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Conversion of 2,3-butanediol over bifunctional catalystsZheng, Quanxing January 1900 (has links)
Doctor of Philosophy / Department of Chemical Engineering / Keith L. Hohn / In this study, Cu/ZSM-5 catalysts were used to catalyze the hydrodeoxygenation of 2,3-butanediol to butenes in a single reactor in the presence of hydrogen. The carbon selectivity of butenes increased with increasing SiO₂/Al₂O₃ ratio (lowering acidity of zeolite) and H₂/2,3-butanediol ratio. Cu/ZSM-5 with a SiO₂/Al₂O₃ ratio of 280 showed the best activity toward the production of butenes. On zeolite ZSM-5(280), the carbon selectivity of butenes increased with increasing copper loading and 19.2wt% of CuO showed the highest selectivity of butenes (maximum 71%). The optimal reaction temperature is around 250 °C. Experiments demonstrated that methyl ethyl ketone (MEK) and 2-methylpropanal are the intermediates in the conversion of 2,3-butanediol to butenes. The optimal performance toward the production of butene is the result of a balance between copper and acid catalytic functions.
Due to the functionalized nature of 2,3-butanediol, a variety of reactions can occur during the conversion of 2,3-butanediol, especially when multiple catalyst functionalities are present. To investigate the role of the metal (Cu) and acid sites in the process of reaction, the reaction kinetics for all major intermediate products (acetoin, MEK, 2-methylpropanal, 2-butanol and 2-methyl-1-propanol) were measured over Cu/ZSM-5(280), HZSM-5(280), and Cu/SiO₂ at 250 °C. The results showed that Cu is the active site for hydrogenation reactions, while the acidic sites on the zeolite are active for dehydration reactions. In addition, dehydration of alcohols over the zeolite is much faster than hydrogenation of ketone (MEK) and aldehyde (2-methylpropanal). A kinetic model employing Langmuir-Hinshelwood kinetics was constructed in order to predict 2,3-butanediol chemistry over Cu/ZSM-5(280). The goal of this model was to predict the trends for all species involved in the reactions. Reactions were assumed to occur on two sites (acid and metal sites) with competitive adsorption between all species on those sites.
Two different types of mesoporous materials (Al-MCM-48, Al-SBA-15) and hierarchical zeolite (meso-ZSM-5) were loaded with ~20wt% CuO and investigated in the conversion of 2,3-butanediol to butenes. The results showed that the existence of mesopores on the catalysts (Al-MCM-48 and Al-SBA-15 types) could decrease the selectivities of products from cracking reactions, especially C₃= and C₅=−C₇= by comparison with the catalyst with ~20wt% CuO loaded on the regular HZSM-5(280); meanwhile, the selectivity of C₈= from oligomerization of butenes was found to increase with increasing pore size of the catalysts. With respect to Cu/meso-ZSM-5(280) catalyst, it can be seen that the catalyst performs in a similar way to both Cu/ZSM-5(280) catalyst and mesoporous copper catalysts (Cu/Al-MCM-48 and Cu/Al-SBA-15) since both micropores (diameter of ~0.55 nm) and mesopores (pore size of ~23 nm) exist on meso-ZSM-5(280).
The results from Cu catalysts were compared with four other metal catalysts (Ni, Pd, Rh and Pt). It was found that Cu is not very active for hydrogenation of butenes, but is active for hydrogenation of carbonyl groups (C=O) to form hydroxyl groups (−OH). Pd, on the other hand, is active in further hydrogenating butenes and other unsaturated hydrocarbons. Both Ni and Rh catalysts are good for hydrogenation of olefins and cracking of heavy hydrocarbons; however, Rh is not as good as Ni for the hydrogenation of the carbonyl group (C=O) of MEK. In addition, Pt favors the formation of heavy aromatics such as 5-ethyl-1,2,3,4-tetrahydro-naphthalene, while Pd is active for the production of xylene.
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Selective Catalytic Reduction (SCR) of nitric oxide with ammonia using Cu-ZSM-5 and Va-based honeycomb monolith catalysts: effect of H2 pretreatment, NH3-to-NO ratio, O2, and space velocityGupta, Saurabh 30 September 2004 (has links)
In this work, the steady-state performance of zeolite-based (Cu-ZSM-5) and vanadium-based honeycomb monolith catalysts was investigated in the selective catalytic reduction process (SCR) for NO removal using NH3. The aim was to delineate the effect of various parameters including pretreatment of the catalyst sample with H2, NH3-to-NO ratio, inlet oxygen concentration, and space velocity.
