Selective reduction of diolefins over the metal catalysts surface-modified by UHV treatment

研究了表面结构对1，3-丁二烯加氢反应活性和选择性的影响。金属和金属氧化物催化剂在超高真空（UHV&lt;10 μ Pa）条件下进行热处理<-7>（UHV处理）。通过超高真空处理，负载型钯催化剂的1，3-丁二烯加氢活性显着提高。超高真空处理提高了1，3-丁二烯转化为1-丁烯的选择性。在热力学上，2-丁烯比1-丁烯更稳定。在经UHV处理的Pd催化剂上，1-丁烯从1，3-丁二烯的较高选择性强烈地表明，1，3-丁二烯的1，2-加成优先在氢化的初始阶段进行。为了形成2-丁烯，需要1，3-丁二烯的1，4-加成。1，4-加成反应的吸附中间体要求Pd的表面更平坦，如（111）基面。在粗糙表面上，预期1，2-加成比1，4-加成多得多。结果表明，经超高真空处理的Pd催化剂具有较高的1-丁烯选择性，表明Pd表面经超高真空处理后变得粗糙。这些结果表明，超高真空处理可以改变金属表面结构，影响端烯烃的选择性。超高压处理也显著提高了ZnO催化剂的活性。这清楚地表明，UHV处理对于金属氧化物催化剂的表面改性也是有效的。

In this study, the influence of surface structure has been investigated on the activity and selectivity of hydrogenation of 1,3-butadiene. Metal and metal oxide catalysts were thermally treated under ultrahigh vacuum (UHV<10^<-7> Pa) condition (the UHV treatment). The hydrogenation activity of 1,3-butadiene was markedly enhanced over supported Pd catalysts by the UHV treatment. The selectivity of 1-butene from 1,3-butadiene was increased by the UHV treatment. Thermodynamically, 2-butenes are more stable than 1-butene. The higher selectivity of 1-butene from 1,3-butadiene over the UHV-treated Pd catalysts strongly suggests that 1,2-addition of 1,3-butadiene proceeded preferentially at the initial stage of the hydrogenation. For the formation of 2-butenes, 1,4-addition of 1,3-butadiene was requested. The adsorption intermediate for 1,4-addition requires a more flat surface of Pd, like (111) basal plane. On a roughened surface, much more 1,2-addition will be expected than 1,4-addition. The high selectivity of 1-butene on the UHV-treated Pd catalysts indicates that the surface of Pd was roughened by the UHV treatment. These results show that the UHV treatment can modified the surface structure of metals and influenced the selectivity of terminal olefins. The activity on ZnO catalysts was also significantly enhanced by the UHV treatment. It is clearly indicated that the UHV treatment was also effective for the surface modification of the metal oxide catalysts.