ZrO_2催化剂上吸附甲酸的TPD和IR研究

TPD AND IR STUDIES ON THE DECOMPOSITION OF FORMIC ACID ADSORBED ON ZrO_2

众多的研究表明甲酸在氧化物催化剂上的吸附分解与催化剂的表面酸碱性质有关。研究吸附相甲酸物种的变化表明甲酸分解反应的选择性除受温度影响外,还与甲酸的表面覆盖度有关。Z_rO_2表现为较典型的弱酸弱碱双功能性催化剂。最近我们的研究表明Z_rO_2表面存在表面键诱导酸-碱相互作用,它的酸-碱双功能催化作用在烷基胺分解转化为腈的反应中得到了较好地体现。本文报导Z_rO_2催化剂上吸附甲酸的程序升温脱附(TPD)和红外光谱(IR)研究结果。

Decomposition of formic acid adsorbed on ZrO_2 catalyst was studied by means of TPD and IR spectroscopy. Two peaks of H_2O were observed at about 423 and 623 K in the TPD process. Between the two peaks of H_2O, evolution of CO appeared and gave a peak at about 563 K. IR study showed that the adsorption of formic acid led to the formation of a formate(Ⅰ)and a dimer species(Ⅱ)of the acid on the surface. At 373-473 K, Ⅱ was decomposed to H_2O which produced the first H_2O peak and some new surface formate species(Ⅰ).At temperature higher than 473 K, the formate species (Ⅰ), either formed in the initial adsorption of formic acid or produced from Ⅱ ,were decomposed further to CO and surface hydroxyl groups. The main part of the surface hydroxyl groups were eliminated at above 573 K , which produced the second H_2O peak.