CH3OH Oxidation Research Articles

Excitonic Interfacial Proton-Coupled Electron Transfer Mechanism in the Photocatalytic Oxidation of Methanol to Formaldehyde on TiO2(110).

CH3OH on a single-crystal rutile TiO2(110) surface is a widely studied model system for heterogeneous photocatalysis. Using spin-polarized density functional theory with a hybrid functional (HSE06), we study the photocatalytic oxidation of CH3OH adsorbed at a coordinately unsaturated Ti site as an excited-state process with triplet spin multiplicity. The oxidation to CH2O is stepwise and involves a CH3O intermediate. The first O-H dissociation step follows an excitonic interfacial proton-coupled electron transfer mechanism where the hole-electron (h-e) pair generated during the excitation is bound, and the h is transferred to the adsorbate. The O-H dissociation paths associated with other h-e pairs are unreactive, and the moderate experimental efficiency is due to the different reactivity of the h-e pairs. The excited-state CH3O intermediate further deactivates through a seam of intersection between the ground and excited states. It can follow three different paths, regeneration of adsorbed CH3OH or formation of the ground-state CH3O anion or an adsorbed CH2O radical anion. The third channel corresponds to photochemical CH2O formation from CH3OH, where a single photon induces one electron oxidation and transfer of two protons. These results expand the current view on the photocatalysis of CH3OH on TiO2(110) by highlighting the role of excitons and showing that adsorbed CH3OH may also be an active species in the photocatalytic oxidation to CH2O.

Silica veils-conductive diamond powder composite as a new propitious substrate for platinum electrocatalysts

An innovative composite was obtained by a straightforward sol-gel procedure, involving boron-doped diamond powder (BDDP) incorporation into a SiO2 veil (SiO2V) matrix. Composite-coated glassy carbon plates were used as substrate for Pt electrochemical deposition, and the electrodes thus obtained (Pt/BDDP–SiO2V) were compared on a relative basis with those prepared in the absence of the silica matrix (Pt/BDDP). SEM measurements have shown that a BDDP substrate promotes Pt cluster formation, whereas on BDDP–SiO2V, particles are much smaller (ca. 45 nm to ca. 140 nm). The activity for CH3OH oxidation was checked by cyclic voltammetry, and it was found that at Pt/BDDP–SiO2V, the main anodic peak is shifted with ca. 0.35 V toward lower potentials, indicating a considerable improvement in the overall process kinetics. Stripping experiments together with long-term polarization measurements demonstrated that when deposited on the BDDP–SiO2V support, Pt particles are less susceptible to CO poisoning and this behavior was tentatively ascribed to the presence of a higher relative surface concentration of more stable, oxidized platinum species, as evidenced by XPS.

CO and VOCs Catalytic Oxidation Over Alumina Supported Cu–Mn Catalysts: Effect of Au or Ag Deposition

Alumina supported Cu–Mn mixed oxide with Cu/Mn molar ratio 2:1 was used as a support of gold and silver catalysts for oxidation of CO, methanol and dimethylether. Different techniques (XRD, HRTEM, XPS, FTIR, EPR, and TPR) were used to investigate structure–reactivity relationship. A strong effect of the nature of the promoters on the catalytic behaviour was observed. Superior catalytic activity in oxidation of CO was measured after addition of Au, while modification by Ag affected very slightly the CO oxidation activity of Cu/Mn 2:1 sample. Both Au and Ag have beneficial effect on CH3OH oxidation activity of Cu–Mn mixed oxides. The combination of the good redox properties of Cu–Mn mixed oxides and gold nanoparticles has proved to be an advantageous approach for developing new catalytic formulations with high effectiveness to eliminate different type pollutants in waste gases from formaldehyde production. The use of high surface area support is beneficial for the stabilization of gold particles in a highly dispersed state and contributes for economic viability in case of practical applications, because of the composition of this catalytic system, that is mostly alumina (80 %).

