Yield Of Formaldehyde Research Articles

Mechanism and active sites for the partial oxidation of methanol to formaldehyde over an electrolytic silver catalyst

In situ Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and fixed-bed microreactor experiments and were used to examine the operating mechanism of an electrolytic silver catalyst in the titled reaction. Methanol oxidation studies were performed at atmospheric pressure, temperatures between 448 and 1073 K and CH 3OH/O 2 feed stoichiometries of 1.5–4.0. Particular attention was given to the role of surface chemisorbed and bulk-dissolved oxygen species in the catalytic cycle, and the influence of oxygen speciation on catalyst selectivity to formaldehyde. The results indicate that the product distribution of CH 3OH oxidation over electrolytic silver catalysts relates intimately to the nature of the oxygen species formed on the catalyst, which is discussed within a framework comprising two distinct surface chemisorbed atomic oxygen species (denoted O α and O γ) and a bulk-dissolved species (denoted O β). The selectivity to formaldehyde was highly dependent on the surface ratio O γ/O α, both of which increased with temperature from 548 to 923 K and CH 3OH/O 2 feed ratio from 1.5 to 2.25. An optimum formaldehyde yield of 84.3% was obtained during microreactor testing of the silver catalyst, under conditions close to those employed industrially (temperature = 923 K, molar ratio CH 3OH/O 2=2.25, GHSV=1.25×10 5 h −1). SEM revealed that pronounced thermal and catalytic etching of the silver catalyst occurred during CH 3OH oxidation at 923 K. Based on these results, a scheme was developed for the interaction of CH 3OH and O 2 with electrolytic silver catalysts under conditions of industrial formaldehyde manufacture. This work clarifies the role of the O α, O β and O γ species in methanol oxidation on silver surfaces and provides a fundamental basis for future formaldehyde yield optimisation.

Excellent Catalytic Performances of SBA‐15‐Supported Vanadium Oxide for Partial Oxidation of Methane to Formaldehyde.

Vanadium oxide supported on SBA-15 exhibits superior catalytic performances for the partial oxidation of methane to formaldehyde. A space-time yield of formaldehyde as high as 93 mol kgcat.−1h−1 has been obtained with a formaldehyde selectivity of 94% over 3 wt % VOx/SBA-15 catalyst, significantly higher than those reported so far.

The Measure of TiO2 Photocatalytic Efficiency and the Comparison of Different Photocatalytic Titania

The dependence of hydroxyl radical yield on the substrate concentration, pH, oxygen concentration, and light intensity, using different TiO2 preparations, was investigated. The quantum yields of formaldehyde and carbon dioxide, obtained with the aid of an integrating sphere in the methanol and formate systems, respectively, were used to derive the primary yield of hydroxyl radicals. The limiting yield of •OHads, achieved at high scavenger concentrations, is independent of the nature of the scavenger (methanol or formate) and is nearly constant in the range 1 < pH < 12. While the presence of air induces a 15-fold increase in product yield, compared to air-free systems, further increase of oxygen concentration has only a small effect. The effect of changing the •OH scavenger concentration, pH, and light intensity corresponds to simple competition between pseudo first- and second-order reactions. Under the conditions of the present work the scavengers CH3OH, HCO2- and HCO2H react only with the hydroxyl radical, not with its precursor hole. Hydrogen peroxide, which is produced in the above systems upon reduction of oxygen by both TiO2 electrons and the organic free radicals, is further reduced to •OH radicals, doubling the products yield. A rigorous treatment of the effect of absorbed photon density on the quantum yield, based on the simple square root dependency, enables the derivation of a constant, Kd, which is related to the efficiency of surface water oxidation to hydroxyl radicals, relative to the electron hole recombination at the given pH and oxygen concentration. This parameter is a property of the TiO2, and is not affected by the experimental conditions such as wavelength and layer thickness. Comparison of Kd using different types of TiO2 shows that in contrast to commonly assumed, preparation methods and sizes of aged titanium dioxide nanoparticles have only a relatively small effect on the basic photocatalytic efficiency. Comparison of the quantum yield in TiO2 layers to results in aqueous suspensions using similar photon flux shows moderate differences. The results are discussed in view of the much larger absorbed photon density in the suspended nanoparticles combined with much larger volume in the bulk of the solution.

Excellent Catalytic Performances of SBA-15-supported Vanadium Oxide for Partial Oxidation of Methane to Formaldehyde

Abstract Vanadium oxide supported on SBA-15 exhibits superior catalytic performances for the partial oxidation of methane to formaldehyde. A space-time yield of formaldehyde as high as 93 mol kgcat.−1h−1 has been obtained with a formaldehyde selectivity of 94% over 3 wt % VOx/SBA-15 catalyst, significantly higher than those reported so far.

