Temperature-programmed desorption studies of methanol and formic acid decomposition on copper oxide surfaces

We have obtained temperature-programmed desorption data for methanol and formic acid adsorption on bulk powders of CuO and Cu₂O. Methanol adsorption on CuO at 300 K results in CO₂, H₂ and H₂O desorption at 550 K indicating formate decomposition; this decomposition temperature is very close to that obtained from the decomposition of formate produced by formic acid adsorption. No significant desorption was observed from vacuum-annealed Cu₂O following exposure to methanol due to the formation of a copper metal film at the surface. However, formic acid was adsorbed on this surface decomposing at significantly lower temperature, 485 K, than on CuO. This revised version was published online in July 2006 with corrections to the Cover Date.     

Probing the electronic structure of an active catalyst surface under high-pressure reaction conditions: the oxidation of methanol over copper

The active phase of a bulk metallic copper catalyst is investigated by surface sensitive X-ray absorption spectroscopy at the oxygen K-edge and the Cu L-edges in the total electron yield mode under practical steady state flow-through conditions. The active catalyst surface contains oxygen atoms revealing significant spectral differences compared to those of known copper oxides. The partial oxidation of methanol to formaldehyde is correlated to the abundance of this copper suboxide. These oxygen atoms probe defects of the copper lattice, which represent catalytically active sites. The suboxide is undetectable under UHV conditions. The total oxidation of methanol is catalysed by a conventional copper(I) oxide species and the abundance of carbon dioxide in the gas phase is increasing with decreasing integrated intensity of the oxide species. This revised version was published online in July 2006 with corrections to the Cover Date.     

Characterisation of active phases of a copper catalyst for methanol oxidation under reaction conditions: an in situ X-ray absorption spectroscopy study in the soft energy range

The oxidation of methanol over copper is investigated by X-ray absorption spectroscopy in the soft X-ray range under reaction conditions. This in situ method allows the surface electronic structure of the catalyst to be correlated with its performance. The correlation reveals information about the catalytic function of various oxygen species on the surface. Oxide and metastable suboxide species affect in distinctly different ways the multiple action of copper as selective or unselective heterogeneous catalyst.     

Oxidation of the copper alloy with pure copper plating

The oxidation failure of a copper alloy lead frame with/without a copper plating layer was investigated. The oxidation rate and adhesion strength of oxide films on copper alloy substrates were studied by measuring the thickness and by carrying out peel tests. The adhesion strength of the oxide film was mainly influenced by the composition but not the thickness of the oxide film. The highest adhesion strength was obtained when the oxide film was composed mainly of Cu₂O. When the thickness of the copper preplated layer was over 0.165?μm, the Cu atoms of the preplated copper were available for oxidation. Thus the oxidation process was within the copper preplated layer, and the main product of the oxidation was Cu₂O. It was found that the large column grain of the oxide film on the copper alloy with a copper plated layer, favored the diffusion of copper or oxygen atoms that led to the formation of Cu₂O, and lead to higher adhesion strength. This indicated that the oxidation resistance of a copper alloy lead frame can be effectively improved by electroplating copper.     

The role of metal oxides in promoting a copper catalyst for methanol synthesis

The coverage of oxygen formed on the surface of catalysts during methanol synthesis from CO₂ has been measured for copper-based catalysts including various metal oxides using a method called reactive frontal chromatography (RFC). An excellent correlation between the specific activity for methanol synthesis and the oxygen coverage () was obtained, where the activity increased linearly with oxygen coverage at<0.16 and then decreased at>0.18. The results strongly indicate that the support effect or addition of metal oxides revealed in methanol synthesis over copper catalysts is ascribed to the ratio of Cu⁺ to Cu⁰ on the surface of copper particles.     

Role of ZnO in methanol synthesis on copper catalysts

The varied results obtained by different groups concerning synergy between ZnO and Cu metal in methanol synthesis catalysts are shown to be a result of different experimental test conditions. It is suggested that synergy, when it occurs, arises from H spillover from ZnO to Cu metal. This revised version was published online in July 2006 with corrections to the Cover Date.     

On the nature of the active state of silver during catalytic oxidation of methanol

Under the applied high reaction temperatures (900 K) the Ag surface is restructured and a tightly held oxygen species is formed on the surface (O) apart from O atoms dissolved in the bulk (O). Methanol oxidation to formaldehyde proceeds through this O species as demonstrated by application of a variety of spectroscopic techniques.     

