Pd-Ce-O[sub.x]/MWCNTs and Pt-Ce-O[sub.x]/MWCNTs Composite Materials: Morphology, Microstructure, and Catalytic Properties

The composite nanomaterials based on noble metals, reducible oxides, and nanostructured carbon are considered to be perspective catalysts for many useful reactions. In the present work, multi-walled carbon nanotubes (MWCNTs) were used for the preparation of Pd-Ce-O[sub.x] /MWCNTs and Pt-Ce-O[sub.x] /MWCNTs catalysts comprising the active components (6 wt%Pd, 6 wt%Pt, 20 wt%CeO[sub.2] ) as highly dispersed nanoparticles, clusters, and single atoms. The application of X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) provided analysis of the samples’ morphology and structure at the atomic level. For Pd-Ce-O[sub.x] /MWCNTs samples, the formation of PdO nanoparticles with an average crystallite size of ~8 nm was shown. Pt-Ce-O[sub.x] /MWCNTs catalysts comprised single Pt[sup.2+] ions and PtO[sub.x] clusters less than 1 nm. A comparison of the catalytic properties of the samples showed higher activity of Pd-based catalysts in CO and CH[sub.4] oxidation reactions in a low-temperature range (T[sub.50] = 100 °C and T[sub.50] = 295 °C, respectively). However, oxidative pretreatment of the samples resulted in a remarkable enhancement of CO oxidation activity of Pt-Ce-O[sub.x] /MWCNTs catalyst at T < 20 °C (33% of CO conversion at T = 0 °C), while no changes were detected for the Pd-Ce-O[sub.x] /MWCNTs sample. The revealed catalytic effect was discussed in terms of the capability of the Pt-Ce-O[sub.x] /MWCNTs system to form unique PtO[sub.x] clusters providing high catalytic activity in low-temperature CO oxidation.