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No description available.

This study focuses on the visible light response of hetero-structures of TiO2-graphene- MoS2 for solar energy harvestings. The commercial P25 TiO2 nano-particles, and selfprepared layered reduced graphene oxides (RG) and MoS2 were assembled for the targeted hetero-structure materials as visible-light responsible solar harvesting cocatalysts. The hydrothermal method was applied for nano-material synthesis, the reduction of graphene oxides, and bonding formation. Multiple characterization methods (SEM-TEM, XRD, XPS, UV-VIS, PL, FT-IR, TGA) have been applied to understand the electron-hole pair separation and recombination, and performance tuning in their visible-light photo-catalysis rhodamine B (Rh.B) degradations process Compared to TiO2, an obvious red shift of light absorption (from 3.1 eV to 2.6 eV) of the as-prepared RG-TiO2 was observed by UV-vis analysis, and an enhanced photocatalytic degradation of the Rhodamine B (Rh.B) using the as-prepared RG-TiO2 was also observed in a Xe lamp exposure test. The explication of these two approaches to photocatalytic improvements were concluded as the energy gap changing, the formation of Ti-O-C chemical bonds between TiO2 and RG for charge transfer and the reduction of the band gap, as well as a likelihood of up-conversion photoluminescence mechanism (UCPL). The synthesis temperature was found to be critical factor to control binding formation and agglomeration of nano-materials. The lower and higher temperatures induced ineffective formations of preferable bonding structures and the significant agglomeration. The optimal synthesis temperature was found to be within 120 ℃-150 ℃ in the TiO2-RG system. For better understanding of the Ti-O-C bonding, a heterostructure of TiO2 nanotube arrays with GO (TNA-GO) was synthesized using the Langmuir-Blodgett (LB) assembly method. The band gap of this assemble was very close to the previous TiO2-RG synthesized below 120 ℃, which is very close to that of TiO2 nano-particles. This lead to the conclusion on the significance of the Ti-O-C bonding in the visible-light-responsible photo-catalysis solar harvestings. This study revealed the fundamental mechanisms on the bonding formations and the significant visible-light-response of hetero-structcures between commercial-available, inexpensive and non-toxic TiO2 and layered materials, such as the zero-band-gap graphene and the smaller-band-gap MoS2. This mechanisms understanding will greatly sustain applications of economical-effective and environmental-safe TiO2.

Orientadora: Profa. Dra. Paula Homem de Mello / Dissertação (mestrado) - Universidade Federal do ABC, Programa de Pós-Graduação em Ciência & Tecnologia - Química, 2014. / Métodos computacionais foram empregados para avaliar os efeitos da substituição de átomos de molibdênio por cobalto, ou níquel, em catalisadores de sulfeto de molibdênio, utilizados nos processos de hidrodessulfurização. O estudo foi feito utilizando duas diferentes abordagens. O método de Monte Carlo para determinar as estrutura mais prováveis envolvidas no processo de adsorção de tiofeno e sulfeto de dimetila, enquanto métodos baseados na teoria do funcional da densidade foram utilizados para otimizar as estruturas obtidas por Monte Carlo e determinar as energias de adsorção. A validação dos clusters utilizados foi feita pela avaliação das distâncias das ligações entre os átomos, principalmente dos átomos localizados nas bordas e encontrado como cluster mínimo a ser utilizado nas simulações o Mo16S32. Foi, em seguida, estudada a adsorção de tiofeno, e a possibilidade de transferência de carga foi avaliada a partir das cargas atômicas, juntamente com os orbitais HOMO-LUMO. Essas propriedades permitiram mostrar que a substituição de átomos de molibdênio por átomos de cobalto, resultam em maior transferência de carga do adsorbato ocorrendo ampliação dos sítios ácidos. / Computational methods were used to evaluate the effect of substitution of atoms of molybdenum by cobalt or nickel in the molybdenum sulfide catalyst used in hydrodesulfurization process. The study was conducted using two different approaches. Monte Carlo method was employed to determine the most probable structures involved in the thiophene and dimethyl sulfide adsorption process. Density functional theory-based methods were used to optimize the structures obtained by Monte Carlo and determine the adsorption energies. Validation of clusters employed in this study was performed by evaluating the bond distances between atoms, particularly atoms from the edges. The results presented herein demonstrate that Mo16S32 cluster can be used to represent the catalyst. Atomic charges analysis and frontier molecular orbitals were employed to evaluate the acidity of the different sites. These properties showed also that the replacement of molibidenium atoms by cobalt atoms results in increasing charge transfer and promotes new acidic sites.