含锰铜基甲醇催化剂的性能及其结构研究

用一步并流共沉淀法制备了CuO/ZnO/Al₂O₃和CuO/ZnO/Al₂O₃/MnO₂两种甲醇合成催化剂。通过测试它们的初活性及耐热后的活性可知, 含锰的催化剂CuO/ZnO/Al₂O₃/MnO₂具有较好的热稳定性。 利用XRD 和SEM 等实验手段, 对催化剂的结构和形貌进行了考察。 并研究了反应条件对催化剂活性的影响。     

Active sites in methanol oxidation on Cu(110) determined by STM and molecular beam measurements

STM has been combined with molecular beam rate measurements to gain an understanding of the oxidative dehydrogenation of methanol to produce formaldehyde, both at the macroscopic and microscopic level. From this a model of the reaction is developed where the methanol initial reacts at very few active oxygen sites located at the short sides of oxygen islands on the Cu(110) surface. Such sites are very much rarer on a surface which is saturated with 0.5 monolayers of oxygen and the reaction rate is initially very low, but shows autocatalytic behaviour, rising in time as vacancies are created in the oxygen layer.     

High-pressure low-energy XAS: a new tool for probing reacting surfaces of heterogeneous catalysts

An instrumentation is presented allowing to study the X-ray absorption edge spectra of light elements (z=3–15) in the surface-sensitive Auger yield detection at elevated pressures (mbar range). Heterogeneous catalysts can be studied for their surface electronic structure under working conditions in a flow-through reactor mode. An example of methanol oxidation to formaldehyde over copper metal is studied in detail. A new form of weakly bound atomic oxygen was found which only exists under reaction conditions. Its existence is linked to defect sites on the Cu. Several mechanistic predictions from earlier low-pressure studies could be verified with this in situ experiment. This revised version was published online in June 2006 with corrections to the Cover Date.     

The role of surface oxygen on copper metal in catalysts for the synthesis of methanol

Discrepancies in experimental measurements of adsorbed oxygen coverage on copper metal surfaces in working Cu/ZnO/Al₂O₃ catalysts are interpreted in terms of two types of adsorbed oxygen. The first, O(a), is identical with that observed in studies of single‐crystal copper surfaces. The second, O^*(a), not seen in single‐crystal studies, is more strongly bonded to the metal surface. It is suggested that the adsorption sites of O^*(a) contain Zn as well as Cu, from surface α‐brass (copper/zinc alloy) formation during catalyst reduction. Earlier experimental results on O(a) coverages on various supported copper catalysts are re‐assessed. Only catalysts containing Zn (or Ga) gave abnormally high coverages: with other supports, basic or acidic, O(a) coverages are less than ∼0.1. This revised version was published online in July 2006 with corrections to the Cover Date.     

中红外光谱法测定甲醇汽油中甲醇含量

利用IROX2000傅立叶红外光谱仪测定不同甲醇含量的甲醇汽油样品,与气相色谱方法进行了对比,找出了红外光谱法准确测定甲醇汽油中甲醇含量的范围,并验证其可靠性。实验证明,中红外光谱法具有分析快速、重复性好、分析成本低等优点。     

Synthesis of methoxysilanes by the reaction of metallic silicon with methanol using copper(II) acetate as the catalyst

The reaction of methanol with silicon was studied using various copper compounds other than the halides. Copper(II) acetate and copper(I) oxide gave high silicon conversions (82%) though the selectivities for trimethoxysilane were low (<19%). The selectivity was appreciably improved by addition of a small amount of thiophene or propyl chloride to the methanol feed.     

Supported foam–copper catalysts for methanol selective oxidation

Structural, mechanical, gas-dynamic and catalytic properties of copper catalysts supported on foam ceramics have been studied. Due to the three-dimensional open-porous cellular structure the foam catalysts have high gas permeability, mechanical strength, and low density. Catalytic activity and selectivity of the foam catalysts in the process of oxidation of methanol to formaldehyde exceed the characteristics of the conventional crystalline and granulated catalysts of the same composition. Different electronic states (ions, charged clusters, nanoparticles and microcrystals) of copper on the catalyst surface have been studied by the method of UV–Vis spectroscopy.     

