Noble metal catalysts (e.g. Ir, Pt, Ru, Pd, et al.) have been extensively employed in the hydrogenolysis of glycerol to 1,2-PDO due to their excellent hydrogenolysis activity^[48−50]. However, during the catalytic hydrogenolysis of glycerol, noble metals tend to not only activate the C−O bonds of glycerol but also promote undesired C−C bond cleavage (e.g. Ru/C catalysts). This effect leads to the formation of by-products such as ethylene glycol, methanol, ethane and methane, which significantly reduces the selectivity of the target product 1,2-PDO. This limitation has prompted researchers to regulate the performance of noble metal catalysts via catalyst modification. Shao et al.^[51] successfully regulated the Lewis acidity of activated carbon (AC)-supported RuO_x catalysts by utilizing the electron coupling effect induced by Pt doping. The catalyst achieved highly efficient conversion of glycerol to 1,2-PDO via in situ hydrogenolysis. Characterization results indicated that the introduction of Pt reconstructs the ligand oxygen in the RuO_x sites, forming a unique Ru-O-Pt structure. The formation of the Ru-O-Pt species promoted the electron transfer from Ru to Pt. This effect allows controllable regulation of the electronic structure of Ru and enhances the Lewis acidity of RuO_x. DFT calculations demonstrated that the synergistic effect of RuPt nanoparticles induces the reconstruction of the 4d orbitals of Ru. This effect results in more electrons distributed near the Fermi level, thereby accelerating the cleavage of C−O and C−H bonds of glycerol. Experimental results show that the conversion of glycerol on the surface of Ru₂Pt₂/AC catalyst followed the “dehydration-hydrogenation” pathway. Here, the dehydration of glycerol at the acidic RuO_x sites is the rate-determining step. First, the hydroxyl groups of glycerol coordinate with the RuO_x sites, catalyzing the activation of the primary hydroxyl group (C1−OH bond) and the secondary C−H bond (C2−H) of glycerol to form 2,3-dihydroxypropene. 2,3-Dihydroxypropene subsequently tautomerizes into hydroxyacetone. Concurrently, another glycerol molecule undergoes reforming reaction catalyzed by RuO_x sites, generating active hydrogen adsorbed on the catalyst surface via the water-gas shift reaction. These in situ generated active hydrogen then participate in the hydrogenation of hydroxyacetone, ultimately yielding 1,2-PDO. Further studies reveal that when the Pt/Ru atomic ratio is controlled within the range of 0.24−0.78, Pt could be effectively embedded into the framework of RuO_x clusters. The corresponding catalyst could achieve a breakthrough improvement in the hydrogenolysis of glycerol without external H₂. The turnover frequency (TOF) reached 827 h⁻¹ at 200 °C, which is 9 times higher than that of the monometallic Ru catalyst. The 1,2-PDO selectivity is approximately 51%. In 2021, Valle et al. reported a Pt catalyst supported on Al₂O₃ (Pt/Al₂O₃). At 240 °C and 2.5 MPa H₂, the conversion of glycerol is up to 38.5%, and the selectivity of 1,2-PDO is 45%^[52]. To further improve the catalytic performance of Pt-based catalysts in the hydrogenolysis of glycerol to 1,2-PDO, Zhang et al. successfully prepared a WO_x-supported Pt-Mn bimetallic catalyst (Mn/Pt/WO_x) by regulating prereduction temperature of the catalyst. They systematically study the regulation mechanism of reduction temperature on the selectivity of the hydrogenolysis of glycerol ^[53]. The results indicated that the prereduction temperature of the Mn/Pt/WO_x catalyst had a significant impact on the product distribution. The Mn/Pt/WO_x catalyst reduced at a low temperature (240 °C) contained WO_x species on its surface, which provide medium-to-strong acid sites. The existence of the medium-to-strong acid sites directs glycerol hydrogenolysis preferentially toward 1-PO with a yield of up to 88.0%. In contrast, the Mn/Pt/WO_x catalyst reduced at a high temperature generates MnWO₄ species on its surface. Compared with WO_x species, the MnWO₄ species formed by high-temperature reduction had fewer acidic sites but more basic sites. This change in acid-base properties is conducive to the base-assisted glycerol dehydrogenation reaction, which promotes the formation of 1,2-PDO with a high yield of 93.0%.

