Decomposition Of CH3CHO Research Articles

Two state reactivity (TSR) and hydrogen tunneling reaction kinetics measured in the Co+ mediated decomposition of CH3CHO.

The electronic structure of a transition metal atom allows it to act as a catalytic active site by providing lower energy alternative pathways in chemical transformations. We have identified and kinetically characterized three such pathways in the title reaction. One is an adiabatic pathway that occurs on a single potential energy surface described within the Born-Oppenheimer approximation. A second pathway opens microseconds into the reaction as a portion of the reacting population competitively transitions from triplet to singlet multiplicity to circumvent energetic barriers on the triplet surface. These pathways are single- and two-state reactive (SSR and TSR) where the Co+ cation mediates an oxidative addition/reductive elimination sequence of the CH3CHO molecule. The third observed reaction pathway is the aldehyde hydrogen tunneling through an Eyring barrier to form high-spin products. First-order rate constants for the adiabatic and nonadiabatic energy lowered pathways, and the hydrogen tunneling pathway, are each measured using the single photon initiated dissociative rearrangement reaction (SPIDRR) experimental technique. We believe that this is the first experimental study where such disparate dynamic features (SSR, TSR, and H-tunneling) are disentangled in a system's chemistry, attributing specific rate constant values to each effect and quantifying the various competitions. Moreover, multi-reference CASSCF/CASPT2 calculations indicate that structures with covalent Co-H bonds are present exclusively along the excited singlet surface. This phenomenon significantly reduces these structures' energy relative to their triplet counterparts, thus enabling the surface crossing and spin inversion that cause the observed two-state reactivity.

Novel cerium-based MOFs photocatalyst for photocarrier collaborative performance under visible light

A novel cerium-based metal–organic framework crystal (Ce-TBAPy) was developed via a one-pot solvothermal method. Interestingly, the Ce-TBAPy photocatalyst material demonstrated an enhanced collaborative photoredox performance in terms of acetaldehyde degradation and water reduction, and the photoreaction rates of Ce-TBAPy shown about 5.06-times and 3.94-times higher, respectively, than those when untreated H4TBAPy was used. A significant finding is that the apparent quantum efficiency value of Ce-TBAPy for CO2 generation from CH3CHO decomposition performs 5.12% at 420 nm. The accumulation of abundant separated holes on the pyrene macrocycles could oxidize CH3CHO to CO2 easily. Meanwhile, cerium integration with TBAPy4− ligands to form a π-conjugated construction further resulted in sufficient photoinduced electrons and exhibited effective interfacial charge separation, which harvesting the reduction of H2O to H2 efficiently. The electronic localization influence arising from the formation of –COO-Ce functional groups in Ce-TBAPy and the direction of electron migration in the photocatalytic system were further confirmed by DFT calculation. This work provides an effective strategy to obtain rare earth-based MOF photocatalysts with dual redox functions and holds promise for advancing the prospect of using MOF materials to convert solar energy into chemical energy.

Plasma-Catalysis for Volatile Organic Compounds Decomposition: Complexity of the Reaction Pathways during Acetaldehyde Removal

Acetaldehyde removal was carried out using non-thermal plasma (NTP) at 150 J·L−1, and plasma-driven catalysis (PDC) using Ag/TiO2/SiO2, at three different input energies—70, 350 and 1150 J·L−1. For the experimental configuration used, the PDC process showed better results in acetaldehyde (CH3CHO) degradation. At the exit of the reactor, for both processes and for all the used energies, the same intermediates in CH3CHO decomposition were identified, except for acetone which was only produced in the PDC process. In order to contribute to a better understanding of the synergistic effect between the plasma and the catalyst, acetaldehyde/catalyst surface interactions were studied by diffuse-reflectance infrared Fourier transform spectroscopy (DRIFTS). These measurements showed that different species such as acetate, formate, methoxy, ethoxy and formaldehyde are present on the surface, once it has been in contact with the plasma. A reaction pathway for CH3CHO degradation is proposed taking into account all the identified compounds in both the gas phase and the catalyst surface. It is very likely that in CH3CHO degradation the presence of methanol, one of the intermediates, combined with oxygen activation by silver atoms on the surface, are key elements in the performance of the PDC process.

