Magkoev Tamerlan T, Mustafaeva Dzhamilya G, Zaalishvili Vladislav B, Ashkhotov Oleg G, Sozaev Zaurbek T
Laboratory of Adsorption Phenomena, Department of Condensed Matter Physics, North Ossetian State University, Vatutina 44-46, 362025 Vladikavkaz, Russia.
Geophysical Institute-The Affiliate of Vladikavkaz Scientific Centre of the Russian Academy of Sciences, Markova 93a, 362002 Vladikavkaz, Russia.
Materials (Basel). 2022 Mar 18;15(6):2245. doi: 10.3390/ma15062245.
Adsorption and interaction of carbon monoxide (CO) and nitric oxide (NO) molecules on the surface of bare Al-Mo(110) system and on that obtained by its in situ oxidation have been studied in ultra-high vacuum (base pressure: ca. 10 Pa) by means of Auger and X-ray photoelectron spectroscopy (AES, XPS), low energy electron diffraction (LEED), reflection-absorption infrared and thermal desorption spectroscopy (RAIRS, TDS), and by the work function measurements. In order to achieve the Al-Mo(110) alloy the thin aluminum film of a few monolayers thick was in situ deposited onto the Mo(110) crystal and then annealed at 800 K. As a result of Al atoms diffusion into the Mo(110) subsurface region and the chemical reaction, the surface alloy of a hexagonal atomic symmetry corresponding to AlMo alloy is formed. The feature of thus formed surface alloy regarding molecular adsorption is that, unlike the bare Mo(110) and Al(111) substrates, on which both CO and NO dissociate, adsorption on the alloy surface is non-dissociative. Moreover, adsorption of carbon monoxide dramatically changes the state of pre-adsorbed NO molecules, displacing them to higher-coordinated adsorption sites and simultaneously tilting their molecular axis closer to the surface plane. After annealing of this coadsorbed system up to 320 K the (CO + NO → CO + N) reaction takes place resulting in carbon dioxide desorption into the gas phase and nitriding of the substrate. Such an enhancement of catalytic activity of Mo(110) upon alloying with Al is attributed to surface reconstruction resulting in appearance of new adsorption/reaction centers at the Al/Mo interface (steric effect), as well as to the Mo d-band filling upon alloying (electronic effect). Catalytic activity mounts further when the Al-Mo(110) is in situ oxidized. The obtained Al-Mo(110)-O ternary system is a prototype of a metal/oxide model catalysts featuring the metal oxides and the metal/oxide perimeter interfaces as a the most active reaction sites. As such, this type of low-cost metal alloy oxide models precious metal containing catalysts and can be viewed as a potential substitute to them.
在超高真空（本底压力：约10⁻¹⁰ Pa）下，借助俄歇电子能谱和X射线光电子能谱（AES、XPS）、低能电子衍射（LEED）、反射吸收红外光谱和热脱附光谱（RAIRS、TDS）以及功函数测量，研究了一氧化碳（CO）和一氧化氮（NO）分子在裸露的Al - Mo(110)体系表面及其原位氧化后所得表面上的吸附和相互作用。为了制备Al - Mo(110)合金，将几层原子厚的铝薄膜原位沉积在Mo(110)晶体上，然后在800 K下退火。由于Al原子扩散到Mo(110)次表面区域并发生化学反应，形成了具有对应于AlMo合金的六方原子对称性的表面合金。如此形成的表面合金在分子吸附方面的特点是，与裸露的Mo(110)和Al(111)基底不同，在裸露基底上CO和NO都会解离，而在合金表面上的吸附是非解离性的。此外，一氧化碳的吸附显著改变了预吸附的NO分子的状态，将它们转移到配位更高的吸附位点，同时使它们的分子轴更靠近表面平面倾斜。将这种共吸附体系退火至320 K后，会发生(CO + NO → CO₂ + N)反应，导致二氧化碳解吸到气相中并使基底氮化。Mo(110)与Al合金化后催化活性的这种增强归因于表面重构，导致在Al/Mo界面出现新的吸附/反应中心（空间效应），以及合金化时Mo d带的填充（电子效应）。当Al - Mo(110)原位氧化时，催化活性进一步提高。所得到的Al - Mo(110)-O三元体系是一种金属/氧化物模型催化剂的原型，其以金属氧化物和金属/氧化物周边界面作为最活跃的反应位点。因此，这种低成本的金属合金氧化物可替代含贵金属的催化剂，并可被视为它们的潜在替代品。
