Gas-Phase Catalytic Transfer Hydrogenation of Methyl Levulinate with Ethanol over ZrO₂

Abstract

This paper reports about the gas-phase reduction of methyl levulinate to γ-valerolactone (GVL) via catalytic transfer hydrogenation using ethanol as the H-donor. In particular, high-surface-area, tetragonal zirconia has proven to be a suitable catalyst for the reaction. Under optimized conditions, the reaction is selective toward the formation of GVL (yield 70%). However, both the deposition of heavy oligomeric compounds over the catalytic surface and the progressive conversion from Lewis to Brønsted acidity, due to the reaction with the water formed in situ, led to a progressive change in the chemo-selectivity, promoting side reactions, e.g. the alcoholysis of angelica lactones to ethyl levulinate. However, the in situ regeneration of the catalyst performed by feeding air at 400 °C for 2 h permitted an almost total recovery of the initial catalytic behavior, proving that the deactivation is reversible. The reaction has been tested also using a true bioethanol, derived from agricultural waste.

Improved Catalytic Transfer Hydrogenation of Levulinate Esters with Alcohols over ZrO2 Catalyst

“…Further investigations by using ethyl levulinate (EL) as the chosen substrate have proved the preferential tendency of methanol to promote both trans-esterification and alcoholysis of the intermediates (angelica lactones) reactions;  isopropanol has been confirmed as the best H-donor for the liquid phase conditions while, in the continuous-flow system in the gas-phase conditions, ethanol and isopropanol have led to very similar results with complete conversion of ML (at least for six hours of reaction) and very good GVL yield (from 60 to 80%);  performing the catalytic tests using EL as substrate (instead of ML), using the same reaction conditions as shown in Figure 2, a slight improvement of the obtained results in terms of catalytic activity and GVL yield have been observed. This phenomenon may be attributed, to a limited extent, to an increased efficiency of EtOH as the leaving group in the intramolecular cyclization of EL to angelica lactones [26]. However, in the long-term stability tests performed with ethanol (Figure 2a), the progressive continuous deposition of heavy carbonaceous compounds over the catalytic surface, have led to the blockage and poisoning of the active Lewis acid sites, and therefore have led to a progressive decrease of conversion and change in the chemo-selectivity, promoting the alcoholysis of angelica lactones back to EL.…”

“…For all the details related to both the continuous-flow gas-phase reactor and the liquid phase autoclave reactor and catalytic tests procedures please refer to ref. [25] and [26].…”

“…In particular, we investigated systematically/thoroughly the effects of different parameters (contact time, reaction temperature, the type of alcohol used as H-donor and the effect of the leaving group of the levulinate ester) as well as the study of reaction and catalyst's deactivation mechanism [25]. The results obtained in the gas-phase were also carefully compared to the ones obtainable in liquid phase and batch conditions [26]. Herein the most interesting results are summarized and highlighted.…”

Bringing Homogeneous Iron Catalysts on the Heterogeneous Side: Solutions for Immobilization

“…On the other hand, plenty of room can be expected for their development in the underexplored world of iron complexes applied in biomass upgrading. Taking the transformation of bio-alcohols as an example [ 26 , 27 ], the advantages of higher conversions and selectivity (e.g., in alcohol homologation) demonstrate how homogeneous catalysis is more promising than the heterogeneous counterpart [ 28 ]. Nevertheless, this reaction still remains a prerogative of ruthenium catalysis [ 29 , 30 , 31 , 32 ].…”

Microemulsion Derived Titania Nanospheres: An Improved Pt Supported Catalyst for Glycerol Aqueous Phase Reforming

“…Together with the overall APR reaction ( Table 1 ), several liquid phase processes need to be considered, leading to a complex pathway of interconnected reactions. In particular, hydrogenation, dehydrogenation, condensation, hydration, and dehydration mechanisms occur starting from both glycerol and reaction intermediates [ 29 , 30 , 31 ]. Other reactions that may occur to some extent in the APR process are water gas shift (WGS) and methanation reactions from CO and CO 2 that may allow the full consumption of CO and the production of methane ( Table 1 ) [ 30 , 32 ].…”