Kinetic effects of polymorphs and surface areas on adsorption and photocatalytic decomposition of acetaldehyde on titania

Adsorption and photocatalytic decomposition behaviors of gas-phase acetaldehyde (CH3CHO), together with carbon dioxide (CO2) formation have been measured for pure titania (TiO2) powders with three types of polymorphs (anatase, brookite, and rutile) under UV-light illumination, and assessed by a kinetic model that takes into account the immediate decomposition of CH3CHO attached on the surface, and the gradual decomposition of CH3CHO adsorbed on the surface. Experimental data are well reproduced by the present model, highlighting how adsorption-related pathways markedly contribute to overall CH3CHO removal kinetics even for pure titanias. Although the initial removal rate depends on the surface area, which affects the adsorption capacity, it is suggested that specific surface area-based adsorbability and decomposition reactivity are enhanced by heightened crystallinity. Our kinetic analysis demonstrates that anatase exhibits the highest photocatalytic activity as a result of superior adsorbability, as well as superior decomposition reactivity, compared to other polymorphs.

Photochemical removal of acetaldehyde using 172nm vacuum ultraviolet excimer lamp in N2 or air at atmospheric pressure.

The photochemical removal of acetaldehyde was studied in N2 or air (O2 1-20%) at atmospheric pressure using side-on and head-on types of 172nm Xe2 excimer lamps. When CH3CHO was decomposed in N2 using the head-on lamp (HL), CH4, CO, and CO2 were observed as products in FTIR spectra. The initial removal rate of CH3CHO in N2 was ascertained as 0.37min-1. In air (1-20% O2), HCHO, HCOOH, CO, and CO2 were observed as products in FTIR spectra. The removal rate of CH3CHO in air using the side-on lamp (SL) increased from 3.2 to 18.6min-1 with decreasing O2 concentration from 20 to 1%. It also increased from 2.5 to 3.7min-1 with increasing CH3CHO concentration from 150 to 1000ppm at 20% O2. The best energy efficiency of the CH3CHO removal using the SL in a flow system was 2.8g/kWh at 1% O2. Results show that the contribution of O(1D) and O3 is insignificant in the initial decomposition of CH3CHO. It was inferred that CH3CHO is initially decomposed by the O(3P) + CH3CHO reaction at 5-20% O2, whereas the contribution of direct vacuum ultraviolet (VUV) photolysis increases concomitantly with decreasing O2 pressure at < 5% O2. After initial decomposition of CH3CHO, it was oxidized further by reactions of O(3P), OH, and O3 with various intermediates such as HCHO, HCOOH, and CO, leading to CO2 as a final product.

Acetaldehyde polymerization on Co(0001): the role of CO.

The adsorption and polymerization of acetaldehyde (CH3CHO) have been investigated on clean and CO pre-covered Co(0001) surfaces using the temperature programmed desorption (TPD) method. On the clean Co(0001) surface, CH3CHO molecules can polymerize to produce paraldehyde with very low efficiency. With pre-dosed CO molecules on Co(0001), the decomposition of CH3CHO is greatly inhibited. When the coverage of pre-dosed CO is <0.33 ML, no enhancement of CH3CHO polymerization is observed. However, when the pre-dosed CO coverage is >0.33 ML, the polymerization of CH3CHO is significantly enhanced during the TPD process. Further results suggest that CO molecules adsorbed at the bridge/hollow sites may initialize the polymerization by nucleophilic attack of CH3CHO molecules with their O atoms. Moreover, the polymerization product induced by CO molecules is not paraldehyde, but linear polymer chains of CH3CHO at low CH3CHO coverages and probably three dimensional polymer structures at high CH3CHO coverages.

