Hydrotalcite-derived Ni-Zn-Mg-Al catalyst for Tri-reforming of methane: Effect of divalent to trivalent metal ratio and Ni loading

A series of Ni-Zn-Mg-Al hydrotalcite-derived catalysts with different divalent to trivalent metal (M-II/M-III) ratio (2.0, 2.5, 3.0 and 3.5) and different Ni loading (1.25, 2.5, 5, 10 and 15 wt%) were prepared, characterized and tested for tri-reforming of methane (TRM). TRM was carried out at 800 degrees C, 1 atm, 49,200 mLh(-1) g(-1) space velocity and molar feed composition CH4:CO2:H2O:O-2:N-2 = 1:0.23:0.46:0.07:0.28. Higher Ni metal dispersion was achieved at lower M-II/M-III ratio. However, increase in M-II/M-III ratio enhanced basic site concentration and basic site strength. The trade-off between Ni dispersion and basic properties resulted in higher activity of catalyst having M-II/M-III ratio of 3.0. The catalysts with 1.25 and 2.5 wt% and 15 wt% Ni loading underwent deactivation in 20 h run due to metal sintering and carbon deposition respectively. The catalysts with 5 wt% and 10 wt% Ni loading showed good stability. Finally, a 80 h long run demonstrated outstanding activity and remarkable stability of Ni-Zn-Mg-Al catalyst having M-II/M-III ratio 3.0 and 5 wt% Ni loading for TRM.