The demand for mixed alcohols has grown since ether compounds were banned as gasoline octane improvers in North America. Molybdenum-based catalysts in sulfide form are an attractive catalyst system for the conversion of synthesis gas to alcohols, due to their excellent resistance to sulfur poisoning and high activity for the water-gas shift reaction. The higher alcohols activity over these catalysts is low, due to the formation of hydrocarbons and CO2. Although a number of catalysts have been developed for this purpose, not any are used commercially at this time. The main objective of this Ph.D. research is to develop a catalyst system that is capable of selectively producing higher alcohols, particularly ethyl alcohols from synthesis gas. In the present series of studies, the investigation of an alkali-promoted trimetallic Co-Rh-Mo catalyst system has led to improvements in product stream composition. The effect of different loadings of active metal (Mo), alkali (K) promoter, and metal promoters (Co and Rh) on higher alcohol synthesis from synthesis gas were investigated using commercially available multi-walled carbon nanotubes (MWCNTs) as the catalyst support. The role of support on higher alcohols synthesis was also studied using different supports, such as ã-Al2O3, activated carbons with different textural characteristics, and MWCNTs. The catalysts were prepared using the incipient wetness impregnation method and extensively characterized in both oxide and sulfide phases using different techniques. Transmission electron microscopy (TEM) results revealed that the metal particles were uniformly distributed inside and outside of the carbon nanotubes, and that metal dispersions were higher on the alkali-promoted trimetallic catalyst supported on MWCNTs. The existence of promoted and un-promoted MoS2 sites was confirmed by diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies of adsorbed CO over sulfided catalysts. Temperature programmed reduction (TPR) tests showed that the addition of metal promoters improved the reduction behaviour of the catalysts. XRD patterns showed that alkali-promoted catalysts were less crystalline compared to that of the catalyst not promoted with K. The formation of Co (Rh)-Mo-S species was evident in the XANES spectra of bimetallic and trimetallic alkali-promoted MoS2 catalysts. The activity and selectivity of the catalysts were assessed in a fixed-bed micro-reactor using temperature, pressure, and gas hourly space velocity in the ranges of 275 to 350°C, 800 to 1400 psig (5.529.65 Mpa), and 2.4 to 4.2 m3 (STP)/(kg of cat.)/h, respectively. The Ni-promoted catalyst showed higher activity towards the formation of hydrocarbons over that of alcohols. The total alcohols space time yield (STY) and higher alcohols selectivities are significantly higher over the activated carbon-supported catalysts compared to those supported on alumina. With increased content of K, the formation of alcohols increased and hydrocarbons formation rate was suppressed. The total alcohols STY increased with increased Co content over the Co-promoted MoS2-K/MWCNTs catalysts, whereas, the maximum ethyl alcohol and higher alcohols selectivities were observed on the catalyst promoted with 4.5 wt % Co. Over the Rh-promoted MoS2-K/MWCNTs catalysts, the maximum total alcohol yield, ethanol selectivity, and higher alcohols selectivity were observed on the catalyst with 1.5 wt % Rh. The MWCNT-supported alkali-promoted trimetallic catalyst with 9 wt % K, 4.5 wt % Co, 1.5 wt % Rh, and 15 wt % Mo showed the maximum higher alcohols STY and selectivity compared to other catalysts investigated. The textural properties of the support, such as average pore diameter, pore volume and surface area, could significantly influence the extent of reduction, morphology, adsorption and has direct influence on the synthesis of mixed alcohols from synthesis gas. The optimum higher alcohols STY and selectivity were obtained over the Co-Rh-Mo-K/MWCNT catalyst at 330°C, 1320 psi (9.1 Mpa), 3.8 m3 (STP)/(kg of cat./h) using a H2 to CO molar ratio value of 1.25. To predict the reaction rate for higher alcohols synthesis, the power law model was used for the reaction between CO and H2 on the catalyst surface and the data of this study are well fitted by the model. The activation energies of ethanol and higher alcohols obtained over Co-Rh-Mo-K/MWCNTs were low compared to those values reported in the literature. The sulfided alkali-promoted trimetallic Co-Rh-Mo catalyst supported on MWCNTs was stable over a period of 720 h of continuous reaction.

