Synthesis of porous and homogeneous Ni/Al2O3 cryogel for CO2 reforming of CH4

Nickel–alumina cryogel was prepared from aluminium sec-butoxide and nickel acetate by one-pot sol–gel processing and subsequent freeze drying. Catalysis for CO2 reforming of CH4 and carbon formation during the reforming were examined on the cryogel by comparison to those on the corresponding xerogel catalyst prepared by employing normal drying in order to evaluate the utility of the freeze drying. While the catalytic activity was not different significantly between the two sol–gel catalysts, carbon formation was suppressed more markedly on the cryogel than on the xerogel. The surface area and pore volume of the catalyst after the calcination and after the subsequent high-temperature reduction were larger for the cryogel than for the xerogel. XRD, UV-visible, FT-IR, and Raman spectra suggested the principal formation of NiAl2O4 after the calcination for both catalysts, whereas the presence of NiO, leading finally to large nickel particle, was suggested for the xerogel although it may be a small portion. Mean diameter of nickel particles estimated from TEM and XRD showed smaller size for the cryogel than for the xerogel. These results suggested that role of the freeze drying was to improve structural and textual properties of alumina gel as well as to give finer nickel particles throughout the gel.