Ethylene glycol, 2-propanol electrooxidation in alkaline medium on the ordered intermetallic PtPb surface

The ethylene glycol and 2-propanol electrooxidation reaction was studied on carbon dispersed ordered intermetallic PtPb nanocatalysts in KOH solution. X-ray diffraction and X-ray photoelectron spectroscopy were used to characterize ordered intermetallic PtPb/C catalysts. The electrochemical behaviors for the ethylene glycol and 2-propanol electrooxidation reaction were measured in a thin film electrode by cyclic voltammetry, Tafel curves and electrochemical impedance spectroscopy. The results showed that in contrast with PtRu/C and Pt/C catalyst, ordered intermetallic PtPb/C had better electroactivity, and kinetic mechanism of PtPb/C is complex. Although the activity of electrocatalysts depends on many factors, such as modification of geometric and electronic structure by Pt-Pb interaction, crystalline size and so on. But the key factor for each electrooxidation reaction was different. For ethylene glycol electrooxidation, the effect of formation and desorption of poisonous species on activity of catalyst was very significant. For 2-propanol electrooxidation, the modification of geometric and electronic structures may be play a decisive role in the enhance activity of electrocatalyst.     

Oxide (CeO2, NiO, Co3O4 and Mn3O4)-promoted Pd/C electrocatalysts for alcohol electrooxidation in alkaline media

This study investigated Pt/C, Pd/C and oxide (CeO₂, NiO, Co₃O₄ and Mn₃O₄)-promoted Pd/C for electrooxidation reactions of methanol, ethanol, ethylene glycol and glycerol in alkaline media. The results show that Pd/C electrocatalysts alone have low activity and very poor stability for the alcohol electrooxidation. However, addition of oxides like CeO₂, NiO, Co₃O₄ and Mn₃O₄ significantly promotes catalytic activity and stability of the Pd/C electrocatalysts for the alcohol electrooxidation. The Pd-Co₃O₄ (2:1, w:w)/C shows the highest activity for the electrooxidation of methanol, EG and glycerol while the most active catalyst for the ethanol electrooxidation is Pd-NiO (6:1, w:w)/C. On the other hand, Pd-Mn₃O₄/C shows significantly better performance stability than other oxide-promoted Pd/C for the alcohol electrooxidation. The poor stability of the Pd-Co₃O₄/C electrocatalysts is most likely related to the limited solubility of cobalt oxides in alkaline solutions.     

Electrochemical performance for the electro-oxidation of ethylene glycol on a carbon-supported platinum catalyst at intermediate temperature

To determine the kinetic performance of the electro-oxidation of a polyalcohol operating at relatively high temperatures, direct electrochemical oxidation of ethylene glycol on a carbon supported platinum catalyst (Pt/C) was investigated at intermediate temperatures (235–255 °C) using a single cell fabricated with a proton-conducting solid electrolyte, CsH₂PO₄, which has high proton conductivity (>10⁻² S cm⁻¹) in the intermediate temperature region. A high oxidation current density was observed, comparable to that for methanol electro-oxidation and also higher than that for ethanol electro-oxidation. The main products of ethylene glycol electro-oxidation were H₂, CO₂, CO and a small amount of CH₄ formation was also observed. On the other hand, the amounts of C₂ products such as acetaldehyde, acetic acid and glycolaldehyde were quite small and were lower by about two orders of magnitude than the gaseous reaction products. This clearly shows that C–C bond dissociation proceeds almost to completion at intermediate temperatures and the dissociation ratio reached a value above 95%. The present observations and kinetic analysis suggest the effective application of direct alcohol fuel cells operating at intermediate temperatures and indicate the possibility of total oxidation of alcohol fuels.     

A remarkable activity of glycerol electrooxidation on gold in alkaline medium

In this paper, the activity and stability of glycerol oxidation on Au electrode have been investigated by cyclic voltametry, chronoamperometry and chronopotentiometry methods in alkaline medium. The glycerol shows a remarkable activity and better performance than methanol, ethanol, n-propanol, isopropanol and ethylene glycol on the Au electrode in alkaline medium. The activity and stability of glycerol oxidation on the Au electrode are higher than that of glycerol oxidation on Pd electrode. The stability of glycerol oxidation on the Au electrode is higher than that of methanol and glycerol oxidation on Pt electrode. The results show that glycerol is an excellent fuel applied in direct alcohol fuel cells with Au as anode catalyst.     

