Catalysts For Oxidation Of Glycerol Research Articles

Polyhedral Coordination Determined Co‐O Activity for Electrochemical Oxidation of Biomass Alcohols

AbstractEarth‐abundant transition metal oxides are promising electrocatalysts for oxidation of biomass alcohols. Here, CoO and Co3O4 are selected as representative cobalt oxide catalysts and grown on carbon fiber paper (CFP) electrodes to reveal the interplay between electronic structure and catalytic activity of catalysts for oxidation of glycerol, diols, and monohydric alcohols. In situ electrochemical tests elucidate that the CoO/CFP electrode has lower interfacial impedance, higher charge transfer, faster oxidation rate, and thereby the higher catalytic activity for alcohol oxidation than the Co3O4/CFP electrode. Especially for glycerol oxidation, the CoO/CFP electrode only requires 1.32 V to reach 10 mA cm−2, the potential is 120 mV lower than that for the Co3O4/CFP electrode. The CoO/CFP electrode can also produce value‐added products such as formate, acetate, and glycolate with high selectivity and efficiency at low energy consumptions from oxidation of biomass alcohols. Theoretical calculations further confirm the dominant role of octahedrally coordinated Co‐O sites in adsorption, activation, and oxidation of C3‐C1 alcohols. This work sheds light on the design of highly efficient transition metal oxide catalysts for oxidation of alcohols by populating octahedral sites in the crystal structure.

Advancements in catalysts for glycerol oxidation via photo-/electrocatalysis: a comprehensive review of recent developments

Photoelectrocatalytic and electrocatalytic oxidation of glycerol to valuable products relies on robust, highly active photo-/electrocatalysts. This review emphasizes glycerol conversion significance and recent advancements in its valorization.

Perovskite Supported Catalysts for the Selective Oxidation of Glycerol to Tartronic Acid

Exceptional selectivity of LaMnO3 perovskite supported Au catalysts for the oxidation of glycerol to the dicarboxylate tartronic acid is reported. Through using monometallic Au, Pt or bimetallic Au:Pt nanoparticles the tartronic acid yield could be altered significantly, with a maximum yield of 44% in 6 h with Au/LaMnO3 and 80% within 24 h. These LaMnO3 supported catalysts were compared with conventionally TiO2 supported catalysts, which at comparable reaction conditions produced lactic acid, via a dehydration pathway, in high yield and a maximum tartronic acid yield of only 9% was observed. The LaMnO3 catalysts produced minimal lactic acid regardless of the supported metal, showing that the support structure influences the prevalence of dehydration and oxidation pathways. The choice of metal nanoparticle influenced product selectivity along the oxidation pathway for both LaMnO3 and TiO2 supported catalysts. Au catalysts exhibited a higher selectivity to tartronic acid, whereas AuPt catalysts produced glyceric acid and Pt catalysts produced predominantly C–C scission products.Graphical

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.

Influence of the Acid Properties of the Support on Au‐Based Catalysts for Glycerol Oxidation in Aqueous Medium

AbstractTuning the surface and structural properties of heterogeneous catalysts is important for alcohol oxidation with the aim of obtaining valuable aldehydes and carboxylic acids. In this work, gold nanoparticles (AuNPs) were dispersed and stabilized on two different supports, ZrO2 and TiO2, and the catalytic properties were evaluated in glycerol oxidation as a model reaction. AuNPs were first synthesized through the reverse micelle (RMs) synthetic strategy, which acted as nanoreactor, by using sodium 1,4‐bis(2‐ethylhexyl) sulfosuccinate (AOT). For instance, the growing was governed by the confined environment provided by the AOT micelle allowing obtaining pseudospherical AuNPs with an average diameter of 6 nm. Further deposition of the synthesized AuNPs on ZrO2 and TiO2 supports allowed, after annealing at 400 °C, obtaining AuNPs on ZrO2 and TiO2. Catalytic properties of these AuNPs on glycerol oxidation under oxygen atmosphere and in aqueous NaOH solution at 90 °C, demonstrated that the support type played a key role in the activity of gold species in terms of conversion of glycerol and selectivity, with lactic acid being the main product formed on Au/ZrO2 while glyceraldehyde was the main product formed on Au/TiO2. The differences in catalytic performance of Au/ZrO2 might be correlated to a better dispersion of AuNPs and a higher density of acid sites with middle strength that modified activation of glycerol and the aldehyde intermediates toward the formation of lactic acid.

