研究了负载Ru,Rh和Pd的WO_3-ZrO_2催化刺在乙烯直接氧化制乙酸反应中的催化性能.结果显示.负载的贵金属对催化剂的催化性能有非常重要的影响.Rh/WO_3-ZrO_2催化剂具有最高的乙烯转化率,而Ru/WO_3-ZrO_2催化剂对反应几乎没有活性.H2化学吸附结果显示,高的催化性能来源于高的金属分散度.Pd/WO_3-ZrO_2催化剂显示了最高的乙酸选择性(75%),而其它两个催化剂的乙酸选择性都非常低(～10%).程序升温氧化和程序升温还原结果显示,贵金属-O键的键强对产物的选择性具有重要的影响.弱的贵金属-O键可以通过将氧插入到乙烯和/或乙醛中而有利于乙酸的生成,而强的贵金属-O键会导致乙烯完全氧化为CO_x.
Ru-,Rh-,and Pd/WO_3-ZrO_2 catalysts were studied for the direct oxidation of ethylene to acetic acid.The catalytic activity and selectivity depended strongly on the noble metals used.Rh/WO_3-ZrO_2 gave the highest conversion of ethylene,whereas Ru/WO_3-ZrO_2 was almost inactive.The higher catalytic activity was attributed to a better metal dispersion.Pd/WO_3-ZrO_2 gave the highest selectivity for acetic acid(75%),with the selectivity of the other two catalysts being rather low(-10%).Temperature-programmed oxidation and H2 reduction experiments were used to show that the strength of the noble metal-oxygen bond played an important role in product distribution.A weak metal-oxygen bond favored the formation ofacetic acid.while a strong metal-oxygen bond favored the combustion ofethylene to Cox.
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