Effect of electrochemical polarization of PtRu/C catalysts on methanol electrooxidation

To determine the influence of electrochemical polarization of PtRu/C catalysts on methanol electrooxidation, this work investigated methanol electrooxidation on as received and different electrochemically polarized PtRu/C catalysts. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) were used to characterize the redox state of PtRu/C after different electrochemical polarization. The methanol electrooxidation activity was measured by cyclic voltammetry (CV), Tafel steady state plot and electrochemical impedance spectroscopy (EIS). The results indicate that the metallic state Pt⁰Ru⁰ can be formed during cathodic polarization and contribute to electrooxidation of methanol, while the formation of inactive ruthenium oxides during anodic polarization cause the negative effect on methanol electrooxidation. Different Tafel slopes and impedance behaviors in different potential regions also reveal a change of the mechanism and rate-determining step in methanol electrooxidation with increasing potentials. The kinetic analysis from Tafel plots and EIS reveal that at low potentials indicate the splitting of the first CH bond of CH₃OH molecule with the first electron transfer is rate-determining step. However, at higher potentials, the oxidation reaction of adsorbed intermediate CO_ads becomes rate-determining step.     

Electrocatalytic oxidation of aliphatic alcohols: Application to the direct alcohol fuel cell (DAFC)

The electrooxidation of some low molecular weight alcohols, such as ethanol, ethylene glycol and n-propanol, is discussed in terms of reaction mechanisms and catalytic activity of the anode material. Some examples of a single cell, using a proton exchange membrane (PEM) as electrolyte, are given to illustrate interesting results, particularly for the direct electrooxidation of ethanol. This alcohol may replace methanol in a direct alcohol fuel cell.     

Catalysed titanium mesh electrodes for ethylene glycol fuel cells

Electrodes comprising thermally deposited Pt, PtRu and PtRuW on titanium mesh were evaluated for the oxidation of ethylene glycol in acidic electrolyte. The electrodes were characterised using cyclic voltammetry, scanning electron microscopy and X-ray diffraction and the effect of reactant concentration and temperature were examined. Single fuel cell tests employing the titanium mesh anode with the PtRuW catalyst showed better performance than that of the PtRu catalyst. A peak power density of 15 mW cm⁻² was obtained at a temperature of 90 °C with 1.0 M ethylene glycol solution. The performance of the catalysed PtRu mesh electrode was comparable to that of a commercial, alcohol oxidation, PtRu carbon supported catalyst.     

Polyol synthesis of highly active PtRu/C catalyst with high metal loading

Highly loaded PtRu/C catalyst with high activity toward methanol electrooxidation was synthesized via a modified polyol process. XRD patterns indicated that the prepared catalyst was highly alloyed and TEM results showed that the metal nanoparticles were small and uniformly distributed on the carbon support despite the high metal loading. EDX results suggested that the two metals distributed uniformly in the catalyst. Electrochemical characterization and single cell test jointly showed that the prepared 40-20 wt.%PtRu/C catalyst possessed high activity toward methanol electrooxidation.     

Pt-CeO2/C anode catalyst for direct methanol fuel cells

In order to develop a cheaper and durable catalyst for methanol electrooxidation reaction, ceria (CeO₂) as a co-catalytic material with Pt on carbon was investigated with an aim of replacing Ru in PtRu/C which is considered as prominent anode catalyst till date. A series of Pt-CeO₂/C catalysts with various compositions of ceria, viz. 40 wt% Pt-3–12 wt% CeO₂/C and PtRu/C were synthesized by wet impregnation method. Electrocatalytic activities of these catalysts for methanol oxidation were examined by cyclic voltammetry and chronoamperometry techniques and it is found that 40 wt% Pt-9 wt% CeO₂/C catalyst exhibited a better activity and stability than did the unmodified Pt/C catalyst. Hence, we explore the possibility of employing Pt-CeO₂ as an electrocatalyst for methanol oxidation. The physicochemical characterizations of the catalysts were carried out by using Brunauer Emmett Teller (BET) surface area and pore size distribution (PSD) measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. A tentative mechanism is proposed for a possible role of ceria as a co-catalyst in Pt/C system for methanol electrooxidation.     