Dynamic metal-support interaction (DMSI) plays a key role in charge transfer, active site reconstruction and interfacial recombination between metals and oxide supports under redox conditions. However, when the reforming reaction is coupled with hydrogenolysis, precise regulation the redox balance—which is strongly influenced by dynamic interactions—remains highly challenging. Shu et al.^[54] achieved efficient coupling of aqueous-phase glycerol reforming and hydrogenolysis by regulating the DMSI effect between sub-nanoscale Pt clusters and iron oxide supports. The redox reaction process of glycerol reforming coupled with hydrogenolysis can be effectively balanced (Figure 8)^[54] by precisely regulating the surface reconstruction and cyclic conversion of active sites (Pt^δ−-O_v-Fe²⁺ ↔ Pt^δ+-O-Fe³⁺). The specific process is as follows: Under the synergistic regulation of strong metal-support interaction (SMSI) and electronic metal-support interaction (EMSI), abundant Pt^δ−-O_v-Fe²⁺ active sites are formed on the catalyst. Subsequently, adsorbed water molecules dissociated at defect sites, inducing the formation of Pt^δ+-O-Fe³⁺ active sites via DMSI. Glycerol molecules adsorbed on Pt^δ+-O-Fe³⁺ sites undergo complete oxidation, generating CO and H₂, CO is converted to CO₂ at the oxidation sites, simultaneously enabling the regeneration of Pt^δ−-O_v-Fe²⁺ active sites. Notably, the hydrogenolysis of glycerol to 1,2-PDO mainly proceeds through two pathways: on one hand, the oxidative dehydration reaction of glycerol occurring on Pt^δ+-O-Fe³⁺ sites generates thermodynamically unstable intermediates, which are converted to more stable hydroxyacetone through intramolecular isomerization; then, under the reduction of CO or H₂, the oxidation sites are converted to reduction sites, and finally the hydrogenation of hydroxyacetone to 1,2-PDO is completed on Pt^δ−-O_v-Fe²⁺ sites. On the other hand, glycerol is first converted to glyceraldehyde through oxidative dehydrogenation reaction, and this intermediate further undergoes oxidative dehydration reaction on Pt^δ+-O-Fe³⁺ sites to form the key intermediate methylglyoxal. Through the reduction of CO or H₂, Pt^δ+-O-Fe³⁺ sites are reversibly converted to Pt^δ−-O_v-Fe²⁺ sites. Subsequently, methylglyoxal is further hydrogenated to 1,2-PDO. Experimental results demonstrated that the 2.5Pt/FeO_x catalyst exhibited excellent performance in the aqueous-phase reforming and hydrogenolysis of glycerol. The conversion of glycerol is 94.7%, the liquid phase selectivity of 1,2-PDO is 78.4%, and the yield of 1,2-PDO is 36.3%.

In glycerol hydrogenolysis to 1,2-PDO, noble metal catalysts exhibit not only high hydrogenolysis activity but also excellent hydrothermal stability. They maintain high catalytic efficiency under harsh reaction conditions. Based on these advantages, researchers have developed many efficient noble metal catalytic systems. Besides the representative catalysts mentioned above, many catalytic systems with outstanding performance have also been reported in the literature. Examples include MOF-808-SO₄-Pd^[55] and bimetallic PtSn^[56], IrFe^[57], CuPd^[58], CuPt^[59] and RuCu^[60] catalysts. The above catalytic systems show their own advantages in improving 1,2-PDO selectivity and inhibiting C−C bond cleavage through different active component combinations and support regulation, which provides an important reference for the optimal design of catalysts for the hydrogenolysis of glycerol.

