Investigation of Toluene Oxidation over 1D Pt@CeO Derived from Pt Cluster-Containing MOF.

A unique 1D nanostructure of Pt@CeO-BDC was prepared from Pt@CeBDC MOF. The Pt@CeO-BDC was rich in oxygen vacancies (i.e., XPS O/(O + O) = 39.4%), and on the catalyst, the 2 nm Pt clusters were uniformly deposited on the 1D mesoporous polycrystalline CeO. Toluene oxidation was conducted in a spectroscopic 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@CeO-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 CO and HO by lattice oxygen and reoxidation of the reduced ceria with consumption of adsorbed oxygen species. The Pt clusters, which mainly exist as Pt with minor amounts of Pt and Pt on the surface, facilitated the adsorption and reaction activation. The Pt-CeO 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 CO and HO mainly by the Mars-van Krevelen mechanism.