Methanol Electrooxidation over Pt/C Fuel Cell Catalysts: Dependence of Product Yields on Catalyst Loading

We have investigated the influence of the catalyst loading (7−35 μgPt·cm-2) on methanol oxidation product yields over Vulcan XC72 supported Pt catalyst by differential electrochemical mass spectrometry (DEMS), both under potentiodynamic and potentiostatic (0.6 VRHE) conditions. Experiments were performed at room temperature and under continuous flow conditions (0.1 M CH3OH in 0.5 M H2SO4 solution). Absolute calibration of the DEMS signal allowed determination of current efficiencies for the final reaction product CO2 and for the reaction intermediates formic acid and formaldehyde. These could be converted into turnover frequencies (TOFs) on the basis of the physical (transmission electron microscopy) and electrochemical (CO stripping, HUPD) determination of the absolute particle surface area. The good agreement between these values indicates 100% utilization of the catalyst. The electrochemical efficiencies, product distribution, and the turnover frequencies of partial reactions (methanol oxidation to formaldehyde, formic acid, and CO2), during the methanol oxidation reaction (MOR) show a pronounced dependence on the catalyst loading. With increasing Pt loading the current efficiency for methanol oxidation to formaldehyde decays significantly (40% to almost 0%), while that for complete oxidation to CO2 increases from 50 to 80%. The variation in current efficiency for methanol oxidation to formic acid is small (ca. 10%). The product distribution varies accordingly; the absolute numbers, however, are different: Low (5−20%) formic acid yields are accompanied by a decaying formaldehyde yield (60% to zero) and increasing CO2 yield (30−80%) with increasing catalyst loading. The total TOF values calculated from the values for the individual reaction pathways and products are significantly higher than the Faradaic TOF numbers at low catalyst loadings, while at high loadings, where complete oxidation of methanol to CO2 is preferred, they agree satisfactorily. The pronounced variations in product distribution/TOF values are attributed to increasing readsorption and subsequent complete oxidation of desorbed reaction intermediates (formaldehyde and formic acid) at higher catalyst loadings, while at low loadings or, even more pronounced, on smooth electrodes these intermediates are more likely to survive. This has to be considered for predictions of MOR characteristics under fuel cell conditions on the basis of studies on smooth electrodes.

Catalytic performance of mesoporous VO x/SBA-15 catalysts for the partial oxidation of methane to formaldehyde

The ordered hexagonal mesoporous pure silica SBA-15 has been used as a support for preparing highly dispersed V-containing catalysts. VO x /SBA-15 samples with different V loading (1.26–5.54 wt.%) have been prepared by impregnation with an aqueous solution of NH 4VO 3, characterized by N 2 adsorption, UV-Vis spectroscopy, and H 2-TPR and then evaluated for the partial oxidation of methane to formaldehyde with oxygen. For vanadium coverages below the theoretical monolayer capacity (corresponding to ca. 4 wt.% V) the SBA-15 surface was predominantly covered by monomeric and low oligomeric vanadium oxide species, while at higher vanadium coverages agglomerated vanadium entities and even some small amounts of microcrystalline V 2O 5 were also formed. The conversion of methane (at constant temperature and GHSV) passed a maximum at a vanadium loading of 3.85 wt.%, while the maximum of activity typically occurs at lower V contents (1–2 wt.%) in amorphous vanadia-silica catalysts. This feature can be related with the much higher surface area of the mesoporous support, which allows the monolayer capacity to be reached at higher loading than in amorphous silica. The influence of the main reaction parameters (temperature, GHSV, CH 4:O 2 ratio) on the productivity of formaldehyde was studied. A maximum space–time yield (STY) of formaldehyde of about 2.4 kg kg −1 h −1 was obtained in this work for the most active VO x /SBA-15 catalyst (3.85 wt.% V) at 618 °C, GHSV=417,000 l (N) kg −1 h −1, and CH 4:O 2 molar ratio of 8:1. This value of STY HCHO is significantly higher than the maximum STY (ca. 1.3 kg kg −1 h −1) reported for VO x /SiO 2, and comparable to that recently reported for VO x /MCM-41 (ca. 2.2 kg kg −1 h −1), thus confirming the promising use of high surface area mesoporous supports for the POM reaction on vanadia based catalysts.

