This study investigated the effects of temperature and humidity on the photocatalytic oxidation of volatile organic compound (VOCs) over titanium dioxide. Benzene, methyl tert-butyl ether (MTBE), perchloroethylene (PCE), and toluene were selected to investigate the influences of temperature and humidity on photocatalytic conversion. Among these four VOCs, benzene and MTBE were selected for the investigation of reaction pathways and kinetics. This work employed a self-designed annular packed-bed photocatalytic reactor to determine the conversion and reaction rates during photocatalytic degradation of VOCs. Degussa P-25 TiO2 was used as the photocatalyst and a 15 W near-UV lamp (350 nm) served as the light source. Benzene conversions increased with temperature below 160 ºC, but decreased above 160 ºC. Moreover, the conversions of MTBE increased with temperature from 30 to 120 ºC, and the thermocatalytic reaction began above 120 ºC. The conversions of PCE decreased as the temperature increased from 120 to 200 ºC. Toluene conversions almost remained constant at 100~200 ºC. Based on the gas-solid catalytic reaction theory, raising the reaction temperature could promote the chemical reaction rate and reduce reactant adsorption on TiO2 surfaces. The overall reaction rate increased with temperature, indicating that the reduction of reactant adsorption did not affect the overall reaction, and thus the chemical reaction was the rate-limiting step. As the chemical reaction rate gradually increased and the reactant adsorption decreased with temperature, the rate-limiting step could shift from the chemical reaction to the reactant adsorption, while the overall reaction rate decreased with temperature. Additionally, the competitive adsorption between VOCs and water for the active sites on TiO2 resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction rate. The mineralization of benzene and the selectivity of CO and CO2 were not obviously affected under various temperatures, humidities, and influent benzene concentrations. The benzene mineralization ratios ranged from 0.85 to 1.0, to which CO and CO2 contributed approximately 5~20% and 80~95%, respectively. Temperature and humidity variation did not influence the photocatalytic reaction pathway of benzene. Acetone (AC) and tert-butyl alcohol (TBA) were two major organic products for the photocatalysis of MTBE. The addition of water transferred the reaction pathway from producing AC to TBA, while the temperature increase transferred the reaction pathway from producing TBA to AC. A modified bimolecule Langmuir-Hinshelwood kinetic model was developed to simulate the temperature and humidity related promotion and inhibition of the photocatalysis of benzene and MTBE. The competitive adsorption of VOCs and water on the active sites resulted in VOCs influent concentration and humidity promoting or inhibiting the reaction. The reaction rate constant increased with temperature while the adsorption equilibrium constants decreased, confirming that increasing reaction temperature enhanced the chemical reaction, but reduced the adsorption of VOCs and water. Furthermore, the correlation developed here was also used for determining the apparent activation energy of photocatalytic oxidation of VOCs and the adsorption enthalpies of benzene, MTBE, water vapor, and oxygen.

In this research, nanoscale zero-valent iron (NZVI) was synthesized using the chemical reduction method. Experimental results have revealed that nanoiron synthesized by the reagent-grade chemicals had a size range of 50-80 nm, as determined by FE SEM. BET specific surface area of thus synthesized nanoparticles was 66.34 m2/g. NZVI prepared by the industrial-grade chemicals had a broader particle size distribution (30-80 nm) and its BET specific surface area was 61.50 m2/g. Results of XRD showed that both types of NZVI were composed of iron with a poor crystallinity. Additional test results further showed that both types of NZVI had similar characteristics. NZVI prepared by the chemical reduction method tends to aggregate resulting in a significant loss in reactivity. To overcome this disadvantage, four water-soluble dispersants were used in different stages of the NZVI preparation process. Of these, Dispersant A (an anionic surfactant) has shown its superior stabilizing capability to others. An addition of 0.5 vol % Dispersant A during the nanoiron preparation process would result in a good stability of NZVI slurry (NZVIS). Degradation of trichloroethylene (TCE) by NZVIS under different atmospheres was carried out in batch experiments. Experimental results have shown that the TCE dechlorination rate increased markedly when the reaction proceeded under hydrogen gas atmosphere as compared with that of air. Methane was the primary end product with a trace amount of ethane and ethylene when the