Dopants adsorbed as single atoms prevent degradation of catalysts

TL;DR

This study reveals that single-atom La dopants adsorbed on catalyst surfaces prevent high-temperature degradation by stabilizing the structure, providing new insights for designing durable catalysts.

Contribution

The paper demonstrates that isolated La atoms adsorbed on catalyst surfaces, rather than bulk incorporation, inhibit structural transformation and degradation at high temperatures.

Findings

La atoms adsorb on surface as single atoms

Strong binding and mutual repulsion stabilize the surface

Dopants inhibit sintering and phase transformation

Abstract

The design of catalysts with desired chemical and thermal properties is viewed as a grand challenge for scientists and engineers. For operation at high temperatures, stability against structural transformations is a key requirement. Although doping has been found to impede degradation, the lack of atomistic understanding of the pertinent mechanism has hindered optimization. For example, porous gamma-Al2O3, a widely used catalyst and catalytic support, transforms to non-porous alpha-Al2O3 at ~1,100C. Doping with La raises the transformation temperature to ~1,250C, but it has not been possible to establish if La atoms enter the bulk, adsorb on surfaces as single atoms or clusters, or form surface compounds. Here, we use direct imaging by aberration-corrected Z-contrast scanning transmission electron microscopy coupled with extended X-ray absorption fine structure and first-principles calculations to demonstrate that, contrary to expectations, stabilization is achieved by isolated La atoms adsorbed on the surface. Strong binding and mutual repulsion of La atoms effectively pin the surface and inhibit both sintering and the transformation to alpha-Al2O3. The results provide the first guidelines for the choice of dopants to prevent thermal degradation of catalysts and other porous materials.