A highly efficient and green process for the hydrogenation of biomass‐derived levulinic acid (LA) to γ‐valerolactone (GVL) has been developed. GVL was obtained in a yield of 99.9 mol % with a turnover frequency as high as 7676 h−1 in aqueous medium by using a Ru/TiO2 catalyst under mild reaction conditions (70 °C). The strong interaction between Ru and TiO2 facilitated both the dispersion of Ru nanoparticles and the stability of the catalyst. In addition, as solvent, water participated in the hydrogenation of LA, which was confirmed by an isotope‐ labeling experiment with D (D2O). Specifically, the H atom(s) in water took part in the hydrogenation of the CO group of LA, which promoted the catalytic activity and GVL yield remarkably.
To develop the high-performance supported
metal catalyst for industrial
processes, it is highly desirable to elucidate and fully utilize the
indispensable support part. Herein, the relationship between catalytic
performance and the structure of support ZrO2 was elucidated
by comprehensive analysis of the progressive calcination experiments,
tests over model catalysts, and various characterizations of catalyst
structures. We demonstrated that combination of Cu and tetragonal
ZrO2 makes a highly active, selective, and especially stable
catalyst for the hydrogenation of dimethyl oxalate to ethylene glycol.
To obtain stable Cu particles, the catalyst was annealed at high temperatures
(e.g., from 450 to 850 °C). The stable large Cu particles were
formed, and the number of exposed Cu sites decreased. Fortunately,
support ZrO2 was motivated into the tetragonal phase, compensating
for and even improving the activity. Thus, the yield of ethylene glycol
was greatly improved from ∼26 to 99%, and a stable performance
was achieved (life span of >600 h). The strategy alleviated the
dependence
of hydrogenation on highly dispersed metal sites and provided an alternative
way to enhance the catalytic stability. This simple way simultaneously
improved the efficiency and reduced the level of irreversible deactivation
due to sintering, which has great potential for industrial applications.
Tetragonal ZrO2 also proved to be effective for a series
of carbonyl hydrogenations (e.g., esters, aldehydes, ketones, and
acids), indicating a general promotion of these reactions by ZrO2.
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