reaction was conducted under the atmosphere of H2. It was suggested that an addition of H2 to the reaction system could promote the hydrogenolysis reaction for better degradation. On the other hand, ethane was the main product when the reaction system consisted of nanoscale palladized iron and H2 atmosphere. It demonstrated that Pd-catalyzed TCE dechlorination has resulted in a direct conversion of TCE to ethane in the study. The greatest dechlorination rate was obtained when 2 g/L nanoscale palladized iron and 50 mL H2 was employed in the reaction system. Under the circumstances, the TCE (10 mg/L) removal efficiency was up to 99 % in 3 minutes. Experimental results have demonstrated that the reaction system with both nanoscale palladized iron and H2 atmosphere would promote TCE degradation rate. The culture of microorganism in soil showed minor changes to microbial community structures between the pre- and post-injection conditions. The number of microorganism colony was found to be increased after adding 1 mL NZVIS to 1 g soil. Experimental results revealed that NZVIS would not cause the inhibition or reduction of microorganism activity. Surface modification of NZVI slurry by Dispersant A could enhance its transport in saturated porous media. Sticking coefficients were determined to be 0.56 and 0.11, respectively, for bare and Dispersant A-modified NZVIS transporting in quartz sand columns. The sticking coefficient for modified NZVIS transport in soil (loamy sand) column was determined to be 0.0061. Apparently, NZVIS modified by Dispersant A would enhance the transport of NZVI in saturated porous media. The results of combining electrokinetic technology and NZVIS injection tests in horizontal soil column illustrated that the sticking coefficient was 0.00034 and the total content of iron reduced 10 wt. %. Experimental results revealed that the transport distance of NZVIS in saturated horizontal soil column would be greatly increased under electronkinetic conditions.

ABSTRACT The increase of carbon dioxide (CO2) concentration in the atmosphere has become a severe environmental problem, since it could cause global warming due to greenhouse effects. Thus, the reduction of CO2 emission to tackle the greenhouse effect has become one of the most important tasks for sustainable development. The outcomes of this study would be valuable to evaluate the feasibility of applying photocatalytic reduction process to remove CO2 from the atmosphere as well as the flue gas. This study investigated the photocatalytic reduction of CO2 in a self-designed batch UV/TiO2 photocatalytic reactor. The photocatalysts tested included commercial TiO2 (Degussa P-25) and synthesized TiO2 via modified sol-gel process (i.e. NO3-/TiO2 and SO42-/TiO2). Stainless steel supports coated with TiO2 were packed in the batch reactor. The initial concentrations of CO2 ranged from 0.5% to 7.5%. The reductants investigated included hydrogen (H2), water vapor (H2O), and hydrogen with water vapor (H2+H2O). The incident UV light with wavelength of 365 nm was irradiated by a 15-watt low-pressure mercury lamp. The photocatalytic reaction was conducted continuously for approximately 48 hours. Reactants and products were analyzed quantitatively by a gas chromatography with a flame ionization detector followed by a methaneizer (GC/FID-Methaneizer). Experimental results indicated that stainless steel coated with TiO2 had better photoreduction efficiency than that of quartz glass. The optimal operating conditions of CO2 photoreduction were observed by using H2 over SO42-/TiO2, which could produce major products of CO and CH4 and minor products of C2H4 and C2H6. Sulfuric acid used as a stabilizer in the sol-gel process could produce TiO2 of high specific surface area. Results obtained from the operating parameter tests showed that the photoreduction rate increased with the initial concentration of carbon dioxide and resulted in more product accumulation. Higher photoreduction efficiency of carbon dioxide was observed by using the hydrogen (H2) than water vapor (H2O). The photoreduction rate of carbon dioxide increased with reaction temperature, which promoted the formation of products. In addition, proper water vapor (ie. relative humidity of water vapor =25%~75%) could increase the photoreduction efficiency. However, the photoreduction efficiency decreased white it was close to (ie. relative humidity of water vapor =75%~100%). Concurred with previous researches, the reaction rate of major products over SO42-/TiO2 were higher than previous investigations of CO2 photoreduction. This study proposed the reaction pathway using hydrogen and/or water vapor as the reductants. Moreover, a one-site Langmiur-Hinshewood kinetic model (L-H model) was successfully applied to simulate the reaction rate of CO2 during the photoreduction reaction process.

