Hydrogenolysis of glycerol over TiO2-supported Pt-WOx catalysts: Effects of the TiO2 crystal phase and WOx loading

The selective hydrogenolysis of glycerol to 1,3-propanediol (1,3-PDO) with high added value is attraction but challenging. Pt-WO_x-based catalysts have been extensively studied in the selective hydrogenolysis of glycerol. The catalyst support and the physicochemical state of WO_x play important roles on this reaction. In this paper, Pt-WO_x catalysts supported on TiO₂ with different crystal forms were prepared and studied for their catalytic performance in hydrogenolysis of glycerol. It was observed that the catalytic performance of anatase-type (A-type) TiO₂-supported catalyst (Pt/W/A-Ti) is much better than that of the rutile-type (R-type) TiO₂ catalyst (Pt/W/R-Ti) due to its higher stability. Furthermore, the influence of W loading amount and state were thoroughly investigated for the Pt/W/A-Ti catalysts, and Pt/W/A-TiO₂ with 5 wt% loading of WO_x achieved the best catalytic performance (100% conversion of glycerol and 41% yield of 1,3-PDO under the optimal reaction conditions), owing to the suitable WO_x domains and high dispersion of W species, as evidenced by XRD patterns and TEM images. Mechanism study by in-situ DRIFTS experiments indicated that glycerol was first converted to 3-hydroxypropanal and then converted to 1,3-PDO through subsequent reactions.

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.

Mechanistic insights into acid-affected hydrogenolysis of glycerol to 1,3-propanediol over an Ir-Re/SiO2 catalyst

Glycerol hydrogenolysis to 1,3-propanediol is identified to follow the dehydration-hydrogenation pathway with the rate-determining step (RDS) of H* + OH* → H₂O* over an IrRe catalyst. The positive effects of solid acids are elucidated to originate from the reduced energy barrier of the RDS by H protons, while the negative ones of liquid acids are from excessively strong adsorption of anions.

Catalytic Conversion of Glycerol into Hydrogen and Value-Added Chemicals: Recent Research Advances

In recent decades, the use of biomass as alternative resources to produce renewable and sustainable biofuels such as biodiesel has gained attention given the situation of the progressive exhaustion of easily accessible fossil fuels, increasing environmental concerns, and a dramatically growing global population. The conventional transesterification of edible, nonedible, or waste cooking oils to produce biodiesel is always accompanied by the formation of glycerol as the by-product. Undeniably, it is essential to economically use this by-product to produce a range of valuable fuels and chemicals to ensure the sustainability of the transesterification process. Therefore, recently, glycerol has been used as a feedstock for the production of value-added H2 and chemicals. In this review, the recent advances in the catalytic conversion of glycerol to H2 and high-value chemicals are thoroughly discussed. Specifically, the activity, stability, and recyclability of the catalysts used in the steam reforming of glycerol for H2 production are covered. In addition, the behavior and performance of heterogeneous catalysts in terms of the roles of active metal and support toward the formation of acrolein, lactic acid, 1,3-propanediol, and 1,2-propanediol from glycerol are reviewed. Recommendations for future research and main conclusions are provided. Overall, this review offers guidance and directions for the sufficient and economical utilization of glycerol to generate fuels and high value chemicals, which will ultimately benefit industry, environment, and economy.

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.

Progress in Production of 1, 3-propanediol From Selective Hydrogenolysis of Glycerol

1,3-propanediol (1,3-PDO) is an important bulk chemical widely used in the polyester and polyurethane industry. The selective hydrogenolysis of glycerol to value-added 1,3-PDO is extremely attractive. However, the formation of 1,3-PDO is less thermodynamically stable than 1,2-PDO, and the steric hindrance effect in the reaction process makes the highly selective production of 1,3-PDO a great challenge. In this mini review, the recent research progress on the selective catalytic hydrogenolysis of glycerol to 1,3-PDO is overviewed and the catalytic mechanism of the reaction is summarized. We mainly focus on the different performances of each type of catalyst (Pt-W-based catalysts, Ir-Re based-catalysts, and other types) as well as the interactions between metals and supports. Finally, several personal perspectives on the opportunities and challenges within this promising field are discussed.

