Catalytic aldol condensation of biomass-derived furfural (FAL) with acetone (AC) into the single-condensation product 4-(2-furyl)-3-buten-2-one (FAC) is a potential and promising strategy for biomass improvement process and still challenging. Metal oxides exposed different crystal facets can regulate their surface structure and adsorption activation ability, which can provide an opportunity to enhance aldol condensation performance. Here, nanoparticles-CeO 2 (P-CeO 2 ), nanorods-CeO 2 (R-CeO 2 ) and nanocubes-CeO 2 (C-CeO 2 ) with (111), (110) and (100) plane predominant exposure was prepared to explore their catalytic performance for the aldol condensation of FAL with AC to obtain FAC. The serial detailed characterizations, experimental results and density functional theory calculation revealed that R-CeO 2 with a dominant (110) facet possesses appropriate surface adsorption energy, abundant oxygen vacancy (Ov) and excellent acid-base properties, which can effectively boost the adsorption and activation of FAL and AC and reduce the barrier of aldol condensation reaction based on the acid-base catalysis mechanism. The work would reveal the influence of CeO 2 crystal facet on the aldol condensation and provide a broad potential for the rational design of metal oxide catalysts for other acid-base catalytic reactions.
Yanan Wei,Yunlei Zhang,Yao Chen,Fang Wang,Yu Cao,Wen Guan,Xin Li
Graphical Saving face : Catalytic performance of Au/CeO 2 with different exposed CeO 2 crystal faces for oxidation of 5-hydroxymethlfurural to 2,5-furandicarboxylic acid is dependent on the oxygen vacancy (V O ) concentration. Higher V O concentration of Au/rod-CeO 2 (110) is more beneficial for adsorption of oxygen and formation of active oxygen species than Au/cube-CeO 2 (100) and Au/oct-CeO 2 (111). Developing an efficient catalyst to upgrade 5-hydroxymethylfurfural (HMF) to high-value-added downstream chemicals is of great significance in biomass conversion. Nanorod (110)-, nanocube (100)-, and nanooctaheron (111)-CeO 2 -supported Au nanoparticles were prepared to investigate the intrinsic effect of CeO 2 crystal faces on the oxidation of HMF to 2,5-furandicarboxylic acid (FDCA). The experimental results and density functional theory calculation revealed that the concentration of oxygen vacancy (V O ) for exposed specific crystal faces was crucial to the oxygen adsorption ability, and Au/nanorod-CeO 2 with the highest V O concentration promoted the formation of more oxygen active species (superoxide radical) on CeO 2 (110) crystal face than (100) and (111) crystal faces. Besides, the higher V O concentration could provide a strong adsorption ability of HMF, greatly boosting the activation of HMF. Thus, these results led to a superior catalytic activity for HMF oxidation over Au/nanorod-CeO 2 (FDCA yield of 96.5 %). In-situ Fourier-transform (FT)IR spectroscopy uncovered the HMF oxidation pathway, and the possible catalytic mechanism was proposed. The deep insight into the role of regulation for crystal faces provides a basis for the rational design of highly active facets for the oxidation of HMF and related reactions.
Feng Jiang,Shanshan Wang,Bing Liu,Jie Liu,Li Wang,Yang Xiao,Yuebing Xu,Xiaohao Liu
CeO2 is an excellent potential material for CO2 hydrogenation attributed to the highly tunable properties including metal–support interaction and abundant oxygen vacancy. In this work, four CeO2 supports with structurally well-defined different shapes and crystal facets are hydrothermally prepared, and their effects on the composition of Pd species and oxygen vacancy over Pd/CeO2 catalysts have been intensively investigated in the reduction of CO2 to methanol. The 2Pd/CeO2-R (rods) shows the highest concentration and number of oxygen vacancies, where the (110) facet with high surface oxygen mobility and low oxygen vacancy formation energy is exposed over the CeO2-R surface. The oxygen mobility at the interface of (111) and (100) facets mainly observed on 2Pd/CeO2-P (polyhedrons) is higher than the single (111) and (100) facets mainly observed on 2Pd/CeO2-O (octahedrons) and 2Pd/CeO2-C (cubs), respectively. The presence of Pd highly promotes the formation of oxygen vacancies by providing dissociated H atoms to facilitate the removal of surface O in ceria support under a H2 atmosphere. Both the PdxCe1–xOδ solid solution dominated on CeO2-R and the PdO species dominated on CeO2-O are reduced to metallic Pd after reduction with 6–10 nm average particle size. As revealed by density functional theory (DFT) calculations, in contrast to the single Pd0 atom on CeO2 and the thermodynamically most unstable PdxCe1−xOδ solid solution, the Pd0 nanoparticles are the most stable species under the realistic reaction conditions. The 2Pd/CeO2-R shows the highest catalytic activity as the abundantly available oxygen vacancies function as CO2 adsorption and activation sites. Moreover, oxygen vacancy reactivity is correlated with its formation energy. The lower formation energy facilitates the formation of oxygen vacancy; however, the reactivity of each oxygen vacancy is lower as the TOFoxygen vacancy of 2Pd/CeO2-O is 15 times as that of 2Pd/CeO2-R. Thus, a suitable oxygen vacancy formation energy is likely favorable for enhancing CO2 reactivity. DFT calculations indicate that the CH3OH formation is most probably from the formate (HCOO*) pathway via the C–O bond cleavage in H2COOH*, with the reduction of HCOO* to HCOOH* as the rate-limiting step. These results would provide experimental and theoretical insights into the rational design of an effective catalyst for CO2 hydrogenation.
危险品化学品经营许可证（带存储）