This study investigated the photocatalytic reduction of CO2 in a self-designed closed circulated batch reactor system and a bench-scale batch photocatalytic reactor. The photocatalysts tested included titanium dioxide (TiO2, Degussa P-25) and zirconium oxide (ZrO2). The reductants investigated included hydrogen (H2), water vapor (H2O), and hydrogen plus water vapor (H2+H2O). The wavelengths of incident near ultra-violet (UV) and UV lights for the photocatalysis of TiO2 and ZrO2 were 365 nm and 254 nm, respectively. The initial concentrations of CO2 ranged from 0.2-5.0% and the reaction temperature ranged from 35-95 ¡³C. The incident near-UV (or UV) light with wavelength of 365 nm (or 254 nm) was irradiated by a 15-watt low-pressure mercury lamp. The photocatalytic reaction was conducted continuously for approximately two hours. Reactants and products were analyzed by a gas chromatography with a flame ionization detector followed by a methanizer (GC/FID-methanizer). Experimental results indicated that glass pellets coated with TiO2 had better photoreduction efficiency than ZrO2. The highest yield rates of the photoreduction of CO2 were obtained using TiO2 with H2+H2O and ZrO2 with H2. Photoreduction of CO2 over TiO2 with H2+H2O formed CH4, C2H6, and CO in the yield of 32.95~94.60, 0.80~18.55, 1.12~21.78 £gmol/g, respectively, while the photoreduction of CO2 over ZrO2 with H2 formed CO in the yield of 0.34~4.99 £gmol/g. Results obtained from the operating parameter tests showed that the photoreduction rate increased with the initial concentration of carbon dioxide and resulted in more product accumulation. The photoreduction rate of carbon dioxide increased with reaction temperature, which promoted the formation of products. Concurred with previous researches, the reaction rate of major products over TiO2 and ZrO2 were higher than previous investigations of CO2 photoreduction. Furthermore, the spectra of FTIR showed that formic acid (HCOOHads), methanol (CH3OHads), carbonate (CO32−ads), bicarbonate (HCO32−ads), formate (HCOO−ads), formic acid (HCOOH ads), formaldehyde (HCOHads) and methyl formate (HCOOCH3 ads) formed on the surface of TiO2 and ZrO2 photocatalysts. The detected reaction products supported the proposal of two reaction pathways for the photoreduction of CO2 over TiO2 and ZrO2 with H2 and H2O, respectively. A modified bimolecular Langmuir-Hinshelwood kinetic model was developed to simulate the reaction temperature, CO2 initial concentration and relative humidity promotion and inhibition of the photoreduction of CO2. Additionally, the modified L-H kinetic model was successfully applied to simulate the photoreduction rate of CO2. The result showed that CO2 could be reduced by used solar light over TiO2 and ZrO2 photocatalysts. The reaction products of CO2 photoreduction over TiO2 were CH4, C2H6, and CO in the yield of 2.16~2.995, 0.057~0.128, 0.078~0.134 £gmol/g, respectively, while the photoreduction of CO2 over ZrO2 formed only CO in the yield of 0.023~0.051 £gmol/g. Furthermore, experimental results indicated that TiO2 gave the highest average photo energy efficiency (AEf) of ~4.13%, and apparent quantum efficiency (£pA) of ~1.05%. However, the ZrO2 gave the highest average photo energy efficiency (AEf) of 5.07¡Ñ10-3%, and apparent quantum efficiency (£pA) of ~1.54¡Ñ10-2%.

No description available.