Selective oxidation of methane to formaldehyde over Mo/ZrO 2 catalysts

The catalytic performance of Mo/ZrO 2 catalysts in selective oxidation of methane to formaldehyde with molecular oxygen as oxidant has been investigated. The maximal yield of formaldehyde, ca. 4.0% (47.8% formaldehyde selectivity), was obtained on 12 wt.% Mo/ZrO 2 catalyst at 400 °C, 5.0 MPa, CH 4/O 2/N 2=10/1/3 and 12,000 ml g −1 catalyst h −1. The physicochemical properties of these catalysts, such as BET surface area, structure, particle size, reducibility, ion oxidation state and surface composition have been comparatively characterized by using BET, X-ray diffractometer (XRD), LR spectra (LRS), H 2-temperature-programmed reduction (TPR) and X-ray photoelectron spectroscopy (XPS) technology. The results clearly show that some interaction between Mo and ZrO 2 occurred. Such interaction induced the changes of physicochemical properties, which in turn determined the catalytic performance. The effects were a function of the Mo-loading. Zr(MoO 4) 2 in Mo/ZrO 2 catalysts were closely related to the formation of formaldehyde. The methane conversion and formaldehyde selectivity has been also correlated to the density of molybdenum oxides. The higher the density of molybdenum oxide, the higher was the specific activity. The MoO species of Zr(MoO 4) 2 enable selective oxidation of methane to formaldehyde, while the many more lattice oxygen species and bulk MoO 3 accelerated the deep oxidation of product formaldehyde.

Preparation of [11C]formaldehyde using a silver‐containing ceramic catalyst

AbstractA ceramic material, prepared from kaolin doped with silver ions in various concentrations, was evaluated as a catalyst for the conversion of [11C] methanol into [11C]formaldehyde in a gas flow system. Employment of [11C] methanol with a minimized water content, 300 mg of catalyst (20% of silver) at 500°C and a carrier gas flow rate of 40 mL/min resulted in a radiochemical decay‐corrected [11C]formaldehyde yield of 67% relative to [11C]methanol. Wet [11C]methanol under the same conditions gave 54% of [11C] formaldehyde. Copyright © 2003 John Wiley &amp; Sons, Ltd.

Methanol oxidative dehydrogenation in a packed-bed membrane reactor: yield optimization experiments and model

For the reaction involving methanol oxidative dehydrogenation to formaldehyde: CH 3 OH → 1/2 O 2 CH 2 O+ H 2 O → 1/2 O 2 CO+2 H 2 O, the performance of the packed-bed membrane reactor (PBMR) is compared with that of the conventional fixed-bed reactor (FBR) over a wide range of operating conditions. An experimentally validated reactor model is used for this purpose. It is found, both by simulations and experimental observations, that relative reactor performance depends strongly on the operating conditions. Using formaldehyde yield as the basis for optimization, optimal reactor performances for a fixed catalyst mass are determined and compared. The results predict higher optimal formaldehyde yield for the PBMR with oxygen fed via the membrane. The optimal reactor performance in this configuration is also less sensitive to variations in operating conditions and exhibits essentially 100% formaldehyde yield over a wide temperature range.

Novel Highly Active Ag–SiO2–MgO Catalysts Used for Direct Dehydrogenation of Methanol to Anhydrous Formaldehyde

Direct dehydrogenation of methanol to anhydrous formaldehyde was carried out over a novel Ag-SiO2-MgO catalyst prepared by the sol-gel method. The catalytic activity was measured over the temperature interval 350-700 °C and the space velocity of 1 × 104 h-1, while the optimum conditions were found to be 20 wt% loading of silver and 650 °C reaction temperature. The catalyst exhibits excellent activity (96% conversion) and selectivity (78%) during the process of dehydrogenation with the yield of formaldehyde up to 75%. X-ray diffraction patterns for the novel Ag(20 wt%)-SiO2-MgO catalyst correspond to α-crystobalite(100) and Ag(111), (200), (220), (311) and (222). Scanning electron microscopy was used to determine the morphology and particle size. Isolated silver particles with a mean size of about 5 μm were observed on the surface of the catalyst.

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 Ols 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 Ols 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 Ols 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.

Quantum yields of hydroxyl radicals in illuminated TiO 2 nanocrystallite layers

The yield of hydroxyl radicals has been determined by illumination of TiO 2 layers immersed in air saturated aqueous methanol solutions. This yield is equal to half the measured formaldehyde yield in the pH range 7–13. A detailed mechanism is proposed, accounting for the lack of accumulation of hydrogen peroxide. The effect of changing methanol concentration, pH and light intensity (the latter by three orders of magnitude) is in agreement with a very simple mechanism. In contrast to hydroxyl radicals, which react via hydrogen abstraction, leading to formation of HCHO, there is no sign for reaction of methanol with mobile holes. Thus, the limiting quantum yield observed at high methanol concentration is related to the maximum yield of OH ads under air saturated conditions at the given pH and light intensity. The effect of light intensity shows the expected inverted square root dependency. The yield of OH ads is nearly constant in the range 7<pH<12. This system may be useful for comparative tests of different TiO 2 preparations.