Single Atom Modified Covalent Triazine Frameworks As Electrocatalysts

Covalent organic frameworks (COFs) are cross-linked porous polymers, which have great potential in catalysis area because of their unique porous structure (i.e. high surface area), mechanical robustness and high design flexibility. Especially, covalent triazine frameworks (CTFs), which have 1,3,5-triazine structure as units, possess the high density of nitrogen (N) atoms in their organic pore for metal coordinations [1,2]. Recently, Palkovits et al. reported that platinum-modified CTF (Pt-CTF) functioned as a solid catalyst for the selective low-temperature oxidation of methane to methanol [3]. In general, the oxidation of methanol can easily proceed compared to methane oxidation because the C-H bond energy of methanol is much smaller than that of methane. Thus, the catalytic activity for methane partial oxidation to methanol let us assume that Pt-CTF has no activity to oxidize methanol (i.e. methanol tolerance).The methanol tolerance is the essential property for the cathode catalyst of direct methanol fuel cells (DMFC) as the methanol-crossover effect is one of the issues to be addressed. However, the application of the frameworks as electrocatalysts has not been achieved to date because of their poor electrical conductivity. In the present work, we have successfully applied CTF-based materials to electrocatalysts by hybridizing non-conductive CTFs with conductive carbon particles (CPs). The hybridized material was obtained by the polymerization of CTFs on CPs in molten ZnCl2. Then, Pt atoms were grafted in the pore of CTFs by the impregnated with platinum chloride.Then, Pt atoms were grafted in the pore of CTFs by the impregnated with platinum chloride (Pt-CTF/CP). The resulting catalyst showed apparent electrocatalytic activity for oxygen reduction reaction (ORR). In case of a commercial 20 wt% Pt/C, after the addition of 1 M CH3OH, the onset potential of the cathodic current shifted approximately 200 mV in the negative direction in the presence of oxygen (Figure, inset). In contrast, surprisingly, the overlap of the CH3OH oxidation current with that of the ORR was almost negligible for Pt-CTF/CP even in the presence of 1 M CH3OH as shown in the Figure [4]. These results clearly showed that Pt-CTF/CP exhibited a high methanol tolerance during the ORR, as we expected. This is the first demonstration of the potential for CTF-based materials to serve as electrocatalysts. The extended X-ray absorption fine structure (EXAFS) and transmission electron microscopy (TEM) results demonstrated that the Cu atoms in Cu-CTF/CP are singly isolated. It has been reported that at least two adjacent Pt sites are required for methanol oxidation. Actually, to the best of our knowledge, there are no works that reported the possibility of the methanol oxidation on single Pt-atom site. Thus, the structural feature of single Pt atoms, which were stabilized by N atoms in the CTF pores, is likely the origin of the methanol-tolerance. [1] K. Iwase, K. Kamiya et al., Angew. Chem. Int. Ed. 38, 11068, (2015)[2] T. Yoshioka, K. Kamiya et al., J. Phys. Chem. C in press. 10.1021/acs.jpcc.5b10962[3] Palkovits et al. Angew. Chem. Int. Ed. 48, 6909, (2009)[4] K. Kamiya et al. Nat. Commun. 5, 5040, (2014) Figure 1

Investigation of zeolite supported platinum electrocatalyst for electrochemical oxidation of small organic species

Zeolite supported Pt electrocatalysts, made by ion exchange method using Pt/Y type zeolite, have been investigated to determine Pt electrochemical activity of HCOOH and CH3OH oxidation using the cyclic voltammetry (CV) and the extended X-ray adsorption fine structure (EXAFS) techniques. The study reveals that the introduction of excess H+ ions during electrocatalyst pre-treatment could enhance electrochemical reaction on Pt surface due to higher Pt dispersion, regardless of zeolite being a direct current electronic conducting insulator. Two possible conduction pathways might contribute to the electrocatalytic reaction on Pt surface with Pt particle size and loading: (1) hydrogen atoms/H+ ions spillover through zeolite framework and at the electrode and solution interface; (2) surface mobility of adsorbed species on electrode surface. The water may act as a carrier in assisting the migration of the H+ ions throughout zeolite channels to facilitate the charger and electron transfer in such an electrical system.

