Continuous catalytic process for the selective dehydration of glycerol over Cu-based mixed oxide

In-depth analysis of embedded-type structures of NixMg4-xAl LDO-composited catalysts and the impacts on glycerol conversion under a base- and H2-free condition

Core-shell composite catalysts composing of AgO@SnO2/ZSM-5 embedded by NixMg4-xAlO LDOs with various Ni/Mg ratios were characterized and tested for the activity on the conversion of glycerol to valuable chemicals under a base-free and external H2-free condition. As a result, the catalytic performance of an embedded composite was found greater than that of its individual constituents, owing to the synergy between a NixMg4-xAlO lodge and embedded AgO@SnO2/ZSM-5. The highest yield of 1,2-propanediol and lactic acid was achieved at the Ni/Mg ratio of 0.2/3.8. NixMg4-xAlO lodges were found to simultaneously drive glycerol dehydration to acetol and glycerol reforming, driven by Ni sites, forming in-situ H2 that enhances 1,2-propanediol formation whereas the AgO@SnO2/ZSM-5 clusters governed acetol oxidation and Cannizzaro reaction that led to the formation of lactic acid. At a high Ni/Mg ratio, the NixMg4-xAlO lodges completely covered AgO@SnO2/ZSM-5 clusters entirely, resulting in the suppression of lactic acid yield due to over-oxidation.

Catalytic dehydration of glycerol over Cu-Fe-Al-based oxides: understanding changes in active sites throughout the reaction

The glycerol conversion into acetol using Fe, Al and Cu-based oxides was investigated. XRD results indicate the formation of nanosized particles with high phase dispersion, however, Raman, Mössbauer, 27Al NMR and XPS spectroscopies suggest the presence of iron(iii) oxide, Al2O3 and CuO phases. The FTIR with pyridine adsorption revealed high Lewis acidity. The TPR profile showed the reduction temperature range for the Fe3+ and Cu2+ sites, indicating the suitable condition for pretreatment. The N2 adsorption-desorption isotherms indicated the presence of micro-mesopores with interesting textural properties and specific area varying between 71 and 220 m2 g-1, while the porous morphology was observed by SEM and TEM images. The optimized catalytic tests showed glycerol conversion of 60% and acetol selectivity of 92% with 17% of coke according to TG profile. The recycling tests confirmed the efficiency of the solid, reaching 28% conversion and 91% acetol selectivity after four reuses and, after reactivation in an oxidizing atmosphere, the catalytic performance obtained results close to the second reuse. The interaction between the different Lewis acid sites involved in the mechanisms for the acetol and coke formation on the catalyst surface is discussed. The charge distribution represented by colors which indicates the acid-base surface was evaluated by a simple theoretical-computational study based on the DFT approach. The synergy between the active sites indicates that the presence of Cu0/Cu+ drastically increases the acetol selectivity which is a more important characteristic than the high Lewis acidity of Fen+ and Al3+.

Catalytic Oxidation of Glycerol over Pt Supported on MOF-Derived Carbon Nanosheets

A series of nitrogen-doped porous carbon nanosheets (NPCNs) doped with transition-metal-supported Pt catalysts were prepared by colloidal deposition and evaluated for the selective oxidation of glycerol to glyceric acid (GLYA) under nonalkaline conditions. The transition metal contained in the catalyst was found to affect its performance and selectivity for GLYA, with the Pt/Zr@NPCN catalyst showing the highest catalytic activity and selectivity. These materials were characterized using Brunauer-Emmett-Teller surface area analysis, transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and CO₂ temperature-programmed desorption. The results showed that the small size of the Pt nanoparticles, the interaction between the Pt nanoparticles and the support, and the unique textural properties of the catalyst all promoted glycerol conversion and GLYA selectivity. A Zr concentration of 1.5 wt % and a support preparation temperature of 800 °C were found to provide a catalyst with the optimal performance that exhibited a glycerol conversion and selectivity for GLYA of 68.62 and 77.29%, respectively, at an initial O₂ pressure of 10 bar and 60 °C after 6 h. Even after being recycled five times, this material provided a GLYA selectivity of approximately 75%, although the glycerol conversion decreased from 68 to 50%. The insights may provide new suggestions on the design of efficient support for the selective oxidation of polyols.

Glycerol Valorization Towards Glycolic Acid Production Over Cu-Based Biochar Catalyst

Glycerol valorization towards high-value chemicals is of particular importance to increase the value chain of biodiesel production. In this study, the catalytic activity of a series of cheap Cu-based catalysts for glycerol conversion is investigated. Cu supported on activated carbon (AC, obtained through carbonization of coconut shell) exhibits outstanding catalytic activity for the selective conversion of glycerol into glycolic acid (GcA) in O₂ atmosphere, affording up to 68.3 % GcA yield. The combination of experimental results with theoretical calculations reveals that glyceraldehyde is the key reaction intermediate. The high specific surface area and surface oxygenated groups of AC enable the formation of CuO nanoparticles with small size and uniform dispersion. In addition, the surface oxygen vacancy on Cu/AC might help to activate reaction intermediates, and the electron transfer from Cu to AC facilitates the oxidation of glycerol to GcA. Cu loaded onto AC also significantly inhibits C-C breakage to generate formic acid as a byproduct. This work might aid the development of approaches for glycerol application and afford profitable possibilities for sustainable biodiesel.

