Thermal Decomposition Of Methanol Research Articles

Probing the pyrolysis of methyl formate in the dilute gas phase by synchrotron radiation and theory

AbstractThe thermal dissociation of the atmospheric constituent methyl formate was probed by coupling pyrolysis with imaging photoelectron photoion coincidence spectroscopy (iPEPICO) using synchrotron VUV radiation at the Swiss Light Source (SLS). iPEPICO allows threshold photoelectron spectra to be obtained for pyrolysis products, distinguishing isomers and separating ionic and neutral dissociation pathways. In this work, the pyrolysis products of dilute methyl formate, CH3OC(O)H, were elucidated to be CH3OH + CO, 2 CH2O and CH4 + CO2 as in part distinct from the dissociation of the radical cation (CH3OH+• + CO and CH2OH+ + HCO). Density functional theory, CCSD(T), and CBS‐QB3 calculations were used to describe the experimentally observed reaction mechanisms, and the thermal decomposition kinetics and the competition between the reaction channels are addressed in a statistical model. One result of the theoretical model is that CH2O formation was predicted to come directly from methyl formate at temperatures below 1200 K, while above 1800 K, it is formed primarily from the thermal decomposition of methanol.

Contribution of SiC and SiO2 to Photoluminescence from SiC-SiO2 Nanocables Grown by Thermal Decomposition of Methanol

A new simple and cheap method to grow large scale SiC-SiO2 nanocables on catalyzed Si substrate directly is presented. The method is based on the thermal decomposition of methanol. The grown nanocables consisted of crystalline 3C-SiC and amorphous SiO2. A simple etching and oxidation process was used to analyze the contribution of SiC and SiO2 components to photoluminescence.

A simple synthesis of large-scale SiC–SiO 2 nanocables by using thermal decomposition of methanol: Structure, FTIR, Raman and PL characterization

Large-scale SiC nanocables were synthesized on a Ni(NO 3) 2-catalyzed Si substrate by using a simple and cheap method based on thermal decomposition of methanol. Based on X-ray diffraction and high-magnification transmission electron microscopy, the as-grown nanocables consisted of crystalline SiC cores and amorphous SiO 2 shells. The diameters of SiC cores were 5.7–10 nm and the thicknesses of SiO 2 shells were 9–20 nm. Dividing of nanocables was observed and its origin was investigated. An asymmetric feature of SiC TO band with a shoulder at the high-frequency side was attributed to the contribution of SiC TO mode. The nanocables displayed strong violet–blue emission. A possible growth mechanism was proposed.

Hierarchical Multiscale Mechanism Development for Methane Partial Oxidation and Reforming and for Thermal Decomposition of Oxygenates on Rh

A thermodynamically consistent C1 microkinetic model is developed for methane partial oxidation and reforming and for oxygenate (methanol and formaldehyde) decomposition on Rh via a hierarchical multiscale methodology. Sensitivity analysis is employed to identify the important parameters of the semiempirical unity bond index quadratic exponential potential (UBI-QEP) method and these parameters are refined using quantum mechanical density functional theory. With adjustment of only two pre-exponentials in the CH4 oxidation subset, the C1 mechanism captures a multitude of catalytic partial oxidation (CPOX) and reforming experimental data as well as thermal decomposition of methanol and formaldehyde. We validate the microkinetic model against high-pressure, spatially resolved CPOX experimental data. Distinct oxidation and reforming zones are predicted to exist, in agreement with experiments, suggesting that hydrogen is produced from reforming of methane by H2O formed in the oxidation zone. CO is produced catalytically by partial oxidation up to moderately high pressures, with water-gas shift taking place in the gas-phase at sufficiently high pressures resulting in reduction of CO selectivity.

Methanol Chemistry on Cu and Oxygen-Covered Cu Nanoclusters Supported on TiO2(110)

The thermal decomposition of methanol has been studied on TiO2(110) as well as on Cu and oxygen-covered Cu nanoclusters supported on TiO2(110) using temperature programmed desorption (TPD). The sizes of the Cu clusters were characterized by scanning tunneling microscopy (STM). Methanol chemistry on the vacuum-annealed, reduced TiO2 surface itself produces ethylene as the main desorption product. Reoxidation of the TiO2 surface quenches the production of ethylene but also results in a new formaldehyde desorption peak at 870 K. The reactivity of methanol on small Cu nanoclusters (40.2 ± 7.0 A diameter, 12.7 ± 2.4 A height) is minimal, but trace amounts of formaldehyde, CO2, methane and H2 are detected in TPD experiments, demonstrating that the Cu nanoclusters are more active than bulk single-crystal Cu surfaces. On oxygen-covered Cu nanoclusters, methanol reaction produces formaldehyde and CO2 as the major gaseous products as well as H2, water, and methane. The yields of formaldehyde and CO2 increase as the...

