Electrocatalytic oxidation of formaldehyde and methanol on Ni(OH)2/Ni electrode

A nickel hydroxide-modified nickel electrode (Ni(OH)₂/Ni) was successfully prepared by the cyclic voltammetry (CV) method and the electrocatalytic properties of the electrode for formaldehyde and methanol oxidation have been investigated respectively. The Ni(OH)₂/Ni electrode exhibits high electrocatalytic activity in the reaction. A new method has been developed for formaldehyde determination at the nickel hydroxide-modified nickel electrode and the experimental parameters were optimized. The oxidation peak current is linearly proportional to the concentration of formaldehyde in the range of 7.0 × 10^?5 to 1.6 × 10^?2 M with a detection limit of 2.0 × 10^?5 M. Recoveries of artificial samples are between 93.3 and 103.5%. The effect of scan rate and methanol concentration on the electrochemical behavior of methanol were investigated respectively.     

Hydrogenation of Cinnamaldehyde on Ir/γ-Al2O3 Catalysts. Influence of the Surface Acidity

The oxidation of methane has been studied in a flow system as a function of the chemical composition of zeolite catalyst using nitrous oxide as oxidant. It is concluded that methanol is a primary oxidation product which may undergo further oxidation to formaldehyde and to carbon oxides. However, it may also undergo conversion over the acidic catalyst to higher hydrocarbons. Reaction with nitrous oxide resulted in the production of carbon oxides, methanol, formaldehyde, C₂ - C₄ , C₅ - C₇ nonaromatics, and aromatics. The effect of Fe₂ O₃ and Al₂ O₃ , with or without, over HZSM5 on products was studied.     

The Kinetics Behavior of the Reduction of Formaldehyde Catalyzed by Alcohol Dehydrogenase (ADH) and Partial Uncompetitive Substrate Inhibition by NADH

Alcohol dehydrogenase (ADH) catalyzes the final step in the biosynthesis of methanol from CO₂. Here, we report the steady-state kinetics for ADH, using a homogeneous enzyme preparation with formaldehyde as the substrate and nicotinamide adenine dinucleotide (NADH) as the cofactor. When changing NADH concentrations with the fixed concentrations of HCHO (more or less than NADH), kinetic studies revealed a particular zigzag phenomenon for the first time. Increasing formaldehyde concentration can weaken substrate inhibition and improve catalytic efficiency. The kinetic mechanism of ADH was analyzed using the secondary fitting method. The double reciprocal plots (1/v～1/[HCHO] and 1/[NADH]) strongly demonstrated that the substrate inhibition by NADH was uncompetitive versus formaldehyde and partial. In the direction of formaldehyde reduction, ADH has an ordered kinetic mechanism with formaldehyde adding to enzyme first and product methanol released last. The second reactant NADH can combine with the enzyme–methanol complex and then methanol dissociates from it at a slower rate than from enzyme–methanol. The reaction velocity depends on the relative rates of the alternative pathways. The addition of NADH also accelerates the releasing of methanol. As a result, substrate inhibition and activation occurred intermittently, and the zigzag double reciprocal plot (1/v～1/[NADH]) was obtained.     

CuMgAlO_x复合氧化物催化甲醇乙醇Guerbet反应:M~(2+)/Al~(3+)比的影响

以类水滑石为前驱体,通过调控M~(2+)/Al~(3+)比制备了系列具有不同表面性质的MgAlO_x(MA)和CuMgAlO_x(CMA)催化剂,并分别应用于甲醛乙醛缩合反应(甲醇乙醇Guerbet反应的第二步反应)和甲醇乙醇Guerbet反应。采用NH_3/CO_2-TPD、XPS、H_2-TPR和H_2-TPD技术对催化剂表面酸碱性以及铜物种的性质进行了表征。结果表明,甲醇乙醇Guerbet反应性能与催化剂表面Cu~0比表面积和中强碱数目有关,提高Cu~0比表面积有利于甲醇乙醇脱氢生成甲醛和乙醛,增强中强碱数目能促进甲醛乙醛缩合反应。     

