Microfibrous-structured silver catalyst for low-temperature gas-phase selective oxidation of benzyl alcohol

A highly active and selective silver on nickel fiber catalyst was successfully prepared for selective oxidation of benzyl alcohol. The Ag/Ni catalyst was obtained by loading Ag (10wt%) on paper-like microfibrous structure (consisting of 5vol% of 8-μm Ni-fiber) by impregnation method. The wettability of Ni-fiber support was vastly improved by a simple water pre-wetting and overnight drying treatment process. This yielded a catalyst (Ag/Ni-fiber-M) with more Ag cations and selectively active oxygen species than the catalyst (Ag/Ni-fiber) using the untreated support. The Ag/Ni-fiber-M showed much higher low-temperature activity/selectivity than the Ag/Ni-fiber, which could be attributed to the differences in their silver morphology and particle size. The best conversion and benzaldehyde selectivity observed were both 97% for Ag/Ni-fiber-M at 300°C, and 91 and 84% for Ag/Ni-fiber at 380°C, respectively. Benzyl alcohol selective oxidation would proceed concurrently through both direct O₂ activation route and NiO_x-participating oxygen spillover route. Formation of Ni_xC phase occurred and hampered the latter reaction route thereby leading to partial deactivation. However, spent catalyst could restore activity through an oxidation treatment at 400°C.