Synthesis and investigation of bimetallic Ni-Co/Al2O3 nanocatalysts using the polyol process

Abstract

Ni-Co/Al2O3 catalysts with different Ni:Co ratios by weight were prepared using a simple polyol process. The activities of the catalysts were evaluated for the catalytic partial oxidation of methane (CPOM) in the temperature range of 600-800 degrees C. Numerous techniques such as x-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) surface area analysis, inductively coupled plasma-mass spectroscopy (ICP-MS), thermogravimetric analysis ( TGA), high-resolution transmission electron microscopy analysis (HRTEM), scanning electron microscopy analysis (SEM-EDS) and temperature-programmed oxidation (TPO) were applied to characterize fresh and spent catalysts. The XRD analysis confirmed that the loaded particles were metals and showed possible bimetallic nano-alloy Ni-Co formation for Ni-and Co-containing catalysts. The highest metal dispersion was 15.7% for the Ni2.8Co2.6/Al2O3 catalyst. The catalytic test results showed no correlation between metal dispersion and the metal particle size, and the activity decreased in the order of Ni-7.7/Al2O3 > Ni2.8Co2.6/Al2O3 approximate to Ni3.8Co1.5/Al2O3 > Ni2.0Co3.8/Al2O3 >> Co-6.8/Al2O3 under a flow rate of 157,500 L kg(-1) h(-1) with CH4/O-2 = 2 (using air as an oxidant) at 800 degrees C. The obtained results also showed that when the actual atomic Ni/Co ratio was 1.07 in the Al2O3-supported catalyst, the dispersion of the active sites appeared to be promoted by Co addition, and the catalytic activity was stable over a reaction time of 10 h. Among all the tested catalysts, the Ni2.8Co2.6/Al2O3 catalyst exhibited acceptable activity (75%) without coking.