Morphological Characteristics of Gold Nanowires and Nanoparticles: Structure Elucidation and Reactivity Toward Water-gas Shift Reaction

Irradiation of gamma-ray to FSM-16 encapsulated HAuCl4. synthesized via chemical vapor deposition, led to the formation of Au nanowires (2 10 nin diameter and 17 147 nm length), Contrarily, reductive carbonylation of impregnated HAuCl4 with FSM-16 using CO (200 torr)/water (20 torr) for 2 h, Followed by it! radiation with a high-pressure Hg lamp at 300 K. for 36 h, resulted in the formation of Au nanoparticles (circular; 8-75 nin diameter). These catalysts have been characterized by XRD, N-2-sorpitometry, TEM, UV-vis-PRS, CO-FTIR spectroscopy, and then tested for water-gas shift reaction (WGSR) under feeding conditions of P-CO = 60 torr and PH2O = 5 torr. Evidently, Au nanowires exhibited higher activity (3 times) than Au nanoparticles. It has been shown that the activity depends on Au geometry rather than structural characteristics, such as surface area, In-situ FTIR CO adsorption and UV-vis-DRS evidenced major changes oil the surface properties of Au nanowires in exposing different oxidation states as well Lis inducing electron deficiencies exceeding those oil Au nanoparticles. Gold nanowires displayed surface plasmon resonance peak at 5 5 nm derivatized from distribution in size and dispersion and Father exceeding that at 484 rim exhibited for gold nanoparticles. It has beet) shown that Au-0 species, including nanowires and small aggregated metallic nanoparticles, contribute significantly, if not predominantly, to the WGS activity. The TEM study provided evidence that reduction pretreatment of Au nanowires prior to carrying out the reaction results in elimination of the activity due to sintering (from 35 to 53 nm)as well as to the exhibited change in geometry and thus altering the nature of active centers.