Hierarchical FAU-Type Hafnosilicate Zeolite as a Robust Lewis Acid Catalyst for Catalytic Transfer Hydrogenation

Abstract

FAU-type hafnosilicate zeolite with a hierarchical structure (Hf-USY) was constructed through a post-synthesis strategy containing the controlled dealumination of the commercial H-USY zeolite and the subsequent dry impregnation of the Cp 2 HfCl 2 precursor. The incorporation of Hf ions into the zeolite framework involved the interaction between the silanol groups from framework dealumination and Cp 2 HfCl 2 molecules. Characterization results from UV−vis and X-ray photoelectron spectroscopy verified that the incorporated Hf ions mainly existed in the tetrahedrally coordinated form in the zeolite framework. The creation of Lewis acid sites associated with Hf incorporation was confirmed by Fourier transform infrared spectroscopy with pyridine and deuterated acetonitrile adsorption. The as-synthesized Hf-USY zeolite served as a highly efficient catalyst in the transfer hydrogenation of ethyl levulinate to γvalerolactone, outperforming the Sn-and Zr-silicate analogues. The Hf-USY catalyst also exhibited good performance in the transfer hydrogenation of more challenging substrates such as furanic, aromatic, as well as alkene-substituted carbonyl compounds into the corresponding alcohols. The influence of Lewis acid sites, preparation parameters, as well as the hydrogen donor on the catalytic activity of the Hf-USY zeolite was investigated in detail.

Improving the Conversion of Biomass in Catalytic Pyrolysis via Intensification of Biomass—Catalyst Contact by Co-Pressing

“…The higher acid density obviously influences its higher initial degradation performance but the frequent deactivation and poor thermal stability are the main drawbacks in its application [42,56,61,62]. On the other hand, USY is the modified form of Y zeolite which exhibits very strong acidic sites [63,64], mesoporous system [64,65] and high thermal stability [62][63][64][65]. This modification happens under controlled conditions by steam treatment at high temperatures leading to the creation of active sites and mesopores that enhance the catalytic activity of USY zeolite [61,62,[65][66][67].…”

“…On the other hand, USY is the modified form of Y zeolite which exhibits very strong acidic sites [63,64], mesoporous system [64,65] and high thermal stability [62][63][64][65]. This modification happens under controlled conditions by steam treatment at high temperatures leading to the creation of active sites and mesopores that enhance the catalytic activity of USY zeolite [61,62,[65][66][67]. The presence of these large cavities enable the macromolecules and heavy initial fragments from the primary reactions to diffuse readily into the internal acid sites, and be converted to hydrocarbons via a series of reactions, such as cracking, deoxygenation (dehydration, decarboxylation, and decarbonylation), and aromatization [29,68,69].…”

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“…Yang, Zhao, Li and coworkers demonstrated the key role of Hf in zeolite (Hf‐USY) to prevent the formation of isopropyl levulinate as main product. [ 196 ] The Hf‐USY catalyst enabled a 95% LA conversion and 92.9% selectivity toward GVL using i‐ PrOH as H‐source at 140 °C.…”

“…Hf-based catalysts showed good performances in the production of GVL at relative mild conditions (140-160 °C). [194][195][196] Han and coworkers developed a heterogeneous hafnium phosphonate catalyst, i.e., Hf-ATMP (ATMP = amino tri(methylene phosphonic acid)) with improved catalytic performances in LA hydrogenation to GVL in comparison to other organic-inorganic catalyst containing Cu, Zn, Al or Cr. [194] The enhanced efficiency was attributed to the presence of acid-base sites Hf 4+ -O 2− .…”

“…A high GVL yield (97%) was also obtained by Fang and coworkers by using a mesoporous hybrid Hf-FDCA (FDCA = 2,5-furandicarboxylic acid) in the MPV reduction of EL at 160 °C for 4 h. [195] Yang, Zhao, Li and coworkers demonstrated the key role of Hf in zeolite (Hf-USY) to prevent the formation of isopropyl levulinate as main product. [196] The Hf-USY catalyst enabled a 95% LA conversion and 92.9% selectivity toward GVL using i-PrOH as H-source at 140 °C.…”