Abstract Density functional theory (DFT) is a well-established tool for calculating the properties of materials. The volume of DFT-related publications doubles every 5–6 years, which has resulted in the appearance of continuously growing open material databases, containing information on millions of compounds. Furthermore, the results of DFT computations are frequently coupled with experimental ones to strengthen the computational findings. In this thesis, several applications of DFT related to physics and chemistry are discussed. The conductivity between MoS₂ and transition metal nanoparticles is evaluated by calculating the electronic structure of two different models for the nanoparticles. Chemical bonding of Ni to the MoS₂ host is proven by the system’s band alignment. To meet the demand for cleaner fuel, the applicability of the (103) edge surface of molybdenum disulfide in relation to the early stages of the hydrodesulfurization (HDS) reaction is considered. The occurrence of the (103) edge surface of molybdenum disulfide in the XRD patterns is explained. A method for calculating oxidation states based on partial charges using open materials databases is suggested. We estimate the applicability of the method in the case of mixed valence compounds and surfaces, showing that DFT calculations can be used for the estimation of oxidation states. / Tiivistelmä Tiheysfunktionaaliteoria (density functional theory, DFT) on yleisesti käytetty työkalu laskennallisessa materiaalitutkimuksessa. DFT:llä tuotettujen julkaisujen määrä kaksinkertaistuu 5–6 vuoden välein, minkä johdosta käytettävissä on jatkuvasti kasvava määrä avoimia materiaalitietokantoja, joihin on talletettu miljoonien yhdisteiden ominaisuuksia. DFT-laskujen tuloksia täydennetään myös usein kokeellisilla tuloksilla. Tässä työssä tarkastellaan tiheysfunktionaaliteorian sovelluksia fysiikassa ja kemiassa. MoS₂:n ja metallisten nanopartikkelien välistä johtavuutta on tutkittu mallintamalla erilaisia nanopartikkeleita. Nikkelin ja MoS₂:n välinen kemiallinen sidos selittyy systeemin energiavöiden kohdistumisella. MoS₂:n (103)-pinnan soveltuvuutta rikinpoistoreaktion varhaisissa vaiheissa on tutkittu tarkoituksena löytää uusia menetelmiä puhtaan polttoaineen tuottamiseksi. Myös (103)-pinnan esiintyminen röntgendiffraktiokuvissa selitetään. Työssä on myös esitetty menetelmä hapetustilojen laskemiseksi tietokannoista löytyvien laskettujen varausjakaumien avulla. Menetelmän soveltuvuutta on tarkasteltu erilaisille yhdisteille ja pinnoille. Tämä tarkastelu osoittaa, että DFT-tuloksia voidaan käyttää hapetustilojen laskemiseen.

<p>Dimerization and oligomerization reactions of alkenes are promising catalytic strategies to convert light alkenes, which can be derived from light alkane hydrocarbons (ethane, propane, butane) abundant in shale gas resources, into heavier hydrocarbons used as chemical intermediates and transportation fuels. Nickel cations supported on aluminosilicate zeotypes (zeolites and molecular sieves) selectivity catalyze ethene dimerization over oligomerization given their mechanistic preference for chain termination over chain propagation, relative to other transition metals commonly used for alkene oligomerization and polymerization reactions. Ni-derived sites initiate dimerization catalytic cycles in the absence of external activators or co-catalysts, which are required for most homogeneous Ni complexes and Ni²⁺ cations on metal organic frameworks (MOFs) that operate according to the coordination-insertion mechanism, but are not required for homogeneous Ni complexes that operate according to the metallacycle mechanism. Efforts to probe the mechanistic details of ethene dimerization on Ni-containing zeotypes are further complicated by the presence of residual H⁺ sites that form a mixture of 1-butene and 2-butene isomers in parallel acid-catalyzed pathways, as expected for the coordination-insertion mechanism but not for the metallacycle mechanism. As a result, the mechanistic origins of alkene dimerization on Ni cations have been ascribed to both the coordination-insertion and metallacycle-based cycles. Further, different Ni site structures such as exchanged Ni²⁺, grafted Ni²⁺ and NiOH⁺ cations are proposed as precursors to the dimerization active sites, based on analysis of kinetic data measured in different kinetic regimes and corrupted by site deactivation, leading to unclear and contradictory proposals of the effect of Ni precursor site structures on dimerization catalysis.