Molybdenum-Incorporated Mesoporous Silica: Surface Engineering toward Enhanced Metal-Support Interactions and Efficient Hydrogenation

In heterogeneous catalysis, strong metal-support interactions are highly desired to improve catalytic turnover on metal catalysts. Herein, molybdenum is uniformly incorporated into mesoporous silica (KIT-6) to accomplish strong interactions with iridium catalysts, and consequently, active and selective hydrogenation of carbonyl compounds. Mo-incorporated KIT-6 (Mo-KIT-6) affords electronic interactions to improve the proportion of metallic Ir⁰ species, avoiding the easy surface oxidation of ultrafine metals in silica mesocavities. Owing to the effective H₂ activation and subsequent hydrogenation on metallic Ir⁰ sites, optimal Ir/Mo-KIT-6 with a high Ir⁰/Ir^δ+ ratio delivers prominent performance in the hydrogenation of amides to amines and α,β-unsaturated aldehydes to unsaturated alcohols. As for N-acetylmorpholine hydrogenation, the Ir/Mo-KIT-6 catalyst achieves efficient turnover toward N-ethylmorpholine with high selectivity (>99%) and exhibits activity that relies on the engineered chemical state of Ir sites. Such promotion is further proved to be universal in cinnamaldehyde hydrogenation. This work will provide new opportunities for catalyst design through surface/interface engineering.

Nanostructured Metal Catalysts for Selective Hydrogenation and Oxidation of Cellulosic Biomass to Chemicals

Conversion of biomass to chemicals provides essential products to human society from renewable resources. In this context, achieving atom-economical and energy-efficient conversion with high selectivity towards target products remains a key challenge. Recent developments in nanostructured catalysts address this challenge reporting remarkable performances in shape and morphology dependent catalysis by metals on nano scale in energy and environmental applications. In this review, most recent advances in synthesis of heterogeneous nanomaterials, surface characterization and catalytic performances for hydrogenation and oxidation for biorenewables with plausible mechanism have been discussed. The perspectives obtained from this review paper will provide insights into rational design of active, selective and stable catalytic materials for sustainable production of value-added chemicals from biomass resources.

Turning Biodiesel Waste Glycerol into 1,3-Propanediol: Catalytic Performance of Sulphuric acid-Activated Montmorillonite Supported Platinum Catalysts in Glycerol Hydrogenolysis

Direct C-O hydrogenolysis of bioglycerine to produce 1,3-propanediol selectively is a vital technology that can expand the scope of biodiesel industry and green chemical production from biomass. Herein we report sulphuric acid-activated montmorillonite clay supported platinum nanoparticles as highly effective solid acid catalysts for the selective production of 1,3-propanediol from glycerol. The catalytic performances of the catalysts were investigated in the hydrogenolysis of glycerol with a fixed bed reactor under ambient pressure. The results were found promising and showed that the activation of montmorillonite by sulphuric acid incorporated Brønsted acidity in the catalyst and significantly improved the selectivity to 1,3-propanediol. The catalytic performance of different platinum loaded catalysts was examined and 2 wt% Pt/S-MMT catalyst presented superior activity among others validating 62% 1,3-propanediol selectivity at 94% glycerol conversion. The catalytic activity of 2Pt/S-MMT was systematically investigated under varying reaction parameters including reaction temperature, hydrogen flow rate, glycerol concentration, weight hourly space velocity, and contact time to derive the optimum conditions for the reaction. The catalyst stability, reusability and structure-activity correlation were also elucidated. The high performance of the catalyst could be ascribed to well disperse Pt nanoparticles immobilized on acid-activated montmorillonite, wider pore-structure and appropriate acid sites of the catalyst.

Selective hydrogenolysis of glycerol to 1,3-propanediol over egg-shell type Ir–ReOx catalysts

The egg-shell catalysts could promote the conversion of glycerol while maintaining an acceptable pressure gradient.