Support morphology effect on the selective oxidation of glycerol over AuPt/CeO2 catalysts

We synthesized a series of CeO2 with controllable morphologies including nanocube (NC), nanorod (NR), and nanopolyhedron (NP), enclosed by different facets, and then explored the support morphology effect on catalytic properties of Au1Pt3 catalysts in glycerol oxidation. As expected, the series of Au1Pt3/CeO2 catalysts exhibit a conspicuous support facet-dependent catalytic performance especially for the catalytic activity. Specifically, the TOF ranks in the order that Au1Pt3/NC (937.8 h−1) > Au1Pt3/NR (713.1 h−1) > Au1Pt3/NP (491.7 h−1). Among three catalysts, Au1Pt3/NC exhibits the most notable interaction strength due to the highest oxidizing capability of Ce6c–O2c sites on NC (1 0 0), confirmed by in situ CO FT-IR. In this case, Pt0 species are more easily oxidized to Pt2+. The strong metal–support interaction promotes the activation ability of oxygen, resulting in the generation of more reactive oxygen species including O2−, O22−, and O−, among which O2− is proved to be the most favorable species.

Reusable and active Pt@Co-NC catalysts for oxidation of glycerol

Exploring active Pt catalysts is essential both in academic and economic for glycerol oxidation. In this paper, a method for the synthesis of highly efficient Pt@Co-NC catalyst for glycerol oxidation was studied. Pt@Co-NC was synthesized by pyrolyzing the composite of Pt nanoparticles (NPs) encapsulated in ZIF-67 (Pt@ZIF-67). Transmission electron microscopy analysis showed that Pt existed in the form of PtCo NPs and PtCo alloys, and X-ray photoelectron spectra analysis demonstrated the interaction of Pt and Co-NC. These results indicated that the activity of Pt@Co-NC by this work was superior to that of Pt/Co-NC by conventional methods, including the polyol reduction method, galvanic replacement method, and sol-gel method. Pt@Co-NC was used five times without deactivation, suggesting its high reusability. The high reusability and activity of Pt@Co-NC were attributed to its structure caused by the synthetic methods. The pore confinement and the interaction of Pt and Co-NC played a key role in the high reusability and activity of Pt@Co-NC.

Ni–Co oxide catalysts with lattice distortions for enhanced oxidation of glycerol to glyceric acid

Developing cheap and highly efficient catalysts for the selective oxidation of glycerol to value-added carboxylic acids still remains a challenge. Here, non-noble-metal Ni–Co oxide catalysts with lattice distortions are reported for the first time as highly efficient and stable catalysts for the oxidation of glycerol to glyceric acid. The Ni1Co1Ox catalyst, prepared by a modified hard template method, exhibits superior activity (1.5 × 10−3 s−1), excellent glyceric acid selectivity (66.5%), and good stability under mild conditions (80 °C, 1 MPa O2). Multiple characterizations demonstrated that the nanosized Ni1Co1Ox catalyst (2.3 nm) contains lattice distortion Ni–Co structures with nickel-rich surfaces. This morphology induces electron transfer from Co cations (mainly Co3+) to Ni cations (mainly Ni3+), resulting in the generation of surface oxygen vacancies. Density functional theory calculations and catalytic kinetics demonstrated that oxygen vacancies on Co species could improve glyceric acid selectivity by preventing the cleavage of CC bond, and oxygen vacancies on the Ni species could promote the activation of CH bonds, which results in the exceptional catalytic performance of Ni1Co1Ox. The novel Ni–Co oxide catalyst with lattice distortions synthesized here may provide some guidance for the rational design of inexpensive and highly efficient catalysts for the catalytic oxidation of biopolyols.

The effects of calcination temperature of support on Au/CuO-ZrO2 catalysts for oxidation of glycerol to dihydroxyacetone

Dihydroxyacetone (DHA) is a fine chemical and has been widely used in the cosmetics industry. In this work, DHA was synthesized with high selectivity over Au catalysts, also supported by Cu-Zr mixed oxide calcined at different temperatures. The effects of the calcination temperature of supports on the properties and catalytic performance for glycerol oxidation to dihydroxyacetone were also studied. BET and CO2-TPD measurements demonstrated that the increase in the support calcination temperature reduced the specific surface area of the catalyst and further reduced the surface basic sites of the catalysts. With increased support calcination temperature, the surface content of Au0 and the dispersion of Au first increase until the calcination temperature of the support was 600 °C and then decrease. It was also observed that the glycerol conversion is positively correlated with the surface content of Au0 and the dispersion of Au, while upon the increase of the amount of the basic sites, the catalytic activity increases first and then decreases. The suitable support calcination temperature is beneficial for the conversion of glycerol, and the best catalytic performance is obtained when the calcination temperature is 600 °C.

