Electrooxidation Of Acetaldehyde Research Articles

Analysis of Reaction Rate and Product Selectivity of Ethanol Electrolytic Oxidation Reaction in the Flow Reactor

Introduction In recent years, the development of the electrolysis hydrogen production process has been vigorously promoted due to the widespread use of hydrogen energy. However, oxygen, a byproduct of the anode reaction, has not been utilized. On the other hand, chemical products are produced industrially by electro-organic synthesis, and if the anode reaction could be used directly as a chemical synthesis reaction, the overall benefit would be further enhanced. At the same time, the high selectivity and controllability of the electrochemical process make it possible to produce highly selective chemical products by anodic reactions. The objective of this study is to develop a process for simultaneous electrolytic hydrogen production at the cathode and highly selective acetaldehyde production at the anode. Experimental A schematic diagram of the experimental setup is shown in Figs. 1 and 2. Platinum electrodes were placed on silicone gaskets with flow channels, and the gaskets were sandwiched between silicone gaskets, PTFE plates, and stainless-steel endplates. A cation exchange membrane NR-212 was placed in the center to separate the reactions at the two electrodes. A 0 to 0.5 mol/L sulfuric acid solution containing 0.01 to 1.0 mol/L ethanol or a 0 to 0.5 mol/L sulfuric acid solution containing 0.01 to 1.0 mol/L acetaldehyde was supplied to the anode, and a 0 to 0.5 mol/L sulfuric acid solution was supplied to the cathode. Results and Discussion The experimental results are analyzed based on the premise of surface reaction rate limitation and steady-state conditions. As shown in Fig. 3, the ethanol conversion increased with rise in A/v (ratio of electrode area to flow rate), reaching its maximum value at A/v of 88.4 min/cm. This can be attributed to the difficulty in discharging bubbles generated from the electro-oxidation reaction as the A/v was raised. To ensure that the reactions occurred under reaction rate-limiting conditions, acetaldehyde electro-oxidation experiments were conducted with feed concentrations of 0 to 0.5 M sulfuric acid solutions containing 1.0 M acetaldehyde at the anode, and 0 to 0.5 M sulfuric acid solutions at the cathode, an A/v of 88.4 min/cm, and a potential difference of 1.0 V. The reaction rate was also affected by the reduction in the hydroxide ion concentration due to the increased sulfuric acid concentration, leading to the lower measured reaction rates. In the result of Fig. 4, it can be inferred that when the concentration of sulfuric acid was below 0.1 M, the reaction rate was governed by diffusion. Subsequently, acetaldehyde electro-oxidation experiments were performed under acetaldehyde concentrations ranging from 0.01 to 1 M, a sulfuric acid concentration of 0.1 M, the fixed A/v, and potential differences between 0.8 and 1.2 V to elucidate the impact of reactant concentration on the reaction rate. The results in Fig. 5 demonstrate that while the reaction rates increased with raising the acetaldehyde concentration, it eventually approached a plateau, attributable to the saturation of active sites with acetaldehyde on the Pt electrode.The results of ethanol electro-oxidation experiments were shown in Figs. 6 and 7, decrease in acetaldehyde selectivity was observed with a feed concentration of a 0.1 M sulfuric acid solution, attributable to the formation of acetic acid and carbon dioxide as byproducts. Subsequently, in comparison to sulfuric acid concentrations below 0.2 M, under the conditions of 0.5 M sulfuric acid concentration and low conversion, the acetaldehyde selectivity exhibited a gradual decline as the conversion increased. This indicates that the influence of sulfuric acid concentration on the oxidation reaction of acetaldehyde to acetic acid was more significant than that on the oxidation reaction of ethanol to acetaldehyde. A plausible explanation for this phenomenon is that the oxidation of acetaldehyde is considerably inhibited by the adsorption of sulfate ions to the active sites, as it is associated with a second-order reaction of adsorbed species concentration. Consequently, altering the sulfuric acid concentration results in changes in the ethanol electro-oxidation reaction selectivity. Conclusions The selectivity of ethanol electro-oxidation reaction was significantly influenced by potential difference and electrolyte concentration. Notably, acetic acid was not produced at potential differences below 0.8 V. Sulfuric acid concentration affected reaction selectivity, with a greater impact on acetaldehyde-to-acetic-acid oxidation. Despite the higher selectivity observed at 0.6 V, the reaction rate was low. Employing an appropriate potential difference and electrolyte concentration can facilitate achievement both of higher selectivity and an enhanced reaction rate. Optimal conversion was achieved at an A/v of 88.4 min/cm, while the maximum acetaldehyde selectivity of approximately 95 % was observed at an applied voltage of 1.2 V and 0.5 M sulfuric acid concentration. Figure 1