Novel Flower‐Like Ag‐SiO2‐MgO‐Al2O3 Material: Preparation,Characterization and Catalytic Application in Methanol Dehydrogenation

Catalytic direct dehydrogenation of methanol to formaldehyde was carried out over Ag‐SiO₂‐MgO‐Al₂O₃ catalysts prepared by sol‐gel method. The optimal preparation mass fractions were determined as 8.3% MgO, 16.5% Al₂O₃ and 20% silver loading. Using this optimum catalyst, excellent activity and selectivity were obtained. The conversion of methanol and the selectivity to formaldehyde both reached 100%, which were much higher than other previously reported silver supported catalysts. Based on combined characterizations, such as X‐ray diffraction (XRD), scanning electronic microscopy (SEM), diffuse reflectance ultraviolet‐visible spectroscopy (UV‐Vis, DRS), nitrogen adsorption at low temperature, temperature programmed desorption of ammonia (NH₃‐TPD), desorption of CO₂ (CO₂‐TPD), etc., the correlation of the catalytic performance to the structural properties of the Ag‐SiO₂‐ MgO‐Al₂O₃ catalyst was discussed in detail. This perfect catalytic performance in the direct dehydrogenation of methanol to formaldehyde without any side‐products is attributed to its unique flower‐like structure with a surface area less than 1 m²/g, and the strong interactions between neutralized support and the nano‐sized Ag particles as active centers.     

Methanol adsorption on γ-irradiated SiO2 surface

The adsorption of methanol on γ-irradiated and un-irradiated SiO₂ surfaces pretreated at 473 K was investigated by Fourier transform infrared spectroscopy, temperature programmed desorption (TPD) and pulse methods. Methanol adsorbed only in molecular form on the un-irradiated sample. Treating the pre-irradiated silica surface with methanol at room temperature formaldehyde and hydrogen were formed. The methanol adsorbed on the irradiated silica transformed to formyl groups during a longer time at room temperature and desorbed as formaldehyde simultaneously with CH₃OH (T_max=395 K) on the TPD.     

Simultaneous determination of formaldehyde and methanol by flow-injection catalytic spectrophotometry

A flow-injection method is proposed for the simultaneous catalytic determination of formaldehyde and methanol on the basis of the catalytic action of formaldehyde upon the redox reaction between crystal violet and potassium bromate in a phosphoric acid medium and on-line oxidization of methanol into formaldehyde using a lead dioxide solid-phase reactor. The indicator reaction is monitored spectrophotometrically by measuring the decrease in the absorbance of crystal violet at the maximum absorption wavelength of 610 nm. A technique based on three sampling loops with a single injection valve is developed. The flow-injection system produces a signal of main peak with two shoulders of the same height. The height of the shoulders corresponds to the formaldehyde concentration, and the height difference between the shoulders and the main peak corresponds to the methanol concentration. The detection limit is 0.1 μg/mL for formaldehyde and 1.0 μg/mL for methanol with the sampling rate of 10 samples per hour. The relative standard deviations for 11 replicate determinations of formaldehyde (1.0 μg/mL) and methanol (10 μg/mL) are 1.1 and 2.1%, respectively. The method has been successfully applied to the simultaneous determination of formaldehyde and methanol in some gas samples. The text was submitted by the authors in English.     