Selective hydrogenolysis of glycerol to propylene glycol on Cu–ZnO catalysts

Hydrogenolysis of biomass-derived glycerol is an alternative route to sustainable production of propylene glycol. Cu–ZnO catalysts were prepared by coprecipitation with a range of Cu/Zn atomic ratio (0.6–2.0) and examined in glycerol hydrogenolysis to propylene glycol at 453–513 K and 4.2 MPa H₂. These catalysts possess acid and hydrogenation sites required for bifunctional glycerol reaction pathways, most likely involving glycerol dehydration to acetol and glycidol intermediates on acidic ZnO surfaces, and their subsequent hydrogenation on Cu surfaces. Glycerol hydrogenolysis conversions and selectivities depend on Cu and ZnO particle sizes. Smaller ZnO and Cu domains led to higher conversions and propylene glycol selectivities, respectively. A high propylene glycol selectivity (83.6%), with a 94.3% combined selectivity to propylene glycol and ethylene glycol (also a valuable product) was achieved at 22.5% glycerol conversion at 473 K on Cu–ZnO (Cu/Zn = 1.0) with relatively small Cu particles. Reaction temperature effects showed that optimal temperatures (e.g. 493 K) are required for high propylene glycol selectivities, probably as a result of optimized adsorption and transformation of the reaction intermediates on the catalyst surfaces. These preliminary results provide guidance for the synthesis of more efficient Cu–ZnO catalysts and for the optimization of reaction parameters for selective glycerol hydrogenolysis to produce propylene glycol.     

Pt-CeO2/C anode catalyst for direct methanol fuel cells

In order to develop a cheaper and durable catalyst for methanol electrooxidation reaction, ceria (CeO₂) as a co-catalytic material with Pt on carbon was investigated with an aim of replacing Ru in PtRu/C which is considered as prominent anode catalyst till date. A series of Pt-CeO₂/C catalysts with various compositions of ceria, viz. 40 wt% Pt-3–12 wt% CeO₂/C and PtRu/C were synthesized by wet impregnation method. Electrocatalytic activities of these catalysts for methanol oxidation were examined by cyclic voltammetry and chronoamperometry techniques and it is found that 40 wt% Pt-9 wt% CeO₂/C catalyst exhibited a better activity and stability than did the unmodified Pt/C catalyst. Hence, we explore the possibility of employing Pt-CeO₂ as an electrocatalyst for methanol oxidation. The physicochemical characterizations of the catalysts were carried out by using Brunauer Emmett Teller (BET) surface area and pore size distribution (PSD) measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) techniques. A tentative mechanism is proposed for a possible role of ceria as a co-catalyst in Pt/C system for methanol electrooxidation.     

Influence of ethylene glycol,ethanol and formic acid on platinum and ruthenium electrodeposition on carbon support material

Carbon supported Pt–Ru catalysts were prepared by potentiostatic deposition at −0.5 V from H₂PtCl₆ + RuCl₃ in H₂SO₄ solution in the presence of ethylene glycol (EG), ethanol (EtOH) and formic acid (HCOOH) as stabilizing agents. The active surface area of the Pt–Ru catalyst was determined by Cu-UPD. The highest value was obtained with HCOOH added, followed by EtOH, and EG. SEM and AFM images showed that the mean particle size of the Pt–Ru nanoparticles was three or four times smaller in the presence of a stabilizer. Electrocatalytic activity measurements indicated that the most active electrode for methanol electrooxidation was obtained with EtOH as additive, followed by EG. The electrode prepared with HCOOH additive gave lower catalytic activity than that without stabilizing agent.     

Catalytic Oxidation of Polyethylene Glycol Dodecyl Ether to Corresponding Carboxylic Acid by Gold, Palladium (Mono and Bimetallic) Nanoparticles Supported on Carbon

Mono and bimetallic catalysts based on Au and Pd nanoparticles were synthesized by sol immobilization method. The catalytic oxidation of polyethylene glycol dodecyl ether was performed using as-synthesized supported catalyst. The use of water as solvent and dioxygen as oxidant makes the reaction interesting from both an economic and environmental point of view. For 100 min, the conversion of polyethylene glycol dodecyl ether using Au–Pd/C bimetallic catalyst was 38%, showing an increase of 9% for Au/C and 15% for Pd/C respectively indicating that a synergetic effect exists between Au and Pd. For the Au–Pd/C catalyst, adding Au after the prior addition and reduction of Pd metal can form the most active catalyst.     