Although noble metal catalysts (e.g., Ir, Pt, Ru, Pd) exhibit excellent catalytic activity in the hydrogenolysis of glycerol to 1,2-PDO, their high cost severely restricts large-scale application. To address this issue, researchers have turned attention to non-noble metal catalysts (e.g., Cu, Ni, Co). Non-noble metal catalysts are not only inexpensive but can also achieve good 1,2-PDO selectivity through simple modification^[61−63]. Among them, Cu-based catalysts have become one of the most practical non-noble metal catalytic systems in glycerol hydrogenolysis due to their low cost and high 1,2-PDO selectivity^[64−66]. In 2022, Omar et al. prepared a novel Cu/ZnO/ZnAl₂O₄/PAAH (PAAH = polyacrylic acid) hybrid nanomaterial via a sol-gel process. The catalyst was applied to glycerol hydrogenolysis for 1,2-PDO production^[64]. Characterization results indicated that the synergistic effect between Al component and PAAH promoted the formation of active metallic copper (Cu⁰) nanoparticles with uniform particle size (4−13 nm) and good dispersion. Pyridine adsorption FT-IR analysis confirmed that the catalyst has Lewis acidity. In addition, the increase in Lewis acid sites could promote the activation and dehydration of the primary hydroxyl group (C1−OH) and C2−H bond of glycerol to generate the intermediate hydroxyacetone. The intermediate hydroxyacetone can be subsequently hydrogenated to 1,2-PDO on well-dispersed Cu⁰ nanoparticles. The optimized Cu-based catalyst achieved 96% glycerol conversion and 83% 1,2-PDO selectivity (Table 1). To further improve the catalytic performance of the Cu-based catalysts, Liu et al.^[65] prepared a ZnO-doped copper carbide (Cu_xC) catalyst. The addition of ZnO improves the dispersion of copper species and enhances the Lewis acidity of the catalyst, which is beneficial for catalyzing the dehydration of glycerol to hydroxyacetone intermediate. The hydroxyacetone intermediate can be subsequently hydrogenated to 1,2-PDO. In addition, this study found that the hydrogenation activity of Cu_xC is significantly higher than that of metallic Cu⁰, which is conducive to improving the catalytic activity of the hydrogenolysis of glycerol in a fixed-bed reactor. The Cu_xC composite catalyst (Cu/Zn = 8) exhibited 100% glycerol conversion and 92.3% 1,2-PDO selectivity at 240 °C, 2.0 MPa H₂ and WHSV = 3 h⁻¹. In 2022, Kumar et al.^[66] further investigated the catalytic activity of Cu-derived oxide catalysts in the hydrogenolysis of glycerol and investigate the effect of different Cu/Al molar ratios on 1,2-PDO selectivity. It is found that glycerol conversion/1,2-PDO selectivity depend on the metal sites dispersion and Lewis acidity of the Cu-based catalyst. With increasing of Cu/Al molar ratio in the catalyst, the surface acidity and the dispersion of metallic Cu⁰ are significantly improved. The enhanced acidity is beneficial for catalyzing the dehydration of glycerol to hydroxyacetone, while the improved dispersion of metallic Cu⁰ nanoparticles is conducive to promoting the hydrogenation of intermediate hydroxyacetone to the target product 1,2-PDO. 3CuAl exhibited 83.5% glycerol conversion and 84.2% 1,2-PDO selectivity (20% glycerol aqueous solution, 210 ℃, 4.0 MPa H₂).

The unique d-electronic structure of metallic cobalt (Co⁰) endows it with excellent H₂ adsorption and dissociation capabilities. Accordingly, Co-based catalysts have been widely investigated for glycerol hydrogenolysis to 1,2-PDO. Cai et al.^[67] evaluated the performance of Co-Al₂O₃ catalysts for the hydrogenolysis of glycerol to 1,2-PDO in batch and flow reactors. The 30Co-Al₂O₃ catalyst exhibits high catalytic activity and good stability in the continuous reactor, achieving a glycerol conversion of 53.7% and a 1,2-PDO selectivity of 76%. The good catalytic performance is mainly attributed to the high acid density and Co dispersion of 30Co-Al₂O₃. To further improve the catalytic performance of the Co-based catalysts in glycerol hydrogenolysis, Gong et al.^[68] reported a hydrotalcite-derived Co₂-Ca₄-Al₃ catalyst, which achieves 100% glycerol conversion and 90.5% 1,2-PDO selectivity in hydrogenolysis of glycerol (Table 1).

This catalyst also shows good cycling stability in batch reactions. Activity tests and characterization results indicate that Co⁰ species present in the catalyst were identified as the primary active sites for hydrogenolysis of glycerol. The strong interaction between Co(II) and Ca(II) oxides led to the formation of CaO-CoAl₂O₄ mixed metal oxides. This structure not only generates more electron-deficient Co(II) sites but also forms a large number of moderate-strength basic sites, promoting the dehydrogenation of glycerol and thus significantly improving the catalytic activity and 1,2-PDO selectivity (Figure 9)^[68]. Notably, CaCO₃ phase on the Co₂-Ca₄-Al₃ catalyst surface could effectively prevent the leaching of medium basic sites and metal active sites by coating the CaO-CoAl₂O₄ mixed metal oxides, which is the key reason for the excellent stability of the Co₂-Ca₄-Al₃ catalyst under aqueous reaction conditions.