Electrooxidation of ethanol and acetaldehyde in neutral electrolyte, an infrared study

• EOR in neutral electrolyte takes place via C1 and C2 pathways. • In situ FTIR reveal the formation of CO adsorbed on the Pt surface at low potentials. • The scission of the C-C bond of ethanol takes place at ca. 300 mv. • Acetic acid is the main reaction product of the EOR or AOR at high potentials. The electrooxidation of ethanol (EOR) in neutral media is attracting a great deal of attention, especially in the area of micro devices and microbial fuel cells. In this work we study the EOR with Pt/C in neutral electrolyte and followed the evolution of the species formed with the potential by in situ FTIR. The EOR in neutral electrolyte displays higher overpotentials than in acid electrolyte but follows a similar reaction pathway, producing mainly C1 species (CO ad , CO 2 ) and C2 species (acetaldehyde, and acetic acid). The scission of the C C bond of ethanol takes place at 200 mV, a potential higher than in acid electrolyte. According to the FTIR experiments, the production of acetaldehyde during the EOR is higher than that of acetic acid. We have also studied the electrooxidation of acetaldehyde (AOR) in a neutral medium with FTIR. We observed the production of CO ad at 300 mV which is oxidized to CO 2 from E ≥ 700 mV.

Selective electrooxidation of acetaldehyde in aqueous ethanol alkaline solutions on silver-containing electrodes

Selective electrochemical oxidation of acetaldehyde in aqueous alkaline ethanol solutions on the silver-containing electrodes has been presented. Several types of silver-containing electrode were used: the smooth silver disk electrode, rough silver electrode and the glassy carbon electrode modified with the silver-polypyrrole composite ink. Silver-polypyrrole (Ag-PPy) composite was synthesized via single-step chemical oxidation with the use of diluted aqueous solutions of silver nitrate and pyrrole in molar ratio 1:50. It has been shown that acetaldehyde is oxidized selectively on silver in the presence of ethanol in alkaline solutions. The influence of various factors (pH, the presence of molecular oxygen, ethanol and acetate anions, surface area extension and polypyrrole presence) on the aldehyde electrooxidation process has been studied. It was shown that for the silver-polypyrrole composites the aldehyde electrooxidation peak potential is shifted to negative direction in comparison with the silver electrode. However, the sensitivity of the silver-polypyrrole composite modified electrode is lower than for smooth or rough silver electrode. The addition of nitrate anions in alkaline solution permits to increase the peak currents for Ag-PPy modified electrode.

Electrooxidation of Ethanol and Acetaldehyde in Neutral Electrolyte, an Infrared Study

The electrooxidation of ethanol (EOR) in neutral media is attracting a great deal of attention, especially in the area of micro devices and microbial fuel cells. In this work we study the EOR with Pt/C in neutral electrolyte and followed the evolution of the species formed with the potential by in situ FTIR. The EOR in neutral electrolyte displays higher overpotentials than in acid electrolyte but follows a similar reaction pathway, producing mainly C1 species (CO ad , CO 2 ) and C2 species (acetaldehyde, and acetic acid). The scission of the C-C bond of ethanol takes place at 200 mV, a potential higher than in acid electrolyte. According to the FTIR experiments, the production of acetaldehyde during the EOR is higher than that of acetic acid. We have also studied the electrooxidation of acetaldehyde (AOR) in a neutral medium with FTIR. We observed the production of CO ad at 300 mV which is oxidized to CO 2 from E ≥ 700 mV.