First Evidence of the Double-Bond Formation by Deoxydehydration of Glycerol and 1,2-Propanediol in Ionic Liquids

Deoxydehydration (DODH) reaction of glycerol (GL) and 1,2-propanediol (1,2-PD), in ionic liquids (ILs), catalyzed by methyltrioxorhenium (MTO) and Re₂O₇, was studied in detail. To better understand the ability of ILs to improve the catalytic performance of the rhenium catalyst, several experiments, employing eight different cations and two different anions, were carried out. Among the anions, bis(trifluoromethylsulfonyl)imide (TFSI) appears to be more appropriate than PF₆ ^-, for its relatively lower volatility of the resulting IL. Regarding the choice of the most appropriate cation, the presence of a single aromatic ring seems to be a necessary requirement for a satisfying and convenient reactivity. With the aim to extend the recyclability of the catalyst, experiments involving the readdition of polyol to the terminal reaction mixture were carried out. Worthy of interest is the fact that the presence of the IL prevents the inertization process of the catalyst, allowing us to obtain the alkene also after a readdition of fresh polyol.

Chemicals Production from Glycerol through Heterogeneous Catalysis: A Review

Utilization of biofuels generated from renewable sources has attracted broad attention due to their benefits such as reducing consumption of fossil fuels, sustainability, and consequently prevention of global warming. The production of biodiesel causes a huge amount of by-product, crude glycerol, to accumulate. Glycerol, because of its unique structure having three hydroxyl groups, can be converted to a variety of industrially valuable products. In recent decades, increasing studies have been carried out on different catalytic pathways to selectively produce a wide range of glycerol derivatives. In the current review, the main routes including carboxylation, oxidation, etherification, hydrogenolysis, esterification, and dehydration to convert glycerol to value-added products are investigated. In order to achieve more glycerol conversion and higher desired product selectivity, acquisition of knowledge on the catalysts, the type of acidic or basic, the supports, and studying various reaction pathways and operating parameters are necessary. This review attempts to summarize the knowledge of catalytic reactions and mechanisms leading to value-added derivatives of glycerol. Additionally, the application of main products from glycerol are discussed. In addition, an overview on the market of glycerol, its properties, applications, and prospects is presented.

Glycerol Valorization over ZrO2-Supported Copper Nanoparticles Catalysts Prepared by Chemical Reduction Method

Copper nanoparticles (NPs) and ZrO2-supported copper NPs (Cu NPs/ZrO2) were synthesized via a chemical reduction method applying different pH (4, 7 and 9) and evaluated in a glycerol dehydration reaction. Copper NPs were characterized with transmission electron microscopy (TEM) and UV–vis spectroscopy. Transmission electron microcopy (TEM) results revealed a homogeneous distribution of copper NPs. A hypsochromic shift was identified with UV–vis spectroscopy as the pH of the synthesis increased from pH = 4 to pH = 9. Zirconia-supported copper NPs catalysts were characterized using N2 physisorption, X-ray diffraction (XRD), TEM, X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), temperature-programmed desorption of ammonia (NH3-TPD) and N2O chemisorption. The presence of ZrO2 in the chemical reduction method confirmed the dispersion of the copper nanoparticles. X-ray diffraction indicated only the presence of tetragonal zirconia patterns in the catalysts. XPS identified the Cu/Zr surface atomic ratio of the catalysts. TPR patterns showed two main peaks for the Cu NPS/ZrO2 pH = 9 catalyst; the first peak between 125 and 180 °C (region I) was ascribed to more dispersed copper species, and the second one between 180 and 250 °C (region II) was assigned to bulk CuO. The catalysts prepared at pH = 4 and pH = 7 only revealed reduction at lower temperatures (region I). Copper dispersion was determined by N2O chemisorption. With NH3-TPD it was found that Cu NPs/ZrO2 pH = 9 exhibited the highest total quantity of acidic sites and the highest apparent kinetic constant, with a value of 0.004 min−1. The different pH applied to the synthesis media of the copper nanoparticles determined the resultant copper dispersion on the ZrO2 support, providing active domains for glycerol conversion.

Highly active and durable WO3/Al2O3 catalysts for gas-phase dehydration of polyols

Gas-phase glycerol dehydration over WO3/Al2O3 catalysts was investigated. WO3 loading on γ-Al2O3 significantly affected the yield of acrolein and the catalyst with 20 wt% WO3 loading showed the highest activity. The WO3/Al2O3 catalyst with 20 wt% WO3 loading showed higher activity and durability than the other supported WO3 catalysts and zeolites. The number of Brønsted acid sites and mesopores of the WO3/Al2O3 catalyst did not decrease after the reaction, suggesting that glycerol has continuous access to Brønsted acid sites inside the mesopores of WO3/Al2O3, thereby sustaining a high rate of formation of acrolein. Dehydration under O2 flow further increased the durability of the WO3/Al2O3 catalyst, enabling the sustainable formation of acrolein. In addition, the WO3/Al2O3 catalyst with 20 wt% WO3 loading showed high activity for the dehydration of various polyols to afford the corresponding products in high yield.

Pd supported on mixed metal oxide as an efficient catalyst for the reductive amination of bio-derived acetol to 2-methylpiperazine

Efficient synthesis of 2-methylpiperazine via reductive cyclo-amination of acetol with ethylenediamine over Pd supported on Ti–Al–O and Ti–Zr–O catalysts.

Copper and sulphur co-doped titanium oxide nanoparticles with enhanced catalytic and photocatalytic properties

Copper and sulphur co-doped titanium oxide nanoparticles have been prepared by the sol–gel method to develop versatile catalysts exhibiting enhanced catalytic and photocatalytic properties.

Cu–Al composite oxides: a highly efficient support for the selective oxidation of glycerol to 1,3-dihydroxyacetone

A series of Au catalysts supported on Cu–Al composite oxides were prepared and applied for the selective catalytic oxidation of glycerol to 1,3-dihydroxyacetone (DHA) in base-free conditions.