The effect of oxygen vacancies in ZnO at an Au/ZnO interface on its catalytic selective oxidation of glycerol

In catalytic reactions, the nature of the support has a major effect on the formation of active sites, especially in the case of catalysts with strong metal–support interactions. Two types of ZnO with different concentrations of oxygen vacancies (ZnO-U, produced by a hydrothermal procedure using urea, and ZnO-C, produced by a precipitation method using sodium carbonate) have been prepared and employed as supports for Au catalysts. The results of O1s X-ray photoelectron spectroscopy and positron annihilation spectroscopy showed that ZnO-U has fewer oxygen vacancies than ZnO-C. After the materials were loaded with Au, the formation of an Au/ZnO interface was demonstrated by high-resolution transmission electron microscopy, Raman spectroscopy, and Fourier transform infrared spectroscopy. Electron paramagnetic resonance spectroscopy and Au4f X-ray photoelectron spectroscopy showed that the formation of the materials involved electron transfer from Au to the ZnO support, resulting in the formation of positively charged Au species. A close correlation between the formation of the interface and the level of oxygen vacancies in the ZnO support was observed: low oxygen-vacancy concentrations result in an increase in the work function of ZnO, which facilitates electron transfer and makes the formation of the Au/ZnO interface more thermodynamically favorable. When they are used as catalysts in glycerol oxidation, the TOF of Au/ZnO-U (1159 h−1) was 1.47 times higher than that of Au/ZnO-C (786 h−1). The higher activity of Au/ZnO-U can be attributed to the abundance of positively charged Au sites, which strengthen the surface coverage of OH* and then promote H abstraction from an O–H bond in glycerol.

Factors affecting the activity and selectivity of niobia-based gold catalysts in liquid phase glycerol oxidation

Abstract The present study aims at the elucidation of the influence of niobia crystallinity, gold deposition method and the presence of copper dopant on the activity and selectivity of niobia supported gold catalysts in liquid phase oxidation of glycerol. The role of niobium pentoxide crystallinity was estimated with the use of gold catalysts supported on three different niobia supports but prepared by the same gold loading method, while the influence of gold deposition method and the presence of copper promoter were studied using mono- (Au, Cu) and bimetallic (AuCu) catalysts supported on the same niobia support but synthesized using different metal loading methods. The activity of the catalysts in glycerol oxidation was tested under different reaction conditions, i.e. different reaction time and various concentrations of sodium hydroxide as a base. Detailed analysis of relationship between the properties of catalysts and their activity/selectivity in glycerol oxidation considered in this study showed that niobia crystallinity had negligible influence on the activity of gold catalysts containing small metal nanoparticles with the size of ca. 5 nm. Furthermore, it was documented that copper species in the bimetallic AuCu catalyst play double roles. Firstly, copper acts as a structural promoter which enhances the dispersion of the active phase, and thus enables high activity in glycerol oxidation. Secondly, copper itself promotes the C C bond cleavage during glycerol oxidation. It was found that the bimetallic catalyst was much more selective to glycolic and formic acids than the monometallic gold catalyst, despite the fact that both catalysts contained gold particles of similar average size of ca. 5 nm. This observation allowed drawing the conclusion that the changes in selectivity of the bimetallic AuCu sample did not result from different size of gold nanoparticles, but were more likely to be related to the presence of copper dopant which improved the catalyst ability to C C bond cleavage.

Enhanced performance of bimetallic PtCo/MCM-41 catalysts for glycerol oxidation in base-free medium

Optimizing the electronic coupling in heterogeneous catalysts by tuning metal–metal interactions remains a significant challenge.

The Enhanced Catalytic Performance and Stability of Ordered Mesoporous Carbon Supported Nano-Gold with High Structural Integrity for Glycerol Oxidation.

