钾对苯甲酸甲酯加氢催化剂MnO_x/γ-Al_2O_3的修饰作用

采用浸渍法引入不同含量的钾元素对MnO_x/γ-Al_2O_3催化剂进行了改性，在 常压固定床反应器上研究了经不同含量修饰的催化剂对苯甲酸甲酯加氢生成苯甲醛 反应的影响。通过XRD，XPS，NH_3-TPD，BET，IR等手段对催化剂进行了表征，结 果表明：修饰后的催化剂并没有改变锰的价态，引入的钾和Al_2O_3发生了作用， 形成了新的晶相K_2Al_2O_4，改性后的催化剂减弱了催化剂表面的酸强度，并且减 少了酸中心数。催化剂表面具有中等强度的L酸中心可以有效抑制副产物甲苯和苄 基甲醚的生成，显著地提高了苯甲醛的选择性。

Effect of Potassium on the MnOx/γ-Al2O3 Catalysts for Hydrogenation of Methyl Benzoate

Elemental potassium was introduced to modify the MnO_x/γ-Al_2O_3 catalysts by impregnating method. The catalytic activities were studied in a continuous flow fixed-bed reactor under atmospheric pressure. The results indicated that the selectivity of benzaldehyde was improved significantly after the catalysts were modified. The optimum potassium loading on the catalysts is about 5% (wt). By means of XRD, XPS, NH_3-TPD, BET and IR, the effects of potassium on the catalysts of MnO_x/γ-Al_2O_3 were characterized. The XRD results reveal that the incorporated potassium acts on the Al_2O_3 to form new crystal K_2Al_2O_4 and that the valence state of manganese is not changed after the catalyst is modified by potassium, which is also verified by the XPS results. NH_3-TPD and FT-IR results show that certain amount of the potassium on the catalysts reduces the intensity and amounts of the acidic centers. The modified catalysts effectively inhibit the formation of toluene and benzyl methyl ether.