On the Existence and Role of Formaldehyde During Aqueous Electrochemical Reduction of Carbon Monoxide to Methanol by Cobalt Phthalocyanine

A long-time challenge in aqueous CO₂ electrochemical reduction is to catalyze the formation of products beyond carbon monoxide with selectivity. Formaldehyde is the simplest of these products and one of the most relevant due to its broad use in the industry. Paradoxically it is one of the less reported product. Such scarcity may be in part explained by difficult identification and quantification using conventional chromatography or proton nuclear magnetic resonance techniques. Likewise, indirect detection methods are usually not compatible with labelled studies for asserting product origin. Recently, the possible production of formaldehyde during electrochemical reduction of carbon monoxide to methanol at cobalt phthalocyanine molecular catalyst in basic media has been the object of contradictory reports. By applying an analytical procedure based on proton NMR along with labelled studies, we provide definitive evidence for HCHO formation. We have further identified the possible scenarios for methanol formation through formaldehyde and revealed that the formation of the intermediate and its subsequent reduction are taking place at the same single active site. These studies open a new perspective to improve selectivity toward formaldehyde formation and to develop a subsequent chemistry based on reacting it with nucleophiles.     

In situ muSR and NMR investigation of methanol dissociation on carbon-supported nanoscaled Pt-Ru catalyst

In situ muSR and nuclear magnetic resonance (NMR) experiments on the investigation of methanol decomposition on Pt-Ru nanoscaled catalyst supported on Vulcan XC-72 carbon black (Pt-Ru/Vulcan XC-72) are presented. Avoided-level-crossing muon spin resonance measurements reveal the resonance line at magnetic field 2.018 T, we assign to transient CH₂?OMu? formaldehyde muonated radical. Results obtained allow us to estimate the contribution of chemical decomposition reaction process for the formaldehyde—carbon oxide—hydrogen conversion on Pt-Ru/Vulcan XC-72 catalytic material. NMR spectrum of the methanol covered Pt-Ru/Vulcan XC-72 consists of three broad resonance lines. Two of them are assigned to OH and CH₃ groups of methanol bound to the carbon black surface. Following the existing literature, which indicates that polymerization of formaldehyde readily takes place when the monomer is adsorbed on some active surface, the third one is assigned to the resonance signal of oligomeric species of formaldehyde. Taking into account the results of our experiments on electrochemical hydrogenation of carbon nanotubes, we do not exclude that the hydrogen arising as a result of methanol decomposition would also contribute to this signal. The high surface area of amorphous carbon nanoparticles of Vulcan XC-72 is favourable to adsorb the hydrogen on their surface.     

Self‐Sufficient Formaldehyde‐to‐Methanol Conversion by Organometallic Formaldehyde Dismutase Mimic

The catalytic networks of methylotrophic organisms, featuring redox enzymes for the activation of one‐carbon moieties, can serve as great inspiration in the development of novel homogeneously catalyzed pathways for the interconversion of C₁ molecules at ambient conditions. An imidazolium‐tagged arene–ruthenium complex was identified as an effective functional mimic of the bacterial formaldehyde dismutase, which provides a new and highly selective route for the conversion of formaldehyde to methanol in absence of any external reducing agents. Moreover, secondary amines are reductively methylated by the organometallic dismutase mimic in a redox self‐sufficient manner with formaldehyde acting both as carbon source and reducing agent.     

The mechanism of methanol formation and other reactions following formaldehyde adsorption on Ni(110)

The adsorption/desorption and reactive behavior of formaldehyde was studied on clean single-crystal Ni(110) at adsorption temperatures down to 200 °K. For low exposures of the surface to formaldehyde, hydrogen and CO binding states were populated due to decomposition of the molecule upon adsorption. Higher exposures gave rise to a decomposition-limited hydrogen peak exhibiting an activation energy of 20 kcal/gmol and an apparent frequency factor of 10¹⁴ sec^?1. At initial coverages of H₂CO exceeding about 0.5, monolayer methanol was observed to form. The formation of methanol involved a hydrogen atom transfer between two adsorbed H₂CO molecules and did not occur totally via surface hydrogen. Self-oxidation to form CO₂ was also observed. The surface exhibited reaction heterogeneity, and the surface reactivity was observed to depend on the temperature of adsorption of reactants, suggesting strong adsorbate-induced surface “reconstruction.”     

