^(13)CH_3OH在Pd-La_2O_3/SiO_2催化剂上的程序升温脱附和分解及共吸附物类的相互作用

TEMPERATURE PROGRAMMED DESORPTION AND DECOMPOSITION OF ^(13)CH_3OH ON Pd-La_2O_3/SiO_2 CATALYSTS AND THE EFFECT OF COADSPECIES INTERACTION

用质谱检测的程序升温脱附研究了^(13)CH_3OH在不同La_2O_3含量的Pd-La_2O_3/SiO_2催化剂上的脱附和分解。高温He处理的催化剂室温下对甲醇的吸附容量随La_2O_3含量增加而增加,但其脱附和分解产物之比几乎为常数。氢还原的催化剂室温下对甲醇吸附容量在Pd/La体相原子比为1:1时达最大值,但甲醇脱附和分解产物之比值随La_2O_3含量增加而增加,且产物中CO_2随La_2O_3含量增加而减少。CH_3OH和^(13)CH_3OH次序吸附后的TPD谱表明在催化剂上有对甲醇的分子吸附中心,可置换的解离吸附中心和不可置换的强解离吸附中心。CO和^(13)CH_3OH共吸附的TPD谱表明:在CO和^(13)CH_3OH共吸附物类之间有相互排斥的作用。这种作用有利于CO吸附态的重新分布和脱附,因此阻止了CO的岐化反应。

TPD and TPDE of 13CH3OH on Pd-La2O3/SiO2 catalysts with different contents of lanthana were studied by multichannel mass spectrometer. The ad-sorptive capacity of methanol increases with lanthana content in the catalysts in both He and H2 treatments. But the mole ratio of dcsorption and decomposition products keeps nearly constant in the He treatment. The catalysts after H2 reduction also produce more CO2 and the additional lanthana in the catalyst diminishes CO2 formation. Three kinds of adsorption sites on the catalyst surface are evidenced by coadsorption of isotopic methanol, namely, the strongest adsorption sites, the medium-strong adsorption sites and the weakest adsorption sites. TPD spectra of coadspecies of CO and 13CH3OH on Pd-La2O3/SiO2 catalysts shows that there is a repulsive interaction between the coadspecies of CO and 13CH3OH. It is such a repulsive interaction which leads to the facile desorption of CO and so prohibits its further disproportionate.