A General Protocol for the Synthesis of Pt–Sn/C Catalysts for the Ethanol Electrooxidation Reaction

A general protocol for the synthesis of Pt–Sn/C catalysts for ethanol electrooxidation by the polyol method is developed after a systematic variation of the preparation variables. This protocol enables the complete transfer of all catalytic elements in the preparation solution to the catalyst support; thereby providing a convenient means of catalyst composition control. Water is a necessary co‐solvent for ethylene glycol in the polyol synthesis of Pt–Sn/C catalysts. The best preparation medium for controlling the particle size to small sizes is 0.1 M NaOH solution in a mixture of equal volumes of water and ethylene glycol. With this medium composition Pt–Sn/C catalysts with the optimized target Pt:Sn atomic ratio of 3:1 could be expeditiously prepared for ethanol electrooxidation.     

Synergistic effect of CeO2 modified Pt/C catalysts on the alcohols oxidation

The effect of the addition of CeO₂ to Pt/C catalysts on electrochemical oxidation of alcohols (methanol, ethanol, glycerol, ethylene glycol) was studied in alkaline solution. The ratios of Pt to CeO₂ in the catalysts were optimised to give the better performance. The electrochemical measurements revealed that the addition of CeO₂ into Pt-CeO₂/C catalysts could significantly improve the electrode performance for alcohols oxidation, in terms of the reaction activity and the poisoning resistance, due to the synergistic effect. The electrode with the weight ratio of Pt to CeO₂ equals 1.3:1 with platinum loading of 0.30 mg/cm² showed the highest catalytic activity for oxidation of ethanol, glycerol and ethylene glycol.     

Enhanced electrooxidation of methanol,ethylene glycol,glycerol, and xylitol over a polypyrrole/manganese oxyhydroxide/palladium nanocomposite electrode

A small quantity of palladium metal (Pd, 5 wt%) nanoparticles supported by a polypyrrole/manganese oxyhydroxide (PPy/MOH) nanocomposite was developed and investigated as an electrocatalyst for the alcohol electrooxidation reaction in alkaline media. In voltammetric studies, the PPy/MOH/Pd catalyst, compared to C/Pd, exhibited improved electrocatalytic activity for methanol electrooxidation. The peak current density ratios (j ^f/j ^b) for the C/Pd and PPy/MOH/Pd nanocomposite electrodes were 0.67 and 2.43, respectively, indicating that the PPy/MOH/Pd nanocomposite electrode was much more resistant to catalytic poisoning. The electrooxidation of ethylene glycol (EG), glycerol, and xylitol was also tested using the PPy/MOH/Pd nanocomposite electrode. Among these alcohol electrooxidations, that of EG exhibited the maximum power density of 430 mA cm^?2. The intermediates formed during the electrooxidation reactions were removed by increasing the upper sweep potential from +0.2 to +1.0 V. The catalytic performance of the PPy/MOH nanocomposite is discussed in detail. The study results demonstrate that PPy/MOH acts as a superior catalytic supporting material for alcohol electrooxidation reactions in alkaline media.     

Molecular surface science of C–H bond activation and polymerization catalysis

Surface science studies of heterogeneous catalysis use model systems ranging from single crystals to monodispersed nanoparticles in the 1–10 nm range. Molecular studies reveal that bond activation (C–H, H–H, C–C, C≡O) occurs at 300 K or below as the active metal sites simultaneously restructure. The strongly adsorbed molecules must be mobile to free up these sites for continued turnover of reaction. Oxide–metal interfaces are also active for catalytic turnover. Examples using C–H and C = O activation are described to demonstrate these properties. Polymerization catalysis demonstrates a strong dependence upon catalyst surface structure, which allows for the selectivity to be tuned by the choice of Ziegler-Natta surface preparation. Novel preparation methods of model catalyst arrays in two and three dimensions are opening the door to a complete understanding of catalytic reaction selectivity.     

