Ni-catalyzed CO₂glycerol reforming to syngas: New insights on the evaluation of reaction and catalyst performance

Glycerol dry reforming (GDR) to syngas was studied on Ni/ZrO2, Ni/La2O3 and Ni/La2O3-ZrO2 catalysts for elucidating the effects of support material on catalyst performance. A methodology was proposed to quantify the produced H2O, which was not reported so far in the GDR literature. At 750 °C, molar inlet CO2-to-glycerol vapor ratio (CO2/G) of 1-3 and residence time of 0.25 mgcat.min/Nml, the average CO2 and glycerol conversions were ordered as 13 % (NiLZ) > 10 % (NiZ) > 9 % (NiL) and 93 % (NiLZ) > 89 % (NiZ) > 83 % (NiL), respectively. NiLZ, the most active catalyst, also delivered > 95 % of the pertinent thermodynamic CO2 conversion at 0.5 mgcat.min/Nml. The 24 h stability of NiL and NiZ catalysts depended strongly on the inlet CO2 concentration. At CO2/G = 2, NiL deactivated by ∼5 % which was doubled at CO2/G = 4 mainly due to coking shown by TGA and Raman spectroscopy. The catalyst also suffered from Ni agglomeration as revealed by SEM-EDX and XRD. NiZ catalyst lost ∼21 and ∼9 % of its initial activity after 24 h aging at CO2/G = 2 and 4, respectively. Despite insignificant coking and sintering, XPS analyses pointed out almost four-fold decrease in the surface atomic Ni concentration on NiZ at CO2/G = 2 and suggested partial blockage of Ni sites by increased reducibility of monoclinic ZrO2 support at the less oxidative, CO2-lean environment. Regardless of the atmosphere, the NiLZ catalyst showed excellent stability features comparable to those of the notably higher-priced Rh and Ru-containing counterparts.