</p> <p> Dimerization of ethene (453 K) was studied on Ni cations exchanged within Beta zeotypes in the absence of externally supplied activators, by suppressing the catalytic contributions of residual H⁺ sites via selective pre-poisoning with Li⁺ cations and using a zincosilicate support that contains H⁺ sites of weaker acid strength than those on aluminosilicate supports. Isolated Ni²⁺ sites were predominantly present, consistent with a 1:2 Ni²⁺:Li⁺ ion-exchange stoichiometry, CO infrared spectroscopy, diffuse reflectance UV-Visible spectroscopy and <i>ex-situ</i> X-ray absorption spectroscopy. Isobutene serves a kinetic marker for alkene isomerization reactions at H⁺ sites, which allows distinguishing regimes in which 2-butene isomers formed at Ni sites alone, or from Ni sites and H⁺ sites in parallel. 1-butene and 2-butenes formed at Ni sites were not equilibrated and their distribution was invariant with ethene site-time, revealing the primary nature of butene double-bond isomerization at Ni sites as expected from the coordination-insertion mechanism. <i>In-situ</i> X-ray absorption spectroscopy showed that the Ni oxidation state was 2+ during dimerization, also consistent with the coordination-insertion mechanism. Moreover, butene site-time yields measured at dilute ethene pressures (<0.4 kPa) increased with time-on-stream (activation transient) during initial reaction times, and this activation transient was eliminated at higher ethene pressures (≥ 0.4 kPa) and while co-feeding H₂. These observations are consistent with the <i>in-situ</i> formation of [Ni(II)-H]⁺ intermediates involved in the coordination-insertion mechanism, as verified by H/D isotopic scrambling and H₂-D₂ exchange experiments that quantified the number of [Ni(II)-H]⁺ intermediates formed.</p> <p> The prevalence of the coordination-insertion cycles at Ni²⁺ cations provides a framework to interpret the kinetic consequences of the structure of Ni²⁺ sites that are precursors to the dimerization active sites. Beta zeotypes predominantly containing either exchanged Ni²⁺ cations or grafted Ni²⁺ cations show noteworthy differences for ethene dimerization catalysis. The deactivation transients for butene site-time yields on exchanged Ni²⁺ cations indicate two sites are involved in each deactivation event, while those for grafted Ni²⁺ cations indicate involvement of a single site. The site-time yields of butenes extrapolated to initial time, and then further extrapolated to zero ethene site-time, rigorously determined initial ethene dimerization rates (453 K, per Ni) that showed a first-order dependence in ethene pressure (0.05-1 kPa). This kinetic dependence implies the β-agostic [Ni(II)-ethyl]⁺complex to be the most abundant reactive intermediate for the Beta zeolites containing exchanged and grafted Ni²⁺ cations. Further, the apparent first-order dimerization rate constant was two orders of magnitude higher for exchanged Ni²⁺ cations than for grafted Ni²⁺ cations, reflecting differences in ethene adsorption or dimerization transition state free energies at these two types of Ni sites. </p> <p> The presence of residual H⁺ sites on aluminosilicate zeotypes, in addition to the Ni²⁺ sites, causes formation of saturated hydrocarbons and oligomers that are heavier than butenes and those containing odd numbers of carbon atoms. The reaction pathways on Ni²⁺ and H⁺ sites are systematically probed on a model Ni-exchanged Beta catalyst that forms a 1:1 composition of these sites <i>in-situ</i>. The quantitative determination of apparent deactivation orders for the decay of product space-time yields provides insights into the site origins of the products formed. Further, Delplot analysis systematically identifies the primary and secondary products in the reaction network. This strategy shows linear butene isomers to be primary products formed at Ni²⁺-derived sites, while isobutene is formed as a secondary product by skeletal isomerization at H⁺ sites. In addition, propene is formed as a secondary product, purportedly by cross-metathesis between linear butene isomers and the reactant ethene at Ni²⁺-derived sites. Also, ethane is a secondary product that forms by hydrogenation of ethene at H⁺ sites, with the requisite H₂ generated <i>in-situ</i> likely by dehydrogenation and aromatization of ethene at H⁺ sites.</p> <a>The predominance of the coordination-insertion mechanism at Ni²⁺-derived sites implies kinetic factors influence isomer distributions within the dimer products, providing an opportunity to influence the selectivity toward linear and terminal alkene products of dimerization. In the case of bifunctional materials, reaction pathways on the Ni²⁺ and H⁺sites dictate the interplay between kinetically-controlled product selectivity at Ni sites and thermodynamic preference of product isomers formed at the H⁺ sites. </a>In summary, through synthesis of control catalytic materials and rigorous treatment of transient kinetic data, this work presents a detailed mechanistic understanding of the reaction pathways at the Ni²⁺ and H⁺ sites, stipulating design parameters that have predictable consequences on the product composition of alkene dimerization and oligomerization.