Compared with Cu- and Co-based systems, Ni-based catalysts have been less extensively investigated for glycerol hydrogenolysis to 1,2-PDO. The main reason is that there is usually a strong metal-support interaction between Ni species and the support. These effects make the Ni species difficult to reduce (usually requiring high reduction temperatures (>500 °C)), thereby limiting the formation of active Ni⁰ sites. Additionally, the electronic structure of Ni could easily induce the cleavage of C−C bonds in glycerol, resulting in low selectivity of the target product 1,2-PDO (most reports show 1,2-PDO selectivity < 70%). In recent years, it has been found that the selectivity of Ni-based catalysts for 1,2-PDO can be improved by adding promoters. Hu et al.^[69] prepared Ni₃P catalysts via citric acid (CA) modification. The catalytic activity of Ni₃P catalysts were tested in the coupled reaction of aqueous-phase glycerol reforming and hydrogenolysis to 1,2-PDO. The CA(1)-Ni₃P catalyst exhibits 74.6% glycerol conversion and 43.2% 1,2-PDO selectivity at 220 °C, 0.5 MPa N₂ and 8 h. The study found that adding CA significantly improved the dispersion of Ni₃P species and increased specific surface area of the catalyst, thereby showing higher catalytic activity. In addition, Nimbalkar et al. successfully prepared a mixed-metal zeolitic imidazolate framework (MM-ZIF) precursor using one-pot synthesis strategy^[70]. By controlling calcination and reduction processes, they obtain a ZnO-supported highly dispersed Ni-Sn nanoalloy catalyst. In-depth characterization studies show that introducing Sn effectively regulated the electronic structure of Ni and inhibit C−C bond cleavage side reaction. Under optimized reaction conditions, this catalytic system exhibits excellent catalytic performance for glycerol hydrogenolysis and achieves 95.2% 1,2-PDO selectivity (Table 1).

The Pt-WO_x catalytic system has attracted much attention from academia and industry owing to its cost advantage and excellent catalytic performance in glycerol hydrogenolysis to 1,3-PDO. It possesses the following outstanding features: (1) Excellent stability under aqueous reaction conditions; (2) High 1,3-PDO selectivity can be achieved by precisely regulating the ratio of Brønsted/Lewis acid sites on the WO_x support; (3) The unique strong metal-support interaction effect could effectively inhibit sintering and deactivation of Pt nanoparticles^[73−74].

These features enable Pt-WO_x catalysts to meet cost control requirements of industrial applications, and could also achieve a balance between catalytic activity and selectivity. These characteristics render it a promising candidate for industrial application in glycerol hydrogenolysis to 1,3-PDO. However, the mechanism of electronic reconstruction at Pt-WO_x interface for regulating glycerol C−O bond activation and Brønsted acidity is still poorly understood and urgently needs clarification. Zhang et al.^[75] revealed the special effect of Pt loading on the electron reconstruction of WO_x. The C−O bond cleavage activity of glycerol is doubled by constructing a new hydrogen spillover path. Related characterizations show that increasing the Pt/W ratio generated additional O 2p orbital holes. This effect promotes charge transfer from the O to W sites, and then forms an electron reconstruction active center that could selectively activate the C−O bonds of glycerol. Based on the 2-butanol dehydration experiment, it was confirmed that the hydrogen spillover process would form Brønsted acid sites in situ through formation of H^δ+(WO₃)_n^δ−. In the 50% glycerol reaction system, the selectivity of Pt/W/Al catalyst to 1,3-PDO can reach 48.1%.

The interaction between Pt and oxygen vacancies can enhance the selective hydrogenolysis of glycerol to 1,3-PDO, and optimizing the concentration and distribution of oxygen vacancies further improves 1,3-PDO selectivity^[76]. Chen et al. reported a solid solution-supported Pt catalyst (Pt/Nb₂W₁₅O₅₀) for glycerol hydrogenolysis to 1,3-PDO, in which a strong interaction between active Pt and oxygen vacancies enables efficient tandem integration of deoxidation and hydrogenation steps^[77]. This strong Pt-oxygen vacancy interaction established by hydrogen spillover effect could induce the formation of 1,3-PDO. This effect enabled the Pt/Nb₂W₁₅O₅₀ catalyst to exhibit excellent catalytic performance under low H₂ pressure of 1.0 MPa. It achieves a glycerol conversion of 75.6% and 1,3-PDO selectivity of 66.5%. Structure-activity relationship study further confirmed that there is a linear correlation among the number of Pt active sites, oxygen vacancy concentration and 1,3-PDO yield. Pt-WO_x-based catalytic systems demonstrate potential for practical applications in glycerol hydrogenolysis to 1,3-PDO. However, these systems usually exhibit low W and Pt atomic efficiency in the production of 1,3-PDO. Zhao et al.^[78] prepared highly dispersed WO_x species on an inert α-Al₂O₃ support through simple high-temperature heat treatment. The number of Pt-WO_x interfacial active sites can be adjusted by Pt loading. The 2Pt/WO_x/α-Al₂O₃ catalyst shows excellent catalytic performance in the hydrogenolysis of glycerol, especially high W efficiency for 1,3-PDO (76 g_1,3-PDO/(g_W·h)). The high catalytic efficiency is due to the strong interaction between isolated WO₄ species and Pt, which can in situ generate Brønsted acid sites during the reaction, thereby promoting the conversion of glycerol to 1,3-PDO (Figure 10). Zhao et al.^[79] further study the effect of structure and chemical state of WO_x species on glycerol hydrogenolysis to 1,3-PDO.

