Search

The reduced oxide graphene (RGO) supported Ni-based catalysts is prepared and modified with ceria (Ni-Ce/RGO) for CO2 methanation for the first time in the present work, and compared with the active carbon (AC) and γ-Al2O3 supported samples. The results show that the catalytic activity of the samples without ceria follow the order Ni/RGO > Ni/γ-Al2O3 > Ni/AC, vs. samples with ceria Ni-Ce/RGO > Ni-Ce/γ-Al2O3 > Ni-Ce/AC. The activities of all samples were greatly improved after ceria modification. The Ni-Ce/RGO works the best for CO2 methanation, which could reach the highest CO2 conversion of 84.5% and the highest methane yield of 83.0% at 350 °C with atmospheric pressure. The excellent catalytic performance of Ni-Ce/RGO could be attributed to the special support effect of RGO and the ceria promotion effect. The support effect of RGO could be attributed to its large surface area and surface oxygen-containing functional groups, which results in stable anchoring of the active metal. The addition of ceria promotes the Ni dispersion on the supports as well as to accelerate the positive reaction due to the oxygen vacancies of ceria.

CeO2 show excellent performance in catalysis due to its oxygen vacancies, high oxygen storage capacity and easy conversation between Ce3+ and Ce4+ oxidation states. The ceria nano-materials with different morphologies were prepared with hydrothermal methods in the present work. It is found that the gold particles on ceria prepared via incipient wetness impregnation method are smaller and more uniform than those prepared via deposition-precipitation method (Applied Surface Science 2017, 416, 183–190). The incipient wetness impregnation method prepared samples also show better catalytic performance for CO oxidation than the samples prepared via deposition-precipitation method. Characterization results reveal that the small sizes as well as the oxidation states of the gold nanoparticles contribute to the higher activity than the deposition-precipitation samples. For the incipient wetness impregnation samples, the 0.5%Au/CeO2NT could reach 100% CO conversion at 70 °C, which shows much better activity and stability than the 0.5%Au/CeO2rod and 0.5%Au/CeO2NC. XPS results indicates that this is because the higher Ce3+/Ce4+ and Auδ+/Au0 of 0.5%Au/CeO2NT than 0.5%Au/CeO2rod and 0.5%Au/CeO2NC, since the presence of a specific Auδ+-Ce3+ structure promotes the adsorption of molecular oxygen and further favors the oxidation of CO. In addition, the gold nanoparticle could grow into larger particles on the ceria nanocubes and leads to the deactivition of the catalysts. In contrast the ceria nanorod and nanotube supported catalysts show excellent stability.

CeO2 is a typical of fluorite structure, semiconductor material, has high oxygen storage capability as well as unique redox property, which is widely used as catalysts supports in catalysis. Ceria nanotubes and nanocubes are prepared via hydrothermal method in the present work, and Au/CeO2 catalysts are prepared using deposition-precipitation technique with HAuCl4 as gold precursor. The prepared samples were used as catalysts for the CO oxidation reaction using a fix-bed reactor at 50–130 °C and characterized by XRD, BET, SEM, TEM, XPS, TPR and ICP. It is found that CeO2-NT and CeO2-NC expose different surface planes. The XPS and H2-TPR results illustrates that the {110} surface exposed by CeO2-NT has stronger interaction with gold particles, which benefits the electron and oxygen transfer between Au and ceria. All these characters of the Au/CeO2-NT(3%) result in the better activity and stability than the Au/CeO2-NC(3%).