Identifying Support Effects in Au-Catalyzed CO Oxidation

Abstract

Some catalytic oxide supports are more equal than others, with numerous variable properties ranging from crystal symmetry to surface chemistry and electronic structure. As a consequence, it is often very difficult to determine which of these act as the driver of performance changes observed in catalysis. In this work, we hold many of these variable properties constant with structurally similar LnScO3 (Ln = La, Sm, and Nd) nanoparticle supports with cuboidal shapes and a common Sc-rich surface termination. Using CO oxidation over supported Au nanoparticles as a probe reaction, we observe higher activation energy and a slower rate using NdScO3 as the support material. This change is found to correlate to the strength of CO2 binding to the support surface, identified by temperature-programmed desorption measurements. The change is due to differences in the 4f electrons of the lanthanide cations, the cations’ Lewis acidity, and the inductive effect they impose.

Wet to Dry Controls Lanthanide Scandate Synthesis

“…From the theoretical side, the value of the optimal P H2O depends on the thermodynamics of the formation of LnScO 3 , Ln­(OH) 3 , and LnOOH from the starting materials, Sc 2 O 3 and Ln 2 O 3 . Since not all lanthanides readily form the LnOOH phase and properties such as Lewis acidity are not linear across the lanthanide series for Ln 3+ or LnScO 3 , , we should not assume linearity with Ln in these thermodynamics. The optimal P H 2 O for LnScO 3 across the lanthanide series may vary according to some other calculable trend.…”

“…Lanthanide scandates (LnScO 3 ) provide a particular challenge in the realm of predictive material synthesis. While LnScO 3 nanoparticles may find potential uses in a wide array of applications owing to their large optical band gap, potential for morphological control, and interesting surface properties, the thermodynamics of lanthanide perovskite formation is still not completely understood. , Each LnScO 3 has a different lattice parameter while retaining the bulk Pbnm orthorhombic perovskite structure. − Across the LnScO 3 series, they also share similar electronic structures and surface terminations. , However, while it is common to extrapolate or assume linear trends across the lanthanide series because of linearly changing properties like Ln 3+ cation radius or Ln–O bond length, , evidence suggests that the Ln 3+ electronic structure − and resulting properties such as Lewis acidity , do not trend linearly with Ln. Thus, without a robust understanding of the thermodynamics of their formation, it is difficult to predict how synthetic conditions for LnScO 3 will vary as the lanthanide is changed.…”

“…8 Lanthanide scandates (LnScO 3 ) provide a particular challenge in the realm of predictive material synthesis. While LnScO 3 nanoparticles may find potential uses in a wide array of applications owing to their large optical band gap, 9 potential for morphological control, 10 and interesting surface properties, 11 the thermodynamics of lanthanide perovskite formation is still not completely understood. 12,13 Each LnScO 3 has a different lattice parameter while retaining the bulk Pbnm orthorhombic perovskite structure.…”

“…14−16 Across the LnScO 3 series, they also share similar electronic structures and surface terminations. 17,18 However, while it is common to extrapolate or assume linear trends across the lanthanide series because of linearly changing properties like Ln 3+ cation radius or Ln−O bond length, 19,20 evidence suggests that the Ln 3+ electronic structure 21−25 and resulting properties such as Lewis acidity 11,26 do not trend linearly with Ln. Thus, without a robust understanding of the thermodynamics of their formation, it is difficult to predict how synthetic conditions for LnScO 3 will vary as the lanthanide is changed.…”