By regulating in-situ migration of WO₃ nanoparticles in H₂ atmosphere, they successfully construct single atom W-doped α-Al₂O₃ support with low chemical state. Characterization results show that compared with octahedral W⁶⁺ species, tetrahedral W⁵⁺ could disperse and stabilize Pt species more effectively, and exhibit stronger Pt-WO_x interaction. The improvement of catalytic performance of Pt-WO_x/γ-Al₂O₃ is attributed to the in situ generated tetrahedral WO_x with rich oxygen defects on catalyst surface. These defects not only promote the construction of the Pt-WO_x interface but also amplify the synergistic effect between them. Structure-activity relationship analysis reveals that monodispersed tetrahedral W⁵⁺ species [(−O−)₃W(=O)] play a key role in regulating catalyst acidity and improving catalytic performance, which can not only assist glycerol adsorption but also capture H atoms to in situ form Brønsted acid sites. These effects ultimately achieve dual regulation of catalytic activity and 1,3-PDO selectivity (1.36 g_1,3-PDO/(g_Pt·h)).

Strong metal-support interaction (SMSI) is a key concept in heterogeneous catalysis that plays a crucial role in enhancing catalytic performance. Interaction between Pt and WO_x is regarded as one of the key factors affecting catalytic activity and selectivity of glycerol hydrogenolysis. But interaction between WO_x and support has been rarely studied. In 2025, Li et al.^[80] systematically investigated the effect of SiO₂-WO_x interaction on glycerol hydrogenolysis over Pt/W-SiO₂ by regulating the number of silanol groups on the surface of SiO₂ support. Studies show that weak SiO₂-WO_x interaction could promote Pt-WO_x interaction (forming more Pt-WO_x coordination structures), which significantly improves the catalytic performance of glycerol hydrogenolysis to 1,3-PDO. Taking Pt/W-SiO₂-700 catalyst (most silanol groups are removed to enhance Pt-WO_x coordination) as an example, 70.9% glycerol conversion and 61.3% 1,3-PDO selectivity can be obtained at 140 ℃ (Table 2). Experimental characterization and theoretical calculations show that the enhanced Pt-WO_x coordination is beneficial to hydrogen spillover, forming more isolated WO_x−H active sites. WO_x−H species play a key role in the selective hydrogenolysis of glycerol to 1,3-PDO. Eqi et al.^[81] further constructed a Pt/WO_x/Nb₂O₅ catalyst through oxygen vacancy engineering. It possessed abundant oxygen vacancies and strong Pt^δ+-O-W interaction. The optimized Pt/WO_x/Nb₂O₅ catalyst achieved remarkable catalytic performance in the hydrogenolysis of glycerol (50.0%), with a glycerol conversion of 94.9% and 1,3-PDO selectivity of 67.3%. The space time yield of glycerol is 0.490 g/(g_cat·h). This study found that Pt^δ+-O-W interaction could promote the selective adsorption of the secondary hydroxyl group of glycerol and the hydrogen spillover from Pt to WO_x for in situ generation of Brønsted acid sites. Both facilitate the selective hydrogenolysis of glycerol to 1,3-PDO (Figure 11)^[81]. In 2024, Chen et al.^[82] further studied the catalytic performance of Pt/Nb₂W₃O₁₄ catalyst in glycerol hydrogenolysis. Compared with Pt/WO₃ and Pt/NbO_x, the space-time yield of 1,3-PDO on Nb-doped Pt/Nb₂W₃O₁₄ catalyst could be increased by 13 times, reaching 596.4 mg/(g_cat·h). It is found that the cationic ordering of Nb and W at the atomic scale gave full play to their unique advantages. Nb₂W₃O₁₄ could effectively promote the dispersion and reduction of Pt nanoparticles. Strong interaction between Nb₂W₃O₁₄ and Pt could promote the adsorption and activation of the secondary hydroxyl group (C2−OH) of glycerol, as well as the subsequent hydrogenation, thereby selectively producing 1,3-PDO. In addition, the electronic structure of Pt-WO_x catalysts can be further optimized by introducing second promoters (such as Sn, Mo, etc.), thus improving their catalytic activity, stability and selectivity in the hydrogenolysis of glycerol. Shaikh et al.^[83] systematically investigated the effects of reaction temperature, pressure and second promoters (Cu, Fe, Rh, Mn, Re, Ru, Ir, Sn, B and P) on the catalytic performance and deactivation behavior of Pt/WO_x/γ-Al₂O₃ catalysts. They found that when Rh, Mn, Re, Ru, Ir, B or P were introduced as second promoters, they could not only promote the dispersion of Pt, but also significantly improve the selectivity of 1,3-PDO by increasing the number of Brønsted acid sites. Analysis of fresh and spent catalysts by characterization methods like XRD, CO chemisorption and TEM shows that Pt particle sintering is the main cause of catalyst deactivation. Notably, the introduction of second promoters could affect the sintering behavior of the catalyst by changing the interactions between Pt, WO_x and γ-Al₂O₃. For example, Re and Mn promoters as electron acceptors could increase the content of Pt²⁺ on the catalyst surface. The formation of Pt²⁺ enhances the interaction between Pt and γ-Al₂O₃ as well as WO_x, and effectively inhibits Pt sintering. However, adding second promoters had no obvious improvement on metal leaching and coking. Their stability still faces challenges. Nevertheless, catalyst stability is crucial in practical applications. Lei et al.^[84] systematically investigated the stability of Pt/WO₃/Al₂O₃ catalyst and observed obvious deactivation in a 700 h continuous operation experiment. Glycerol conversion decreases by more than half during the whole process, from 57.5% to 25.1% at 700 h. In-depth analysis revealed that neither leaching of W species nor coking is the main cause of deactivation. Characterization results from XRD, HAADF-STEM and CO chemisorption clearly show that the significant aggregation of Pt particles led to a sharp decrease in Pt-WO_x interfacial sites. This structural change resulted in a decrease in the number of strong Brønsted acid sites originally formed in situ through H₂ dissociation at the Pt-WO_x interface. This issue ultimately led to catalyst deactivation.

