Probing the morphological effects of ReO/CeO catalysts on the CO hydrogenation reaction

• Published in: Catalysis science & technology Vol. 12; no. 4; pp. 1159 - 1172
• Main Authors: Yang, Bin, Wang, Yifu, Li, Longtai, Gao, Biao, Zhang, Lingxia, Guo, Limin
• Format: Journal Article
• Published: 21.02.2022
• ISSN: 2044-4753; 2044-4761
• DOI: 10.1039/d1cy02096j

The performance optimization of ceria (CeO 2 )-supported catalysts in heterogeneous reactions can be enabled by the control of crystal morphology. However, insights into how the CeO 2 morphology affects the CO 2 hydrogenation performance are still lacking. Here, in situ diffuse reflectance infrared Fourier transform spectroscopy and temperature-programmed surface reaction techniques are utilized to identify and characterize the morphological effect of CeO 2 supported rhenium (Re) catalysts, including CeO 2 nanocube supported Re (ReO x /CeO 2 -C), CeO 2 nanorod supported Re (ReO x /CeO 2 -R), and CeO 2 nanopolyhedron supported Re (ReO x /CeO 2 -P). ReO x /CeO 2 -R exhibits enhanced CO 2 conversion (14.7%) compared to ReO x /CeO 2 -C (1.5%) and ReO x /CeO 2 -P (1.3%) at 2 MPa and 613 K. The CH 4 selectivity on ReO x /CeO 2 -R (40.9%) also far exceeds those on ReO x /CeO 2 -C and ReO x /CeO 2 -P (∼5%). The electronic metal-support interaction between Re and CeO 2 is found to be largely dependent on the CeO 2 morphology and closely linked with H 2 activation and CO 2 adsorption. The strongly adsorbed carbonate (CO 3 2− ) is identified to cover the surface of ReO x /CeO 2 -P and ReO x /CeO 2 -C during CO 2 hydrogenation but is absent over ReO x /CeO 2 -R. This stable and irreversible intermediate locally modifies the catalytic performance. The metallic Re 0 in ReO x /CeO 2 -R favors H 2 dissociation to generate oxygen vacancies and thus promotes chemisorption of CO 2 as CO 2 δ − rather than CO 3 2− . Moreover, the facile elimination of CO 3 2− in ReO x /CeO 2 -R is a key step for highly catalytic performance. This work uncovers the CeO 2 morphological effects which play a significant role in CO 2 hydrogenation. These findings offer a new understanding of the morphology-dependent catalytic mechanism and open a new avenue to control the reactivity of CeO 2 -supported metal catalysts for CO 2 hydrogenation. The proposed reaction mechanism of different morphological CeO 2 supported Re catalysts for CO 2 hydrogenation.