Selective Levulinic Acid Hydrogenation in the Presence of Hybrid Dendrimer‐Based Catalysts. Part I: Monometallic

Abstract

Hybrid Ru‐containing catalysts, based on poly(propylene imine) (PPI) dendrimers, immobilized in silica pores, were synthesized and characterized by transmission electron microscopy and X‐ray photoelectron spectroscopy. The synthesized Ru catalysts proved their efficiency in the selective hydrogenation of levulinic acid and its esters at 80 °C, 30 bar of H2, and 50 % volume substrate concentration in water. Quantitative yields of γ‐valerolactone were obtained for both micro‐ and mesoporous Ru catalysts within 2 h with catalytic activity as high as 1610 h−1. The reaction rate and selectivity on γ‐valerolactone were found to depend on several factors such as carrier structure, temperature, presence of water, and substrate/Ru ratio. The novelty of these hybrid materials is the presence of both weak acid (SiO2) and organic base centers (dendrimer amino groups), enhancing the dispersion of Ru nanoparticles. The presence of amino groups in the catalyst stabilizes the Ru nanoparticles during the synthesis and promotes the adsorption of levulinic acid on the surface of Ru nanoparticles during the reaction. Synthesized hybrid Ru catalysts can be reused several times without significant loss of activity.

Hydrogenation of Levulinic Acid to γ-Valerolactone in the Presence of Ru-Containing Catalysts Based on Carbon Material “Sibunit”

“…For catalysts based on ruthenium, for example, Ru/C or Ru/Al 2 O 3 , from previous works devoted to the process of direct hydrogenation of LA to GVL, TOF values vary in the range 200 -3322 h -1 [18,20,24]. For the series of catalysts presented in this work, TOF values vary in the range 1229-5503 h -1 .…”

“…4) that when using water as a solvent, the maximum GVL yield (92 mol.%) was obtained in 45 minutes, while in isopropanol the maximum yield (92 mol.%) was achieved only at 105 minutes, although the maximum conversion of LA, in isopropanol, was reached faster than in water (by 15 and 75 minutes, respectively). This phenomenon can be explained by several factors: water, as a solvent, has a promoting effect on the hydrogenation process when using a ruthenium catalyst [17,23,24], and avoids formation of ethers (using alcohols as a solvent) as unwanted by-products the formation of which reduces the rate of formation of GVL [17][18][19]25]. The promoting effect of water can be described as follows; on the one hand, coadsorbed water molecules, interacting with adsorbed acid molecules, are capable of lowering the activation energy of the hydrogenation of the carbonyl group [22]; on the other hand, water molecules adsorbed on the surface of ruthenium can polarize and undergo dissociation, which leads to the formation of surface Ru -OH groups and H + ions, which are involved in the protonation of the carbonyl group [26].…”

“…6). As an intermediate product, when using Ru/C catalysts, γ-hydroxyvaleric acid (GHV)/GHV esters [25] are predominantly formed, but in some cases, for example when using dendrimer support, the main intermediate product may be angelica lactone [24] (Fig. 1).…”

Ru@hyperbranched Polymer for Hydrogenation of Levulinic Acid to Gamma-Valerolactone: The Role of the Catalyst Support

“…Among numerous heterogeneous catalysts developed for LA transformation such as supported catalysts based on Ru [ 10 , 11 , 12 , 13 , 14 ], Co [ 15 ], Pt [ 16 ], Pd [ 17 ], Cu [ 18 , 19 ], and Ni [ 20 , 21 ], and Ru-containing systems are shown to be the most active. Typically, catalytically active metal is deposited on different supports including activated carbon [ 12 , 22 ], metal oxides [ 10 , 11 , 18 ], silica [ 14 , 17 , 21 ], and polymers [ 23 , 24 ]. In LA hydrogenation, a strong influence of the support on the catalysis rate, conversion and selectivity has been observed [ 25 , 26 , 27 ].…”

Silsesquioxane Modified with PAMAM Dendrimer and a Bimetallic Complex for Electrochemical Detection of Ascorbic Acid

“…Dendrimers are macromolecules that have a highly branched, three‐dimensional structure [20]. The intrinsic characteristics of dendrimers make them promising for several applications, such as micelles [21, 22], the encapsulation of different substances [23–25] including liquid crystals [26, 27], electroanalysis [28, 29], sensors [30–32], electroluminescent devices [33, 34], catalysts [35, 36], and others [37–39].…”