Due to the high cost, research on Ir-ReO_x based catalytic systems for the hydrogenolysis of glycerol to 1,3-PDO remains limited. In 2011, Amada et al.^[36] explored the reaction mechanism of the hydrogenolysis of glycerol to 1,3-PDO over Ir-ReO_x/SiO₂ catalysts. Systematic studies showed that glycerol conversion increases with the increase of Re content (reaching a maximum when Re/Ir = 2). In contrast, the high selectivity of 1,3-PDO (approximately 60%) is barely affected by Re content. XRD and TEM characterizations indicated that the average size of Ir particles gradually decreases with the increase of Re content. Characterization results of CO adsorption, TPR, XANES and EXAFS confirmed that the Ir metal surface is partially covered by ReO_x clusters regardless of the Re content. Kinetic studies showed that reaction order of Ir-ReO_x/SiO₂ (Re/Ir = 1) with respect to H₂ pressure is first-order. The low reaction order with respect to glycerol concentration indicated a strong interaction between glycerol and the catalyst surface. Combining reaction and characterization results, authors propose a reaction mechanism where glycerol is directly converted to 1,3-PDO via a 2,3-dihydroxypropoxy intermediate (“direct hydrogenolysis” route). Liu et al.^[85] further systematically investigated the effect of supports on the catalytic performance of Ir-ReO_x catalysts for the hydrogenolysis of glycerol to 1,3-PDO. It is found that rutile TiO₂ support exhibits extremely high catalytic activity, even superior to the aforementioned SiO₂ support. In contrast, Ir-ReO_x catalysts supported on anatase TiO₂, C, ZrO₂, CeO₂, Al₂O₃ and MgO all show low catalytic activity. Without adding H₂SO₄, even with a low Re/Ir ratio (0.24), Ir-ReO_x/rutile TiO₂ catalyst still exhibits higher Ir-based 1,3-PDO yield than Ir-ReO_x/SiO₂ at the initial stage of reaction. The important role of rutile TiO₂ support is that it can provide a unique environment to stabilize uniform small-sized Ir-ReO_x particles, which significantly increases the number of active sites per unit Re. Comprehensive characterization methods including TPR, TEM, XPS, XAS, CO adsorption and CO FT-IR, combined with kinetic studies, show strong interaction between Ir and partially oxidized ReO_x clusters (the average valence state of Re is +3). The active sites are at the Ir-ReO_x interface. In 2021, Sarun Chanklang et al. explored the performance of Ir-ReO_x catalyst supported on H-ZSM-5 (Ir-ReO_x/H-ZSM-5) in the hydrogenolysis of glycerol to 1,3-PDO^[86]. It is found that glycerol conversion and 1,3-PDO yield largely depends on catalyst composition (Re/Ir ratio) and metal loading. Adding Re promotes the high dispersion of Ir. In addition, a strong electronic interaction between Ir and Re is observed in the Ir-ReO_x/H-ZSM-5 catalyst. In the study of the influence of reaction conditions, it is found that increasing reaction temperature and time can lead to higher glycerol conversion. But over-hydrogenolysis would occur, reducing the selectivity of 1,3-PDO. Increasing pressure has a positive effect on the selectivity of 1,3-PDO. Under optimal conditions, the conversion of glycerol is 14.9% with 19.0% 1,3-PDO selectivity on Ir-ReO_x/H-ZSM-5 (Table 2).

