Catalysis Division , National Chemical Laboratory , Dr. Homi Bhabha Road , Pune 411 008 , India.
Centre of Excellence on Surface Science , National Chemical Laboratory , Pune 411 008 , India.
ACS Appl Mater Interfaces. 2018 Dec 5;10(48):41268-41278. doi: 10.1021/acsami.8b12940. Epub 2018 Nov 21.
Bimetallic nanostructures with a combination of noble and nonnoble metals hold promise for improving catalyst activity and selectivity. Here, we report the synthesis of Pd@Co (PC) core-shell morphology nanoparticles with three different ratios of palladium (Pd) and cobalt (Co), and a possibility to fine tune the ratio of core and shell thickness. PC exhibits superior and selective hydrogenation as well as oxidation catalytic activity at ambient or near-ambient conditions. Various characterization techniques have been employed to confirm the core-shell morphology. Without any pre-treatment or activation, fresh catalysts with different Pd to Co ratios, that is, 2:1, 1:1, and 1:2, were subjected to olefin (phenylacetylene) hydrogenation and oxidation (styrene to styrene oxide) reaction. The catalytic activity results demonstrate that the 1:1 ratio of Pd/Co is the most active composition for controlled and stepwise reduction of phenyl acetylene to styrene and then to ethyl benzene; 1:1 Pd/Co shows 100% styrene conversion in 30 min. with an order of magnitude higher turnover frequency than other catalysts. The 1:1 PC ratio is also the most active composition for selective oxidation of styrene to styrene oxide. NAPXPS (near-ambient pressure XPS) results show that the active sites for catalytic C═C hydrogenation and oxidation reaction are Co and Co, respectively. However, the superior catalytic performance can be attributed to Co (for reduction) or Co (for oxidation), and the Pd-Co interface plays a critical role in stabilizing the required functional character. NAPXPS results confirm that the superior catalytic performance can be attributed not only to Co or Co, but also to the Pd-Co interface. The electronic effect and synergism between Co and Pd helps Co to stabilize in different oxidation states depending on the reaction conditions, and making it a dual functional catalyst.
具有贵金属和非贵金属组合的双金属纳米结构有望提高催化剂的活性和选择性。在这里，我们报告了具有三种不同钯（Pd）和钴（Co）比例的 Pd@Co（PC）核壳形貌纳米粒子的合成，并且有可能精细调整核壳厚度的比例。PC 在环境或接近环境条件下表现出优异的选择性加氢和氧化催化活性。采用各种表征技术来证实核壳形态。无需任何预处理或活化，具有不同 Pd 与 Co 比的新鲜催化剂，即 2:1、1:1 和 1:2，被用于烯烃（苯乙炔）加氢和氧化（苯乙烯到苯乙烯氧化物）反应。催化活性结果表明，Pd/Co 的 1:1 比例是将苯乙炔可控且逐步还原为苯乙烯，然后为乙苯的最活性组成；1:1 Pd/Co 在 30 分钟内显示出 100%的苯乙烯转化率，其周转频率比其他催化剂高一个数量级。1:1 PC 比例也是苯乙烯选择性氧化为苯乙烯氧化物的最活性组成。NAPXPS（近环境压力 XPS）结果表明，催化 C═C 加氢和氧化反应的活性位分别为 Co 和 Co。然而，优越的催化性能可以归因于 Co（用于还原）或 Co（用于氧化），并且 Pd-Co 界面在稳定所需功能特征方面起着关键作用。NAPXPS 结果证实，优越的催化性能不仅归因于 Co 或 Co，还归因于 Pd-Co 界面。Co 和 Pd 之间的电子效应和协同作用有助于 Co 根据反应条件稳定在不同的氧化态中，并使其成为双功能催化剂。
