CO-Induced Dynamic\nBehavior of Al<sub>2</sub>O<sub>3</sub>‑Supported Pd Nanoparticles\nat Room Temperature

Supported metal nanoparticles may undergo adsorbate-induced\nphenomena,\nwith evident consequences for their performance in catalytic applications.\nCO-induced surface phenomena involving Pd nanoparticles have been\ndocumented mostly at high temperatures. In this work, we report an\nunusual step-shaped CO adsorption isotherm at 30 °C on Pd/Al<sub>2</sub>O<sub>3</sub>, associated with an unexpected increase in the\nheat of adsorption and with a modification in the relative abundance\nof the different Pd-carbonyl species. These three independent observations\ncan be reconciled by considering a partially reversible CO-induced\nroughening of the Pd(100) facets, entailing the creation of novel\ndefective sites. The detailed knowledge of the interaction of CO with\nPd nanoparticles at mild temperatures in terms of strength, coverage,\nand adsorption mode/sites is a key to control reactivity and has analytical\nrelevance for the correct interpretation of CO chemisorption measurements.\nOur experimental strategy has the potential to become a benchmark\nin the investigation of the adsorbate-induced dynamic behavior of\nsupported metal nanoparticles.