Noble metal catalysts are widely used in the catalytic hydrogenolysis of glycerol to 1-PO due to their high hydrogenolysis activity. Li et al. ^[88] prepared a series of Pt catalysts supported on Zr-Al composite oxides with varying Zr/Al molar ratios (denoted as 2.5%Pt/Zr_xAl_1−xO_y). Their performance in the selective hydrogenolysis of glycerol to 1-PO were evaluated. The results reveal that the Zr/Al molar ratio in the support markedly influenced both the Pt particle size and the nature of the acid sites on the catalyst surface. A clear correlation is observed between the catalytic behavior and acidity. Higher concentration of acidic sites promotes the conversion of glycerol. While strong acidic sites within a specific strength range favor deep hydrogenolysis of glycerol to 1-PO. Under the reaction conditions of 10% aqueous glycerol solution, 240 °C, and 6.0 MPa H₂ pressure, the 2.5%Pt/Zr_0.7Al_0.3O_y catalyst exhibited the best catalytic performance. It achieved 81.2% glycerol conversion with >86% selectivity to 1-PO (Table 3).

Additionally, Wang et al.^[89] developed a one-pot hydrogenolysis of glycerol to 1-PO using a double-layer catalyst system in a continuous flow fixed-bed reactor (Figure 12). The zirconium phosphate (ZrP) catalyst was placed in the upper layer and responsible for catalyzing the dehydration of glycerol to acrolein. Supported Ru catalyst in the lower layer was used for hydrogenating acrolein to 1-PO. This study found that the presence of strong acid sites on the lower hydrogenation catalyst promoted the formation of glycerol decomposition products, such as methanol, ethanol, methane, and CO₂. In contrast, 2%Ru/SiO₂ catalyst possessing only weak acid sites delivered the highest 1-PO selectivity (76.5%). This catalytic system also shows good long-term stability (80 h).

Metal phosphates usually possess abundant acidic sites and exhibit excellent hydrothermal stability, which are beneficial for the hydrogenolysis of glycerol to 1-PO. Luo et al.^[90] developed a WO_x-modified amorphous zirconium phosphate (ZrP)-supported Pt catalyst (Pt/7WO_x-ZrP) for the selective hydrogenolysis of glycerol to 1-PO in a fixed-bed reactor. Studies showed that introducing WO_x significantly increases the total acidity of the catalyst and dispersion of Pt nanoparticles. Among them, the Pt/7WO_x-ZrP catalyst achieved complete glycerol conversion with 1-PO yield of 81% in the long-term stability test (≥ 70 h). Catalytic performance tests and characterization results indicate that the acidic sites on the catalyst could promote the selective dehydration of glycerol to acrolein. Pt sites are responsible for H₂ molecule dissociation and subsequent hydrogenation of acrolein intermediate to 1-PO. Bhanuchander et al.^[91] synthesized a series of metal phosphate-supported Pt catalysts (Pt/AlP, Pt/TiP, Pt/ZrP and Pt/NbP) for the direct hydrogenolysis of glycerol to propanol. The reaction conditions for hydrogenolysis of glycerol to propanol has been optimized by systematically investigating parameters such as Pt loading, reaction temperature, hydrogen flow rate, glycerol concentration and reaction time.

Among them, 2Pt/TiP exhibits excellent catalytic performance in the gas-phase hydrogenolysis of glycerol. Under the conditions of 220 °C and atmospheric pressure, achieving complete glycerol conversion with 1-PO selectivity of approximately 81.0%. High catalytic efficiency of the 2Pt/TiP catalyst is attributed to its strong acidity and uniformly dispersed Pt nanoparticles on the TiP. These effects facilitate the conversion of glycerol to 1-PO via the “dehydration-hydrogenation” pathway. Samudrala et al.^[92] used Pd/MoO₃-Al₂O₃ as catalyst to realize the selective hydrogenolysis of glycerol to 1-PO and 2-PO in a fixed-bed reactor. Catalytic performance results showed that this system not only achieves a glycerol conversion of >80% but also exhibit a total selectivity of >90% for 1-PO (about 50.0%) and 2-PO. Characterization analysis indicated that the synergistic effect between Pd and MoO₃ on the Al₂O₃ support is the key factor for obtaining excellent catalytic activity. In addition, Ryneveld et al. ^[93] compared Pd catalysts supported on different supports. They found that the Pd/C catalyst could achieve 38% glycerol conversion and 52% 1-PO selectivity under the reaction condition of 250 °C. Under the same operating conditions, although the Ru/C catalyst could reach approximately 99% glycerol conversion, its 1-PO selectivity decreases to about 18% due to the occurrence of C−C bond cleavage.

