Reaction kinetics and modelling of the gold catalysed glycerol oxidation

The Application of Copper-Gold Catalysts in the Selective Oxidation of Glycerol at Acid and Basic Conditions

The crude glycerol is produced during the transesterification of animal fats and vegetable oils, but it is a by-product of this process. Currently, its elimination is a problem in the chemical industry. The main goal of this work was the preparation, characterization and application of mesoporous cerium-zirconium oxide as supports for copper and gold species and the comparison of selected factors on the properties of catalysts in glycerol oxidation in the liquid phase. The samples were characterized using adsorption and desorption of nitrogen, XRD, UV-vis, XPS, TEM, SEM, and STEM-EDXS. The obtained results of glycerol oxidation show that the bimetallic copper-gold catalysts are more active and selective to glyceric acid in this reaction than analogous monometallic gold catalysts. Additionally, bimetallic catalysts are also characterized by the catalytic stability, and their application leads to the increase of selectivity to glyceric acid during their reusing in glycerol oxidation in alkali media. In this work, the influence of selected factors, e.g., oxygen source and its pressure, solution pH, and base content on the catalytic activity of bimetallic catalysts is discussed.

Enhancing the understanding of the glycerol to lactic acid reaction mechanism over AuPt/TiO2 under alkaline conditions

The oxidation of glycerol under alkaline conditions in the presence of a heterogeneous catalyst can be tailored to the formation of lactic acid, an important commodity chemical. Despite recent advances in this area, the mechanism for its formation is still a subject of contention. In this study, we use a model 1 wt. % AuPt/TiO₂ catalyst to probe this mechanism by conducting a series of isotopic labeling experiments with 1,3-¹³C glycerol. Optimization of the reaction conditions was first conducted to ensure high selectivity to lactic acid in the isotopic labeling experiments. Selectivity to lactic acid increased with temperature and concentration of NaOH, but increasing the O₂ pressure appeared to influence only the rate of reaction. Using 1,3-¹³C glycerol, we demonstrate that conversion of pyruvaldehyde to lactic acid proceeds via a base-promoted 1,2-hydride shift. There was no evidence to suggest that this occurs via a 2,1-methide shift under the conditions used in this study.

The Effect of Polymer Addition on Base Catalysed Glycerol Oxidation Using Gold and Gold–Palladium Bimetallic Catalysts

Abstract

The oxidation of glycerol represents both a viable route to catalytic upgrading of biomass and has become a model reaction for catalytic polyol oxidation. Gold and gold–palladium nanoparticle catalysts prepared by colloidal methods involving polymer additives have been extensively studied. However, the effect of residual polymer at the catalyst surface on reaction pathways has not been decoupled from particle size effects. We show that when using catalysts prepared without polymer stabilisers the addition of either polyvinyl alcohol or polyvinylpyrrolidone to the reaction changes the reaction rate and results in a change in reaction selectivity. We conclude that the polymer additive has a significant effect on the reaction pathway and that these systems should be considered as a metal surface–polymer interface catalytic systems and properties should not be rationalised solely based on nanoparticle size.

Graphic Abstract

Supported Gold Nanoparticles as Catalysts for the Oxidation of Alcohols and Alkanes

Supporting gold nanoparticles have shown to be extremely active for many industrially important reactions, including oxidations. Two representative examples are the oxidation of alcohols and alkanes, that are substrates of industrial interest, but whose oxidation is still challenging. This review deals with these reactions, giving an insight of the first studies performed by gold based catalysts in these reactions and the most recent developments in the field.

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.

Toward the Sustainable Synthesis of Propanols from Renewable Glycerol over MoO3-Al2O3 Supported Palladium Catalysts

The catalytic conversion of glycerol to value-added propanols is a promising synthetic route that holds the potential to overcome the glycerol oversupply from the biodiesel industry. In this study, selective hydrogenolysis of 10 wt% aqueous bio-glycerol to 1-propanol and 2-propanol was performed in the vapor phase, fixed-bed reactor by using environmentally friendly bifunctional Pd/MoO3-Al2O3 catalysts prepared by wetness impregnation method. The physicochemical properties of these catalysts were derived from various techniques such as X-ray diffraction, NH3-temperature programmed desorption, scanning electron microscopy, 27Al NMR spectroscopy, surface area analysis, and thermogravimetric analysis. The catalytic activity results depicted that a high catalytic activity (>80%) with very high selectivity (>90%) to 1-propanol and 2-propanol was obtained over all the catalysts evaluated in a continuously fed, fixed-bed reactor. However, among all others, 2 wt% Pd/MoO3-Al2O3 catalyst was the most active and selective to propanols. The synergic interaction between the palladium and MoO3 on Al2O3 support and high strength weak to moderate acid sites of the catalyst were solely responsible for the high catalytic activity. The maximum glycerol conversion of 88.4% with 91.3% selectivity to propanols was achieved at an optimum reaction condition of 210 ∘ C and 1 bar pressure after 3 h of glycerol hydrogenolysis reaction.

The controlled catalytic oxidation of furfural to furoic acid using AuPd/Mg(OH)2

The selective oxidation of furfural to furoic acid is achieved at mild reaction conditions over an AuPd/Mg(OH)₂ heterogeneous catalyst.

Factors affecting activity and selectivity in the oxidation of glycerol promoted by platinum catalysts

Selectivity in glycerol oxidation with Pt catalysts depends strongly on reaction conversion because of poisoning by the accumulated products.

Volcano-shape glycerol oxidation activity of palladium-decorated gold nanoparticles

Activity and selectivity of glycerol oxidation were highly dependent upon Pd surface coverage of Pd-on-Au bimetallic catalysts.

Green synthesis of gold nanoparticles using glycerol-incorporated nanosized liposomes

There has been enormous interest in the last decade in development methods for the inorganic synthesis of metallic nanoparticles of desired sizes and shapes because of their unique properties and extensive applications in catalysis, electronics, plasmonics, and sensing. Here we report on an environmentally friendly, one-pot synthesis of metallic nanoparticles, which avoids the use of organic solvents and requires mild experimental conditions. The developed method uses liposomes as nanoreactors, where the liposomes were prepared by encapsulating chloroauric acid and exploited the use of glycerol, incorporated within the lipid bilayer as well as in its hydrophilic core, as a reducing agent for the controlled preparation of highly homogeneous populations of gold nanoparticles. The effects of temperature, the presence of a capping agent, and the concentration of glycerol on the size and homogeneity of the nanoparticles formed were investigated and compared with solution-based glycerol-mediated nanoparticle synthesis. Well-distributed gold nanoparticle populations in the range of 2-8 nm were prepared in the designed liposomal nanoreactor with a clear dependence of the size on the concentration of glycerol, the temperature, and the presence of a capping agent whereas large, heterogeneous populations of nanoparticles with amorphous shapes were obtained in the absence of liposomes. The particle morphology and sizes were analyzed using transmission electron microscopy imaging, and the liposome size was measured using photon correlation spectroscopy.