Effect of Metals on the Hydrogenolysis of Glycerol to Higher Value Sustainable and Green Chemicals Using a Supported HSiW Catalyst

Advances for Biorefineries: Glycerol Hydrogenolysis to 1,3-Propylene Glycol

Humanity’s growing dependence on non-renewable resources and the ensuing environmental impact thus generated have spurred the search for alternatives to replace chemicals and energy obtained from petroleum derivatives. Within the group of biofuels, biodiesel has managed to expand worldwide at considerable levels, going from 20 million tn/year in 2010 to 47 million tn/year in 2022, boosting the supply of glycerol, a by-product of its synthesis that can be easily used as a renewable, clean, low-cost raw material for the manufacture of products for the chemical industry. The hydrogenolysis of glycerol leads to the production of glycols, 1,2-propylene glycol (1,2-PG) and 1,3-propylene glycol (1,3-PG). In particular, 1,3-PG has the highest added value and has multiple uses including its application as an additive in the polymer industry, the manufacture of cosmetics, cleaning products, cooling liquids, etc. This review focuses on the study of the hydrogenolysis of glycerol for the production of 1,3-PG, presenting the main reaction mechanisms and the catalysts employed, both in liquid and vapor phase. Engineering aspects and the effect of the operating variables to achieve maximum yields are discussed. Finally, studies related to the stability and the main deactivation mechanisms of catalytic systems are presented.

Adsorption of Keggin-Type Polyoxometalates on Rh Metal Particles under Reductive Conditions

The adsorption of POMs on Rh/SiO₂ in water solvent under strongly reductive conditions was investigated. Aqueous solutions of α-Keggin type silicotungstate and silicovanadotungstates were mixed with Rh/SiO₂ at 393-473 K under 1 MPa of H₂. Monovanadium-substituted silicotungstate, α-SiVW₁₁O₄₀^5- (SiVW₁₁), was more readily adsorbed than nonsubstituted silicotungstate, α-SiW₁₂O₄₀^4- (SiW₁₂). After adsorption at 433 K, SiVW₁₁ was desorbed from Rh/SiO₂ by oxidation with Br₂ water without change of the Keggin structure, as evidenced by ⁵¹V NMR. Trivanadium-substituted silicotungstate, α-1,2,3-SiV₃W₉O₄₀^7-, was not stable, and the desorbed species from Rh/SiO₂ by oxidation with Br₂ did not maintain the Keggin structure. The very high temperature for adsorption (473 K) also led to the decomposition of the Keggin structure of SiVW₁₁. An increase in the concentration of SiVW₁₁ in the liquid phase gave a saturation of the amount of desorbable SiVW₁₁, up to five SiVW₁₁ anions per one Rh particle with a 3 nm size. The elemental analysis and W L₃-edge extended X-ray absorption fine structure of Rh/SiO₂ after the adsorption of SiVW₁₁ showed that a part of SiVW₁₁ was decomposed and irreversibly adsorbed as metallic W species incorporated into the surface of Rh metal particles. The amount of decomposed SiVW₁₁ was almost the same as that of SiVW₁₁ adsorbed as the original Keggin structure. The desorbable SiVW₁₁ was probably bonded on the W atom incorporated on the Rh metal particles as the two-electron-reduced form (α-SiV^IIIW₁₁O₄₀^7-).

Effect of Tungsten Species on Selective Hydrogenolysis of Glycerol to 1,3-Propanediol

Glycerol, as the major byproduct of biodiesel industry, is a cheap and green chemical feedstock. Following the expanded production of biodiesel, the oversupply of glycerol has led to increasing research of the catalytic conversion of glycerol. The selective hydrogenolysis of glycerol is an economical and sustainable way to produce 1,3-propanediol, which experiences a global growing demand, and valorize glycerol. However, the secondary hydroxy group of glycerol is sterically hindered by two primary hydroxy groups. As a result, 1,2-propanediol is the preferential product rather than 1,3-propanediol during conventional hydrogenolysis of glycerol. Currently, tungsten-containing bifunctional catalysts with metal and Brønsted acid sites are considered as a highly effective and atom-economical catalytic system for the selective hydrogenolysis of glycerol to 1,3-propanediol. Therefore, this Minireview summarized various tungsten-containing bifunctional catalysts for the hydrogenolysis of glycerol in detail and deeply discussed the relationship between tungsten species, metal active sites, and glycerol for selectively producing 1,3-propanediol.