Effect of Oxygen Precoverage on the Reactivity of Methanol on Ru(001) Surfaces

The thermal decomposition of methanol on oxygen modified Ru(001) surfaces was investigated by reflection−absorption infrared spectroscopy (RAIRS), under UHV conditions. The stability of the different intermediates was interpreted in terms of the oxygen coverage (θO ranging from 0.25 to 0.75 ML), as well as of the methanol dose. For a low methanol exposure at 90 K, dissociative adsorption into methoxide (CH3O−) is favored by increasing oxygen coverage up to 0.6 ML, becoming almost inhibited for θO = 0.75 ML. The reactivity of methoxide is also enhanced by increasing θO from 0.25 to 0.6 ML, as the oxidation temperature drops from 130 to 100 K. Regardless of the oxygen coverage, the oxidation of methoxide yields the intermediate formaldehyde (H2CO), whose stability decreases with increasing θO. Formate (HCOO−) was only identified on surfaces with θO ≥ 0.5 ML, in the temperature range 100 K ≤ T < 130 K, with maximum yield for θO ≈ 0.6 ML. This was the first spectroscopic observation of the intermediate format...

Methanol adsorption and reactivity at uranium and UO 2 surfaces

The interaction of methanol (CH 3OD) with polycrystalline uranium and UO 2 has been studied by X-ray photoelectron spectroscopy (XPS), thermal desorption–mass spectrometry (TDMS) and secondary-ion mass spectrometry (SIMS) over the temperature range 90–500 K. Low-temperature (~90 K) adsorption on uranium resulted in the formation of methoxy species along with condensed-phase adsorbed methanol. Room-temperature adsorption of methanol (or annealing an adsorbed methanol adlayer to 300 K) on uranium produces a mixture of methoxy and a uranium oxycarbide. Further heating to 400 K completely decomposes the adsorbed methoxy species, with 10% desorbing as methane and the remaining methoxide irreversibly converting to an uranium oxycarbide overlayer of nominal composition UO 0.66C 0.34. Concomitant with these carbon-fragment-conversion processes, desorption of hydrogen and deuterium are also seen over a wide temperature regime (325–450 K). Methanol–d adsorption on UO 2 also produces a methoxy surface species at surfaces temperatures <150 K. Adsorbate decomposition following thermal desorption releases gaseous CH 4, H 2, HD, D 2 and CO. Most of the oxygen derived from the methanol molecule (>90%) was incorporated into the UO 2 layer and all of the adsorbed carbon desorbs from the surface as one of the molecular species identified above. The reactive adsorption and thermal decomposition of methanol at uranium and UO 2 surfaces is compared with that observed at other metal and metal oxide surfaces.

Adsorption and Thermal Decomposition of Methanol on the (100) Surface of NiAl: A Comparison to NiAl(110)

The surface reactivity of the (100) plane of stoichiometric NiAl toward methanol has been investigated with temperature-programmed desorption (TPD), X-ray and ultraviolet photoelectron spectroscopy (XPS and UPS), and high-resolution electron energy loss spectroscopy (EELS). The atomic composition of the outermost surface of NiAl(100) is predominately Al, in contrast to the (110) plane of NiAl which is capped by an outermost layer that contains both Al and Ni. In an effort to understand the effects of the atomic composition of the surface on reactivity, results for CH3OH/NiAl(100) are compared to prior results for CH3OH/NiAl(110). Methanol chemisorption on both planes of NiAl, at 120 K, is primarily associative (some dissociation cannot be ruled out). Chemisorbed methanol transforms into surface methoxy in the temperature interval of 120 and 200 K on both NiAl(100) and NiAl(110). On the (110) surface, subsequent C-H and C-O bond breaking steps at higher temperatures lead to the evolution of gaseous H2, CO, CH4, CH3 radicals, and small amounts of C2H4, in addition to the deposition of surface oxygen and carbon. The peak temperature of CH4 desorption from NiAl(110) is near 350 K and the maximum rate of CH3 radical desorption is located at 570 K. In contrast, methoxy decomposition on the NiAl(100) surface generates a much smaller amount of CH4 and the reaction channel leading to gaseous CO is completely suppressed. The presence of Ni atoms in the top layer of the (110) surface is suspected to be responsible for both CH4 and CO production on NiAl(110).