Electrooxidation of Acetaldehyde on Pt(111) Surface Modified by Random Defects and Tin Decoration

Acetaldehyde oxidation was studied on well-ordered Pt(111), stepped Pt(554), and disordered Pt(111). Random superficial defects of the {110}-type were electro-generated on well-ordered Pt(111) surface by successive potential cycling at 0.05 V s−1 between 0.05 and 1.3 V in 0.1 M HClO4 solution. In general, well-ordered Pt(111) is more active than stepped or disordered platinum surfaces for acetaldehyde oxidation. The reaction follows a dual pathways mechanism, leading each pathway to CO2 and acetic acid, respectively, as final products. The CO2 is produced via adsorbed CO and CHx reaction intermediates. Acetic acid comes from the adsorbed acetaldehyde oxidation. Additionally, acetaldehyde was also investigated on well-ordered Pt(111) and disordered Pt(111) surfaces, both modified by deposited tin submonolayers. An outstanding performance was observed when both, well-ordered and disordered Pt(111) surfaces, were modified by Sn. It was observed an extraordinary displacement of the onset potential for more negative potentials and an increased production of CO2 and acetic acid.

A facile chemical synthesis of CuxNi(1\u2212x)Fe2O4 nanoparticles as a nonprecious ferrite material for electrocatalytic oxidation of acetaldehyde

In the present work, Cu-doped nickel ferrite (CuxNi(1−x)Fe2O4) nanoparticles (CuNFNPs) were chemically fabricated by adding citric acid as a capping agent followed by combustion and calcination for acetaldehyde oxidation reaction (AOR) in KOH electrolytes. The as-prepared CuNFNPs were studied in terms of Fourier-transform infrared spectroscopy (FT-IR), Transmission electron microscopy (TEM), Field emission scanning electron microscope (FE-SEM), Energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Brunauer-Emmett-Teller (BET) specific surface area analyses. The morphology of CuNFNPs has sponges-structure containing irregular pores. Additionally, XRD analysis indicated that the prepared CuNFNPs have a cubic-crystals ferrite without the existence of impurities and the crystal size around 20.2 nm. The electrooxidation of acetaldehyde by the presented CuNFNPs was investigated using cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) in −OH media. Furthermore, the effects of −OH and acetaldehyde on the electrocatalytic performance were studied with and without Cu-doping in addition to EIS and CA studies which confirm the high-performance of CuNFNPs as an electrocatalyst for AOR.

Catalytic Activity of Pt-Based Nanoparticles with Ni and Co for Ethanol and Acetaldehyde Electrooxidation in Alkaline Medium

In this work, Pt-based nanoparticles with Ni and Co on carbon support were prepared and used as electrocatalysts in the oxidation reactions of ethanol and acetaldehyde in alkaline solution. The nanoparticles were prepared by chemical reduction with sodium borohydride and characterized by means of energy dispersive X-ray spectroscopy, X-ray powder diffraction, and transmission electron microscopy. The catalytic activity was determined from cyclic voltammetry and chronoamperometry measurements. Our results indicate that in our Pt-based catalysts, the presence of Ni promotes the initial steps of the oxidation process, while Co promotes later steps involving acetyl species. The catalytic behavior of the materials can be understood when considering factors as chemical composition and alloy degree in the prepared nanoalloys.