Recovery of MoO3 from spent catalysts of partial oxidation of methanol to formaldehyde

An effect of an ammonia solution concentration, temperature, l: s ratio on a MoO₃ extraction process was revealed in studying ammonia leaching of molybdenum oxide from spent iron-molybdenum catalyst of oxidation of methanol to formaldehyde The data obtained allow to optimize the extraction process of MoO₃ from the spent Fe-Mo catalysts.     

Selective oxidation of methane to formaldehyde by oxygen over silica-supported iron catalysts (Special column of methane transformation, Article)

FeO_x-SiO₂ catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeO_x-SiO₂ with an iron content of 0.5 wt% at 898 K. This 0.5 wt% FeO_x-SiO₂ catalyst demonstrated significantly higher catalytic performances than the 0.5 wt% FeO_x/SiO₂ prepared by an impregnation method. The correlation between the catalytic performances and the characterizations with UV-Vis and H₂-TPR suggested that the higher dispersion of iron species in the catalyst prepared by the sol-gel method was responsible for its higher catalytic activity for formaldehyde formation. The modification of the FeO_x-SiO₂ by phosphorus enhanced the formaldehyde selectivity, and a single-pass formaldehyde yield of 2.4% could be attained over a P-FeO_x-SiO₂ catalyst (P/Fe = 0.5) at 898 K. Raman spectroscopic measurements indicated the formation of FePO₄ nanoclusters in this catalyst, which were more selective toward formaldehyde formation.     

THE U.V. PHOTOLYSIS (Λ= 185nm) OF ETHYLENE GLYCOL IN AQUEOUS SOLUTION*

Abstract— –The u.v. photolysis (Λ= 185 nm) of 2 M aqueous solutions of ethylene glycol was studied at 22°C. Products (quantum yields) are hydrogen (0.20₄) formaldehyde (0.19₄), glycolaldehyde (0.08), methanol (0.07₄), glycerol (0.06), erythritol (0.03), acetaldehyde (0.02), 3,4-dihydroxybutanal (0.01) and succinaldehyde (0.001). With increasing temperature the yields of all products remain essentially unchanged except that of acetaldehyde (φ= 0.32 at 90°C) which is formed in a chain reaction. The photolysis of (CD₂OH)₂ yields 91% HD, indicating that the most important primary process is the homolytic splitting of the O-H bond. The resulting oxy radicals fragmentate largely into formaldehyde and CH₂OH radicals. Molecular fragmentation processes yielding hydrogen and glycolaldehyde, as well as formaldehyde and methanol, are discussed in the proposed decomposition scheme.     

In Situ Study of the Selective Oxidation of Methanol to Formaldehyde on Copper

Combined use of X-ray photoelectron spectroscopy (XPS) and in situ mass spectrometry made it possible to simultaneously obtain the O1s spectra and the mass spectrometric signal of formaldehyde (m/z = 30) in the course of heating (420–670 K) of polycrystalline foil in a flow of the reaction mixture of methanol and oxygen (with a total pressure of 0.1 mbar and a ratio of 3/1). It is shown that the O1s spectra contain two lines with E _b = 530.1 and 531.2 eV, whose relative intensities depend on the sample temperature. At a low temperature (420 K) the line with a lower binding energy dominates, whereas sample heating leads to a drastic decrease in its intensity and its replacement by a line with a higher value of E _b. A decrease in the intensity of the latter line occurs at T > 550 K, in the same temperature range as a drastic increase in the intensity of the formaldehyde signal. These lines were assigned on the basis of literature data and data obtained by the authors for the known forms of oxygen on copper and for the intermediate species of the reaction, such as methoxy and formate. The O1s line with E _b = 530.1 eV was assigned to methoxy groups, and the line with E _b = 531.2 eV was assigned to suboxide oxygen. The correlation of the intensity of the XPS signal of suboxide oxygen with the yield of formaldehyde was supported by stationary experiments using in situ XPS that prove its participation in the key step of the selective oxidation of methanol to formaldehyde.     