Catalyst-Selective Direct Liquid Fuel Cells without the Need for an Ion-Exchange Membrane to Separate the Anode Fuel and the Cathode Oxidant

Among the several types of direct liquid fuel cells (DLFCs) under development with various liquid fuels, the direct methanol fuel cell (DMFC) is in the forefront. However, this technology is currently in a difficult situation. The challenges of the relatively well-developed DMFCs with the proton-exchange membrane (PEM) include (1) the high-cost of Nafion membrane, (2) the sluggish kinetics of electrode reactions (rely on the high-loading Pt-based catalysts), and (3) the crossover of the methanol fuel through the PEM.1 , 2 According to the above issues, two approaches have recently been proposed and attempted, which can individually overcome the challenges of (1) – (3). Operation of the DMFCs under alkaline condition is able to enhance the kinetics of the electrode reactions.3 Operation of the DMFCs under a laminar-flow principle can avoid the use of the expensive PEMs and without the fuel crossover concerns. However, each of these two approaches brings new unexpected problems. Operation of the DMFCs under alkaline conditions needs an OH--exchange membrane which is currently not quite available. The laminar-flow membraneless DMFCs can only be built to a miniature scale, which limits their practical applications.4 Herein we present a membraneless alkaline DLFC approach developed under a catalyst-selective philosophy. By employing a non-platinum, highly selective cathode catalyst (MnNiCoO4/N-MWCNT, MnNiCoO4 nano-particles on a nitrogen-doped multi-wall carbon nanotube)5 with favorable activity for the oxygen reduction reaction (ORR) but without any activity for the fuel oxidation reaction (FOR), membraneless-operation of the DLFCs is turned into reality without any concerns about the fuel crossover from the anode to the cathode. The first example of this presentation is an alkaline membraneless DMFC system with methanol as the anode fuel. The second example is an alkaline direct formate fuel cell (DFFC) with aqueous potassium formate solution as fuel. In comparison to the CH3OH-favorite catalyst PtRt/C and the HCOOK-favorite catalyst Pd/C, the MnNiCoO4/N-MWCNT does not show activities for oxidation of either CH3OH or HCOOK. The fuel cell performances of the membraneless DMFC (PtRu/C ǁ CH3OH/KOH ǁ MnNiCoO4/N-MWCNT) and the membraneless DFFC (Pd/C ǁ HCOOK/KOH ǁ MnNiCoO4/N-MWCNT) are superior to those of the traditional membrane-based DMFCs.

Silver–Alumina Catalysts for Low-Temperature Methanol Incineration

The use of methanol as an alternative fuel for gasoline or diesel engines increases the unregulated CH3OH emission. γ-Al2O3 modified with Cu, Mn, Ce, K, Ag, Cu–Mn, Cu–Ce, Cu–Ag or Cu–K (0.5, 1.0, 0.5:0.5, 1.0:1.0 wt% of metal) catalysed the process of methanol incineration. The highest activity reached samples containing 1.0 wt% of silver. Dispersed Ag+ species on Al2O3 served as active species for selective oxidation of CH3OH to CO2 over both Ag/Al2O3 and Cu–Ag/Al2O3. Additionally, the XPS and EPR results revealed the AgO interface between the Ag2O and CuO in the Cu–Ag system.

The effect of niobium and tantalum on physicochemical and catalytic properties of silver and platinum catalysts based on MCF mesoporous cellular foams

MCF, NbMCF and TaMCF Mesostructured Cellular Foams were used as supports for platinum and silver (1wt%). Metallic and bimetallic catalysts were prepared by grafting of metal species on APTMS (3-aminopropyltrimethoxysilane) and MPTMS (2-mercaptopropyltrimethoxysilane) functionalized supports. Characterizations by X-ray diffraction (XRD), ultraviolet–visible (UV–Vis) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray fluorescence (XRF) spectroscopy, and in situ Fourier Transform Infrared (FTIR) spectroscopy allowed to monitor the oxidation state of metals and surface properties of the catalysts, in particular the formation of bimetallic phases and the strong metal–support interactions. It was evidenced that the functionalization agent (APTMS or MPTMS) influenced the metals dispersion, the type of bimetallic species and Nb/Ta interaction with Pt/Ag. Strong Nb–Ag interaction led to the reduction of niobium in the support and oxidation of silver. MPTMS interacted at first with Pt to form Pt–Ag ensembles highly active in CH3OH oxidation. The effect of Pt particle size and platinum–silver interaction on methanol oxidation was also considered. The nature of the functionalization agent strongly influenced the species formed on the surface during reaction with methanol and determined the catalytic activity and selectivity.