Spectroscopic studies of methanol decomposition on Pd[lcub]111[rcub

The thermal decomposition of methanol on a clean Pd[lcub]111[rcub] surface has been investigated using X-ray photoelectron spectrometry (XPS), secondary ion mass spectrometry (SIMS) and thermal desorption spectrometry (TDS). In this work, we observe that the methanolic C–O bond activation on Pd[lcub]111[rcub] is a strongly coverage dependent process. At lower and higher coverages, XPS data suggest that CH 3O ads is the principle product. At near monolayer coverage the methanolic C–O bond dissociates at 175 K to produce CH 3,ads, which is characterized by a C 1s binding energy of 283.8 eV, and is stable up to 400 K. A stepwise dehydrogenation of CH 3,ads to form CH 2,ads (methylene) and CH ads (methylidyne) is observed above 400 K. Surface methyl and its dehydrogenated forms are characterized both by the chemical shift of the XPS C 1s peak from 283.8 to 284.8 eV and by positive ion SIMS peaks with m e = 15, 14 and 13 . The gaseous products detected by TDS are methanol, CO, hydrogen, methane and water. This observation implies that the methanolic C–O bond cleavage is contingent upon a special molecular arrangement of precursors before reaction and that the CH 3,ads product is stabilized by ancillary reaction products, such as CO.

Adsorption and thermal decomposition of methanol on 3d transition metal (iron, nickel, titanium) aluminides: FeAl(110), NiAl, and TiAl

The adsorption and thermal decomposition of methanol on FeAl(110), polycrystalline NiAl, and polycrystalline TiAl have been investigated. Temperature-programmed desorption (TPD) and ultraviolet and X-ray photoelectron spectroscopies (UPS and XPS) are used to investigate the electronic structure and thermal decomposition reactions on 3d transition metal aluminide surfaces. Methane and hydrogen are the two primary products that result from methanol decomposition on all the 3d transition metal aluminides. UPS of CH[sub 3]OH/FeAl(110) and CH[sub 3]OH/NiAl at 200 and 270 K, respectively, supports the existence of a methoxy intermediate (CH[sub 3]O) on the Al component of FeAl(110) and NiAl. XPS results support a surface picture that has carbon chemisorbing on [open quotes]transition metal[close quotes] sites and the oxygen remaining on Al during the decomposition of the intermediate species. The peak temperatures of methane desorption from TiAl, FeAl(110), and NiAl are 450, 550, and 590 K, respectively. 84 refs., 12 figs., 2 tabs.

鉄バリウムゆうの化学状態に関する研究 （第３報） メタノール熱分解生成ガスによる還元雰囲気下での鉄バリウムゆう中の鉄の挙動

ゆう(釉)原料の焼成途中の各段階で温度保持中に還元雰囲気を導入し,ゆうの固体状態およびFe3+のガラス相への移行率とFe2+生成比の相関について,粉末X線回折およびMossbauerスペクトルの測定によって検討した。還元雰囲気は,メタノール熱分解によって生じる水素,一酸化炭素ガスなどの還元性ガスとして導入した。保持温度が750℃ では熱分解による水素,一酸化炭素ガス発生量の不足からFe2+化学種は生成しなかったが,850,940,1030,1120,1260℃ では量の多少に関わらずFe2+が生成した。Fe2+生成比は,750,1030,850,1120,940,1260℃ の順に増加しており最高温度1260℃ まで昇温した後,冷却中940℃ で導入したものでの値が昇温途中940℃ および1260℃ で導入したものと比較していちじるしく小さかった。また,粉末X線回折上に新らたなピークを生じ,Mossbauerスペクトルの線幅が細くなることなどから,昇温途中反癒温度940℃ で安定なPellyite相が形成されることが明らかとなり,このためFe2+生成比が特異的に大きくなることがわかった。

Thermal decomposition of methanol in shock waves

The thermal decomposition of methanol behind reflected shock waves with 1372 < T{sub 5} < 1842 K and 1.81 {times} 10{sup {minus}5} < {rho}{sub 5} < 2.15 {times} 10{sup {minus}5} mol/cm{sup 3} was studied by IR laser kinetic absorption spectroscopy and gas-chromatographic analysis of reaction products. The absorption profiles and product yields were satisfactorily modeled with a 26-reaction mechanism. The initial rate of decrease of IR absorption intensity and the product yields were very sensitive to the rate constants of the reactions CH{sub 3}OH + M = CH{sub 3} + OH + M, CH{sub 3}OH + H = CH{sub 3} + H{sub 2}O, CH{sub 3}OH + H = CH{sub 2}OH + H{sub 2}, and CH{sub 2}OH + M = CH{sub 2}O + H + M. The rate constant expression for the last reaction was derived.

Thermal Decomposition of Methanol behind Shock Waves

The thermal decomposition of methanol in argon behind incident and reflected shock waves is studied. The reaction was followed by ultraviolet (UV) absorption between 1900 and 2200 Å and by infrared (IR) emission of methanol at wavelengths 2.4–2.9 µm, 3.1–3.9 µm and 4.8–5.2 µm and of formed species at wavelengths 2.7 µm, 3.6 µm and 4.9 µm. The temperature and the density dependences of the decomposition rate constants were observed at temperatures from 1500 to 1900 K, at total densities from 10-5 to 2×10-4 mol/cm3 and at concentrations from 0.01% to 1.0% methanol. The experimentally-determined signals are compared with the calculated values and the density-dependent rate constants of the unimolecular reaction of methanol are obtained.