载体对负载型银催化剂催化乳酸乙酯氧化制丙酮酸乙酯的影响

Effect of Support on Selective Oxidation of Ethyl Lactate to Ethyl Pyruvate over Supported Silver Catalyst

为了提高电解银催化剂催化乳酸乙酯选择性氧化制丙酮酸乙酯的性能,选用SiO_(2),α-Al_(2)O_(3)和γ-Al_(2)O_(3)为载体,制备了负载型银基催化剂。系统地考察了催化剂的载体类型、负载量和焙烧温度对反应的影响,并通过X射线衍射(XRD)、紫外可见漫反射(UV-vis DRS)和H_(2)程序升温还原(H_(2)-TPR)等手段对负载型银基催化剂进行了表征。证明了游离的Ag^(+)离子和带正电荷的银团簇Ag_(n)^(δ+)是该反应的活性物种,当载体类型为α-Al_(2)O_(3),银负载量为7.8%,焙烧温度为600℃时得到性能较佳的催化剂。在反应温度为340℃、氧和乳酸乙酯物质的量比为1.4、液时空速(LHSV)为0.6 h^(-1)的条件下,乳酸乙酯的转化率为96.8%,丙酮酸乙酯的选择性达90.7%。经过100 h反应后的催化剂仍具有较高活性,通过原位烧炭可实现再生,具备良好的工业应用前景。

In order to improve the performance of electrolytic silver catalyst for the selective oxidation of ethyl lactate to ethyl pyruvate,the supported silver-based catalysts were prepared using SiO_(2),α-Al_(2)O_(3) and γ-Al_(2)O_(3) as carriers.The effects of carrier type,loading and calcination temperature on the reaction were systematically investigated.X-ray diffraction(XRD),UV-Vis diffuse reflectance spectrum(UV-Vis DRS)and H_(2) temperature programmed desorption(H_(2)-TPR)were used to characterize the loaded silver-based catalysts.It was demonstrated that the free Ag^(+)ions and the positively charged silver cluster of Ag_(n)^(δ+)were the active species of the action.The optimal catalyst with better performance was obtained when carrier type was α-Al_(2)O_(3),the loading of Ag was 7.8% mass fraction and calcination temperature was 600℃.The conversion of ethyl lactate was 96.8% and the selectivity of ethyl pyruvate reached 90.7% under the conditions of the reaction temperature being 340℃,molar ratio of oxygen to ester being 1.4 and liquid hourly space velocity(LHSV)being 0.6 h^(-1).After 100 h of reaction,the catalyst still had high activity and could be regenerated by in-situ carbon burning,which showed a good industrial application prospect.