Effect of FSP-inserted Cu on Physicochemical Properties of Cu/Al2O3 Catalyst

The copper inserted on Cu/Al2O3 catalysts with various Cu loading (10-40 wt%) were synthesized via flame spray pyrolysis (FSP). These catalysts were characterized using X-ray diffraction (XRD), N2 physisorption, temperature programmed reduction (TPR) and X-ray absorption near edge spectroscopy (XANES). The XRD results confirmed the formation of copper aluminate spinel (CuAl2O4) on the FSP-inserted Cu catalyst. The CuO crystallite size of the Cu/Al2O3 catalysts was increased with increasing Cu loading during the flame spray pyrolysis step. The incorporation of copper and aluminum precursors during the flame spray pyrolysis step can inhibit the growth of Al2O3 particles resulting in higher BET surface area and smaller particle size than pure Al2O3 support. The data from TPR and XANES results can predict the ratio of CuO and CuAl2O4 in the FSP-made support. Less than 20 wt% loading of the FSP-inserted Cu showed high concentration of CuAl2O4 phase in the FSP-made material. The composition of CuO and CuAl2O4 phase can be controlled by varying Cu loading in flame spray pyrolysis step. This is a promising alternative way to synthesize the desired catalyst. An example was the catalytic testing of the selective hydrogenolysis of glycerol. The presence of both CuO and CuAl2O4 phases in the Cu/Al2O3 catalyst enhanced the catalytic activity and promoted the selectivity to acetol product. Copyright © 2021 by Authors, Published by BCREC Group. This is an open access article under the CC BY-SA License (https://creativecommons.org/licenses/by-sa/4.0). 

Effect of support acidity during selective hydrogenolysis of glycerol over supported palladium-ruthenium catalysts

We report the role of the acidity of support during the selectivity hydrogenolysis of glycerol over supported bimetallic palladium-ruthenium (PdRu) catalysts. The PdRu nanoparticles were supported on a series of metal oxides and zeolitic supports via the modified impregnation method and tested for the liquid-phase hydrogenolysis of glycerol using gaseous hydrogen. The relative acid site densities of selected catalysts were determined by ammonia temperature-programmed desorption and pyridine desorption experiments. Based on these studies, we report a direct correlation between the catalytic activity (conversion and 1,2 propane diol yield) and two different acid sites (strong acid sites and very strong acid sites). Besides zeolite-supported catalysts, TiO₂ supported PdRu nanoparticles exhibit moderate catalytic activity; however, this catalyst shows high selectivity for the desired C-O bond cleavage to produce C3 products over the undesired C-C bond cleavage to produce < C3 products. This article is part of a discussion meeting issue 'Science to enable the circular economy'.

High Yield to 1-Propanol from Crude Glycerol Using Two Reaction Steps with Ni Catalysts

The objective of the present work is to achieve high yield to 1-propanol (1-POH) by crude glycerol hydrogenolysis in liquid phase and find an alternative to the use of noble metals by employing Ni catalysts. Two Ni catalysts with different supports, alumina (γ-Al2O3), and a phosphorous-impregnated carbon composite (CS-P) were studied and characterized in order to determine their acid properties and metallic phases. With the Ni/γ-Al2O3 catalyst, which presented small particles of metallic Ni interacting with the acid sites of the support, it was possible to obtain a complete conversion of crude glycerol with high selectivity towards 1,2-propylene glycol (1,2 PG) (87%) at 220 °C whereas with the Ni/CS-P catalyst, the presence of AlPOx species and the Ni2P metallic phase supplied acidity to the catalyst, which promoted the C-O bond cleavage reaction of the secondary carbon of 1,2 PG to obtain 1-POH with very high selectivity (71%) at 260 °C. It was found that the employment of two consecutive reaction stages (first with Ni/ γ-Al2O3 at 220 °C and then with Ni/CS-P at 260 °C) allows reaching levels of selectivity and a yield to 1-POH (79%) comparable to noble metal-based catalysts.