Effect of metal doped and co-doped TiO2 photocatalysts oriented to degrade indoor/outdoor pollutants for air quality improvement. A kinetic and product study using acetaldehyde as probe molecule

This study demonstrates the photocatalytic decomposition of an indoor air pollutant, acetaldehyde (CH3CHO), over 0.04 mol% metal-doped TiO2 (Mn-, Co- and Mn/Co-) nanoparticles activated by ultraviolet and visible irradiation. The photocatalytic activity, the photodegradation kinetics, and the final product analysis were examined using a Static Photochemical Reactor coupled with a FTIR spectrophotometer. CH3CHO undergoes efficient decomposition over all photocatalysts under UV irradiation in the presence of one atmosphere N2 or synthetic air (SA). Metal doping causes substantial influence to photocatalysis by altering the amount of electron/hole pairs generated and/or the electron/hole recombination rates. Simulating the experimental results with pseudo-first order kinetics the corresponding degradation rate coefficients were determined for each photocatalyst under UV irradiation and SA environment: kdUV(Mn-TiO2) = (1.9 ± 0.2)×10−1 h−1, kdUV(Co-TiO2) = (2.8 ± 0.3)×10−1 h−1, and kdUV(Mn/Co-TiO2) = (6.0 ± 0.7)×10−1 h−1. These degradation kinetics under UV light irradiation are significantly faster than undoped TiO2 revealing that the transition metal doping of TiO2 nanomaterials boosts the photocatalytic degradation of organic pollutants. Substantial decomposition of CH3CHO was achieved over Mn-TiO2 under visible light in oxygen presence kdVis(SA) = (0.44 ± 0.04)×10−1 h−1 while for other samples no visible light photocatalysis was observed. CO2, CO, and H2O were the main oxidation products, with CO2 yields almost 100% under UV excitation, and CO yields up to 20% under UV and <1% under visible excitation. Our experimental results suggest that Mn-TiO2 (0.04 mol%) nanoparticles may be considered as a potentially safe photocatalyst to remove acetaldehyde particularly from indoor atmospheric environments under visible irradiation, without yielding significant toxic by-products. Other possible atmospheric implications are also discussed in the paper.

Theoretical Studies on the Kinetics of Multi-Channel Gas-Phase Unimolecular Decomposition of Acetaldehyde.

Theoretical kinetic studies are performed on the multichannel thermal decomposition of acetaldehyde. The geometries of the stationary points on the potential energy surface of the reaction are optimized at the MP2(full)/6-311++G(2d,2p) level of theory. More accurate energies are obtained by single point energy calculations at the CCSD(T,full)/augh-cc-pVTZ+2df, CBS-Q and G4 levels of theory. Here, by application of steady-state approximation to the thermally activated species CH3CHO* and CH2CHOH* and performance of statistical mechanical manipulations, expressions for the rate constants for different product channels are derived. Special attempts are made to compute accurate energy-specific rate coefficients for different channels by using semiclassical transition state theory. It is found that the isomerization of CH3CHO to the enol-form CH2CHOH plays a significant role in the unimolecular reaction of CH3CHO. The possible products of the reaction are formed via unimolecular decomposition of CH3CHO and CH2CHOH. The computed rate coefficients reveal that the dominant channel at low temperatures and high pressures is the formation of CH2CHOH due to the low barrier height for CH3CHO → CH2CHOH isomerization process. However, at high temperatures, the product channel CH3 + CHO becomes dominant.

A visible-light active TiO2 photocatalyst multilayered with WO3.

Sputter-deposited TiO2 films with high visible-light photocatalytic activity were successfully realized by a hybrid TiO2/Pt/WO3 film structure with Pt nanoparticles uniformly distributed at the interface of the TiO2 and WO3 films. The TiO2/Pt/WO3 hybrid films enable the complete decomposition of CH3CHO under visible-light irradiation. The water contact angle of the TiO2/Pt/WO3 hybrid films reaches below 5° under visible-light irradiation. Pt nanoparticles are considered to act as a cocatalyst to improve the electron-hole separation efficiency. We demonstrate that the photogenerated holes in WO3 are transferred to the surface of the TiO2 film with less hole-trapping and induce high visible-light photocatalytic activity and hydrophilic behavior, and the photogenerated electrons are accumulated in the Pt nanoparticles. The highly hydrophilic thin films with high visible-light photocatalytic activity can be applied to various indoor products possessing self-cleaning and antifogging properties.