Reaction Mechanism of Methanol to Formaldehyde over Fe‐ and FeO‐Modified Graphene

We employed periodic DFT calculations (PBE‐D2) to investigate the catalytic conversion of methanol over graphene embedded with Fe and FeO. Two possible pathways of dehydrogenation to formaldehyde and dehydration to dimethyl ether (DME) over these catalysts were examined. Both processes are initiated with the activation of methanol over the catalytic center through O?H cleavage. As a result, a methoxo‐containing intermediate is formed. Subsequently, H‐transfer from the methoxy to the adjacent ligand leads to the formation of formaldehyde. Conversely, the activation of the second methanol over the intermediate gives DME and H₂O. Over Fe/graphene, the dehydration process is kinetically and thermodynamically preferable. Unlike Fe/graphene, FeO/graphene is predicted to be an efficient catalyst for the dehydrogenation process. Oxidative dehydrogenation over FeO/graphene takes place through two steps with free energy barriers of 5.7 and 10.2 kcal mol^?1.     

水对甲醇在Rutile-TiO2(110)-(1 ×1)表面光催化解离的影响简

采用程序升温脱附方法研究了甲醇分子吸附在真空退火后的二氧化钛（110）表面的光催化过程,对比分析了单独吸附甲醇分子以及甲醇分子与水分子共吸附情况下的光催化解离过程. 结果表明,在二氧化钛（110）表面吸附的甲醇分子对共吸附水分子的光催化解离过程并没有直接的帮助作用. 共吸附状态下的水分子也同样没有影响到甲醇的光致解离过程,但是水分子的存在抑制了甲醇光解产物甲醛的光致脱附过程,同时促进了甲酸甲酯的形成.     

Interaction of methanol with ruthenium

The interaction of methanol with a clean (110) ruthenium surface has been studied using temperatures programmed desorption methods. Methanol dissociates upon adsorption at 300 K and yields H₂(g) and chemisorbed CO as the dominant products. Randomization of evolved hydrogen was shown to occur during methanol adsorption and also upon subsequent thermal desorption using isotopically labeled methanol, CH₃OD. In addition to hydrogen and CO, small amounts of H₂CO, CH₃OH, CO₂, and H₂O, are also observed upon thermal desorption. In contrast with a previous study of formaldehyde on Ru(110), no detectable CH₄ product is found upon methanol desorption.     

Fe-Mo/KZSM-5上甲醇氧化为甲醛的研究

采用浸渍法制备了ＦｅＭｏ／ＨＺＳＭ５和ＦｅＭｏ／ＫＺＳＭ５分子筛催化剂,利用ＮＨ３ＴＰＤ和Ｏ２ＴＰＤ对催化剂的表面酸性和吸附Ｏ２物种进行了表征,考察了温度、Ｍｏ／Ｆｅ摩尔比、空气／甲醇摩尔比及ＷＨＳＶ对催化性能的影响．实验结果表明,在ＦｅＭｏ／ＫＺＳＭ５催化剂上,适宜的反应条件下,甲醇转化率接近１００％,甲醛选择性达到９０６％．同时还进行了９６ｈ的催化剂的稳定性实验     

利用第一性原理研究氧化铟在甲醇水蒸气重整反应中的催化作用

基于第一性原理方法,证明了甲醛在In₂O₃(110)表面可以选择性地转化为CO₂. 水分解得到的OH物种有利于甲醛脱氢得到CHO,后者不易直接脱氢,其H原子被周围的OH捕获生成CO和H₂O. 最后,相比较其从表面直接脱附,CO更容易获得一个晶格氧生成CO₂. 计算结果表明,在没有PdIn合金参与催化的甲醇水蒸气重整反应过程中,In₂O₃确实扮演着非常重要的角色,进而从理论上证实了甲醇在氧化铟表面选择性生成CO₂的实验结果.