The demand for mixed alcohols has grown since ether compounds were banned as gasoline octane improvers in North America. Molybdenum-based catalysts in sulfide form are an attractive catalyst system for the conversion of synthesis gas to alcohols, due to their excellent resistance to sulfur poisoning and high activity for the water-gas shift reaction. The higher alcohols activity over these catalysts is low, due to the formation of hydrocarbons and CO2. Although a number of catalysts have been developed for this purpose, not any are used commercially at this time. The main objective of this Ph.D. research is to develop a catalyst system that is capable of selectively producing higher alcohols, particularly ethyl alcohols from synthesis gas. In the present series of studies, the investigation of an alkali-promoted trimetallic Co-Rh-Mo catalyst system has led to improvements in product stream composition. The effect of different loadings of active metal (Mo), alkali (K) promoter, and metal promoters (Co and Rh) on higher alcohol synthesis from synthesis gas were investigated using commercially available multi-walled carbon nanotubes (MWCNTs) as the catalyst support. The role of support on higher alcohols synthesis was also studied using different supports, such as ã-Al2O3, activated carbons with different textural characteristics, and MWCNTs. The catalysts were prepared using the incipient wetness impregnation method and extensively characterized in both oxide and sulfide phases using different techniques. Transmission electron microscopy (TEM) results revealed that the metal particles were uniformly distributed inside and outside of the carbon nanotubes, and that metal dispersions were higher on the alkali-promoted trimetallic catalyst supported on MWCNTs. The existence of promoted and un-promoted MoS2 sites was confirmed by diffuse reflectance infrared fourier transform spectroscopy (DRIFTS) studies of adsorbed CO over sulfided catalysts. Temperature programmed reduction (TPR) tests showed that the addition of metal promoters improved the reduction behaviour of the catalysts. XRD patterns showed that alkali-promoted catalysts were less crystalline compared to that of the catalyst not promoted with K. The formation of Co (Rh)-Mo-S species was evident in the XANES spectra of bimetallic and trimetallic alkali-promoted MoS2 catalysts. The activity and selectivity of the catalysts were assessed in a fixed-bed micro-reactor using temperature, pressure, and gas hourly space velocity in the ranges of 275 to 350°C, 800 to 1400 psig (5.529.65 Mpa), and 2.4 to 4.2 m3 (STP)/(kg of cat.)/h, respectively. The Ni-promoted catalyst showed higher activity towards the formation of hydrocarbons over that of alcohols. The total alcohols space time yield (STY) and higher alcohols selectivities are significantly higher over the activated carbon-supported catalysts compared to those supported on alumina. With increased content of K, the formation of alcohols increased and hydrocarbons formation rate was suppressed. The total alcohols STY increased with increased Co content over the Co-promoted MoS2-K/MWCNTs catalysts, whereas, the maximum ethyl alcohol and higher alcohols selectivities were observed on the catalyst promoted with 4.5 wt % Co. Over the Rh-promoted MoS2-K/MWCNTs catalysts, the maximum total alcohol yield, ethanol selectivity, and higher alcohols selectivity were observed on the catalyst with 1.5 wt % Rh. The MWCNT-supported alkali-promoted trimetallic catalyst with 9 wt % K, 4.5 wt % Co, 1.5 wt % Rh, and 15 wt % Mo showed the maximum higher alcohols STY and selectivity compared to other catalysts investigated. The textural properties of the support, such as average pore diameter, pore volume and surface area, could significantly influence the extent of reduction, morphology, adsorption and has direct influence on the synthesis of mixed alcohols from synthesis gas. The optimum higher alcohols STY and selectivity were obtained over the Co-Rh-Mo-K/MWCNT catalyst at 330°C, 1320 psi (9.1 Mpa), 3.8 m3 (STP)/(kg of cat./h) using a H2 to CO molar ratio value of 1.25. To predict the reaction rate for higher alcohols synthesis, the power law model was used for the reaction between CO and H2 on the catalyst surface and the data of this study are well fitted by the model. The activation energies of ethanol and higher alcohols obtained over Co-Rh-Mo-K/MWCNTs were low compared to those values reported in the literature. The sulfided alkali-promoted trimetallic Co-Rh-Mo catalyst supported on MWCNTs was stable over a period of 720 h of continuous reaction.

