Morphology Dependent Reactivity of CsOx Nanostructures on Au(111): Binding and Hydrogenation of CO2 to HCOOH,ACS Nano

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Morphology Dependent Reactivity of CsOx Nanostructures on Au(111): Binding and Hydrogenation of CO2 to HCOOH
ACS Nano ( IF 15.8 ) Pub Date : 2023-11-10 , DOI: 10.1021/acsnano.3c08324
Vikram Mehar ₁ , Wenjie Liao ₁ , Mausumi Mahapatra _{1,

2} , Rui Shi ₃ , Hojoon Lim _{1,

4} , Irene Barba-Nieto ₁ , Adrian Hunt ₄ , Iradwikanari Waluyo ₄ , Ping Liu _{1,

3} , José A Rodriguez _{1,

3}

Affiliation

Cesium oxide (CsO_x) nanostructures grown on Au(111) behave as active centers for the CO₂ binding and hydrogenation reactions. The morphology and reactivity of these CsO_x systems were investigated as a function of alkali coverage using scanning tunneling microscopy (STM), ambient pressure X-ray photoelectron spectroscopy (AP-XPS), and density functional theory (DFT) calculations. STM results show that initially (0.05–0.10 ML) cesium oxide clusters (Cs₂O₂) grow at the elbow sites of the herringbone of Au(111), subsequently transforming into two-dimensional islands with increasing cesium coverage (>0.15 ML). XPS measurements reveal the presence of suboxidic (Cs_yO; y ≥ 2) species for the island structures. The higher coverages of cesium oxide nanostructures contain a lower O/Cs ratio, resulting in a stronger binding of CO₂. Moreover, the O atoms in the Cs_yO structure undergo a rearrangement upon the adsorption of CO₂ which is a reversible phenomenon. Under CO₂ hydrogenation conditions, the small Cs₂O₂ clusters are hydroxylated, thereby preventing the adsorption of CO₂. However, the hydroxylation of the higher coverages of Cs_yO did not prevent CO₂ adsorption, and adsorbed CO₂ transformed to HCOO species that eventually yield HCOOH. DFT calculations further confirm that the dissociated H₂ attacks the C in the adsorbate to produce formate, which is both thermodynamically and kinetically favored during the CO₂ reaction with hydroxylated Cs_yO. These results demonstrate that cesium oxide by itself is an excellent catalyst for CO₂ hydrogenation that could produce formate, an important intermediate for the generation of value-added species. The role of the alkali oxide nanostructures as active centers, not merely as promoters, may have broad implications, wherein the alkali oxides can be considered in the design of materials tuned for specific applications in heterogeneous catalysis.

中文翻译：

Au(111) 上 CsOx 纳米结构的形态依赖反应性：CO2 与 HCOOH 的结合和氢化

在 Au(111) 上生长的氧化铯 (CsO _x ) 纳米结构充当 CO ₂结合和氢化反应的活性中心。_{使用扫描隧道显微镜 (STM)、常压 X 射线光电子能谱 (AP-XPS) 和密度泛函理论 (DFT) 计算，研究了这些 CsO x}系统的形态和反应性作为碱覆盖率的函数。STM 结果表明，最初 (0.05–0.10 ML) 氧化铯簇 (Cs ₂ O ₂ ) 在 Au(111) 人字形的肘部位置生长，随后随着铯覆盖率的增加转变成二维岛 (>0.15 ML) 。XPS 测量揭示了岛结构中存在低氧化 (Cs _y O; y ≥ 2) 物质。氧化铯纳米结构的覆盖率越高，O/Cs比率越低，从而导致CO ₂的结合力更强。_{此外，Cs y} O结构中的O原子在吸附CO ₂时发生重排，这是可逆现象。在CO ₂氢化条件下，小的Cs ₂ O _{2簇被羟基化，从而阻止CO}₂的吸附。然而，较高覆盖度的Cs _y O的羟基化并没有阻止CO ₂吸附，并且吸附的CO ₂转化为HCOO物质，最终产生HCOOH。DFT 计算进一步证实，解离的 H ₂攻击吸附物中的 C 生成甲酸盐，这在 CO ₂与羟基化 Cs _y O 反应期间在热力学和动力学上都是有利的。这些结果表明，氧化铯本身就是一种优异的催化剂CO ₂加氢可产生甲酸盐，甲酸盐是产生增值物质的重要中间体。碱金属氧化物纳米结构作为活性中心而不仅仅是作为促进剂的作用可能具有广泛的含义，其中碱金属氧化物可以在针对多相催化中的特定应用而调整的材料设计中被考虑。

更新日期：2023-11-10

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