Photoinduced decomposition of acetaldehyde on a reduced TiO2(110) surface: involvement of lattice oxygen.

We have investigated the photo-induced decomposition of acetaldehyde (CH3CHO) on TiO2(110) at 400 nm using temperature programmed desorption (TPD) and time of flight (TOF) methods. Formate (HCOO-) and acetate (CH3COO-) products have been detected. The initial step in the decomposition of CH3CHO on TiO2(110) is the formation of a CH3CHO bidentate intermediate in which the carbonyl O atom of CH3CHO is bound to the five-fold-coordinated Ti4+ lattice site (Ti5c) and the carbonyl C atom is bound to a nearby bridge-bonded oxygen (BBO) atom. During 400 nm irradiation, the decomposition of the CH3CHO bidentate mainly occurs through two parallel pathways. Part of the CH3CHO bidentate on the surface undergoes a facile photoreaction to form formate by ejecting the methyl radical of CH3CHO into gas phase. The remaining CH3CHO bidentate reacts on the surface to produce acetate by transferring the H atom of -CHO to a BBO site or by ejecting the H atom into the vacuum. Thus we have found that BBO atoms are intimately involved in the photo-induced decomposition of CH3CHO on TiO2(110).

Visible-light active thin-film WO3 photocatalyst with controlled high-rate deposition by low-damage reactive-gas-flow sputtering

A process based on reactive gas flow sputtering (GFS) for depositing visible-light active photocatalytic WO3 films at high deposition rates and with high film quality was successfully demonstrated. The deposition rate for this process was over 10 times higher than that achieved by the conventional sputtering process and the process was highly stable. Furthermore, Pt nanoparticle-loaded WO3 films deposited by the GFS process exhibited much higher photocatalytic activity than those deposited by conventional sputtering, where the photocatalytic activity was evaluated by the extent of decomposition of CH3CHO under visible light irradiation. The decomposition time for 60 ppm of CH3CHO was 7.5 times more rapid on the films deposited by the GFS process than on the films deposited by the conventional process. During GFS deposition, there are no high-energy particles bombarding the growing film surface, whereas the bombardment of the surface with high-energy particles is a key feature of conventional sputtering. Hence, the WO3 films deposited by GFS should be of higher quality, with fewer structural defects, which would lead to a decrease in the number of centers for electron-hole recombination and to the efficient use of photogenerated holes for the decomposition of CH3CHO.

Resolving Some Paradoxes in the Thermal Decomposition Mechanism of Acetaldehyde.

The mechanism for the thermal decomposition of acetaldehyde has been revisited with an analysis of literature kinetics experiments using theoretical kinetics. The present modeling study was motivated by recent observations, with very sensitive diagnostics, of some unexpected products in high temperature microtubular reactor experiments on the thermal decomposition of CH3CHO and its deuterated analogs, CH3CDO, CD3CHO, and CD3CDO. The observations of these products prompted the authors of these studies to suggest that the enol tautomer, CH2CHOH (vinyl alcohol), is a primary intermediate in the thermal decomposition of acetaldehyde. The present modeling efforts on acetaldehyde decomposition incorporate a master equation reanalysis of the CH3CHO potential energy surface (PES). The lowest-energy process on this PES is an isomerization of CH3CHO to CH2CHOH. However, the subsequent product channels for CH2CHOH are substantially higher in energy, and the only unimolecular process that can be thermally accessed is a reisomerization to CH3CHO. The incorporation of these new theoretical kinetics predictions into models for selected literature experiments on CH3CHO thermal decomposition confirms our earlier experiment and theory-based conclusions that the dominant decomposition process in CH3CHO at high temperatures is C-C bond fission with a minor contribution (∼10-20%) from the roaming mechanism to form CH4 and CO. The present modeling efforts also incorporate a master-equation analysis of the H + CH2CHOH potential energy surface. This bimolecular reaction is the primary mechanism for removal of CH2CHOH, which can accumulate to minor amounts at high temperatures, T > 1000 K, in most lab-scale experiments that use large initial concentrations of CH3CHO. Our modeling efforts indicate that the observation of ketene, water, and acetylene in the recent microtubular experiments are primarily due to bimolecular reactions of CH3CHO and CH2CHOH with H-atoms and have no bearing on the unimolecular decomposition mechanism of CH3CHO. The present simulations also indicate that experiments using these microtubular reactors when interpreted with the aid of high-level theoretical calculations and kinetics modeling can offer insights into the chemistry of elusive intermediates in the high-temperature pyrolysis of organic molecules.

