Huang Erwei, Orozco Ivan, Ramírez Pedro J, Liu Zongyuan, Zhang Feng, Mahapatra Mausumi, Nemšák Slavomír, Senanayake Sanjaya D, Rodriguez José A, Liu Ping
Department of Chemistry, Stony Brook University, Stony Brook, New York 11794, United States.
Facultad de Ciencias, Universidad Central de Venezuela, Caracas 1020-A Venezuela.
J Am Chem Soc. 2021 Nov 17;143(45):19018-19032. doi: 10.1021/jacs.1c08063. Epub 2021 Nov 4.
Because of the abundance of natural gas in our planet, a major goal is to achieve a direct methane-to-methanol conversion at medium to low temperatures using mixtures of methane and oxygen. Here, we report an efficient catalyst, ZnO/CuO/Cu(111), for this process investigated using a combination of reactor testing, scanning tunneling microscopy, ambient-pressure X-ray photoemission spectroscopy, density functional calculations, and kinetic Monte Carlo simulations. The catalyst is capable of methane activation at room temperature and transforms mixtures of methane and oxygen to methanol at 450 K with a selectivity of ∼30%. This performance is not seen for other heterogeneous catalysts which usually require the addition of water to enable a significant conversion of methane to methanol. The unique coarse structure of the ZnO islands supported on a CuO/Cu(111) substrate provides a collection of multiple centers that display different catalytic activity during the reaction. ZnO-CuO step sites are active centers for methanol synthesis when exposed to CH and O due to an effective O-O bond dissociation, which enables a methane-to-methanol conversion with a reasonable selectivity. Upon addition of water, the defected O-rich ZnO sites, introduced by Zn vacancies, show superior behavior toward methane conversion and enhance the overall methanol selectivity to over 80%. Thus, in this case, the surface sites involved in a direct CH → CHOH conversion are different from those engaged in methanol formation without water. The identification of the site-dependent behavior of ZnO/CuO/Cu(111) opens a design strategy for guiding efficient methane reformation with high methanol selectivity.
由于地球上天然气储量丰富，一个主要目标是利用甲烷和氧气的混合物在中低温下实现甲烷直接转化为甲醇。在此，我们报道了一种用于该过程的高效催化剂ZnO/CuO/Cu(111)，通过反应器测试、扫描隧道显微镜、常压X射线光电子能谱、密度泛函计算和动力学蒙特卡罗模拟相结合的方法对其进行了研究。该催化剂能够在室温下活化甲烷，并在450 K下将甲烷和氧气的混合物转化为甲醇，选择性约为30%。其他非均相催化剂通常需要添加水才能实现甲烷向甲醇的显著转化，而该催化剂并未表现出这种性能。负载在CuO/Cu(111)衬底上的ZnO岛独特的粗糙结构提供了多个中心的集合，这些中心在反应过程中表现出不同的催化活性。当暴露于CH和O时，ZnO-CuO台阶位点是甲醇合成的活性中心，这是由于有效的O-O键解离，从而实现了具有合理选择性的甲烷到甲醇的转化。加入水后，由锌空位引入的富含缺陷氧的ZnO位点对甲烷转化表现出优异的性能，并将整体甲醇选择性提高到80%以上。因此，在这种情况下，参与直接CH→CHOH转化的表面位点与不加水时参与甲醇形成的表面位点不同。ZnO/CuO/Cu(111)位点依赖性行为的确定为指导具有高甲醇选择性的高效甲烷重整开辟了一种设计策略。