No description available.

Trifluoromethylierung von Mischungen hoeherer Fullerene mit CF3I wurde in Ampullen bei 400-420 Grad Celsius und 500-600 Grad Celsius durchgefuehrt. Die Produktmischungen wurden mittels mehrstufiger HPLC getrennt. In mehreren Versuchen konnten aus den isolierten HPLC-Fraktionen Kristalle fuer die Roentgenstrukturanalyse gewonnen werden. Die folgenden Strukturen der CF3-Derivate der Fullerene C84, C86 und C88 wurden bestimmt: 1 Isomer von C84(4)(CF3)12, C84(11)(CF3)10, C84(11)(CF3)12, C84(11)(CF3)16, C84(16)(CF3)8, C84(16)(CF3)14, C84(18)(CF3)10, C84(18)(CF3)12, C84(22)(CF3)20, C84(23)(CF3)8, C84(22)(CF3)10, C84(22)(CF3)12, C84(22)(CF3)18, C86(17)(CF3)10, C86(17)(CF3)16, C88(33)(CF3)16, C88(33)(CF3)18 und C88(33)(CF3)20. 2 Isomere von C84(22)(CF3)12, C84(22)(CF3)14 und C84(23)(CF3)14. 3 Isomere von C84(11)(CF3)14. 4 Isomere von C84(22)(CF3)16. Die Additionsmuster der Strukturen wurden diskutiert. Die experimentell nachgewiesenen Strukturen wurden mit berechneten Modellstrukturen verglichen. Dabei wurde auch die Stabilitaet der experimentellen Strukturen vorausgesagt. Zusaetzlich wurden die moeglichen Reaktionspfade fuer die Bildung hoeherer Derivate ausgehend von niedrigen Derivaten diskutiert. Sie zeigen, dass die Regioselektivitaet der Addition vom Kaefigisomer abhaengig ist. Die Reaktionspfade von vier Fullerenkaefigen werden in dieser Arbeit vorgestellt. C84(11)(CF3)10 --> C84(11)(CF3)16 C84(22)(CF3)2 --> C84(22)(CF3)20 C84(23)(CF3)10 --> C84(23)(CF3)18 C86(17)(CF3)10 --> C86(17)(CF3)16 / Trifluoromethylation of higher fullerene mixtures with CF3I was performed in ampoules at 400 to 420 degree Celsius and 500 to 600 degree Celsius. The obtained product mixtures were separated by multistep HPLC. Subsequent crystal growth and X-ray diffraction measurements allowed for structural characterization of the CF3 derivatives of fullerenes C84, C86 and C88 listed as the following. 1 isomer of C84(4)(CF3)12, C84(11)(CF3)10, C84(11)(CF3)12, C84(11)(CF3)16, C84(16)(CF3)8, C84(16)(CF3)14, C84(18)(CF3)10, C84(18)(CF3)12, C84(22)(CF3)20, C84(23)(CF3)8, C84(22)(CF3)10, C84(22)(CF3)12, C84(22)(CF3)18, C86(17)(CF3)10, C86(17)(CF3)16, C88(33)(CF3)16, C88(33)(CF3)18 and C88(33)(CF3)20. 2 isomers of C84(22)(CF3)12, C84(22)(CF3)14 and C84(23)(CF3)14. 3 isomers of C84(11)(CF3)14. 4 isomers of C84(22)(CF3)16. The molecular structures of isolated isomers were discussed in terms of their addition patterns and relative formation energies. DFT calculations were used to predict stable molecular structures of the CF3 derivatives. Calculated model structures have been compared with the experimental ones. In addition, the reaction pathways from the lower derivatives to higher ones of selected compounds were predicted. The pathways indicate the regioselectivity of additions depending on the fullerene cage isomer. Reaction pathways are presented for four fullerene cages in this work. C84(11)(CF3)10 --> C84(11)(CF3)16 C84(22)(CF3)2 --> C84(22)(CF3)20 C84(23)(CF3)10 --> C84(23)(CF3)18 C86(17)(CF3)10 --> C86(17)(CF3)16