Because of spontaneous agglomeration effect and undesirable electronic state of Zr sites on the surface, zirconium (hydro)oxides generally exhibit suboptimal defluoridation capacity. Herein, a template confinement-ligand anchoring strategy is developed by utilizing confined growth of zirconium hydroxide (ZH) inside chitosan hydrogel beads (CHB) and subsequent anchoring of fumaric acid (fm) on its surface Zr sites in a monodentate mononuclear coordination mode. This technique leads to uniform dispersion of ultrafine fmZH (≈3.4 nm) and tunable electron density at the Zr sites. Due to the electron-withdrawing ability of fm, electron-delocalized Zr sites increase the orbital energy level matching and vacate Zr 4d orbitals to promote hybridization with the F 2p orbitals. Ultimately, robust Zr F bond can be formed as a result of reduced the adsorption energy toward fluoride ions. The defluoridation capacity shows positive linear relationship with the electron extraction ability of ligands. The saturation adsorption capacity and dynamic treatment capacity of CHB@fmZH are 10.8 and 45.9 times higher than that of CHB@ZH, respectively, owing to high electron extraction (0.098 e − ) of fm. This study offers a novel insight into the design and synthesis of high-efficiency metal oxide adsorbents by steering its surface metal sites’ electronic state through ligand effect.
Ravi Balaga,Peifang Yan,Kishore Ramineni,Hong Du,Zhi Xia,Mahender Reddy Marri,Zongchao Conrad Zhang
Furfural is an important bio-based platform chemical in the production of valuable products such as biofuel intermediates and polymeric materials. In this work, isolated Zr on mesoporous silica catalysts at varied Zr loading were prepared and evaluated for aldol condensation of furfural with acetone to 4-(2-furyl)− 3-buten-2-one(FAc) and 1,5-bis-(2-furanyl)− 1,4-pentadien-3-one(F 2 Ac). A remarkable effect of the Zr loading on the catalyst performance is revealed. The catalysts are characterized by XRD, BET, NH 3 -TPD, Py-FTIR, XPS, UV–visible, and TGA. The connectivity of Zr was characterized by XPS and UV–visible spectroscopy. For the 25 wt% Zr loading, Zr is present predominantly as isolated monomeric species on mesoporous SiO 2 . The types and densities of different acid sites of the catalysts are measured with Py-FTIR analysis. The results show that isolated Zr on mesoporous SiO 2 enhanced Lewis acid site densities and exhibited superior catalytic activity for aldol condensation between furfural and acetone to produce FAc and F 2 Ac.
Haoxi Jiang,Shuning Jiang,Debin Kong,Lingtao Wang,Guochao Yang
Metallosilicates with isolated framework metal sites as well as Lewis acidity, e.g., Zr- β zeolite , is proven to be one of the most active for the conversion of ethanol to 1,3-butadiene (ETB), which is a potential process for sustainable butadiene production. However the development process of isolated Zr sites in *BEA framework and their structure–activity relationship in ETB process are still under debate. In this work, three post-synthetic procedures, Liquid Phase Incorporation (LPI), Solid State Ion Exchange (SSIE), and Direct Loading were applied for isolated framework Zr sites development, and the procedure as well as catalytic performance and mechanism were systematically investigated. The isolated framework sites could be developed by Liquid Phase Incorporation (LPI) process, where calcination was the key step for Zr-O-Si bond formation, thus representing Zr incorporation into *BEA framework, accompanying the absence of Zr ion exchange. Isolated Zr framework site was the active site in ETB process, for the strong Lewis acidity upon Zr incorporation. DRIFT and TPSR results revealed that the MPV reduction of crotonaldehyde on Zr site was rate-determining in ETB process.
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