How do crystal shapes of nano-ceria determine its ketonization performance during biomass pyrolysis?

Catalytic pyrolysis of biomass over CeO₂ to prepare ketonic chemicals is an important way to achieve carbon emission reduction, whereas the role of catalyst structure has long been overlooked. In this work, nano-CeO₂ with different crystal shapes, namely nanorods (R-CeO₂), nano-polyhedra (P-CeO₂), and nanocubes (C-CeO₂), were synthesized and then tested in catalytic ketonization of xylan. Results showed that among all the three catalysts, C-CeO₂ produced the highest yield of ketones. Characterization results revealed that C-CeO₂ presented the lowest content of oxygen vacancies while exhibiting the highest proportion of {100} facets, proving that the {100} facets made a greater contribution to the total yield of ketones. On the other hand, P-CeO₂ and R-CeO₂ displayed a better selectivity to linear ketones, which was beneficial to improving the product quality. The relative contents of {111} facets of these catalysts were higher than C-CeO₂, demonstrating that the {111} facets could selectively produce linear ketones. The proposed mechanism indicated that P-CeO₂ and R-CeO₂ principally enhanced the ketonic deoxygenation reactions, while C-CeO₂ also promoted the recyclization reaction, producing more cyclic ketones. These findings disclose that the {111} facets of CeO₂ are more favorable to producing valuable linear ketones.