Dry Reforming of Methane over Rare-Earth Metal Oxide Ni-M-Al (M = Ce, La) Catalysts

Dry reforming of methane (DRM) was investigated using Ni–M oxide catalysts prepared by solution combustion synthesis (SCS) and compared with Ni/α-Al2O3 synthesized by impregnation. According to X-ray diffraction, fresh oxide Ni–La and Ni–Ce catalysts displayed low crystallinity, which was improved after DRM, accompanied by the appearance of metallic Ni. Ni–Ce–Al and Ni–La–Al catalysts formed, respectively, CeAlO3 and LaAlO3 phases during the reaction. For studied catalysts featuring low surface areas ranging from 3 to 12 m2/g, the average metal particle sizes were 12–32 nm according to transmission electron microscopy, with the particles growing larger with time-on-stream (TOS) apart from Ni–α-Al2O3. DRM tests were conducted for different TOSs, demonstrating that the highest CH4 transformation rate was concomitant with the highest deactivation rate during 30 min of time-on-stream. The most stable performance in temperature stability experiments was demonstrated by the Ni–Ce–Al catalyst, for which, similar to other catalysts, the H2/CO ratio remained close to unity. In long-term stability tests, the Ni–Ce–Al catalyst displayed a 3.1-fold higher turnover frequency (TOF) compared with Ni–α-Al2O3, with no significant deactivation. The TOF values were comparable to the literature, highlighting the potential of SCS as an alternative approach for synthesis of DRM catalysts.