Catalytic naphthalene hydrogenation to tetralin in water/hydrocarbon emulsions with simultaneous water gas shift as the hydrogen source was performed in a 300 ml batch autoclave as a model for aromatic hydrogenation in water/bitumen emulsions. The catalyst utilized was an unsupported and dispersed type based on molybdenum sulfide (MoS2). Distinguishing the fate of hydrogen from water as opposed to molecular hydrogen in hydrogenation and water gas shift was accomplished by utilizing deuterium oxide (D2O) with NMR spectroscopy. The use of D2O allowed determination of isotope effects when compared with H2O. Diffuse Reflectance Infrared Fourier Transform Spectroscopy was performed to observe CO adsorption on the MoS2 sulfide surface. Ruthenium was tested as a potential candidate to enhance the activity of the Mo catalyst. Iron, nickel and vanadium were utilized in combination with molybdenum to test promotional/inhibitive activity during naphthalene hydrogenation and water gas shift since Ni and V are found in significant quantities in real bitumen feed. Finally, a multifactorial experiment was performed to test the hydrogenation and water gas shift activity of a binary VNiMo-sulfide catalyst towards H2S partial pressure, temperature and H2 versus CO atmospheres. Deuterium from D2O was incorporated into both saturated and aromatic hydrogen positions in tetralin products. Calculation of a Hydrogenation Index and Exchange Index indicated the extent of H-exchange is greater than hydrogenation. Exchange between D2O and organic products was enhanced with the MoS2 catalyst under H2 or CO compared to N2. A kinetically measured isotope effect of 1.58 was in agreement with a quasi-equilibrium thermodynamic isotope effect for O-H dissociations measured in the literature. A true kinetic isotope effect may be masked by transient surface concentrations occurring under batch conditions. Two strong vibrational bands associated with adsorbed CO were observed over MoS2 above 160 °C. Activation of the MoS2 surface with CO produces COS, suggesting an analgous mechanism to the production of H2S during reduction in H2. In the presence of H2S, Ru displayed low catalytic activity for both water gas shift and naphthalene hydrogenation, attributed to incomplete sulfidation to active RuS2. FeMo and VMo exhibited lower hydrogenation activity than Mo, but the water gas shift activity of VMo was high. A ternary VNiMo displayed lower hydrogenation activity than NiMo and Mo but was higher than VMo, implying Ni could offset the inhibition caused by V. Recycle of V and Ni rich asphaltene residues in catalytic slurry upgrading may therefore be feasible. An analysis of the effect of H2S pressure, temperature and type of reduction gas (CO vs. H¬2) concluded that temperature had the greatest positive effect on rate, followed by a small interaction effect of temperature/gas type and PH2S/gas type. The proximity to equilibrium conversions in WGS limited the analysis, while equilibrium limited the conversion of naphthalene at 380 °C in the batch reactor.

