当温度高于370K时,吸附的CO会完全脱附。H_2与吸附的CO相互作用可削弱CO吸收峰的强度,并逐步在低波数(1980cm^(-1))处产生一个小肩。水与吸附的CO相互作用产生一种甲酸基物种(1585、1390cm^(-1))。该物种被认为是Kòlbel-Engelhardt反应的中间体。

Infrared studies have been undertaken of the adsorption of CO and interaction of CO with H2 or H2O on a silica-supported cobalt cata-lyst. The chemisorption of CO on the catalyst leads to four kinds of adsorption bonds. Band 2002 cm-1 and 2027 cm-1 are due to terminal adsorption, band 2120 cm-1 is due to adsorption on the cobalt ions, band 1.870 cm-1 arises from bridged adsorption of CO and band 1720 cm-1 from multicentre adsorption of CO on Co/SiO2. The observed frequency of CO adsorption bands is dependent on the CO pressure. The adsorbed CO species is desorbed completely above 373 K. The interaction of H2 with the adsorbed CO reduces the intensity of the main adsorbate band, but a shoulder develops at a lower frequen-cy (1980 cm-1) after 4 h exposure to H2 at room temperature. The adsorption of H2 will weaken the adsorbed CO bond. Interaction of water vapor with the CO adsorbate at Kolbel-Englhardt reaction condition (523 K, O.lMPa, CO : H2O = 3 : 1 ) yields a formate species, characterized by two bands at 1585 cm-1 and 1390 cm-1. This was confirmed by the adsorption of HCOOH on the Co/SiO2 at the same condition. The interaction of D2O with the adsorbed CO under this condition also leads to a deuterated formate species. The formate species may be a stable intermediate in the Kolbel-Englhardt reaction.