Methanol oxidative dehydrogenation in a catalytic packed-bed membrane reactor: experiments and model

Methanol oxidative dehydrogenation to formaldehyde over a Fe–Mo oxide catalyst was studied experimentally in three reactor configurations: the conventional fixed-bed reactor (FBR) and the packed-bed membrane reactor (PBMR), with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined independently from FBR experiments. A steady state plug-flow PBMR model, utilizing these kinetics and no adjustable parameters, fit the experiments accurately. It is shown experimentally and in accordance with the model that for given overall feed conditions, the reactor performance for methanol conversion and formaldehyde yield is in the order PBMR-M < FBR < PBMR-O.

Packed-Bed Reactor Performance Enhancement by Membrane Distributed Feed: The Case of Methanol Oxidative Dehydrogenation

ABSTRACTFor methanol oxidative dehydrogenation to formaldehyde, the performance of the packed-bed membrane reactor (PBMR) is compared with that of the conventional fixed-bed reactor (FBR) over a wide range of operating conditions. The reaction was studied in three reactor configurations: the conventional FBR and the packed-bed membrane reactor, with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined and incorporated in a PBMR model. Both experimental data and model considerations demonstrate that the PBMR enhances reactant conversion and selectivity.Small oscillations in CO production were observed experimentally. Their amplitude was taken as a basis for comparison of packed-bed operation instability. The likely source of oscillatory behavior is the non-uniformity in reaction conditions along the reactor. It was found that membrane distributed feed, by providing a more uniform reactor operation, is an effective remedy from these instabilities.It is found, both by simulations and experimental observations, that relative reactor performance depends strongly on the operating conditions. Using formaldehyde yield as the basis for optimization, optimal reactor performances are determined to be in the order: PBMR-O &gt; FBR &gt; PBMR-M. Further PBMR productivity enhancement is possible by optimizing the membrane feed distribution pattern.

The detailed mechanism of the OH-initiated atmospheric oxidation of α-pinene: a theoretical studyElectronic Supplementary Information available. See http:/sol;www.rsc.org/suppdata/cp/b1/b106555f/. This information is also available directly from the authors at http://arrhenius.chem.kuleuven.ac.be/labpeeters

A detailed mechanism is developed for the OH-initiated atmospheric oxidation of α-pinene in the presence of NOx, based solely on quantitative structure–activity relationships and on theoretical quantum chemistry methods, combined with transition state theory calculations or RRKM master equation analyses. Thus, on objective theoretical grounds, the fate of some 40 organic (oxy) radical intermediates is predicted. Addition of OH onto the monoterpene double bond accounts for ∼90% of the reaction and leads to chemically activated P1OH† (∼44%) and P2OH† (∼44%) radicals. The subsequent chemistry of these radicals is described, and the quantitative importance of the pathways leading to first-generation products such as pinonaldehyde, acetone, formaldehyde, formic acid and nitrates is discussed. H-atom abstraction by OH from α-pinene is a minor route (∼12%) but contributes importantly to the overall yield of formaldehyde. Total product yields are obtained by propagating the product fractions of each step in the mechanism. Overall predicted product yields for the usual conditions of laboratory experiments are, on a molar basis: 35.7% pinonaldehyde, 18.8% formaldehyde, 19% organic nitrates, 17.9% acetone, 25.9% other (hydroxy)carbonyls, 17.2% C1 and C2 carboxylic acids and 30.7% CO2, in general agreement with measured yields. For the much lower NO levels of real atmospheric conditions, on the other hand, our theoretically predicted yields differ significantly: 59.5% pinonaldehyde, 12.6% formaldehyde, 13.1% organic nitrates, 11.9% acetone, 16.4% other (hydroxy)carbonyls, 8.7% CO2 and a negligible fraction of C1 and C2 carboxylic acids. Some specific effects relating to the hyperconjugation-stabilization of terpene-derived (bi)cyclic radicals are discussed.