The concentrations of the species (e.g. NO, NH3, and others) were determined using a Fourier Transform Infrared (FTIR) spectrometer. The temperature was varied from ambient (25 C) to 500 C. The investigation showed that all of the above parameters (except pre-treatment with H2) significantly affected the peak NO reduction, the temperature at which peak NO reduction occurred, and residual ammonia left at higher temperatures (also known as 'NH3 slip'). Depending upon the particular values of the parameters, a peak NO reduction of around 90% was obtained for both the catalysts. However, an accompanied generation of N2O and NO2 species was observed as well, being much higher for the vanadium-based catalyst than for the Cu-ZSM-5 catalyst. For both catalysts, the peak NO reduction decreased with an increase in space velocity, and did not change significantly with an increase in oxygen concentration. The temperatures at which peak NO reduction and complete NH3 removal occurred increased with an increase in space velocity but decreased with an increase in oxygen concentration. The presence of more ammonia at the inlet (i.e. higher NH3-to-NO ratio) improved the peak NO reduction but simultaneously resulted in an increase in residual ammonia. Pretreatment of the catalyst sample with H2 (performed only for the Cu-ZSM-5 catalyst) did not produce any perceivable difference in any of the results for the conditions of these experiments.
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Catalisadores Cu-, Co- ou Fe-ZSM-5 caracterização e avaliação na redução de NO a N2 com hidrocarbonetos na presença ou ausência de vapor de água.Fernandes, Juliana Esteves 04 March 2005 (has links)
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Previous issue date: 2005-03-04 / Universidade Federal de Sao Carlos / The minimization of the emissions of nitrogen oxides (NOx) in the atmosphere has been one of the great goals in the area of environmental
protection. Among the possible processes to treat the NOx, the selective catalytic reduction of NO with hydrocarbons (SCR-HC) has presented
important expectations. For this process, the metal/ZSM-5 type catalysts have appropriate levels of conversion in oxidative conditions.
In this context, the aim of this work was to prepare Cu, Co and FeZSM-5 catalysts. The samples were characterized by XRD, DRS-UVVIS, FTIR, H2-TPR, SEM and tested in the reduction of NO to N2 with propane or methane in oxidative atmosphere in the presence or absence of water steam. The H2-TPR data showed that the cationic species present in the
prepared Cu, Co and FeZSM-5 catalysts, after thermal activation, were mainly Cu2+ (Cuα
2+ e Cuβ 2+), Co2+ and Fe3+ cations located in charge compensation sites in the zeolite, respectively. From FTIR and DRS-UVVIS
it was also possible identify oxide species, which were present in a lower content.
In the reduction of NO to N2 in the absence of water steam, the CuZSM-5 catalysts showed higher levels of conversion of NO than those
based in Co and Fe. However, the FeZSM-5 catalysts showed, in this condition, activity at lower temperatures. This behavior makes them
potentially interesting to be applied for practical purposes. On the other hand, in the presence of water steam, it was verified a higher loss of
activity of the CuZSM-5 catalyst, which was totally restored removing the water in the feed. For the Co and FeZSM-5 catalysts, the activity loss in
the presence of water steam was partially recovered during time on stream. / A minimização das emissões de óxidos de nitrogênio (NOx) na atmosfera tem sido um dos grandes desafios da área de proteção
ambiental. Dentre os processos para o tratamento dos NOx possíveis, a redução catalítica seletiva do NO com hidrocarbonetos (RCS-HC) vem apresentando excelentes perspectivas. Para este processo os
catalisadores metal/zeólita ZSM-5 possuem adequados níveis de conversão em condições oxidantes. Dentro deste contexto, este trabalho teve como objetivo preparar catalisadores Cu, Co e FeZSM-5. As amostras foram caracterizadas por DRX, DRS-UVVIS, FTIR, RTP-H2, MEV e sua atividade verificada através da redução de NO a N2 com propano ou metano em atmosfera oxidante, na presença ou ausência de vapor de água. Os resultados de RTP-H2 mostraram que as espécies presentes nos catalisadores Cu, Co e FeZSM-5, após ativação térmica, foram
principalmente os cátions Cu2+ (Cuα
2+ e Cuβ 2+), Co2+ e Fe3+ compensando
carga na zeólita, respectivamente. A partir de FTIR e DRS-UVVIS foi possível, também, identificar espécies oxidas, as quais estavam presentes em teores menores. Na redução de NO a N2 na ausência de vapor de água os
catalisadores CuZSM-5 apresentaram maiores conversões de NO que os contendo Fe ou Co. Entretanto, os catalisadores FeZSM-5 apresentaram, nessa condição, atividade em temperaturas menores, o que mostra uma
vantagem para o seu uso prático. Na presença de vapor de água, verificou-se uma maior queda da atividade no catalisador CuZSM-5,
somente recuperada com a retirada desse composto na alimentação, sendo que para os catalisadores CoZSM-5 e FeZSM-5 a perda de
atividade foi parcialmente recuperada ao longo do tempo.
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