Electrode Reactions Coupled with Chemical Reactions of Oxygen, Water and Acetaldehyde in an Ionic Liquid: New Approaches for Sensing Volatile Organic Compounds

Water and oxygen are ubiquitous present in ambient conditions. This work studies the unique oxygen, trace water and a volatile organic compound (VOC) acetaldehyde redox chemistry in a hydrophobic and aprotic ionic liquid (IL), 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide ([Bmpy][NTf2]) by cyclic voltammetry and potential step methods. One electron oxygen reduction leads to superoxide radical formation in the IL. Trace water in the IL acts as a protic species that reacts with the superoxide radical. Acetaldehyde is a stronger protic species than water for reacting with the superoxide radical. The presence of trace water in the IL was also demonstrated to facilitate the electro-oxidation of acetaldehyde, with similar mechanism to that in the aqueous solutions. A multiple-step coupling reaction mechanism between water, superoxide radical and acetaldehyde has been described. The unique characteristics of redox chemistry of acetaldehyde in [Bmpy][NTf2] in the presence of oxygen and trace water can be controlled by electrochemical potentials. By controlling the electrode potential windows, several methods including cyclic voltammetry, potential step methods (single-potential, double-potential and triple-potential step methods) were established for the quantification of acetaldehyde. Instead of treating water and oxygen as frustrating interferents to ILs, we found that oxygen and trace water chemistry in [Bmpy][NTf2] can be utilized to develop innovative electrochemical methods for electroanalysis of acetaldehyde.

The electrooxidation of acetaldehyde on platinum–ruthenium–rhodium surfaces: A delicate balance between oxidation and carbon–carbon bond breaking

In this work we investigate the electrooxidation of acetaldehyde in acidic media on platinum–ruthenium–rhodium electrodeposits of several compositions. Combined results of electrochemistry and in situ FTIR spectroscopy show that the Ru/Rh ratio plays a pivotal role on the electrooxidation of acetaldehyde on PtRuRh surfaces. The combination of these metals apparently establishes a delicate balance between the ability of a surface to oxidize adsorbed species and to promote the C–C bond breaking. Overall, by estimating the charges involved in each oxidation pathway we were able to mimic the electrochemical behavior as a function of the composition. The global output suggests that the proper combination of platinum–ruthenium–rhodium can lead to the development of active catalysts towards the oxidation of small organic molecules.

The effect of acetaldehyde and acetic acid on the direct ethanol fuel cell performance using PtSnO2/C electrocatalysts

PtSnO2/C with Pt:SnO2 molar ratios of 9:1, 3:1 and 1:1 prepared by an alcohol-reduction process were evaluated as anodicelectrocatalysts for direct ethanol fuel cell (DEFC). Acetaldehyde, acetic acid and mixtures of them with ethanol were also tested as fuels. Single cell tests showed that PtSnO2/C electrocatalysts have a superior electrical performance for ethanol and acetaldehyde electro-oxidation when compared to commercial Pt3Sn/C(alloy) and Pt/C electrocatalysts. For all electrocatalysts, no electrical response was observed when acetic acid was used as a fuel. For ethanol electro-oxidation, the main product was acetaldehyde when Pt3Sn/C(alloy) and Pt/C electrocatalysts were employed. Besides, PtSnO2/C electrocatalysts led to the formation of acetic acid as the major product. CO2 was formed in small quantities for all electrocatalysts studied. A sharp drop in electrical performance was observed when using a mixture of ethanol and acetaldehyde as a fuel, however, the use of a mixture of ethanol and acetic acid as a fuel did not affect the DEFC performance.

Electrooxidation of acetaldehyde on a carbon supported Pt catalyst at elevated temperature/pressure: An on-line differential electrochemical mass spectrometry study

The electrooxidation of acetaldehyde on a Pt/Vulcan catalyst was investigated over a wide range of temperatures (23–100°C) in a flow cell under controlled transport conditions, employing high temperature/high pressure (3 bar overpressure) on-line differential electrochemical mass spectrometry (DEMS). Potentiodynamic and potentiostatic measurements of the Faradaic current and of the CO2 formation rate reveal that complete oxidation to CO2 prevails only at higher temperatures and lower potentials, with ∼80%/40% current efficiency for CO2 formation at 0.5V/0.6V in 0.1M solution and at 100°C, in contrast to a few percent at room temperature. Oxidation to acetic increases at higher potential. The increase of the CO2 current efficiency with temperature is reflected by a higher apparent activation barrier for complete oxidation to CO2 (39±2kJmol−1 at 0.6 V, 0.1M) compared to that of the overall acetaldehyde oxidation reaction given by the Faradaic current (32±2kJmol−1) and that for oxidation to acetic acid (27±3kJmol−1). Analogous measurements on the electrooxidation of acetic acid show very low reactivities even at 100°C, and a high apparent activation energy (173±6kJmol−1). The importance of fuel cell relevant reaction and mass transport conditions in model studies is discussed.