Photoproduction of hydroxyl radicals from Fe(III)-hydroxy complex: a quantitative assessment

Photolysis of aqueous solutions of ferric perchlorate in the presence of methanol, benzene and 2-deoxy-d-ribose at low pH has been investigated using sunlight and UV light in order to quantitatively assess the involvement of hydroxyl radicals (OH) in the photolysis of Fe(III)-hydroxy complexes. Time-dependent formation of formaldehyde, phenol and thiobarbituric acid-reactive substance (TBA-RS) was observed in the presence of methanol, benzene and 2-deoxy-d-ribose, respectively. The observed quantum yields of formaldehyde, phenol and TBA-RS are 0.025, 0.0098 and 0.0038, respectively, using UV light. A slightly lower quantum yields are obtained with sunlight owing to its lower intensity. The mechanistic aspects of these reactions are proposed based on the formation of OH from the photo-excited Fe(OH)2+ complex and their subsequent reactions with methanol, benzene and 2-deoxy-d-ribose. The quantum yield of OH is calculated from the observed quantum yields of formaldehyde, phenol and TBA-RS based on the reported percentage contribution of OH in the formation of these products using radiation chemical techniques from the respective reactions. The calculated quantum yields of OH were in the range 0.018–0.025 and 0.014–0.018 with UV light and sunlight, respectively. The results obtained with the photolytic studies have been compared with those from radiation chemical studies.

Gas evolution and the mechanism of cellulose pyrolysis

The real time evolution kinetics of formaldehyde, hydroxyacetaldehyde, CO and CO 2 during the pyrolysis of cellulose, Whatman 41, were studied in a fast evolved gas-FTIR apparatus (EGA). The samples were subjected to rapid exponential temperature increases ranging from 400 to 800°C within about one minute. A total of ten compounds were simultaneously detected in the gas phase by FTIR. Four of these: formaldehyde, hydroxyacetaldehyde, CO, and CO 2, were studied in detail as a function of time. The yields of formaldehyde, hydroxyacetaldehyde and CO were found to approximately double with heating rate over the range of the experimental temperature profiles while that of CO 2 decreased slightly. The kinetics of formaldehyde and CO formation were analyzed in terms of two competing first order reactions. The rate constants for the formation of formaldehyde and CO were found to have activation energies of 47 kcal/mole each while the competing reactions had activation energies of 35 kcal/mole in both cases. The case of hydroxyacetaldehyde was found to be more complex, with the same initial reactions as were found for formaldehyde and CO but requiring a third reaction step subsequent to the 47 kcal/mole reaction. The kinetics for CO 2 were consistent with a single first order reaction with an activation energy of 35 kcal/mole. The results indicate that the formation reactions of formaldehyde, hydroxyacetaldehyde, CO and CO 2 exhibit identical rate limiting steps that involve the major pyrolytic pathways of cellulose.

Methanol Oxidative Dehydrogenation in a Catalytic Packed-Bed Membrane Reactor: Experiments and Model

Abstract Methanol oxidative dehydrogenation to formaldehyde over a Fe–Mo oxide catalyst was studied experimentally in three reactor configurations: the conventional fixed-bed reactor (FBR) and the packed-bed membrane reactor (PBMR), with either methanol (PBMR-M) or oxygen (PBMR-O) as the permeating component. The kinetics of methanol and formaldehyde partial oxidation reactions were determined independently from FBR experiments. A steady state plug-flow PBMR model, utilizing these kinetics and no adjustable parameters, fit the experiments accurately. It is shown experimentally and in accordance with the model that for given overall feed conditions, the reactor performance for methanol conversion and formaldehyde yield is in the order PBMR-M

Direct Dehydrogenation of Methanol to Formaldehyde over Novel Ag-Containing Ceramics

Abstract A novel silver-ceramics supported catalyst showing excellent activity and selectivity in the direct dehydrogenation of methanol to formaldehyde was prepared. The selectivity was as high as 100% and the yield of formaldehyde reached 70%.

Cellulose pyrolysis: the kinetics of hydroxyacetaldehyde evolution

The kinetics of formaldehyde, hydroxyacetaldehyde, CO and CO 2 evolution during the pyrolysis of cellulose, Whatman 41, were studied in a fast evolved gas-FTIR apparatus (EGA). The samples were subjected to exponential temperature increases from ambient to final temperatures ranging from 400°C to 800°C within about 1 min. The yields of formaldehyde, hydroxyacetaldehyde and CO approximately doubled with heating rate over the experimental range of heating rates while that of CO 2 decreased slightly. The kinetics for CO 2 evolution are consistent with a single first order reaction. The kinetics of formaldehyde and CO formation require a pair of competing first order reactions. The behavior of hydroxyacetaldehyde is more complex. In this case a third reaction step is required following the initial pair of competing reactions. The reactions involved in the evolution of all four gases, with the exception of the third step in the hydroxyacetaldehyde mechanism, exhibit essentially identical activation parameters. This suggests their formation involves common rate limiting steps. These are, most likely, the decomposition pathways of cellulose which are followed by rapid secondary reactions to yield the individual gases.