Effects of PVP on the preparation of nanosized Al2O3 supported Ni catalysts by polyol method for catalytic partial oxidation of methane

Small Ni metal nanoparticles (< 10 nm) supported on γ-Al2O3 were prepared by a simple polyol method in ethylene glycol (EG) medium. The effects of PVP (polyvinylpyrrolidone) ratio on the crystallite and particle sizes were determined by XRD and TEM analysis. The activities of the catalysts were evaluated for partial oxidation of methane (CPOM). The results indicated that in polyol process varying the ratio of PVP resulted in smaller Ni crystallite sizes, good metal dispersion and high catalytic activity. When the weight ratio of PVP to metal salt increased from 0:1 to 5:1 in the as-prepared catalyst the particle sizes decreased from 13.10 nm to 8.0 nm, and methane conversion increased from 69.40% to 92.00% at 800 °C. The activity of the catalysts in CPOM reaction also depended on the thermal treatment. H2-pretreated catalysts exhibited higher activity than non pre- treated catalyst, suggesting that the presence of organic matrix hinders the access to the nickel active sites. Among the catalysts tested, Ni/γ-Al2O3 catalyst with a weight ratio of PVP to metal salt 5:1 exhibited the higher activity (92%) and stability with a gas hour space velocity of 157,500 (Lkg− 1 h− 1) at 800 °C.