Perovskite La_xM_(1-x)Ni_(0.8)Fe_(0.2)O3 catalyst for steam reforming of toluene: Crucial role of alkaline earth metal at low steam condition

摘要

The effect of alkaline earth metal (Mg, Ca, and Sr) substitution to LaNi_(0.8)Fe_(0.2)O3 perovskite catalyst was investigated for steam reforming of toluene as a model compound of tar at various steam amounts. Catalytic performance of La_(0.8)Sr_(0.2)Ni_(0.8)Fe_(0.2)O3 (LSNFO) catalyst at high steam condition (S/C = 3.4) is higher than the activity of La_(0.8)Mg_(0.2)Ni_(0.8)Fe_(0.2)O3 (LMNFO) and La_(0.8)Ca_(0.2)Ni_(0.8)Fe_(0.2)O3 (LCNFO) catalysts due to higher amount of active sites and higher amount of lattice oxygen on LSNFO catalyst. However, the activity of LSNFO catalyst is still lower than the activity of LaNi_(0.8)Fe_(0.2)O3 (LNF0) catalyst even though carbon deposition on spent LSNFO catalyst is the lowest among other catalysts. Interestingly, the activity of LSNFO catalyst is comparable with the activity of LNFO catalyst at S/C of 2 and outperforms LNFO catalyst at S/C of 1. Moreover, the carbon deposition on LNFO catalyst increases with increasing temperature while it decreases with increasing temperature on LSNFO catalyst due to lattice oxygen desorbed at 700-800 °C. Further characterization shows that water is adsorbed strongly on LSNFO catalyst and is only able to desorb at higher temperature near the reaction temperature. This strongly adsorbed water property of LSNFO catalyst enables this catalyst to have better catalytic performance at low steam condition.