Although Ni-based catalysts have the disadvantages of high reduction temperature, they often show high activity for the hydrogenolysis of glycerol to 1-PO. However, in hydrothermal reactions, Ni nanoparticles tend to be agglomerated or leached, leading to catalyst deactivation^[94]. To improve the stability of Ni-based catalysts, Gatt et al.^[95] investigated the catalytic performance of phosphorus-modified carbon supported Ni catalysts in the hydrogenolysis of glycerol to 1-PO. They prepared a series of nickel phosphide catalysts using mesoporous carbon as the support and Al(H₂PO₄)₃ and NiCl₂ as metal precursors. It was found that these Ni-based catalysts would form different phases (Ni_xP_y, NiPO_x, AlPO_x). Enhancement of acidity was directly related to the content of Al(H₂PO₄)₃. When the content of Al(H₂PO₄)₃ precursor was in the range of 4%−10%, the increase in catalyst surface acidity could improve glycerol conversion and enhance the selectivity of 1-PO. Studies showed that the presence of phosphate is necessary for achieving high catalytic activity. However, when the Al(H₂PO₄)₃ content exceeds 10%, the selectivity of 1-PO decreased due to the intensified dehydration reaction on the acidic sites of the support. Among them, the Ni/CPAl(10) catalyst achieved 97% conversion of glycerol and 74% 1-PO selectivity after reacting for 6 h in the 80% aqueous glycerol solution. Lin et al. adopted a double-layer catalyst system to realize the hydrogenolysis of glycerol to 1-PO through sequential catalysis^[96]. In a continuous flow fixed-bed reactor, the acidic H-β catalyst layer was placed upstream of the Ni/Al₂O₃ catalyst layer. This double-layer catalyst system exhibited excellent 1-PO selectivity (up to 69%) with nearly 100% conversion of glycerol. Preliminary mechanism studies indicated that the conversion of glycerol to 1-PO proceeds via the two sequential dehydration-hydrogenation pathway. Solos et al.^[97] further studied the process of dehydration and hydrogenation of glycerol to 1-PO over a tandem catalytic system consisting of HZSM-5 and supported Ni catalysts. First, glycerol was completely converted to acrolein and PA (selectivity >82%) via dehydration over the first bed (HZSM-5) at 300 °C. Ni/MgO, Ni/SiO₂, Ni/Mg-Al-LDH, Ni/TiO₂ or Ni/Al₂O₃ (20% Ni loading) were used as hydrogenation catalysts in the second bed. Acrolein and PA produced in the first bed were hydrogenated to 1-PO in the second bed at 175 °C (Figure 13) ^[97]. HZSM-5¦20Ni/Al₂O₃ system with high Ni dispersion provide high stability and 1-PO yield (>73%).

In addition to Ni-based catalysts, Cu-based catalysts also showed excellent performance in glycerol hydrogenolysis to 1-PO. In 2022, Folkard et al.^[98] explored the application of Cu−HSiW catalyst in glycerol hydrogenolysis to 1-PO. For the first time, the direct conversion of glycerol to 1-PO was achieved on the Cu-based catalysts. Systematic studies on fresh and spent catalysts were carried out using various characterization techniques. It was found that when silicotungstic acid with moderate acidity (maintaining intact Keggin structure units) is distributed near the Cu clusters, the catalytic performance and lifetime of the catalyst are significantly improved. 98% glycerol conversion was obtained with 71% selectivity to 1-PO (Table 3). In 2024, Zhou et al. prepared a simple Cu20/HZSM-5 (Si/Al = 120) catalyst. It achieved a 1-PO selectivity of approximately 71.1% under mild reaction conditions^[99]. This catalyst has a high Lewis acid site density and a favorable Cu²⁺/Cu^0/1+ ratio, which significantly enhances the hydrogenolysis of glycerol to 1-PO. In addition, Cu20/HZSM-5 exhibited excellent selectivity for removing the secondary hydroxyl group from the intermediate 1,2-PDO. It is crucial for the high yield of 1-PO.