Methanol oxidation on Ru(0001) for direct methanol fuel cells: analysis of the competitive reaction mechanism

Competitive oxidation of CH3OH to CH2O occur via CH3OH → CH3O → CH2O vs. CH3OH → CH2OH → CH2O, further to COOH by the OH group via CH2O → CHO → CO + OH → COOH vs. CH2O + OH → CH2OOH → CHOOH → COOH, and finally oxidation to CO2 on Ru(0001).

Highly active carbon supported palladium-rhodium PdXRh/C catalysts for methanol electrooxidation in alkaline media and their performance in anion exchange direct methanol fuel cells (AEM-DMFCs)

In this study carbon supported PdXRh electrocatalysts synthesized by wet chemical reduction process were tested for the potential use in anion-exchange membrane direct methanol fuel cells (AEM-DMFC) and compared to Pd/C and commercially available Pt/C. A metal loading of 20wt% on carbon was confirmed by thermogravimetric analysis (TGA) and catalyst compositions of PdRh3/C, PdRh/C and Pd3Rh/C were found via inductively coupled plasma optical emission spectroscopy (ICP-OES). Transmission electron microscopy (TEM) and x-ray diffraction (XRD) studies showed that the average particle and crystallite sizes of the PdXRh/C catalysts are in the range of 3.1 to 4.3nm. It was also found that these catalysts are not alloyed. Cyclic voltammetry (CV) data reveals a 85–140mV lower CH3OH oxidation onset potential and higher mass current densities for PdXRh/C catalysts compared with Pd/C. Steady-state measurements via chronoamperometry (CA) showed a good stability against poisoning during methanol oxidation and higher mass activities for PdRh/C and Pd3Rh/C compared to Pt/C. By using differential electrochemical mass spectrometry (DEMS) it was successfully shown that adding Rh to Pd results in an enhanced CO2 current efficiency (CCE) compared to Pd/C or Pt/C. AEM-DMFCs free from platinum were fabricated and single cell tests at 60°C showed a significant increase of power density at 0.5V cell potential from 4.8mWcm−2 for Pd/C to 16.5mWcm−2 for PdRh/C with the anode and cathode fed with 1M methanol+2M KOH and synthetic air, respectively. Peak power density of 104.9mWcm−2 was reached for PdRh/C anode catalyst at 80°C using higher KOH and methanol concentrations in anodic fuel and oxygen as cathodic oxidizer.

Influence of Structural Effects on Platinum Electrodes in the Preferential Adsorption of CO and Methanol in Acid Media

The complete methanol electro-oxidation on platinum single crystal electrodes produces CO2, H2O and 6 e- in acidic medium. However methanol adsorption is sensitive to the platinum surface orientation, showing different reactivity for different platinum crystallographic planes. In this work, it was studied the preferential adsorption and oxidation of carbon monoxide (CO) and methanol in acid media on polycrystalline and low index planes of platinum single crystals. In the experimental procedure carbon monoxide was bubbled in methanol solution with the platinum electrode polarized at 0.1 V vs. RHE. Then, the potential was scanned from 0.1 to 0.8 or 1.0 V vs ERH depending on platinum single crystal electrode. From Figure 1a the carbon monoxide oxidation occurs at potential above 0.6 V vs. RHE for all platinum surfaces. Besides data from Figure 1b methanol oxidation on Pt(111), Pt(100) and polycrystalline platinum electrodes exhibited high potential, above 0.8 V (RHE). After adsorption of carbon monoxide on platinum electrodes, on polycrystalline platinum and Pt(100) the peak maximum occurred at more positive potential compared with methanol reaction. In this case methanol oxidation only was promoted after carbon monoxide oxidation reaction. On Pt(100) and Pt(111) the adsorption of CO contributed to reduce the potential for methanol oxidation. Thus, these experiments suggest that carbon monoxide competes with methanol for adsorption on platinum electrode. For polycrystalline Pt and Pt(110) single crystals, the mixture CO+CH3OH showed potential of oxidation larger than with pure reactants. On the other hand, on Pt (111) and Pt(100) the oxidation of methanol happens at potential above that for the mixture of methanol and carbon monoxide, so that, it is possible that the electrochemical reaction follows different pathways on these surfaces. Figure 1. (a) first potential scan at platinum electrodes in 0.2 M CH3OH + 0.1M H2SO4, obtained at 10 mV s-1. Insert show CO peak between 0.2 – 0.4 V (RHE). (b) Potential peak maximum dependence for CO, CH3OH and CO + CH3OH oxidation. Acknowledgedment:CNPq for financial support (process 150885/2012-1).

