Hydrogenolysis of Glycerol to 1,3‐Propanediol: Are Spatial and Electronic Configuration of “Metal‐Solid Acid” Interface Key for Active and Durable Catalysts?

Selective Hydrogenation of Diethyl Malonate to 1,3-Propanediol Over Ga-Promoted Cu/SiO2 Catalysts With Enhanced Activity and Stability

Cu catalysts with different compositions and different Cu and promoter contents were prepared by precipitation-gel method and studied for the selective hydrogenation of syngas or biomass-based diethyl malonate (DEM) to valuable 1,3-propanediol (1,3-PDO). The Ga-promoted 70Cu6Ga/SiO2 catalyst was found to exhibit the highest catalytic performance, achieving 100 % DEM conversion and 76.6 % 1,3-PDO selectivity under reaction conditions of 160 °C and 8 MPa H2. The 70Cu6Ga/SiO2 bimetallic catalyst also presented obviously better stability than that of the monometallic 70Cu/SiO2 catalyst in a continuous flow reactor over 180 h time-on stream. Characterization results showed that the incorporation of Ga increased the interaction between Cu and Ga species, hindered the full reduction of Cu2+ species, and thus increased the proportion of Cu+ and the number of Lewis acidic sites on the catalyst surface. The synergistic effect between Cu0 and Cu+ enhanced the adsorption and activation of ester carbonyl groups and their subsequent hydrogenation, eventually contributed to the outstanding performances of the CuGa/SiO2 bimetallic catalysts.

Highly Efficient Iridium-Iron-Molybdenum Catalysts Condensed on Boron Nitride for Biomass-Derived Diols' Hydrogenolysis to Secondary Monoalcohols

A trade-off of activity-selectivity exists in primary C-O hydrogenolysis of biomass-derived diols to secondary alcohols over bimetallic catalysts, especially the combination of noble metal and early transition metal in the metallic state and metal oxide state, respectively. Herein, the combination of high surface concentration of boron nitride (BN)-supported metals and the addition of Mo as third metal broke the trade-off. High yields (>50%) of secondary alcohols were obtained with robust productivity up to 25-fold based on Ir over Ir-Fe0.13-Mo0.08/BN (Ir = 20 wt %, Fe/Ir = 0.13, Mo/Ir = 0.08) than previously reported Ir-Fe catalysts. In contrast, simply increasing the loading amount of Ir-Fe catalysts or the addition of Mo species only enhanced the productivity by <2-4-fold. Various characterizations showed that large Ir loading enables the formation of condensed nanostructures (∼2 nm) on the BN support, which further alloy with Mo and Fe to form an face centred cubic (fcc)-type trimetallic alloy with surface enrichment of Fe. On the other hand, in Ir-Fe0.25-Mo0.08/BN with lower Ir (5 wt %) and lower Ir-based activity, the Mo species were rather bound on the support surface possibly as the MoBx state. These structures were formed by simple impregnation and reduction with H2 at the reaction temperature (453 K). The high activity of Ir-Fe0.13-Mo0.08/BN (20 wt % Ir) is derived from two aspects: (1) the formation of condensed nanostructures (∼2 nm) exposing more active sites and (2) alloying with Mo to modify the electronic state of Ir to enhance the H2 activation ability, as shown by the decreased Ea (82-84 → 67 kJ mol-1).

Recent Progress in Catalyst Development of the Hydrogenolysis of Biomass-Based Glycerol into Propanediols-A Review

