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Gaining an insight into the interface structure resulting from the interaction between metal nanoparticles and their supports, particularly under relevant reaction conditions, has been an important topic in heterogeneous catalysis and materials science. In this contribution, the active sites and interfaces of Pt sub-nanocrystals supported on carbon nanofibers (CNFs) are investigated and visualized at the atomic level by highly integrated X-ray absorption near-edge structure, X-ray absorption fine structure (EXAFS), and molecular dynamics (MD) simulations based on a reactive force field. Experimental and theoretical results indicate that the surface structure of the CNFs is one of the key parameters that governs the metal–support interface structure, which in turn determines the metal–support interaction strength and the structural properties of Pt clusters, including cluster size, Pt coordination number, and Pt–Pt bond length. Owing to the strong interaction between Pt and CNFs, sub-nanometer-sized Pt clusters are stabilized on CNFs. The Pt–Pt coordination number determined from EXAFS suggests Pt clusters of ∼1 nm size are deposited on platelet-type CNFs (p-CNFs), whereas clusters smaller than 0.6 nm are supported on fishbone-type CNFs (f-CNFs). The catalysts exhibit high selectivity toward CO oxidation at relatively low temperatures in the presence of H2, and their activity is related to the Pt coordination number and Pt–Pt bond length. The Pt clusters on the p-CNFs with relatively high coordination number have much higher activity than those on f-CNFs. The combined EXAFS analysis and MD simulations provide a better understanding of the catalyst properties at the atomic level and pave the way to use the CNF structure as a platform to tune the Pt particle size and metal activity through manipulating the metal–support interaction.

It was found that the Pt loading obtained by immobilization of colloidal Pt oxide particles on carbon nanofibers (CNFs) at a pH of 9−10 varied from 1.4 to 19.6 wt % (nominal loading 19.4 wt %). The amount of Pt deposited depended significantly on the CNF properties. The study targeted the identification of the determining carbon support properties for the successful preparation of Pt catalysts. CNFs, multiwall carbon nanotubes (MWNTs), and Vulcan XC-72R were utilized as supports. Platelet and fishbone CNFs with different surface areas, graphene layer stacking angles, and amount of surface oxygen groups were obtained by catalytic chemical vapor deposition. The carbon supports were thoroughly characterized by transmission electron microscopy (TEM), N2-adsorption measurements, X-ray diffraction (XRD), temperature-programmed oxidation (TPO), ζ-potential measurements, and X-ray photoelectron spectroscopy (XPS). Characterization of the deposited Pt particles by TEM revealed similar sizes but differences with respect to particle location. Based on TEM, BET, XRD, and XPS, a clear indication of the importance of surface defects and edge sites for successful immobilization of Pt oxide colloid particles was found for all carbon supports. From XPS a linear relationship was found between the fraction of species originating at a binding energy of 285.1 eV and the final Pt loading. These species can be sp3-hybridized carbon, defects, and/or dangling bonds (edge structure). The surface oxygen groups were found to have a decisive effect on the immobilization of Pt. Negative linear trends were found between the Pt loading obtained on CNFs and the O 1s/C 1s ratio and number of carboxylic groups determined from XPS. It is based on the results believed that the oxygen-free defect and edge structure can play a vital and important role in the preparation of more effective CNF-supported catalysts.

Abstract: A compact, internally heated, catalytic reactor is demonstrated for the low-temperature oxidation of carbon monoxide. Carbon nanofibres were grown on carbon felt and used as a support material for Au/TiO2 catalysts. The carbon composite plays two roles; as a support material for the catalyst and for providing heat to the reaction by the Joule effect. The internal heating offers a stable reactor system with quick temperature response at relatively low energy input. Comparison between external and internal heating shows higher conversion of CO in the low-temperature range when using internal heating. The Au/TiO2 catalyst supported on the carbon-carbon composite shows good stability at 250°C.