Carbon dioxide reforming of methane over Ru catalysts supported on Mg-Al oxides: A highly dispersed and stable Ru/Mg(Al)O catalyst

Ru catalysts (2 wt%) supported on Mg and/or Al oxides including γ-Al2O3, MgAl2O4, Mg3(Al)O, and MgO were prepared by incipient wetness impregnation and compared for the CH4-CO2 reforming to investigate the effect of support on the Ru dispersion and catalytic performance. The catalysts before and after reaction were well characterized by using N2 physical adsorption, ICP, SEM-EDX, XRD, H2-TPR, TEM, CO chemisorption, FTIR of CO adsorption, XPS, CO2-TPD, TG, and Raman spectroscopy. The characterization results revealed that Ru metal was very highly dispersed on the Mg3(Al)O mixed oxide obtained from Mg-Al layered double hydroxide, probably existing in very small nanoparticles and/or clusters. The order of Ru metal dispersion was Ru/Mg3(Al)O > Ru/MgO > Ru/MgAl2O4 > Ru/γ-Al2O3. The catalytic activity and stability of the Ru catalysts were greatly dependent on the support. Both Ru/MgO and Ru/Mg3(Al)O showed higher activity than Ru/MgAl2O4 and Ru/γ-Al2O3, which might be related to the strong base intensity of support and more accessible surface Ru0 atoms, respectively. During 30 h of reaction at 1023 K, a significant deactivation occurred on Ru/γ-Al2O3, Ru/MgAl2O4, and Ru/MgO, which was mainly attributed to the sintering of Ru metal particles. In contrast, the Ru/Mg3(Al)O catalyst exhibited superior stability and no significant sintering of Ru metal was observed, suggesting that the highly dispersed Ru metal was stable. A 300 h long-term test further demonstrated the excellent stability of Ru/Mg3(Al)O. These results highlight the significant effect of Mg(Al)O mixed oxide on the improvement of Ru dispersion and catalytic performance, and this might be related to the unique properties of Mg(Al)O mixed oxide including memory effect, low crystallinity, and its strong interaction with Ru.