Ordered mesoporous carbon (OMC) supported gold nanoparticles of size 3-4 nm having uniform dispersion were synthesized by sol-immobilization method. OMCs such as CMK-3 and NCCR-56 with high surface area and uniform pore size were obtained, respectively, using ordered mesoporous silicas such as SBA-15 and IITM-56 as hard templates, respectively. The resulting OMC supported monodispersed nano-gold, i. e., Au/CMK-3 and Au/NCCR-56, exhibited excellent performance as mild-oxidizing catalysts for oxidation of glycerol with high hydrothermal stability. Further, unlike activated carbon supported nano-gold catalysts (Au/AC), the OMC supported nano-gold catalysts, i. e., Au/CMK-3 and Au/NCCR-56, show no aggregation of active species even after recycling. Thus, in the case of Au/CMK-3 and Au/NCCR-56, both the fresh and regenerated catalysts showed excellent performane for the chosen reaction owing to an enhanced textural integrity of the catalysts and that with remarkable selectivity towards glyceric acid. The significance of the OMC supports in maintaining the dispersion of gold nanoparticles is explicit from this study, and that the activity of Au/AC catalyst is considerably decreased (∼50 %) upon recycling as a result of agglomeration of the active gold nanoparticles over the disordered amorphous carbon matrix.

Au Supported TiO<sub>2</sub>-Nanofibers as Novel Catalysts for Glycerol Oxidation

Composites of Au supported on the TiO2-nanofibers (Au/NF-TiO2) were synthesized and tested in glycerol oxidation processes. TiO2-nanofibers were prepared by a microwave-assisted hydrothermal synthesis method. Chemical deposition method was used for nanofibers modification with Au nanoparticles. Oxidation of aqueous glycerol solutions by molecular oxygen in the presence of Au/NF-TiO2 nanocomposites was performed. It was found that Au/NF-TiO2 composites are catalytically active in alkaline glycerol water solutions. The main product of glycerol catalytic oxidation was glyceric acid, by-products were – tartronic, lactic, glycolic, oxalic, acetic and formic acid. It was shown that Au/NF-TiO2 catalysts’ activity and selectivity depend on Au weight loading, glycerol/Au molar ratio, oxygen pressure and NaOH initial concentration. The best result was achieved using the 0.5 wt%Au/NF-TiO2 catalyst: selectivity by glyceric acid was 76% with glycerol conversion 100%.

NiO and CoO<sub>x</sub> Promoted Pt Catalysts for Glycerol Oxidation

Two kinds of Pt/CeO2 catalysts supplemented with NiO or CoOx additives were synthesized by extractive-pyrolytic method and tested in glycerol oxidation processes. It was found that only NiO additive promotes Pt/CeO2 catalysts activity and selectivity to glyceric acid. NiO promoted Pt catalysts activity depends on NiO composites’ calcination temperature, oxygen partial pressure, initial NaOH concentration, as well as temperature. Glycerol conversion increases along with increased oxygen partial pressure from1 to 6 atm and along with decreased glycerol/Pt molar ratio from 5000 to 300. It was found that presence of base is significant in the glycerol oxidation processes over NiO promoted Pt/CeO2 catalysts, and optional NaOH initial concentration is 0.6 mol/L. The best yield of glyceric acid (68%) was reached in the presence of 4.8wt%Pt/5wt%NiO/CeO2 (300 °C) catalyst, when temperature was elevated up to 70 °C.

Enhanced photoelectrochemical activity of Nickel-phosphate decorated phosphate-Fe2O3 photoanode for glycerol-based fuel cell

The nickel-phosphate decorated phosphate-Fe2O3 photoanode (NiPi/Pi-Fe2O3) was fabricated by coating phosphate modified hematite (Pi-Fe2O3) with naturally abundant nickel-phosphate complexes (NiPi). X-ray powder diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy studies showed that NiPi was uniformly distributed on Pi-Fe2O3 surface as amorphous form. With the decoration of NiPi, the photocurrent of Pi-Fe2O3 was enhanced by ca. 2 times at 1.5V (vs. RHE). The NiPi/Pi-Fe2O3 also exhibited higher maximum power generation in photoelectrochemical (PEC) glycerol-based fuel cell, which was ca. 2.4 times than that of Pi-Fe2O3. Electrochemical impedance spectroscopy analysis revealed the charge transfer resistance at the interface of Pi-Fe2O3/electrolyte was remarkably decreased by NiPi decoration. NiPi was believed to be not only a hole-conductor that promoting the charge separation but also a catalyst for glycerol oxidation through cyclic changes between the lower and the higher oxidation states of Ni, which were the main reasons for the enhanced PEC response and power generation. The intermediates from glycerol were verified using high performance liquid chromatography, indicating the efficient cleavage of C-C bonds in glycerol on NiPi/Pi-Fe2O3. This work demonstrates NiPi/Pi-Fe2O3 has great potential in PEC fuel cells for the generation of electricity from light energy and biomass energy.

