Bimetallic Ni-Co/SBA-15 catalysts prepared by urea co-precipitation for dry reforming of methane

Abstract

A series of NixCo(10-x)/SBA-15 catalysts with constant metal loading (10 wt%) and different Co/Ni mass ratios (0/10–10/0) were prepared by urea co-precipitation and applied to the dry reforming of methane (DRM). The physicochemical properties of the catalysts were characterized in detail by various techniques (N2 physisorption, H2 chemisorption, XRD, TPR, ICP-OES, TGA, HRTEM and XPS), revealing that Ni and Co particles were embedded into the channel of SBA-15 and Ni was alloyed with Co. In addition, the bimetallic catalysts with a Co/Ni ratio (RCo/Ni) lower than 1 had relatively high metal dispersion (ca. 17–20%) and small metal particle sizes (ca. 4–5 nm). The DRM activity and stability of NixCo(10-x)/SBA-15 in terms of coke- and sintering- resistance were systematically examined and compared, which showed that the activity and stability of the catalysts depended strongly on the metal particle size, indicating the structure-sensitive character of the DRM reaction. Compared to monometallic Ni10/SBA-15 and Co10/SBA-15, bimetallic NixCo(10-x)/SBA-15 with RCo/Ni < 1 possessed improved activity and stability, which was mainly attributed to the small metal particle size, the synergetic effect of Co and Ni as well as the confinement effect of SBA-15 mesoporous channels. In particular, Ni9Co1/SBA-15 exhibited the highest activity, stability and H2/CO molar ratio (close to 1) during 50 h of operation at a gas hourly space velocity of 72000 mL/(gcat h) under 973 and 1073 K. Moreover, no coke deposition occurred on the catalyst, with only slight metal particle size growth to around 5 nm, indicating excellent coke- and sintering-resistance.