The use of biomass-based glycerol to produce chemicals with high added value is of great significance for solving the problem of glycerol surplus and thus reducing the production cost of biodiesel. The production of 1,2-propanediol (abbreviated as 1,2-PDO) and 1,3-propanediol (abbreviated as 1,3-PDO) via the hydrogenolysis of glycerol is one of the most representative and highest-potential processes for the comprehensive utilization of biomass-based glycerol. Glycerol hydrogenolysis may include several parallel and serial reactions (involving broken C-O and C-C bonds), and therefore, the catalyst is a key factor in improving the rate of glycerol hydrogenolysis and the selectivities of the target products. Over the past 20 years, glycerol hydrogenolysis has been extensively investigated, and until now, the developments of catalysts for glycerol hydrogenolysis have been active research topics. Non-precious metals, including Cu, Ni, and Co, and some precious metals (Ru, Pd, etc.) have been used as the active components of the catalysts for the hydrogenolysis of glycerol to 1,2-PDO, while precious metals such as Pt, Rh, Ru, Pd, and Ir have been used for the catalytic conversion of glycerol to 1,3-PDO. In this article, we focus on reviewing the research progress of the catalyst systems, including Cu-based catalysts and Pt-, Ru-, and Pd-based catalysts for the hydrogenolysis of glycerol to 1,2-PDO, as well as Pt-WOx-based and Ir-ReOx-based catalysts for the hydrogenolysis of glycerol to 1,3-PDO. The influence of the properties of active components and supports, the effects of promoters and additives, and the interaction and synergic effects between active component metals and supports are also examined.

Heterogeneous Catalysts for Glycerol Biorefineries: Hydrogenolysis to 1,2-Propylene Glycol

Research on the use of biomass resources for the generation of energy and chemical compounds is of great interest worldwide. The development and growth of the biodiesel industry has led to a parallel market for the supply of glycerol, its main by-product. Its wide availability and relatively low cost as a raw material make glycerol a basic component for obtaining various chemical products and allows for the development of a biorefinery around biodiesel plants, through the technological integration of different production processes. This work proposes a review of one of the reactions of interest in the biorefinery environment: the hydrogenolysis of glycerol to 1,2-propylene glycol. The article reviews more than 300 references, covering literature from about 20 years, focusing on the heterogeneous catalysts used for the production of glycol. In this sense, from about 175 catalysts, between bulk and supported ones, were revised and discussed critically, based on noble metals, such as Ru, Pt, Pd, and non-noble metals as Cu, Ni, Co, both in liquid (2-10 MPa, 120-260 °C) and vapor phase (0.1 MPa, 200-300 °C). Then, the effect of the main operational and decision variables, such as temperature, pressure, catalyst/glycerol mass ratio, space velocity, and H₂ flow, are discussed, depending on the reactors employed. Finally, the formulation of several kinetic models and stability studies are presented, discussing the main deactivation mechanisms of the catalytic systems such as coking, leaching, and sintering, and the presence of impurities in the glycerol feed. It is expected that this work will serve as a tool for the development of more efficient catalytic materials and processes towards the future projection of glycerol biorefineries.

The Application of the Nanofiltration Membrane NF270 for Separation of Fermentation Broths

The potential for nanofiltration (NF) in removing both relatively low molecular weight (MW) organic species and charged solutes from complex media is noteworthy. The main aim of the current work was to improve understanding of the separation mechanisms of fermentation broths components in the NF process. For this purpose, the experimental investigations were performed using the commercial polyamide NF270 membrane. The feed solution was ultrafiltered 1,3-propanediol (1,3-PD) broths. The separation results were analyzed and discussed in light of the detailed characteristics of both the membrane and the broth components. It has been noted that the membrane ensured the complete 1,3-PD permeability and significant rejection of some feed components. A thorough analysis showed that the retention of carboxylic acids was based on both the Donnan effect and sieve mechanism, according to the following order: succinic acid > lactic acid > acetic acid > formic acid. Indeed, acids retention increased with increasing charged acids ions valency, Stokes radius (rS) as well as MW, and decreasing diffusion coefficient (D). In turn, for ions, the following orders retention was determined: SO42− = PO43− > Cl− and Ca2+ > Na+ > NH4+ ~ K+. It indicated that the ions retention increased with increasing ions charge density, hydrated radius (rH), and hydration energy (Eh). It showed that the separation of the ions was based on the Donnan exclusion, sieving effect, and dielectric exclusion.

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.