Search

The performance optimization of ceria (CeO2)-supported catalysts in heterogeneous reactions can be enabled by the control of crystal morphology. However, insights into how the CeO2morphology affects the CO2hydrogenation performance are still lacking. Here, in situdiffuse reflectance infrared Fourier transform spectroscopy and temperature-programmed surface reaction techniques are utilized to identify and characterize the morphological effect of CeO2supported rhenium (Re) catalysts, including CeO2nanocube supported Re (ReOx/CeO2-C), CeO2nanorod supported Re (ReOx/CeO2-R), and CeO2nanopolyhedron supported Re (ReOx/CeO2-P). ReOx/CeO2-R exhibits enhanced CO2conversion (14.7%) compared to ReOx/CeO2-C (1.5%) and ReOx/CeO2-P (1.3%) at 2 MPa and 613 K. The CH4selectivity on ReOx/CeO2-R (40.9%) also far exceeds those on ReOx/CeO2-C and ReOx/CeO2-P (∼5%). The electronic metal–support interaction between Re and CeO2is found to be largely dependent on the CeO2morphology and closely linked with H2activation and CO2adsorption. The strongly adsorbed carbonate (CO32−) is identified to cover the surface of ReOx/CeO2-P and ReOx/CeO2-C during CO2hydrogenation but is absent over ReOx/CeO2-R. This stable and irreversible intermediate locally modifies the catalytic performance. The metallic Re0in ReOx/CeO2-R favors H2dissociation to generate oxygen vacancies and thus promotes chemisorption of CO2as CO2δ−rather than CO32−. Moreover, the facile elimination of CO32−in ReOx/CeO2-R is a key step for highly catalytic performance. This work uncovers the CeO2morphological effects which play a significant role in CO2hydrogenation. These findings offer a new understanding of the morphology-dependent catalytic mechanism and open a new avenue to control the reactivity of CeO2-supported metal catalysts for CO2hydrogenation.

The process driven by “redox–precipitation” reactions between Mn7+, Co2+and Mn2+can yield CoMnxOynanosheet catalysts with (quasi)molecular scaled dispersed compounds which can achieve excellent catalytic activity in toluene combustion with T50(temperature of 50% toluene conversion) values of 172 °C and 218 °C (GHSV = 67 500 h−1and 540 000 h−1, respectively). The as-prepared CoMnxOynanosheets demonstrated high specific surface area, and their overall morphology changed when Mn2+was substituted with Mn7+during the preparation process. The enhanced catalytic performance in toluene combustion can be ascribed to very high amounts of oxygen electrophilic species (O−/O2−), as evidenced by XPS, H2-TPR and O2-TPD. In addition to the MnCo2O4.5phase, Co3O4formation can further improve the catalytic properties. According to TEM observations, the Co3O4species were well dispersed on MnCo2O4.5and strongly interacted with MnCo2O4.5by forming an active Co3O4–MnCo2O4.5interface. Toluene adsorption and O2dissociation could occur at the active interface by creating abundant oxygen vacancies, further providing adequate O22−species to take part in toluene oxidation. The influences of water vapor and other VOCs in simulated exhaust were also evaluated. The excellent performance of the catalysts in catalytic toluene combustion demonstrates that they have great potential for practical applications.