Effects of noble metals doped on mesoporous LaAlNi mixed oxide catalyst and identification of carbon deposit for reforming CH_4 with CO_2

摘要

BACKGROUND: The effect of the B cation on the surface properties and catalytic activity in the dry reforming reaction over La_(0.4)M_(0.6)Al_(0.2)Ni_(0.8)O_3 (M=noble metal) perovskite-type oxides with surface area 3.26–4.14m~2 g~(-1) and rhombohedral structure was studied. RESULTS: Among LaAl_xNi_(1-x)O_3 series, LaAl_(0.2)Ni_(0.8)O_3 had the highest catalytic activity, but suffered a slow deactivation with time-on-stream (TOS). It is observed that all samples presented similar activity at low reaction temperatures (500–600?C), while at higher temperatures (600–850?C) the prepared solid was more active and perovskite phase was transformed into Ni~0 or La_2O_2CO_3. It was found that among the noble metal samples, La_(0.4)Rh0.6Al_(0.2)Ni_(0.8)O_3 possessed the highest surface area and surface oxygen concentration and the best low-temperature reducibility. For the Rh catalyst the CH_4 and CO_2 conversions were 89.1 and 86.2%, which were the most resistant against coke deposition and showed very high stability without decrease in reforming and remained constant during the 3000 min TOS. The following order of activitywas observed: La_(0.4)Rh_(0.6)Al_(0.2)Ni_(0.8)O_3> La_(0.4)Ru_(0.6)Al_(0.2)Ni_(0.8)O_3 > LaAl_(0.2)Ni_(0.8)O_3> La_(0.4)Ir_(0.6)Al_(0.2)Ni_(0.8)O_3 ≥La_(0.4)Pt_(0.6)Al_(0.2)Ni_(0.8)O_3 > La_(0.4)Pd_(0.6)Al_(0.2)Ni_(0.8)O_3. CONCLUSIONS:It is believed that thehigh surface areaandsurfaceoxygenconcentrationandgoodlow-temperature reducibility were responsible for the good catalytic performance of the La_(0.4)Rh_(0.6)Al_(0.2)Ni_(0.8)O_3 sample.