Influence of the Synthesis Method for Pt Catalysts Supported on Highly Mesoporous Carbon Xerogel and Vulcan Carbon Black on the Electro-Oxidation of Methanol

Platinum catalysts supported on carbon xerogel and carbon black (Vulcan) were synthesized with the aim of investigating the influence of the characteristics of the support on the electrochemical performance of the catalysts. Three synthesis methods were compared: an impregnation method with two different reducing agents, sodium borohydride and formic acid, and a microemulsion method, in order to study the effect of the synthesis method on the physico-chemical properties of the catalysts. X-ray diffraction and transmission electron microscopy were applied. Cyclic voltammetry and chronoamperometry were used for studying carbon monoxide and methanol oxidation. Catalysts supported on carbon xerogel presented higher catalytic activities towards CO and CH3OH oxidation than catalysts supported on Vulcan. The higher mesoporosity of carbon xerogel was responsible for the favored diffusion of reagents towards catalytic centers.

Ultrathin Platinum Films for Methanol and Formic Acid Oxidation: Activity as a Function of Film Thickness and Coverage

Self-terminating electrodeposition was used to grow ultrathin Pt overlayers on 111 textured Au thin films. The Pt thickness was digitally controlled by pulsed potential deposition that enabled the influence of overlayer thickness on electrocataytic reactions, such as methanol and formic acid oxidation, to be examined. Bimetallic and ensemble effects associated with submonolayer coverage of Pt on Au yield enhanced catalysis. For films grown using one deposition pulse, the peak rate of CH3OH oxidation was enhanced by a factor of 4 relative to bulk Pt. The overlayer consisted of 2 nm diameter monolayer Pt islands that covered 75% of the surface; however, voltammetric cycling resulted in a loss of the enhanced activity associated with the as-deposited submonolayer films. For thicker Pt films, the electrocatalytic activity decreased monotonically with thickness until bulk Pt behavior was obtained beyond three monolayers. For HCOOH oxidation improvements in the Pt area, normalized activity in excess of a 100-fold were observed for submonolayer Pt films. The performance improved with voltammetric cycling as a result of a combination of Pt dissolution, Au segregation, and Pt–Au alloy formation. The maximum activity was associated with fractional surface coverage between 0.28 and 0.21, although the films were subject to a deactivation process at longer times related to a diffusional process. Bulk Pt behavior for formic acid oxidation was observed for Pt films greater than three monolayers in thickness.

Oxidation of formaldehyde, carbon monoxide and methanol over manganese-cerium-aluminum oxides supported on cordierite monoliths

Catalytic oxidation of formaldehyde, carbon monoxide, and methanol over cordierite-supported manganese-cerium-aluminum mixed oxides was investigated in a laboratory reactor. The activities of base metal oxides (BMO) comprising 27% MnO2, 21% CeO2, and 52% Al2O3 supported on cordierite monoliths calcined at 1,000 °C for 3 h in air dropped very rapidly due to the migration of mobile silicon dioxide (SiO2) from the cordierite to the base metal oxides to react with or physically block the active catalysts. To immobilize migrating SiO2, barrier coats composed of alkali metal (Ba, Sr, Ca, Mg) oxides and alumina were applied to the cordierite prior to coating with active base metal oxides. The base metal oxides supported on cordierite monoliths pretreated with BaO-Al2O3 barrier coats and calcined at 1,000 oC for 3 h in air, initiated the oxidation of HCHO, CO, and CH3OH at 150, 220, and 170 °C, respectively. These catalysts turned out to be more effective for the formaldehyde oxidation than 0.5% Pt/Al2O3 precious metal catalysts. Carbon monoxide and methanol oxidation conversions were comparable. The incorporation of small amount of palladium (0.147 wt%) to base metal oxides supported on cordierite monoliths pretreated with BaO-Al2O3 barrier coats, showed the superiority for HCHO, CO, and CH3OH oxidation to 0.5% Pt/Al2O3 precious metal catalysts. The temperatures of 50% conversion of formaldehyde, carbon monoxide and methanol were 70 °C lower over base metal oxides catalysts than over precious metal catalysts.

