The catalytic synthesis of 1,3-butadiene (1,3-BD) from bio-based ethanol offers an alternative and sustainable process beyond petroleum. However, the intrinsic active sites and corresponding mechanism of 1,3-BD formation have not been fully elucidated yet. By correlating systematic characterization results with catalytic performance, the open Zr species, i.e., Zr(OH)(OSi) 3 moieties, were identified as the active site over the Zr/MFI-BM catalysts for the catalytic transformation of ethanol-acetaldehyde into 1,3-BD. In conjunction with controlled experiments and theory calculations, ethanol and acetaldehyde are proposed to synergistically co-adsorb on the Zr(OH)(OSi) 3 species in a bi-molecular mode, which assists the acetaldehyde condensation and accelerates the critical Meerwein-Ponndorf-Verley-Oppenauer reduction, and accordingly promotes 1,3-BD formation. These findings will stimulate the search towards new metal-zeolite combinations for efficient production of value-added 1,3-BD via biomass-derived ethanol and beyond.
Developing efficient and stable solid functional materials for the catalytic upgrading of biomass-based platform furanic molecules is of great significance to produce value-added chemicals and biofuels. We herein report β-zeolite (β)/biobased carbon hybrids supported Zr species towards the cascade conversion of furfural into γ-valerolactone (GVL) with high activity and favorable stability. The role and importance of carbon modifier were highlighted. The cellulose (CEL) modified Zr/β-CEL catalyst was found to be uniquely effective, leading to an increase of GVL yield from 49.3% to 81.1%. Catalyst characterizations revealed that the structural integrity of β was largely preserved using CEL as the carbon modifier, accompanied by the increased mesopore volume and pore size for better accessibility of active sites and diffusion of reactants. Simultaneously, the presence of CEL offered an appropriate ratio of Lewis and Brønsted acid sites due to the well incorporation and dispersion of Zr species, which ensured the successive transfer hydrogenation and ring-opening reactions. Kinetic studies demonstrated the positive effect of CEL modification on reducing the apparent activation energy and thereby facilitating the GVL formation. More importantly, Zr/β-CEL with enhanced structural stability also exhibited markedly higher recyclability compared with the pristine Zr/β. The understanding on the roles of carbon modifier can be employed to optimize the physicochemical properties of zeolite-based catalysts for roundly improving the catalytic reactivity of biomass-related compounds.
Meerwein–Ponndorf–Verley (MPV) reduction of biomass-derived carbonyl compounds is a greatly promising route for biomass valorization. Robust, facile-prepared, and cost-effective inorganic Zr-based catalysts for this transformation remain highly desirable. Herein, Zr-containing montmorillonite (denoted as Zr-MMT) was constructed by the ion exchange of Zr4+ with the interlayer cations of montmorillonite (MMT). Very interestingly, as an inorganic catalyst, the prepared Zr-MMT showed high catalytic activity for MPV reduction of various biomass-derived carbonyl compounds. Systematic investigations revealed that the excellent performance of Zr-MMT predominantly originated from more positively charged Zr species ([Zrx(OH)y(H2O)n](4x−y)+), which could boost the activation of the carbonyl group and simultaneously promote the hydrogen transfer process assisted by suitable basic sites on MMT. Notably, the preparation of Zr-MMT avoided the utilization of surfactants or expensive organic ligands, and the prepared Zr-MMT showed better or comparable catalytic performance than most reported Zr-containing catalysts, significantly enabling it to be more practical.
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