Synthesis of ethylene and propylene on a SAPO-34 silica—alumina—phosphate catalyst

A process for the preparation of ethylene and propylene from methanol on a microporous silica—alumina—phosphate SAPO-34 catalyst is described. The influence of the temperature and the nature and concentration of the diluting agent on the catalyst activity, its selectivity with respect to C₂₌-C₄₌ olefins, and ability to be regenerated were studied. The SAPO-34 catalyst was shown to be highly effective in the selectivity of ethylene and propylene formation; the total yield of C₂₌-C₄₌ olefins at 350–450°C was 77–84% and methanol conversion was up to 96–99%. In the conversion of methanol under helium at 450°C, the yield of ethylene (∼36%) was higher than at 375°C (∼29%), while the yield of propylene (∼30%) was lower (∼38%). The use of water and helium vapors as a diluent increased the yield of ethylene to ∼36% at 375°C and to ∼50% at 450°C. In the conversion of methanol at 450°C in water vapors without helium, the yield of ethylene reached ∼44–49% and the yield of propylene was 24–29%. The C₃₌ to C₂₌ ratio in the process varied from ∼0.5 to 1.5. The high efficiency of the SAPO-34 catalyst is the consequence of the microporous structure of zeolite and the high content of acid centers of medium strength. In the course of methanol conversion, the catalyst was deactivated due to coking. After regeneration with air at 550°C, the catalyst activity was completely restored, while the crystal structure and the acid properties did not change. The activity of the catalyst in a cycle is prolonged if water vapors are used as a diluent and the catalyst is processed at a high temperature with vapors. The industrial processes for the production of ethylene and propylene from nonpetroleum materials are not used in Russia. The results of this study are comparable to the data obtained from the UOP/Norsk Hydro process on the SAPO-34 catalyst. The catalyst can be recommended for further trials on an FCC type pilot plant with a moving catalyst bed.     

Synthesis of well-dispersed PtRuSnOx by ultrasonic-assisted chemical reduction and its property for methanol electrooxidation

PtRuSnO_x supported on multi-wall carbon nanotubes (MWCNTs) was prepared by ultrasonic-assisted chemical reduction method. The as-prepared catalyst was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The XRD patterns indicate that Pt exists as the face-centered cubic structure, Ru is alloyed with platinum, while non-noble metal oxide SnO_x exists as an amorphous state. From TEM observation, PtRuSnO_x is well dispersed on the surface of MWCNTs with the particle size of several nanometers. The electrochemical properties of the as-prepared catalyst for methanol electrooxidation were studied by cyclic voltammetry (CV) and chronoamperometry (CA). The onset potential of methanol oxidation on PtRuSnO_x and PtRu catalysts is much more negative than that on Pt catalyst, shifting negatively by about 0.20 V, while the peak current density of methanol oxidation on PtRuSnO_x is higher than that on PtRu. Electrochemical impedance spectroscopy (EIS) studies also show that the reaction kinetics of methanol oxidation is improved with the presence of SnO_x. The addition of non-noble metal oxide SnO_x to PtRu promotes the catalytic activity for methanol electrooxidation and the possible reaction mechanism is proposed.     

Adsorption and decomposition of ethanol on supported Au catalysts

The adsorption and reactions of ethanol are investigated on Au nanoparticles supported by various oxides and carbon Norit. The catalysts are characterized by means of XPS. Infrared spectroscopic studies reveal the dissociation of ethanol to ethoxy species at 300 K on all the oxidic supports. The role of Au is manifested in the enhanced formation of ethoxy species on Au/SiO₂, and in increased amounts of desorbed products in the TPD spectra. The supported Au particles mainly catalyse the dehydrogenation of ethanol, to produce hydrogen and acetaldehyde. An exception is Au/Al₂O₃, where the main process is dehydration to yield ethylene and dimethyl ether. C–C bond cleavage occurs to only a limited extent on all samples. As regards to the production of hydrogen, the most effective catalyst is Au/CeO₂, followed by Au/SiO₂, Au/Norit, Au/TiO₂ and Au/MgO. A fraction of acetaldehyde formed in the primary process on Au/CeO₂ is converted above 623 K into 2-pentanone and 3-penten-2-one. The decomposition of ethanol on Au/CeO₂ follows first-order kinetics. The activation energy of this process is 57.0 kJ/mol. No deactivation of Au/CeO₂ is observed during 10 h at 623 K. It is assumed that the interface between Au and partially reduced CeO₂ is responsible for the high activity of the Au/CeO₂ catalyst.