Effect of operational parameters of mini-direct methanol fuel cells operating at ambient temperature

There is currently increased interest in small-size direct methanol fuel cells for portable applications. This work presents results of the influence of operational parameters on the performance of a mini-direct methanol fuel cell. The effects of methanol concentration, Pt load, membrane thickness and PTFE content in the cathode diffusion layer on the performance were studied. Two anodic materials were prepared, PtRu 75:25 at.% and PtRu 90:10 at.%, as nanoparticles supported on Vulcan XC-72 carbon, while for the cathodes Pt/C E-TEK catalysts were used. The materials were characterized physically by EDX and DRX and electrochemically in a half-cell. The results with single cells showed better performances with cells operating with 3 mg Pt cm^?2, 5 mol l^?1 methanol solution, Nafion^® 112 membrane and with 30 wt.% PTFE in the cathode diffusion layer deposited on only one face of the electrode support.     

Electro-Catalytic Oxidation of Methanol on a Ni–Cu Alloy in Alkaline Medium

The electro-catalytic oxidation of methanol on a Ni–Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0–600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10⁻⁴ cm² s⁻¹ and 1979.01 cm³ mol⁻¹ s⁻¹, respectively. EIS studies were employed to unveil the charge transfer rate as well as the electrical characteristics of the catalytic surface. For the electrochemical oxidation of methanol at 5.0 m concentration, charge transfer resistance of nearly 111 Ω was obtained while the resistance of the electro-catalyst layer was ca. 329 Ω.     

Improved methanol yield from methane oxidation in a non-isothermal reactor

Partial oxidation of methane to methanol was carried out homogeneously in a non-isothermal reactor that contained a non-permselective membrane. A tubular reactor was used with a smaller-diameter tubular membrane of 5 nm pore diameter alumina or 0.5 μm pore diameter metal. The membrane provided a uniform flow distribution and separated the hot reactor wall from a cooling tube located in the centre of the reactor. The cold region in the reactor rapidly quenched further reaction. The selectivity for CH₃OH formation at 4.6% conversion increased from 34 to 52% when quenching was used. The highest yield (selectivity times conversion) obtained was 3.8% at 55 MPa and 800 K. Methanol selectivity increased with increasing pressure and decreased with increasing temperature, residence time and O₂ concentration. The combined selectivity to partial oxidation products (CO, CH₃OH, CH₂O) was almost constant at 86%.     

Platinum-macrocycle co-catalysts for the electrochemical oxidation of methanol

Metal phthalocyanines (Fe, Co, Ni and Sn) and ruthenium tetramethylcyclam 14 and 15 were studied as cocatalysts for methanol oxidation on platinum supported catalysts. The formation of well defined monolayers of the adsorbed complexes was inferred from the Langmuirian form of the adsorption isotherms in solutions of macrocycles. The coverage at monolayer levels was low, e.g. 1.25 to 2.25×10¹³ molecules cm⁻² or 400 to 800 Ų molecule⁻¹. Enhancement for the methanol oxidation reaction was observed for Pt co-catalyzed with Sn phthalocyanine and Ru tetramethylcyclam. Ru tetramethylcyclam showed an enhancement for methanol oxidation on a per unit weight basis over pure Pt, approaching the activity of PtRu at lower potentials. Increasing the size of the nitrogen ring from 14 to 15 resulted in a lower redox potential and increase in the activity of methanol oxidation. The activity of Pt co-catalyzed with Ru TMC 15 decreased with time suggesting that the macrocycle was desorbing from the supported catalyst surface.     

The role of iodide promoter in selective oxidation of methanol to formaldehyde

The interaction of a CH₃I promoter and a commercial electrolytic silver catalyst was investigated using XPS, UPS and in situ confocal microprobe Raman spectroscopy. XPS and UPS results show evidence for formation of AgI on the surface of the silver catalyst. Interestingly, XPS results show no evidence for formation of any carbon species on the silver catalyst at room temperature, implying that CH₃I can be used as a “pure” I‐modifier in the catalytic oxidation of CH₃OH to HCHO. UPS results show a positive work function change (Δφ > 0) for the I‐modified catalysts. In situ Raman studies show that both the adsorption and reaction of methanol were promoted on the modified silver surface. The present experimental results provide not only an understanding of the surface chemistry of the silver catalyst but also a further understanding of the promotion effect of CH₃I in the selective oxidation of CH₃OH to HCHO. This revised version was published online in July 2006 with corrections to the Cover Date.     

甲醇氧化重整催化剂的研究

制备并优选了甲醇氧化重整的催化剂 ,实验表明在相同的温度下 ,Pd催化剂、Cr2 O3 ZnO氧化物催化剂和Cu催化剂相比 ,活性、选择性以及氢产率都表现为Cu >Cr Zn >Pd。其中 ,Cu催化剂在低温时、Cr Zn催化剂在高温下表现出良好的活性和选择性 ,而且Cr Zn催化剂的热稳定性较好