Electrochemical and Spectroscopic Studies of Ethanol and Acetaldehyde Oxidation Onto Pt(110) Modified by Osmium

This paper presents the studies of ethanol and acetaldehyde electrooxidation onto Pt(110) electrode modified by different osmium coverage. These oxidation reactions were studied by in situ Fourier transform infrared spectroscopy. It was shown that the catalytic activity of Pt(110) after osmium deposition for ethanol oxidation is greater than that observed on unmodified Pt(110). It was also demonstrated that the mechanistic pathway for this reaction depends directly on the degree of osmium coverage. Thus, for low osmium coverage (θ Os ≤ 0.12), the formation of CO and CO2 is not so effective when compared with other coverage degrees, and hence the full oxidation of adsorbed ethanol to CO2 is increased when the Os is deposited in the range of 0.30–0.80 ML. Additionally, the formation of acetaldehyde is also observed in low degree of osmium coverage. For a complete osmium layer (θ Os > 1.0), the catalytic activity of the electrode for ethanol oxidation shows the lowest value. The acetaldehyde oxidation reaction on Pt(110)/Os favors the CO2 production. For electrodes covered completely by Os layer, a considerable presence of CO2 above 0.8 V was observed; in contrast with the very low quantity of adsorbed COlinear, this suggests that the CO2 can also be formed from the oxidation of a possible strongly adsorbed species at high potentials on this surface, or it can also be considered that acetaldehyde can be oxidized to CO2 by the cleavage of C–C bond.

Search for multi-functional catalysts: The electrooxidation of acetaldehyde on Platinum–Ruthenium–Rhodium electrodeposits

Preliminary studies on the influence of Platinum–Rhodium electrodeposits upon the rate of acetaldehyde electrooxidation showed that Rhodium plays a dual role during electrooxidation, because it favors the break of C–C bonds whilst prevents the deliverance of oxygen-containing species, thus inhibiting the oxidation steps. Based on these results, in this work Platinum–Ruthenium and Platinum–Ruthenium–Rhodium electrodeposits were prepared and characterized by electrochemical and spectroscopic methods (FTIR in situ). The addition of Ruthenium is justified by its ability to promote a facile oxidation of adsorbed species by activation of water molecules. The results indicate a compromise between the existence of superficial sites able to break carbon chains (provoked by Rhodium) and responsible by the oxidation of adsorbed species (provoked by Ruthenium). Among the atomic compositions investigated, PtRuRh (73:23:04) shows the maximum activity towards acetaldehyde electrooxidation, but the production of acetic acid seems to be the main responsible for this activity.

Understanding the electrocatalytic activity of Pt xSn y in direct ethanol fuel cells

In the present work, the activity of Pt x Sn y /C catalysts towards ethanol, acetaldehyde and acetic acid electrooxidation reactions is investigated for each one separately by means of cyclic voltammetry. To this purpose, a series of Pt x Sn y /C catalysts with different atomic ratio ( x: y = 2:1, 3:2, 1:1) and small particle size (∼3 nm) are fast synthesized by using the pulse microwave assisted polyol method. The catalysts are well dispersed over the carbon support based on the physicochemical characterization by means of XRD and TEM. Concerning the ethanol electrooxidation, it is found that the Sn addition strongly enhances Pt's electrocatalytic activity and the contributing effect of Sn depends on: (i) the Sn content and (ii) the operating temperature. More precisely, at lower temperatures, Sn-rich catalysts exhibit better ethanol electrooxidation performance while at higher temperatures Sn-poor catalysts give better performance. In the case of acetaldehyde electrooxidation, Pt 1Sn 1/C catalyst exhibits the highest activity at all the investigated temperatures; due to the role of Sn, which could effectively remove C 2 species and inhibit the poison formation by supplying oxygen-containing species. Finally, it is found that the Pt x Sn y /C catalysts are almost inactive (little current was measured) towards the acetic acid electrooxidation. The above findings indicate that Sn cannot substantially promote the electrooxidation of acetic acid to C 1 species.

