Material Physics, KTH Royal Institute of Technology, SCI, S-164 40 Kista, Sweden.
Applied Physical Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, S-100 44 Stockholm, Sweden.
J Chem Phys. 2017 Jun 28;146(24):244702. doi: 10.1063/1.4989472.
Adsorption and desorption of methanol on the (111) and (100) surfaces of CuO have been studied using high-resolution photoelectron spectroscopy in the temperature range 120-620 K, in combination with density functional theory calculations and sum frequency generation spectroscopy. The bare (100) surface exhibits a (3,0; 1,1) reconstruction but restructures during the adsorption process into a Cu-dimer geometry stabilized by methoxy and hydrogen binding in Cu-bridge sites. During the restructuring process, oxygen atoms from the bulk that can host hydrogen appear on the surface. Heating transforms methoxy to formaldehyde, but further dehydrogenation is limited by the stability of the surface and the limited access to surface oxygen. The (√3 × √3)R30°-reconstructed (111) surface is based on ordered surface oxygen and copper ions and vacancies, which offers a palette of adsorption and reaction sites. Already at 140 K, a mixed layer of methoxy, formaldehyde, and CHO is formed. Heating to room temperature leaves OCH and CH. Thus both CH-bond breaking and CO-scission are active on this surface at low temperature. The higher ability to dehydrogenate methanol on (111) compared to (100) is explained by the multitude of adsorption sites and, in particular, the availability of surface oxygen.
采用高分辨率光电子能谱，结合密度泛函理论计算和和频发生光谱，在 120-620 K 的温度范围内，研究了甲醇在 CuO(111)和(100)表面的吸附和解吸。裸露的(100)表面呈现(3,0;1,1)重构，但在吸附过程中，通过甲氧基和氢在 Cu-桥位的结合，重构为 Cu-二聚体稳定的几何形状。在重构过程中，能够容纳氢的体相中的氧原子出现在表面上。加热将甲氧基转化为甲醛，但进一步脱氢受到表面稳定性和表面氧有限可用性的限制。基于有序表面氧和铜离子及空位的(√3×√3)R30°-重构(111)表面，提供了一系列吸附和反应位点。在 140 K 时，就已经形成了甲氧基、甲醛和 CHO 的混合层。加热到室温时，留下 OCH 和 CH。因此，在低温下，CH 键的断裂和 CO 的断裂在这个表面上都是活跃的。与(100)相比，(111)表面上甲醇脱氢的能力更高，这可以解释为吸附位点的多样性，特别是表面氧的可用性。
