Effect of support materials on the performance of Ni-based catalysts in tri-reforming of methane

摘要

Tri-reforming of methane (TRM) utilizing CO2, H2O and O-2 is an emerging technique for the production of synthesis gas and CO2 abatement. Nevertheless, formulation and design of low-cost, active and stable catalyst for TRM is a major challenge due to its complex reaction network and rapid catalyst deactivation. The support effect is a critical factor influencing the activity and stability of supported Ni catalyst. Thus, a series of supported Ni catalysts over different metal oxides such as Al2O3, ZrO2, TiO2, SBA-15, MgO and CeO2-ZrO2 were prepared. The catalysts were characterized by using N-2 - physisorption, XRD, EDX, SEM, TEM, TPR, CO2 - TPD, NH3 - TPD, H-2 - pulse chemisorption and TGA. The performance of these catalysts was evaluated at 800 degrees C, 1 atm, WHSV 17220 mLh(-1) g(-1) and molar feed composition CH4:CO2:H2O:O-2:N-2 = 1:0.23:0.46:0.07:0.28 in a fixed-bed reactor. The initial activity of these catalysts followed the order: Ni/Al2O3 Ni/SBA-15 Ni/ZrO2 Ni/CeO2-ZrO2 Ni/TiO2 Ni/MgO. Ni/Al2O3 derived from spinet precursor NiAl2O4 resulted in well-dispersed smaller Ni particles, stronger metal-support interaction, a higher degree of reducibility and higher basic sites concentration, which led to its superior activity with 8.72 x 10(-2) mmol/g(cat).s, 2.31 x 10(-2) mmol/g(cat).s and 4.2 x 10(-2) mmol/g(cat).s CH4, CO2, and H2O conversion rate respectively. On the contrary, the stability of SBA-15 and ZrO2 supported Ni catalysts was remarkably high. Hexagonal porous network of SBA-15 confined Ni particles that resulted in high resistance against metal sintering and carbon deposition whereas Ni/ZrO2 offered resistance to Ni re-oxidation owing to its oxophilic property. Experimental investigations reveal that Ni/TiO2 and Ni/MgO resulted in poor CH4, CO2 and H2O conversion rates for TRM due to lower degree of reducibility. Furthermore, Ni/CeO2-ZrO2 catalyst had weak metal-support interaction as observed from TPR studies. Due to larger Ni crystallite size, it exhibited lower conversion compared to Ni/Al2O3, Ni/SBA-15, and Ni/ZrO2.