Rhodium in presence of platinum as a facilitator of carbon–carbon bond break: A composition study

In this work we investigate the acetaldehyde electrooxidation reaction on PtRh electrodeposits as a function of their composition. Potentiodynamic results show that the balance between CO 2 and acetic acid pathways depends on the PtRh composition. By using in situ FTIR we interpret this dependence in terms of a dual role played by Rh during acetaldehyde electrooxidation. Rh seems to favor the break of C–C bonds (favoring the production of CO 2) whilst prevents the deliverance of oxygen-containing species, thus inhibiting the oxidation steps.

Acetaldehyde electrooxidation: The influence of concentration on the yields of parallel pathways

Parallel pathways forming CO2 and acetic acid occur during the electrooxidation of acetaldehyde at Pt in acid medium. The yields of products depend on potential and acetaldehyde concentration. In the whole range of concentrations investigated (2.5 × 10−3 – 0.5 M) and at potentials below 0.6 V, CO2 is the only product of acetaldehyde oxidation. Acetic acid is detected at potentials higher than 0.7 V. According to the analysis of products using FTIR spectroscopy, a maximum yield of CO2 production is obtained for an acetaldehyde concentration of 0.01 M at 0.6 V. The pathway forming CO2 is strongly inhibited for 0.5 M of acetaldehyde. It is suggested that, at high concentrations, a competition with water for active sites occurs, which inhibits the oxidation of adsorbed species, which probably follow a Langmuir–Hinshelwood mechanism.

Electrooxidation of acetaldehyde on carbon-supported Pt, PtRu and Pt3Sn and unsupported PtRu0.2 catalysts: A quantitative DEMS study

The oxidation of acetaldehyde on carbon supported Pt/Vulcan, PtRu/Vulcan and Pt3Sn/Vulcan nanoparticle catalysts and, for comparison, on polycrystalline Pt and on an unsupported PtRu0.2 catalyst, was investigated under continuous reaction and continuous electrolyte flow conditions, employing electrochemical and quantitative differential electrochemical mass spectroscopy (DEMS) measurements. Product distribution and the effects of reaction potential and reactant concentration were investigated by potentiodynamic and potentiostatic measurements. Reaction transients, following both the Faradaic current as well as the CO2 related mass spectrometric intensity, revealed a very small current efficiency for CO2 formation of a few percent for 0.1 m acetaldehyde bulk oxidation under steady-state conditions on all three catalysts, the dominant oxidation product being acetic acid. Pt alloy catalysts showed a higher activity than Pt/Vulcan at lower potential (0.51 V), but do not lead to a better selectivity for complete oxidation to CO2. C–C bond breaking is rate limiting for complete oxidation at potentials with significant oxidation rates for all three catalysts. The data agree with a parallel pathway reaction mechanism, with formation and subsequent oxidation of COad and CHx, ad species in the one pathway and partial oxidation to acetic acid in the other pathway, with the latter pathway being, by far, dominant under present reaction conditions.

Adsorption and electrooxidation of some simple organic molecules on rhodium(111) as probed by real-time FTIR spectroscopy: comparisons with platinum (111)

