## 4 HPS-Based Catalysts for the Synthesis and Transformation of Platform Chemicals
### Hydrogenation of Levulinic Acid  
Levulinic acid (LA) is one of the most valuable multifunctional substances obtained from biomass. LA is a precursor to many industrially important chemicals and is widely used in the production of lubricants, chiral reagents, resins, biologically active substances, adsorbents, electronics, and batteries [7; 180]. Due to the presence of two highly active functional groups (carbonyl and carboxyl), LA easily enters oxidation, reduction, esterification, substitution, and condensation reactions, which makes it a very valuable platform compound [181]. One of the most important reactions involving LA is hydrogenation to form \(\gamma\)-valerolactone (GVL) (Figure 14), a key reaction in the conversion of plant carbohydrates into renewable fuels and chemicals [182]. GVL can be used as an environmentally friendly solvent, an additive to liquid fuels, and also for the synthesis of polymer precursors such as adipic acid and diols [183; 184]. Today, the mostly used in the LA selective hydrogenation to GVL are bifunctional catalysts based on inorganic supports containing Lewis acid sites (LAS) and Bronsted acid sites (BAS). Despite the advantages of bifunctional catalysts in this process, there are some problems caused by the presence of LAS and BAS in the oxide supports. Thus, the high acidity of the support may lead to the formation of coke, which can initiate rapid deactivation of catalysts [186; 187; 188]. In addition, during the hydrogenation of LA in an aqueous environment, agglomeration and leaching of active metal from the support can occur, which can affect the catalyst stability and significantly complicates its effective reuse [189]. The stability of catalysts can be increased by using carbon supports, which include polymers with a variety of useful properties: high porosity, the presence of functional groups, the ability to vary molecular weight, and hydrophilicity. [PERSON] et al. [190] synthesized uniformly distributed Ni nanoparticles (NPs) with narrow size distribution around 6 nm embedded in a mesoporous carbon substrate (Ni@C) obtained from an organic copolymer. The mesoporous carbon support provided various defect sites for the attachment of Ni particles, and strong interactions between the carbon phase were observed. A total of 100% conversion of LA was achieved in 4 h at 200 \({}^{\circ}\)C and 3 MPa in 1,4-dioxane. [PERSON] et al. [191] also synthesized copper NPs (5.5 nm in diameter) embedded in an ordered mesoporous carbon (OMC) carrier by a multicomponent assembly method using chelates. The OMC surface was functionalized with various oxygen-containing functional groups, which enhanced the interaction with copper NPs. The synthesized Cu/OMC catalyst demonstrated  
Figure 14: Scheme of LA hydrogenation to GVL. Reprinted from ref. [185], Copyright 2021, with permission from Elsevier (Amsterdam, The Netherlands). high activity and stability in the hydrogenation of LA to GVL in continuous mode (260 \({}^{\circ}\)C, 0.1 MPa H\({}_{2}\)) due to the effects of Cu retention in mesoporous carbon. [PERSON] et al. [192] synthesized catalysts based on ruthenium NPs (with a diameter of about 1.5 nm) deposited on the graphite-like mesoporous carbon material Sibunit-4 (initial and oxidized at different temperatures). The presence of oxygen-containing functional groups on the surface of the support was responsible for the distribution of Ru NPs and the acidic properties of the catalyst. The resulting catalysts containing 1% and 3% (wt.) Ru showed high activity in the hydrogenation of LA to GVL (GVL yield 98 mol.% at 160 \({}^{\circ}\)C, 1.2 MPa H\({}_{2}\)). Common catalytic supports are carbon nanotubes (CNTs) and graphene (Gs), including oxidized ones (GOs) [193]. [PERSON] et al. [194] used CNTs to support porphyrin (PP) complexes containing ruthenium. Ru-PP/RGO catalyst was prepared in a similar manner. Ru-PP/CNTs and Ru-PP/RGO were used for the hydrogenation of LA and its esters giving GVL.