Complementary methods for cluster size distribution measurements: supported platinum nanoclusters in methane reforming catalysts

• Published in: Journal of molecular catalysis. A, Chemical Vol. 228; no. 1; pp. 299 - 307
• Main Authors: Ramallo-López, J.M., Requejo, F.G., Craievich, A.F., Wei, J., Avalos-Borja, M., Iglesia, E.
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Amsterdam Elsevier B.V 16.03.2005; Elsevier
• Subjects: Catalysis; Chemistry; Cluster size; Exact sciences and technology; General and physical chemistry; HRTEM; Methane reforming; SAXS; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; XAFS; Cluster size; Methane reforming; XAFS; SAXS; HRTEM; Cerium Oxides; Methane; Transition metal; Reforming; Small angle X ray scattering; Supported catalyst; Heterogeneous catalysis; Transmission electron microscopy; Platinum; Distribution; Zirconium Oxides; Alumina; Catalyst
• ISSN: 1381-1169; 1873-314X
• DOI: 10.1016/j.molcata.2004.09.032

Pt cluster size strongly influences the reactivity of surfaces for C H bond activation during CH 4 steam reforming. C H bond activation turnover rates for H 2O reforming of CH 4 increased with decreasing Pt cluster size, suggesting that coordinatively unsaturated surface Pt atoms are more reactive than Pt atoms in low-index surfaces prevalent in larger clusters. Near-edge fine structure in X-ray absorption spectra clearly shows electronic changes in Pt clusters relative to bulk Pt crystallites, though differences in the 5d electronic density among samples with different cluster size could not be related directly to Pt surface atom coordination. These results suggest that catalytic consequences of cluster size arise from surface structure changes leading to coordinative unsaturation of surface atoms. X-ray absorption and small angle X-ray scattering techniques were used to measure the size of Pt metal nanoclusters and the results are compared with H 2 chemisorption and transmission electron microscopy data. Pt cluster size strongly influences the reactivity of surfaces for C H bond activation during CH 4 steam reforming. C H bond activation turnover rates for H 2O reforming of CH 4 increased with decreasing Pt cluster size, suggesting that coordinatively unsaturated surface Pt atoms are more reactive than Pt atoms in low-index surfaces prevalent in larger clusters. Near-edge fine structure in X-ray absorption spectra clearly shows electronic changes in Pt clusters relative to bulk Pt crystallites, though differences in the 5d electronic density among samples with different cluster size could not be related directly to Pt surface atom coordination. These results suggest that catalytic consequences of cluster size arise from surface structure changes leading to coordinative unsaturation of surface atoms. X-ray absorption and small angle X-ray scattering techniques were used to measure the size of Pt metal nanoclusters and the results are compared with H 2 chemisorption and transmission electron microscopy data. ▪