Zeolites Y modified with palladium as effective catalysts for low-temperature methanol incineration

Alumina, as well as zeolites HY and NaY modified with palladium (0.5–2.5wt%) were tested in the process of methanol incineration to found an effective catalyst for the elimination of volatile organic compound (VOCs). Parent materials as well as their modifications with palladium were investigated with regards to their structural, textural and acidic/redox properties. The IR spectroscopy, X-ray diffraction, TEM, and low temperature N2 sorption methods were employed for these purposes. This research shows that the Pd deposited on highly acidic steamed zeolite HY is considered as promising catalyst for the elimination of volatile organic compounds (VOCs). Both Pd0 and Pd2+ species were found to be responsible for the oxidation process. Superior catalytic activity of 1.5%Pd/HY resulted from a synergistic effect of a high acidity of the zeolitic support and Pd species dispersion. The validity of Mars-van Krevelen pathway can be proposed as suitable for HCHO, CH3OH and CH4 oxidation.

Nature and Role of Activated Molecular Oxygen Species at the Gold/Titania Interface in the Selective Oxidation of Alcohols

The heterogeneously catalyzed selective oxidation of alcohols has been studied by using methanol on gold nanoparticles supported on reduced titania surfaces. Our density functional theory based simulations shed light on the atomistic details of the mechanism responsible for the CH3OH oxidation toward formaldehyde, CH2O, at these complex Au/TiO2 interfaces. The selectivity and high catalytic activity of the Au/TiO2 nanocatalyst in the oxidation of methanol is traced back to the presence of active sites right at the interface between the Au nanoparticle and the TiO2 support where preadsorbed molecular oxygen is activated as a result of significant metal–support interactions. The activation of O2 at such dual perimeter sites occurs via charge transfer from Au/TiO2 leading to the formation of peroxide species, O2δ−. These activated O2δ− species open up an efficient low-temperature reaction channel for the oxidation of methanol to yield formaldehyde and water.

Catalytic consequences of the identity and coverages of reactive intermediates during methanol partial oxidation on Pt clusters

Rate measurements, carried out after elimination of transport corruptions, show that CH3OH partial oxidation on Pt clusters proceeds via three distinctly different kinetic regimes defined by the operating oxidant-to-reductant (O2-to-CH3OH) ratio. These kinetic regimes, each with unique rate dependencies for HCHO, HCOOCH3, and CO2 formation, arise from a dynamic shift in the identity and coverages of reactive intermediates on Pt cluster surfaces from saturated with chemisorbed oxygen, to uncovered, and then to partially covered with methanol derived species as the oxygen chemical potential at cluster surfaces decreases with decreasing O2-to-CH3OH ratio. HCHO formation rates first remain insensitive to O2 on Pt cluster surfaces saturated with chemisorbed oxygen (O*), then increase proportionally with O2 as cluster surfaces depleted of oxygen and as unoccupied Pt sites become the most abundant surface intermediates, and eventually increase more than linearly with O2 on Pt surfaces predominantly covered with CH3OH derived intermediates. The transition in rate dependence on O2 is accompanied by a concomitant transition on CH3OH dependence: HCHO formation rates are linearly proportional to, then independent of, and eventually inhibited by CH3OH as the O2-to-CH3OH ratio decreases. Similar transition in reaction orders is also found for HCOOCH3 and CO2 formation. The first-order rate coefficient for CH3OH oxidation is a single-valued function of the operating O2-to-CH3OH ratio, because the ratio determines the oxygen chemical potential at Pt cluster surfaces via the kinetic coupling of O2 and CH3OH activation steps and, in turn, the identity and coverage of reactive intermediates, the nature and availability of active sites, and the identity of kinetically-relevant steps.