Pt supported TiO2-nanofibers and TiO2-nanopowder as catalysts for glycerol oxidation

Novel TiO2 nanofiber supported platinum catalysts Pt/NF–TiO2 were synthesized and compared with TiO2 nanopowder supported catalysts Pt/NP–TiO2 in selective glycerol oxidation. It was found that Pt/NF–TiO2 and Pt/NP–TiO2 composites are catalytically active in alkaline glycerol solutions; glyceric acid is obtained as the main product of reaction. Catalyst activity and selectivity dependency on NaOH initial concentration, oxygen pressure and n(glycerol)/n(Pt) ratio were studied. Selectivity to glyceric acid of 63 % with full glycerol conversion and selectivity of 68 % with 95 % glycerol conversion is obtained correspondingly over Pt/NF–TiO2 and Pt/NP–TiO2 catalysts.

Selective Oxidation of Glycerol to Glyceric Acid in Base‐Free Aqueous Solution at Room Temperature Catalyzed by Platinum Supported on Carbon Activated with Potassium Hydroxide

AbstractPt supported on KOH‐activated mesoporous carbon (K‐AMC) was used to catalyze glycerol oxidation under base‐free conditions at room temperature. To study the relationship between the carbon surface chemistry and the catalytic performance of the K‐AMC‐based Pt catalysts, different levels of surface oxygen functional groups (SOFGs) on the AMC supports were induced by thermal treatment at different temperatures under inert or H2 gas. A strong effect of the surface chemistry was observed on AMC‐supported Pt catalysts for glycerol oxidation. The presence of carboxylic acid groups impedes the adsorption of glycerol, which leads to the reduction of catalytic activity, whereas the presence of high‐desorption‐temperature SOFGs, such as phenol, ether, and carbonyl/quinone groups, provide hydrophilicity to the carbon surface that improves the adsorption of glycerol molecules on Pt metal surface, which is beneficial for the catalytic activity.

PdSn alloy supported on phenanthroline-functionalized carbon as highly active electrocatalysts for glycerol oxidation

Functionalized carbon is an effective material to immobilize nanoparticles for producing high efficient electrocatalysts. In this paper, phenanthroline is used to direct functionalize carbon (phen-C), and different molar ratios of PdSn (Pd:Sn = 1:1–1:3) nanoparticles are deposited subsequently. According to the electrochemical results, the Pd3Sn/phen-C catalyst has the largest electrochemically active surface area (577.2 cm2 mg−1Pd), best activity and stability among as-prepared PdxSny/phen-C, Pd/phen-C and Pd/C catalysts for glycerol oxidation. Furthermore, the durability and poisoning tolerance of Pd3Sn/phen-C are also superior to that of Pd/C. The Pd3Sn/phen-C would be a potential electrocatalyst for glycerol oxidation.

Insight into effect of acid/base nature of supports on selectivity of glycerol oxidation over supported Au-Pt bimetallic catalysts

Au-Pt bimetallic catalysts were supported on different supports, including acidic (TiO2 and CeO2), basic (MgO, Mg(OH)2, (MgCO3)4Mg(OH)2, ZnO, and CaCO3), and amphoteric (Al2O3 and hydrotalcite) supports with the aim to study the effect of the acid/base properties of supports upon the performance of Au-Pt bimetallic catalysts in glycerol oxidation. The results showed that these properties significantly affected the selectivity of products. The selectivity to glyceraldehyde was inversely proportional to the strength of supports’ basic sites, and the selectivity to tartronic acid (or glycolic acid, or glyoxalic acid) was proportional to the strength of basic sites. In contrast, the selectivity to glyceric acid was neither proportional to the strength of basic sites nor proportional to the strength of acid sites. The doping of another weaker basic site also affected the selectivity to glyceric acid. Furthermore, the role of the acid/base nature of the supports in affecting the products’ distribution is proposed.