Thermal decomposition of CH3CHO studied by matrix infrared spectroscopy and photoionization mass spectroscopy

A heated SiC microtubular reactor has been used to decompose acetaldehyde and its isotopomers (CH(3)CDO, CD(3)CHO, and CD(3)CDO). The pyrolysis experiments are carried out by passing a dilute mixture of acetaldehyde (roughly 0.1%-1%) entrained in a stream of a buffer gas (either He or Ar) through a heated SiC reactor that is 2-3 cm long and 1 mm in diameter. Typical pressures in the reactor are 50-200 Torr with the SiC tube wall temperature in the range 1200-1900 K. Characteristic residence times in the reactor are 50-200 μs after which the gas mixture emerges as a skimmed molecular beam at a pressure of approximately 10 μTorr. The reactor has been modified so that both pulsed and continuous modes can be studied, and results from both flow regimes are presented. Using various detection methods (Fourier transform infrared spectroscopy and both fixed wavelength and tunable synchrotron radiation photoionization mass spectrometry), a number of products formed at early pyrolysis times (roughly 100-200 μs) are identified: H, H(2), CH(3), CO, CH(2)=CHOH, HC≡CH, H(2)O, and CH(2)=C=O; trace quantities of other species are also observed in some of the experiments. Pyrolysis of rare isotopomers of acetaldehyde produces characteristic isotopic signatures in the reaction products, which offers insight into reaction mechanisms that occur in the reactor. In particular, while the principal unimolecular processes appear to be radical decomposition CH(3)CHO (+M) → CH(3) + H + CO and isomerization of acetaldehyde to vinyl alcohol, it appears that the CH(2)CO and HCCH are formed (perhaps exclusively) by bimolecular reactions, especially those involving hydrogen atom attacks.

Photocatalytic Activity of WO3 Films Crystallized by Postannealing in Air

We devised an effective method of deposition of photocatalytic WO3 films for the decomposition of volatile organic compounds. Amorphous WO3 films were deposited on unheated fused silica glass substrates by reactive DC magnetron sputtering with a W metal target, followed by crystallization through annealing at 300–800 °C in air. Under visible light irradiation, a film annealed at 400 °C proved significantly more effective than a WO3 film crystallized during deposition on a heated (800 °C) substrate for achieving photocatalytic decomposition of CH3CHO. Even more remarkable photocatalytic results were obtained for a film that was loaded with Pt nanoparticles after postannealing.

Steam reforming of ethanol over carburized alkali-doped nickel on zirconia and various supports for hydrogen production

The steam reforming of ethanol over carburized alkali-, La- and Ce-doped nickels on zirconia and various supports was studied to determine the support effects, alkali addition and carburization. The 823 K-carburized Ni/ZrO 2 and Ni/V 2O 5 catalysts exhibited higher activities than the Ni catalysts supported on CeO 2, Al 2O 3, SiO 2–Al 2O 3 and MgO and a reduced catalyst. The cesium-doped Ni/ZrO 2 promoted more hydrogen formation than the Li-, K-, La- and Ce-doped catalysts. From the XRD measurement, crystals of ZrO 2, Ni carbide and Ni metal were formed during the carburization of the Ni/ZrO 2 catalyst at 823 K. No Ni carbide was observed on the MgO, CeO 2 Al 2O 3, and V 2O 5 carburized catalysts. The Cs 0.2Ni/ZrO 2 and Cs 0.5Ni 0.5/Zr exhibited no carbon deposition at 7 h. The carburized and cesium-doped Ni/ZrO 2 was more effective in decreasing the carbon deposition. From the IR study, the formed carbonated species were attributed to the formation of CO 3 − from the formed CO 2 (CO 2 + O 2 − → CO 3 −). In the pulse experiment of H 2 18O, Cs 0.2Ni/ZrO 2 helped to facilitate the dissociation of H 2O to 2H and O and the decomposition of CH 3CHO to hydrogen and CO 2 through the CH 3CO species. The TPD after ethanol adsorption on Ni/ZrO 2 with and without Cs-doping showed that the Cs-doped Ni/ZrO 2 catalyst promoted the C–H breaking through the CH 3CO species more than the Ni/ZrO 2 catalyst.