Catalytic naphthalene hydrogenation to tetralin in water/hydrocarbon emulsions with simultaneous water gas shift as the hydrogen source was performed in a 300 ml batch autoclave as a model for aromatic hydrogenation in water/bitumen emulsions. The catalyst utilized was an unsupported and dispersed type based on molybdenum sulfide (MoS2). Distinguishing the fate of hydrogen from water as opposed to molecular hydrogen in hydrogenation and water gas shift was accomplished by utilizing deuterium oxide (D2O) with NMR spectroscopy. The use of D2O allowed determination of isotope effects when compared with H2O. Diffuse Reflectance Infrared Fourier Transform Spectroscopy was performed to observe CO adsorption on the MoS2 sulfide surface. Ruthenium was tested as a potential candidate to enhance the activity of the Mo catalyst. Iron, nickel and vanadium were utilized in combination with molybdenum to test promotional/inhibitive activity during naphthalene hydrogenation and water gas shift since Ni and V are found in significant quantities in real bitumen feed. Finally, a multifactorial experiment was performed to test the hydrogenation and water gas shift activity of a binary VNiMo-sulfide catalyst towards H2S partial pressure, temperature and H2 versus CO atmospheres. Deuterium from D2O was incorporated into both saturated and aromatic hydrogen positions in tetralin products. Calculation of a Hydrogenation Index and Exchange Index indicated the extent of H-exchange is greater than hydrogenation. Exchange between D2O and organic products was enhanced with the MoS2 catalyst under H2 or CO compared to N2. A kinetically measured isotope effect of 1.58 was in agreement with a quasi-equilibrium thermodynamic isotope effect for O-H dissociations measured in the literature. A true kinetic isotope effect may be masked by transient surface concentrations occurring under batch conditions. Two strong vibrational bands associated with adsorbed CO were observed over MoS2 above 160 °C. Activation of the MoS2 surface with CO produces COS, suggesting an analgous mechanism to the production of H2S during reduction in H2. In the presence of H2S, Ru displayed low catalytic activity for both water gas shift and naphthalene hydrogenation, attributed to incomplete sulfidation to active RuS2. FeMo and VMo exhibited lower hydrogenation activity than Mo, but the water gas shift activity of VMo was high. A ternary VNiMo displayed lower hydrogenation activity than NiMo and Mo but was higher than VMo, implying Ni could offset the inhibition caused by V. Recycle of V and Ni rich asphaltene residues in catalytic slurry upgrading may therefore be feasible. An analysis of the effect of H2S pressure, temperature and type of reduction gas (CO vs. H¬2) concluded that temperature had the greatest positive effect on rate, followed by a small interaction effect of temperature/gas type and PH2S/gas type. The proximity to equilibrium conversions in WGS limited the analysis, while equilibrium limited the conversion of naphthalene at 380 °C in the batch reactor.

The purpose of this study is to develop catalysts for conversion of synthesis gas (H₂ and CO) to higher alcohols, primarily ethanol and propanol. Crude oil is consumed at a rate of more than 20 million barrels a day in the United States, mainly for producing fuels and chemical feedstocks. However, the total amount of crude oil is limited, and alternative ways of producing alcohols as precursors for chemical feedstocks are desirable. In this study, using a known K/MoS₂/metal oxide catalyst as the starting point, two different approaches were explored to improve catalytic properties: 1) Co promotion on K/MoS₂/mixed metal oxide (MMO) catalysts, and 2) Preparation of K/MoS₂/metal oxide catalysts with molybdenum carbide as a precursor, instead of molybdenum oxide. With respect to Co promotion on K/MoS₂/MMO catalysts, the effect of varying the Co content in the K/Mo-Co/MMO catalysts prepared by a co-impregnation method did not produce significant changes in catalytic acitivities or selectivities. It was due to the premature precipitation of cobalt molybdate during synthesis. Cobalt molybdate precipitation can generally be prevented by using water as a solvent, but this approach is not appropriate for this study because of the use of hydrotalcite-derived mixed metal oxide as the support. Co loadings on K/Mo/MMO-Co catalysts did not change selectivities significantly, either. However, they changed catalytic activities, represented by gas hourly space velocity (GHSV) required to obtain 8% conversion while maintaining high selectivities for higher alcohols. As a result, C ₂₊ alcohol productivities reached 0.01g(alcohol)/g(catalyst)/hr with Co loadings higher than 8%. With respect to using Mo2C as the precursor of Mo species instead of MoO3, comparisons between catalysts with different precursors for Mo species and different pretreatments were investigated. In this study, both K/Mo catalysts supported on MgO and α-Al₂O₃ showed similar tendencies of catalytic activities and selectivities. The highest C₂₊ alcohol selectivities and productivities were obtained on presulfided MoO₃ catalysts on both supports. In comparison of K/Mo ₂C catalysts with different pretreatments, higher C₂₊ alcohol selectivities and lower MeOH selectivities were obtained on presulfided catalysts compared to non-pretreated catalysts.