Formaldehyde Oxidation Over Manganese–Cerium–Aluminum Mixed Oxides Supported on Cordierite Monoliths at Low Temperatures

The activities of base metal oxides comprising 27 % MnO2, 21 % CeO2, and 52 % Al2O3 supported on cordierite monoliths calcined at 1,000 °C for 3 h in air dropped very rapidly due to the migration of mobile silicon dioxide (SiO2) from the cordierite to the base metal oxides to react with or physically block the active catalysts. After immobilizing migrating SiO2, cordierite-supported base metal oxides catalysts pretreated with BaO–Al2O3 barrier coats and calcined at 1,000 °C for 3 h in air, initiated the oxidation of HCHO, CH3OH, and CO at 150, 170, and 220 °C, respectively. These catalysts turned out to be more effective for the formaldehyde oxidation than 0.5 % Pt/Al2O3 precious metal catalysts. The incorporation of small amount of palladium (0.147 wt%) to cordierite-supported base metal oxides pretreated with BaO–Al2O3 barrier coats, showed the superiority for HCHO, CH3OH, and CO oxidation to 0.5 % Pt/Al2O3 precious metal catalysts. The temperatures of 50 % conversion of formaldehyde, methanol, and carbon monoxide were 70 °C lower over base metal oxides catalysts than over precious metal catalysts. Cordierite-supported Mn–Ce–Al oxides.

A DFT study of methanol oxidation on Co3O4

By means of spin polarized density functional theory with the GGA+U framework, the reaction mechanism of CH3OH oxidation on the Co3O4 (110)-B and (111)-B surfaces has been investigated. Adsorption situation and a part of reaction cycle for CH3OH oxidation are clarified. Our results indicated that: i) U value can affect the calculated energetic result significantly; ii) CH3OH can adsorb with surface lattice oxygen atom (O2f/O3f) to form CoO bond directly, and the adsorption of CH3OH and its decomposition products on (110)-B is more stable than on (111)-B, which means CH3OH prefers Co3+ better than Co2+; iii) on the (110)-B surface, CH3OH can form CO2, H2O and adsorbed H atom. But on the (111)-B surface, CH3OH can just form formaldehyde (CH2O) and adsorbed H atom, this means oxidative capacity of (110)-B (Co3+) is higher than (111)-B (Co2+). The possible reasons corresponding to the high oxidative of (110)-B come from both Co3+ and O2f: Co3+ tends to bind adsorbed species for further decomposition and O2f tends to bind more hydrogenation atom involved in methanol due to its low-coordinates number compared to that of O3f.

Porous NiCo2O4 nanostructures as bi-functional electrocatalysts for CH3OH oxidation reaction and H2O2 reduction reaction

Abstract Porous nickel cobaltite (NiCo2O4) nanostructures were synthesized via a facile chemical deposition route. Their physicochemical properties were characterized via X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectra (XPS) and nitrogen sorption measurements. Their electrocatalytic performances were investigated by cyclic voltammetry (CV), chronoamperometry (CA) and electrochemical impedance spectroscopy (EIS) tests. The obtained NiCo2O4 materials exhibit typical agglomerate porous nanostructures with the specific surface area (SSA) and pore volume of 190.1 m2 g−1 and 1.136 cm3 g−1. Remarkably, the NiCo2O4 materials exhibit higher electrocatalytic activity, lower overpotential, better stability and greater tolerance compared to those of NiO and Co3O4 materials synthesized by the same procedure. As for the NiCo2O4 electrode, a current density of 98 mA cm−2 was obtained toward CH3OH electro-oxidation at 0.6 V in 1 M KOH and 0.5 M CH3OH electrolytes, and a current density of 223 mA cm−2 was achieved toward H2O2 electro-reduction at −0.3 V in 3 M NaOH and 0.5 M H2O2 electrolytes. Moreover, the NiCo2O4 electrode shows a desirable stability for both electrocatalytic reactions. The impressive electrocatalytic activity is largely attributable to the binary electroactive sites of Co and Ni species, intrinsic high electronic conductivity and superior porous nanostructures of the NiCo2O4 electrode, which are very promising for further development of high performance non-Pt catalysts alkaline fuel cells (AFCs).