<i>Operando</i> Investigation of Toluene Oxidation over 1D Pt@CeO₂ Derived from Pt Cluster-Containing MOF

Abstract

A unique 1D nanostructure of Pt@CeO₂-BDC was prepared from Pt@CeBDC MOF. The Pt@CeO₂-BDC was rich in oxygen vacancies (i.e., XPS O_β/(O_α + O_β) = 39.4%), and on the catalyst, the 2 nm Pt clusters were uniformly deposited on the 1D mesoporous polycrystalline CeO₂. Toluene oxidation was conducted in a spectroscopic <i>operando</i> Raman-online FTIR reactor to elucidate the reaction mechanism and establish the structure-activity relationship. The reaction proceeds as follows: (I) adsorption of toluene as benzoate intermediates on Pt@CeO₂-BDC at low temperature by reaction with surface peroxide species; (II) reaction activation and ring-opening involving lattice oxygen with a concomitant change in defect densities indicative of surface rearrangement; (III) complete oxidation to CO₂ and H₂O by lattice oxygen and reoxidation of the reduced ceria with consumption of adsorbed oxygen species. The Pt clusters, which mainly exist as Pt²⁺ with minor amounts of Pt⁰ and Pt⁴⁺ on the surface, facilitated the adsorption and reaction activation. The Pt-CeO₂ interface generates reduced ceria sites forming nearby adsorbed peroxide at low temperature that oxidize toluene into benzoate species by a Langmuir-Hinshelwood mechanism. As the reaction temperature increases, the role of lattice oxygen becomes important, producing CO₂ and H₂O mainly by the Mars-van Krevelen mechanism.