(439a) Effect of Synthesis Methods on Dry Reforming of Methane over Ni/CexZr1-XO2

Greenhouse gases are responsible for global warming and recent climate changes. Dry reforming of methane has drawn much attention as it converts two greenhouse gases (CH₄ and CO₂) to syngas with a H₂/CO ratio of 1. The reaction is attractive for eliminating greenhouse gases, exploiting natural gas resources with high CO₂ content and producing syngas for at H₂/CO ratio closer to unity for further chemical production. Ni-based catalysts have shown great activity towards dry reforming of methane. Unfortunately, such catalysts often suffer from severe coking and sintering during the reaction which leads to fast deactivation of the catalysts and prevents the industrial application of the reaction.

To address the challenge, our group designed and synthesized a series of Ni/Ce_0.82Zr_0.18O₂ (Ni/CZ) that were found to activate methane at low/moderate temperatures. Synthesis methods applied include dry impregnation (DI), strong electrostatic adsorption (SEA), co-precipitation (CP) and combustion synthesis (CS). Catalysts with different nickel loading were synthesized to tune the accessibility of surface nickel particles for bulk synthesis methods (CP and CS). XRD analysis showed that only the CP catalysts with 6 and 10 wt.% contained detectable nickel particles. EXAFS analysis on fresh samples confirms the presence of small and well-dispersed nickel particles on all catalysts. For 2CS and 2CP, almost atomic dispersion of nickel was achieved.

Reactivity tests showed that all catalysts were active for dry reforming of methane at 700 °C to the thermodynamic limit. The catalyst remains active after 12 hours of experiment. Carbon deposit production occurred only within the first hour of the reaction. TGA of spent catalyst showed that a limited amount of carbon deposits formed within 12 hours of reaction. XANES spectra of the spent catalysts showed that except for the DI catalyst, all nickel stayed reduced after the reaction, indicating carbonaceous deposits might prevent re-oxidation during sample handling in air. To further differentiate the performance of each catalysts, reactivity tests were performed with a diluted catalyst loading. The results showed that catalysts with smaller and better dispersed nickel clusters have better activity and are more resistant to deactivation.