CO为探针分子的原位FT-IR技术研究Pd/HM表面金属的分散态

CO AS A PROBE MOLECULE FOR IN SITU FT IR INVESTIGATION OF METAL DISPERSION ON SURFACE OF PALLADIUM/H MORDENITE

以ＣＯ为探针分子的ＩＲ研究表明，在Ｐｄ／ＨＭ上，钯还原前后具有不同对ＣＯ的线式吸附态．还原前分别在２１５６ｃｍ－１和２０４５ｃｍ－１处有两个ＩＲ吸收峰；而还原后在２０００ｃｍ－１附近出现几个重叠在一起的ＩＲ吸收峰，２１５６ｃｍ－１处小峰几乎消失，这是因为Ｐｄ２＋被还原引起的．ＣＯ的ＩＲ－ＴＰＤ谱说明低于２０００ｃｍ－１的峰是ＣＯ的桥式强吸附态，高于此波数的峰是线式弱吸附．氢还原前后的Ｐｄ／ＨＭ表面活性差异明显．同时，３７５℃氢还原将导致表面钯积块，分散度下降．

Studies of in situ FT IR,CO as a probe molecule,showes that different absorption features have been attributed to linear bonded CO on Pd/HM before and after palladium ion reduced.Infrared spectroscopy of unreduced Pd/HM gaves CO absorption bands at 2156cm -1 and 2045cm -1 ,however reduced one presented a broad band newly formed in the range of 1995～2045cm -1 and the band at 2156cm -1 nearly disappeared.This was due to the reduction of palladium ion on H mordenite.IR TPD spectra of carbon monoxide on Pd/HM catalyst indicated that the bands below 2000cm -1 were strongly absorbed bridge bonded CO and the bands above 2000cm -1 were weakly adsorbed linear bonded CO. It was obviously that the surface properties of reduced catalyst changed a great deal.In addition metal dispersion would dropped since palladium bulked on the surface of the catalyst as reduced by hydrogen at 375℃.