Determination of photo-catalytic activity of un-doped and Mn-doped TiO 2 anatase powders on acetaldehyde under UV and visible light

Titanium dioxide (TiO 2) photocatalytic powder materials doped with various levels of manganese (Mn) were synthesized to be used as additives to wall painting in combating indoor and outdoor air pollution. The heterogeneous photocatalytic degradation of gaseous acetaldehyde (CH 3CHO) on Mn–TiO 2 surfaces under ultraviolet and visible (UV/Vis) irradiation was investigated, by employing the Photochemical Static Reactor coupled with Fourier-Transformed Infrared spectroscopy (PSR/FTIR) technique. Experiments were performed by exposing acetaldehyde (~ 400 Pa) and synthetic air mixtures (~ 1.01 × 10 5 Pa total pressure) on un-doped TiO 2 and doped with various levels of Mn (0.1–33% mole percentage) under UV and visible irradiation at room temperature. Photoactivation was initiated using either UV or visible light sources with known emission spectra. Initially, the photo-activity of CH 3CHO under the above light sources, and the physical adsorption of CH 3CHO on Mn–TiO 2 samples in the absence of light were determined prior to the photocatalytic experiments. The photocatalytic loss of CH 3CHO on un-doped TiO 2 and Mn–TiO 2 samples in the absence and presence of UV or visible irradiation was measured over a long time period (≈ 60 min), to evaluate their relative photocatalytic activity. The gaseous photocatalytic end products were also determined using absorption FTIR spectroscopy. Carbon dioxide (CO 2) was identified as the main photocatalysis product. It was found that 0.1% Mn–TiO 2 samples resulted in the highest photocatalytic loss of CH 3CHO under visible irradiation. This efficiency was drastically diminished at higher levels of Mn doping (1–33%). The CO 2 yields were the highest for 0.1% Mn–TiO 2 samples under UV irradiation, in agreement with the observed highest CH 3CHO decomposition rates. It was demonstrated that low-level (0.1%) doping of TiO 2 with Mn results in a significant increase of their photocatalytic activity in the visible range, compared to un-doped TiO 2. This elevated activity is lost at high doping levels (1–33%). Finally, the photocatalytic degradation mechanism of CH 3CHO on 0.1% Mn–TiO 2 surfaces under visible irradiation leading to low CO 2 yields is different than that under UV irradiation resulting to high CO 2 yields.

Steam reforming of ethanol on Ni–CeO2–ZrO2 catalysts: Effect of doping with copper, cobalt and calcium