The electrooxidation pathways of seven simple organic molecules in 0.1 M HClO{sub 4} on ordered Rh(111) were examined by means of real-time sequences of FTIR spectra obtained during slow (2 mV s{sup {minus}1}) voltammetric sweeps. The reactants studied are formic acid, methanol, ethanol, acetaldehyde, ethylene glycol, glyoxal, and oxalic acid for concentrations between 0.05 and 0.5 M. High coverages ({theta} {ge} 0.4) of adsorbed CO are formed in most cases, as detected from a band at about 1880-1890 cm{sup {minus}1} at the most negative potentials ({minus}0.25 to +0.05 V vs SCE), which is replaced by a band at 2030-2040 cm{sup {minus}1} at more positive potentials. These two features are assigned to C-O vibrations, {nu}{sub CO}, associated with CO adsorbed in bridging and terminal coordination geometries, respectively. The former configuration is apparently engendered by hydrogen coadsorption. For cyclic voltammograms between {minus}0.25 and +0.6 V, the adsorbed CO formed by dissociative reactant chemisorption only undergoes complete electrooxidation during the reverse portion of the potential sweep, at ca. 0.4V. This inability to remove adsorbed CO on ordered Rh(111) appears to be at least partly responsible for the observed weakly electrocatalytic properties of this surface for organic electrooxidations. The production of CO{sub 2} evenmore » from formic acid, which occurs readily on Pt(111), does not commence in earnest on Rh(111) until CO is removed during the reverse scan. The electrooxidation of the other reactants on ordered Rh(111) is largely limited to the production of small amounts of CO{sub 2}, although some electrooxidation of acetaldehyde (but not ethanol) to acetic acid is detected. These results are compared with corresponding reactions on ordered Pt(111) and for the electrooxidation of solution CO.« less

Real-time FTIR spectroscopy as an electrochemical mechanistic probe: Electrooxidation of ethanol and related species on well-defined Pt (111) surfaces

The electrooxidation pathways of ethanol and acetaldehyde in 0.1 M HClO 4 on ordered Pt (111) surfaces in comparison with disordered Pt (111) and polycrystalline Pt were examined by means of FTIR spectra obtained in real time during slow (2–10 mV s −1) thin-layer voltametric sweeps. This “single potential alteration infrared” (SPAIR) procedure enables the potential-dependent quantity of the various reaction products, acetic acid, acetaldehyde, and CO 2 to be determined quantitatively, and the role of CO and other CO 2-producing adsorbates in the reaction kinetics to be assessed. For ethanol electrooxidation on ordered Pt (111), acetic acid and acetaldehyde are formed, along with smaller amounts of CO 2 beyond ca. 0.3 V (vs. SCE) where oxidation of adsorbed CO occurs; acetic acid is the major product during the reverse potential sweep. Only small CO coverages (θ ≈ 0.1) are obtained for ethanol concentrations of 0.05-0.5 M. Substantially higher CO coverages are obtained for disordered Pt (111) and especially polycrystalline Pt. The product distributions are not altered greatly from ordered Pt (111). Markedly different behavior, however, was observed for acetaldehyde electrooxidation on ordered Pt (111) in that little acetic acid is formed until near the end of the positive-going potential sweep, 0.8 V. A greater quantity of adsorbed CO (θ ≈ 0.15) is present, but this undergoes complete electrooxidation by 0.45 V. This marked reaction inhibition is attributed instead to the presence of another (or other) adsorbed species, which is observed to undergo oxidation to CO 2 only between 0.5–0.7 V. The inhibition of acetic acid formation is much less marked on disordered Pt (111), and essentially absent on polycrystalline Pt. Comparisons are also made between the electrooxidation kinetics for some related unifunctional reactants, including formic acid and isopropanol, on ordered and disordered Pt (111) surfaces. Markedly smaller amounts of adsorbed CO are generally formed from organic species on the former surface; some possible electrocatalytic consequences are discussed.

The effect of the length and the type of the carbon chain of the aliphatic aldehydes on the process of their electrooxidation

The effect of the length and the type of the carbon chain of aliphatic aldehydes on their electrooxidation in sulphuric acid media on a bright Pt electrode was investigated. 0.01 M solutions of formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde and isobutyraldehyde in 0.5 M sulphuric acid were studied under conditions of triangular potential sweep control. Acetone and ethyl methyl ketone were comparatively electrooxidized. It is concluded that the mechanism of acetaldehyde electrooxidation proposed earlier by the authors can be extended over the homologous series of the aliphatic aldehydes.