Steam reforming (SR) and oxidative steam reforming (OSR) of ethanol were investigated over undoped and Cu, Co and Ca doped Ni/CeO2–ZrO2 catalyst in the temperature range of 400–650 °C. The nickel loading was kept fixed at 30 wt.% and the loading of Cu and Co was varied from 2 to 10 wt% whereas the Ca loading was varied from 5 to 15 wt.%. The catalysts were characterized by various techniques, such as surface area, temperature programmed reduction, X-Ray diffraction and H2 chemisorption. For Cu and Co doped catalyst, CuO and Co3O4 phases were detected at high loading whereas for Ca doped catalyst, no separate phase of CaO was found. The reducibility and the metal support interactions were different for doped catalysts and varied with the amount and nature of dopants. The hydrogen uptake, nickel dispersion and nickel surface area was reduced with the metal loading and for the Co loaded catalysts the dispersion of Ni and nickel surface area was very low. For Cu and Ca doped catalysts, the activity was increased significantly and the main products were H2, CO, CH4 and CO2. However, the Co doped catalysts showed poor activity and a relatively large amount of C2H4, C2H6, CH3CHO and CH3COCH3 were obtained. For SR, the maximum enhancement in catalytic activity was obtained with in the order of NCu5. For Cu–Ni catalysts, CH3CHO decomposition and reforming reaction was faster than ethanol dehydrogenation reaction. Addition of Cu and Ca enhanced the water gas shift (WGS) and acetaldehyde reforming reactions, as a result the selectivity to CO2 and H2 were increased and the selectivity to CH3CHO was reduced significantly. The maximum hydrogen selectivity was obtained for Catalyst N (93.4%) at 650 °C whereas nearly the same selectivity to hydrogen (89%) was obtained for NCa10 catalyst at 550 °C. In OSR, the catalytic activity was in the order N > NCu5 > NCa15 > NCo5. In the presence of oxygen, oxidation of ethanol was appreciable together with ethanol dehydrogenation. For SR reaction, the highest hydrogen yield was obtained on the undoped catalyst at 600 °C. However, with calcium doping the hydrogen yields are higher than the undoped catalyst in the temperature range of 400–550 °C.

AgBr/Al-MCM-41 visible-light photocatalyst for gas-phase decomposition of CH 3CHO

AgBr/Al-MCM-41 catalyst was active for the photooxidation of acetaldehyde in the gas phase under visible and UV light. Upon visible light illumination, continuous production of CO 2 with a decrease in CH 3CHO concentration was observed without the destruction of AgBr. The crystallite sizes of AgBr increased, as seen from powder X-ray diffraction after photocatalytic reaction under both visible and UV irradiation. It appears that AgBr together with Ag 0 is the photoactive species in the decomposition of CH 3CHO, and the high-surface-area Al-MCM-41 helps in high dispersion of AgBr on the support.

Photocatalytic and photophysical properties of visible-light-driven photocatalyst ZnBi 12O 20

Newly prepared ZnBi 12O 20 can absorb light irradiation below 540 nm. The representative organic contaminant acetaldehyde is decomposed easily on this photocatalyst under visible-light irradiation ( λ > 440 nm). Wavelength dependence of CH 3CHO decomposition proved further that the catalytic activity of this material is dominated by its light absorption. The theoretical calculations show that the VB of the photocatalyst is a hybridized band composed of O 2p, Zn 3d and Bi 6s. Furthermore, the band edge position of ZnBi 12O 20 was rough speculated according to the electronegativity of the constituent atoms. These calculation results confirm the strong oxidative property of the photocatalyst under the light illumination.

Characterization of Bi/TiO 2 nanometer sized particle synthesized by solvothermal method and CH 3CHO decomposition in a plasma-photocatalytic system

This study focuses on the relationship between the plasma-photocatalytic activity for CH 3CHO (acetaldehyde) decomposition and the surface properties of pure TiO 2 and 10.0 mol% Bi/TiO 2 nano-sized. The TiO 2 and Bi/TiO 2 particles, which were synthesized through the solvothermal method, exhibited a uniformly spherical anatase structure with particle size below 25 nm. The surface area was large (310 m 2/g) as compared with that of pure TiO 2 (140 m 2/g). Bi/TiO 2 adsorbed a smaller amount of water than pure TiO 2. From the H 2-TPR result, it was identified that Ti 3+ could be easily transferred into Ti 0, which affected the photoreaction, over Bi/TiO 2 compared with pure TiO 2. Based on these results, without H 2O addition, acetaldehyde decomposition was higher on Bi/TiO 2 (80% after 40 min). In particular, the by-product (mainly CH 3COOH), a serious problem in the plasma system, was very small in Bi/TiO 2 (below 5.0%) compared with that in pure TiO 2, which was above 20.0%. However, the acetaldehyde removal slightly increased over Bi/TiO 2 with H 2O addition, while it remarkably enhanced over pure TiO 2. This result means that H 2O addition did not have a good influence on acetaldehyde removal over the Bi/TiO 2 with hydrophobic property. However, it did exert a better influence on pure TiO 2 with hydrophilic property.